1

1. Water Water plays a vital role in our life. It is most abundant, wonderful and useful solvent.

Although it is the most abundant commodity in nature it is the most misused one also.

80% of the earth’s crust is covered with water. The quantity available for actual use in

the form of rivers, lakes, wells and ponds is hardly 0.5% of the world’s water

resources. This is because more than 96% of water is locked in oceans which are too

saline to drink or to be used directly for agricultural, industrial or domestic purposes.

2% of the water is locked up in polar ice caps and glaciers. About 1% is deeply

underground and not accessible. Due to rapid industrialisation, urbanisation and

growth in population man has successfully polluted most of the water available on

earth. Industrial and domestic waste has caused significant—pollution of the aquatic

ecosystem (Trivedi and Goel 1986). Hence monitoring and control of pollution is

essential for better future. 1.1 - SOURCES OF WATER (i) Surface waters: (Rivers, lakes, seawater, etc.) Water present on the surface is

called surface water. River water, stream water (flowing water, moorland si-face

drainage) as well as water in the ponds, lakes and reservoirs (low and surface

drainage) is called surface water. (ii) Underground water: (Wells) Some part of rain water penetrates through the

soil. It goes down and down till it reaches impermeable rocks. If the top of this

rock is flat, it stays there. If the layers of rock have slope, water will flow the

slope down. We get this water in the form of well or spring water. Water from

lower measures of coal mines is also underground water. (iii) Rainwater: it is purest form of water obtained by natural distillation 1.2 - IMPURITIES IN NATURAL WATER When rainwater reaches the earth and flows on the earth, it becomes impure

because of absorption of impurities. The absorbed impurities are of the following

types. (i) Dissolved gases: Gases like oxygen, nitrogen, carbon dioxide, etc. from the

atmosphere dissolve in water and make the water acidic. Lake water contains

more carbon dioxide due to biological oxidation of organic matter present at the

bottom of the lake.

C6 H12O6 + 6O2 bacteriaAerobic

6CO2 + 6H2O

Hexose

C6 H12O6 Anaerobic

bacteria 2C2 H5OH + 2CO2 Hexose

2

The colour and odour of the natural water is due to the presence of dissolved

organic matter. Underground water is colourless and odourless, but some deep

well water possess rotten egg’s smell which is due to dissolved hydrogen sulphide

(H2S). Well water of wells located in oil and gas areas contain dissolved methane.

(ii) Suspended matter: Surface water appears turbid due to the presence of finely

divided impurities, which remain suspended in water. These impurities—clay

particles, iron hydroxide, silica which are inorganic type while decaying vegetable

and animal matter which are organic type are called suspended impurities. They

are negligible in underground water because of filtering action of the soil.

(iii) Micro organism or bacterial impurities: Micro organisms like algae, fungi

and bacteria are present in surface water.

(iv) Dissolved mineral salts: When rainwater falls on the ground it reacts with

rocks and different minerals present on the earth. Salts like sodium chloride,

calcium chloride, sodium nitrate, dissolve in water; carbonates of calcium and

magnesium get converted to bicarbonates by the action of carbon dioxide from

water.

CaCO3

+ H2O

+ CO2

Ca(HCO3)2

Calcuim Carbonate

Calcium bicarbonate

MgCO3

+H2O +CO2

Mg(HCO3)2

Magnesium Carbonate

Magnesium bicarbonate

Thus, because of dissolution of many salts water becomes impure. Underground

water contains more soluble salts than the surface water.

1.3 - HARDNESS OF WATER

Hardness can be defined as the soap consuming capacity of water sample. Soaps

are sodium salts of fatty acids like oleic acids, palmetic acid and stearic acid. They

dissolve readily in water to form lather due to which it has cleansing property.

C17H35COONa C17H35COO-+ Na

+Sodium

stearate

But compounds of fatty acids with other metals do not dissolve in water If water

contains other metal ions like calcium and magnesium ions, they react with

sodium salts of long chain fatty acids to form insoluble soap which we observe as

curd.

2C17H35COONa + Ca++

(C17H35COO)2Ca

+ 2Na+

Calcium stearate These other metals ions are responsible for the hardness of water. Most important

metal ions which cause hardness to water are calcium and magnesium ions. The

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hardness of water can be calculated from the amounts of calcium and magnesium

ions present in water along with bicarbonates, sulphates, chlorides and nitrates.

The relation between the type of water and degree of hardness is as given below.

Type of water Hardness as ppm of CaCO3

Soft 0—75

Moderately hard 75 — 150

Hard 150— 300

Very hard above 300

Standards of water for drinking - As per Indian Standards (IS: 10500-1983)

Sr. No. Characteristics Desirable limit

1 pH value 6.5 to 8.5

2 Odour unobjectionable

3 Colour (Hazon unit), maximum 10

4 Test Agreeable

5 Turbidity (NTU) maximum 5

6 Total dissolved solids (TDS) ppm 500

7 Total hardness maximum as (CaCO3 ppm) 300

8 Calcium (ppm) 75 - 200

9 Magnesium (ppm) 30 – 150

10 Iron as Fe (ppm) 0.1 – 1.0

11 Chloride (as Cl-) pm 200 – 600

12 Nitrate (as NO3-) pm 45

13 Sulphate as (SO4) pm 200 – 400

14 Phosphate as (PO4) ppm 10 – 15

15 Organic matter (pm) 0.2 – 1.0

1.3.1 - TYPES OF HARDNES

Hardness due to the presence of calcium and magnesium bicarbonates is called

hardness.

(1) Temporary hardness: When water containing calcium and magnesium

bicarbonates is heated, soluble bicarbonates are converted into insoluble

carbonates and hydroxide. On filtering of such water, soft water is obtained. The

hardness which can be removed by boiling is referred as ‘temporary hardness’ or

bicarbonate hardness.

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(ii) Permanent hardness: ‘Permanent hardness’ is the term applied to the

hardness caused by dissolved chlorides, nitrates and sulphates of calcium and

magnesium and other heavy metal ions. This hardness cannot be removed by

boiling the water sample. Sum of temporary and permanent hardness is referred to

as total hardness. Permanent hardness can only be removed by lime-soda, ion

exchange or zeolite process.

(iii) Alkaline or carbonate hardness and non-alkaline or non-carbonate

hardness: Like all carbonates and bicarbonates, calcium and magnesium

carbonates and bicarbonates are alkaline. Then hardness due to the bicarbonates

and carbonates is called alkaline hardness or carbonate hardness. The alkalinity

can be measured by titration with standard mineral acid using methyl orange or

phenolphthalein as an indicator. As the sulphates and chlorides are neutral salts,

the hardness caused by the presence of calcium and magnesium sulphates,

chlorides and nitrates is termed non-alkaline hardness or non-carbonate hardness.

1.3.2 - UNITS OF HARDNESS

Hardness in water is expressed in terms calcium carbonate equivalents as:

1. Parts Per Million (ppm):

It expresses the concentration of hardness causing salt as the number of parts of

substance by weight in million parts by weight of water.

One part per million, i.e., 1 ppm hardness means one part of CaCO3 equivalent

hardness is present in one million parts of water. For calculation, the units of

weight used should be same for the substance and water (1 ppm = 1 mg/litre).

2. Degree Clark (°CI)

It is the number of grains of CaCO3 equivalent hardness per gallon of water. It is

also expressed as parts of CaCO3 equivalent hardness per 70,000 parts of water.

Thus, 1° Clark is equal to one grain of CaCO3 equivalent hardness in one gallon

of water which is same as 1 part of CaCO3 equivalent hardness per 70,000 parts of

water.

3. French Unit (°F)

It is the part of CaCO3 equivalent hardness per 105 parts of water.

The various units of hardness are inter-convertible and by using the following

information, hardness in one unit can be expressed in other units as -

1 ppm ≡ 1mg/litre ≡ 0.1℉ ≡ 0.07° Cl

1° Cl ≡ 14.3ppm ≡ 14.3mg /litre ≡ 1.43℉

1℉ ≡ 10 ppm ≡ 10 mg/litre ≡ 0.7° Cl

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1.4 - EFFECTS OF HARD WATER IN INDUSTRIES Industries like paper, sugar, chemical textile, pharmaceutical industries, etc.

require large amount of water—and for steam generation, heat exchangers and

condensers. Water free from all kinds of impurities with hardness below 25 ppm

is desirable for the industrial purpose. The pH of the water used in industries

should be 7 to 8.0 and free from all types of impurities. Water of higher hardness causes the following problems in industries. 1. In textile industry calcium/magnesium soap precipitates adhere to the fabric

material and interfere with dyeing process which affects the shades.

2. In boilers it leads to the formation of scales and sludges which reduces

efficiency of boilers.

3. In sugar industry presence of calcium magnesium salt interfere with the

crystallisation of sugar.

4. In paper industry smooth finish and proper colour cannot be obtained if hard

water is used.

5. Pharmaceutical industry: If hard water is used for preparing pharmaceutical

products like drugs, injections, lotions, syrups, etc., then the hardness causing

ions in water may react with them to produce undesirable products. This may

reduce efficiency of the material or create adverse action. 6. Concrete making: If the water containing chlorides, sulphates, etc. is used

may affect the hydration of compounds in cement and final strength of

concrete will be affected. 1.5 - ESTIMATION OF HARDNESS Hardness of water can be determined by two methods: 1.5.1 - Soap Titration Method Total hardness of water can be determined by titrating a fixed volume of water

sample (100 ml) against standard alcoholic soap solution. Formation of stable

lather which persists for two minutes is the end point of titration. In the beginning

sodium soap will precipitate all hardness causing ions as their respective stearates.

2C17H35COONa + CaCl2

(C17H35COO)2Ca

+ 2NaCl

Calcium stearate

2C17H35COONa

+ MgSO4

(C17H35COO)2Mg

+ Na2SO4

Magnesium stearate

(Thus, water which readily lathers with soap is called soft water whereas water

which forms scum or precipitate and does not form lather immediately is called

hard water.)

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1.5.2 EDTA Method (Complexometric Titration)

Principle: It is based on the fact that hardness causing ions like Ca++

, Mg++

form

unstable complexes with the indicator Eriochrome Black T. However, when such

a complex is treated with EDTA, since EDTA has more affinity to form stable

complexes with metal ions, it extracts the metal ions from the metal ion-dye

complex to form stable metal EDTA complex. The colour of dye -metal complex

and dye are different. However, the change in colour is sharper at pH 10.0 than at

other pH ranges. The metal-dye complex has wine red colour at pH 10.0 where the

dye itself has blue colour at pH 10.0. Hence, by observing the sharp change in

colour, the exact end point of reaction involving complete extraction metal ions by

EDTA can be determined. The results obtained by this method are more accurate

than those obtained by soap titration method.

Ethylene diamine tetra acetic acid (EDTA)

Metal - EDTA chelate Ca+2 or Mg+2 +EBT ⟶

CaEBT or MgEBT Wine red complex (unstable)

CaEBT or MgEBT + EDTA ⟶ CaEDTA or MgEDTA + EBT Blue Colurless

The various steps involved in estimation of hardness by EDTA method are given

as below.

Preparation of Solutions

1. Standard hard water

1.0 gm of pure CaCO3 dissolved in minimum quantity of cone. HCI and dilated to

a one litre with distilled water. Each ml contains 1 mg CaCO3.

2. EDTA solution

4 gm of pure EDTA (disodium salt) is dissolved in one litre of water.

7

3. Eriochrome Black T Indicator 0. 5 gm of the dye is dissolved in 100 ml of pure alcohol 2 to 3 drops of indicator

is usually sufficient. Freshly prepared solutions are more suitable in order to

obtain more accurate results. 4. Buffer of pH = 10.0

67.5 of NH4Cl is mixed with 570 ml of liquor ammonia, and diluted upto a litre

with distilled water. Estimation of Hardness 1. 50 ml of standard hard water is pipetted out a clean 250 ml conical flask. Add

5 to 10 ml pH 10.0 buffer and mix well. Add 3 to 4 drops of Eriochrome

Black T. The colour of solution is wine red. 2. Fill the burette with EDTA solution and titrate against standard hard water in

flask. Let the volume of EDTA required be ‘A’ ml when the colour changes

to blue. 3. Pipette out 50 ml of sample of hard water adds to 10 ml buffer and 3 to 4

drops of indicator and titrate against EDTA from burette. Let the volume be

‘B’ ml. 4. Boil 50 ml of sample of hard water. Cool and filter, add 5 to 10 ml pH 10.0

buffer, 3 to 4 drops of indicator and titrate against EDTA till the colour

changes to blue. Let the volume of EDTA consumed be ‘C’ ml. Calculations Since standard hard water contains 1 mg/ml of CaCO3 hardness equivalent, 50 ml of standard hard water ≡ 50 mg of CaCO3 hardness 50 ml of standard hard water requires ≡ ‘A’ ml of EDTA

∴ ‘A’ ml of EDTA ≡ 50 mg of CaCO3 hardness

∴ Each ml of EDTA ≡ 50 mg of CaCO3 hardness. 50 ml of water sample requires ‘B’ ml of EDTA solution

≡ 50 mg of CaCO3 hardness (∴ 1 ml of EDTA = 50 mg of CaCO3 hardness equivalent)

∴ 1000 ml of water sample ≡ 50 100050 mg of CaCO3, hardness equivalent. Total hardness ≡ x 1000

mg of CaCO3

50 ml of water sample after boiling requires ‘C’ ml of EDTA

≡ × 50 mg of CaCO3 hardness equivalent

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(∴ 1 ml of EDTA = 50 mg of CaCO3 hardness equivalent)

∴ 1000 ml water sample after boiling

≡ × 50 × 100050 mg of CaCO3 hardness equivalent

≡ 1000 × mg of CaCO3 hardness equivalent. Permanent hardness = × 1000 mg of CaCO3 Temporary hardness = Total hardness - Permanent hardness

= × 1000 − × 1000

= 1000 × � − � mg of CaCO3

1.5.3 Problems on Hardness Calculations

Problem 1.1: 50 ml of standard and hard water containing 1 mg of pure CaCO3

per ml consumed 10 ml of EDTA solution. 50 ml of the given water sample

required 10 ml of same EDTA solution. Calculate the total hardness of water

sample in ppm.

Solution:

50 ml of standard hard water ≡ 10 ml of EDTA solution

∴ 1 ml of EDTA solution ≡ 5010 ml of std hard water

≡ 1050 mg of CaCO3

≡ 5 mg of CaCO3

50 ml of water sample ≡ 10 ml of EDTA solution ≡ 10×5 mg of CaCO3

≡ 50 mg of CaCO3

50 ml of water sample ≡ 50 mg CaCO3

∴ 1000 ml of water sample ≡ 50 × 100050

≡ 1000 mg CaCO3

Hardness of water sample ≡ 1000 ppm. Problem 2.2: In the determination of hardness by EDTA method, 50 ml of

standard hard water (containing 1 mg of CaCO3 hardness per ml of solution)

required 30 ml of EDTA solution, while 50 ml of the sample of hard water

consumed 20 ml of EDTA solution. After boiling 50 ml of the same sample which

required 10 ml of EDTA solution. Calculate the various hardnesses in ppm.

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Solution:

1 ml of std. hard water ≡ 1 mg of CaCO3

50 ml of std. hard water ≡ 50 mg of CaCO3

50 ml of std. hard water ≡ 30 ml of EDTA

≡ 50 mg of CaCO3

∴ 1 ml of EDTA ≡ 50 mg of CaCO3

30

≡ 20 × 5030 mg of CaCO3 1000 ml of sample water ≡ 20 × 5030 × 20 mg of CaCO3 Total hardness ≡ 664 mg of CaCO3

≡ 664 ppm. 50 ml of boiled water sample ≡ 10 ml of EDTA solution

≡ 10 × 5030 mg of CaCO3

∴ 1000 ml of boiled water sample ≡ 10 × 5030 × 20 mg of CaCO3 ≡332mg of CaCO3 i.e.

Permanent hardness

≡ 332 ppm.

i.e.

Temporary hardness ≡ Total – Permanent

≡ 664 – 332 = 332 ppm.

1.6 - SOFTENING OF WATER Softening of water means removal of hardness. Since hardness is mainly due to

the presence of soluble salts of calcium and magnesium, softening methods aim at

removal of these components from water. The lime soda process involves

converting soluble impurities into insoluble precipitates by treatment with lime

and washing soda. The precipitates are then removed by sedimentation and

filtration. Other softening methods involving replacing the calcium and

magnesium by harmless ions through exchange as in zeolite and ion exchange

processes, are more effective and efficient in removal of hardness. These methods

are discussed in detail below. 1.6.1 - Lime Washing Soda Method Principle: Calculated quantities of lime and soda (10% excess) are added to hard

water to convert soluble impurities into insoluble one which can be easily

10

removed by filtration. Reactions are as follows. If process is carried out at room

temperature it is called cold lime soda process. • Removal of temporary hardness

Ca(HCO3)2 + Ca(OH)2 2CaCO3 + 2H2O Mg (HCO3)2 + 2Ca(OH)2 Mg(OH)2 ↓ + 2CaCO3 + 2H2O

• Removal of permanent hardness causing magnesium compounds MgCl2 + Ca(OH)2 Mg(OH)2 ↓ + CaCl2 MgSO4 + Ca(OH)2 Mg(OH)2 ↓+ CaSO4

• Removal of ions like iron, aluminium, manganese

FeSO4 + Ca(OH)2 Fe(OH)2 + CaSO4 2Fe(OH)2 + 12 O2 + H2O O2 + H2O + 2Fe(OH)3 ↓ Al(SO4)3 + 3Ca(OH)2 2A1(OH)3 ↓ + 3CaSO4 2AlCl3 + 3Ca(OH)2 2A1(OH)3 ↓ + 3CaCl2

• Neutralisation of free acids

2HCI + Ca(OH)2 CaCl2 + 2H2O

H2SO4 + Ca(OH)2 CaSO4 + 2H2O • Removal of dissolved gases

CO2 + Ca(OH)2 CaCO3 + H2O

H2S + Ca(OH)2 CaS + 2H2O • Reaction with bicarbonate ions

2NaHCO3 + Ca(OH)2 CaCO3 +2H2O + Na2CO3 The above reactions also enable us to calculate the lime requirement on

quantitative basis assuming that purity of lime is 100% pure.

Reaction with washing soda

Permanent Calcium (Ca) hardness is removed by washing soda

CaCI2 + Na2CO3 CaCO3 + 2NaCl

CaSO4 + Na2CO3 CaCO3 + Na2SO4 It is to be noted that magnesium permanent hardness as well as those due to iron,

aluminium and neutralisation of acids also generate equivalent quantities of

calcium permanent hardness. Hence, while calculating the washing soda

requirement, these factors have to be taken into consideration.

As a result of lime soda treatment, hardness causing ions like Ca++

, Mg++

, Al+++

,

Fe+++

, etc. are converted into insoluble precipitates like CaCO3, Mg(OH)2,

AI(OH)3 and Fe(OH)3 which settle down and are removed. The anions, on the

other hand, combine with sodium ions to form sodium salts. Hence, in lime soda method, the hardness causing compounds are converted eventually into near equivalent amount of sodium salts. Since these chemical reactions take time and hence sufficient time should be allowed for the completion of reactions. Otherwise, precipitation can occur later causing problems. In order to ensure complete precipitation and settling, coagulants such as alum are used.

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1.6.2 - Cold Lime Soda Process Lime soda process can be carried either by batch or continuous process. a). Batch Process In this process, raw water and the required quantities of chemicals (lime, soda,

coagulants) are mixed thoroughly in big tanks provided with certain agitation

devices. Usually, two such tanks are constructed side by side so that tanks can be

used alternately. The softening process gets completed as the tank gets filled. The

stirring continues for another fifteen minutes so that the chemicals get uniformly

distributed throughout. As coagulants are included, the precipitates formed settle

down easily when stirring is stopped. The clear supernatant is then passed through

filter bed to remove any suspended particles which do not settle down easily. The

settled sludge at the bottom is removed through an outlet at the bottom of tank.

Batch process of softening is very useful to meet the requirement of soft water on

smaller scale. For industrial requirement, continuous softening treatment methods

are followed. b). Continuous Lime Soda Process In order to obtain soft water on large scale, continuous treatment methods are

used. This involves treating raw water with chemicals in continuous manner and

removing the precipitated material partly by settling and by filtration. The

equipment consists of two concentric vertical chambers. The inner chamber is

provided with stirrer whose action not only mixes the chemicals and raw water

intimately but also helps to gather the precipitated matter at the bottom in the

conical portion. The treated water containing some floating particles of precipitate

passes through a filter pad provided through which water passes. The treated

water flows out from the top of outer chamber and is filtered and used.

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Continuous Lime Soda

Process 1.7.2 - Hot Lime Soda Process

Hot lime soda softener

13

The shortcomings of cold lime soda process like incomplete precipitation, slow

reaction and reduction of residual hardness only to 30-50 ppm are overcome by

carrying out the reaction at higher temperature 50-60°C. The softening is carried out in large steel tanks having two chambers. The upper

chamber is separated from lower chamber by funnel shaped inlet. The raw water

and chemicals flow into upper chamber where they are heated directly by high

pressure steam. The treated water passes down the funnel. The precipitated matter

settles down in the conical portion of chamber and is periodically removed. The softened water is removed from an opening at top lower chamber and passed

through filter bed to remove any suspended impurities still remaining in water. The main advantages of this method are: a. The time required for treatment is reduced considerably so that larger

volumes of water can be treated. Thus, it is more economical.

b. The chemical reactions take place faster, the precipitate settles faster. The

amount of coagulant if added is very low. b. Higher temperature of water, coupled with alkaline conditions reduces the

bacterial count to minimum.

c. Iron and manganese salts are precipitated out and their content in water is also

reduced.

d. The final hardness of water after treatment is between 20-25 ppm which is

almost 50% of the value obtained by the cold process.

e. The solubility of gases like oxygen, carbon dioxide is reduced at higher

temperature and hence corrosion of boilers due to dissolved oxygen and

carbon dioxide is reduced. Though there are many advantages, use of steam for heating will add on to cost of

production. Treating large volumes of water will also generate large volumes of

sludge material which has to be disposed of simultaneously. The residual hardness

of 20-30 ppm is high and such water cannot be used in high pressure boilers. 1.7.4 - Zeolite Process of Softening (Permutit’s Process) Zeolites are naturally occurring (hydrated) sodium aluminium silicates, having

different amounts of water of crystallisation. They are represented as Na2O.

A12O3. x SiO2. y H 2O, where x varies from 2 to 10 and y from 2 to 6. The naturally occurring mineral though more durable, non-porous and has lower exchange capacity. Synthetic zeolites, on the other hand, are porous and have more exchange capacity per unit weight. Whether natural or synthetic, zeolite

have the property of exchanging their Na+ ions for hardness causing ions like

Ca++

and Calcium and magnesium zeolite on treatment with a solution of NaCI

can replace Ca++

and Mg++

ion with Na++

ions, thereby regenerating the zeolite. The reactions taking place during the process of softening are presented below:

Ca(HCO3 )2 + Na2 Ze →CaZe + 2NaHCO3

14

MgSO4 + Na2 Ze → MgZe + Na2 SO4

CaCl2 + Na2 Ze → CaZe + 2NaCl

Where Ze represents zeolite.

The zeolite mineral gets exhausted when all the Na++

ions are replaced by Ca++

and Mg++

ions. This indicates such an exhausted zeolite no longer has the

capacity to exchange any more Ca++

and Mg++

ions. Under such situation, the hardness of incoming water and outlet will be same. Zeolite can be regenerated by passing NaCI solution.

CaZe + 2NaCl CaCl2 + Na2Ze

MgZe + 2NaCl MgCl2 + Na2Ze

The regenerated zeolite can now be used for replacing Ca 2+

and Mg2+

from hard

water. Zeolite softening is carried out in large cylindrical tanks which holds the

zeolite material on a perforated platform. Sometimes it is contained between two

layers of sand. The tank is provided with two inlets, one for feeding raw water and

the other for passing saturated NaCI solution. There are two outlets, one for

softened water and the other to remove the CaCl2 and MgCl2, the wash water

formed by the regeneration process.

Fig. Zeolite process of water softening

In the process of softening, raw water is passed through the bed of zeolite where the hardness causing ions are exchanged for the sodium ion on zeolite. The water

coming out of zeolite bed now contains equivalent amount of Na + ions, instead of

Ca++

and Mg++

The presence of sodium ions does not impart any hardness to

water. However, the total dissolved solid content remains almost the same. By testing the hardness of emerging water from the zeolite bed, it would be possible

15

to determine when the bed is exhausted. When the zeolite bed is exhausted, the

hardness of incoming and outgoing waler will be the same. Zeolite bed is then

regenerated by passing NaCl solution. CaCl2 and MgCl2 formed flow down the

bed and are drained. The bed is washed with soft water and made ready for

softening more raw water. The hardness of treated water is in the range of 5 to 15

ppm. Limitations of Zeolite Process In order to achieve best results, the following points should be noted. 1. Raw water should be free of turbidity and suspended impurities as they

interfere with the exchange process by forming a coat on the zeolite material. 2. Highly acidic or alkaline water is not suitable as it affects the mineral. 3. Calcium and magnesium zeolite can be easily regenerated by passing NaCl

solutions whereas iron and manganese zeolites cannot be so easily

regenerated. Hence, iron and manganese impurities in water should be

minimum. Disadvantages of Zeolite Process 1. As compared to the lime soda process the dissolved solid is more in zeolite

process since calcium and magnesium salts are replaced by sodium salts.

2. The presence of bicarbonate and carbonates generates NaHCO3 and Na2CO3 in

softened water. This alkalinity in water is not desirable since in boilers it leads to

caustic embrittlement due to formation caustic soda.

Na2CO3 + H

2O → 2NaOH + CO2 ↑

NaHCO3 → NaOH + CO2 ↑ NaOH formed in process react with iron at high temperature of boiler to cause

corrosion. Further CO2 evolved dissolve in condensed water and causes corrosion

of condenser tubes. Advantages of Zeolite Process 1. By careful monitoring it will be possible to achieve very low hardness of less

than 5 ppm.

2. The zeolite bed gets adjusted to any hardness of incoming water, i.e.,

variation in hardness of raw water does not affect the exchange process. The

rate at which regeneration has to be carried out will vary. 3. The equipment is compact and materials used are cheap and easily available.

Suitably trained people can handle the equipment without any problem.

4. The process can be operated under pressure also. 5. Since the reaction involves only replacement of Ca

++ and Mg

++ ions with Na

+

ions, there is no chance of sludge formation after precipitation at later stage.

16

1.7.5 - Ion Exchange Process

Ion exchange resins are used for softening of water. Ion exchange resins are

organic polymers with long chains with cross links and having functional groups

through which various ions are exchanged. The resins are porous and insoluble in

water.

There are two types of ion exchange resins-cationic exchange resins which

exchange their H+ ions for cations present in water. These resins have functional

groups like − SO3 H + ,−COO H + , OH(phenolic) where the H+ ion get replaced

with other cations present in water. The anion exchange resins have functional

groups like —NH2, = NH, OH which can be exchanged with anions present in

The principle of ion exchange method is based on ability of the ion exchange

resins to exchange their functional group like H + with cations like Ca

++, M

++,

Na+ and (OH)

- with all anions present. The process of softening in the ion

exchange process involves passing raw water through cationic exchange resin and

followed by passing it through the anion exchange resin. The equipment consists

of two cylinders which contain the cation exchange resin and the anion exchange

resin. The outlet from cation exchange resin is connected to anion exchange

cylinder. Separate outlets are provided for draining purposes. Tanks provided at

the top of cylinders contain the regeneration chemicals.

As the raw water passes through the cation exchange resin, Ca ++

, Mg++

their ions

are exchanged with H+ ions of the resin.

R − H 2 + MgCl2 → R − Mg + 2HCl

Thus, sulphates, Chlorides, bicarbonates, get converted into sulphuric,

hydrochloric and carbonic acids.

The acidic water emerging from the cation exchange bed is passed through the

anion exchange bed where the anions are exchanged for the OH ions of resin.

R1 − (OH )2 + H2SO4 → R1 − SO4 + 2H2O

R1 − (OH )2 + 2HCl → R1 − Cl2 + 2H2O

The water emerging from the anion exchange bed is free from both canons and

anions and hence completely demineralised. It means it does not have any

hardness at all. However water may contain some dissolved gases. In order to

remove the dissolved gases, water is passed through degassifiers where the water

is heated, the escaping gases are removed by applying vacuum.

The cation exchange resin and the anion exchange resin are regenerated when they

get saturated with cations and anions. Cation exchange resins are generated by

passing dilute acids and anion exchange resins by passing alkali.

RCa + 2HCl → R(H)2 + CaCl2

17

R1SO4 + 2NaOH → R1(OH)2 + Na2SO4 The regenerated resins can be used for treating further fresh raw water. Thus, the

same amount of resins can be used over and again after regeneration. Water obtained from ion exchange softening process has very low residual

hardness of less than 2 ppm. It can be safely used for high pressure boilers. Limitations due to presence of certain impurities As in the case of zeolites, ion exchange resins do not function effectively in the

presence of turbidity or suspended matter as they tend to cover the surface of resin

and prevent easy exchange of ions. Similarly, very high total solid content in raw

water will mean frequent regeneration of the resin. Hence, for efficient

performance, raw water is pretreated to reduce the total dissolved solid content.

Fig. 2.5 Ion exchange method of softening of

water Advantages of Ion Exchange Process 1. The process can be used for softening acidic or alkaline waters. 2. Where mineral free water is required as in the case of some pharmaceutical,

cosmetics and explosives and other manufacturing processes, ion exchange

process of softening is the only process available for getting such pure

3. The residual hardness after treatment is less than 2 ppm and this makes water

suitable for high pressure boilers. 4. Continuous supply of softened water can be made available by providing

storage facilities and two columns of each resin.

18

Disadvantages of the Ion Exchange Process

1. The resins used are costly, the regeneration chemicals like acids and alkalis

are costlier.

2. The initial investment in equipment is more. 3. Where water is highly turbid and contains a large amount of dissolved matter,

pretreatment of such water is essential to get the best results from the ion

exchange method.

1.8 - Calculation of Water Softening Reagents

1. Calculation of hardness

Hardness should be expressed in terms of weight of CaCO 3 i.e. in milligrams per

litre (mg/l) or parts per million (ppm) or degree clark (°Cl).

2. Lime requirements

Lime, i.e. Ca(OH)2 is required for

a) Temporary calcium hardness Ca (HCO3)2.

b) Temporary magnesium hardness, Mg(HCO3)2. Lime requirement temporary

Mg hardness is double that required for Ca hardness. c) Lime eliminates permanent magnesium hardness but introduces equivalent

permanent calcium hardness.

d) Lime also reacts with dissolved CO2. iron and aluminium salts, free acid and

introduces an equivalent Ca hardness. e) Lime also reacts with bicarbonates of Na and K to form carbonates.

Since 100 parts of CaCO3 is equivalent to 74 parts of Ca(OH)2 Lime required for

softening,

74 Temp..Ca.hardness + 2 × temp. Mg hardness + perm.(Mg + Fe + 3Al) hardness

=

1

100 HCl + H 2 SO4 + HCO3 + CO2 − NaAlO2 all in terms of CaCO3 equivalents

2

3. Washing soda requirement

Washing soda is required for eliminating salts of calcium other than temporary

hardness.Since 100 parts of CaCO3 is equivalent to 106 parts of sodium

carbonate, Washing soda requirement Perm.Ca hardness + Perm.(Mg + Fe + 3Al)hardness

106

1

= HCl + H 2 SO4 − HCO − − NaAlO 2

100 2 3

all in terms of CaCO3 equivalents

Above mentioned formula are used when CaCO3 equivalents are calculated

directly. When it is calculated by using multiplication factor with respect to

chemical reaction then HCI, Aluminium equivalents are to be added directly.

19

If NaAlO2is present in water, it undergoes hydrolysis to NaOH and Al(OH)3 as

follows:

NaAlO2+2H2O → NaOH + Al(OH) 3 ↓ NaAlO2 does not need lime or soda, but since one equivalent of it produces one

equivalent of (OH) ion it can be considered equal to one equivalent of lime,

Hence, in calculation involving NaAlO2, the corresponding CaCO3 equivalent

should be deduced from lime and soda requirement.

The conversion factor for CaCO3 equivalent is 100

82 × 2

When aluminium salt present in water is other then A12(SO4)3 then multiplication

factor will be with respect to the reaction with lime.

Table: Comparison of different softening processes

Lime Soda Zeolite Demineralisation

1. Capital cost is less; Capital cost is very high, Very high capital

operational cost is high. operational cost is low. cost; but operational

cost is low.

2. It can be used for turbid it cannot be used for turbid It cannot be used for

water. water turbid water.

3. Hardness is reduced to 15 Hardness is reduced below Hardness is reduced

-30 ppm. 10 ppm. to 0 to 2 ppm.

4. Total dissolved solids are Total dissolved solids are The total dissolved

reduced. not reduced. solids are removed

completely.

5. It removes mineral acids It cannot soften acidic It removes mineral

water water. from acids from

water. 6. It removes Fe++ and Mn++ Only small quantity of It removes all cations

ions. Mn++

and Fe++

ions can be present.

removed.

7. Water softened by this Water softened by this Water softened by this

method due to residual method due to dissolved method is free from

hardness and dissolved use sodium salts is not suitable all problems and is

salts is not suitable for use for boiler use; as it creates ideal for in boiler.

in boiler as it involves problems such as scale and

problems such as scales and sludge formation, priming

sludge formation, carry foaming corrosion, etc.

over, corrosion, etc.

8. Involves many steps like No such steps involved; No such steps

coagulation, settling of gets softened in one involved water gets

precipitate, filtration, operation. softened in none

removal and disposal of operation.

20

sludge etc.

9. Change in hardness of Process gets automatically Process gets

water requires change in adjusted to change in automatically adjusted

lime and soda dose. hardness. to change in hardness.

10. Due to sludge formation No sludge formation, thus No sludge formation

it is not a clean process. it is a clean process. thus it is a clean eel

11. Reagent used cannot be The exchange medium can The exchange

regenerated, be regenerated. medium can be

regenerated.

12. It removes dissolved It does not remove It removes all

CO2 hard water. dissolved CO2 from hard dissolved from gases.

water

1.9 – Reverse Osmosis

When two solutions of different concentrations are separated by a semi permeable

membrane, solvent flows from low region concentration to higher one until

concentration is equal in both sides. This process is known as osmosis. This

technique is used for the removal of dissolved salts from seawater called

desalination or desalting of water.

Demineralised water is produced by forcing water through semi permeable

membrane at high pressure.

Principle of reverse osmosis: In this process dissolved salts are separated from

water by using semi permeable membrane. When membrane is placed in between

water containing dissolved salts and pure water. Water flows through a membrane

into salty water due to osmotic pressures.

Reverse Osmosis

21

This natural tendency of water may be reversed by applying a higher pressure on

the salty water part. This tends to flow water from higher concentrations to lower

one. This reverse process of osmosis is called as reverse osmosis. The membranes

used are cellulose acetate, cellulose butyrate, etc. This method is also known as

super filtration. This is a single and continuous process, involves no phase

changes and needs low energy. This technique is also used for the separation of

toxic ions from plating wastes, concentration of radioactive waste and removal of

organics from vegetable and animal wastes. 1.10 – Ultra Filtration Some of the toxic chlorinated organisms are removed by filtering industrial waste

with activated charcoal as follows. Aldrin, Dieldrin, Endrin, DDT, etc. are removed nearly 99%. Synthetic organic ion exchange resins are very useful for reoval of industrial

waste chemicals. Styrene-divinyl-benzene copolymer can rmove chlorinated

pesticides by adsorption at the surface. Ionic dyes from text1e mill wastewater can

be eliminated by using cation and anionic ion exchange rfrsins.

Cation exchanger- COOH+ + M

+ → COOM+

+ H+

Anion exchanger—NH+ CI

- + A

- → NH+A

- + CI-

Fig. 2.11 Filtration of industrial wastes with activated charcoal The ion exchange membrane finds an important application in the removal of

toxic wastes by ultrafiltration In ultrafiltration, the solution is pushed under

pressure through a membrane which contains pores of size 2 to 10,000 nm (20 x

105A) whereby big molecules are retained and the effluent that passes off is free

22

of the big molecules. In reverse osmosis, the membrane pores are smaller— 0.04

to 600 nm—in size. Both these techniques have found extensive application in

purification of industrial wastewater in metal, textile, protein isolation, paper and

pulp and food industries.

Industrial wastewater purification by ultra

filtration 1.11 – Sterilisations and Disinfection of water

The most important and common disinfecting agent used to treat water is chlorine

and chlorine compound like bleaching powder. Most important ingredient of our

life is water it can be purified methods like filtration boiling bleaching powder

treatment solar water disinfection (Recommended by United Nations). Filtration

and Coagulation of water through sand purify it from suspended solids and partly

decrease its bacteriological contamination. Complete disinfection is attained by

chemical reagents which kill pathogenic bacteria or microorganisms.

Chlorine gas and chlorine compounds, such as chlorinated lime, chloramines,

chlorine dioxide, hypochlorite as well as ozone, and salts of heavy metals are

effective against microorganisms. Ultraviolet radiation, ultrasound and other

physical factors also kill pathogenic organisms.

Sterilization is carried by physical methods like boiling of water and exposure to

sunlight and ultraviolet light.

1.12 - Ozonisation

Drinking water is treated with ozonized oxygen. The plant consists of a tower

made of enamelled iron, and divided into several compartments by means of

perforated celluloid partitions. The tower is provided with two inlets at the bottom

and an outlet at the top. The ozonized oxygen and water to be treated are allowed

23

to pass through separate inlets provided at the bottom and sterilized water is

collected from the outlet provided at the top. The perforated partition breaks up

the gas and water stream into minute bubbles, as a result of which intimate contact

between gas and water is affected. Ozone is produced by passing a high voltage

current through dry air using either plate or cylindrical electrodes made of

stainless steel aluminum. In industry ozone is prepared by passing dry and clean air through an ozoniser

under constant pressure, when it is subjected to a silent electric discharge. The

ozonised air is then mixed with water in special chambers. Modern equipment is

provided with bubblers and jet ejectors. In nature, ozone is formed by discharges of atmospheric electricity during storms

and by oxidation of a number of organic substances. An allotropic modification of oxygen is ozone. Under normal condition it is a

bluish gas. In liquid state, ozone is dark blue and in the solid state it is almost

black. Its solubility in water is higher than that of oxygen. Small concentration of

ozone in the air is beneficial to man, especially in respiratory pathology. But

ozone becomes harmful when concentrations reach relatively high levels.

Prolonged exposure to ozone causes irritability, headache and fatigue. At higher

concentrations nausea, nasal bleeding, and inflammation of the eye mucosa

develop. Chronic ozone poisoning results in serious illness, the maximum

allowable concentration of ozone in industrial air is 0.1 mg/cu.m Due to high oxidation potential of ozone (2.076v) and the ease with which it

passes through the cell membranes of microbes. Ozone oxidises the organic

substances in the microbe cell in order to kill it. It has stronger bacterial action

than chlorine (1.36v). Experimental investigations show that if one ml of water contains 274-325 E. coli

type bacteria, 86% arc killed by an application of 1 mg/litre of ozone and 2

mg/litre of ozone fully disinfects the water. Spore forming bacteria are more

resistant to ozone than non -spore forming bacteria, but they are resistant to

chlorine as well. The dose of ozone required for water disinfection depends on the

degree of pollution, but usually varies from 0.5 to 4.0 mg/litre. Ozone consumption increases with water turbidity and higher doses are required

for turbid waters. The disinfecting action of ozone is almost independent of the

temperature of water. Ozonisation not only decontaminates water but also gives it

a pleasant taste, reduces its colour and deodorises produced by oxidation and

mineralisation of organic impurities. Humins are completely broken down by

ozone to give CO2 and H2O.

24

Ozonisation of water also has some advantages over chlorination.

(a) It improves the organolepetic properties of water and does not add to its

chemical pollution (b) Ozonisation does not require additional processes to

remove excess bacterial agents from purified water hence higher doses of ozone

can be used (c) Ozone can be prepared in situ. Only electricity is required, and a

single chemical reagent, silica gel, on which moisture is adsorbed from the air.

Sterilization with ozone has several advantages for example

(a) Ozone sterilizes, bleaches, decolourises and deodorizes water. (b) An excess of

ozone in water causes no danger because being unstable it decomposes into

oxygen. (c) It causes no Irritation of mucous membrane ax in case of chlorine

treatment (d) The taste of water is improved with ozone. Highly palatable water is

thus sterilised wish ozone. The most important disadvantage of the ozone

sterilization is the high cost involved in the treatment.

Ozonisation is not used widely because of the complexity of ozone manufacture

and the large amounts of high frequency and high voltage electricity required.

Ozonisation of water will be profitable only if a suitable material is found,

electricity is cheap, and the method of bringing water in contact with ozone is

improved.

Ozone is a corrosive agent the gas and its aqueous solutions destroy steel, cast

Iron, copper, rubber, and ebonite. All apparatus for the manufacture of ozone and

the pipes through which its solutions pass should be of stainless steel or

aluminium. Stainless steel can withstand the corrosion for 15-20 years and

aluminium for 5-7 years.

1.13 – Chlorination

Chlorination or shock chlorination is the process of flushing your well and water

system with a chlorine solution to kill bacterial and other micro organisms. It is

probably the best and cheapest method of sterilization of water and it is most

effective in checking pathogenic microorganisms. Chlorine may be used directly

in the liquid form or as bleaching powder. The excess of chlorine is removed by

suiphites anti- chlor.

The disinfecting action of chorine and its compounds depends on the oxidation-

reduction processes occurring in microbial cells subjected to the influence of these

chemicals. The Hypochlorous acid (HOCl) reacts with bacterial enzymes to

interfere with the metabolism inside the cell Free and bound active chlorine have

25

different oxidation potentials and the reaction rates and the required contact time

are also different. HOCl is most effective chlorine compound. The chemical action of chlorine is that it reacts with water to form hypochlorous

acid and nascent oxygen. Both these are powerful germicides.

Cl2

+ H2O

HOCl + HCl

Hypochlorous Acid

HOCl

HCl

+ [O] Nascent Oxygen

The chlorine effectiveness against microbes depends on the initial dose of

chlorine, the time it is in the water, and the pH of the water. Chlorine is consumed

to oxidise organic mineral impurities in water. Organic impurities in water are

destroyed with chlorine. Humins are mineralised to CO2, Fe2+

is oxidised to Fe3+

,

Mn2+

is oxidised to Mn4+

and stable suspensions are converted into unstable ones

because of decomposition of protective colloids. Sometimes plant and animal

organisms destroyed by chlorine in the water are converted into decay products

with a strong odour. Chlorination of water containing phenols and other aromatic

substances gives an especially unpleasant odour. Smack and odour develop in

water containing quantities of phenols as small as 1 : 10000,000. They strengthen

with time and do not disappear on heating. Large doses of chlorine are sometimes

required to destroy the aromatic compounds. Chlorination is very important for the purification of water. It discolours water

and provides good condition for clarification and filtration. When chlorine is

dissolved in water gives two acids, HCl and HOCl, the latter being a very weak

acid, its dissociation depends on the pH of the medium, The lower the pH of the

medium, the higher the concentration of HOCl, which disinfects water because of

its high redox potential.

Cl- + H2O ⇌ HOCl + H+ +2e- ; + 1.49 V

When chlorine compound added to water, they are hydrolysed to give HOCl.

For example 2CaOCl2 + 2H2O ⇌ CaCl2 + Ca(OH)2 + 2HOCl Chlorinated lime

Ca(OCl)2 + 2H2O

⇌ Ca(OH)2 + 2HOCl

Calcium Hypochlorite

NaOCl + H2CO3 ⇌ NaHCO3 Sodium Hypochlorite + HOCl

NaOCl

+ H2O

⇌ NaOH + HOCl

26

Hydrolysis of salts is slower than that of free chlorine, and the formation of HOCI

is therefore slower as well. But the further action of HOCI is the same as the

dissociation of Cl2 gas in water.

The quantity of molecular chlorine corresponding to the oxidizing power of a

given compound w.r.t potassium iodide in an acid medium is called active

chlorine. Each pair of electrons accepted by the oxidant is equivalent to 71 carbon

units of free chlorine. Therefore the compounds Cl2, NaOC1, CaOCl2, NH2Cl,

H2O2 correspond to 71 parts by weight of active chlorine, and the compound

NHCl2 to 142 parts.

The concept of active chlorine describes oxidizing power of a compound (w.r.t KI

in an acid medium) rather than the actual chlorine content of a given compound

example a gm. molecule of NaCl contains 35.5 g. of chlorine, but the active

chlorine content is zero. The actual chlorine content of a gm. molecule of NaOCl

is 35.5 g. and the active chlorine content is 71 g.

The active chlorine content in. a chlorine compound in percent can be calculated

by the relation.

Cl2 Percent = 0 x 10

n the number of hypochlorite ions In a molecule of a chlorine compound, M0, the

molecular mass of chlorine compound and M the molecular mass of chlorine. For

example the active chlorine content of chlorinated lime of the composition

3CaOC12.Ca(OH)2.5H2O is:

Cl2 % = 3 71 100

= 39.08 % 545

Here n = 3, M0 = 545 g. and M = 71 g.

1.14 – ELECTRODIALYSIS

In the electrodialysis method positive and negative ions are separated out of a

flowing current of saline or brackish water when it is allowed to pass through ion

exchange membranes under the influence of an electric field. Infect when a direct

current of electricity is passed through a saline water in a series of closely spaced,

alternately placed, cation exchanger and anion exchanger membranes, cations pass

through the cation exchanger membranes and anions through the anion exchanger

membranes. As movement of cations and anions result in the salinity decreases in

one space and increases in the next space, and so on throughout the stack. The

water containing more salt (increased salinity) is run to waste, while the water

containing less salt (decreased salinity) may either be re - circulated through the

stack or may be passed through a series of stacks in this manner, saline water may

be converted into drinking water.

27

Completely deminerlised water is not obtained by this method. The method

reduces the salinity of brackish water so as to make it suitable for drinking and

general use. The process is capable at reducing salt contents of brackish water

from 2000 to about 300 ppm, but it is very costly. For more efficient separation, Ion selective membranes, which are permeable to

only one kind of ions with specific charge, have been used in recent years. cation

selective membranes . Permeable to cation only and anion selective membranes

are permeable to anions only. The permeability of permeable ions, inside the

membrane pores. The ion selective membrane pores and designed with fixed

charge which exclusively allows one type of charged ions to pass through its pores

and does not allow oppositely charged ions to flow. 1.15 – BLEACHING POWDER

Bleaching powder CaCl2 (Calcium Hypochlorite is widely used as a bleaching

agent. After removing organic matter, suspended impurities etc, water is mixed

with required amount of bleaching power and mixture is allowed to stand for

several hours for the completion of sterilization.

CaOCl2 + H2O Ca(OH)2+ Cl2

Cl2 + H2O HOCl + HCl

HOCl HCl + [O]

Nascent Oxygen Both HOCl and Nascent oxygen are powerful germicides. Solubility of bleaching

powder is part 1 in 20 parts of water. It is very important to use calculated amount

of bleaching powder because excess of it gives bad odour and disagreeable taste,

28

while less quantity of it than required, will not sterilize the water completely. The

various factors on which the quantity of bleaching powder to be added for

complete sterilization depends are temperature, turbidity of water, time allowed

for sterilization and quantity of oxidisable micro organisms present in water.

The disadvantages of using bleaching powder are:

(a) Excess of bleaching powder in water causes unpleasant odour and disagreeable

taste. (b) As it introduces calcium in water as a result water becomes hard. (c) The

amount of chlorine liberated from a sample of bleaching powder with excess of

dilute acids or CO2 is called available chlorine, hence it is priced based on the

quantity of available chlorine.

CaOCl2+ H2SO4 CaSO4 + H2O+ Cl2 (Available chlorine)

More the available chlorine in bleaching powder better is its quality. A good

sample of bleaching powder contains 35-38% available chlorine.

Example 1: The water works department of a city, which has a population of

50,000 has to meet its water demand at the rate of 150 litres per capita per day.

Water is disinfected by making use of bleaching powder having 30% available

chlorine. Determine the quantity of the bleaching powder, is added annually. The

dose required at the works is 0.2 ppm of chlorine for disinfection.

Solution : Water required for the city per day =150 x 50000 = 7500000 litres =

7.5 x 106 litres. The dose of chlorine required per day = 0.2 ppm = 0.2 mg per litre

= 0.2 x l0-6

kg per litre. Hence amount of chlorine required = 7.5 x 10 6 x 0.2 x

10-6

kg = 1.50 kg.

The bleaching powder has 30% of available chlorine. So bleaching powder

required = 1.5 x 100/30 = 5.0 kg per day.

or 5.0 x 365 = 1825 kg per year.

Bleaching powder contains about 56% of chlorine (71 x 100/127) = 55.9%. whole

of it is not available for reaction because on standing it undergoes slow auto

oxidation and gets converted into calcium chloride and calcium chlorate. Hence

percentage of available chlorine in bleaching powder decreases on storage.

Whenever it is to be added, it analysed for its available chlorine content.

6Ca(OCI)2 5CaCI2 + Ca(ClO3)2

High test hypochlorite (HTH), Ca(OCI)2 has also been used for sterilization. It

has got an advantage over bleaching powder in that the percentage of chlorine in it

is higher than that in bleaching power. Ca(OCl)2 + 2H2O ⇌ Ca(OH)2 + 2HOCl

29 HOCI ⇌ HCl + [O]

Nascent oxygen Chlorination is the best method because of its various advantages. (a) liquid chlorine it more effective as well us cheapest. (b) Liquid chlorine can be

obtained in pure form and its storage without any problem. (c) on its storage no

deterioration or decomposition occur for many days because it is stable. (d) liquid

chlorine can be used at low, moderate or even at high temperatures. (e) No

impurities are introduced by adding liquid chlorine to water. Chlorination of water to such an extent that not only the living organisms. but

other impurities in water are completely destroyed is called break point

chlorination. Depending on the stage of treatment at which chlorine is added and also the

expected results of chlorination, various forms of chlorination are (a) Plain chlorination. (b) Prechorination, (c) Poatcodnation. (d) Double chlorination. (e) Super chlorination. (f) Breakpoint chlorination. (g) Decholrination (a) Plain chlorination only chlorine treatment is given to raw water, Water from

deep wells, lakes, reservoirs etc is comparatively dear with turbidity less than 30

ppm. In such cases no treatment such as sedimentation, coagulation etc is

necessary. The chlorine is added to raw Water in order to control the Forth of

algae and to remove pathogenic bacteria. it also removes organic matter and

colour from water. The quantity of chlorine to be added to raw water is about 0.50

ppm or more. Thus when no other treatment except chlorination is given before

supplying water to consumers, it is called plain Chlorination. (b) Pre chlorination: When chlorine ii added to raw water before any treatment,

it is called pre chlorination. It is usually done before raw water enters

sedimentation tanks. It reduces the taste and odour of water, improves coagulation

and less quantity of coagulant is required when this treatment is adopted. It also

controls the growth of algae in sedimentation tanks as well as in filters and

prevents the purification of sludge in the settling tanks (c) Post chlorination - After all the treatments of purification of water are

completed, it is called pent chlorination. Chlorine is applied to water. The dosage

of chlorine should be such that a residual chlorine of about 0.10 to 0.20 ppm

appears in water at the point of its entry into the distribution system. (d) Double chlorination- When more than one point, chlorine is added to raw

water the process is called double chlorination. Pre chlorination as well as post

30

chlorination is necessary when raw water is highly contaminated and contains a

large amount of bacteria or microorganism. The second unit of chlorination, in

addition, serves as a standby unit and as a result load of impurities is greatly

reduced.

(a) Super chlorination- Super chlorination is generally adopted for highly

polluted water. The application of chlorine beyond the stage of break point is also

known as super chlorination. Super chlorination is generally practicised in

waters where plain chlorination produces taste and odour, the water is coloured

and Mn and Fe are to be oxidised. This is also resorted to when the contact time is

limited at the pre chlorination stage. The super chlorination can also be adopted

when there is high content of organic impurities. The residual chlorine content

after break point may be 0.50 to 2.0 ppm. The excess chlorine may be added at the

end of filtration. Super chlorination effectively destroys organisms. The contact

period is generally 10-30 minutes. After super chlorination, it is necessary to be

removing excess chlorine by the process of dechlorination before water is sent for

consumption. The method of super chlorination followed by dechlorination

affords a maximum degree of security. The process can be installed in the form of

a 1oop. At one end of the loop, the water is chlorinated and at the other end of the

loop, it is dechlorinated.

(7) Dechlorination: Chlorine removal from water is called dechlorination. It is

done in such a manner that at the end for dechlorination process some residual

chlorine still remains in water to disinfect it when it is flowing through the

distribution system. The usual chemical compounds used are sodium thiosulphate,

sodium bisulphate, sodium sulphite activated carbon and potassium permanganate

but dechlorination is best carried out by the addition of sulphur dioxide or by

aeration. Water after breakpoint chlorination is subjected to dechlorination and

hence filtered through activated carbon which removes decomposition products as

well as excess of chlorine. A sulphur dioxide treatment is very common. Some

plants also make use of sodium bisulphite and sodium thiosulphate as antichlor.

H2O + SO2 H2SO3 H2O +Cl2 HClO + HCl

HClO +H2SO3 HCl + H2SO4

SO2+ Cl2+ 2H2O H2SO4 + 2HCl 1.16 – OTHER IMPORTANT METHODS

Chloramine process - this method consists in adding ammonia and chlorine to

water when mono and dichloroamines are formed, which destroy all the bacteria.

2NH3 + Cl2 NH4Cl + NH2Cl

3NH3+Cl22NH4Cl+NH4Cl2

31

The method does not impart chlorinous taste and odour to water. Further growth

of any bacteria is prohibited by the presence of high residual chlorine contents in

water. Ammonia used is generally half the quantity of chlorine. The chloramines

compounds are more bacterial than chlorine alone, because these are more lasting

than chlorine alone. Treatment with chloramines is slower than with free chlorine. The water and the

chloramines must be in contact for two hours. Chlorine consumption during

chlorination with ammoniation is the same as for treatment with chlorine alone.

But chloramines are good for disinfecting water containing large quantities of

organic matter, because the chlorine requirements are much lower in this case. If

water contains aromatic substances it acquires an unpleasant chlorophenolic

odour. The odour begins to develop at the point when chlorine stops binding Into

the chioramines. The latter do not react with aromatic hydrocarbons and do not

therefore, impair the organoleptic properties of the water. Chlorine dioxide - Chlorine dioxide, ClO2 has been found to be more effective in

the removal of bacteria than chlorine. Its advantage over chlorine is that ClO2

oxidises phenols to quinone and maleic acid, which do not give off the unpleasant

chlorophenolic odour. It also removes tastes and odours present in water. ClO2 is

very unstable and so it is used immediately after its production. It can be prepared

by passing Cl2 gas through sodium chlorite.

2NaClO2 + Cl2 2NaCl + 2ClO2 It can also be prepared by the action of HCl on sodium chlorite.

5NaClO2+4HCl 5NaCl+4ClO2+H2O

The dosage of ClO2 varies from 0.50 to 1.50 ppm. Its action is unaffected by pH

values between 6 to 10 and hence it is useful for water with high alkalinity. Iodine method - Water in swimming pools is iodinated, A saturated iodine

solution in water is used. The concentration of the solution increases with

temperature. For example, at 10C, the solubility of iodine in water is 100 mg per

litre, at 200C, 300 mg per litre, and at 50

0C, 750 mg per litre. At pH less than 7,

the iodine dose for the disinfection of water from natural sources varies from 03 to

1.0 mg/litre. The odour of iodine cannot be smelled because it can be sensed at

concentrations above 1.5 mg/litre. If the water contains chioramines, iodic acid

(because of lower oxidising power) remains inactive till the moment when a

strong oxidant is exhausted. This increases the time of the bactericidal action of

iodic acid. Water can also be disinfcted by organic iodine compounds, known as

Iodophores Potassium permanganate method— In villages the well water is sterilized by

adding calculated amount of potassium permanganate. This method is,

however, not popular because it is costly.

32

1.17 - CHEMICAL OXYGEN DEMAND (COD)

Chemical oxygen demand (COD) is the amount of oxygen used while oxidising

organic matter by means of strong oxidising agent. All organic matters are

converted into CO2 and H 2O. In chemical oxidation both biologically oxidisable

organic matter like starch, sugar, inert materials like cellulose, etc. are oxidised

and hence COD values are always higher than BOD. COD can be determined in 3

hours.

The wastewater sample is refluxed with a known excess of potassium dichromate

in a dilute sulphuric acid in the presence of silver sulphate as a catalyst or HgSO4.

The organic matter of the sample is oxidised to water, carbon dioxide and

ammonia. The unreacted excess of dichromate remaining is titrated with standard

solution of ferrous ammonium sulphate.

COD =

(V1 −

V

2

)× N

×

8

×100mg / L x

V1 = volume of ferrous ammonium sulphate required for blank

V2 = volume of ferrous ammonium sulphate required or test

N = normality of ferrous ammonium sulphate

x = volume of the sewage sample taken.

If an inorganic substances like chlorides, nitrates and organic substances like

benzene pyridine are present in wastewater they interfere as they are also oxidised

by dichromate and create an inorganic COD. Chloride interference can be

eliminated by adding mercuric sulphate prior to the addition of other reagents and

nitrite interference by adding sulphanic acid to the dichromate solution. COD is

much more useful than the BOD for estimating amount of oxygen in industrial

wastes. Ratios of BOD/COD can be employed to get an indication of the degree of

the bio-treatability of the waste. 0.8 or higher ratio indicates wastes are highly

amenable to biological treatment, while lower ratios indicate that the wastes is not

favourable to biological treatment. COD is important in calculating the efficiency

of treatment plants and proposing standards for discharge of domestic effluents.

Sewage: Water containing domestic or municipal waste is called sewage, which

contains nearly 99.95% water and 0.05% waste materials. Strength of sewage is

expressed in terms of Biological Oxygen Demand (BOD) and Chemical Oxygen

Demand (COD).

1.18 BIOLOGICAL OXYGEN DEMAND (BOD)

Is the quantity of dissolved oxygen required by bacteria for the oxidation of

organic matter under aerobic conditions or it is a measure of the oxygen utilised

by micro organisms during the oxidation of organic materials. The demand for

oxygen is directly proportional to the amount of organic wastes which has to be

broken down. Hence, BOD is a direct measure of oxygen requirement and an

33

indirect measure of biodegradable organic matter. Greater BOD greater is the

pollution. A known volume of sewage sample is diluted with known volume of dilution

water. This diluted sample is taken in two stoppered bottles of 300 ml. The

dissolved oxygen (DO) content of one of the bottles is immediately determined by

Winkler’s method (blank). Another bottle is incubated at 20°C for a period of 5

days. Then unused oxygen is determined. The different in the BOD of water

sample.

BOD = (DOb — DOS) x dilution factor

DOb = dissolved oxygen present in the blank.

D OS = dissolved oxygen of sewage after incubation BOD is expressed in mg/l. 5 days BOD of wastewater can be obtained in 2.5 days

if the temperature is 35°C rather than 20°C. BOD enables us to determine the

degree of pollution hence it has special significance is pollution control. BOD

values are useful generally in process design and loading calculations,

measurement of treatment efficiency and operation, self pollution control and in

determination of self purifying capacity of a steam. 1.19 - ACTIVATED SLUDGE PROCESS Activated sludge is a process for treating sewage and industrial wastewaters

using air and a biological floc composed of bacteria and protozoans. It is an

important part of the municipal wastewater treatment is the BOD-removal. The

removal of BOD is done by a biological process, such as the suspended growth

treatment process. This biological process is an aerobic process and takes place

in the aeration tank, in where the wastewater is aerated with oxygen. By creating

good conditions, bacteria will grow fast. The growth of bacteria creates flocks and

gases. These flocks will removed by a secondary clarifier.

34

Where:

Q = flow rate of influent [m3/d]

QW = waste sludge flowrate [m3/d]

Qr = flowrate in return line from clarifier [m3/d]

V = volume of aeration tank [m3]

S0 = influent soluble substrate concentration (bsCOD) [BOD g/m3] or

[bsCOD g/m3]

S = effluent soluble substrate concentration (bsCOD) [BOD g/m3] or

[bsCOD g/m3]

X0 = concentration of biomass in influent [g VSS/m3]

XR = concentration of biomass in return line from clarifier [g VSS/m3]

Xr = concentration of biomass in sludge drain [g VSS/m3]

Xe = concentration of biomass in effluent [g VSS/m3]

This system is usually placed between the primary clarifier and the disinfection of

a municipal wastewater treatment plant.

The parameters of which the symbols are shown in the schematic diagram, are

used to model a suspended growth process. In a Summary of all the Related

Calculations one can calculate all the necessary design characteristics of a

Complete - Mix Suspended Growth Process.

Process: The picture below shows a simplified flow diagram for biological

processes used for wastewater treatment. The influent wastewater (e.g. municipal

wastewater) goes through several stages in which different compound are

removed out of the wastewater.

Simplified flow diagram for a biological wastewater treatment with a activated-

sludge process.

▪ In the Bar Rack coarse solids are removed, such as sticks, rags, and other

debris in untreated wastewater by interception. By use of fine screening even

floatable matter and algae are removed.

35

▪ In the Grit Chamber grit is removed consisting of sand, gravel, cinders, or

other heavy solid materials that have subsiding velocities or specific gravities

substantially greater than those of the organic putrescible solids in

wastewater.

▪ The Primary Clarifier is a basin where water has a certain retention time

where the heavy organic solids can sediment (suspended solids). Efficiently

designed and operated primary sedimentation tanks should remove from 50 to

70 percent of the suspended solids and 25 to 40 percent of the BOD.

▪ The influent of the aeration tank is mixed with activated sludge and in the

Aeration Tank the mixed liquor is aerated. By aerating the mixed liquor the

aerobic processes will be stimulated, the growth rate of bacteria will be must

faster.

▪ Because the bacteria deplete the substrate, flocculation takes place . The

soluble substrate becomes a solid biomass. These flocks of biomass will

sediment in the Secondary Clarifier.

▪ At the end of the process the effluent water is treated to disinfect it and make

it free of disease-causing organisms.

36

Solved Problems for Practice

1. A sample of water found to contain following impurities in mg/litre.

Mg(HCO3)2 = 73 MgSO4 = 120 mg , CaCl2 = 222mg, Ca(NO3)2 = 164 mg.

calculate lime and soda requirement for treatment of 10000 liters of water.

Solution : Conversion of the impurities in CaCO3 equivalent .

Substance quantity conversion CaCO3 equivalent mg / liter

mg/liter factor

Mg(HCO3)2 73 100 100

× 73 = 50 146 146

MgSO4 120 100 100

× 120 = 100

120 120

CaCl2 222 100 100

× 222 = 200

111 111

Ca(NO3)2 164 100 100

× 164 = 100

164 164

Lime requirement for softening. (Temp. Ca hardness + 2 × Temp. Mg hardness + Perm. Mg hardness)

(0 + 2 × 50 + 100)

(200) = 148 mg/liter.

Lime requirement for 10,000 liters of water = 148 × 10000 × 10-6

= 1.480 Kgs.

Soda requirement for softening = 106 [ Perm. Ca + Perm. Mg]

100

= 106 [ 200 + 100 + 100]

100

= 106 [400] = 424 mg/liter

100

Soda requirement for 10,000 liter = 424 × 10,000 × 10-6 = 4.24 kg.

= 74 100

= 74 100

= 74 100

37

2. Calculate quantities of lime and soda required for softening of 20,000 liters of

water containing following salts in ppm (16.4 ppm NaAlO2 used as a coagulant) Ca2+

= 160 ppm, Mg2+

= 72 ppm, HCO3 - = 73.2 ppm, CO2 = 44 ppm, Al2(SO4)3 =

34. 2, HCl = 36.5 ppm

Solution : Conversion of the impurities in CaCO3 equivalent .

ion or salt amount conversion CaCO3 equivalent (ppm)

present (ppm) factor

Ca2+

160 100 100 × 160 = 400 40 40

Mg2+

72 100 100

× 72 = 300 24 24

HCO3 73.2 100 100 × 73.5 = 60

122 122

CO2 44 100 100

× 44 = 100 44 44

NaAlO2 16.4 100 100 × 16.4 = 10

164 164

Al2(SO4)3 34.2 100 100 × 34.2 = 10

342 342

HCl 36.5 100 100 × 36.5 = 100 36.5 36.5

Lime requirement for softening.

= 74 (300 + 3(10) + 1�2 (100) +100 + 60 - 10)

100

= 74 (530) = 392.2 mg/liter. 100

Lime requirement for 20,000 liters of water = 392.2 × 20000 × 10-6 = 7.84 Kgs.

Soda requirement for softening

= 106 [ 400 + 300 + 3(10) + 1�2 (100) – 60 – 10]

100

= 106 [710] = 752.6 mg/liter 100

Soda requirement for 20,000 liter = 752 × 20,000 × 10-6

= 15.05 kg.

38

3. A water sample contains following impurities per liter. Ca(HCO3)2 = 81 mg,

Mg(HCO3)2 = 73 mg, CaSO4 = 68 mg, MgSO4 = 60 mg, KCl = 100 mg. Calculate

(a) Temporary hardness and permanent hardness in water.(b) Quantity of lime

and soda required in kg for softening 50,000 liters of water if the purity of lime

and soda are 80 % and 90 % respectively .

Solution : Conversion of the impurities in CaCO3 equivalent .

Substance quantity conversion CaCO3 equivalent mg / liter

mg/liter factor

Ca(HCO3)2 81 100 100

× 81 = 50

162 162

Mg(HCO3)2 73 100 100

× 73 = 50

146 146

CaSO4 68 100 100

× 68 = 50

136 136

MgSO4 60 100 100

× 60 = 50

120 120

1. KCl does not react with lime or soda and its presence can be ignored

2. Temporary hardness in water = hardness due to Ca(HCO3)2 and Mg(HCO3)2

= 50 + 50 = 100 mg / liter

3. Permanent hardnes in water = hardness due to CaSO4 and MgSO4

= 50 + 50 = 100 mg / liter

4. Lime requirement for softening. = 74 (Temp. Ca hardness + 2 × Temp. Mg hardness + Perm. Mg hardness)

100

= 74 (50 + 2 × 50 + 50) 100

= 74 (200) = 148 mg/liter. 100

Since lime purity is only 80 %

So actual lime requirement for 50,000 liters of water

= 148 × 100 × 50000 × 10-6 80

= 9.25 kg.

39

5. Soda requirement for softening = 106 [ Perm. Ca + Perm. Mg]

100

= 106 [ 50 + 50 ] 100

= 106 [100] = 106 mg/liter 100

Since purity of soda is only 90 %

So actual Soda requirement for 50,000 liter

= 106 × 100 × 50,000 × 10-6 90

= 5.89 kg.

4. Calculate the amount of lime and soda required for softening 50,000 liters of

hard water containing the following salts in ppm.

Ca(HCO3) 2 = 162 ppm, MgCl2 = 9.5 ppm, Fe2O3 = 100 ppm, NaCl = 58.5 ppm,

SiO2 = 25 ppm, H 2SO4 = 98 ppm, MgSO4 = 60 ppm, CaCO3 = 100 ppm.

Also calculate cost of lime and soda if cost of lime is Rs. 530 / 100 kg and soda

is Rs. 450/10 kg.

Solution : Conversion of the impurities in CaCO3 equivalent .

Salt Amount conversion CaCO3 equivalent ppm

Present ppm factor

Ca(HCO3)2 162 100 100 × 162 = 100

162 162

MgCl2 9.5 100 100

× 9.5 = 10 95 95

Fe2O3 100 ppm does not contributes to hardness

NaCl 58.5 ppm -

-

SiO2 25ppm

H2SO4 98 100 100 × 98 = 100 98 98

MgSO4 60 100 100

× 60 = 50 120 120

CaCO3 100 100 100 × 100 = 100

100 100

40

Lime requirement for softening. = 74 (200 + 10 + 50 + 100)

100

= 74 (360) = 266.4 mg/liter. 100

Lime requirement for 50,000 liters of water = 266.4 × 50000 × 10-6 = 13.32 kg. = Rs. 70.59

Soda requirement for softening = 106 [ 10 + 50 + 100]

100

= 106 [160] = 169.6 mg/liter 100

Soda requirement for 50,000 liter = 169 × 50,000 × 10-6 = 8.48 kg. = Rs. 38.16

Total Cost = 70.59 + 38 .16 = Rs. 108.6

5. Calculate the quantity of lime and soda required for softening 1,00,000 liters of

water containing the following impurities. Ca(HCO3)2 = 30.2 ppm, Mg(HCO3)2 =

20. 8 ppm, CaCl2 = 28.1ppm, MgCl2 = 8.7 ppm, CaSO4 = 35.0 ppm, MgSO4 =

6.7 ppm. The purity of lime is 70 % and the purity of soda is 85 % (At. wt. for H

= 1, C = 12, O = 16, Na = 23, Mg = 24)

Solution : Conversion of the impurities in CaCO3 equivalent .

Impurity amount in conversion CaCO3 equivalent in ppm

ppm factor

Ca(HCO3)2 30.2 100 100 × 30.2 = 18.64 162 162

Mg(HCO3)2 20.8 100 100 × 20.8 = 14.24 146 146

CaCl2 28.1 100 100 × 28.1 = 25.31 111 111

MgCl2 8.7 100 100

× 8.7 = 9.15 95 95

CaSO4 35 100 100

× 35 = 25.73

136 136

MgSO4 6.7 100 100

× 6.7 = 5.58 120 120

41

Lime requirement for softening. = 74 (18.64 + (2 ×14.24) + 9.15 +5.58)

100 = 45.769 mg/liter or ppm

Since Lime is 70 % pure

So lime requirement for 100,000 liters of water = 45.769 × 100

70 × 100000 × 10-6

= 65.384 kg.

Soda requirement for softening = 106 [ 25.31 + 25.73 + 9.15 +5.58]

100 = 69.71 mg/liter

Since purity of soda is 85% So requirement of soda for 100,000 liter = 69.71× 10085 × 100,000 × 10-6

= 82.01 kg.

6. Calculate the quantity of lime and soda required for softening 10,000 liters of water containing the following impurities per liter. Ca(HCO3)2 = 7.8 mg,

Mg(HCO3)2 = 8.0 mg, CaSO4 = 12.2 mg, MgSO4 = 10.6 mg, NaCl = 5.5 mg,

SiO2 = 2.2 mg. (At. wt. for H = 1, C = 12, O = 16, Na = 23, Mg = 24)

Solution : Conversion of the impurities in CaCO3 equivalent .

impurity amount conversion CaCO3 equivalent mg / liter

mg/liter factor

Ca(HCO3)2 7.8 100 100

× 7.8 = 4.8

162 146

Mg(HCO3)2 8.0 100 100

× 8.0 = 5.4

146 146

CaSO4 12.2 100 100 × 12.2 = 8.9

136 136

MgSO4 10.6 100 100 × 10.6 = 8.8

120 120

Lime requirement for softening.

= 74 (4.8 + 2 × 5.4 + 8.8) 100

42

= 18.05 mg/liter. For 10,000 liters of water lime requirement = 18.05 × 10000 × 10-6

= 0.1805 kg. = 180.5 gm

Soda requirement for softening = 106 [8.9 +8.8]

100

= 18.23 mg/liter Soda requirement for 10,000 liter = 18.23 × 10,000 × 10-6

= 0.1823 kg. = 182.3gm

7. Calculate the amount of lime (90% pure) and soda (95% pure) required to

soften one million liters of water which contains the following impurities.

CaCO3 = 15 ppm, MgCO3 = 9 ppm, CaCl2 = 20 ppm, MgCl2 = 8 ppm, CO2 = 30

ppm, HCl = 9.2 ppm.

Solution : Conversion of the impurities in CaCO3 equivalent .

impurity amount in conversion CaCO3 equivalent in ppm

ppm factor

CaCO3 15.0 100 100 × 15.0 = 15.0

100 100

MgCO3 9.0 100 100 × 9.0 = 10.7 84 84

CaCl2 20.0 100 100 × 20.0 = 18.0

111 111

MgCl2 8.0 100 100 × 8.0 = 8.42 95 95

CO2 30.0 100 100

× 30.0 = 68.18 44 44

HCl 9.2 100 100

× 9.2 = 12.6 36.5 36.5

Lime requirement for softening.

= 74 (15 + 3(10.7) +8.42 +68.18 + 12.6) ×

100 (90 % purity of lime)

90 100

= 103.27 mg/liter Lime requirement for 10,00,000 liters of water = 103.27 × 10,00,000 × 10

-6

43

= 103.27 kg.

Soda requirement for softening

= 106 [ 18+ 8.42 + 12.6 –17.6] ×

100 (95% purity of lime)

95 100

= 41.07 mg/liter

Soda requirement for 10,00,000 liter = 41.07 × 10,00,000 × 10-6 = 41.07 kg.

8. Calculate of lime and soda required for softening 50,000 liters of water

containing following salts ( Purity of lime is 95 % and soda = 93 %) CaCO3 =

34.1 mg /liter, Mg(HCO3)2 = 29.2 mg / liter, Mg(NO 3) 2 = 29.6 mg, MgSO4 =

36.0 mg / liter , CaSO4 = 27.2 mg / liter, MgCl2 = 47.5 mg / liter, SiO2 = 105 mg /

liter , NaCl = 52 mg / liter, H2SO4 = 9.8 mg/lit.

Solution : Conversion of the impurities in CaCO3 equivalent .

Substance quantity conversion CaCO3 equivalent mg / liter

mg/liter factor

CaCO3 35.0 100 100 × 35.0 = 35

100 100

Mg(HCO3)2 29.2 100 100 × 29.2 = 20

146 146

Mg(NO3)2 29.6 100 100 × 29.6 = 20

148 148

MgSO4 36 100 100

× 36 = 30

120 120

CaSO4 27.2 100 100 × 27.2 = 20

136 136

H2SO4 9.8 100 100

× 9.8 = 10 98 98

Lime requirement for softening.

= 74 (35 + 2(20) + 100 +10)× 50,000 ×

100 ×10-6 (Purity of lime is 95%)

95

100

= 7.408 kg.

Soda requirement for softening

= 106 [ 20 + 100 + 10] × 50,000 ×

100 ×10-6 (Purity of soda is 93%)

93 100

44

= 15.05 kg.

9. Calculate amount of lime and soda required for softening of 20,000 liters

of water containing following salts in ppm CaSO4 = 13.6, Ca(HCO3)2 = 16.2,

MgCO3 = 16.8, HCl = 36.5, AlCl3 = 13.5, KCl = 5.1

Solution : Conversion of the impurities in CaCO3 equivalent .

impurity amount in conversion CaCO3 equivalent in ppm

ppm factor

CaSO4 13.6 100 100 × 13.6 = 10

136 136

MgCO3 16.8 100 100 × 16.8 = 20 84 84

AlCl3 13.5 100 100 × 13.5 = 10 133.5 133.5

Ca(HCO3)2 16.2 100 100 × 16.2 = 10

162 162

HCl 3.65 100 100 × 3.56 = 10 36.5 36.5

KCl 5.1 Do not contribute to hardness

Reaction

2AlCl3 + 3 Ca(OH)2 → 2Al(OH)3↓ + 3

CaCl2

Lime requirement for softening.

= 74 (Temp. Ca + 2 × Temp. Mg + Perm.(1.5Al) + 1�2 HCl)

100

= 74 (10 + 2(20) + 1.5(10) +1�2 (10))× 20,000 × 10

-6

100

= 1.036 kg.

Soda requirement for softening

= 106 [ Perm. Ca + Perm.(1.5Al) + 1�2 HCl]

100

= 74 (10 + 1.5(10) +1�2 (10))× 20,000 × 10

-6

100

= 0.636 kg.

10. Calculate the hardness in a given hard water sample having the following data.

1. 50 ml of standard hard water containing 1 mg of CaCO3 per

ml consumed. 2. 50 ml of standard hard water consumed 25 ml of EDTA using

eriochrome black T as indiacator. 3. 50 ml of water sample consumed 40 ml EDTA using the same indicator.

45

4. 50 ml water sample after boiling consumed 25 ml of EDTA using the

same indicator. Solution: 50 ml of std. hard water ≡ 25 ml of EDTA

≡ 50 mg of CaCO3

∴ 1 ml of EDTA ≡ 50

mg of CaCO3 25

Now 50 ml of sample water ≡ 40 ml of EDTA solution

≡ 40 × 5025 mg of CaCO3

1000 ml of sample water ≡ 100050 × 5025 × 40 mg of CaCO3 Total hardness ≡ 1600 mg of CaCO3

≡ 1600 ppm. 50 ml of boiled water sample ≡ 25 ml of EDTA solution

≡ 25 × 5025 mg of CaCO3

∴ 1000 ml of boiled water sample ≡ 25 × 5025 × 100050 mg of CaCO3 ≡1000 mg of CaCO3 i.e. i.e.

Permanent hardness ≡ 1000 ppm. Temporary hardness ≡ Total - Permanent

≡ 1600 - 1000 = 600 ppm.

11. 50 ml of hard water Sample required 8 ml of 0.05 N EDTA solution for

titration. 30 ml of the same water sample after boiling required 5 ml of 0.02

EDTA solution for titration. Calculate the hardness of water. Solution: 1000 ml of 1N EDTA ≡ 50 gm CaCO3 1 ml of 1N EDTA ≡ 50 mg CaCO3 Now 50 ml of hard water sample ≡ 8 ml of 0.05 N EDTA solution

≡ (8 × 0.05) ml of 1N EDTA solution ≡ (8 × 0.05× 50) mg CaCO3 ≡ 20 mg CaCO3

1000 ml of hard water sample ≡ 20

× 1000 mg of CaCO3

50

≡ 400 mg CaCO3

46 Total hardness ≡ 400 mg of CaCO3

≡ 400 ppm.

30 ml of boiled water sample ≡ 5 ml of 0.02N EDTA solution ≡ (0.02 × 5) ml of 1N EDTA ≡ (0.02 × 5 × 50) mg of CaCO3

∴ 1000 ml of boiled water sample ≡ 0.02 × 5 ×50 × 1000 mg of CaCO3 30

≡ 166.6 mg of CaCO3 i.e.

Permanent hardness

≡ 166.6 ppm.

i.e.

Temporary hardness ≡ Total — Permanent

≡ 400 - 166. = 234 ppm.

12. A standard hard water sample contains 0.20 mg of CaCO3 per ml. 100 ml of

this water consumed 25 ml 0.02 N EDTA. 25 ml sample water consumed 12 ml of

0.05N EDTA. The sample water is boiled and filtered, 50 ml of this water

sample consumed 4 ml of 0.01 N EDTA. Calculate the hardness of water.

Solution:

Given : a). 100 ml of std. hard water (0.2mg/liter of CaCO3) ≡ 25 ml of 0.02N EDTA mg of CaCO3

b). 25 ml of sample water ≡ 12 ml 0.02 N EDTA

c). 50 ml of boiled hard water

≡ 4 ml of 0.01N EDTA

∴ 25 ml of 0.02N EDTA ≡ (100 × 0.20) mg of CaCO3 1 ml of 1N EDTA ≡ 100×0.2025×0.02 mg of

CaCO3 ≡ 40 mg of CaCO3

Now 25 ml of sample water ≡ 12 ml of 0.02 N EDTA solution ≡ 12 × 0.02 ml of 1N EDTA

≡ 12 × 0.02 × 40 mg of CaCO3 ≡ 9.60mg of CaCO3

Total hardness ≡ 9.60 × 10025 mg of CaCO3

≡ 384 mg /liter ≡ 384 ppm.

50 ml of boiled water sample ≡ 4 ml of 0.01N EDTA solution ≡ (4 × 0.01) ml of 1N EDTA solution

≡ 40 × 4 × 0.01 mg of CaCO3 ≡ 1.6 mg CaCO3

47 ∴ 1000 ml of boiled water sample ≡ 1000 × 150.6 mg of CaCO3

≡32mg of CaCO3

i.e. Permanent hardness ≡ 32 ppm.

i.e. Temporary hardness ≡ Total - Permanent

≡ 384 - 32 = 352 ppm.

13. 1000 liters of hard water is softened by zeolite process. The zeolite was

regenerated by passing 20 liters of sodium Chloride Solution containing 1500 mg/

liter NaCl. Caculate the hardness of water. Solution: 20 liter of NaCl solution Contains = 20 × 1.5 = 30 gm of NaCl

2 NaCl = CaCO3 2 × 58.5 gm = 100 gm

Now 30 gm NaCl = 30 × 5850.5 gm of CaCO3 equivalent 1000 liters of water = 30 × 5850.5 gm of

CaCO3 emits 1 liter water = 1,00030 × 5850.5 = 0.02564 gm = 25.64 ppm Hardness of water = 25.64 ppm 14. By passing 50 liters of NaCl solution containing 250 mg/ liter of NaCl, a

exhausted zeolite softener bed was regenerated. Calculate the liters of hard water

sample ( Hardness equal to 200 ppm as CaCO3) which can be soften by

regenerated bed of zeolite softener. Solution: 50 liter of NaCl Solution Contains = 50 × 250 = 12,500gm of NaCl CaCO3 = 2 NaCl

100 gm = 2 × 58.5 gm

50 gm = 58.5 gm

Now 58.5 gm NaCl = 50 gm of CaCO3 equivalent ∴ CaCO3 equivalent would be = 12,500 ×50 gm

58.5

As hardness is 200 ppm ie. 200mg/liter of CaCO3 = 0.2 gm/liter ∴ 12500 × 58.5

50 gm of CaCO3 will be present in

48 = 12,5000.2 × 58.550 = 53, 418.89 liter of water Thus zeolite bed can soften 53,418.80 liter of water.

15. An exhausted zeolite softener was regenerated by passing 100 liters of NaCl

solution containing 150 gm per liter of NaCl. How many liter of a Sample of H2O

of hardness 300 ppm can be softened by this softener. ? (Given At. wt. for C = 12,

O = 16, Na = 23, Cl = 35.3, Ca = 40)

Solution:

1 liter of NaCl solution Contains = 150 gm of NaCl

∴ 100 liter of NaCl solution Contains = 100 × 150 = 15000 gm of NaCl Now 58.5 gm NaCl = 50 gm of CaCO3 equivalent ∴ 15,000 gm NaCl = 15,000 ×50 gm

58.5

As hardness is 300 ppm ie. 300mg/liter of CaCO3 = 0.3gm/liter

∴ 15,000 × 58.550 gm of CaCO3 will be present in = 15,0000.3 × 58.550 = 42,735.04 liter of water Thus zeolite bed can soften 42,735.04 liter of water.

16. A Hard water sample containing 4.5 gm/liter of CaCl2 is passed through a

permutit softener, what is the amount of NaCl present per liter of the soft water

(H2O)? (At. wt. Na = 23, Cl = 35.5, Ca = 40)

Solution:

Softening reaction is, CaCl2 + Na2Ze → CaZe + 2NaCl Mol. Wt. of CaCl2 = 40 + ( 2× 35.5) = 111

NaCl = 23 + 35.5 = 58.5

∴ 111 gm CaCl2 leaves 2× 58.5 gm NaCl in Soft water ∴ 4.5 gm CaCl2 will leave = 2 ×58.5 ×4.5 gm of NaCl

111

= 4.7 gm / liter of NaCl

17. How many liters of 10% Brine Solution will be required to regenerate an exhausted zeolite bed after softening 10 liters of hard water of 750 ppm hardness.

49

Solution:

Hardness of water = 750 ppm Total quantity = 10 × 750 = 7500 mg of CaCO3 equivalent.

NaCl used is 10% ie 100 gm / liter

Now 58.5 gm NaCl = 50 gm of CaCO3 equivalent ∴ 100 gm NaCl = 100 ×50 = 85.47 gm

58.5

= 85.47 mg/ml ∴ 7500 mg CaCO3 equivalent → 85

7500.47

= 87.75 ml of NaCl

18. Hardness of 77,500 liters of water was completely removed by zeolite

method. The exhausted zeolite softener then required 15 liter of NaCl(2%) for

regeneration. Calculate hardness of water sample.

Solution:

1 liter of NaCl Contains = 20 gm of NaCl

∴ 15 liter of NaCl Contains = 20 × 15 = 300gm of NaCl Now 58.5 gm NaCl = 50 gm of CaCO3 equivalent

∴ 300 gm NaCl = = 256.41 gm

Total quantity of water = 77,500 liters

77,500 liters of water = 256.41 gm of CaCO3 emits

1 liter water = = 0.0033gm = 3.30 ppm

Hardness of water = 3.30 ppm

Questions

1. Define soft and hard water, 2. what are temporary hardness and permanent hardness?

3. Distinguish between soft and hard water 4. Distinguish between temporary and permanent hardness

77, 500

256 .41

58. 5

300 ×50

50

5. What is the principle involve in the estimation of hardness of water by EDTA

titration method?

6. Why water is required to be softened ? mention the methods available for

softening.

7. What are zeolites? Discuss the zeolite process of softening of hard water .

8. Explain in detail the demineralization process. State advantages and

disadvantages.

9. Give the compairisn between ion exchange process and zeolite process.

10.Describe the process of lime soda method of softening of water. Mention its

advantages and disadvantages.

11. Explain with the help of chemical reactions the principle of softening of water

by lime soda method.

12. What is reverse osmosis? Explain in details.

13. What is ultrafiltration? Write its industrial applications.

14. What are the different methods to determine extent of water pollution?

Explain anyone in detail.

15. Write short note on:

a) BOD

b) COD

c) Chlorination process

d) Electro dialysis method

e) Effect of hard water in manufacturing sector.

f) Activated Sludge process

Numerical practice problems

1. Caculate the hardness of water sample whose 100 ml required 20 ml EDTA, 20

ml of calcium chloride solution (whose strength is equivalent to 4.5 gm of

Calcium corbonate per liter) required 30 ml of the same EDTA. (Ans. – 600 ppm)

2. 0.5 gm of CaCO3 are dissolved in dilute HCl and diluted to 500 ml, 25 ml of

this solution required 24.0 ml of EDTA using Eriochrom black T as indicator. 50

ml of hard water sample required 22.5 ml of the same EDTA , 100 ml of the water

sample after boiling required 12.0 ml of the said EDTA. Calculate the hardness in sample. (Total hardness = 468.75 ppm, permanent hardness = 125 ppm)

3. Calculate the quantity of lime and soda required for softening one million liters of

the following sample of water. The purities of lime and soda are 80 % and 85 %

51

respectively. The impurities are, Silica = 75 mg/liter, MgCl2 = 19 mg / liter, MgSO4

= 30 mg / liter, CaSO4 = 68 mg / liter, MgCO3 = 884 mg/ liter, CaCO3 = 120 mg/liter. (Lime =337 kg, Soda = 118.847 kg.) 4. Calculate the quantity of lime and soda required for softening one million liter

of hard water which on analysis was found to contain the following impurities.

Mg(HCO3)2 = 87.6 mg/liter, Mg(NO3)2 = 29.6 mg/liter, MgCl2 = 95 mg/liter,

CO2 = 33 mg/ liter, H2SO4 = 19.6 mg/ liter, KCl = 100 mg/ liter. ( Lime = 247.9

kg, Soda = 127.2 kg.)

5. A sample of water has hardness 304 ppm CaCO3 equivalent. Find the

hardness in terms of degree clark, degree French and mg/liter. 6. Calculate the quantities of lime (85% pure) and Soda (95% pure) for softening one

million liter of water if it has analysis as follows: CaCl2 = 49.95 ppm, MgSO4 = 12

ppm, NaHCO3 = 500 ppm, Mg(HCO3)2= 51.1 ppm, NaCl = 500 ppm, SiO2 =

10 ppm, CO2 = 3 ppm, Fe2+

= 3ppm, AlCl3 = 15 ppm. 7. Calculate lime (90% pure) and Soda (90% pure) required to soften 1,00,000 liters

of water containing, Mg(HCO3)2 = 146 mg/ liter, MgCl2 =95 mg / liter, Ca(HCO3)2

= 81 mg /liter, CaCl2 = 111 mg/ liter, Na2SO4 = 15 mg / liter, SiO2 = 10 mg/liter.

8. 50 ml of standard hard water (1.2 gm CaCO3/liter) requires 32 ml of EDTA

solution. 100 ml of water sample consumes 14 ml EDTA solution. 100 ml of

the boiled and filtered water sample consumes 8.5 ml of EDTA solution.

Calculate temporary hardness of this sample. 9. Calculate quantity of lime (90% pure) and soda (95% pure) required for

softening of one million liters of water containing CaCO3 = 140 ppm, CaSO4 =

136 ppm, MgCO3 = 8.4 ppm, MgSO4 = 60 ppm, MgCl2 = 38 ppm, SiO2 = 25 ppm. 10. A sample of water was found to contain following impurities in mg/liter

Mg(HCO3)2 = 7.3 gm, CaCl2 = 22.2 mg, HCl = 3.65 mg, H2SO4 = 9.8 mg, Ca(NO3)2

= 16.4 mg, MgSO4 = 12.0 mg, FeSO4 = 15.2 mg, Al2(SO4)3 = 340mg. Calculate

Amount of lime and soda required to softening or 10,000 liters of water.

52

2. Polymers

Man used eight kinds of materials such as different metals, wood, ceramics,

glasses, skins, horns and natural fibers until nineteenth century. In the nineteenth

century, plastics and rubber were developed. The mass production of these

materials was possible only after the Second World War with the growth of oil

industry. Oil industry provided cheap raw materials for the production of synthetic

polymers and synthetic rubbers. Since then these materials are contributing in

raising the standard of living of mankind significantly. Everyday features of the

modem life such as motor cars, scooters, refrigerators, washing machines,

telephones, etc. depend for their existence on these materials. The construction of

printed circuit boards for electronic instruments and controls, computers,

televisions, etc. is possible only with the use of polymers.

Polymeric materials are extensively used as cheap substitute to older materials.

Sometimes polymeric materials are used because the properties shown by these

materials are unattainable by any other materials. The assets of polymers are—

they are most versatile materials available in the wide range of strength,

toughness, abrasion resistance and flexibility. They are resistant to corrosion.

Some of them have non-stick properties, electrical insulation capacity and

transparency. They can be produced in a variety of colours and show colour

fastness. They are available in wide range of chemical and solvent resistance.

Being light in weight their transportation and labour cost is low. The strength to

weight ratios is high. The ability of polymers to soften and flow at least once, one

of their most valuable assets, as it allows them to be formed into complex shapes

easily and inexpensively by processing them.

Fig. 1.1 Chronological development of important engineering polymers

53

Petroleum oil is the major source of raw materials required for manufacturing of

polymeric materials. The cost of polymeric materials is thus dependent on the cost

of oil. Fabrication is shaping of already processed parts. Thus, it involves additional

shaping operation, e.g., extruded sheets are vacuum formed into finished product,

such as case of some instrument or PVC plastic film is laminated to cloth, etc.

Finishing, assembly and integration, include operations as cutting, bonding,

painting, etc. 2.1- Definition of Polymers and Elastomers The word polymer derives from two Greek words “poly’ meaning many and “mer” meaning parts or units. The reactants from which such repeat units combine

are monomers (mono means single and titer means part or unit). In order to

facilitate polymerization, functionality of a monomer must be two or more than two. Such a monomer is known as polyfunctional monomer. Functionality of a

monomer refers to its ability to form new bonds. Thus, the functionality is the

number of reactive sites or functional groups in the molecule (e.g., —OH,—

COOH —NH2, —SH, etc.). Thus, ethylene glycol (HO—CH2-CH2----OH), adipic

acid (HOOC—(CH2)4—COOH) are bifunctional monomers. The unsaturated

compounds show polyfunctionality due to the presence of either double or triple

bond in them. Thus, ethylene, (H2C = CH2) is a bifunctional monomer as double

bond can open up and form two new sigma bonds. Plastics are the polymers which are shaped into hard and tough utility articles by

application of heat and pressure, e.g., polyethylene, nylon, polystyrene, PVC, etc. Elastomers or rubbers are the polymers which can be vulcanized into rubbery

product exhibiting good strength and can undergo large reversible elongation at

relatively low stress, e.g., natural rubber, synthetic rubbers such SBR (styrene

butadiene rubber), BR (butyl rubber), etc. Synthetic fibers are the polymers used for clothing. They can give rise to long

filament- like materials having good strength and low elongation, e.g., nylon,

terelene. Liquid resins are potentially reactive chemicals which on curing give cross-

linked polymers which can be used as adhesives, potting compounds, sealants etc.

Examples are epoxy adhesives, melamine formaldehyde resin, polysuiphide

sealants, etc. 2.2 - Degree of Polymerization (DP) The degree of polymerization (DP) refers to the average number of repeat units in

the chain. The number of repeat units (DP) in chain specify the length of polymer

chain. The molecular weight of a polymer can be calculated by multiplying DP by

molecular weight of repeat unit. The molecular weight of polyethylene with DP

54

equal to 1000 is 28,000 as the molecular weight of repeat unit involved-(-CH2-

CH2-) n is 28 n refers to DP. By controlling DP (chain length and thus the

molecular weight), it is possible to vary the physical properties of polymers. The

polymers having low molecular weight are quite soft and gummy and those

having higher molecular weight are tougher and heat resistant. This is because in

linear and branched chain polymers the individual chains are held together by

weak intermolecular forces of attraction. The strength of these forces increases

with the chain length or molecular weight. For the polymers to be used for plastic

films, etc., the molecular weight should be more than a certain critical value

referred to as Mc-critical molecular weight. DP increases with time and

temperature also depends upon concentration of monomer and the initiator.

Strength of a polymer increases with increase in DP. Polymers are classified as:

2.3 – Classification of Polymers

(i) Homopolymer and Copolymer: Whenever a polymer chain is made up of a

single repeat unit, (represented as A), it is known as a homopolymer. It can be

represented as

- A- A-A-A-A-A-A-A-A-A-

A homopolymer

Polyvinyl chloride is a homopolymer, the repeat unit [— CH2—CH-] is repeated

throughout the chain as shown in the structure.

Polyvinyl chlorider [A homopolymer]

The polymer which has more than one repeat unit, repeated throughout the chain

is known as a copolymer. If the two different repeat units are represented as A and

B, the copolymer can be represented as

– A – A – B – A – B – B – B – A – A – B –

A copolymer

SBR (styrene butadiene rubber) is a copolymer obtained from styrene and

butadiene.

55

SBR (styrene butadiene rubber), A copolymer When two different repeat units in a copolymer are distributed at random

throughout the chain, the polymer is called a random copolymer. It can be

represented as

– A – A – B – A – A – B – B – A – B – B – A random copolymer

When two repeat units are distributed alternately throughout the chain, the

polymer is known as alternating copolymer. It can be represented as

– A – B – A – B – A – B – A – B – A – B – A – B – A – B – An alternating copolymer

When the sequence or block of one repeat unit is followed by a block of other

repeat unit, which in turn is followed by a block of first repeat unit, and so on,

then the polymer is known as block copolymer. They are usually linear polymers

and can be represented as – [A – A – A – A] – [B – B – B]n − [A – A – A – A]m – [B – B – B] –

A block copolymer The branched polymer in which, main chain is made up of entirely one repeat unit

and the branch chain is made up of other repeat unit, is known as graft copolymer.

It can be represented as

Schematic copolymer arrangements, (a) A copolymer in which the different

units are randomly distributed along the chain (b) A copolymer in which the

units alternate regularly, (c) A block copolymer, (d) A graft copolymer. When the same type of atoms are present in the polymer backbone chain, it is

known as a homochain polymer, e.g.. polyethylene (polythene).

The backbone chain is made by

carbon atoms only

56

Polyethylen

When the polymer chain is made up of more than one type of atoms, it is known

as heterochain polymer, e.g., polyamides (nylon), polyester, etc.

The backbone chain has

heteroatom (nitrogen)

Nylone - 6

(ii) Linear, branched or cross-linked polymers: The above classification is

based upon the structural shape of the polymer molecules.

2.3.1 Linear Polymers

Repeating units have been linked together in a continuous length to form polymer

molecules.

Linear polymer Branched polymer

2.3.2 Branched Polymers

Attached to main chain there can be short branches. e.g. (1) Low density linear

polyethylene (LDPE) (Fig. 1 .4a) or there can be long branches, e.g. (2) (Fig. 1

.4b) or there can be branched branches (Fig. 1 .4c).

Fig. 1.4 A schematic representation of different types of branched polymers

57

Linear and branched polymers can be amorphous or semi crystalline depending on

either secondary force between the polymer chains or close packing possible due

to regularity in their structure. 100% crystalline structure is not possible in

polymers because when solidification starts, the viscosity of material rises and

long chains of polymer find it difficult to move around and arrange them in a

symmetrical pattern needed for crystallisation. Examples of amorphous polymers: Polystyrene, Polyvinl chloride (PVC)

(rigid), Polymethyl methyl acrylate (PMMA), Some of the amorphous polymers

are rubbery at ambient temperature (e.g., natural rubber, SBR), while some are

rigid and transparent (e.g., PMMA, polystyrene, polycarbonates, PVC, etc.) Examples of semicrystalline polymers: Polyethylene, polypropylene, polyamide

(nylons such as nylon 6, nylon 66), etc. Semicrystalline polymers may be

transparent, translucent or opaque depending upon the size of crvstallites present

in amorphous matrix of the polymer (Crystallites are regions of crystallinity

embedded in amorphous matrix). Crystallites have dense packing of polymer

chains and thus there are strong intermolecular forces in this region. Thus,

presence of crystallinity enhances heat resistance, tensile strength, hardness while

amorphous region may constitute to toughness and flexibility of the polymer. 2.3.3 Cross-linked Polymers The cross-linked polymers have primary bonds

between polymer chains and thus resultant structure is strong and rigid, three-

dimensional structure. Most of the thermosetting polymers have such structure.

Greater the cross-linking, greater is the rigidity (less is the mobility of polymer

chains) of materials, less is its solubility and less it responds to remelting. Most thermosetting polymers have a cross-linked structure and some can

withstand high temperature. Linear polymers with their less complicated structure

can be rarely used at higher temperature. The cross-linking can be brought about

after polymerization by various chemical reactions. The number of cross-links and

their length can be controlled by using specific reaction conditions. Vulcanization

of rubber provides light cross-links due to which rubber gets good elastic

properties. High degree of cross-linking leads to impart high rigidity and

dimensional stability, e.g., urea formaldehyde (UF) or phenol formaldehyde (PF)

resins, ebonite.

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Cross-linked polymer (A schematic representation)

(iii) Organic and Inorganic Polymers: This classification is based on chemical

composition of polymer chain. The backbone chain of organic polymers is

essentially made up of carbon atoms. The hetero atoms such as 0, N, S usually

satisfy the side valencies of carbon atoms, e.g., polyethylene, polymethyl

methyacrylate, PVC.etc.

2.4 PLASTICS

A material consists of an essential ingredient, an organic material of high

molecular weight which has the property of plasticity.

Plastics are vet important materials. Polymers are the materials made by

polymerisation have repeated units in its structure. The plastic is the material in

finished form. It is processed by either forming or molding into a shape.

They are classified into thermoplastics and thermosetting on the basis of their

structure and thermal stability.

Termoplastics Thermosetting

(i) Linear structure (i) Cross-linked structure

(ii) Softens on heating and becomes (ii) Softens on first heating and

hard or rigid on cooling becomes hard on further heating

(iii) Hardening does not involve any (iii) Chemical change involved

chemical change

(iv) Low molecular weights as (iv) High molecular weights

compared to thermosetting

(v) They are soft (v) Harder, stronger and more brittle

than thermoplastics

(vi) E.g. polyethylene, (vi) Silicones, phenol formaldehyde,

polyvinyl chloride, polystyrene, etc. urea formaldehyde, etc.

2.5 - Compounding of Plastic

Properties of plastics are further improved by addition of certain additives and are

called compounding of plastics.

• Resin binds the various constituents.

• Plasticizers, are added to improve property of plasticity, e.g., vegetable oils,

camphor, esters of staric, oleic, phthalic acids, tricresyl, tributyl, triphenyl

phosphates.

59

• Fillers are added to improve workability, tensile strength and hardness. They

reduce cost, e.g., marble floor, paper pulp, carbon black, metallic oxides like

ZnO, PbO, metal powders like Al, Cu, Pb, etc. • Pigment and dyes—are resistant to the action of sunlight used to provide

• desired colour. TiO2, BaSO4, ZnO - white, ultramarine-blue, PbCrO4- yellow,

ZnCrO4-Green, quinacridone -violet. 2.6 - Glass Transition Temprature Amorphous polymers when cooled below certain temperature become hard, brittle

and glassy, but above this temperature they are soft, flexible and rubbery This

transition temperature of polymer is called ‘glass transition temperature’. (Tg). The hard brittle state is known as the glassy state and the rubbery is the soft one.

All chain motions are completely frozen in the glassy state, these are neither

segmental nor molecular motions.

When a polymer is heated beyond Tg the polymer passes from glassy state to

rubbery state. Only segmental motion while molecular mobility is forbidden is

rubbery state. Further heating much above Tg melt polymer starts flowing as each

polymer chain eventually obtains sufficient energy. The temperature below which the polymer is in rubbery state and above which it

is a liquid is called melting point of polymer (Tm) . As no sharp melting points are

shown by polymers. The transition temperature at which polymer passes from

rubbery state to liquid state is called its flow temperature (Tf). Determination of glass transition temperature: Polymer appropriately

contained in bulb at the bottom is kept immersed in a suitable liquid, usually

mercury so as to give a column of the liquid in the capillary up to a convenient

height for measurement.

The positioning of the glass plug, as shown enables heating the test specimen

avoiding overheating. The dilatometer placed in an outer bath may be heated at

the present rate and pattern. From the rise of the liquid in the capillary on heating

and consequent rise in the temperature the change in the volume of the specimens

may be conveniently obtained.

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Dilatometer

Tm and Tg values of some of the polymers.

Polymer R-unit TmoC Tg

oC

Polyethylen -CH2-CH2- 137 - 115

Polystyrene -CH2-CH-C6H5 240 95

Polysiloxane -OSi(CH3)2 -85 -123

2.7 - Conducting Polymers

Initially, organic polymers are normally used as insulators because of their

excellent insulating properties. In 1977, Heegar, Macdianid and Shirkawa for the

first time showed that electrical conductivity of polyacetylene can be increased by

13 fold of magnitude by doping with electron acceptor and donors. Norman and

others have achieved conductivity as high as copper metal in polyacetylene.

Polymers have π backbone when dopped results in drastic electrical, electronic,

magnetic and optical properties. The important doping reactions are oxidative,

reductive and proton acid doping. An organic polymer with highly delocalised π -electron system, having electrical

conductance of the order of conductor is called a conducting polymer. These

compounds have various applications because of flexibility, ease of fabrication,

stability, ease of process ability with the low cost.

Conducting Polyaniline: (PANI) Alan Mediarmid in 1985 investigated

polyaniline as an electrically conductivity polymer. Polymerised form of aniline

monomer polyaniline can be found in one of three idealised oxidation states.

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Leucoemeraldine - white/clear, Emeraldine - greenor blue, Pernigraniline -

blue / violet.

As it shows semi-metallic properties it is considered an organic metal. It is

transparent and stable in air when heated. Specific conductivity is — 55 cm1. In

the conducting slate its redox active green material may change its colour and

conductivity when exposed to different media. Under reducing conditions it turns

yellow and blue under oxidising or basic ones. It has wide and controllable range

of conductivity with other interesting properties like multicolour, chemical

sensitivity etc. PANI has application potentials in electromagnetic interference

shielding, as gas sensors, in gas separation, as an electrode rechargeable batteries,

electrochromic and in static charge dissipation.

Polyacetylene

nHC ≡ CH → Polymerisation →− CH CH − CH =CH − CH = CH −

Conjugate structure makes it behave like a semiconductor as some of the π

electrons can be thermally excited out of the bonds giving rise to small electrical

conductivity. Other conducting polymers are polydiacetylene, polythiosphere, polypyrrole, poly

- phenylene sulphide (PT’S) are also synthesised by polymerisation.

2.8 - Photoconductivity Enhancement of electrical conductivity on exposure to light or irradiation is called

photoconductivity. These materials are commonly insulators in dark and they

behave like semiconductors when exposed to light, e.g. P(N-vinyl carbacole)

PNVC. Metals are used in the form of powder of flakes or reinforcing agents in a

polymer matrix by making various moulded articles. They impart good electrical

and thermal conductivity into the composites. Electrical conductivity of a

conductive composite depends on intrinsic properties of the filler material as well

as matrix filler interaction and processing conditions. Applications of conducting polymers ▪ Used for corrosion protection, printed circuit boards, conductive fabrics,

pipes and smart windows.

▪ Used for coating of films and semi finished articles.

62

▪ It is very useful as a secondary electrode in rechargeable batteries and

electrochromic display devices due to its electrochemical response during

anodic and cathodic reaction (oxidation-reduction).

2.9 - Electrical Properties of Polymers

Till about the first few decades of the twentieth century common polymers were

used only as insulators in electronics and electrical areas. For these applications,

selection is done on the basis of electrical property parameters.

Resistivity: A material having high electrical resistance is a good insulator.

Volume resistivity of a material is the resistances between opposite faces of a unit

cube when the current flow is confined to the volume of the test specimen and it is

commonly expressed in ohm. cm. The reciprocal of resistivity is conductivity.

Moisture affects volume resistance of different insulators to markedly different

extent. Non-polar polymers such as polystyrene and polyethylene are unaffected

but polar organic polymers are affected to a greater extent. Affection depends on

their degree of moisture absorption. Porosity favours moisture absorption and

lowers volume resistance. However, polar inorganic polymers like quartz and

glass remain unaffected by moisture. Resistance suffers appreciably with rise in

temperature.

Dielectric constant: Dielectric constant depends on the geometry of the test

specimen and applied voltage. At high voltages failure of electrical insulation

occurs. The maximum potential gradient that an insulating material can withstand

without breakdown and passage of discharge is known as breakdown voltage. The

voltage required for breakdown is dependent on, rate of voltage application

thickness of test specimen, frequency of applied voltage, temperature, dimensions

and geometry of the electrodes and nature of the environment flexible materials

with high dielectric strength and mechanical strength are used as insulating tapes.

2.10 - Applications of Polymers in Medicine and surgery

Polymers are used as biomaterial in thereputic and diagonastic system they are

also used in many pharmaceutical preparations, for example, as coatings for

tablets or capsules or as components of transdermal patches. Biomaterials play a

central role in extra Corporeal devices, from contact lenses to kidney dialyses, and

are essential components of implants, from vascular grafts to cardiac pacemakers.

Biodegradable polymers take center stage in a great variety of research efforts.

Materials that can decompose and disappear from the body are desirable for short-

term applications in orthopedics, tissue engineering, and other areas, where, for

example, a physician may need a device to hold a bone in place long enough for

the body to heal. Listed some of polymers having medical applications

i. Cellophane: Often used in everyday life to package our products or to keep

our food fresh, cellophane is one of the most critical materials for the

treatment of many kidney malfunctions. ii. Polydimethyl siloxane (PDMS): The polymer polydimethyl siloxane

63

(PDMS) is used in pacemakers, the delivery of vaccines, and the construction

cerebrospinal fluid shunts. iii. PGA( polyglycolic acid), PLA, and PLGA : PGA, PLA, and PLGA allow

the polymers to be used for a wide variety of applications within the human

body. These polymers are then used for drug-delivery systems, to construct

synthetic scaffolding, etc. The latest treatment in treating brain tumors

involves attaching dime- sized wafers directly into the skull8. The wafers are

made out of PLA or PLGA and slowly distribute cancer-killing. iv. Polyethylene and Polymethylmethacrylate (PMMA): used in Joint

replacements, particularity at the hip, and bone fixation devices have become

very successful applications of materials in medicine. The use of pins, plates,

and screws for bone fixation to aid recovery of bone fractures. v. Polytetrafluoroethylene: Polytetrafluoroethylene is useful for some

orthopedic and dental devices. It also has Biomaterials are used in many

blood-contacting devices. These include artificial heart valves, synthetic

vascular grafts, ventricular assist devices, drug releases, and a wide range of

invasive treatment and diagnostic systems. vi. Polyurethane: polyurethane today is one of the most important materials in

use for ventricular assist devices. Differing from artificial hearts, VAD’s are

for short-term assistance to cardiac circulation attached to one or both of the

heart ventricles. Most commonly seen in the operating room during open-

heart surgery, postoperatively and of extreme cardiac trauma.

Polymer Application

PDMS Catheters, heart Valves

Polytetrafluoroethylene Heart valves, Vascular grafts, Nerve

repair

Polyurethane ventricular assist Devices

Polyethylene Catheters, hipprostheses

Polymethylmethacrylate (PMMA) Fracture fixation

PGA, PLA, And PLGA Drug delivery, devices

Cellophane Dialysis membranes

2.11 - Fabrication of Polymers

All plastic resins can be shaped into a variety of products by initially making them

plastic and then subjecting them to the action of temperature and pressure in a

mould. The different fabrication methods available are as follows. • Compression moulding • Injection moulding • Transfer moulding

64

• Extrusion moulding

2.11.1 - Compression Moulding

Thermoplastic and thermosetting resins can be moulded by this method. The die

used for moulding purposes consists of two parts, upper and lower parts of male

and female parts. In closed condition, the clearance between the two halves gives

the desired shape to the product. Generally, the lower part of mould is fixed, the

upper part moves up and down, the movement being properly aligned because of

guide pins present. The lower part of the die also has arrangement for heating and

cooling by circulating fluids through pipe work.

Compression moulding involves transfer of required quantity of polymer mix

consisting of other ingredients and polymer, into the cavity. A slight excess of

material is taken to ensure that the cavity gets completely filled with material

during the compression process. The charge in cavity is heated to make it easy to

mould. The upper part of mould is then lowered and the mould cavity closed by

applying the necessary pressure and heat. This ensures the plastic mass get

completely distributed uniformly in the mould, taking the shape of mould. Any

excess runs off in the form of ‘flash’.

Fabrication by compression moulding.

For thermoplastic material, the die is allowed to cool so that the article becomes

rigid enough to be expelled from the mould by the eject in mechanism. For

thermosetting resins, the temperature is maintained at the curing temperature for

the desired time to ensure the articles are properly cured. Moulding temperatures

and pressures for thermosetting polymers can be as high as 200°C and 70 kg/cm2

respectively.

The mould cycle starts with filling up of cavity with the material and end with the

ejection of product formed from the mould cavity. This may vary from article to

65

article depending upon its size and complexity. After the removal of article, the

mould is made ready to receive the next charge by cleaning the mould with a blast

of compressed air. 2.11.2 Transfer Moulding In compression moulding, there are limitations with regards to size of die,

effective heat transfer, and ability to mould intricate parts. Transfer moulding

overcomes many of these limitations. The charge is preheated in transfer chamber,

a pot which may sometimes form part of mould. The fluidised material from the

pot is transferred to mould cavity due to plunging action of plunger through

heated flow channels. This permits moulding of large and intricate parts, as the

melted polymer flows easily. It is also possible to include inserts into the article.

The mould itself is maintained at high temperature to facilitate curing of set resin

in the mould. Thick sections are uniformly cured so that dimensional accuracies

are maintained within limits. Cycle times in the case transfer moulding are shorter than those of compression

moulding as the initial charge is in fluidised state and the mould is maintained at

right temperature for proper curing. Thick portions and mechanically strong

section can be fabricated by transfer moulding technique.

2.11.3 - Injection Moulding Technique

66

This technique is used for high, speed moulding of thermoplastic resins. The

machine consists of two parts—injection unit and the clamping unit which carries

the mould.

Fig. 1.13 Fabrication through injection moulding

The injection unit is a hollow cylindrical device fitted inside with screw conveyer

or plunger. The end attached to mould narrows down to form the nozzle. Part of

the forward section carries electrical heaters which heat the charge as it moves

along the cylinder length. The movement of screw conveyer pushes the charge

forward where it gets heated and melts. The molten mass is then pushed through

the nozzle into the cold mould. It immediately solidifies to rigid form. The mould

is opened to eject the product and again closed and clamped tightly. Since the

molten mass is pushed at high pressure, arrangements for keeping the two halves

of mould should be secure. High pressure also ensures that molten material is

evenly distributed in the mould cavity.

2.11.4 - Extrusion Moulding

It is mainly used for continuous moulding of thermosoftering plastics. Pipes. rods,

hoses, tubes are some of the products manufactured by extrusion process. This

method is also used to coat cables with a layer of plastic insulating material. The

extruder is designed in such a way that as the raw mix passes along the length of

extruder, it melts and flows out at uniform rate towards the die section. The

extruded product is shaped according to die characteristics, into rods, pipes or

67

tubes and carried along a conveyer belt to be cut into specified lengths. Then

tubular films are also made by extrusion process. Besides these methods of

fabrication, blow moulding and calendering are some of the other methods used

extensively for fabrication purposes.

Fig. 1.14 Horizontal extrusion moulding of plastics.

2.12 - Rubbers Natural rubber, also called India Rubber or caoutchouc, is a mixture of

organic compound polyisoprene and small amounts of other organic compounds

as well as water. This polymer is the main component. This material is classified

as an elastomer (an elastic polymer). It is derived from latex, a milky colloid

produced by some plants. The plants are ‘tapped’, that is, an incision made into

the bark of the tree and the sticky, milk colored latex sap collected and refined

into a usable rubber. Polyisoprene can also be produced synthetically. Natural

rubber is used extensively in many applications and products, as is synthetic

rubber. It is normally very stretchy and flexible and extremely waterproof. The rubber latex can be mixed with the required compounding substance and

precipitated in the shape that is needed for use. For example, rubber gloves are

easily prepared in this manner 2.12.1 – Commercial forms of Rubber Rubber is made available in the following forms for commercial purposes. The

latex after dilution and coagulation yields the precipitated mass which is the

coagulum. The coagulum is separated by filtration and treated further, to obtain

the various forms of rubber. Crepe Rubber: The coagulated mass of rubber is made into sheets by passing the

coagulum repeatedly through rollers. Addition of sodium bisulphate bleaches the

colour of the rubber. The sheets obtained may be pressed and passed again through the

rollers to obtain the required thickness. The sheets are then dried in hot air at about

50°C. Smoked Rubber: The coagulum obtained after coagulation of rubber latex is made

into thick sheets by passing through rollers without using bleaching agents and dried at

about 40°— 50°C in the presence of smoke obtained by burning wood or shells. This

treatment prevents the growth of mould and bacteria and preserves rubber against

oxidation. Exposing the rubber sheets to smoke makes them stronger and brownish in

colour. Alternately the rubber sheets are prepared in long tanks provided with vertical

grooves fitted with metal plates. The latex, after initial purification is poured into

the tank a4d coagulated by adding formic or acetic acid and stirred. After inserting

the plates in the groove, the tank is kept at rest for nearly 16-18 hours. The slabs

of rubber obtained are removed and passed through a series of rollers having

decreasing clearance between them. Water is sprayed in between the rollers. The

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final roller can be adjusted to get ribbed pattern on the rubber sheets and facilitates

easy drying. The dried sheets are hung in smoke house at 40°-50°C.

Gutta-Percha: It is another kind of natural rubber obtained from the leaves of

Dichopsis gutta and palagium gutta trees found in Malaya, Sumatra and Borneo. The

leaves are ground and treated with water at about 70°C and poured into water when

the latex material floats on water. It can also be extracted by solvent extraction when

the resins and gums being insoluble get separated. Structurally, it is found to be trans-

polyisoprene.

2.12.2 – Properties of Natural Rubber

Structure

(i) It is a polymer of isoprene (2 methyl- 1, 3 -butadiene), the polymer consisting

over two thousand monomers linked together (C5H8) where stands for the number

of monomers. It may be represented as below.

It can exist in cis and trans forms. Natural rubber is cis-l, 4-poly isoprene and

gutta percha which is another form of natural rubber is a trans isomer.

The molecule of rubber in the unstressed condition is in the form of a coil which

can b stretched like a spring. It can be deformed to a large extent and yet can

recover its original shape and size after the removal of the applied stress.

General Properties

▪ Pure rubber becomes soft and sticky in summer and hard and brittle in winter.

▪ On heating, it decomposes to form isoprene (C5H8) an unsaturated

hydrocarbon.

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▪ Action of Ozone (O3) on rubber produces levulinic aldehyde, CH3—CO-

CFI2-CH2—CHO as the principal product showing that rubber is a head-to-

tail polymer of isoprene.

▪ Rubber shows marked resemblance to unsaturated hydrocarbons as indicated

by its reaction with different chemical reagents.o When rubber is made to react with hydrogen chloride, addition product,

i.e., Rubber hydrochloride (C5H9Cl)n.

o Chlorine reacts with rubber forming both addition and substitution

products (Chlorinated rubber). o Hydrogen reacts with rubber and produces addition product (C5H10).

o The effect of atmospheric oxygen is to cause hardness and brittleness in

rubber. o Corresponding derivatives are obtained by reactions with sulphuric acid,

sulphonic acid and oxides of nitrogen.

o Moderately strong acids and alkalies have no significant action on rubber.

▪ Rubber is insoluble in water and water - like solvents such as alcohol,

acetone, etc. but it disperses freely in benzene, toluene, gasoline, carbon

disulphide, turpentine, chloroform, carbon tetrachioride, etc. to form viscous

liquids which are used as adhesives. 2.12.3 Drawbacks of Natural Rubber Raw rubber shows the following drawbacks on account of which it needs to be

suitably compounded and heat treated. ▪ It is found to be unsuitable at low as well as at higher temperatures. At lower

temperatures, it is found to be brittle and at higher temperatures, it is soft and

sticky. It is found to be useful only in the temperature range of 10°C to 60°C.

▪ It has a low tensile strength, i.e. (200 kg/cm2).

▪ It has high water absorption property.

▪ It is easily oxidised by 02 of air and other oxidising agents like Nitric acid,

Sodium hypochlorite, Chlorine, Chromic acid, etc.

▪ It is not resistant to the action of solvents like vegetable and mineral oils,

benzene, gasoline, carbon tetrachloride, etc.

▪ It swells in organic solvents undergoing disintegration.

▪ It possesses marked tackiness: i.e. two pieces or sheets in fresh condition get

adhered to each other under pressure.

▪ It is less durable, non-resistant to scratches, and suffers permanent

deformation on being stretched strongly. 2.12.4 – Vulcanisation of Rubber The process was carried out first by Goodyear in 1839 using sulphur for effecting

cross-linking of the poly-isoprene molecules in natural rubber.

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Vulcanisation process is important for improvements in the properties of both

natural as well as synthetic rubbers. It is a process of cross-linking the rubber

molecules using a vulcanising agent. In addition to sulphur, certain compounds of

sulphur are also found to bring about the cross-linking in rubber molecules. The

cross-linking may take place either at the double-bond or even without affecting

the double-bond in the polymer followed by elimination of substances like I-lBS,

sulphur. The evolved sulphur may bring about further cross-linking reactions.

Some of the reactions are as follows:

Vulcanisation is also brought about by compounds of sulphur like thioacids,

mercaptans, etc. Addition of 0.5 to 5% sulphur gives soft and elastic rubber and

increasing the quantity of sulphur increases the hardness and stiffness of the

rubber.The time needed for the vulcanisation process depends on the quality of

product. The process can be accelerated by adding oxides of metals like zinc,

calcium, lead, magnesium, etc. which are the accelerators for the process.

The process of cross-linking can also be achieved by using peroxides, amine

derivatives and oximes in the case of certain varieties of rubber. Sulphur can be

partially replaced by selenium and tellurium in the case of diene rubbers.

The use of sulphur or any vulcanising agent together with the accelerator gives

only limited improvements in physical and mechanical properties. For improving

stability, flexibility, processability, resistance to abrasion, etc. various other

additives accelater, antioxidants, reinforcing agent are added and vulcanisation

together is carried out.

2.12.5 - Buna - S (styrene-butadiene rubber) describe families of synthetic rubbers derived from styrene and butadiene. These materials have good abrasion

resistance and good aging stability when protected by additives. About 50% of car

tires are made from various types of SBR. The styrene/butadiene ratio

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influences the properties of the polymer: with high styrene content, the rubbers are

harder and less rubbery. The material was initially marketed with the brand name Buna S. Its name derives Bu for butadiene and Na for sodium (natrium in several languages including Latin, German and Dutch), and S for styrene.

Types of SBR SBR is derived from two monomers, styrene and butadiene. The mixture of these

two monomers are polymerised by two basically different processes: from

solution (S-SBR) or as an emulsion (E-SBR). Structure of Buna - S

Emulsion polymerisation E-SBR produced by emulsion polymerisation is initiated by free radicals.

Reaction vessels are typically charged with the two monomers, a free radical

generator, and a chain transfer agent such as an alkyl mercaptan. Radical initiators

include potassium persulfate and hydroperoxides in combination with ferrous

salts. Emulsifying agents include various soaps. By "capping" the growing organic

radicals, mercaptans (e.g. dodecylthiol, control the molecular weight, and hence

the viscosity, of the product. E-SBR is more widely used. Typically,

polymerizations are allowed to proceed only to ca. 70%, a method called "short

stopping". In this way, various additives can be removed from the polymer. Solution polymerisation

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Solution-SBR is produced by an anionic polymerization process. Polymerisation

is initiated by alkyl lithium compounds. Water is strictly excluded. The process is

homogeneous (all components are dissolved), which provides greater control over

the process, allowing tailoring of the polymer. The organolithium compound adds

to one of the monomers , generating a carbanion that then adds to another

monomer, and so on. Relative to E-SBR, S-SBR is increasingly favored because it

offers improved wet grip and rolling resistance, which translate to greater safety

and better fuel economy, respectively.

Properties

Property S-SBR E-SBR

Tensile strength (MPa) 18 19

Elongation at tear (%) 565 635

Mooney viscosity (100 °C) 48.0 51.5

Glass transition temperature (°C) -65 -50

Polydispersity 2.1 4.5

Applications

The elastomer is used widely in pneumatic tires, shoe heels and soles, gaskets and

even chewing gum. It is a commodity material which competes with natural

rubber. Latex (emulsion) SBR is extensively used in coated papers, being one of

the most cost-effective resins to bind pigmented coatings. It is also used in

building applications, as a sealing and binding agent behind renders as an

alternative to PVA, but is more expensive. In the latter application, it offers better

durability, reduced shrinkage and increased flexibility, as well as being resistant to

emulsification in damp conditions. SBR can be used to 'tank' damp rooms or

surfaces, a process in which the rubber is painted onto the entire surface

(sometimes both the walls, floor and ceiling) forming a continuous, seamless

damp proof liner; a typical example would be a basement.

Additionally, it is used in some rubber cutting boards.

2.12.6 - Polyethylene (PE)

Polyethylene is obtained by polymerisation of ethylene. Depending on the

reaction conditions two types of polyethylene are available

(i) Low density polyethylene (LDPE) (density 0.915 to 0.940 g/cm3)

(ii) High density polyethylene (HDPE) (density 0.945 to 0.960 g/cm3)

Manufacture of LDPE

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Highly punifiea ethylene is compressed at 1500-2000 atm pressure in e presence

of traces of oxygen at 160-170°C.

nH C = CH 2

150 − 1700 C [CH 2

− CH ]

2 1500atm.

2 n

Ethylene LDPE Manufacture of HDPE Polymerisation reactions can be carried out at much high temperature and pressure

in the presence of catalyst containing metallic oxides, e.g., catalyst mixture

contain Cr203, Silica and aluminice is activated by heating at 250°C. The

activated catalyst is then dispersed in a solvent cyclohexane. The temperature of

polymerisation is around 130-150°C and 15 to 30 atm pressures.

LPDE HDPE

(1) Density 0.9 15 to 0.940 g/cm3

0.945 to 0.960 g/cm3

(ii) Temp. 160-170°C and pressure Temp. 130-150°C and pressure 15 to

1500-2000 atm. 30 atm.

(iii) Softening temp. 110-117°C 125-130°C

(iv) 2 to 50 branches for 1000 carbon 2.5 branches for 1000 carbon atoms.

atoms.

(v) Low tensile strength High tensile strength

(iv) Soluble in toluene at 60-70°C. soluble in toluene at 60-70°C.

2.12.7 - Polyurethane Polyurethane is a type of cross linked polymer prepared from two liquid i.e.a

polyol and isocynate

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Properties

It is also be foamed like polystyrene but unlike thermocoal, it is soft, spongy

known as “U foam”. It has low thermal conductivity. Its greatest advantage lies in

the fact that it can be made where they needed without any complex machinery

and two liquid ingrediants can be mixed and moulded.

Uses: it is used as insulating material in refrigerator. Due to its spongy nature used

in making pillow and mattresses. It is also used as coating on leather goods such

as shoes and hand bags, which improve appearances of leather goods. It is used in

making chair. It is also used in foundation garments and swim suits.

2.12.8 - Silicones

Silicones having alternate silicon – oxygen bonds and radical attached to silicon

atom

The monomers of silicon are prepared from alkyl silicon halides.

2 R – Cl + Si →Cu R2SiCl2

Or from Grignard reagent

SiCl4 + RMgCl ⟶ RSiCl3 + MgCl2 The monomer is obtained by fractional distillation of reaction products whereby

different organo silicon chloride are obtained

In next step chlorides are polymerized by hydrolysis by following steps ≡SiCl + H2O ⟶ ≡SiOH + HCl ≡SiOH + HOSi≡ ⟶ ≡Si –O – Si ≡+ H2O

Thus the Oh group of Si are involved in polymerization hence when there is one

or two – OH groups in Si, it leads to long chain polymers but when there are three

- OH groups, a cross linked polymer obtained reactions

2 R – Cl + Si →Cu R2SiCl2

From Grignard reagent

SiCl4 + RMgCl ⟶ RSiCl3 + MgCl2

Me2SiCl2 →H2O

Me2Si(OH)2

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HO.SiMe2 – [OSiMe2]n- OSiMe2OH Di – alkyl – di chlorosilicane and alkyl trichloro silicon undergo hydrolysis and

condensation polymerization to give a cross linked silicon polymer

Cross linked polymerisation Complete condensation of all the – OH gives rise to hard, insoluble product, thus

a mixture of monomers containing one or more – OH group along with sufficient

water for hydrolysis is heated for polymerization. Different types of silicones

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Depends on proportion of various alkyl silicon halides used, the final silicones

may be liquid, semisolid and solid. Their properties and uses also differ

accordingly

i. Silicone fluid - they are of relatively low molecular weight, sparkling clear

fluids with an oily feel, insoluble in water but soluble in aromatic and

chlorinated solvents. They possess good resistance to heat and oxidation, low

surface tension and show low change in viscosity with temperature. They

used as autofoam agents, high tempreture lubricants , used in cosmatics as

damping and hydrolic fluids and to give water repellent finish to textiles and

leather. ii. Silicone greases - these are formed from the oils by adding silica, carbon

black etc. they are used as lubricants particularly for very high and low

tempreture applications. iii. Silicone resins – ther are highly cross linked polymers, having good

insulating properties, heat resitance and good di electrical properties. Used as

high voltage insulator, high tempreture insulating foam, silicon glass

laminates for high tempreture application for different electrical and

electroninc equipments and parts manufacturing. iv. Silicon rubber - silicone rubber are formed by reaction of dimethyl silicone

fluid with peroxide and appropariate inorganic fillers like ZnO SiO2 TiO2

etc. they retain rubbery properties over much wide tempreture span, good heat

transfer properties, good resistance to dilute acid and alkalis. Using in tyre

manufacturing for fighter aircraft, as an insulator of electrical wires in ship, as

adhesive for artificial heartvalves, transfusion tubings, for special boots to be

used at very low tempreture, for making lubricants,paints , protative coatings

etc.

2.12.9 - PMMA (Polymethyl Methacrylate) or Lucite or Plexig lass

It is prepared by polymerisation of methyl-methacrylate an ester of methyl acrylic

acid, CH2=C. (CH3)—COOH in presence of actyl peroxide. It is an acrylic

polymer

Properties

Colourless thermoplastic, hard, fairly rigid material with high softening

temperature 130— 140°C, it becomes rubber like above 65°C. It has high optical

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transparency, high resistance cured conditions. Its refractive index is 1.59. Its

most important drawback is low resistance to hot acids and alkalis and low scratch

resistance. Uses ▪ Mainly used for protective coating, and for manufacture of safety glass as it

can be moulded easily to almost any shape.

▪ Emulsions of acrylic resins have been widely used as textile and leather

finish, base coats on rubberised surfaces, etc.

▪ Widely used in industry in making lenses, banber noses, transport models of

complicated mechanisms, artificial eyes, emulsions, paints, adhesives,

automobiles, wind screens, TV. screens, optical parts of instruments,

jewellery, etc. • Solution polymer in volatile solvents used for adhesive and for heat and fume

resistant enamels, luminecent paints, etc. 2.12.10 - KEVLAR Kevlar is the registered trademark for a para-aramid synthetic fiber, related to

other aramids such as Nomex and Technora. Developed at DuPont in 1965, this

high strength material was first commercially used in the early 1970s as a

replacement for steel in racing tires. Typically it is spun into ropes or fabric sheets

that can be used as such or as an ingredient in composite material components. Synthesis of Kevlar Kevlar is synthesized in solution from the monomers 1,4-phenylene-d iamine

(para-phenylenediamine) and terephthaloyl chloride in a condensation reaction

yielding hydrochloric acid as a byproduct. The result has liquid crystalline

behavior, and mechanical drawing orients the polymer chains in the fiber's

direction. Hexamethylphosphoramide (HMPA) was the solvent initially used for

the polymerization, but for safety reasons, DuPont replaced it by a solution of N-

methyl-pyrrolidone and calcium chloride.

Kevlar production is expensive because of the difficulties arising from using

concentrated sulfuric acid, needed to keep the water- insoluble polymer in

solution during its synthesis and spinning.

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Several grades of Kevlar are available:

1. Kevlar K-29 – in industrial applications, such as cables, asbestos replacement, brake linings, and body/vehicle armor.

2. Kevlar K49 – high modulus used in cable and rope products.

3. Kevlar K100 – colored version of Kevlar

4. Kevlar K119 – higher-elongation, flexible and more fatigue resistant.

5. Kevlar K129 – higher tenacity for ballistic applications.

6. Kevlar AP – has 15% higher tensile strength than K-29.

7. Kevlar XP – lighter weight resin and KM2 plus fiber combination.

8. Kevlar KM2 – enhanced ballistic resistance for armor applications

The ultraviolet component of sunlight degrades and decomposes Kevlar, a

problem known as UV degradation, and so it is rarely used outdoors without

protection against sunlight.

Molecular structure of Kevlar: bold represents a monomer unit, dashed

lines indicate hydrogen bonds.

Properties :

When Kevlar is spun, the resulting fiber has a tensile strength of about 3,620 MPa,

and a relative density of 1.44. The polymer owes its high strength to the many

inter - chain bonds. These inter-molecular hydrogen bonds form between the

carbonyl groups and NH centers. Additional strength is derived from aromatic

stacking interactions between adjacent strands. These interactions have a greater

influence on Kevlar than the van der Waals interactions and chain length that

typically influence the properties of other synthetic polymers and fibers such as

Dyneema. The presence of salts and certain other impurities, especially calcium,

could interfere with the strand interactions and caution is used to avoid inclusion

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in its production. Kevlar's structure consists of relatively rigid molecules which

tend to form mostly planar sheet-like structures rather like silk protein.

Thermal properties Kevlar maintains its strength and resilience down to cryogenic temperatures (−196

°C); in fact, it is slightly stronger at low temperatures. At higher temperatures the

tensile strength is immediately reduced by about 10–20%, and after some hours

the strength progressively reduces further. For example at 160 °C (320 °F) about

10% reduction in strength occurs after 500 hours. At 260 °C (500 °F) 50%

strength reduction occurs after 70 hours. Applications of Kevlar ▪ Cryogenics : Kevlar is used in the field of cryogenics for its low thermal

conductivity and high strength relative to other materials for suspension

purposes.

▪ Armor : Kevlar is a well-known component of personal armor such as

combat helmets, ballistic face masks, and ballistic vests.

▪ Personal protection : Kevlar is used to manufacture gloves, sleeves, jackets,

chaps and other articles of clothing designed to protect users from cuts,

abrasions and heat.

▪ Sports equipment: It is used as an inner lining for some bicycle tires to

prevent punctures. In table tennis, plies of Kevlar are added to custom ply

blades, or paddles, in order to increase bounce and reduce weight

▪ Shoes : With advancements in technology, Nike used Kevlar in shoes for the

first time.

▪ Audio equipment : Kevlar has also been found to have useful acoustic

properties for loudspeaker cones, specifically for bass and midrange drive

units.

▪ Strings: Kevlar can be used as an acoustic core on bows for string

instruments.

▪ Drumheads: Kevlar is sometimes used as a material on marching snare

drums. It allows for an extremely high amount of tension, resulting in a

cleaner sound.

▪ Woodwind reeds : Kevlar is used in the woodwind reeds of Fibracell.

▪ Fire dancing: Wicks for fire dancing props are made of composite materials

with Kevlar in them.

▪ Frying pans: Kevlar is sometimes used as a substitute for Teflon in some

non-stick frying pans.

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▪ Rope, cable, sheath:The fiber is used in woven rope and in cable, where the

fibers are kept parallel within a polyethylene sleeve.

▪ Electricity generation: Kevlar was used by scientists at Georgia Institute of

Technology as a base textile for an experiment in electricity-producing

clothing.

▪ Brakes : The chopped fiber has been used as a replacement for asbestos in

brake pads.

▪ Expansion joints and hoses: Kevlar can be found as a reinforcing layer in

rubber bellows expansion joints and rubber hoses, for use in high temperature

applications, and for its high strength.

▪ Particle physics: A thin Kevlar window has been used by the NA48

experiment at CERN to separate a vacuum vessel from a vessel at nearly

atmospheric pressure, both 192 cm in diameter.

▪ Smartphones :The Motorola Droid RAZR has a kevlar backplate, chosen

over other materials such as carbon fiber due to its resilience and lack of

interference with signal transmission.

▪ Composite materials: Aramid fibers are widely used for reinforcing

composite materials, often in combination with carbon fiber and glass fiber.

2.12.11 - Phenol formaldehyde resins (PF) are synthetic polymers obtained

by the reaction of phenol or substituted phenol with formaldehyde. Phenolic resins are

mainly used in the production of circuit boards. They are better known however for

the production of molded products including pool balls, laboratory countertops, and as

coatings and adhesives. In the form of Bakelite, they are the earliest commercial

synthetic resin.

Phenol-formaldehyde resins, as a group, are formed by a step-growth

polymerization reaction that can be either acid- or base-catalysed. Since

formaldehyde exists predominantly in solution as a dynamic equilibrium of

methylene glycol oligomers, the concentration of thereactive form of

formaldehyde depends on temperature and pH.

Phenol is reactive towards formaldehyde at the ortho and para sites (sites 2, 4 and 6) allowing up to 3 units of formaldehyde to attach to the ring. The initial reaction

in all cases involves the formation of a hydroxyl methyl phenol:

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In aqueous solution, formaldehyde exists in equilibrium with methylene glycol.

Depending on the pH of the catalyst, these monomers react to form one of two

general resin types: NOVOLAC RESINS and RESOL RESINS. Novolac Resins An acidic catalyst and a molar excess of phenol to formaldehyde are conditions

used to make novolac resins. The following simplified chemistry illustrates the

wide range of polymers possible. The initial reaction is between methylene glycol and phenol.

The reaction continues with additional phenol, and splitting off of water.

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The reaction creates a methylene bridge at either the ortho position or the para

position of the phenolic aromatic rings. The "rule of thumb" is that the para

position is approximately twice as reactive as the ortho position, but there are

twice as many ortho sites (two per phenol molecule) so the fractions of ortho-

ortho, para-para and ortho-para bridges are approximately equal.

Branching occurs because reaction can occur at any of three sites on each ring. As

the reaction continues, the random orientations and branching quickly result in an

extremely complex mixture of polymers of different sizes and structures. The

reaction stops when the formaldehyde reactant is exhausted, often leaving up to

10% of un-reacted phenol. Distillation of the molten resin during manufacturing

removes the excess phenol and water.

The final novolac resin is unable to react further without the addition of a cross-

linking agent.

Because an additional agent is required to complete the resin's cure, the industry

commonly refers to novolac resins as "two-stage" or "two-step" products. The

most common phenolic resin cross-linking agent is hexamethylenetetramine, also

known as hexa, hexamine, or HMTA. Ground and blended with the resin, hexa

serves as a convenient source of formaldehyde when heated to molding and curing

temperatures. A special attribute of hexa is that it reacts directly with resin and

phenol without producing appreciable amounts of free formaldehyde. Hexa cures

the resin by further linking and polymerizing the molecules to an infusible state.

Due to the bond angles and multiple reaction sites involved in the reaction

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chemistry, the resulting polymer is not a long straight chain but rather a complex

three-dimensional polymer network of extreme molecular weight. This tightly

cured bonding network of aromatic phenolics accounts for the cured materials'

hardness, and heat and solvent resistant properties. Certain catalysts can affect the orientations of the methylene linkages. Catalysts

that preferably promote ortho-ortho linkages tend to preserve the more reactive

para positions:

Novolac resins made with these catalysts tend to cure more rapidly than the

standard randomly linked resins. Novolac resins are amorphous (not crystalline)

thermoplastics. As they are most typically used, they are solid at room

temperature and will soften and flow between 150° and 220°F (65°C - 105°C).

The number average molecular weight (Mn) of a standard phenol novolac resin is

between 250 and 900. As the molecular weight of phenol is 94 grams per mole, a

Mn of 500 corresponds to a resin where the average polymer size in the entire

distribution of polymers is five linked phenol rings. Novolac resins are soluble in

many polar organic solvents (e.g., alcohols, acetone), but not in water. Resol Resins A basic (alkaline) catalyst and, usually but not necessarily, a molar excess of

formaldehyde is used to make resol resins. The following two stages describe a

simplified view of the reaction: First, phenol reacts with methylene glycol to form methylol phenol: Methylol phenol can react with itself to form a longer chain methylol phenolic:

or form dibenzyl ether:

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or react with phenol to form a methylene bridge.

The most important point in resol resin chemistry is that, when an excess of

formaldehyde is used, a sufficient number of methylol and dibenzyl ether groups

remain reactive to complete the polymerization and cure the resin without

incorporation of a cure agent such as hexa. For this reason, the industry commonly

refers to resol resins as "single-stage" or "one-step" type products. Resol resin

manufacture includes polymerizing to the desired extent, distilling off excess

water and quenching or tempering the polymerization reaction by rapid cooling.

Because resol resins continue the polymerization reaction at even ambient

temperatures, albeit at much slower rates than during manufacturing, they

demonstrate limited shelf lives dependent on the resin character, storage

conditions and application.

By manipulating the phenolic to aldehyde monomer ratio, pH, catalyst type,

reaction temperature, reaction time, and amount of distillation, a variety of resin

structures demonstrating a wide range of properties are possible. The typical

number average molecular weight (Mn) of a straight phenol resol resin is between

200 and 450. Plastics Engineering Company supplies resol resins as liquids or in

solvents with viscosities from 50 to 50,000 cps, or as solids in the form of lumps,

granules, or fine powders. Organic solvents and the amount of water or phenol

monomer left in the resin control the viscosity of the liquid resin products. Resol

resins are usually water-soluble to a certain degree.

Crosslinking and the phenol/formaldehyde ratio

When the molar ratio of formaldehyde : phenol reaches one, in theory every

phenol is linked together via methylene bridges, generating one single molecule,

and the system is entirely crosslinked. This is why novolacs (F: P <1) don't harden

without the addition of a crosslinking agent, and that’s why resoles with the

formula F: P >1 will.

Characteristics of phenol formaldehyde

Bonding Strength: The primary use of phenolic resin is as a bonding agent.

Phenolic resin effortlessly penetrates and adheres to the structure of many organic

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and inorganic fillers and reinforcements, which makes it an ideal candidate for

various end uses. A brief thermal exposure to complete the cross-linking or

"thermoset" process results in attainment of final properties. The unique ability of

phenolic resin to "wet out" and to cross-link throughout the fillers and

reinforcements provides the means to engineer the desired mechanical, thermal,

and chemically resistant properties. High Temperature Performance: A key characteristic of thermoset phenolic

resin is its ability to withstand high temperature under mechanical load with

minimal deformation or creep. In other words, cured phenolic resin provides the

rigidity necessary to maintain structural integrity and dimensional stability even

under severe conditions. Chemical Resistance: Phenolic resins accommodate the harsh exposure of severe

chemical environments. The inherent nature of phenolic resin provides an

impervious shield to protect a variety of substrates from the corrosive effects of

chemicals. Laboratory tests confirm minimal degradation from many chemicals

after prolonged exposure, often at elevated temperatures. Low Smoke and Toxicity: Burning phenolic resin typically generates hydrogen,

hydrocarbons, water vapor, and carbon dioxide. Phenolic resin produces a

relatively low amount of smoke at a relatively low level of toxicity. Manufacturers

use phenolic resins extensively to address the safety concerns of the transportation

industry. Automotive and mass transit industries choose phenolic resin for its high

heat resistance and excellent flame, smoke, and toxicity properties. Another

critical application is in air support systems for the mining industry and related

electrical conduit supports. Phenolic resins designed to meet specific flammability

ratings are available. Selective use of inorganic fillers and reinforcements often

enhances protection in the event of contact with an ignition source. High Carbon and Char Yield: Phenolic resins demonstrate higher char yields

than other plastic materials when exposed to temperatures above their point of

decomposition. In an inert atmosphere at high temperatures (600° - 2,000°F, 300 -

1,000°C), phenolic resin will convert to a structural carbon known as vitreous

carbon. In many ways, this material behaves similar to ceramic and may actually

contribute to structural integrity when exposed to fire situations. Manufacturers of

structural composite gratings and pipes for offshore oilrigs, where fires are a

constant threat, utilize phenolic resins for the characteristic. Phenolic resin is also

useful in designing vitreous carbon articles such as special analytical electrodes,

crucibles for melting rare earth metals, rocket nozzles, extremely high temperature

bearings and seals, and heat shields for missiles. Automotive applications that

benefit from the formation of a thin carbonized layer, such as brake blocks and

pads, brake linings, and clutch facings also use phenolic resins.

The aerospace, defense, and electrical industries are heavily reliant on phenolic

resins. Phenolic resin advantages include high heat resistance, excellent

dimensional stability, as well as having a United Laboratories rating. Phenolic

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molding compound applications within these industries include electrical

commutators, switches, business equipment, and wiring devices. Phenolic resin

retains its strength at high temperatures, resists creep under load, and possesses

chemical and corrosive resistance. Phenolic resins are widely incorporated in

household appliances because of their excellent electrical resistance, dimensional

and thermal stability, and resistance to water and solvents.

Applications of phenol formaldehyde

• Ablation: Phenolic resin chars when heated to temperatures greater than

480°F (250°C). This process continues at very high temperatures greater than

1,000°F (>500°C), until the resin completely converts to amorphous carbon.

This characteristic contributes to the unique ablative properties of phenolic

resins. Examples are rocket nozzles, rocket blast shields, and atmospheric

reentry shields. • Abrasives:The variety of abrasive products available in the market is

practically endless, as they have to meet the specific needs of the individual

grinding applications and substrates. Generally, there are three groups of

abrasive products: bonded, coated, and non-woven. • Bonded abrasives: Bonded abrasives like grinding wheels are

comprised of abrasive particles embedded in a bonding matrix.

• Coated Abrasives: Coated abrasives are flexible grinding materials

typically available as sheets, discs or belts. These applications require

abrasive grains fixed to the surface of a variety of backings, like paper

or fabric, by special liquid phenolic resin binders. • Non-Woven Abrasives: Household and industrial applications use non-

woven abrasives, also called abrasive pads. The characteristically green

pads used for cleaning the dishes are the most publicly visible non-

woven abrasive.

▪ Adhesives: Wood bonding applications such as particleboard or wafer-

board have traditionally used phenolic resin binders.

▪ Carbon: Phenolic resins have an excellent affinity for graphitic and

other forms of carbon. Manufacturers often use the resin simply as a

binder and adhesive for their carbon materials.

▪ Coatings: Cured phenolic resins demonstrate exceptional chemical

resistance. Railroad cars, storage tanks and heat transfer equipment are

coated using phenolic resins as part of baked phenolic coating systems.

▪ Composites: Phenolic resins are the polymer matrix of choice in

composite products especially when meeting high flame, smoke and

toxicity (FST) properties.

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▪ Felt Bonding: Fiber felt manufacturers use phenolic resins with reclaimed

or virgin fibers to produce thermal and acoustical insulation for the

automotive and household appliance industries.

▪ Foam:Special phenolic resins in combination with the proper cure

catalysts, surfactants and blowing agents produce foam products

▪ Foundry: Many technologies are available to foundries for the production of

dies for metal castings.

▪ Friction:Phenolic thermoset resin is the choice for composite friction

materials: the pads, blocks, linings, discs and adhesives used in brake &

clutch systems that create retarding or holding forces with application against

a moving part.

▪ Proppants (Frac Sand): Oil and natural gas producers improve well yields

using hydraulic fracturing fluids containing round specialty sands coated

with phenolic resin.

▪ Refractory: High carbon yield, wear resistance, and excellent particle

wetting and bonding properties make phenolic resins ideal for refractory

products.

▪ Rubber:Tires and technical rubber goods use straight phenolic novolac

resins as reinforcing agents.

▪ Substrate Saturation:Many applications use liquid phenolic resins

to saturate substrates such as paper, fabrics, and wood. 2.12.12 - Urea Formaldehyde Urea reacts with formaldehyde in alkaline medium to produce monomethylol and

dimethylol urea. These when heated under pressure with catalyst forms a cross-

linked urea formaldehyde polymer.

88

Properties

High tensile strength and compressive strength, good electrical insulation. Good

resistance to heat, water and chemicals except strong acids and alkalies. Available

in liquid, waxy and rubbery form, good dielectric properties and a sustain

temperature between — 50 to 300°C.

Uses

For making laminates, insulation goods, control knobs, plates, dishes, etc. Fevicol

used as adhesive is also used in making varnishes, surface coating, light weight

foams in aeroplanes.

Questions

1. What are polymers? Describe the classification of polymers.

2. Distinguish between thermoplastics and thermosetting polymers.

89

3. Write a note on melting and glass transition phenomena. 4. What is polymerization? Explain the degree of polymerisation. 5. Discuss various types of polymerisation with suitable examples. 6. What are plastics? Explain compounding of plastics. 7. What are elastomers? 8. What is vulcanization? How drawbacks of natural rubber are rectified. 9. What are advanced polymer materials? 10. Describe conducting polymers in detail 11. What are electrical properties of polymers? 12. What is meant by fabrication of plastics? Mention various methods of

fabrication of plastics. Describe two methods of fabrication of plastics. 13. Write synthesis, properties and uses of

(i) Polyethylene (PE) (ii) Phenolformaldehyde

(iii)Kevler (iv) Buna -S 14. Write a short note on polymer composite materials.

(ii) PMMA formaldehyde resin. 15. What are the applications of kevler 16. Write down applications of polymer in medical uses

3. Lubricants

Smooth surfaces when viewed through microscope it is observed they contain

many peaks and troughs. Peaks are called asperities and contact between surfaces

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takes place through these asperities. When two surfaces are in contact and when

movement is initiated by sliding or rotation, there is considerable resistance to

such movement.

Friction is defined as the force resisting motion when two contacting surfaces are

moved with respect to each other. The frictional resistance results considerable

loss of energy and damage to the contacting surfaces. In between the molecules of

contacting surfaces there exists molecular force of cohesion, known as van der

Waals force of attraction. When such surfaces are in contact with each other, the

actual contacting points are a few asperities. The pressure at these points is very

high as they have to bear the total load and this result in interlocking or welding of

these junctions. Thus, the vander Waals forces, as well as the welded junctions

offer resistance to motion. As one surface slides over the other surface some of the

asperities break and this results in wear and tear of the surfaces. Thus, the friction

generates heat and is also associated with high pressure developed even under

small loads, which causes fusion of the material at the peaks and accounts for

formation of welded junctions. If the relative motion of the contacting surfaces is

to be maintained, an additional force is required to break these welded junctions,

which results in generation of more heat. Thus, generation of heat becomes a self-

accelerating process which may ultimately result in a grinding halt.

Fig. 3.1 Surface roughness as seen through microscope

The friction and wear can be minimised by lubrication which involves

interposition of the substance, of low shear strength between the moving surfaces,

which is adequate in preventing or at least minimizing asperity contact. It reduces

the frictional resistance and the loss of energy due to friction is considerably

reduced.

A substance which is capable of reducing the friction between two surfaces which

are sliding over each other is called ‘lubricant.’ The process of reducing friction or

introduction of lubricant between two sliding surfaces is called lubrication.

3.1 - PURPOSE OF LUBRICATION

i. It covers the surface abnormalities, prevents metal to metal contact and then

reduces wear and tear and surface deformation, by avoiding direct between

the rubbing surfaces.

91

ii. To act as a coolant or heat transfer medium by absorbing the heat of friction

created by rubbing of surfaces.

iii. To increase the efficiency of the machine by reducing the consumption of

energy.

iv. To prevent entry of dust and moisture between the moving parts. This

prevents corrosion of the metal surfaces.

v. In internal combustion engines, it acts as a seal and prevents leakage of

gases at high pressure in the combustion chamber and hence reduces the

maintenance as well as running cost of the machine to a large extent. vi. It reduces frictional resistance.

3.2 CLASSIFICATION OF LUBRICANTS Lubricants are classified on the basis of physical state as follows:

i. Solid lubricants: e.g., Graphite, molybdenum disulphide, strong, PTFE,

teflon, talc, mica, metals like Ga, In, etc.

ii. Semi-solid lubricants: e.g., Soaps, greases, vaselines, etc. iii. Liquid lubricants: Vegetable oils, blended oils and silicon oils, etc. iv. Emulsions: e.g., oil in water and water in oil emulsions. v. Synthetic lubricants: Hydrocarbons, phosphates, esters, polyglycols,

silicones, chlorofluorocarbons, etc. 3.2.1 Solid Lubricants Solid lubricants are used in the form of powder or a suspension in water or oil. The coefficient of friction lies in the range 0.005 to 0.01. The solid lubricants separate two moving surfaces under boundary conditions.

They are economical, non-toxic, easy to apply, chemically inert, thermally stable

and are resistant to radiations. Solid lubricants are generally used where use of

liquid or semi-solid lubricant is not desirable and where high load, temperature,

pressure and low speeds are involved. They include materials having layer lattice structure because of which they are

soapy and can be used as lubricant, e.g., graphite, molybdenun disuiphide, talc,

mica, etc. (i) Graphite: Graphite is a black crystalline form of carbon. The layers are

arranged parallel to one another with an interlayer distance of 3.35A. The layers

are held together by weak van der Waals forces, so they can slide one over other

easily. It is soapy to touch, non-inflammable and resistant to oxidation in air

below 350°C. It can be used as a dry powder or as a paste or as a suspension.

Aqua dag and oil dag are suspensions of graphite in which it is dispersed in water

and oil respectively. Graphite greases can be used at high temperature. Graphite is

used as a lubricant in intern & combustion engines, lathes, railway track-joints,

gears, cast iron bearing, in hot industrial processes such as wire drawing, tube

drawing, forging, etc.

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Fig. 3.2 Structure of graphite (ii) Molybdenum disulphide (MoS2): It has sandwich like structure in which a layer of molybdenum atoms is between the two layers of sulphur atoms. The layers are arranged parallel to each other and interlayer distance is 3.13 A°.

Mo layer

Sulphar Layer

Mo layer

Fig. 3.2.1 Structure of molybdenum disulphide

The layers are held together by weak van der Waals forces, so they can slide one

over the other easily and account for the softness of MoS2. It can be used as a

lubricant, as a dry powder, as a paste or as suspension. It is stable in air up to

400°C. It is added to greases, which are then used in automotive and truck chassis.

It can be used in vacuum and thus can be used in spacecraft (graphite cannot be

used). Its other applications are similar to graphite.

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(iii) Mechanical lubricants: A continuous adherent film of materials like plastics

and metals is formed on moving surfaces and thus their wear is reduced. Among

all plastics, polytetrafluoroethylene (PTFE) is a superior material. It provides

lowest coefficient of friction (0.03 - 0.01). It is effective from - 200 to 250°C. It is

chemically inert. Soft metal films such a gallium, indium, thallium, lead, tin, gold

and can be used for this purpose. (iv) Chemically Active Lubricants: They include extreme pressure additives and

chemicals which react with metal surface to wide inorganic surface compounds.

One of the best known treatments for steel is phosphating which the surface is

coated with a layer of mixed zinc, iron and manganese phosphates. (v) Refractories, ceramics and glasses: They are used in defense programmes

and in rockets. Refractory materials can be used at temperature for a short period

as a lubricant. The glass is used in hydrodynamic cation as it gets softened at

operating temperature. 3.2.2 Semi-Solid Lubricants Grease and vaselines are the most important semi-solid lubricants. Grease is made

from lubricating oil thickened with metallic soaps or sometimes by adding solids

such as graphite, bentonite, silica, talc, etc. to petroleum oil. Lubricating greases

are not simply very lubricating oils. They are lubricating oils in which thickener is

dispersed to produce a colloidal structure or gel. In dispersion of solid particles in

a liquid, if solid particles prevented from sticking together and settling out by

electrical charges, such a stabilised erosion of fine solid particle in a liquid is

called a colloidal dispersion. When a dispersion whole is concentrated enough to

behave as a solid it is called a gel. The properties of grease depend upon the nature and amount of soap used and

characteristic of oil used in their preparations. Due to soap the grease sticks to the

metal surface more firmly. The nature of soap decides resistance of grease to

temperature, its consistency, its resistance to water and oxidation and its ability to

stay in place. The grease on storage separates into oil and soap. It has very little

cooling effect in bearings. Due to these properties grease has limited applications.

Nearly, all greases soften under working condition, but reharden slowly on

standing. The viscosity of the greases in high, thus they cause more friction. With

increase in speed the friction increases and m1re heat will be generated. As

greases are poor coolants they will thus get overheated. This imposes lower speed

limit on grease lubricated bearing in comparison to oil lubricated bearing.

Petroleum oil is used, in about 99% of the grease produced. On the basis of

composition or soap used and method of preparation the greases can be classified

as: a. Calcium base or cup greases: They are prepared by mixing slaked lime

(calcium hydroxide) solution to tallow oil with constant stirring, in hot

condition. After soap formation is complete hot petroleum is added and

mixed with it. Certain amount of water is usually incorporated with grease to

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obtain smooth mixture of soap and oil. They are also known as axle greases.

These greases are very economical and are widely used. As calcium soap is

insoluble in water, these greases are water resistant. They are useful in

lubricating water pumps, tractors, caterpillar threads, etc. b. Sodium base greases: They are obtained by thickening of petroleum oil with

sodium soaps. Since sodium soaps are water soluble they are not water

resistant. Since they are not stabilized with water, they can be used upto

175°C. They can be used in ball and roller bearings where lubricant gets

heated due to friction. These greases provide protection against corrosion by

absorbing moisture and forming an emulsion with it. c. Lithium soap greases: They are obtained by thickening of petroleum oil with

lithium soaps. They have combined advantages of both the calcium base and

sodium base greases and thus they are water resistant. They can be used at

high temperature. Due to these properties they have wide range of

applications. About 65% of the market is captured by lithium base greases.

They have high mechanical stability and are stable on storage. They are

expensive and thus are used for specific application such as in aircraft. d. Complex greases: The particles or fibres formed by reacting two dissimilar

acids with single alkali are used as thickener in most of the commercial

complex greases. Calcium complex grease can be made from lime, a fatty

acid and acetic acid. Similarly, grease can be made with sodium, aluminium

and lithium, they have very high melting point. They are useful in still mills

and automotive wheel hub bearing, ball and roller bearing, household

appliances, machine tools, aircraft accessories, etc. Additives such as

antioxidants, corrosion inhibitor and extreme pressure additives are added to

greases.

3.2.3 Liquid Lubricants

The Liquid lubricants have a high cooling ability when circulated through bearing

areas. So they are widely used in industry. They also 4ct as sealing agent and

prevent corrosion. Good liquid lubricant should possess the following properties. i. An adequate viscosity

ii. High boiling point iii. Low freezing point iv. Good oiliness v. Stability towards heat and oxidation

vi. Should not undergo decomposition and corrodes the machine part.

The liquid lubricants are:

a. Minerals oils b. Blended oils

Table 3.1: Some vegetable and animal oils used in lubricant

Name Use as Lubricant

95

Vegetable oils:

1. Olive oil For bearing and machine parts working under low pressures

and high speed.

2. Castor oil For bearing and machinery operating at low pressure and

high speed. In medical, printing and plastic industry.

3. Palm oil For delicate instruments like watches and scientific

instruments.

4. Rapeseed oil Steam cylinders and delicate apparatus.

Animal oils:

1. Whale oil For light machinery

2. Lard oil For ordinary machine parts and as a cutting oil.

3. Tallow oil For ordinary machinery, team cylinders.

4. Neats foot oil For guns, sewing machines, watches and clocks.

a. Petroleum oils: They contain C12 to C15 hydrocarbons. These oils, are

obtained from crude petroleum on fractional distillation. They are known as

lubricating oils and aress essentially hydrocarbon oils. They are cheap and

have wide applications. Around 98% market is captured by them. The

hydrocarbons found in mineral oils are mainly straight and branched chain

paraffinic compounds, naphthenes (cycloparaffines or cycloalkanes) and

aromatics. They are very efficient in preventing corrosion.

The lubricating oil must be refined to remove wax, asphaltic matter and

aromatic constituents. These impurities if not removed, crystallise at lower

temperature and thus interfere with the flow properties of lubricating oils. The

% of wax in petroleum oil decides its pour point and cloud point. Easily

oxidisable impurities cause sludge formation during operating conditions.

Asphaltic, naphthenic and resinous impurities decompose at higher

temperature resulting in formation of carbon and sludge. These impurities are

removed by refining methods like dewaxing (to remove wax), acid- refining

(to remove unsaturated hydrocarbons) and solvent refining (to remove

aromatic compounds).

b. Blended oils: Although refined petroleum oils serve as lubricants, for

achieving satisfactory performance in a particular machinery, some of their

properties are necessary to be improved by adding chemical reagents known

as additives. These oils having improved properties are known as blended

oils. Types of additive added are as follows.

3.4 TYPES OF ADDITIVE

The common types of additive are

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Oxidation inhibitors

The most common reason of degradation of petroleum oils is their oxidation. At

high temperature the hydrocarbons in petroleum oil undergo homolytic fission to

generate free radicals. One of the reactions of these free radicals involves reaction

with oxygen which results in formation of hydroperoxides. Some hydroperoxides

decompose to form alcohols, aldehydes, ketones and organic acids which may

polymerise or break down further to viscous soluble polymers, insoluble sludge

and finally dark coloured varnish-like deposits.

The oxidation inhibitor terminates hydroperoxide chain reactions by reacting or

combining with hydroperoxide. The common oxidation inhibitors are di-tert-butyl

p-cresol, 2-naphthol, l- naphthyl (phenyl) amine, etc.

Rust inhibitors

They are surface active additives which form adsorbed film on iron and steel and

guard them from water corrosion. In shipping and storage machinery, sodium and

calcium sulphonates, organic phosphates are used as rust inhibitors. For protection

against non-ferrous and copper alloy corrosion, thiadiazole and triazole

derivatives are useful.

Antiwear and extreme pressure agents

For reducing wear in gears and high pressure hydraulic components, zinc dialkyl

dithiophosphates are used as antiwear agents. In steel -and-steel lubrication zinc

dialkyl dithiophosphate forms a brown surface film of ZnO, ZnS, FeO and some

iron and zinc organophosphates prevent the wearing of steel surface. Tricresyl

phosphate is a effective antiwear agent as it forms protective metal phosphite or

phosphate film. Under extreme rubbing conditions extreme pressure additives are

used in hypoid gears, machine tool slideways and various machine cutting

operations.

Friction modifiers

These additives are used in automotive applications as mild extreme pressure

agent in boundary lubrication condition. They prevent stickslip oscillations and

noise in automatic transmissions and also conserve energy. The fatty acids with 12 – 18 carbon atoms and fatty alcohols or esters of fatty acids. e.g., glycerides of

rapeseed and lard oil are used as friction modifiers.

Detergents and dispersants

They reduce deposition of oil insoluble sludge, varnish and carbon from fuel

combustion in internal combustion engine. Along with surface cleaning action, a

detergent also adsorbs on insoluble particles (as described above) to maintain

them as suspension in bulk oil and hence minimise deposits on rings, valves and

c1inder walls. A dispersant serves almost similar purpose.

97

Calcium, sodium and magnesium salts of alkylabenzene sulphonic acid,

carboxylic acids, alkyl phosphoric acid are commonly used detergents. Most

commonly used dispersants are polybutenyl succinic acid. Pour-point depressants The pour-point of low viscosity paraffinic oil may be lowered by 30-40°C by

pour-point depressants such as polymethyl methacrylate, styrene esters, etc. On

cooling below the normal pour-point, wax crystallises out of solution from liquid

oil. The additive molecule prevent such crystallisation as they get adsorbed on

crystal faces. Viscosity index improvers The viscosity index can be improved by addition of linear polymers such as

polyisobutylenes, polymethacrylates, polyalkylstyrene having molecular weight

ranging from 10,000 to 100,000. They function by thickening light oil to a higher

viscosity while retaining the original viscosity temperature coefficient. These

viscosity index improvers are used in multi grade automotive engine oils,

automatic transmission oils, and gear oils, in aircraft and in some industrial

hydraulic fluids. Foam inhibitors They are used to prevent foaming of oil in internal combustion engines, turbines,

gears and aircraft applications. In the absence of the foam inhibitors, severe

churning and mixing of oil with air may result in foam formation which may

overflow from lubricating system or interfere with normal oil circulation. Methyl

silicone polymers are effective foam inhibitors. They are not completely soluble

in oil, thus they form a dispersion of minute droplets of low surface tension which

help in breaking foam bubbles. Oiliness improvers They improve oiliness of lubricants by adding oiliness carriers like vegetable oils

such as castor oil, oleic acid, etc., the compounds containing strong polar group

such as dibenzyl disulphide, amyl phenyl phosphate, etc. They make oil to adhere

more strongly to metal surface. 3.5 LUBRICANT EMULSIONS A dispersion system consisting of two immiscible liquids is called an emulsion

and it is stabilized by adding a third component called emulsifying agent. The

emulsifiers or emulsifying agents are the substances which exhibit polar as well as

non-polar character, because they contain hydrophobic as well as hydrophilic end.

The hydrophobic end of the emulsifier molecule is wetted by oil and hydrophilic

end will be wetted by water. Hence, emulsifier molecule is adsorbed at the

interface of the two immisicible phases or liquids (oil and water), resulting in the

formation of a protective film around the dispersed droplets. A simple example of

98

emulsifying agent is sodium soap, which possesses hydrophilic or water loving

group -COONa and hydrophobic or water hating end -C15H31.

Fig 3.3 Function of emulsifier molecules around the droplets in o/w and

w/o emulsions.

There are two types of emulsions.

These are oil in water emulsion and water in oil emulsions.

(A) Oil in water emulsions are obtained by adding oil to a suitable quantity of

water in the presence of 3-20% water soluble emulsifying agent, such as sodium

soap or sodium or potassium salts of sulphonic acids. These emulsions are

generally used as cooling and lubricating liquids for cutting tools. These

emulsions are also as rust preventers and as lubricant for certain heavy sliding

components such as pistons in marine diesel engines.

(B) Water in oil emulsions are prepared by mixing water containing 1-10% water-

soluble emulsifier such as alkaline earth soap (calcium stearate) to the oil. These types

of emulsions are widely used to lubricate compressors and provide cooling effect

because of evaporation of water, in addition to lubrication. These emulsions possess

higher viscosity, than that of the oil from which they are prepared.

3.6 SYNTHETIC LUBRICANTS

They are either oils or greases which are very costly. They are prepared so as to

facilitate better characteristics compared to petroleum oil for lubrication purpose.

They have a high resistance to oxidation and with thermal stability and are

resistant to hydrolysis. They have high viscosity index, high flash or firepoint and

low pourpoint.

The types, structures and properties of important synthetic lubricants can be

tabulated as Table 3.2.

Table 3.2: Types and uses of synthetic greases

99

Sr. No. Type Uses

1 Synthetic hydrocarbons, (1) Auto engines

e.g., (2) Gas turbine gears for army, navy. nuclear

(1) Poly-butylenes and industrial applications

(2) Poly (a-olefins)

(3) Alkylated benzene

2 Polyalkylene glycols (1) Fire resistant hydraulic fluids in

combination with 30-60% water in foundry,

steel mills and mines.

(2) Brake fluids for automobiles.

(3) Textile fibre and textile machine Lubricants

as they are nonstaining and easily washable.

(4) Compress or lubricants for ethylene, natural

gas, helium, nitrogen.

(5) Lubrication of food processing equipment.

(6) Non-sludging lubricant for bearings and

gears in mills used by rubber, paper and plastic

industry upto 175°C.

(7) It is used as additive in water- based

synthetic cutting and grinding fluids. At high

temp, polyalkylene glycol comes out of solution

as fine droplets, which coat hot metal surface.

3 Phosphate esters (1) In air compressors

(2) In aircraft.

(3)In hydraulic control of steam turbines in

power stations.

4 Silicones (1) For lubriation of glasswares and rubber

surfaces.

(2) They can be used as extreme pressure

lubricants.

(3) They are used in aircraft and missiles.

5 Chlorouluoro ethylenes (I) Used in vacuum pump oils:

(2) They can be used with a wide range of

chemicals including O2,Cl2H2O2 and mineral

acids.

(3) They are used as lubricant in oxidiser

section of missiles.

3.7 MECHANISM OF LUBRICATION

100

The purpose of lubrication is achieved by forming a film of lubricants between the

contacting surfaces. The formation of the film of the lubricant can be achieved by

three mechanisms.

(1) Fluid film or hydrodynamic or thick film lubrication (2) Boundary or thin film lubrication (3) Extreme pressure lubrication.

3.7.1 Fluid or Hydrodynamic Lubrication (Thick Film Lubrication)

In this type of lubrication the sliding surfaces are separated completely by

applying a thin uniform film of liquid lubricants between them. The thickness of

liquid film is at least 1000 A. The liquid lubricants do not have any chemical

affinity to the metal surface and it sticks to it due to its physical property known

as viscosity or “stickness”. The liquid film covers all irregularities in the sliding

surface and thus it prohibits formation of welded junction and prevents contact

between sliding surface. Since instead of sliding surfaces the liquid film comes in

contact with each other it offers resistance to motion due to its viscosity. Thus, the

liquid lubricant must have sufficient viscosity so as to maintain the fluid film in its

place. If the lubricant viscosity is higher, a large amount of energy is required to

circulate and maintain the viscous lubricant film. The coefficient of friction under

these conditions is as low as 0.001 to 0.01. [The coefficient of friction for

unlubricated surface ranges from 0.1 to 1.5].

In such type of lubrication when the load is applied, the corresponding pressure

developed in the lubricant is sufficient to keep moving surfaces apart and

therefore, it is known as hydrodynamic lubrication.

Fig. 3.4 Fluid film lubrication (coefficient of friction 0.001 to 0.01)

Hydrodynamic lubrication occurs in journal bearing and its effectiveness depends

on the design of bearing, load and the rate of rotation of shaft.

This type of lubrication is useful in delicate machinery like watches, clocks,

sewing machine, etc. It is also used in electric motors, steam turbines, car axels,

automobile engine main bearing, and automobile connecting-rod bearings.

3.7.2 Boundary Lubrication (Thin Film Lubrication)

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Under the condition such as high load, slow rate of rotation, very low viscosity of

oil, etc., a continuous fluid film cannot be maintained between the rubbing

surfaces. Under such condition the thickness of the fluid film should be less than

1000 A. The coefficient of friction under these conditions is 0.05 to 0.15. Such a

thin film consists of one or two molecular layers and to forth it. The lubricant has

to be adsorbed on the metal surface by physical or chemical force or by both. The

adsorption of lubricant results in the formation of an oily film by attachment of

polar molecules to the metal surface. In some cases, the lubricant may chemically

react with metal surface forming a thin film which acts as lubricant. This film is

also known as boundary film. Although this film fills the regularities in metal

surface, some peaks may have more height than the thickness of this thin film and

thus this mechanism provides partial separation of moving surfaces. They may

establish contact which further leads to formation of welded junctions and results

in friction as well as wear and tear of metal surfaces involved.

Fig. 3.5 Boundary lubrication (coefficient of friction 0.05 to 0.15) The property of oil, responsible for its adsorption to metal surface, is known as

‘oiliness’. Vegetable and animal oils, containing fatty acids in them having

general formula R—COOH, have more oiliness, e.g., saturated stearic acid

C17H35COOH, unsaturated oleic acid C17H33COOH, etc. These oils have polar

carboxylic group which react with metal surface to form a continuous

monomolecular film of adsorbed molecules. The hydrocarbon chain (R) of fatty

acid gets oriented outwards in a perpendicular direction as shown in above figure.

The petroleum oils do not contain such polar groups and thus have less oiliness. The solid lubricants separate two sliding surfaces under boundary condition. 3.7.3 Extreme Pressure Lubrication Under boundary lubrication condition, a thin film of lubricant is formed between

the two moving metal surfaces which may permit a small contact between them.

This results in friction and generation of heat. Thus, welded junction and metal

tearing do take place. Under the conditions of high load and extreme pressure, the

contact between the metal surfaces increases and more heat is generated due to

increased friction. As a result of this, the liquid lubricant may get decomposed or

evaporated and thus it becomes ineffective. For effective lubrication under these

conditions special additives known as extreme pressure additives are used along

with the lubricant. These are generally chloride, sulphur, phosphorus, oxygen and

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lead containing organic compounds. Compounds of chlorine (e.g., chlorinated

ester), sulphur (e.g., sulphurised fats and oil) and phosphorus (e.g., tricresol

phosphate) are used as additives. Under these extreme conditions, these additives

undergo a chemical reaction with metal surface and form a solid surface film of

metallic chlorides or sulphides or phosphides. Thus, now while moving, instead of

metallic surfaces, these additive films which have relatively low shear strength,

come in contact with each other and thus they protect the metal surfaces. If this

film breaks from the metal surface, extreme pressure additives further react with

the metal surface and additive film is again formed.

The extreme pressure additives are used in ‘cutting and in machining of tough

metals. Cutting fluid is a lubricant and/or cooling medium used to reduce wear

and heating of metal cutting tools. They are also used in wire drawing. Metals like

titanium, chromium can be drawn into wire in the presence of chlorine-containing

additive which react with metal surface to form a stable oxide film.

3.8 PROPERTIES OF LUBRICANTS AND THEIR SIGNIFICANCE

3.8.1 Viscosity and Viscosity Index

Viscosity is the property of lubricant by virtue of which it offers resistance to its

own flow. The viscosity of an oil decreases with increase in temperature. In

certain cases like internal combustion engine, aeroplanes, the lubricant has to

function at low starting temperature as well as at high operating temperature.

Thus, viscosity should remain constant over a wide range of temperature. A good

lubricating oil should possess moderate viscosity

Viscosity index: Rate of change of viscosity with rise in temperatures is measured

by an arbitrary scale and is known as viscosity index.

The viscosity index can be found out by comparing viscosity of oil under test at

100°F, with two standard oils. One of these reference oils is chosen from a

standard set made from Pennsylvania crude, as it exhibits relatively small

decrease in viscosity with increasing temperature, and arbitrarily assigned a V.I.

of 100; the other is chosen from a standard set made from Gulfcoast crude and

arbitrarily assigned a V.I. of 0 as it shows relatively rapid change in viscosity with

temperature.

Mathematically

Viscosity index = LL

−−

U

H ×100

where U = Viscosity at 100°F of the oil under the test.

L= Viscosity at 100°F of standard Gulf coast oil having V.I. zero

and

H= Viscosity at 100°F of std. Pennsylvanian crude oil having V.I. 100

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An oil whose viscosity changes rapidly with change in temperature has a low

V.1., while the one whose viscosity changes only slightly has a high V.1. Addition

of linear polymers increases V.I. and oils with V.I. higher than 100 have been

prepared.

Fig. 3.6 Viscosity-temperature curves for the standards (L and H) and the oil

under test (U). Significance of Viscosity Viscosity is the single most important property of the lubricating oils which

determines their performance under operating conditions. For example, it is not

possible to maintain a liquid oil film between two moving or sliding surfaces if

the viscosity of the lubricant is too low and hence excessive wear will occur.

Excessive friction will take place, if the viscosity of the lubricant is too high. A

lubricating oil should have sufficient viscosity to enable it to stay in position. On

machine parts moving at slow speeds under high pressures a heavy oil should be

used as it better resists being squeezed out from between the rubbing pans. Light

oils can be used when lower pressures and higher speeds are preferred as they do

not impose as much drag on high speed parts. Therefore, for minimum friction,

the thinnest (least viscous) oil that will stay in position should be used. Determination of Viscosity by Redwood Viscometer Redwood No. 1: It is used to find viscosity of light or thin lubricating oils and

have efflux time of 2000 seconds or less. Redwood No. 2: It is used to find out viscosity of highly viscous oil such as fuel

oils. Its jet for the outflow of the oil is of a larger diameter and efflux time is 200

seconds or less. By using Redwood viscometer we can find out relative viscosities of oils by

measuring the time of efflux of 50 ml of oil through a standard orifice of the

instrument under standard conditions.

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Redwood Viscometer No. 1

Description of Apparatus:

Redwood Viscometer No. 1 consists of the following parts.

Fig. 3.7 Redwood viscometer

(1) Oil cup: It is a standard cylindrical oil cup which is made up of brass. It is

silvered from inside. Its height is 290 mm and diameter is 46.5 mm. It is open at

upper end and at base it is fitted with an agate jet, with bore of diameter 1.62mm

and internal length 10mm. The jet is opened or closed by a ‘valve rod’ which is a

small silver plated brass ball fixed to a stout wire. The level to which the cup is to

be fixed with oil is indicated by a stout wire fixed in the side of the oil cup. The

wire is turned upwards and it is tapered to sharp point to indicate level properly.

The cup is provided with thermometer which indicates oil temperature. The lid of

cup is provided with spirit level for vertical levelling of the jet.

(2) Heating bath: The oil cup is surrounded by cylindrical copper vessel which

serves as water bath. It is provided with a tap for emptying water from it and a

long side tube projecting outwards for heating water bath by means of gas burner

or spirit lamp. The copper vessel is provided with thermometer to indicate

temperature of water.

(3) Stirrer: The water bath is provided with a stirrer having four blades to

maintain uniform temperature in the bath to facilitate uniform heating of the oil.

(4) Tripod stand: The entire apparatus rests on a sort of tripod stand provided

with leveling screws at the bottom of three legs.

Flask: It has a specific shape. It receives the oil from jet outlet. Its capacity is 50

ml. This flask is known as Kohlrauch flask.

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Working The instrument is levelled by using levelling screws on the tripod stand. The water

is filled in the water bath upto the tip of indicator upto which the oil is to be filled

in the cylindrical cup. Agate jet is sealed by keeping brass ball valve in position.

Then the oil to be tested is filled in the oil cup upto the tip of the oil level

indicator. The Kohlrauch flask is kept exactly below the jet. The water bath is

slowly heated by heating the side tube, and thus the oil also gets heated

simultaneously. The temperature of water and oil is kept uniform by continuous

stirring. Their temperatures are recorded by the thermometers as T1 and T2. When

the desired temperature is maintained, the oil is allowed to fall through the jet in

Kohlrauch flask. A stopwatch is started simultaneously and when exactly 50 ml

oil is collected in the flask, the stopwatch is stopped and the efflux time required

is noted in seconds. The experiment is repeated and mean value of time of flow

for 50 ml oil is reported as t seconds, Redwood 1 at t°C. Usually, the viscosity is

recorded at 21.11°C (70°F), 60°C (140°F) and 93.33°C (200°F). From this value of time of efflux, the kinematic viscosity and absolute viscosity

can be determined if the density of oil is known. The absolute viscosity of liquid or oil is given by

η = × t

1

D2 , where

t2 D1

t1 = time in seconds, taken for the flow of 50 cc. of oil.

t2 = time in seconds, taken for the flow of 50 c.c. of standard oil or liquid (usually

rapeseed oil)

D1 = specific gravity of oil to be tested.

D2 = specific gravity of standard liquid. K = an arbitrary constant, which for water is equal to 1 and for rapeseed oil 100. The kinematic viscosity of oil can be calculated by the formula, if density (p) of

the oil is known.

ν = η

p

3.8.2 Neutralization Number (Acid Value) or Acid Number Acid number or value of lubricating oil is mgs of KOH, required to neutralise all

acidic constituents of I gram of the oil. Sources of Acidity and Significance Fatty oil consists mostly of glyceryl or other esters of higher fatty acids and in

some cases notable amount of free acids are present. The acid count increases with

time due to hydrolysis with moisture and is therefore, a rough indicator of the age

of the oil; i.e., it gives an idea of how old is a fatty oil. Periodic determination of

acid number is useful to indicate the progress of oxidation of lubricant and with

106

this information we can predict the stage at which the lubricating oil should be

replaced. The acid value of lubricating oil should be less than 0.1

New, unblended petroleum oils should have very low neutralisation values usually

ranging from 0.02 to 0.1. Values higher than this indicate faulty refining. Blended

or compounded oils may have higher values of neutraliiation number because of

the presence of additives such as oiliness carriers, oxidation and corrosion

inhibitors, etc.

As the oil is used, the neutralisation number may increase due to contamination

(e.g., SO2 from combustion of sulphur in the fuel, CO2 from combustion or that

present in atmosphere) and/or oxidation of the oil. The oxidation of the oil results

in the formation of all soluble alcohols, ketones, acids and peroxides thereby

increasing the acid number, viscosity and darkening of the oil colour.

Although the neutralisation number gives the amount of acid or base present in the

lubricating oil, it gives no information about their source and corrosive nature.

Determination of Total Acid Number of Oil

10 gm of oil and 50 ml of alcohol are mixed in a flask. The flask is heated on a

water bath for half an hour. Flask is cooled and contents titrated against 0.1 N

KOI-1 using phenolphthalein as an indicator

Acide value = Volume of 0.1 N KON used x 5.6

or Vol. KOH x N KOH x 56

Weight of the oil taken Weight of oil

3.8.3 Saponification Value or Number

Saponification number of value of an oil is defined as the number of mgs of KOH

required to saponify fatty material present in 1 gm of the oil. It is alkaline

hydrolysis of fatty oils which led to formation of soaps.

Mineral oils, being mixtures of hydrocarbons do not react with KOH and so are

not saponifiable. Vegetable and animal oils, however, are mixtures of glyceryl

esters of fatty acids and hence require large amounts of alkali to get hydrolysed.

Their saponification values are very high and each fatty oil has its characteristic

value.

Sap Value = Volume of KOH x N KOH x 56

Weight of the oil taken

Sr. No. Name of oil Acid value Sap value

1. Groundnut oil 0.2 – 0.8 194— 196

2. Castor oil 0.4 – 0.8 201 — 203

3. Coconut oil 10.0 – 35.2 253 — 260

4. Cottonseed oil 0.4 – 2.2 194— 195

5. Whale oil 0.3 – 51.4 190— 191

6. Rapeseed oil 1.4 – 4 .0 177 — 199

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Significance In distinguishing fatty and mineral oil

a) To identify a given fatty oil. b) To determine the extent of adulteration, if any, in a given oil. c) To determine the extent of compounding in a lubricant. When the type of

fatty ingredient in a compounded oil is known, its exact amount is given

by

Percentage of fatty oil = C

F × 100 Where, C = Saponification value of the compounded or lubricating oil

F = Saponification value of the fatty oil Determination of saponification value of an oil Theory: A known weight of the sample is mixed with a known excess of standard

alcoholic KOH solution and refluxed for 1 hr

CH2COOR CH2OH

CHOH + RCOOK + R2COOK + R1COOK

CHCOOR1 + 3KOH ⟶

CH2COOR2 CH2OH

Triglyceride Glycerol Potassium of fatty acid (acid)

Where R, R1 and R2 are alkyl groups The unreacted KOH is titrated back with standard acid using phenolphthalein as

an indicator.

H + OH − → H 2O unreacted

Procedure Transfer about 1 g of accurately weighed oil sample to 500 ml round bottom flask.

Add 25 ml of 1 N alcoholic KOH and 20 ml of alcohol. Fit the flask with water

condenser and reflux the contents on a water bath for one hour. Cool the content

and disconnect the condenser dilute to 250 ml in standard measuring flask. Pipette

out 25 ml in 250 ml conical flask. Add few drops of phenolphthalein indicator and

titrate the 0.1 N HC1 until pink colour has just disappeared. (a) Pipette out 25 ml of 1 N alcoholic KOH in 250 ml standard measuring flask

and dilute upto the mark. Pipette out 250 ml diluted solution in 250 ml conical

flask and titrate against 0.1 N HCl using phenolphthalein as an indicator. Example 3.1: In determination of saponfication value of vegetable oil, 2.5 gm of

oil sample was refluxed with 50 ml of alcohol and 50 ml of 0.5 N alcoholic KOH.

To get the endpoint 10 ml of 0.5 N HCl was required. The blank reading obtained

was 26 ml. Find saponification value of an oil.

108

Solution:

1. Weight of oil, w = 2.5 gm 2. Volume of 0.5 N HCI required for main titration, A = 10 ml. 3. Blank titration reading. B = 26 ml

As saponification value of sample is given by (B

−

A)

×

56

×

0.5

w

= 26 − 10 × 28 = 179.2 2.5

Saponification value is 179.2

Example 3.2 2.0 gm of oil was saponified by using 0.5 N alcoholic KOH. The

mixture required 6.0 ml of 0.5N HCI. The blank titration reading 18.0 ml of same

HCl. Calculate saponification value of the oil Wt. of the oil = 2.0 gm, Back

titration reading 6.0 ml.

Solution:

Blank titration reading 18.0 ml.

Sap. value = vol. of KOH × N KOH × 56 wt. of the oil in gm

= 12 × 0.5× 56 1.0

= l68 mg of KOH.

Example 3.3: l.0 gm of an oil sample required 1.0 ml of 0.01 N KOH for

neutralisation. Find acid value of the oil.

Solution: Wt. of the oil = 1.0 gm, vol of 0.01 N KOH = 1.0 ml

Acid value = vol. of KOH × N KOH × 56

wt. of the oil in gm

= 1.0 × 0.01× 56 1.0

= 0.56 mg/gm.

Example 3.4 Find the acid value of a vegetable oil whose 10 ml required 4.0 m of

0.01 N KOM during titration, (d = 0.92). Solution: Wt. of the Oil (mass) = Density × volume

= 0.92 × 10

= 9.2gm

Acid value = vol. of KOH required × N KOH × 56 wt. of the oil in gm

= 4.0 × 0.01× 56 = 0.243mg 9.2

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3.8.4 Cloud Point and Pour Point Definition of Cloud Points It is that temperature, expressed as multiple of 1°C, at which a cloud or haze of

wax crystal appears at the test jar when the oil is cooled under prescribed

condition. Significance The cloud point of petroleum oil is an index of the lowest temperature of its utility

for certain applications. Definition of Pour Point The pour point is the lowest temperature, expressed as a multiple of 3°C at which

the oil is observed to flow when cooled and examined under prescribed condition. Significance The pour point of petroleum oil is an index of lowest temperature limit for utility

of lubricating oil and it also indicates dissolved wax concentration of lubricating Apparatus Test jar: A cylindrical test jar of clear glass, flat bottom, approximately 3.0 to

3.35 cm in inside diameter and 11.5 to 12.5 cm in height. There is mark upto

which the sample must be taken. The cork should fit the test jar, and bored

centrally to insert the test thermometer

Fig. 3.8 Determination of pour point Jacket: A watertight cylindrical jacket of glass or metal with flat bottom, about

11.5 cm in depth is used. The jacket is fitted with a disk. It is provided with a

gasket which prevents test jar from touching the jacket. Cooling Bath: It contains suitable freezing mixture for cooling.

110

Procedure

Pour the oil into test jar to the level mark. Cork it tightly. Insert the test jar in the

jacket. Start cooling. After every 1°C remove the test jar from jacket quickly but

without disturbing the oil, inspect for cloudiness. If the oil does not show cloud

replace the test jar in jacket and repeat the same procedure. When such inspection

first reveals a distinct cloudiness or haze in the oil at the bottom of the test jar,

record the reading of thermometer as cloud point.

For finding out pour point continue coding, after cooling by 3°C remove test jar

from the jacket, tilt the jar to horizontal position for exactly 5 seconds. The

temperature at which it does not flow is taken as pour point of the oil.

3.8.5 Oxidation Stability

Rate of oxidation in the petroleum oils proceeds slowly at room temperature but at

elevated temperature (above 200°C), the rate is high. The factors which increase

the oxidation are moisture in the environment and the presence of oxidation

catalyst like iron, aluminium and copper. In most commercial oils the rate of

oxidation is retarded by adding sacrificial oxidation inhibitors like phenyl -

naphthylamine.

Oxidation in lubricants is undesirable because the insoluble product or sludge may

clog oil holes, oil pipe lines, filters and other parts of the lubricating system. If the

oxidation product is soluble it circulates with the oil and may corrode or pit

bearing surfaces or may form vanish-like deposits and gums.

3.8.6 Aniline Number

Definition

Aniline number is thus minimum equilibrium solution temperature for equal

volume of aniline and lubricating oil sample.

Significance

The tendency of a lubricant to mix with aniline is expressed in terms of aniline

point of the sample. As like dissolves like, aniline being an aromatic compound, it

is miscible with oil having high percentage of aromatic hydrocarbons at lower

temperature. A high aniline point thus indicates lower percentage of aromatic

hydrocarbons, and thus higher percentage of parafinic hydrocarbons in oil and

vice-a-versa.

Aniline point of lubricant is thus measure of its aromatic content. A lubricant with

high aniline point is recommended for systems in which rubber seals, gaskets and

packing materials are involved. A lubricating oil with low aniline point will tend

to attack these rubber parts, used in system to prevent leakage. This results in

deterioration of rubber parts and leakage may take place.

Aniline point of an oil is indication of tendency of deterioration of an oil when it

comes in contact with packing, rubber sealing, etc. Usually, the aromatic

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hydrocarbons have tendency to dissolve natural as well as some synthetic rubbers. Thus, presence of aromatic hydrocarbons in oil is not desirable. Determination of Aniline Point Description of Apparatus (1) Test tube: It is made up of heat resistant glass, approximately 25 mm in

diameter and 150 mm in length. The cork of test tube is fitted with stirrer and

thermometer (2) Jacket tube: It is made up of heat resistant glass, approximately 37 to 42 mm

in diameter and 175 mm in length. Cork of jacket is fitted with test tube. It

provides air jacket. (3) Stirrer: It is a metal stirrer with a concentric ring at the bottom. A glass sleeve

is usually used as a guide for the stirrer. (4) Heating bath: A suitable non-aqueous, non-volatile, transparent liquid bath is

used (usually a paraffin bath).

Fig. 3.9 Aniline point

apparatus Working of aniline point Clean and dry the apparatus perfectly as aniline is hygroscopic. Since aniline is

highly toxic pipette out 10 ml of aniline by using aspirator in the test tube. Add

exactly same amount of dry sample of an oil to it. Fit the test tube with cork fitted

with stirrer and thermometer. See that they do not touch the bottom of tube. Fit the

tube in air jacket. Heat it in paraffin bath and simultaneously stir the mixture

rapidly till a homogeneous liquid is obtained. Remove the jacket from hot paraffin

bath and cool it with constant stirring till two distinct phases separate (appearance

of cloudiness throughout). This is called aniline point of given oil.

112

3.8.7 Flash and Fire Point

Definition

‘Flash -point’ is the lowest temperature at which an oil gives off enough vapour,

which give momentary flash of light when a flame is brought near it. ‘Firepoint”

is the lowest temperature at which the vapours of oil burn continuously for at least

5 seconds when a small flame is brought near it. Usually, the fire-point of an oil is

about 5 to 40°C higher than its flash-point. Significance

Many times the lubricant under use has to face high temperature. A good lubncant

should not volatilise under the working conditions and even if it volatilises, the

vapour formed should not catch fire under the working temperature conditions.

Thus, the lubricant used must have reasonably high flash-point than the working

temperature so as to insure safety. Pensky - Marten’s Apparatus

The apparatus is useful for determination of flashpoint between 80°C and 370°C.

Description of Apparatus

(1) Oil cup: It is made up of brass or other non-rusting metal of equivalent heat

conductivity. Its diameter is 5 cm and depth is 5.5 cm. The level upto which the

oil has to be filled is shown by oil level mark. The lid is made up of brass. The lid

of the cup is provided with four openings for stirrer, standard thermometer, for

introducing flame and air inlet. The cup is supported by its flange over a heating

vessel in such a way that there is clearance between them. The flange is equipped

with device for locating the position of the cup in the air bath.

Fig. 3.10 Pensky-Marten’s flash point apparatus

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(2) Shutter: it is made up of brass and is provided at the top of lid of cup. It has

lever mechanism; the shutter can be moved to open the opening for air and

opening for introducing flame exposure device which carries the flame. (3) Flame exposure device: It is connected with the shutter in such a way that

when the shutter is moved to open the opening in it, the flame exposure device is

dipped into the opening. (4) Air Bath: The oil cup is supported by flange over an air bath which is heated

by gas burner. (5) Pilot burner: When the test flame is introduced in the opening, it gets

extinguished, but when it returns to its original position, it is automatically

relighted by the pilot burner. Working The oil to be tested is filled upto the oil level mark in the oil cup and it is heated

by heating the air bath by a burner. The oil is stirred continuously at a rate of

about 1 to 2 revolutions per second. The heating is done in such a way that the

temperature rises by 5C per minute. Shutter is moved and oil is exposed to flame

at every 1°C rise in temperature. While applying the test flame, the stirring is

simultaneously interrupted. The temperature at which a distinct flash appears

inside the cup is recorded as flashpoint. The heating is further continued and the

test flame is introduced after every 1°C rise in temperature; in similar way. The

temperature at which oil ignites and continues burn for 5 seconds is recorded as

fire point. 3.8.8 Oiliness Is the property of lubricant to stick on the surface of the machine parts. Vegetable

and animal oils have good oiliness but mineral oils have poor oiliness. Oiliness of

mineral oils can be improved by adding certain additives. 3.9 SELECTION OF LUBRICANTS At a high temperature lubricant used may undergo volatilisation or decompose

leaving a residual oil, which will have different lubricating properties. So a careful

study of various properties and their correct interpretation is necessary for the

selection of lubricants. Selection of a lubricant for typical job is illustrated as : 3.9.1 Lubricants for Cutting Tools In these operations, a metal is continuously removed from the surface and fresh

metal surface is continuously exposed to the tool used. For heavy cutting: the most effective lubricants are cutting oils. The cutting oils

are, essentially, mineral oils of flow viscosities containing additives like fatty oils,

sulphurized fatty oils and chlorinated compounds, which by virtue of their polar

groups attached themselves to the surface of continuously exposed fresh metals.

As the shear strength of such an oil film is much less than that of the metal, a

considerable reduction in friction results, thereby decreasing both the power

consumption and the extent of heat generation.

114

In light cuttings: The most effective lubricants are oil-emulsions. Oil- emulsions

have somewhat smaller lubricating effects than cutting oils, but they are more

efficient as cooling media, due to the high heat capacity of water, which is present

in them as an external phase.

3.9.2 Lubricants for Internal Combustion Engines

The lubricant is to be exposed to high temperatures in an internal combustion

engine. Therefore, the lubricant should possess high viscosity-index and high

thermal stability, petroleum oils containing additives, which impart high viscosity-

index and oxidation stability to them, are used as lubricants for internal

combustion engines.

3.9.3 Lubricants for Gears

Subjected to extreme pressures lubricants for gears should: (i) possess good

oiliness, (ii) not to be removed by centrifugal force from the place of application, (iii) possess high resistance to oxidation, and (iv) have high load-carrying

capacity. Usually, thick mineral lubricating oils, containing extreme-pressure

additives are employed.

3.9.4 Lubricants for Delicate Instruments

Watches, clocks, scientific equipment, sewing machines, etc. are not exposed to

high temperature or to water or to extreme load. etc., so properties relating to

these conditions are not considered for such uses. Consequently, for such

purposes, thin vegetable and animal oils like palm oil, neat oil, etc. are employed.

3.9.5 Lubricants for Very High Pressure and Low Speeds

Such as for tractor rollers, concrete mixers, lathes, railway track joints, etc. Under

these conditions, oil/grease films cannot be maintained, so solid lubricants MoS2

like graphite, soapstone, mica, etc. are employed either in dry powder form or as

emulsion in oil or water.

3.9.6 Lubricants for High Pressure and Low Speeds

Rail axle boxes, wire ropes, tractor rollers, etc., are greases and blended thick oils.

3.9.7 Lubricants for Transformers

Transformer oils should be properly filtered and dried, before being put into use. They must possess good dielectric strength.

3.9.8 Lubricants for Spindles in Textile Industry

For spindles moving at very high speeds, thin oils are used. For better results,

oxidation and rust inhibitors are added to the oil.

3.9.9 Lubricants for Refrigeration System

Oil with low pour-point, low viscosity and low cloud-point is needed. So

naphthalene-base oils, possessing such characteristics, are accordingly employed

mostly. The pour-point requirements are - 40°F (maximum) for the lightest grade

and - 13°F for the heaviest grade oils. Their viscosity range is 85 to 325 SUS

(Seybold Universal Seconds) at 100°F

115

Questions 1. What is a lubricant? How they classified? 2. Explain the following properties of lubricants with their significance.

a. Viscosity and viscosity index c. Flashpoint and firepoint b.

Saponification number d. Neutralization number 3. Discuss the condition for which solid lubricants are used. Explain the use of

graphite as lubricant. 4. Distinguish between third film and boundary lubrication. 5. How would you determine viscosity of lubricating oil by using Redwood

viscometer? 6. Write short notes on:

a. semi solid lubricants c. synthetic lubricants b. selection of lubricant d. extreme pressure lubrication

7. A sample of vegetable oil was tested for acid value. 10 gm of oil was titrated

against N/40 KOH and burette reading was found to 2.6 ml. state whether oil

is a proper lubricant.

8. Find acid value of the used oil whose 10 ml require 3.5 ml of N/50 KOH

during titration (density of the oil 0.81)

9. 1.532 gm of cottonseed oil was refluxed with 25 ml of 0.5N al. KOH. The

back titration reading was 15.7 ml of 0.5 N HCl and standardization readings

26 ml. calculate sap value of the oil.

10. 5 gm of cod-liver oil sample require 11.3 ml of N/50 KOH. Find acid value of

the oil (6.3 gm.). 11. 2.5 gm of oil was saponified with al. KHO (0.25N). The blank titration

reading with 0.5 N HCl was 40 ml while back titration reading was 20ml with

same HCl, find sap value of oil.

12. 1.55 gm of oil is saponified with 26 ml of N/2 alcoholic KOH, after refluxing

the mixture it require 15 ml of N/2 HCl. Find saponification value of oil. 13. In determination of saponification value of vegetable oil 5 gm of oil sample

was refluxed with 50 ml of alcohol and 50 ml of 0.5 N KOH solution. To get

end point 20 ml of 0.5N HCl was required the blank reading was 52 ml. find

saponification value of oil.

14. Find acid value of 3 gm of an oil which required 0.2 ml of 0.025 N KOH to

neutralize free acid present. 15. 16 gm of blended oil was heated with 50 ml KOH. The mixture than require

31.5 ml of 0.5N HCl. 50 ml of KOH required 45 ml of 0.5 N HCl. Find % of

Cottonseed oil, is saponification value is 192mg. 16. Find acid value of a used oil sample whose 7.0 ml required 3.8 ml of N/20

KOH during titration (density of oil = 0.88). state whether oil is proper

lubricant or not from acid value.

116

4. Phase Rule

4.1 GIBB’S PHASE RULE

The equilibrium conditions of a heterogeneous system involving number of

components, is influenced by temperature, pressure and concentrations of

reactants. Under such conditions, there exists a relationship between the phases

present, components taking part in equilibrium and degrees of freedom available.

This relationship was first proposed by Willard Gibb’s and is known as Gibb’s

Phase Rule. It is represented as follows.

F + P = C + 2 or F = C – P + 2 where P = phase, C = component, F = degree of freedom.

It is assumed that the equilibrium is not affected by gravitational, electrical or

magnetic forces, or by surface tension.

4.2 DEFINITION OF VARIOUS TERMS

4.2.1 Phase

It is defined as “any homogeneous and physically distinct part of system which is

separated from such other parts of system by well-defined boundary surfaces”.

(a) Air is a mixture of various gases such as oxygen, nitrogen, carbon dioxide,

argon, etc. constitute a single phase. This is because, air is homogeneous, the

different gases are uniformly distributed and there is no definite boundary

surfaces separating them. Hence, air, a mixture of gases, constitutes a single

phase. (b) Two liquids like alcohol and water which are miscible in all proportions,

constitute a single phase, since there is no separating boundary surfaces

between alcohol and water. other examples are acetone and water, ethanol

and water, etc. (c) When two liquids are immiscible, they constitute two phases, e.g., benzene or

chloroform and water.

Two Phase

(d) A solution of salt constitutes a single phase even though salt may be complex

salt. For instant Mohrs salt, FeSO4 .(NH4)2 SO4.6H2O containing FeSO4, and

(NH4)2 SO4 constitute a single phase solution.

(e) Each solid constitutes separate phase. For instance, different forms of sulphur

when present in equilibrium, each form constitutes separate phase.

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(f) Homogeneous solid solution constitutes a single phase. (g) Water can exist in solid form as ice, in liquid form as water and in vapour

form as steam. Each is a phase and can be represented as:

Ice ⇌ water ⇌ steam

(Solid) (liquid) (vapour) 4.2.2 Component The number of components of a system at equilibrium is the smallest number of

independently variable constituents by means of which, the composition of each

phase, can be directly expressed or represented by chemical equation. Consider

the decomposition of CaCO3 into CaO and CO2.

CaCO3 ⇌ CaO + CO2

100 56 44 Since each solid constitutes a single phase, this system has three phases, 2 solids

and one gaseous, namely, CO2. Since the reaction is represented by chemical

equation, by knowing any two the third one can be calculated. The composition of

each phase can be represented as follows. Phase 1 due to CaCO3 is represented as

CaO + CO2 ⇌ CaCO3

Phase 2 due to CaO is represented as

CaO ⇌ CaO + 0.CO2 (here CO2 is Zero)

Phase 3 due to CO2 is represented as CO2 ⇌ CO2 + 0.CaO (Here CaO is Zero)

Thus, composition of each can be represented by knowing CaCO3, CaO or

CaCO3, CO2 or by CaO and CO2. This means only two constituents are sufficient

to represent each phase in the system and hence it is a two-component system. Considering water system, though water is present as solid, liquid and gaseous

phases, it is the same substance chemically. Hence, it is a single component

system. In a similar way all the different forms of sulphur can only represent sulphur It is

once again a single component system.

The decomposition of CuSO4.5H2O into CuSO4.3H2O + 2H2O is a two-

component system. The decomposition of steam by iron can be shown as three-component system. Fe (s) + H2O (g) ⇌FeO (s) + H2O(g)

118

4.2.3 Degree or Freedom or Variance

The number of degrees of freedom of a system is the number of variable factors

like temperature, pressure and concentration which must be specified so that the

system can be defined completely In order to understand this aspect, consider a single-component system like water

system. If we consider any one phase individually only, then by applying the

phase rule, F = C – P + 2,

We have

C = 1, P = 1

Substituting,

F = 1 – 1 + 2 = 2

The degree of freedom is two. The system is bivariant. This means to define the

system consisting of a single phase, two variables, namely, temperature and

pressure should be known.

When two phases are in equilibrium, say liquid water and water vapour, and then

the number of phases is two. By applying the phase rule, F = C – P + 2,

We have C = 1, P = 2

∴ F = 1 – 2 + 2 = 1

That means, the degree of freedom is one. The system is univariant. Consider

water boiling at 100°C. It is a case of liquid water being in equilibrium with water

vapour. Two phases are in equilibrium at 100°C and 1 atmospheric pressure. In

other words, two phases, liquid water and water vapour can be in equilibrium at

100°C, only at 1 atmospheric pressure or at 1 atmospheric pressure, the two

phases can coexist at 100°C. That is either pressure or temperature alone can

define the system.

When we consider all the three phases to be present in equilibrium, the number of

phases is three and by applying the phase rule, F = C – P + 2,

We have C = 1, P = 3

∴ F= 1 – 3 + 2 = 0

The degree of freedom is zero, the system is invariant. That means, all three

phases can coexist only at an unique temperature and pressure. When one of them

is altered, the number of phases will not remain three, one of the phases will

disappear.

4.3 ONE-COMPONENT SYSTEM WATER

It is a single -component system and water can exist in different phases—solid

phase as ice, liquid phase as water and gaseous phase as steam or water vapour.

These three phases can exist as three two-phase equilibrium and one three-phase

equilibrium. They are:

119

Two-phase equilibria

Three-phase equilibriim

Solid

⇌ Liquid Solid

⇌ Liquid

⇌ Vapour

Liquid

⇌ Vapour

Vapour

⇌ Solid

The curve OB represents the equilibrium between liquid w er and water vapours.

Water boils at 100°C to get converted into vapour at atmospheric pressure, i.e. if

the pressure is reduced, water will vaporise at lower temperature and if pressure is

increased water will vaporise at higher temperature. That means water can remain

in liquid form even at high temperatures provided, the pressure is high. The upper

limit is 374°C at 220 atmospheric pressure. Above this temperature water cannot

exist in liquid state. Again along the curve for every temperature there is a

corresponding pressure when both liquid water and water vapour can coexist. By

applying the phase rule, F = CV – P + 2

We have C = 1, P = 2

∴ F = 1 – 2 + 2 = 1 The system is univariant, the degree of freedom is one. That means by knowing

the pressure or temperature, the system can be completely defined. Similarly, the curve OC represents the equilibrium between solid ice and liquid

water. Here again for every pressure, there is a corresponding temperature when

solid ice is in equilibrium with liquid water. This curve is also known as freezing

point curve and degree of freedom along this line is one. The system is univariant.

Since by applying the phase rule, F = C – P + 2

We have C = 1, P = 2

∴ F = 1 – 2 + 2 = 1 As the curve slopes towards the pressure axis, it can be inferred that freezing point

of water is lowered as the pressure increases. The following figure describes the equilibrium conditions between various phases.

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Now consider the existence of all the three phases in equilibrium. The point where

the curves OA, OB, OC meet, the point 0 is called the triple point, signifies an

unique situation. Such an equilibrium is only possible at a particular temperature

0.0075°C and pressure 4.58 mm. Any change in temperature or pressure will

disturb the equilibrium between the three phases, resulting in the disappearance of

one of the phases.

The three curves OA, OB, OC represent the equilibrium conditions between two

phases solid with vapour, vapour with liquid and liquid with solid phase of water.

These curves divide the diagram into three areas representing single phase system,

i.e., AOB representing vapour, BOC representing liquid and COA representing

solid phase. Within these regions of single phase, both temperature and pressure

have to be stated to define the system completely

Taking individually the two-phase equilibria one by one, curve OA represents the

equilibrium between solid and vapour phases of water. This curve is also known

as vapour pressure curve or sublimation curve. Along this line OA, for every

temperature, there is a corresponding pressure at which both solid ice and water

vapour coexist in equilibrium. Applying the phase rule, F = C – P + 2,

We have C = l, P =2

∴ F= 1 – 2 + 2 =1

The degree of freedom is 1, the system is univariant and by knowing either the

temperature or the pressure, the system can be completely defined.

An unstable equilibrium can exist when cooling is carried under careful conditions

without the separation of solid phase. This is represented by curve 00’. Under

these conditions equilibrium can exist even at lower temperatures. However, such

equilibrium is very unstable and can easily be disturbed by providing small

amounts of nucleating substances. This will immediately result in solidification of

super cooled liquid to solid ice.

4.4 TWO-COMPONENT SYSTEM

For a two-component system, the phase equation becomes:

F= 2 – P + 2 = 4 – P

Since in any equilibrium, at least one phase must be present, F= 4 – 1 = 3, i.e., the

degrees of freedom for a two-component system becomes three. This means, all

the three factors like temperature, pressure and concentrations have to be specified

in order to define the system completely. it is only possible to represent such

equilibria by three-dimensional diagram. To depict such diagram on paper, will be

a difficult proposition. If one of the variables can be kept constant, the other two

variables can be used for representing the equilibrium. It is also possible that one

of the phases may have little effect on the equilibrium condition and can thus be

ignored.

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Examples of two-component system can be made up of the following types:

1. liquid – solid equilibria

2. liquid – liquid equilibria

3. liquid – gas equilibria

4. solid – gas equilibria Of these four, liquid-solid equilibria is of practical importance and will be studied.

Further such systems do not have gas phase and effect of pressure under such

conditions is negligible. These equilibria exist under atmospheric pressure so that

the degree of freedom is reduced by one. The phase equation can be written as:

F = C – P + 1 This is known as condensed (reduced) phase equation and is used to represent

equilibrium with only two variables, namely, temperature and concentrations. Let us study a two-component system with the two components completely

miscible in liquid state. The temperature composition curve for such a system can

be represented as follows

Fig. 4.2 The two components of the system are represented by A and B, and they are

miscible in molten state completely. In the figure point A and point B represent the melting points of pure A and pure

B. If B is added to A in molten state, the melting point decreases along the line

AC. Similarly, point B represents the melting of it of pure B. Any addition of A,

lowers its melting point as represented by line B

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The curve A C is also called freezing point curve of A and represents the

composition of the solutions saturated with component A in the range of

temperatures from A to E. Similarly, curve BC is known as freezing point of

component B and represents the composition of solution saturated with B and at

temperature range from B to F

Since two phases are present, applying the reduced phase rule to the system, we

have F = C – P + 1,

We have C = 2, P = 2

∴ F = 2 – 2 + 1 = 1

The system is univariant along the lines AC and BC.

The two curves intersect at C, where both solids A and B are in equilibrium with

the liquid phase. There are three phases in equilibrium at C and applying the

reduced phase rule, F = C – P + 1

We have C = 2, P = 3

∴ F = 2 – 3 + l = 0

The system is invariant and thus at C the temperature and composition remains

constant as long as all the three phases coexist. If either the temperature or

composition is changed the equilibrium will be changed. Further, C represents the

lowest temperature at which any liquid state can exist since below this

temperature, the liquid phase completely disappears. Point C is called as eutectic

point, temperature corresponding to this state is called as eutectic temperature and

the composition of solids is called eutectic composition.

As an example of such liquid-solid system the extraction of silver from lead ores

is described below. This is also referred to as the process of desilverisation of

lead. The fig. shows Lead – Silver system

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The lead ores contain 0.1% of silver and it is difficult to extract such small

quantities. The silver content can be increased by adopting the following

procedure. The ore is melted and cooled. As the cooling takes place, lead begins

to separate out and is removed from the molten liquid. Further cooling separates

out more lead, so that the resulting mixture is more of silver. The maximum

concentration of silver that can be obtained by this method is 2.6% Ag with 97.4%

lead to 303°C. 4.5 APPLICATIONS OF PHASE RULE ▪ It indicates the behaviour of a system under a particular set of conditions.

Different systems with the same degree of freedom behave in a similar

manner.

▪ It helps to find out, under a set of conditions whether all substances involved

in an equilibrium can exist or whether a particular phase ceases to exist or

whether any transformation has taken place.

▪ It does not require any knowledge of molecular or microstructure and it does

not take into consideration nature and quantities of components present in

equilibrium.

▪ Phase rule facilitates study of different equilibria and classify them

accordingly. Limitations of Phase Rule ▪ Phase rule deals with systems in equilibrium and is not of much help in study

for systems which attain equilibrium slowly.

▪ Since no quantitative analysis is done, it is necessary to determine exactly the

number of phases present under equilibrium conditions.

▪ Though each solid is supposed to constitute a single phase, phase rule cannot

be applied to solids in finely divided state.

▪ It does not furnish enough information regarding the extent of changes that

take place when the system shifts from one equilibrium to another.

QUESTIONS 1. State Gibb’s phase rule. Explain various terms involved in it. 2. Explain the terms (I) phase (ii) component (iii) degree of freedom. 3. Explain the applications of phase rule to one-component system. 4. Explain the term condensed phase rule. 5. State and explain limitations of phase rule. 6. Discuss in brief lead – silver equilibrium with diagram. 7. What do you mean by reduced phase rule?

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5. Important Engineering Materials

5.1 Cement

Cement is a powdered material initially have plastic how when mixed with water

and which possessing adhesive and cohesive Properties which is capable of

binding materials like bricks, stones and building blocks of concrete. In the

presence of water, cement form a pasty plastic mass, which after a time, sets to a

hard rock like material, due to reactions of various constituents of cement with

water. These reactions help to bind the various materials like sand, bricks, stones

etc. in a firm manner. Concrete is a mixture of cement, stone aggregate, sand and

water mixed in definite proportion and this mixture sets to become hard and

durable material. Modern cement was discovered by Joseph Asphidin, an English

brick layer in 1924. But cement like materials have been in use from earlier times.

5.1.1 - Types of cements

There are many types of cements are available depends on their composition and

properties. Some of these cements are given as follows

Natural Cements: When lime stone which contains impurities of silica, alumina

and iron oxide to the extent of 20 - 40%, is calcined and powdered, natural cement

is obtained. In the calcination process, the impurities present react with lime to

form calcium silicates and aluminates. However the proportion of these

constituents varies depending upon the initial proportion of these impurities.

Because of these reasons, such cement never possessed uniform properties when

mixed with water and allowed to set. However since they were able to bind bricks

and stones they were used for construction purposes during the early days.

Portland cement:It is obtained by grinding a mixture of lime and clay that has

been burnt. Clay supplies the silicate and aluminate portion whose proportion

determines the setting strength and durability of cement.

Pozzolona Cements:Romans were the first to use cements of different kind. They

used a mixture of volcanic ash and lime, ground to a fine powder. The volcanic

ash contained the silicates and aluminates of calcium and with lime, readily

formed a cement like material capable of setting even under water. Once again

because of their non uniform properties, they were discarded eventually.

Super sulphate cement: is available and manufactured by fusing together blast

furnace slag small amount of lime and large amount of gypsum in a kiln. It has

greater resistance to the sulphate water.

White cement: it is ordinary portland cement containing Fe203 as one of the

consistent Mainly used for decorative constructions.

Acid resisting cement: special type of cement is prepared by taking into

consideration it capability if resisting corrosion by acids. It is used in concrete and

concrete reinforced structures.

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Slag Cements With development of steel industry, another material became available as a good

binding material. This is the blast furnace slag which is made up of silicates of

calcium and aluminum. The chemical composition of blast furnace slag resembles

that of Portland cement. CaO, SiO2, and Al2O3 constitute 90 - 95% of slag. The

quality of slag is determined by relative proportion of oxides which in turn

determine its basicity and activity of material. If the ratio of sum of percentages of

CaO and MgO is greater than sum of percentages of SiO2 and Al2O3, the material

is basic in nature and if the ratio of M203 to SiO, is greater than 1, slag cement

has good setting property even under water and setting is also faster. The binding

and setting properties are also dependent upon the manner in which the stag is

cooled. Rapid cooling results in the formation of amorphous material which has

better binding properties whereas slow cooling results in more crystalline product

which has less binding property. 5.1.2 - Portland cement It is the mostly widely used reliable cementing material used for construction

purposes. It was discovered in 1924 by English brick layer Joseph Aspidin. After

setting the stone like mass resembled famous Portland rock (stone) of England

hence it was named Portland and cement depending upon the rate of setting heat

evaluation and strength characteristics. Portland cement is of following types Type - 1 Regular Portland cement Type - 2 Modified Portland Cement Type - 3 High Cary Strength Type - 4 Low heat Portland cement Type - 5 Sulphate resisting Portland cement Raw materials required for the manufacture of Portland cement Raw materials required for the manufacture of portland are broadly classified as

follows: 1. Calcarius Raw Materials These supply the calcium part required in cement. These are calcium compounds

like calcium carbonate - lime, stone, marble marl, shells, calcium sulphate, lime

etc. 2. Argillaceous Raw Materials These supply silica and alumina part of cement. These are various types of clays,

shale, cement rock, blast furnace slag etc.

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Table 5.1 - Sources of Various Raw Materials

Lime Silica Alumina Iron Oxide

Lime Stone Sand Alumina Iron Ore

Chalk Calcium Silicate Clay, Shale Iron Dust

Sea Shells Quartzite Slags, Kaolin Iron Oxide

Marl Fullers earth Aluminium Ore Iron Sinters

Cement Rock Refuse

Marble

Alkali Waste

In modem manufacturing processes, the requirement for producing cement of

reliable and consistent quality are more exacting. Variations in quality of raw

materials should be taken care of for producing good quality cement. For instance,

if the proportion of CaO is less in raw material mix, it may result in deficiency of

constituents responsible for strength and durability. Higher than the required

amount of CaO, also leads to expansion of hardened cement on setting which is

also not a desirable property in good quality cement. Hence it is essential that raw

materials are mixed in proper proportion to ensure that quality of cement

produced is good and consistent. This is achieved by specifying the range of

various compositions in the mixture as follows.

Composition of the Various Raw Materials in the Mixture

Lime as CaO 60-68%

Silica as SiO2 20-25%

Alumina as Al203 4-11%

Iron oxide as Fe2O3 0-4%

Magnesia as MgO 0-5%

Sulphur trioxide as SO3 0-3%

Alkali Oxides as (Na2O + K20) 0.3-1.5%

Lime Saturation Factor

Lime saturation factor is calculated from the following ratio:

CaO − 0.7SO3

2.8 SiO2 +1.2 Al2O3 + 0.65Fe2O3

It should be between 0.66 to 1.02 to ensure the four main constituents of cement

are in proper proportion.

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Modulus of Silica (n)

Modulus of silica is the ratio of Si02 to sum of A12O3 and Fe2O3 present in raw

material mix. i.e.

n = SiO2

This ratio should be between 2.2 to 3.5 Al O + Fe O 2 3 2 3

Alumina Module

p = %Al2O3

The ratio should not less than 0.66 %Fe O

2 3 The Concentration of MgO should be below 5% All these specifications would eventually ensure that cement produced would

have desirable properties of setting and hardening. Further such cement retains its

properties for a long time. Functions of Various Ingredients of Raw Material Mix The various raw materials present in the mixture when calcined gives good quality

cement. Each of the ingredients react with other ingredients to form the various

constituents of cement namely di calcium silicate, tri calcium silicate which are

responsible for early and final strength of cement and tri calcium aluminates and

tetra calcium aluminofurite which are responsible for the setting quality of

cement. The proportion of various ingredients ensures that final proportion of four

constituents in cement is as required for good quality cement. 1. Lime: It is the principal ingredient, contributes towards setting and strength of

cement, if lime is present in excess, cement formed has lower strength, since the

cement expands on setting and disintegrates. If the lime content is below the

desired level, the proportion of four constituents namely di calcium silicate, tri

calcium silicate, tri calcium aluminate and tetra calcium aluminofurite will

change. This will alter the properties like setting and hardening of cement. Such

cements have poor strength. . 2. Silica: Lime reacts with silica to form both di calcium and tricalcium silicate.

They are responsible for early and final strength of cement. 3. Alumina: Alumina reacts with lime to form tricalcium aluminate. The setting

quality of cement depends upon the proportion of tricalcium aluminate. If cement

were to set very fast it may not be possible to complete all the operations like

mixing, pouring, leveling etc. This could lead to imbalance in structures. If the

setting is too slow, heavy loads can result in sagging. Hence the right proportion

of alumina in raw material would ensure the right quality of setting in cement. 4. Iron Oxide: Iron oxide is responsible for the peculiar colour of cement. It also

contributes towards strength and hardness.

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Manufacture of Portland Cement

There are three processes employed for the manufacture of cement. They are:

1. Dry process - 2. Wet process - 3. Semi dry process -

The selection of process for the manufacture is very much dependent upon the

availability and nature of raw material, the climate of the place and cost of fuel.

Where the raw materials are hard and dry and the place is dry, dry process is

preferred as it will consume less fuel. On the other band where raw materials are

soft or obtained in wet condition from processes, the climate humid, wet process

is preferred. Another main consideration is fuel cost as it is directly related to

manufacturing cost. In many countries the trend is towards adopting dry process

in view of escalating fuel cost. Basically the manufacturing process adopted in the

processes is the same. It involves mixing the raw materials in proper proportion,

calcining them in kiln and powdering the clinkers formed. The sequences of

operations in details are as follows 1. Selection of Raw Materials

Lime stone is available in various forms and the quality also varies. Low grade

lime stones are concentrated by froth floatation process. Very high grade materials

like marble and sea shell are available only in limited quantities. Clay, bauxite,

shale, blast furnace slag are the other raw materials. These are selected on the

basis of uniformity in composition and availability on regular basis. Large

variation in composition would entail frequent checking to ensure proper

proportioning of various ingredients. Water is another raw material used in mixing

in wet process. Coal in powder form, furnace oil, natural gas is the fuels generally

used for heating the kiln to the desired temperature. 2. Crushing and Grinding

The raw materials are first broken down to smaller pieces by jaw crushers and

then pulverised in ball mills. In dry, process crushing is carried out after

subjecting the raw materials to initial drying to remove the inherent moisture

present by making use of available waste heat. In the wet process, wet grinding is

carried out using water to make slurry of raw materials. This not only makes the

mixture uniform, but also makes it easier to adjust the composition to the desired

temperature. 3. Storage and Proportioning

The raw materials are crushed to fine powder and stored separately in big storage

tanks. In the case of wet process, the prepared slurry is stored and then led to

correction tank where the final adjustment of composition is done after analysing

the sample from the storage tank. From the correction tank, the slurry is led into

the rotary kiln. In the case of dry process, the dry powders from the bins are

transferred to mixing tanks provided with a stirrer. The dry powders are mixed

together, analysed and correction made so as to get a proper composition.

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4. Rotary Kiln

The rotary kiln constitutes that part of the assembly where the different raw

materials react with one another at high temperature to form cement clinkers. The

rotary kiln consists of a long cylindrical tube, lined inside with refractory and

rotating at a speed of 0.5 to 2 rpm. The tube is slightly inclined to facilitate

movement of feed through the cylinder. The fuel either powdered coal or furnace

oil sprayed into the combustion chamber, the burning hat gases are forced through

the kiln by means of a blower. The hot gases travel along the length of the tube

mixing and heating the raw material while flowing down. The temperature near

the combustion chamber is highest whereas the temperature at the end where

slurry enters the kiln, is lowest. The burnt gases along with particles of cement,

raw materials etc. passes through cyclones and dust chambers because of exhaust

system before they are led into the atmosphere through tall chimney. The

temperature profile of kiln is such that the various chemical reactions get

completed by the time the raw material mix, fed at the top of the kiln travels to the

other end of the kiln. Broadly the entire length is divided-into three zones. They

are (a) Evaporation zone, (b) Calcining zone and (c) Clinker formation zone. (a) Evaporation zone: The inherent moisture present in raw material, water

added to form a slurry, are evaporated in this zone. The temperature varies from

400 - 700°C. All moisture (including water of crystallisation) is completely

removed and the material is absolutely dry as it enters the calcination zone.

(b) Calcination zone: The temperature varies from 700 - 1100°C. In this zone

CaCO3 undergoes decomposition forming CaO and CO2. CaO formed

immediately start reacting with other constituents like Si02, Al203, Fe203 etc. to

form various constituents of cement. A number of intermediate compounds are first formed in this zone which later decomposes at higher temperature to form cement clinkers.

(c) Clinker formation zone: The various chemical reactions which begin at the

calcining zone go to completion in this zone because of higher temperature. The

temperature varies from 1200 - 1500°C.

The various reactions taking place in the three zones can be summarised as below

Temperature Reactions and Formation

~800°C Formation of CaO Al2O3, 2CaO Fe2O3 2CaO SiO2 begins

800- 900°C Formation of 12CaO. 7Al2O3 begins

900-11000C 2CaO SiO2. Al2O3 forms and decomposes formation of

3CaO.Al2O3, 4CaO.Al2O3 starts. All CaCO3 undergoes

decomposition, CaO content Maximum

1100-12000C Formation of major part of 3CaO Al2O3, 4CaO A12O3

Fe2O2CaO SiO2 content reaches maximum

12600C First liquid formation

1200-14500C All reactions go to completion. No free CaO is present.

Fusion of compounds results in clinker formation

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The final products formed are:

2 CaO + SiO2 → 2 CaO.SiO2 dicalcium silicate

3 CaO + SiO2 → 3 CaO.SiO2 tricalcium silicate

3 CaO + A12O3 → 3 CaO.Al2O3 Tricalcium aluminate

4CaO + Al2O3 + Fe2O3 → 4CaO.Al2O3.Fe2O3 tetra calcium alumino ferrite

The clinkers formed are discharged at the lower end of kiln where they are cooled

by blast of air. The resulting hot air is used for preheating the fuel.

5. Grinding of Clinkers

The clinkers are ground into fine powder after mixing with 5% of gypsum.

Without gypsum the setting of cement is very fast. Inclusion of gypsum in final

stage of grinding of clinkers helps to retard the setting of cement paste.

6. Storage and Packing

Cement in the fine powdery form is transferred to concrete silos and kept agitated

by means of compressed air. ft is packed in jute bags lined inside with polythene

or laminated woven bags. Cement absorbs moisture rapidly and is always kept in

dry place. Otherwise it will absorb moisture and set to become hard rock like

material.

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Constituents of Cement

The proportion of various constituents in cement determines its properties. The

following table gives the relevant information.

Name of Constituent Chemical Abbreviated % in Setting time

Formula Form Cement in days

Tricalcium silicate 3CaO.SiO2 C3S 48 7

Diacalcium silicate 2CaO.SiO2 C2S 27 28

Tricaclium Aluminate 3CaO. Al2O3 C3A 10 1

Ferrite FeO3 C4AF 9 1

Calcium Sulphate CaSO4 5

Free CaO CaO 1

MgO MgO 4

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1. Tricalcium Silicate 3CaO.SiO2 (C3S): Tribalism silicate undergoes hydration

and develops good strength quite early in setting. Its ultimate strength is highest of

the four constituents. Its heat of hydration is around 120 cal/gm.

2. Di Calcium Silicate 2CaO.SiO 2 (C2S): Di Calcium silicate undergoes

hydration slowly developing strength over longer period of time. Its ultimate

strength is comparable to that of tricalcium silicate. Its heat of hydration is also

lowest at 60 cal/gm.

3. Tricalcium Aluminate: Tricalcium aluminate hydrates very fast so much so it

actually prevents hydration of other constituents in cement. Hence to retard this

rapid hydration gypsum is added. Its early strength is good but its contribution to

final strength is low. Its heat of hydration is highest at 210 cal/gm.

4. Tetra Calcium Aluminoferrite: It hydrates slowly developing strength over a

period of time. However its ultimate strength is lowest of the four constituents. Its

heat of hydration is 100 cal/gm.

Setting and Hardening of cements: The usefulness of cement arises out of the fact

that it forms a pasty mass, when mixed with water and the pasty mass helps to bind

various materials like sand, bricks, stones and hold them together strongly for long

duration. All the constituents of cement undergo hydration forming hydrated

compounds. However the rate of hydration is not the same for all the constituents. The

first compound to hydrate when cement comes in contact with water is C3A. Its rapid

hydration leaves little water for hydration of other constituents. With enough water all

the constituents get sufficiently hydrated to form hydrated

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compounds. The solubilities of these hydrates are lower and hence they get

precipitated out in the form of gels and crystals. It is these gels and crystals which

help to bind the different materials like sand, bricks and stone. The paste formed

when cement is mixed with water does not remain plastic for ever but becomes

quite rigid after some time. It is called as initial set and depending upon cement,

the time can vary from 30 minutes to 1 hour. This initial set is due to hydration of

tricalcium aluminate C3A.

3CaO Al2O3 + 6H2O → 3CaO Al2O3 .6H2O As stated earlier, this reaction is so fast that it prevents hydration of other

constituents of cement. Hence gypsum is added to cement clinkers in the final

grinding stage. Gypsum helps to retard the setting of cement by forming complex

hydrates which as slower hydration rates:

3CaO Al2O3 + x H20 + y CaSO4 2H2O Water

→ gypsum

3CaO . A12O3 .y CaSO4 . Z H2O (Insoluble complex calcium sulpho aluminate) The complex formed does not undergo rapid hydration and its takes more time for

the cement paste to become rigid. This is of practical importance since many of

the operations like mixing, laying, leveling, compacting require rime and if

cement paste were to become rigid, many of these operations cannot be done

smoothly. Like C3A, C4AF undergoes rapid hydration forming both gels and crystals

4CaO. Al2O3. Fe2O3 + 7H2O→ 3CaO. Al2O3. 6H2O + CaO. Fe2O3. H2O

gel crystals Both dicalcium silicate and tricalcium silicate hydrate to form gels and crystals.

As the time passes the gels shrink and form capillaries through which water

continues to seep to allow for completion of hydration and hydrolysis processes.

Hence the final strength of concrete structures are only realised at the end of the

year.

3CaO.SiO2 + xH2O→, 2CaO. SiO2(x—1) H2O + Ca (OH)2

gel crystals

2CaO. SiO2 + x H2O → 2CaO. SiO2. xH2O

gel Setting and hardening of cement paste has been explained on the basis of colloidal

theory of Michaelis and crystalline theory of Le Chattier. According to Michaelis,

the silicate gels, undergo hardening and bind the various materials with which it is

in contact. On the other hand, Le Chatlier’s explanation rests on the formation of

crystals which interlock as they grow to hind various materials. In fact both these

reactions contribute towards hardening of set cement paste.

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This is represented as follows

5.1.3 - Concrete: A mixture of cement, sand (below 3/16 inch mesh size) with

calculated amount of water. The size of gravel or coarse aggregates varies with the

purpose for which the concrete is required. Common maximum sizes of coarse

aggregates are 0.75 inch or 1.5 inch, but coarse aggregate of even 0.5 inch have

also been used for some purposes. In case of heavy mass concrete the size may be

even 6 inch or more. The common proportions of cement, sand and coarse gravel

may be in ratios

(a) 1 : 1.5 : 3

(b) l : 2: 4

(c) l : 3 : 6

When the cement concrete is filled in and around a wire netting of iron rods and

allowed to set, the resulting structure. Concrete has high compressive strength and

relatively low tensile strength. So in order to impart high strength as high tensile

strength so that it can rest loads which lend to crush concrete, another form of

concrete, known as reinforced concrete is used. The reinforced concrete can

withstand not only high tensile strength but also the compressive stresses. The

combination of steel and concrete produces a structure known as reinforced

concrete construction (RCC), which is capable of bearing all types of loads RCC

possesses greater rigidity, moisture and fire resistance than plane concrete. RCC is

easier to make and cast into any desired shape, which can withstand all types of

loads.

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Curing of concrete Setting and hardening of concrete is due to hydration of the cement constituents.

The process continues indefinitely but maximum amount of strength as well as

hardness is developed during few early days after placement. It is, therefore,

necessary to keep the concrete damp for about 7 days in order to enable hydration

reactions to go to completion. The chemical reactions taking place between cement and water occur only under

favourable conditions of temperature. At low temperature, the rate of reactions in

concrete is slow but completely stops, when water in concrete is frozen. The

process of dampening concrete by spraying water is known as curing of concrete.

Hence curing may be regarded as the process of maintaining a satisfactory

moisture content and favourable temperature in concrete during the period

immediately following placement, in order to allow the process of hydration to

continue, until the desired properties such as strength are developed to a sufficient

extent. Decay of concrete The cement concrete is mechanically very strong, but because of the presence of

some free lime (CaO), it becomes highly susceptible to chemical attack, especially

in acidic water (pH > 7). In acidic water, the lime present in flue concrete

dissolves and makes the concrete weak in strength. Alkaline waters (pH > 7) do

not have any marked effect on the strength of concrete. Moreover lime is more soluble in soft water than hard water. Consequently

concrete undergoes decay or deterioration in contact with acidic water and soft

water. Hence decay is quicker as the pH of water decreases and softness of water

increases from hard to soft. Sulphates and chlorides present in hard water also

remove lime present in concrete. The resistance of abrasion decreases when

concrete is soaked in mineral oils. Even minute amount of sugar present in concrete has been found to increase the

setting time of concrete and as a result, strength of concrete is also reduced

considerably, especially during first 30 days. Sulphates cause maximum damage

to concrete, because they react with tricalcium aluminate to form

sulphoaluminates, which occupy more volume and hence undergo expansion. As a

result, life of concrete is greatly reduced. This can be prevented by eliminating tricalcium aluminate from the cement

composition and using cement manufactured from tetra calcium alumina ferrite in

place of aluminate. In general, concrete can be protected by giving a coating of bituminous material

which is capable of preventing direct contact between concrete and water. Decay

of concrete can also be prevented by coating the surface with silicon fluorides

(soluble) together with ZnO, MgO or Al2O3. The CaF2 so formed in the

capillaries prevents the dissolution of lime in concrete.

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5.1.4 - Corrosion of concrete or cement stone

In addition to the external mechanical loads acting on concrete and allowed for in

the design of structures concrete is acted upon physically and chemically by the

environments. Concrete is said to be exposed to physical and chemical processes

of weathering. The failure of concrete is usually related to the action of water on

it. If concrete is not saturated with water systematically, its failure at temperatures

below zero is precluded, because the concrete will not suffer multiple freezing and

thawing, no chemical corrosion of the fabricated stone will occur due to lime

being washed out of it, or, for instance, decay due to the formation of new

chemical compounds which lack cementing properties, the formation of chemical

compounds of a volume exceeding that of its components etc. Besides water,

concrete and stone are also acted upon by other weathering agents.

The corrosion of cement stone is as if identical to the corrosion (weathering) of

rock and metal (rusting). It results in a loss of bond between newly formed

particles of the cement stone and between the stone materials- aggregates (sand.

crushed stone, gravel) in concrete. Since any of the weathering (corrosion) cases

leads to the destruction of concrete, none of them is tolerated.

Leaching corrosion manifests itself only when the hydrocarbonate alkalinity of

water is insufficient to ensure stable existence of lime in the cement stone,

separating by the reaction

3CaO. SiO2+ aqueous → 2CaO.SiO2 aqueous +

Ca(OH)2 and of other hydrated compounds.

The, rate of corrosion depends on: density of concrete , water pressure, flow

velocity etc.

Soft water dissolves Ca(OH)2, resulting in that the cement stone loses strength. It

is known that when concrete sets and hardens under optimum conditions, at the

end of 90 days upto 15% of free lime, expressed as Ca(OH)2 by mass, is separated

from the cement stone.

In the presence of soft water near nondense concrete conditions are created for the

physical decay of concrete, irrespective of the kind of portland cement and its

compressive strength, because the lime forming in the course of cement hydrolysis

will be removed from the concrete by leaching due to its good solubility in water. This

is the manner in which conditions for further decay of other hydrated newly formed

minerals are created. The removal of 30% of lime due to its dissolution in water

(leaching) reduces the strength of concrete by more than 50%. Concrete undergoing

this kind of weathering loses its other engineering properties, such as water

impermeability, resistance to frost, salt resistance, abrasion resistance, deformability

etc. The density of concrete is of great importance to the rate of lime removal by

dissolution (leaching). Concretes characterized by high water tightness reliably serve

in soft water because of considerable retardation of lime diffusion into the surrounding

medium (water basin, water saturated soil etc.)

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Acid corrosion is provoked by any acid. The possible destruction of concrete in an

aqueous medium is determined by the magnitude of the pH value. The final decay

products of the cement -stone constituents of concrete are silicic acid gel, calcium

and aluminium salts of the acid attacking the cement stone or when a weak acid is

involved-the gel of aluminium hydroxide.

mCaO.SiO2. aqueous + nH2O →SiO2.aqueous +

mCa(OH)2 Silicic acid gel.

qCaO.Al2O3 aqueous + pH2O → 2Al(OH)3 +

qCa(OH)2 Aluminium hydroxide gel. The corrosiveness of free acids is often but little responsible for the corrosion of

concrete. However, these acids contribute to dissolution of the carbonate film on

the surface of concrete and prevent the possible formation of a new carbonate

film. The action of these acids creates favourable conditions for the removal of

lime by the process of leaching. Carbon dioxide corrosion resembles in many aspects to the acid and magnesia kinds of corrosion, because the action they produce may be reduced by the action of f ions on the cement stone or concrete. When water contains magnesia salts,

MgCl2 and MgSO4, the hydrogen ions are formed due to the hydrolysis of these

salts. The free CO 2 contained in natural water may not corrode concrete, corrode

it partly or act as a fully corrosive agent. Let us consider what causes the various

corrosive actions of free CO2.

The action of H2O and CO2 on carbonate rocks results in the formation of

bicarbonates.

CaCO3 + CO2 + H2O→Ca(HCO3) 2

MgCO3 + CO2 + H2O → Mg(HCO3) 2 This process, turning insoluble carbonates into the soluble bicarbonates, only

develops in a definite time and its reversibility can be expressed as follows.

CaCO3 (in solution) + CO2 + H2O Ca(HCO3) 2

CaCO3 (solid)

Only a fraction of CO2 dissolved in the layers of water adjoining the solid carbonate,

reacts with the latter (having reached a definite concentration of Ca(HCO3) 2. The

rates of forward and backward reactions become equal, that is, an ordinary chemical

equilibrium sets in. The non-reacting fraction of free CO2 is called as equilibrium

carbon dioxide. The formation of Ca(HCO 3)2 or dissolution of solid bicarbonate will

continue if the concentration of CO2 increases or the concentration of Ca(HCO3)2

diminishes. Even a small amount of corrosive CO2 in

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water is sufficient to provoke dissolution of the solid film of CaCO3 on the

surface of concrete.

Ca(OH) 2 + CO2 → CaCO3 + H 2 O

lime in concrete. CaCO3+CO2+H2O

→Ca(HCO3)2 hardened film in concrete.

The surface of concrete may sometimes be strengthened by the corrosive CO2

provided this strengthening process proceeds till the entire corrosive CO2 is

bonded (only until the formation of CaCO3) in accordance with the reactions,

Ca(OH)2 + CO2 → CaCO3 + H2O

Ca(OH) 2 + Ca(HCO3) 2→2CaCO3 + 2H2O

The destruction of concrete due to soleplate Carrolton is associated with the

formation of a stable complex compound (hydrogen cement, from hydrated

tricalcium aluminate and gypsum under certain conditions.

3CaSO4 + 3CaO.Al2O3.6H2O + 25H2O→ 3CaO.A12O3.3CaSO4.31 H2O

The volume of this compound considerably exceeds the sum of the initial volumes

of its constituents and this causes failure of concrete, resulting from the internal

stresses originating in the cement stone. This compound, however, lacks stability

with a change in the humidity of surroundings.

Gypsum corrosion manifests itself in the formation of gypsum crystals. It may be

provoked by an aqueous medium containing a large amount of Na2SO4 or K2SO4

and cause destruction of concrete.

Sulphate and gypsum corrosions may attack concrete structures simultaneously.

Magnesia and sulphate magnesia corrosion may also occur. There are Ca2+

ions in

the pores and capillaries of concrete. Stable composition of the liquid phase filling

the pores and capillaries of the cement stone ensures stability of the solid phase,

ie, of the newly formed mineral components of the cement stone. This stability

changes when water contains magnesia sails of definite concentrations. Then the

following reactions proceed in hydrated portland cement (mortars and concretes). 3MgSO4 ⇌3Mg2+ + 3SO4

2- Complete dissolution of magnesium sulphate; formation from OH

- ions of

hydrated cement lime and Mg2+

ions that diffuse into the cement stone, of

insoluble Mg(OH)2 having no cementing properties. 3Mg2+ + 6OH- ⇌ 3Mg(OH)2

3Ca(OH)2+ 3 MgSO4 3 Mg(OH)2 + 3Ca2+

+3 SO42-

4CaO.A12O3.12H2O + 3Ca2+

+ 3SO42-

+ 20H20 3CaO.Al2O3.3CaSO4.31H2O

+ Ca(OH)2

139 Ca2+ + SO4

2- ⇌ [Ca2SO4 + 2H2O CaSO4.2H2O] In addition to the destruction of concrete due to chemical weathering or varios

kind of corroision failure of concrete as a result of the repeated combined attack of

water and froast must also be taken into consideration. Such failure of concrete is

due to : (a). Systematic thawing of the water frozen in to pores and capillaries. (b). Repeated filling of the pores and capilliaries with water and its freezing in

concrete. The frozen water gradually expands in concrete on cooling.

The formation of a complex salt in hardening cement containing alkalies (K2O

and Na2O ) and Amorphous sillica (SiO2.nH2O) of the stone material (sand,

gravel, crushed stone) Proceeds with a considerable increase in its volume

resulting in concrete cracking. This kind of corrosion may occure even at a slight

content of sillica ( less than 0.6% of the Mass of Cement). 5.2 REFRACTORIES Word refractory implies resistant to melting or fusion. In technology refractory are

materials which can withstand very high temperatures without softening melting

or deformation. They are mainly inorganic materials or ceramic materials

possessing high thermal stability, resistance to abrasion and corrosion. They are

essential structural materials used where resistance to both high temperature and

oxidation are needed. They are used widely in the construction of steel making

and glass making furnaces. They are also used in the lining of furnaces used for

metallurgical purposes and in cement manufacturing kilns. Refractory materials

are used in the form of bricks, crucibles, ladles, etc. in ferrous and nonferrous

industries. Special kinds of refractory materials are used in rockets, lets and

nuclear power plants. Refractory materials are generally constituted of oxides having high melting

points such as SiO2, Al2O 3 and MgO. Refractories having very high melting

points are made from oxides such as ZrO2, BeO etc. Apart from these oxides,

carbon, carbides, borides, nitrides may also be used as good refractory materials.

The purpose of refractory material in a furnace may be to confine heat within the

furnace or to transmit heat from one surface to the other surface as in the case of

recuperators and retorts or to store heat as is needed in the case of regenerators

used along with furnaces. 5.2.1 REQUIRMENTS OF GOOD REFRACTORIES A refractory material selected for structural purposes should possess the following

characteristics. - 1. The refractory materials should possess proper refractoriness. It should retain

its structure without undergoing any deformation at the operating temperature

of the furnace i.e. It should not begin to fuse at the temperature to which it is

exposed.

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2. It should have good spalling resistance i.e. when the refractory material is

exposed to sudden changes in temperature, it should be able to maintain its

original form without cracking, splitting or flaking. Spalling may occur due to

the compressive stresses caused by the surrounding furnace structure and the

charge inside the furnace. 3. It should be capable of withstanding the load put into the furnace at the

operating temperature and also at other service conditions of the furnace.

4. A refractory material used in a furnace should possess uniform rate of

expansion and contraction when the temperature changes in the furnace are

uniform. 5. It should possess good resistance to abrasion caused due to the movement of

the solid particles of the charge, molten slags, molten metals, and gases like

CO2, CO, SO2 etc evolved during the process.

6. It is also necessary that a good refractory material resists chemically the

action of gases evolved and slags produced in the furnace. Chemical reactions

of the refractory materials with substances in the furnace may result on

account of the dissimilarity in the nature of the two materials. Thus in a

furnace where acidic gases or slags are produced, only acidic refractory

materials should be used for lining.

5.2.2 CLASSIFICATION

Refractory materials are classified into three kinds depending upon their

constituents:

1. Acidic Refractories

They are constituted of acidic substances like A12O3, SiO2 etc. These materials

are not affected by acidic slags and gases produced in the furnace but are attacked

by basic substances in the furnace. Example: Silica and Fire clay refractories.

2. Basic Refractories

They are composed of basic materials which are easily attacked by acidic

substances but not attacked by basic substances in the furnace. Example:

Magnesite, Chrome-magnesite, dolomite.

3. Neutral Refractories

They contain mildly acidic or mildly basic substances. They can withstand the

action of acidic and basic substances, Examples Graphite, Silicon Carbide,

Chromite etc.

Apart from these refractories, there are refractory materials which are used for

special purposes and have superior properties. They are the refractories like

Alumina, Zirconia, Magnesia, Carbides, Silicides, and Borides etc.

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5.2.3 SCLECT1ON OF REFRACTORY MATERIALS A refractory material for a particular purpose is decided by various conditions

existing in the operation of furnace. The important aspects to be taken into

consideration are (i) the operating temperature of the furnace and the nature of

variations in temperature. (ii) the type of materials loaded into the furnace and the

possible chemical reactions with the surrounding substances. Since a single refractory does not serve the purpose of withstanding different

conditions existing in different parts of the furnace, a combination of different

refractories is used for constructing furnaces. 5.2.4 PROPERTIES OF REFRACTORY MATERIALS 1. Refractoriness It is the ability of the material to withstand high temperature without significant

softening or deformation in shape and size under normal working conditions of

the furnace. It is measured in terms of the temperature upto which there is no

softening or fusion of the refractory material. Normally, the softening temperature

of the material used in a furnace is higher than the operating temperature of the

furnace. However a refractory material may be used to withstand i slightly higher

temperature above its softening temperature as the outer portion of the brick is

normally at a much lesser temperature than the inner portion and as the brick

being in solid condition gives strength to the refractory lining - The softening

temperature of a refractory is measured in terms of pyrometric cone equivalent or

P.C.E. value. 2. Strength or Refractoriness under Load R.U.L. A refractory material should be strong enough to withstand the load put into the

furnace and should not be worn out due to physical impacts. It should possess

proper mechanical strength even at high temperatures, so that it can withstand

varying loads without cracking. Refractories like fire clays, alumina, soften under

the effect of heavy load much below their real fusion points, though they undergo

softening gradually over a wide range of temperatures under normal

circumstances. Silica bricks, though soften in a short range of temperature are able

to show good load bearing capacity even close to their true fusion points. The load

bearing characteristics at high temperature of a refractory material is given by

refractoriness under load or R.U.L. - 3. Thermal Conductivity Thermal conductivity of the refractories depends on chemical composition and

porosity. Thermal conductivity decreases with porosity due to the insulating effect

of air in the pores. In general, thermal conductivity increases with rise in

temperature. Fire clay, Silica, Magnesite etc. possess low thermal conductivity

whereas Carbon, Silicon, Carbide are fairly good conductors. Furnaces like blast

furnace, open-hearth furnace etc. are lined with materials of low thermal

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conductivity to prevent heat losses whereas recuperators, muffle furnaces, retorts

etc. need to be lined with refractories of high thermal conductivity.

4. Thermal Expansion and Contraction

Refractory materials undergo expansion or contraction when heated and thereby

cause change in the volume. If there are large changes in the volume, cracks may

appear, joints may get damaged and the furnace lining may undergo destruction.

Fireclay bricks, magnesite bricks and chrome-magnesites are found shrink

whereas silica bricks are found to show expansion due to allotropic

transformations.

When the refractory material shows resistance to changes in volume when

exposed continuously to high temperature, it is. said to possess dimensional

stability. Refractory bricks when subjected to rapid heating or cooling show

uneven expansion, or contraction due to temperature gradients, resulting into

thermal spalling. Spalling is the cracking of the material in such a manner as to

expose a fresh surface to the action of the environment.

5. Porosity and Permeability

The refractory material may contain pores which may be open or almost closed

depending upon the method of manufacture. When the refractory brick is more

porous, molten charges, gases etc. enter the pores and cause changes in the

properties of the brick which may lead to internal stresses during heating.

A porous brick also has low thermal conductivity due to the insulating effect of

the air entrapped in the pores. Less porous and dense bricks have better thermal

conductivity. A porous brick has less strength and abrasion resistance and is also

subjected to corrosion by slags.

6. Electrical Conductivity

Almost all refractories except graphite are bad conductors of electricity.

7. Specific Gravity

It is an important property which decides the cost of the material. Materials of

high specific gravity yield fewer bricks compared to those of lower specific

gravity. Appropriate materials to suit the different parts in furnace may be used.

Portions of the furnace which are not subjected to heavy loads may be lined with

materials of low specific gravity.

8. Chemical Composition

The refractory material used in a furnace should not be subjected to corrosion,

abrasion and erosion due to the action of slags, molten metal, and gases.

Refractory material of proper composition should be chosen so that there is no

possibility of any chemical reaction with the substances in the furnace.

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5.2.5 MANUFACTURE OF REFRACTORIES The manufacture of refractory bricks involves several preliminary treatments of

the raw materials such as calcination, grinding, sizing etc. The method of

manufacture of the bricks is nearly same for all kinds of refractories. The

following procedure is used in making the bricks. 1. Grinding The necessary raw materials are crushed in jaw crushers or gyratory crushers and

finely ground in ball mills or tube mills. Generally coarse and fine particles

together are used in the manufacture. The impurities from the raw material may be

separated by magnetic separation, electrostatic separation and froth flotation. 2. Mixing and Blending The ground raw materials are mixed with suitable binding agent and the required

quantity of water. The size of the particles, the quantity of water used depend on

the porosity of the refractory brick and also the type of the molding to be

followed. Mixing in pug mills or paddle mills enables the distribution of the

plastic constituent throughout the mass thereby facilitating easy mounding.

Meting and blending eliminates the entrapped air in the mass and improves the

density and strength. It also prevents laminations and cracking. 3. Moulding Moulding may be done by mechanical methods such as hand moulding using high

pressure or it may be done by methods such as extrusion, casting etc. 4. Drying Drying is done to remove moisture from the refractory material. It is done slowly

and under selected conditions of temperature and humidity. It may be done in

different types of dryers such as hot floor dryers or tunnel dryers. It may be done

by placing the bricks in sunlight. 5. Fixing and Burning The dried bricks are burnt in down draught or continuous tunnel kiln. By burning

there is formation of permanent bond and the material develops into stable

mineral forms which will not undergo any change in dimensions on further

heating in furnaces. During burning, there is elimination of water, calcination of

carbonates to form oxides, oxidation of metals to their higher oxidation states.

These chemical changes result in the shrinkage in volume which may produce

stresses in the material. Excessive shrinkage can be prevented by using

prestabilised raw materials of appropriate size and proper pressing. 5.2.6 - Silica Refractories Silica refractories are one of the important acidic refractories used extensively in

the construction of furnaces.

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Raw materials

i. Natural deposits of silica in the crystalline form such as quartz, quartzite,

sand, sandstone etc. are the principal raw materials which contain very little

alkaline oxides as impurities. Presence of excess of alkaline oxides may lower

the temperature of fusion. ii. Binding materials such as lime, clay, magnesia, silicates of magnesium,

sodium, aluminium and waste products of petroleum industries such as tar,

heavy mineral oil etc.

Manufacture

The raw materials are subjected to grinding in gyratory crushers and stored

separately. The materials are then ground to fine powder in ball mills or edge

runners. Powdered silica is mixed with the binding material like lime (2%) and

water to a paste of proper consistency in an edge runner. This process of mixing is

called tempering. When the mixture has attained enough plasticity, it is made into

brick by machine pressing or by hand moulding. The moulded bricks are dried in

air, heated rooms or in the sun and drying is completed normally in 18 to 24 hrs.

The dried bricks are transferred to kilns and heated. The temperature of the kiln is

slowly increased to 1500°C in about 24 hrs. They are kept at this temperature for

nearly 15 hrs for the conversion of quartzite to a more stable form like tridymite

or crystoballite. The kiln is then slowly cooled and it requires nearly 1 to 2 weeks

for cooling.

The following changes occur during the burning of the bricks.

a. Elimination of water : mechanically and chemically held water gets

eliminated first.

b. Lime reacts with silica to form calcium silicate which binds the various

particles by fusion.

c. Conversion of quartz into more stable cristobalite or tridymite resulting

into changes in. the volume of the brick. Tridymite and cristobalite possess different specific gravities and they exist in and

β forms. The conversion can be represented as below.

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On account of such conversions, the overall linear expansion of the silica brick is

by 3.5%. Tridymite and cristobalite are the stable forms which should be produced while

making the bricks. If the conversion of quartz to tridymite and.cristobalite does not occur due to

improper firing, the changes in the forms may occur during its use in the furnace

and may cause weakness in the structure.. Properties 1. The colour of the bricks vary from yellowish to brownish colour. 2. The specific gravity of the brick varies from 2.3 to 2.6. 3. Porosity is roughly 25%. 4. The refractoriness of good quality bricks is 1750° and their softening

temperature depends on quantities of lime, and other alkaline oxides, 5. The refractories under load (R.U. L.) can be as high as 1680°C for bricks free

from alumina. 6. Even though the bricks are light, they possess good mechanical strength and

good rigidity. 7. These bricks cannot withstand thermal shocks below 600°C. 8. The thermal conductivity of these bricks is more than fire-clay bricks. A good silica brick should withstand up to 1690°C and should possess good

crushing strength. When used in furnace should not show any volume change and

should not have tendency to spalling when subjected to sudden changes in

temperature. Uses Silica bricks are used where high resistance to temperature is needed and where

there are no rapid temperature changes. They cannot be used in conjunction with

basic slags or basic fluxes. Silica refractories are used to the largest extent by iron

and steel industries for constructing steel making furnaces. It is used in coke

ovens, glass furnaces, roofs of electrical furnaces, linings of acid converters. 5.2.7 - Dolomite bricks Manufacture These are prepared by mixing CaO and MgO mixture in equimolecular proportions

with silica as a binding material for magnesium silicate basic slags quick lime

hematite from oxide Fe2O 3 clays etc are also used as binding materials.

Dolomite of Composition CaMg(CO3)2 is calcined and mixed with binding agent

and water in edge runner or pug mill then the mixture is allowed to age by storing

in wet conditions By hand moulds or pressing finally it is moulded into a bricks.

These bricks are air dried and fixed at 1500C for about 24 hours.

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Properties of Dolomite Bricks

1. These are less strong. 2. They have great volume shrinkage then magnesia bricks. 3. These are more resistant to slags and spalling than margining bricks. 4. Porous, soft and wear away quickly.

Properties of dolomite bricks are further modified by stabilization in which

dolomite is mixed with serpentine (MgO.SiO2) and mixture is calcined these are

more resistant towards basic slags.

Uses

1. It is rarely used as a direct refractory mainly useful as repair material 2. Stabilized dolomite bricks are used for basic electric furnace linings ladhe

linings bessemer converters open hearth furnaces.

5.2.8 - SILLICON CARBIDE REFRACTORY

These are also known as carborundum refractories. Silicon carbide comes under

the class of super refractories which are capable of resisting the chemical changes

in contact with stags, fluxes, molten metals etc. They also withstand thermal

shocks.

Manufacture

They are manufactured by mixing silicon carbide and clay as the binding agent. The moulded bricks are fired in the furnace at a temperature of 1400° - 1600°C. The firing is done in a reducing atmosphere.

They are also manufactured by heating sand 50 - 52%, coke 35% saw dust 8 - 11% and a little amount of salt, 1 - 3% in an electric furnace at 1300° - 2200℃ when silica combines with carbon to form silicon carbide.

SiO2 +3C — SiC + 2CO ↑

The material obtained from the furnace is finely ground and mixed with binding

agents like clay, molasses, tar, lime, resin or plaster of paris and the mixture so

obtained is moulded into bricks and fired in an electric furnace at temperature

around 2000°C.

Properties

1. They are dark grey or blackish blue possesing high hardness. 2. Although it can withstand temperatures up to 2500°C it may undergo

decomposition at around 2200°C.

3. It possesses very low thermal expansion but possesses a high thermal

conductivity.

4. It possesses very good mechanical strength and good abrasion resistance and

resistance to spalling.

5: It is not affected by reducing agents but may get oxidised above 1750°C.

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6. It gets oxidised to silica when heated in air to a temperature around 1000°C. Uses I. As it possesses high thermal conductivity it is used to a larger extent in muffle

furnace, in the form of rods and bars. 2. It is used for partition walls of chamber kilns, coke ovens, recuperators etc. 5.3 NANO MATERIALS Nanotechnology (sometimes shortened to "nanotech") is the study of

manipulating matter on an atomic and molecular scale. Generally, nanotechnology

deals with developing materials, devices, or other structures with at least one

dimension sized from 1 to 100 nanometres. Quantum mechanical effects are

important at this quantum-realm scale. Nanotechnology is considered a key

technology for the future. Consequently, various governments have invested

billions of dollars in its future. The Nanoscience and Nanotechnology market

expected to be 350 billion dollors.

Nanotechnology is very diverse, ranging from extensions of conventional device

physics to completely new approaches based upon molecular self-assembly, from

developing new materials with dimensions on the nanoscale to direct control of

matter on the atomic scale. Nanotechnology entails the application of fields of

science as diverse as surface science, organic chemistry, molecular biology,

semiconductor physics, micro fabrication, etc. Nanotechnology may be able to create many new materials and devices with a

vast range of applications, such as in medicine, electronics, bio - materials and

energy production. On the other hand, nanotechnology raises many of the

same issues as any new technology, including concerns about the toxicity and

environmental impact of nanomaterials, and their potential effects on global

economics, as well as speculation about various doomsday scenarios. Nanomaterials The nanomaterials field includes subfields which develop or study materials

having unique properties arising from their nanoscale dimensions. ▪ Interface and colloid science has given rise to many materials which may be

useful in nanotechnology, such as carbon nanotubes and other fullerenes, and

various nanoparticles and nanorods. Nanomaterials with fast ion transport are

related also to nanoionics and nanoelectronics.

▪ Nanoscale materials can also be used for bulk applications; most present

commercial applications of nanotechnology are of this flavor.

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▪ Progress has been made in using these materials for medical applications, the

study under field of Nanomedicine.

▪ Nanoscale materials are sometimes used in solar cells which combats the cost

of traditional Silicon solar cells

▪ Development of applications incorporating semiconductor nano -particles to

be used in the next generation of products, such as display technology,

lighting, solar cells and biological imaging.

5.3 - CARBON NANOTUBES

Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical

nanostructure. Nanotubes have been constructed with length-to-diameter ratio of

up to 132,000,000:1, significantly larger than for any other material. These

cylindrical carbon molecules have unusual properties, which are valuable for

nanotechnology, electronics, optics and other fields of materials science and

technology. In particular, owing to their extra -ordinary thermal conductivity and

mechanical and electrical properties, carbon nanotubes find applications as

additives to various structural materials. For instance, nanotubes form only a tiny

portion of the material(s) in (primarily carbon fiber) baseball bats, golf clubs, or

car parts.

Nanotubes are members of the fullerene structural family, which also includes the

spherical buckyballs, and the ends of a nanotube may be capped with a

hemisphere of the buckyball structure. Their name is derived from their long,

hollow structure with the walls formed by one-atom-thick sheets of carbon,

calledgraphene. These sheets are rolled at specific and discrete ("chiral") angles,

and the combination of the rolling angle and radius decides the nanotube

properties; for example, whether the individual nanotube shell is a metal or

semiconductor.

Nanotubes are categorized as single-walled nanotubes (SWNTs) and multi-walled

nanotubes (MWNTs) . Individual nanotubes naturally align themselves into

"ropes" held together by van der Waals forces, more specifically, pi-stacking.

Applied quantum chemistry, specifically, orbital hybridization best describes chemical bonding in nanotubes. The chemical bonding of nanotubes is composed

entirely of sp2 bonds, similar to those of graphite. These bonds, which are stronger

than the sp3 bonds founding alkanes and diamond, provide nanotubes with their

unique strength.

These are one of the most commonly mentioned building blocks of nano –

technology, with one hundred times the tensile strength of steel. When graphite

sheets are coiled, and then form nanotubes. These sheets come in a variety of

forms and have different properties. They may be valueable component for

nanoelectronics or as storage devices.

149

Nanotubes come in a variety of diameters and length. They may have different

sized internal cylindrical cavities and may have more than one sheath. The end

caps are half fullerene balls and these can differ. There are also possibilities in the

arrangement of hexagonal sheet, leading to left and right spiraled forms (chirality)

and also folds and indentation in sheets. The CNT growth is so huge that is hard to locate a zeolite particle in the as-grown

CNT bunches. Careful diameter measurement from several TEM image showed a

diameter distribution from 5nm to 15 nm with a peak at ~ 10 nm. Presence of

amorphous carbon or graphite particles was negligible. However, the CNTs were

not very straight or high crystallinity like those grown at high temperature; typical

surface defects of low temperature CVD – grown CNTs were prevalent. The CNT purity was determined by thermogravimetric analysis. Such a CNT

specimen may directly be used for many applications without further purification. Nevertheless, for high purity applications, the zeolite content of the as- grown specimen can easily removed by 6M NaOH treatment and the CNT purity can be

increased over 99 percent. Typical TEM micrograph of octylamine capped Fe2O3,

Co3O4, Fe3O4 and dodecylamine capped Fe3O4 nanoparticle is shown in fig. ZnO

and ZnS nanoparticles obtained by thermal decomposition of Zn cupferron complex under argon and H2S atmosphere respectively such as magnetic M

Fe2O4 (M represents Fe, Co, Mg, Zn of Mn) could effectively prepared.

Micrographs of CoFe2O4 and MnFe2O4 spinel ferrite nanoparticles with dia ~ 10

nm, showed good uniformity. The details of structural and magnetic properties of nanoparticles prepared by this technique are described by Saravanan. 5.3.1 - Types of Carbon Nanotubes Carbon nanotubes come in various forms – chiral, zigzag and armchair. A

nanotube may consist of one tube of graphite (single walled nanotubes, SWNT) or

a number of concentric tubes, called multi walled nanotubes (MWNT) when

viewed by transmission electron microscopy these tubes appear as planes.

Whereas in SWNT two planes are observed, representing the edge in MWNTs

more than two planes are observed, and these can be seen as a series of parallel

lines. 5.3.2 - Formation of Nanotubes: Following are preparation methods of carbon nanotubes. i. Laser Method: In 1996 a dual pulsed laser vaporization technique was used to optimize the laser

method to produce SWNT in gram quantities and yield of >70 %. Samples were

prepared by laser vaporization of graphite rods with 50 : 50 mixture of CO and Ni

powder (particle size 1 mm) at 1200 in flowing organ, followed by heat treatment in vacuum at 1000 to remove the C60 and fullerenes.

150

The initial laser vaporization pulse was followed by a second pulse to vaporize the

target more uniformly.

The use of two successive laser pulses to minimize the amount of carbon

deposited as soot. The second laser pulse breaks up the larger particles ablated by

the first one, and feeds them in to the growing nanotubes structure.

The material thus produced appears as a mat of ‘ropes’ 10 – 20 nm in diameter

and up to 100 or more in length. Each rope is found to consist primarily of bundle

of SWNTs aligned along a common axis. By varying the growth, the temperature,

the catalyst composition and other process parameters, the average nanotube

diameter and distribution can varied.

ii. Chemical Vapour Deposition Method (CVD)

Discharge and laser vaporization are currently the principal methods for obtaining

quantities of high quality carbon nanotubes. However, both methods suffer from

some drawback. The first is that both methods involve evaporating the carbon

source so that is has been nuclear how to scale up nanotubes production to the

industrial level using these approaches. The second issue relates to the fact that

vaporization method grow nanotubes in highly tangled forms mixed with

unwanted forms of carbon or metal species. The nanotubes are difficult to purify

manipulate and assemble for building nanotube device architecture.

In this method an organometallic precursor is mixed with carbon containing feed

gas, it is polymerized in a quartz tube and nanotubes are collected from the cooler

end of the reaction vessel. The feed gas may contain several species and is often

mixed with an inert gas.

151

Nanotubes are also grown on solid catalytic substrates such as SiO2, quartz,

alumina, etc. which contain transition metal precursors. Such approaches are

important for making supported MWNT assemblies for specific application.

5.3.3 - Properties of Nanotubes: i. Electronic properties: Conductivity in multi walled nanotubes is quite

complex. The conductances of MWNTs jumped by increments as additional nanotubes were touched to the mercury surface. This quantized conductance was found in all sizes of nanotubes and is also observed in metal nanowires. Some types of armchair nanotubes appear to conduct better than other metallic nanotubes. The conductivity and resistivity of rope SWNTs has been measured directly with a technique in which four electrodes have been placed at different part of the nanotubes. The resistivity of those SWNT ropes was in

order of 10−4 ohms per cm at 27 . This means that the ropes are the most highly conductive carbon fibers known. Individual SWNTs may contain defects. These defects allow the SWNTs to act as transistors. Likewise, joining nanotubes together may form transistor like devices. A single nanotube with a natural junction (that is, where a straight section is joined to a chiral section) behaves as rectifying diode – a half transistor in a single molecule.

152

ii. Mechanical Properties: SWNTs are stiffer than steel and are resistant to

damage from physical forces. Pressing on the tip of the nanotube will cause it

to bend without damage to tip. When the force is removed the tip of nanotube

will recover to its original state. Young’s Modulus value (which describes

elasticity, hardness, ease of fracture and conduct, are all important properties)

of SWNTs is 1.8 TPa. Armchair nanotube had a Young’s Modulus of 640.30

CPa.

5.3.4 - Uses of Carbon Nanotubes:

Carbon nanotubes behave as transistor. They can conduct electricity and have

been made into simple logic circuits. CNTs can store hydrogen and may also be

useful with lithium as batteries. They have unusual tensile strength and can be

used in making valuable building materials if manufacture cheaply in quantity.

Questions

1. What are the raw materials used in the manufacture of Portland cement

what are their functions. ?

2. What are the criteria adopted to ensure that the quality of cement

produced is good. ?

3. Describe the manufacture of Portland cement with neat flow diagram. 4. What are the sources of calcarius and argillaceous raw materials? 5. Describe the properties of various constitutes of cement explain

significance of gypsum.

6. Write note on setting and hardening of cement 7. What substances are added to cement to enhance its properties? Describe

any one with its applications.

8. Explain the following

a) RCC c) RUL b) Decay of Concrete d) CNTs

9. What are refectories explain their general properties mention the various

raw materials used in the manufacture of silica bricks outline the

manufacture of silica bricks 10. Explain manufacture properties and uses of Dolomite bricks.

153

Experiments EXPERIMENT NO. 1 Aim: To determine hardness of water by EDTA method.

Requirement: Std. hard water (1mg CaCO3/ml), 0.01 M EDTA EBT, buffer pH

= 10. Theory: Estimation of water hardness as applied to boiler water is of great

importance for the chemical industries in general. It is an important factor in the

manufacturing of sugar, dyes, pharmaceuticals, food processing and textile

industries, etc. Hardness in water prevents lathering of soap due to the presence of dissolved salts

of calcium magnesium, etc.

2C17H35COONa + Ca+2

or Mg+2

→ (C17H35COO)2 CaOOMg + NaCl) This method is based on the fact that ethylene diamine tetra acetic acid (EDTA)

forms stable complexes with di and polyvalent metal ions. The indicator

Eriochrome Black T used in the estimation also forms complexes with metal ions

but they are unstable and can be easily broken down. Erichrome Black T is a fri

basic acid dye which dissociates at different pH to form different coloured ions as

shown below

Eriochrome Black T ←→ ‘ Eriochrome Black T ←→ Eriochrome Black T

Red < pH 6 > Blue < pH 12 > Orange

At pH 10, in the presence of Ca2+

or Mg2+

ions Erichrome Black forms an

unstable wine red complex. Erichrome Black T

+ Ca+2

→ EBT- Ca or EBT - Mg

Blue

wine-red in colour unstable complex

When EDTA is added to water, EDTA combines with all Ca++

ions and Mg++

present in water, as the stability of EDTA complexes is greater.

If we represent EDTA disodium salt as Na2H2Y, it dissociates as follows:

Na2 H 2Y ←→ 2Na+ + H 2Y −

Eriochrome Black T Ca complex + H2Y ←→ Ca H2 Y + Erichrome Black T

unstable complex Stable complex Blue Preparation of Solutions

1. Standard Hard Water: Accurately weighed 1 gm pure CaCO3 dissolved in

minimum amount of HCl and evaporated to dryness. The residue is dissolved

in distilled water and diluted to one litre.

154

2. Standard 0.01 M EDTA Solution: 3.722 gm of disodium ethylene diamine

tetra acetate dihydrate dissolved in one litre of distilled water.

3. pH 10.0 buffer: Dissolve 70 gm of pure ammonium chloride with 570 ml of

liquor ammonia and dilute to litre with distilled water.

4. Eriochrome Black T Indicator Solution: Dissolve 0.5 gm of Eriochrome

Black T a indicator in 100 ml of alcohol 3-4 drops of this solution are used as

indicator during estimation.

Procedure

1. Standardisation of EDTA Solution: Pipette out 25 ml of standard hard

water in a 250 ml conical flask. Add half test tube buffer solution, 3- 4 drops

of indicator. Titrate against EDTA solution from burette. The end point is

from wine red to blue. Repeat the titration with another 25 ml of standard

hard water. Note down the volume of EDTA solution consumed. Let this

reading be ‘x’ ml. 2. Determination of Total Hardness of Unknown Solution: Pipette out 25 ml

of solution in flask. Add half test tube of buffer solution, 3 - 4 drops of

indicator solution. Titrate against EDTA solution from burette. Repeat the

titration with another 25 ml of the same solution. Note down the reading. Let

this reading be ‘Y’ ml. 3. Determination of Permanent Hardness of Water: Pipette out 25 ml of

unknown water in a flask, boil for 5 minutes cool and add half test tube of pH

10.0 buffer, 3 - 4 drops of indicator solution and titrate against EDTA

solution. Repeat the titration with another 25 ml of tap water sample. Note the

volume of EDTA consumed. Let this reading be ‘Z’ ml.

Observations Standardization of EDTA

1. Burette EDTA solution 0.01 M: Solution in flask 25 ml of standard hard

water + half test tube of buffer solution pH 10 Indicator

Indicator 3- 4 drops of Eriochrome Black T

End point Wine red to blue

Sr. No. EDTA solution in ml 1 2 3 Constant burette reading

1 Initial burette reading

2 Final burette reading

3 Difference

2. Determination of total hardness of water: Burette EDTA Solution 0.01 M

Flask 25 ml f unknown solution + 5 ml ammonia buffer pH 10.0

Indicator 3 - 4 drops of Eriochrome Black T

End point

Wine red to blue

155

Sr. No. EDTA solution in ml 1 2 3 Constant burette reading

1 Initial burette reading

2 Final burette reading

3 Difference

3. Determination of permanent hardness: Burette EDTA Solution 0.01 M

Flask 25 ml tap water + 5 ml pH 10.0 ammonia buffer

Indicator 3 - 4 drops of Eriochrome Black T

End point Wine red to blue

Sr. No. EDTA solution in ml 1 2 3 Constant burette reading

1 Initial burette reading

2 Final burette reading

3 Difference

Calculation

In order to understand the calculation better, let us assume the following data:

1. 25 ml of standard hard water requires 25 ml of EDTA 0.01 M EDTA

solution.

2. 25 ml of unknown solution requires 12.5 ml of EDTA 0.01 M EDTA

solution.

3. 25 ml of water after boiling requires 6.3 ml of EDTA 0.01 M EDTA solution.

We know standard hard water contains l mg/ml of CaCO3 hardness.

Hence, 25 ml of standard hard water has 25 mg of CaCO3 hardness.

Since 25 ml of standard hard water requires 25 ml EDTA solution.

∴ 25 ml of EDTA solution = 25 mg CaCO3 hardness.

∴ each ml of EDTA solution = 25

mg CaCO3, hardness 25

= 1 mg CaCO3 hardness

1. Hardness equivalence of EDTA solution

1 ml of 0.01 M EDTA = 1 mg CaCO3.

l x 1000 = 1000 ppm

156

2. 25 ml of unknown solution requires 12.5 ml of EDTA solution

∴ 25 ml of unknown solution = 12.5 x 1 mg CaCO3 hardness

∴ 1000 ml of unknown solution = 12.5 x 1000

mg CaCO3 hardness 25

∴ Hardness of unknown solution = 500 ppm

3. 25 ml water after boiling requires 6.3 ml of EDTA

∴ 25 ml water = 6.3 x 1 mg of CaCO3 hardness.

∴ 1000 ml of tap water = 6.3 x 1000

m of CaCO3 hardness 25

∴ Hardness of tap water = 252 ppm

Temporary hardness = Total hardness - Permanent hardness

Results

1. Hardness equivalence of EDTA solution = 1000 ppm 2. Total hardness of water = 500 ppm 3. Permanent hardness of water = 252 ppm 4. Temporary hardness of water = 248 ppm

EXPERIMENT NO. 2

Aim: Removal of hardness by using ion exchange resin.

Requirement: Cation exchange resin, hard water sample, 0.01 M EDTA, buffer

solution, Eriochrome Black T indicator, etc.

Theory: When hard water is passed through cation exchanger resin in the form of

H ions the Ca+2

, Mg+2

and metal ions present in the hard water are absorbed by

resin and H ions become free.

R- H2 + Ca+2

→ R – Ca + 2H+

R- H2 + Mg +2

→ R – Mg + 2H +

Procedure

Part I. Pipette out 25 ml of hard water in 250 ml conical flask add half test tube of

buffer pH = 10 and titrate against 0.01 M EDTA using EBT indicator, till it

becomes wine red to blue.

Part II. Prepare 25 cm cation exchange column and pass approx. 100 ml of 0.5 N

HCI at the rate of 2 ml per minute then wash the column with distilled water till it

is free from acidity (test by using litmus paper). Then pass 25 ml of hard water

sample through the column with adjustment of above-mentioned rate and collect

157

the eluate in a 250 ml standard measuring flask then wash the column with 100 ml

distilled water collect the washings and dilute to 250 ml. Titrate 50 ml of diluted

solution with 0.01 M EDTA by using Eriochrome Black T indicator till it

becomes wine red to blue. Calculation

25 ml of hard water required = ‘X’ ml of 0.01 M EDTA

50 ml of diluted eluate required

= ‘Y’ ml of 0.01 M EDTA

∴ 250 ml of

“

“

“

=Y x 5 ml of 0.0l MEDTA

Hence, 25 ml of hard water after passing through the cation exchanger required

= Y x 5 ml 0.01 M EDTA % Efficiency of the operation If the ‘Y’ is zero, then efficiency of operation is

100% X – 5Y = Z’ ml of 0.01 M EDTA

% Efficiency = Z x 100 X

Result % Efficiency =_______

EXPERIMENT NO. 3 Aim: To determine saponification value of the given sample of oil. Requirement: 1N alcoholic KOH, 0.1 N HC1, phenolphthalein, etc. Theory: Oils are triesters of glycerol when treated with excess of alcoholic KOH

solution gets hydrolysed into free glycerol potassium salt of fatty acid. When hydrolysis is completed the excess of alkali is back titrated against a

standard acid.

C17H35 COOH + KOH → C17H35 COOK + H2O. Saponification number is the amount of KOH in milligrams required to saponify

fatty acid present in 1 gram of oil. Procedure Part I Standardization of KOH solution Pipette out 10 ml supplied 1N alcoholic KOH (approx) in a 100 ml standard

measuring flask and dilute upto the mark with distilled water. Then pipette out

diluted 25 ml of KOH in a 250 ml conical flask add 1 - 2 drops of phenolphthalein

indicator and titrate against standard 0.1 N HCl from the burette. The end point

will be from pink to colourless. Take three constant readings.

158

Part II Determination of saponification value of the oil

Add 25 ml of supplied in alcoholic KOH to the accurately weighed I gm of oil

sample in a 250 ml round bottom flask attach it with water condenser. Reflux the

mixture on water bath for about 20 minutes till the hydrolysis is completed. Cool

the flask and dilute the contents to 250 nil with distilled water in a standard

measuring flask. Pipette out 25 ml of it in 25 ml conical flask; add 1 - 2 drops of

phenolphthalein and titrate against 0.1 N HCl. From the burette, end point will be

from pink to colourless. Take three constant readings.

(I) Observation and Calculation Part

Solution in burette 0.1 N HCl

Solution in conical flask 25 ml of KOH + 1-2 drops phenolphthalein

Indicator Phenolphthalein

Change in colour Pink to colourless

Sr No. 0.01 N HCl I II III Constant reading

1 Initial reading

3 Final reading

2 Difference Xml.

Calculation

25 ml of diluted KOH required “X” mil of 0.1 NHCl solution.

∴ NKOH = N1V1 = N2V2

NKOH

×

VKOH

=

NHCI

×

VHCI

NKOH × 25 = 0.1 × X

NKOH

= 0.1X

25 = AN

(II) Observations and calculations (Part II)

Solution in burette 0.1 N HCl

Solution in conical flask 25 ml of saponified solution and 1 - 2 drops of

phenolphthalein

Indicator Phenolphthalein

Change in colour Pink to colourless

159

Sr No. 0.01 NHCl I II III Constant reading

1 Initial reading

3 Final reading

2 Difference Xml.

Calculation

Amount of KOH added in terms of 0.1 N HCl from burette is 25 ml of AN.

∴ Volume of HCl = 25 x A/0.1 = B mg of KOH

Hence, 250 mg will be ≡ 10 B mg of KOH

Amount of KOH unused in terms of 25 ml of dilute solution = “Y” ml. ∴ 250 ml of diluted KOH solution = Y X 10 = 10 Y ml of 0.1 N HCL.

Hence amount of KOH used up for saponification = (10x – 10y) = “Z” ml.

Now 10ml of 1 N HCl = 56 gm of KOH

∴ Yml of AN HCl = 56 × A× Z

= C gm 1000

Saponification value of the oil = C/ weight of oil = ….. gm = …. mg

Result

Saponification value of the oil = ….. mg

EXPERIMENT NO. 4

Aim: To determine acid value or neutralisation number of the oil.

Requirement: 0.01N KOH, 0.01N HCl, Phenolphthalein indicator, distilled

water, etc.

Theory: Acid value is defined as the milligrams of potassium hydroxide required

to neutralise free acid present in 1 gm of oil sample. Most of the fatty acids

contain free acid. Higher acidity indicates oil has been oxidised and hence roughly

it is an indicator for the age of the oil or it gives an idea how old the fatty oil is.

Preparation of Solutions

1. O.1 N KOH: Weigh 5.6 gm of A.R. potassium hydroxide and dissolve in

distilled water dilute up to a litre in a standard measuring flask.

2. 0.1 N Oxalic Acid: Weigh 6.3 gm of A.R. oxalic acid and dissolved in

distilled water dilute to a litre.

160

3. Neutral 95% Alcohol: A drop of phenolphthalein solution is added to 95%

alcohol and neutralised with just enough KOH solution to give faint colour.

This is to ensure that reagent used for experiment does not contribute to the

acidity. 4. Phenolphthalein Indicator: 1gm of phenolphthalein dissolve in 100 ml of pure

alcohol.

5. Methyl Orange Indicator: 1 gm of methyl orange dissolved in 100 ml of 50%

alcohol.

Procedure

Part I Standardisation of KOH solution

Pipette out 25 ml of 0.01 N KOH (approx) in a 250 ml Conical flask add 4 -5

drops of phenolphthalein indicator and titrate against 0.01 N HCl from the burette

till it becomes pink to colourless. Take three constant readings.

Part II Determination of acid value

Take clean and dry 100 ml conical flask weigh it accurately then add 5 ml of oil

sample weigh it again from the difference in weight, Note down the actual weight

of the lubricating oil. With the help of pipette add 25 ml of 0.01 N KOH to the

conical flak and shake it vigorously to dissolve the oil, add few drops of

phenolphthalein indicator and titrate against 0.01 N HCl from the burette till it

becomes pink to colourless.

Observation and Calculation

I. Standardization of KOH

Solution in burette: 0.01 N HCl

Solution in conical flask: 25 ml 0.01 N KOH and phenolphthalein.

Indicator: Phenolphthalein.

Change in colour: Pink to colourless

Reaction : KOH + HCl → KCl + H2O

Sr. No. 0.01 NHCI I II II Constant reading

1. Initial reading

2. Final reading

3. Difference X ml.

161

Calculations

N1V1 = N2V2

NHCI

×

VHCI

=

NKOH

×

VKOH

0.01× x = NKOH × 25

0.01× x =

NKOH

25

II. Determination of acid value

Solution in burette 0.01 N HCl

Solution in conical flask Oil + 25 ml of 0.01 KOH + Phenolphthalein

Change in colour Pink to colourless

Sr. No. 0.01 NHCI I II II Constant reading

1. Initial reading

2. Final reading

3. Difference Y ml.

Calculation

Volume of 0.01 N KOH required = ‘Y’ ml

Volume of 0.01N KOH used against HCI with respect to the lubricant or

oil = (x- y) ml.

Acid value of the oil = KOH used(x - y)x 56 x

NKOH wt of oil

Result

1. Normality of KOH =... N

2. Acid value of the oil = ... mg

162

Experiment No. - 5

Chemical oxygen Demand

Chemical oxygen Demand is related to biochemical oxygen and can be carried in

3 hours as against 5 days for BOD. COD is defined as amount of oxygen used

oxidizing organic matter by means of a strong oxidizing agent. Both biologically

oxidisable organic matter like starch and sugar, inert material such as cellulose,

etc. are oxidised and hence COD values are always higher than those of BOD.

COD determination being quicker offers a means of taking corrective steps in

treatment process without waiting for ultimate BOD results.

Reagents Required

1. 0.25 N potassium dichromate 2. 0.25 N ferrous ammonium sulphate 3. Silver sulphate-sulphuric acid reagent 4. Mercuric sulphate 5. Ferroin indicator

Procedure

50 ml of sample of sewage taken in a 50 ml round bottom flask, add 1 gm of

H2SO4 and pour in 75 ml of silver sulphate - sulphuric acid reagent slowly,

cooling the contents. Add 25 ml of 0.25 ml 0.25 N K2Cr2O7 and mix well. Attach

a water condenser to the flask and reflux for 2 hours. Wash the condenser with little water, cool the contents in the flask and add few drops of ferroin indicator Titrate against 0.25 N ferrous ammonium sulphate standard solution. A blank

estimation is carried out with 25 ml 0.25 N K2Cr2O7 solution adding the reagents

used in identical manner and refluxing the contents for 2 hours.

Observations and Calculation

Volume of sample taken = 50 ml

Volume of 0.25 N ferrous amm. sulphate used in blank titration = (x) ml

Volume of 0.25 N ferrous amm. sulphate used in test titration = (y) ml

∴ Volume of 0.25 N ferrous amm. sulphate consumed. = (x — y) ml

∴ Chemical oxygen demand = (x

−

y)×

8

×1000

mg / liter 50 × 4

= (x − y)× 40mg / litre

Precaution to be taken while adding silver sulphate H2S04 reagent, as this addition

liberates large amount of heat and hence it is better to cool the mixture

thoroughly.

Result : Chemical oxygen demand =...

163

EXPERIMENT NO. 6 Aim: To determine the melting point/glass transition temperature of a polymer. Requirement: Thermometer, oil bath, burner, dilatometer, etc. Theory: The temperature of which the polymer or any substance changes from

solid to liquid state at NTP is called its melting point. Glass transition temperature (Tg) is conveniently measured in the laboratory by

dilatometry. Amorphous polymer when cooled below a certain temperature

becomes hard, brittle and glassy, but above this they are soft, flexible and rubbery.

This transition temperature of polymer is called glass transition temperature (Tg). Procedure: Determination of glass transition temperature: The polymer

appropriately confined in the bulb at the bottom is kept immersed in a suitable

liquid, usually mercury so as to give a column of the liquid in the capillary up to a

convenient height for measurement. The positioning of the glass plug as shown,

enables heating the test specimen’s avoiding overheating. The dilatometer placed

in an outer bath may be heated at a present rate and pattern. From the rise of the

liquid in the capillary on heating and consequent rise in temperatures, the change

in the volume of the specimen may be conveniently, obtained.

Result (i) M.P. of given polymer = ….. °C (ii) Glass transition temperature of given polymer = …. °C

164

EXPERIMENT NO. 7

Aim: To determine flash point and fire point of the lubricant.

Requirement: Oil sample, Abel’s flash point apparatus, Pensky and Martens

apparatus.

Theory: Flash point of the lubricant is defined as the lowest temperature at which

a lubricant gives off enough vapours that ignite when a small flame is brought

near to it. The fire point is defined as the ionest temperature of which the oil

vapours turns continuously at least for seconds. The flash points are determined

by using (1) Abel’s apparatus (ii) Pensky and Martens apparatus.

(a) Abel’s flash point apparatus

As water bath is used in Abel’s flash point apparatus, it is used to determine flash

point upto 90°C. 1. Oil Cup

Oil cup consists of a flanged cylindrical brass up, placed on another copper cup

separated by means of air gap. The oil cup is covered by means of tightly fitting

covet Attached to cover is a knob which rotates a stirrer attached to it. There is a

point for inserting a thermometer inside the cup. The cover has a rectangular

opening which is covered by means of shutter device which can be moved so as to

open and close the opening in the cup covet Attached to the shutter device is

arrangement for providing a small flame. The arrangement consists of a small oil

reservoir with a small protruding pipe. A piece of cotton thread passes through the

pipe and dips in small reservoir containing some oil. The shuttle mechanism

operates in such a way that when the opening is made, the flame automatically

dips inside the cup. The copper cup is placed in the water bath and the whole

assembly is completely covered.

The oil cup is 5 cm in diameter and 5 cm in depth. It carries a L-shaped pointer

attached to it to indicate the required level of oil in cup.

Abel’s flash point apparatus

165

Working The cup is filled with lubricant to the desired level and placed in the apparatus.

The cover placed on the top and secured. The cotton thread dipped in oil is passed

through the small tube. Thermometer inserted into port and secured. The shutter

mechanism is in closed position. The water bath filled with water and heating is

started. The stirrer is rotated manually to ensure uniform heating of lubricant in

cup. The thread is lighted to provide a small flame. As heating continues, the

shutter mechanism is operated intermittently so that the flame dips inside the cup.

If the oil is sufficiently heated it gives off vapours which will suddenly burn in a

flash when flame dips inside the cup. The temperature at which this flash is

observed is noted as the flash point of lubricant. Result The flash point of given lubricant is °C Heating: Since water bath is used for Abel’s apparatus allows flash points

deternination of lubricant upto 90°C for heating (b) Pensky Martens Apparatus

Description of Apparatus

There is flanged brass oil cup 5 cm in diameter and 5.5 cm in depth resting in

another cup and separated from it by air gap. The outer cup forms part of

assembly which can be heated directly by gas or heater. The cover of oil cup has

four openings, one for stirrer, one for inserting thermometer, air inlet and a device

for inserting the flame. When the mechanism is operated, a small gap is made in

the cover and at the same time flame device allows the flame to dip inside the cup.

By operating the mechanism flame can be dipped and opening closed as desired.

A pilot lamp attached to mechanism allows the standard flame to be lighted again

if it gets extinguished in the process of dipping.

Pensky Martens Apparatus

166

Working

Oil cup is filled with oil to the desired level and the thermometer is placed in it.

The assembly is slowly heated and stirred to heat it uniformly. The standard flame

and pilot lamp are lighted. Shutter mechanism operated periodically to allow the

frame to dip and come in contact with the vapours evolved. The temperature at

which the vapour of the oil burns suddenly with flash is noted down as the flash

point of lubricant.

Flash point of some solvents.

Sr.No. Solvent Flash point

1 Terpentine 35

2 Diesel 31

3 Petrol 42

4 Kerosene 43

5 Decane 63

6 Ethylene glycol 113

7 Transformer oil 171

Result

(i) The flash point of the given lubricant = ... °C

(ii) The fire point of the given lubricant = ... °C

EXPERIMENT NO. 8

Aim: To estimate the amount of chloride present in the given sample of water by

Mohr’s method.

Requirement: 0.025 N NaCl, 0.025 N AgNO3, 5% K2CrO4 solution.

Theory: Natural water contains small amounts of chlorides of calcium,

magnesium and sodium. When water containing chlorides are used in boilers,

some of the chlorides undergo hydrolysis at high temperature to produce corrosive

acid HCI.

MgCl2 + 2H2O → Mg (OH)2 ↓ + 2HCl

CaCl2 also undergoes hydrolysis though to smaller extent producing corrosive

hydrochloric acid. It corrodes boiler plates and can cause serious damage to boiler.

Hence, it is essential to estimate amount of chloride present in water.

167

Mohr’s method of estimation of chloride involves titration against standard

AgNO3 solution using K2CrO4 solution as indicator.

Ag + + NO 3 + Cl → AgCl ↓ + NO 3

2 Ag + + 2NO3 + CrO42− → AgCrO4 ↓ + 2NO3

In the presence of both chloride and chromate ions, silver ions react with chloride ions to form silver chloride precipitated since its solubility product is reached

earlier. As long as chloride ions are present, precipitate of Ag2CrO 4 will not be

formed. This is the basis of chloride estimation. Further colour of Ag2CrO4

precipitate is brick red and that of AgCl is white and hence the end point can be easily detected. The titration should be carried out at slightly alkaline medium, since under acidic

condition chromate ions get converted into dichromate ions and silver dichromate

is soluble and the end point cannot be so easily followed. Hence, solution should

be made slightly alkaline by adding small amounts of Na2CO3 or CaCO3. Preparation of Solutions

Approximate 0.025 N AgNO3 Solution Weigh accurately 4.250 gm of pure silver nitrate, dissolve in distilled water and

dilute to one litre in a standard measuring flask. AgNO3 is Store in dark brown

bottle. Standard 0.025 M NaCl solution This primary standard is prepared by 1.46 gm of A.R. NaCI is dissolved in

distilled water and diluted to one litre with distilled water. 0.5% Potassium Chromate Indicator Solution

Weigh accurately 5.0 gm of pure K2CrO4 and dissolve in distilled water and dilute

to 100 ml with distilled water. Procedure 1. Standardisation of AgNO3 Solution: Pipette out 25 ml of standard 0.025 N

NaCl solution in a 250 ml conical flask. Then add pinch of Na2CO3 or

CaCO3 to ensure the slightly alkaline medium, add 1 to 2 ml of freshly

prepared 5% K2CrO4 indicator and titrate against std 0.025 N AgNO3. From the burette till the formation of slight reddish brown (chocolate coloured)

precipitate of Ag2CrO4. (Supernatant solution remains yellow in colour).

Note down the reading and calculate normality of AgNO3 solution.

Solution in Burette AgNO3 solution (0.02 N approx)

Solution in Conical Flask 25 ml of standard 0.1 N NaCl sol + a pinch of

Na2CO3 as CaCO3

168

Indicator 5% K2CrO4 solution 3-4 drops

Change in colour White ppt. to brick red

Sr. No. I II II Constant reading

1. Initial reading

2. Final reading

3. Difference X ml.

2. Estimation of Chloride Content of Water sample: Pipette out 25 ml of given

water sample in a 250 ml conical flask and titrate against 0.025 N AgNO3 as

above. Note the reading and calculate the amount of chloride present.

Solution in Burette AgNO3 solution

Solution in Conical Flask 25 ml of diluted chloride solution + a pinch of

Na2CO3 as CaCO3 +3 - 4 alcoholic KOH

Indicator 3- 4 drops of K2CrO4 solution

Change in Colour White ppt to brick red ppt.

Sr. No. I II II Constant reading

1. Initial reading

2. Final reading

3. Difference X ml.

Calculation

Normality of AgNO3 Solution

using N1 V1 = N2 V2 where

N1 = Normality of AgNO3 solution

V1 = Volume of AgNO3 solution

N2 = Normality of standard NaCI solution [0.025 N known]

V2 = Volume of standard solution taken [25ml]

Let the normality as determined by the observations be denoted by N

Now AgNO3 + NaCl → AgCl + NaNO3

1000 ml 1 N AgNO3 = 35.5gm of chloride

169

∴ 1000 ml 0.1 N AgNO3 = 3.55gm of chloride

∴ 1 ml of 0.1 N AgNO3 = 0.00355 gm of chloride

∴ 1ml of 0.025 N AgNO3 = gm of chloride

∴ Actual normality of AgNO3 as found out is N

1 ml of AgNO3 of N normality = 0.00355× N gm of chloride

0.1 Estimation of chloride content 25 ml of diluted chloride solution required

= B ml of AgNO3 solution ∴ 25 ml of diluted chloride solution contains

= B

×

0.00355

×

N

gm of chloride 0.1

∴ 1000 ml solution contains = B

×

0.00355

×

N

× 1000

gm of chloride 0.125

Chloride content of given water sample = gm/litre Results Amount of chloride present in the given sample of water

= ....... gm/litre = ... …. mg/lit = ... …. ppm.