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THARMOGRAVITOMETRIC ANALYSIS

HAFIZ ADNAN HANIFE11-341METALLURGY AND MATERIAL ENGINEERING

IntroductionTGA is a technique which measures the

change in the mass of a sample over a range of temperatures.

Principle:• The basic principle of TGA is that as a sample is heated, its mass changes. This change can be used to determine the composition of a material or its thermal stability, up to 1000oC. Usually, a sample loses weight as it is heated up due to decomposition, reduction, or evaporation

What TGA Can Tell You

•Thermal Stability of Materials•Oxidative Stability of Materials•Composition of Multi-component Systems•Estimated Lifetime of a Product•Decomposition Kinetics of Materials•The Effect of Reactive or Corrosive Atmospheres

on Materials•Moisture and Volatiles Content of Materials

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Type Of Thermogrvimetry

1. Isothermal / Static Thermogravimetry2. Quasistatic Thermogravimetry3. Dynamic Thermogravimetry

4. Isothermal/ Static Thermogravimetry:

In this technique the sample weight is recorded as a function of time at constant temperature.

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2.Qasistatic Thermogravimetry:

In this technique the sample is heated to constant

weight at each of the series of increasing temperature.

3. Dynamic Thermogravimetry:

In this technique a sample is heated in an environment whose temperature is changing in predetermine manner generally at linear rate.

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Thermogravimetric Curve:

A to B - Thermal stability of material.

B to C -Weight loss.

C – Procedural decomposition temperature.

D- Final temperature

AB

C

D

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Factor Affecting TGA Curve:

A. Instrumental factor:-

1. Heating Rate2. Furnace

atmosphere3. Sample Holder

B. Sample Characteristic:-

1. Effect of sample mass

2. Effect of sample particle size

3. Effect of heat reaction

4. Compactness of sample

5. Previous history of sample

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Instrumentation

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Components of Instrumentation:A. Recording balanceB. Sample HolderC. FurnaceD. Furnace temperature

programmer/ControllerE. RecorderF. Thermobalance

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A. Balance:-

Recording balance

1. Deflection balancei. Beam typeii. Spring/ Helical typeiii. Cantilever typeiv. Torsion type

2. Null balance

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1. Deflection balance:-

i. Beam type:- A conversion of

beam deflection about the fulcrum into a suitably identifiably weight change.

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ii.Spring/Helical type:-

An elongation or contraction of spring with weight change. This changes the length of the spring .

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iii. Cantilever type:-

One end of the beam is fixed & other end on which the sample is placed, is free to undergo deflection.

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iv. Torsion type:-

In this type of balance the beam is attach to torsion wire.

The wire is fixed at one or both ends so that deflection of beam are proportional to weight change.

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2. Null point balance:-In this balance

there should be a sensor to detect the deviation of the balance to detect the null position .

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B. Sample Holder:-Types of sample holder:-

1.Shallow Pans2.Deep crucibles 3.Loosely covered crucibles 4.Restort cups

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1.Shallow Pan:

Used for such sample necessary to eliminate diffusion as a volatile material.

2. Deep Crucible: Used to study industrial scale

calcination & surface area measurement.

3.Loosely curved crucible: Used in self generated atom study. 4. Retord cups: Useful in boiling point study.

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C.Furnace:- Position of furnace with respect

to balance:

A B C

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The choice of furnace heating element and type of furnace depend upon the range being studies:-

Temperature Material

1100˚c 1100-1500˚c 1100- 1750 ˚c

Nichrome Platinum /Alloy of

rhodium Tungsten

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D.Temperature Measurement:-

The most common method is thermocouple.

The temperature 1100,chromel/alumel thermocouple are made up of alloys of Pt and rhodium are used.

Higher temperature tungsten or rhenium thermocouple are used.

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E. Recorder:-Two Types:-

A. Time-base potentiometric strip chart recorder

B. X-Y recorderAdvantage:-

1. To check the heating rate of the furnace for linearity.

2. X,Y recorder we get curve having plot of weight directly against temperature.

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F. Thermobalance:- It records continuously weight change

of the sample as a function of temperature.

The sensitivity of balance depends on the size of the sample used.

The temperature recorded to an accuracy of better than ±1%

The weight loss recovered to an accuracy ±1%

In market large number of balance are available.

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Applications:- Purity and thermal stability. Solid state reaction. Decomposition of organic and inorganic

compound. Determining composition of material. Corrosion of metals in various

atmosphere. Pyrolysis of coal , petroleum and wood. Roasting and calcination of minerals. Evaluation of gravimetric precipitates. Oxidative and Reductive stability.

Thermogravimetric analyses and mineralogical study of polymer modified mortar with silica fume

RESEARCH ARTICLE

Alessandra Etuko Feuzicana de Souza Almeida*; Eduvaldo Paulo Sichieri

RESERCH ARTICLE

TGA curves of pastes with silica fume content of 5% and 10% respectively. It can be seen that TGA curves for these pastes consist of four zones:

~ 25-123.3 °C: dehydration of pore water

~ 123.3-420 °C: dehydration of calcium silicate hydrates

~ 420-480 °C: dehydroxylation of calcium hydroxide

~ 480-730 °C: decarbonation of CaCO3

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Thanks