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Lecture Notes By Dr Tanweer Hussain
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SCIENCE VS. ENGINEERING
SCIENCE Analysis: ask questions, look for
patterns, develop knowledge
Produce knowledge
Characteristic activity: research
( learn about nature) Study of what is
Tryscience.org
ENGINEERING Synthesis: integrate bits of
knowledge to create somethingnew
Produce processes and things
(part of technology) Characteristic activity: creative
design
Study of what never was
Tryengineering.org
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It is the field of engineering that encompasses the spectrum of materials types and how to use
them in manufacturing. Materials engineering is different from Materials science. Materials science involves
investigating the relationships that exist between the structures and properties of materials,
whereas, Materials engineering, on the basis of these structurepropertycorrelations, design or
engineer the structure of a material to produce a predetermined set of properties. From a
functional perspective, the role of a materials scientist is to develop or synthesize new materials,
whereas a materials engineer is called upon to create new products or systems using existing
materials, and/or to develop techniques for processingmaterials.What is a Material?
Everything we see and use is made of materials
Engineers make things.
They make them out of materials.
Why Study Materials Engineering?
In order to be a good designer, an engineer must learn what materials will be appropriate to use indifferent applications.
Any engineer can look up materials properties in a book or search databases for a material that
meets design specifications, but the ability to innovate and to incorporate materials safely in a
design is rooted in an understanding of how to manipulate materials properties and functionality
through the control of the materialsstructure and processing techniques.
WHAT IS MATERIALS ENGINEERING?Lecture Notes By Dr Tanweer Hussain
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Engineering
Materials
Metals
Advanced
MaterialsPolymersCeramics Composites
Metals and Alloys
Atoms in metals and their alloys are arranged in a very orderly manner, and in comparison
to the ceramics and polymers, are relatively dense . Metals have High electrical
conductivity, good formability, Castable, machinable. An alloy is a metal that contains
additions of one or more metals or non-metals. Metals and alloys have relatively high
strength, high stiffness, ductility or formability, and shock resistance.
Ceramics
Thermally insulating, Refractories. Ceramics can be defined as inorganic crystalline
materials. Beach sand and rocks are examples of naturally occurring ceramics. Traditional
ceramics are used to make bricks, tableware, toilets, bathroom sinks, refractories (heat-
resistant material), and abrasives. In general, due to the presence of porosity (small
holes), ceramics do not conduct heat well; they must be heated to very high temperatures
before melting. Ceramics are strong and hard, but also very brittle. Advanced ceramics
are materials made by refining naturally occurring ceramics and other special processes.
Glasses
Optically transparent. Glass is an amorphous material, often, but not always, derived from
a molten liquid. The term amorphous refers to materials that do not have a regular,periodic arrangement of atoms.
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Polymers (Greek; Polys + mers = many + parts)
Polyethylene Food packaging Easily formed into thin, flexible, airtight film. Electrically insulating and moisture-resistant.
Polymers are typically organic materials. They are produced using a process known as polymerization. Polymeric
materials include rubber (elastomers), PE, nylon, PVC, PC, PS, and silicone rubber. and many types of adhesives.
Polymers typically are good electrical and thermal insulators although there are exceptions such as the semiconducting
polymersComposites
The main idea in developing composites is to blend the properties of different materials. The design goal of a composite
is to achieve a combination of properties that is not displayed by any single material, and also to incorporate the best
characteristics of each of the component materials.
Advanced Materials
SemiconductorsUsed in Silicon Transistors and integrated circuits. Unique electrical behaviour, converts electrical signals to light,
lasers, laser diodes, etc.
Biomaterials
Biomaterials are employed in components implanted into the human body to replace diseased or damaged body parts.
These materials must not produce toxic substances and must be compatible with body tissues (i.e., must not cause
adverse biological reactions).
Smart Materials
These materials are able to sense changes in their environment and then respond to these changes in predetermined
manners. Smart material include some type of sensors, and actuators. Piezoelectric actuators expand and contract in
response to an applied electric field .
Nanomaterials
Nanomaterials may be any one of the four basic types; metals, ceramics, polymers, & composites. the term is limited to
dealing with particles whose dimensions range in size from a few nanometres up to around 100 nm.
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SOME EXAMPLES OF ADVANCED MATERIALS
Engineers had developed many types of materials with respect to their use and suitable
conditions, as discussed earlier, to meet the rushing needs of technology. Such as
Liquid crystals, superconductors, semiconductors, biosynthetic materials, nano-
materials, smart materials and so on. Here we shall discuss only Liquid crystals and
Superconductors.
Liquid Crystals
One of the rising types of advanced materials is Liquid Crystals. Liquid crystals are
produced from organic compounds and is thought of as the phase of matter between thesolid and liquid state of a crystal.The study of liquid crystals began in 1888 when an
Austrian botanist named Friedrich Reinitzer observed that a material known as
cholesteryl benzoate had two distinct melting points. In his experiments, Reinitzer
increased the temperature of a solid sample and watched the crystal change into a hazy
liquid. As he increased the temperature further, the material changed again into a clear,
transparent liquid.In liquid crystals it is observed that when a crystalline solid is melted it first convert
into a turbid liquid phase, which can flow as liquid, but it has crystalline structure in it.
After providing more heat it becomes clear liquid. The turbid liquid phase is known as
Liquid Crystal.
A liquid crystalline state exist between two temperatures, the melting point and the
clearing point or temperature. Liquid crystals are always anisotropic.
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One common item that presents some interesting material property requirements is the container for
carbonated beverages. The material used for this application must satisfy the following constraints: (1)provide a barrier to the passage of carbon dioxide, which is under pressure in the container; (2) be
nontoxic, non-reactive with the beverage, and, preferably, recyclable; (3) be relatively strong and
capable of surviving a drop from a height of several feet when containing the beverage; (4) be
inexpensive, including the cost to fabricate the final shape; (5) if optically transparent, retain its optical
clarity; and (6) be capable of being produced in different colours and/or adorned with decorative labels.
All three of the basic material typesmetal (aluminium), ceramic (glass), and polymer (PE plastic)areused for carbonated beverage containers. All of these materials are non- toxic and un-reactive with
beverages. In addition, each material has its pros and cons.
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For example, the aluminium alloy is relatively strong (but easily dented), is a very good barrier to the
diffusion of carbon dioxide, is easily recycled, cools beverages rapidly, and allows labels to be painted onto
its surface. On the other hand, the cans are optically opaque and relatively expensive to produce. Glass is
impervious to the passage of carbon dioxide, is a relatively inexpensive material, and may be recycled, butit cracks and fractures easily, and glass bottles are relatively heavy. Whereas plastic is relatively strong,
may be made optically transparent, is inexpensive and lightweight, and is recyclable, it is not as impervious
to the passage of carbon dioxide as the aluminium and glass. For example, you may have noticed that
beverages in aluminium and glass containers retain their carbonization (i.e., fizz) for several years,
whereas those in two-litre plastic bottles goflatwithin a few months.
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The properties of some materials are directly related to their structures. The structure of
a material usually relates to the arrangement of its internal Components. There are four
levels of materials structure:
Subatomic structure involves electrons within the individual atoms and interactions
with their nuclei.
Atomic structure involves arrangement of atoms in materials and defines interaction
among atoms (interatomic bonding).
Microscopic structure involves arrangement of small grains of material that can be
identified by microscopy.
Macroscopic structure relates to structural elements that may be viewed with the
naked eye.
Materials Structure
Subatomic levelAtomic level
Microscopic structure
Macroscopic
structure
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Ionic bonds:When one or more electrons from an outer orbit are
transferred from one material to another, a strong attractive forcedevelops between the two ions.
All matters are made up of atoms containing a nucleus of protons and neutrons and
surrounding clouds, or orbits, of electrons. Atoms can transfer or share electrons; in
doing so, multiple atoms combine to form molecules. Molecules are held together by
attractive forces called bonds.
Metallic bonds: Metals and alloys form metallic bonds. Metals have
relatively few electrons in their outer orbits; thus, they cannot complete
the outer shell of other self-mated atoms. Instead, the metallic elements
have electropositive atoms that donate their valence electrons to form a
cloud of electrons surrounding the atoms, whereby the availableelectrons are shared by all atoms in contact. The resultant electron
cloud provides attractive forces to hold the atoms together and results
in generally high thermal and electrical conductivity.
Covalent bonds:ln a covalent bond, the electrons in outer orbits are
shared by atoms to form molecules. The number of electrons shared
is reflected by terms such as single bond, double bond, etc.
Polymers consist of large molecules that are covalently bonded
together. Solids formed by covalent bonding typically have low
electrical conductivity and can have high hardness.
Atomic Structure (Arrangement of Atoms)Lecture Notes By Dr Tanweer Hussain
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why we study the crystal structure of metals?
By studying the crystal structure of metals, information about various properties can be
inferred. By relating structure to properties, one can predict processing behaviour or
select appropriate applications for a metal. Metals with face-centered cubic structure, for
example, tend to be ductile whereas hexagonal close-packed metals tend to be brittle.
Difference between Unit Cell and Single Crystal
A unit cell is the smallest group of atoms showing the characteristic lattice structure of a
particular metal. It is the building block of a crystal,
A single crystal consists of a number of unit cells. All unit cells interlock in the same way
and have the same orientation For a crystalline solid, when the periodic and repeated
arrangement of atoms is perfect or extends throughout the entirety of the specimen
without interruption, the result is a single crystal. Single crystals exist in nature, but they
may also be produced artificially. Examples include; turbine blades and electronic
microcircuits, which employ single crystals of silicon and other semiconductors.
Crystalline Structure Of Metals
Polycrystalline Materials
Most crystalline solids are composed
of a collection of many small crystals
or grains; such materials are termedpolycrystalline..
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The Figure shows three thin disk specimens placed over some printed matter. It is
obvious that the optical properties of each of the three materials are different; the one on
the left is transparent, whereas the disks in the center and on the right are, respectively,
translucent and opaque. All of these specimens are of the same material, aluminum
oxide, but the:
Leftmost one is what we call a single crystalthat is, it is highly perfectwhich givesrise to its transparency.
The center one is composed of numerous and very small single crystals that are all
connected; the boundaries between these small crystals scatter a portion of the light
reflected from the printed page, which makes this material optically translucent.
The specimen on the right is composed not only of many small, interconnected crystals,but also of a large number of very small pores or void spaces. These pores also
effectively scatter the reflected light and render this material opaque.
Thus, the structures of these three specimens are different in terms of crystal
boundaries and pores, which affect the optical transmittance properties. Furthermore,
each material was produced using a different processing technique.
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GRAINS AND GRAIN BOUNDARIES
When molten metal solidifies, crystals begin for formindependently of each other. They have random and
unrelated orientations. Each of these crystals grows intoa crystalline structure or GRAIN.
The number and size of the grains developed in a unitvolume of the metal depends on the rate at which
NUCLEATION (the initial stage of crystal formation) takesplace
Is this what I
mean by grain?
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FIGURE 1.10 SCHEMATIC ILLUSTRATION OF THE STAGES DURING THE
SOLIDIFICATION OF MOLTEN METAL; EACH SMALL SQUARE REPRESENTS A
UNIT CELL. (A) NUCLEATION OF CRYSTALS AT RANDOM SITES IN THE MOLTEN
METAL; NOTE THAT THE CRYSTALLOGRAPHIC ORIENTATION OF EACH SITE IS
DIFFERENT. (B) AND (C) GROWTH OF CRYSTALS AS SOLIDIFICATION
CONTINUES. (D) SOLIDIFIED METAL, SHOWING INDIVIDUAL GRAINS ANDGRAIN BOUNDARIES; NOTE THE DIFFERENT ANGLES AT WHICH
NEIGHBORING GRAINS MEET EACH OTHER.
Rapid coolingsmaller grains
Slow coolinglarger grains
Grain boundariesthe surfaces that separate individual
grains
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Face-Centered Cubic Crystal Structure
Body-Centered Cubic Crystal Structure
Hexagonal Close-Packed Crystal Structure
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APF
s
Volume of atoms in unit cell
Volume unit cellTotal number of atom in unit cell Volume of unit atoms
Volume unit cell
ATOMIC PACKING FACTOR
For BCC APF 0.68
For FCCAPF 0.74
For HCP APF ?
Show that the atomic packing factor for the BCC crystal structure is 0.68.
Show that the atomic packing factor for the FCC crystal structure is 0.74.
What is the atomic packing factor for the HCP crystal structure?.Show that for HCP the c/a ratio is 1.633
23 3
2
aArea of a Hexagon
1. Calculate the volume of an BCC unit cell in terms of the atomic radius R.
2. Calculate the volume of an FCC unit cell in terms of the atomic radius R.
3. Calculate the volume of an HCP unit cell in terms of the atomic radius R.
Numerical Problems
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Allotropy is the ability of an element to exist in different structural forms while in the
same state of matter. The allotropes depend on both the allotropy temperature andthe external pressure. For example, the allotropes of carbon include diamond (where
the carbon atoms are bonded together in a tetrahedral lattice arrangement),
graphite (where the carbon atoms are bonded together in sheets of a hexagonal
lattice). Graphite is the stable polymorph at ambient conditions, whereas diamond is
formed at extremely high pressures. Also, pure iron has a BCC crystal structure at
room temperature, which changes to FCC iron at 912C
Allotropy
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IMPERFECTIONS IN THE CRYSTAL STRUCTURE OF METALS
The arrangement of the atoms or ions in engineered materials contains imperfections or defects.
These defects often have a profound effect on the properties of materials. Following are the basictypes of imperfections: point defects, line defects (or dislocations), and surface defects.
Point defects-vacancy, missing atoms, interstitial atom extra atom in the lattice or impurity
foreign atom that has replaced the atom of pure metal.
Linear defects also called dislocations.
Planar imperfections such as grain boundaries and phase boundaries. Volume or bulk imperfections-voids, inclusions, other phases, cracks.
In many applications, the presence of such defects is useful. For example, defects known as
dislocations are useful for increasing the strength of metals and alloys; however, in single crystal
silicon, used for manufacturing computer chips, the presence of dislocations is undesirable.
Often the defects may be created intentionally to produce a desired set of electronic, magnetic,optical, or mechanical properties. For example, pure iron is relatively soft, yet, when we add a
small amount of carbon, we create defects in the crystalline arrangement of iron and transform it
into a plain carbon steel that exhibits considerably higher strength.
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POINT DEFECTS:(a) vacancy, (b) interstitial atom, (c) small substitutional atom,(d) large substitutional atom, (e) Frenkel defect, and (f) Schottky defect.
IMPERFECTIONS IN THE CRYSTAL STRUCTURE OF METALS (CONTD.)
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Vacancies: A vacancy is produced when an atom or an ion is missing from its normal site in the crystal
structure. When atoms or ions are missing (i.e., when vacancies are present), the overall randomnessor entropy of the material increases, which increases the thermodynamic stability of a crystalline
material. All crystalline materials have vacancy defects. Vacancies are introduced into metals and alloys
during solidification, at high temperatures, or as a consequence of radiation damage.
Interstitial Defects:An interstitial defect is formed when an extra atom or ion is inserted into the crystal
structure at a normally unoccupied position. Interstitial atoms such as hydrogen are often present asimpurities, whereas carbon atoms are intentionally added to iron to produce steel.
A substitutional defectis introduced when one atom or ion is replaced by a different type of atom or
ion.
A Frenkel defectis a vacancy-interstitial pair formed when an ion jumps from anormal lattice point to an interstitial site.
A Schottky defect, is unique to ionic materials and is commonly found in many ceramic materials.
When vacancies occur in an ionically bonded material, a stoichiometric number of anions and cations
must be missing from regular atomic positions if electrical neutrality is to be preserved. For example,
one Mg+2 vacancy and one O-2 vacancy in MgO constitute a Schottky pair.
IMPERFECTIONS IN THE CRYSTAL STRUCTURE OF METALS (CONTD.)
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DISLOCATIONS
Dislocations are line imperfections in an otherwise perfect crystal. They typically are introduced
into a crystal during solidification of the material or when the material is deformed permanently.
There are three basic types of dislocations.
Screw Dislocations
The screw dislocation can be illustrated by cutting partway through a perfect crystal and thenskewing the crystal by one atom spacing.
Edge Dislocations
An edge dislocation can be illustrated by slicing partway through a perfect crystal, spreading thecrystal apart, and partly filling the cut with an extra half plane of atoms.
Mixed Dislocations
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Slip is the movement of an edge dislocation across the crystal lattice under a shear stress.
SLIP AND SLIP SYSTEMLecture Notes By Dr Tanweer Hussain
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DEFORMATION & STRENGTH OF SINGLE CRYSTALS
A single crystal exhibits different properties when tested in different directions and this
property is called AnisotropyElastic deformation- a single crystal is subject to an external force, but returns to its
original shape when the force is removed
Plastic deformation-a permanent deformation when the crystal does not return to its
original shape.
Slippingof one plane of atoms over another adjacent plane (slip plane) under shear stress
Twinning- the second and less common mechanism of plastic deformation where a portion
of the crystal forms a mirror image of itself across the plane of twinning
Two Basic Mechanisms for Plastic Deformations
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Permanent deformation of a single crystal under a tensile load. The highlighted grid ofLecture Notes By Dr Tanweer Hussain
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Permanent deformation of a single crystal under a tensile load. The highlighted grid ofatoms emphasizes the motion that occurs within the lattice. (A) deformation by slip. The
b/a ratio influences the magnitude of the shear stress required to cause slip. (B)
deformation by twinning, involving the generation of a twinaround a line of symmetry
subjected to shear. Note that the tensile load results in a shear stress in the plane
illustrated.
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CONCEPT OF
STRESS AND STRAIN
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Work hardening or strain hardening If we apply a stress S1 that is greater than theLecture Notes By Dr Tanweer Hussain
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flow at stress
level S1
the new flow
stress is S2
Each time we apply a higher
stress, the flow stress and
tensile strength increase,and the ductilit decreases
Strain Hardening Mechanism
Work hardening, or strain hardening, If we apply a stress S1 that is greater than the
yield strength Sy, it causes a permanent deformation or strain. When the stress is
removed, a strain of e1 remains. Our new test specimen would begin to deform
plastically or flow at stress level S1. We define the flow stress as the stress that is
needed to initiate plastic flow in previously deformed material. Strain hardening results in
an increase in the strength of a material due to plastic deformation. Plastic deformation =adding dislocations
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Iron ores are rocks and minerals from which metallic iron can be economically
extracted. The ores are usually rich in iron oxides and vary in colour from dark grey,
bright yellow, deep purple, to rusty red. The iron itself is usually found in the form of
magnetite (Fe3O4), hematite (Fe2O3), goethite (FeO(OH)), limonite (FeO(OH)n(H2O))or siderite (FeCO3).
Smelting
To convert it to metallic iron it must be smelted or sent through a direct reduction
process to remove the oxygen. Oxygen-iron bonds are strong, and to remove the iron
from the oxygen, a stronger elemental bond must be presented to attach to theoxygen. Carbon is used because the strength of a carbon-oxygen bond is greater
than that of the iron-oxygen bond, at high temperatures. Thus, the iron ore must be
powdered and mixed with coke, to be burnt in the smelting process.
PRODUCTION OF IRONLecture Notes By Dr Tanweer Hussain
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IronPure iron rarely exists outside of the laboratory. Iron is produced by reducing iron ore to pig
iron through the use of a blast furnace. From pig iron many other types of iron and steel are
produced by the addition or deletion of carbon and alloys. The following paragraphs discuss the
different types of iron and steel that can be made from iron ore.
PIG IRON.Pig iron is composed of about 93% iron, from 3% to 5% carbon, and various amounts
of other elements. Pig iron is comparatively weak and brittle; therefore, it has a limited use and
approximately ninety percent produced is refined to produce steel. Cast-iron pipe and some fittings
and valves are manufactured from pig iron.
Carbon 3.04.5%
Manganese 0.152.5%Phosphorus 0.12.0%
Silicon 1.03.0%
Sulphur 0.050.1%
WROUGHT IRON. Wrought iron is made from pig iron with some slag mixed in during
manufacture. Almost pure iron, the presence of slag enables wrought iron to resist corrosion and
oxidation. The chemical analyses of wrought iron and mild steel are just about the same. The
difference comes from the properties controlled during the manufacturing process. Wrought iron
can be gas and arc welded, machined, plated, and easily formed; however, it has a low hardness
and a low-fatigue strength.
CAST IRON.Cast iron is any iron containing greater than 2% carbon alloy. Cast iron has a high
compressive strength and good wear resistance; however, it lacks ductility, malleability, and impactstrength.
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Wrought
IronPig Iron
Iron OreLecture Notes By Dr Tanweer Hussain
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Conventional Blast Furnace
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Modern Blast FurnaceLecture Notes By Dr Tanweer Hussain
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1: Iron ore + Calcareous sinter
2: coke
3: conveyor belt
4: feeding opening, with a valve
that prevents direct contact with the
internal parts of the furnace
5: Layer of coke
6: Layers of sinter, iron oxide
pellets, ore,
7: Hot air (around 1200C)
8: Slag
9: Liquid pig iron10: Mixers
11: Tap for pig iron
12: Dust cyclon for removing dust
from exhaust gasses before
burning them in 13
13: Air heater
14: Smoke outlet (can beredirected to carbon capture &
storage (CCS) tank)
15: feed air for Cowper air heaters
16: Powdered coal
17: cokes oven
18: cokes bin19: pipes for blast furnace gas
Modern Blast FurnaceLecture Notes By Dr Tanweer Hussain
PRODUCTION OF IRONLecture Notes By Dr Tanweer Hussain
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Iron is the fourth most plentiful element in the earths crust, it is rarely found in the
metallic state. Instead, it occurs in a variety of mineral compounds, known as ores, the
most attractive of which are iron oxides coupled with companion impurities. To produce
metallic iron, the ores are processed in a manner that breaks the ironoxygen bonds.Ore, limestone, coke (carbon), and air are continuously introduced into specifically
designed furnaces and molten metal is periodically withdrawn.
The production of iron in a blast furnace is a continuous process. The furnace is heated
constantly and is re-charged with raw materials from the top while it is being tapped from
the bottom. Iron making in the furnace usually continues for about ten years before the
furnace linings have to be renewed.
Blast furnace is a furnace for smelting of iron from iron oxide ores (hematite, Fe2O3or
magnetite, Fe3O4). Coke, limestone and iron ore are poured in the top, which would
normally burn only on the surface. The hot air blast to the furnace burns the coke andmaintains the very high temperatures that are needed to reduce the ore to iron. The
reaction between air and the fuel generates carbon monoxide. This gas reduces the iron
oxide in the ore to iron.
Fe2O3(solid) + CO(gas) Fe(solid) + CO2(gas)
PRODUCTION OF IRONy
BLAST FURNACE CHEMISTRY FOR THE PRODUCTION OF IRONLecture Notes By Dr Tanweer Hussain
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At 500o
C3Fe2O3+CO -> 2Fe3O4+ CO2
Fe2O3+CO -> 2FeO + CO2
At 850oC
Fe3O4+CO -> 3FeO + CO2
At 1000o
CFeO +CO -> Fe + CO2
At 1300 oC
CO2+ C -> 2CO
At 1900oC
C+ O2-> CO2
FeO +C -> Fe + CO
BLAST FURNACE CHEMISTRY FOR THE PRODUCTION OF IRON
The significant reactions occurring within the Blast Furnace can be described as follows:
1. Iron is extracted from its ores by the chemical reduction of iron oxides with carbon in
a furnace at a temperature of about 800C - 1900C.
2. Coke, the source of chemical energy in the blast furnace, is burnt both to release heat
energy and to provide the main reducing agent:3. Calcium oxide, formed by thermal decomposition of limestone, reacts with the silicon
oxide present in sand, a major impurity in iron ores, to form slag (which is less dense
than molten iron). Overall, the chemical processes can be summarized by these
equations:
All of the phosphorus and most
of the manganese will enter the
molten iron. Oxides of silicon
and sulphur compounds are
partially reduced, and these
elements also become part of
the resulting metal. Other
contaminant elements, such as
calcium, magnesium, and
aluminium, are collected in the
limestone-based slag and are
largely removed from the
system.
y
PRODUCTION OF STEELLecture Notes By Dr Tanweer Hussain
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When iron is smelted from its ore by commercial processes, it contains more carbon
than is desirable. In order to convert the pig iron into steel, it must be melted and
reprocessed to reduce the carbon to the correct amount, at which point other elements
can be added. This liquid is then continuously cast into long slabs or cast into ingots.
Approximately 96% of steel is continuously cast, while only 4% is produced as cast steelingots. The ingots are then heated in a soaking pit and hot rolled into slabs, blooms,
or billets. Slabs are hot or cold rolled into sheet metal or plates. Billets are hot or cold
rolled into bars, rods, and wire. Blooms are hot or cold rolled into structural steel, such
as I-beams and rails. In modern foundries these processes often occur in one assembly
line, with ore coming in and finished steel coming out. Sometimes after steels final
rolling it is heat treated for strength, however this is relatively rare.
Iron as obtained from blast furnace
contains from 3-4% of Carbon, and
variable amount of silicon,
manganese sulphur and
phosphorus.
1. Dead mild steel up to 0.15% carbon
2. Low carbon or mild steel 0.15% to 0.45% carbon
3. Medium carbon steel 0.45% to 0.8% carbon
4. High carbon steel 0.8% to 1.5% carbon
y
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STEEL MAKING PROCESSES
Bessemer Process
Crucible Process
Open Hearth Process
Electric Process (Arc, Induction)
Duplex Process
Linz Donnawitz Process
Kaldo Process
Modern Process
Bessemer ProcessLecture Notes By Dr Tanweer Hussain
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Bessemer Process
Bessemer process was invented in1875 by Thomas Gilchrest. In Bessemer process
the molten pig iron from blast furnace is poured into converter. The converter is
made of steel plates lined inside with refractory material. In the bottom of converter
vessels, a no of holes are introduced through which air is blown at a pressure of
200-250KN/m2. Based on full capacity, the converter is charged with 100-150 ton,and this charge is carried out from 10 to 15 ton at different time intervals. Their first
oxidizes silicon, and manganese which together with iron oxide rise to the top from
slag. During this air blowing process the carbon begins to burn and blowing
continued, until 0.25% of carbon is eliminated. In Bessemer process acids are used
to burn and eliminated silicon and phosphorus. The finished steel is then poured into
ladles and from ladle it is poured into ingot moulds for subsequently rolling and
forging process.
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Crucible Process
In Crucible process wrought iron together with a small amount of pig iron, necessary
alloying metals and slagging materials are placed in a clay or clay-graphite crucible,
covered with an old crucible bottom and melted in a gas or coke-fired furnace. After
the charge is entirely molten, with sufficient time allowed for the gases and impurities
to rise to the surface, the Crucible is withdrawn, the slag removed with a cold ironbar, and the resulting steel poured into a small ingot which is subsequently forged to
the desire shape.
There are three types of Crucible Furnaces:
(a) lift-out crucible,
(b) stationary pot, from which molten metal must be ladled, and(c) tilting-pot furnace
Open Hearth ProcessLecture Notes By Dr Tanweer Hussain
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Open Hearth Process
The open-hearth furnace is rectangular and rather low, holding from 15 to 200 ton of
metal in a saucer-like shallow pool. It is heated either by producer gas, oil, tar, mixed
blast furnace and coke oven gas, pitch, mixture of creosote and pitch and heavy fuel
oil. Flames come from first one end and then the other. Waste gases pass through
regenerators. The furnace is charged with ore and limestone. The lime stone beginsto decompose in carbon di-oxide and calcium oxide.
A. gas and air enter
B. pre-heated chamber
C. molten pig iron
D. hearth
E. heating chamber
F. gas and air exit.
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Electric Furnace
An Electric Arc Furnace(EAF) is a furnace that heats charged material by means
of an electric arc. An electric arc furnace used for steelmaking consists of
a refractory-lined vessel, usually water-cooled in larger sizes, covered with a
retractable roof, and through which one or more graphite electrodes enter the
furnace. Arc furnaces differ from induction furnaces in that the charge material isdirectly exposed to an electric arc, and the current in the furnace terminals passes
through the charged material.
An induction furnace is an electrical furnace in which the heat is applied
by induction heating of metal. The advantage of the induction furnace is a clean,
energy-efficient and well-controllable melting process compared to most othermeans of metal melting.
The one major drawback to Electric furnace usage in a foundry is the lack of refining
capacity; charge materials must be clean of oxidation products and of a known
composition and some alloying elements may be lost due to oxidation.Induction furnace is based on the principle of heating by induced currents. If a conductor is
placed within a coil through which an alternating current is flowing, a current is induced in theconductor. By the normal la of electricity this conductor is heated. The magnitude of the current
generated depends on:
_the physical dimensions of the coil;
_the resistivity of the conductor and
_the frequency of the current.
Linz-Donawitz (LD) or Basic oxygen steel making (BOS) ProcessLecture Notes By Dr Tanweer Hussain
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The basic oxygen steel-making process is as follows:
1. Molten pig iron from a blast furnace is poured into a large refractory-lined container
called a ladle. Besides the BOS vessel is one-fifth filled with steel scrap.
2. The metal in the ladle is sent directly for basic oxygen steelmaking or to a pre-
treatment stage. Pre-treatment of the blast furnace metal is used to reduce therefining load of sulphur, silicon, and phosphorus. In desulfurising pre-treatment,
several hundred kilograms of powdered magnesium are added. Sulphur impurities
are reduced to magnesium sulphide in a violent exothermic reaction. The sulphide is
then raked off. Similar pre-treatment is possible for desiliconisation and
dephosphorisation using lime as reagents. The decision to pretreat depends on the
quality of the blast furnace metal and the required final quality of the BOS steel.3. Fluxes (lime or dolomite) are fed into the vessel to form slag, which absorbs
impurities of the steelmaking process. During blowing the metal in the vessel forms
an emulsion with the slag, facilitating the refining process.
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The Kaldo process, is a modification of LD process. It was originally developed in Sweden by Prof.
Kalling. This process is based on the advantage of evolution of heat by high phosphorus(2%) pig
iron to as low as 0.02% P.
The converter in Kaldo Process is inclined at 150 to 200with the horizontal, and rotated at a speed
of 25-30 r.p.m. The oxygen lance is introduced through the open end of the vessel, which also actsas the outlet for the exhaust gases. The use of oxygen allows simultaneous removal of carbon and
phosphorus from the (p 1.85%) pig iron. The rotation of the converter ensures better slag-metal
reaction.
MODERN STEEL MAKING PROCESSLecture Notes By Dr Tanweer Hussain
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Vacuum Induction Melting process:
This process is similar to the induction melting process with suitable arrangement for creating a
vacuum. This process is used for making super alloys containing nickel and cobalt as base metals.
It is very suitable process for further remelting for investment casting. Due to vacuum prevailing in
the chamber , non-metallic inclusions can be minimized and composition of chemically reactiveelements like titanium , boron and aluminium can be controlled accurately. New alloys of steel
possessing greater uniformly and reproducibility of properties accompanied by greater strength,
creep resistance, etc can be produced.
Consumable Electrical Vacuum Arc Melting Process:
It is direct arc steel melting process in which the electrode is consumed during melting. This
process was originally used for titanium. Since this process eliminates hydrogen, oxygen, and
volatile materials, it is extensively used for special-purpose steels, as in moving parts of aircraft
engines, due to need of high strength, uniformity of properties, greater toughness and freedom from
tramp and volatile elements.
Electric slag refining (ESR) Process:
This process is commonly known as ESR. It is a larger form of the original welding process . It is the
electrical resistance heating process that remelts the preformed electrode into a water-cooled
crucible. Due to resistance to flow of current, the metal melts and drops onto the crucible through alayer of slag around the ingot. The process is used for making high alloy, high quality steels for
obtaining superior properties normally not achieved in conventional processing. For example, ultra
high strength weldable steel.
MODERN STEEL MAKING PROCESS
EQUILIBRIUM PHASE DIAGRAMLecture Notes By Dr Tanweer Hussain
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EQUILIBRIUM PHASE DIAGRAM
An equilibrium phase diagram is a graphic mapping ofthe natural tendencies of a material or a material
system, assuming that equilibrium has been attained
for all possible conditions. There are three primary
variables to be considered: temperature, pressure,
and composition. The simplest phase diagram is a
pressuretemperature (PT) diagram for a fixed-composition material. Areas of the diagram are
assigned to the various phases, with the boundaries
indicating the equilibrium conditions of transition.
PT phase diagrams are rarely used for engineering applications. Most engineering
processes are conducted at atmospheric pressure, and variations are more likely tooccur in temperature and composition.
One-component or Unary Phase Diagram
(P-T Diagram)
A phase may be defined as a homogeneous portion of a
system that has uniform physical and chemical
characteristics.
COMPLETE SOLUBILITY IN BOTH LIQUID AND SOLID STATES
Th li i h li id li h l f hi h h i l i 100%
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The upper line is the liquidusline, the lowest temperature for which the material is 100%
liquid. Above the liquidus, the two materials form a uniform-chemistry liquid solution. The
lower line, denoting the highest temperature at which the material is completely solid, is
known as a solidus line. Below the solidus, the materials form a solid-state solution in
which the two types of atoms are uniformly distributed throughout a single crystalline
lattice. Between the liquidus and solidus is a freezing range, a two-phase region where
liquid and solid solutions coexist.
CONDITIONS FOR UNLIMITED SOLID SOLUBILITY
1. Size factor: The atoms or ions must be of similar size, with no more than a 15%difference in atomic radius.
2. Crystal structure: The materials must have the same crystal structure; otherwise,
there is some point at which a transition occurs from one phase to a second phase with
a different structure.
3. Valence: The ions must have the same valence; otherwise, the valence electron
difference encourages the formation of compounds rather than solutions.
Binary Phase Diagram
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PARTIAL SOLID SOLUBILITY Lecture Notes By Dr Tanweer Hussain
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INSOLUBILITY
If one or both of the components are totally
insoluble in the other, the diagrams will also
reflect this phenomenon. The following Figure
illustrates the case where component A is
completely insoluble in component B in both the
liquid and solid states.
Many materials do not exhibit
complete solubility in the solid state.
Each is often soluble in the other up
to a certain limit or saturation point,
which varies with temperature.
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THE GIBBS PHASE RULE
This rule represents a criterion for the number of phases that will coexist within a system
at equilibrium, and is expressed by the simple equation:
F + P = C + N
where, P is the number of phases present. The parameter F is termed the number of
degrees of freedom or the number of externally controlled variables (e.g., temperature,
pressure, composition), F is the number of these variables that can be changed
independently without altering the number of phases that coexist at equilibrium. Theparameter C in above equation represents the number of components in the system.
Components are normally elements or stable compounds and, in the case of phase
diagrams, are the materials at the two extremities of the horizontal compositional axis.
Since pressure is constant (1 atm), the parameter N is 1temperature is the only non
compositional variable. Gibbs equation now takes the form (F + P = C + 1)
Furthermore, the number of components C is 2 (Cu and Ag), and (F + P = 2 + 1=3)Now consider the case of single-phase fields on the phase diagram. Because only one
phase is present, P . 1 and (F + P = 3-1=2)
This means that to completely describe the characteristics of any alloy that exists within
one of these phase fields, we must specify two parameters; these are composition and
temperature, which locate, respectively, the horizontal and vertical positions of the alloy
on the phase diagram.
INTERPRETATION OF PHASE DIAGRAMS
In a phase diagram for each point of temperature and composition following three
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In a phase diagram, for each point of temperature and composition, following three
pieces of information can be obtained:
1. The phases present:The stable phases can be determined by simply locating the
point of consideration on the temperaturecomposition mapping and identifying the
region of the diagram in which the point appears.
2. The composition of each phase: If the point lies in a two-phase region, a tie-line
must be constructed. A tie-line is simply an isothermal (constant-temperature) line drawn
through the point of consideration, terminating at the boundaries of the single phase
regions on either side. The compositions where the tie-line intersects the neighbouring
single-phase regions will be the compositions of those respective phases in the two-
phase mixture.3. Amount of each phase:
i. The tie line is constructed across the two-phase region at the temperature of the
alloy.
ii. The overall alloy composition is located on the tie line.
iii. The fraction of one phase is computed by taking the length of tie line from the
overall alloy composition to the phase boundary for the other phase, and dividing
by the total tie line length.
iv. The fraction of the other phase is determined in the same manner.
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Th th h ti th t li th h 183C b itt
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The three-phase reaction that occurs upon cooling through 183C can be written as:
The leadtin phase diagram
Figure given below summarizes the various forms of three-phase reactions that may
occur in engineering systems along with the generic description of the reaction shown
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occur in engineering systems, along with the generic description of the reaction shown
below the figures. These include the eutectic, peritectic, monotectic, and syntectic
reactions, where the suffix -ic denotes that at least one of the three phases in the
reaction is a liquid. If the same prefix appears with an -oid suffix, the reaction is of a
similar form but all phases involved are solids. Two such reactions are the eutectoid and
the peritectoid. The separation eutectoid produces an extremely fine two-phase mixture,
and the combination peritectoid reaction is very sluggish since all of the chemistry
changes must occur within (usually crystalline) solids.
If components A and B form a compound, and the compound cannot tolerate any
deviation from its fixed atomic ratio, the product is known as a stoichiometric
intermetallic compoundand it appears as a single vertical line in the diagram
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IRONCARBON PHASE DIAGRAMLecture Notes By Dr Tanweer Hussain
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IRONIRON CARBIDE PHASE DIAGRAMLecture Notes By Dr Tanweer Hussain
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Steel, composed primarily of iron and carbon, is the most important of the engineering
metals. For this reason, the ironcarbon equilibrium diagram assumes special
importance. We normally are not interested in the carbon-rich end of the Fe-C phase
diagram and this is why the full ironcarbon (Fe-C) diagram is not normally encountered,
but we examine the Fe-Fe3C diagram as part of the Fe-C binary phase Diagram.
In the Figure, stoichiometric intermetallic
compound, Fe-Fe3C, is used to terminate
the carbon range at 6.67 wt% carbon.
Immediately after solidification, iron forms
a BCC structure called -ferrite. Onfurther cooling, the iron transforms to aFCC structure called , or austenite.
Finally, iron transforms back to the BCC
structure at lower temperatures; this
structure is called , or ferrite. Both of the
ferrites ( and ) and the austenite aresolid solutions of interstitial carbon atoms
in iron.
Eutectic : L + Fe3C (4.30 wt% C, 1147 C)
upon cooling, a liquid phase is transformed
into the two solid phases at the temperature
TE; the opposite reaction occurs upon heating.
The fourth single phase is the stoichiometric intermetallic compound which goes by the
name cementite or iron carbide Like most intermetallics it is quite hard and brittle and
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name cementite, or ironcarbide. Like most intermetallics, it is quite hard and brittle, and
care should be exercised in controlling the structures in which it occurs. Alloys with
excessive amounts of cementite, or cementite in undesirable form, tend to have brittle
characteristics. Because cementite dissociates prior to melting, its exact melting point is
unknown, and the liquidus line remains undetermined in the high-carbon region of thediagram.
EUTECTOID is a solid-state reaction in which
one solid phase transforms to two other solidphases: S = S1+ S2 (0.77 wt%C, 727 C)
The main microscopic constituents of iron and steel are as follows:Lecture Notes By Dr Tanweer Hussain
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1. Austenite 2. Ferrite 3. Cementite 4. Pearlite
AUSTENITE ()is a solid solution of free carbon and iron in gamma iron. On heating the
steel, after upper critical temperature, the formation of structure completes into austenite
which is hard, ductile and non-magnetic. It is able to dissolve large amount of carbon. Itis formed when steel contains carbon up to 1.8% at 1130C. On cooling below 723C, it
starts transforming into pearlite and ferrite. Austenitic steels cannot be hardened by
usual heat treatment methods and are non-magnetic.
FERRITE ()contains very little or no carbon in iron. It is the name given to pure iron
crystals which are soft and ductile. The slow cooling of low carbon steel below thecritical temperature produces ferrite structure. Ferrite does not harden when cooled
rapidly. It is very soft and highly magnetic.
CEMENTITE is a chemical compound of carbon with iron and is known as iron carbide
(Fe3C). Cast iron having 6.67% carbon is possessing complete structure of cementite.
Free cementite is found in all steel containing more than 0.83% carbon. It increases withincrease in carbon % as reflected in Fe-C Equilibrium diagram. It is extremely hard. The
hardness and brittleness of cast iron is believed to be due to the presence of the
cementite. It decreases tensile strength. This is formed when the carbon forms definite
combinations with iron in form of iron carbides which are extremely hard in nature. The
brittleness and hardness of cast iron is mainly controlled by the presence of cementite in
it. It is magnetic below 200C.
PEARLITE is a eutectoid alloy of ferrite and cementite It occurs particularly in medium
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PEARLITEis a eutectoid alloy of ferrite and cementite. It occurs particularly in medium
and low carbon steels in the form of mechanical mixture of ferrite and cementite in the
ratio of 87:13. Its hardness increases with the proportional of pearlite in ferrous material.
Pearlite is relatively strong, hard and ductile, whilst ferrite is weak, soft and ductile. It is
built up of alternate light and dark plates. These layers are alternately ferrite andcementite. When seen with the help of a microscope, the surface has appearance like
pearl, hence it is called pearlite. Hard steels are mixtures of pearlite and cementite while
soft steels are mixtures of ferrite and pearlite.
As the carbon content increases beyond 0.2% in the temperature at which the ferrite is
first rejected from austenite drop until, at or above 0.8% carbon, no free ferrite is
rejected from the austenite. This steel is called eutectoid steel, and it is the pearlite
structure in composition.
P-135, Introduction to Basic Manufacturing Processes and Workshop Technology
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METAL ALLOYS
There are two types of metal alloys
Ferrous AlloysNon-Ferrous Alloys
Compared to other engineering materials, the carbon steels offer high strength and high
stiffness, coupled with reasonable toughness. Unfortunately, they also rust easily and
generally require some form of surface protection, such as paint, galvanizing, or other
coating. The plain-carbon steels are generally the lowest-cost steel material and shouldbe given first consideration for many applications.
The differentiation between plain-carbon and alloy steel is often somewhat arbitrary.
Both contain carbon, manganese, and usually silicon. Copper and boron are possible
additions to both classes. Steels containing more than 1.65% manganese, 0.60%
silicon, or 0.60% copper are usually designated as alloy steels. Also, a steel is
considered to be an alloy steel if a definite or minimum amount of other alloying elementis specified. The most common alloy elements are chromium, nickel, molybdenum,
vanadium, tungsten, cobalt, boron, and copper, as well as manganese, silicon,
phosphorus, and sulphur in amounts greater than are normally present. If the steel
contains less than 8% of total alloy addition, it is considered to be a low-alloy
steel. Steels with more than 8% alloying elements are high-alloy steels.
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IMPORTANT ORES OF COPPER
EXTRACTION OF COPPERLecture Notes By Dr Tanweer Hussain
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IMPORTANT ORES OF COPPER
Copper pyrite or chalcopyrite (CuFeS2).
Chalocite (Cu2S) or copper glance.
Malachite green [CuCO3.Cu(OH)2].
Azurite blue [2CuCO3.Cu(OH)2].
Bornite (3Cu2S.Fe2S3) or peacock ore.
Melaconite (CuO) etc.
EXTRACTION OF COPPER FROM SULPHIDE ORE
Large amount of copper are obtained from copper pyrite (CuFeS2) by
smelting. Ores containing 4% or more copper are treated by smeltingprocess. Very poor ores are treated by hydro-metallurgical process(Leaching, Solution concentration and purification, Metal recovery).
EXTRACTION OF COPPER BY SMELTING PROCESS
Following steps are involved in the extraction of copper.
1. CONCENTRATION
The finely crushed ore is concentrated by Froth-Floatation process. Froth
flotation is a process for separating minerals from gangue by taking
advantage of differences in their hydrophobicity. The finely crushed ore is
suspended in water containing a little amount of pine oil. A blast of air is
passed through the suspension. The particles get wetted by the oil and float
as a froth which is skimmed. The gangue sinks to the bottom.
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The concentrated ore is then roasted in a furnace in the presence of a
current of air. Sulphur is oxidized to SO2 and impurities of arsenic (As) and
antimony (Sb) are removed as volatile oxides. The following reaction takes
place during the roasting process.
2CuFeS2 + O2 Cu2S + 2FeS + SO2
S + O2 SO2
4As + 3O2 As2O3
4Sb + 3O2 2Sb2O3
Cuprous sulphide and ferrous sulphide are further oxidized into their oxides.
2Cu2S + 3O2 2Cu2O + 2SO2
2FeS + 3O2 2FeO + 2SO2
3. SMELTING
The roasted ore is mixed with coke and silica (sand) SiO2 and is introduced
in to a blast furnace. The hot air is blasted and FeO is converted in to
ferrous silicate (FeSiO3).
FeO + SiO2 FeSiO3
Cu2O + FeS Cu2S + FeO
FeSiO3 (slag) floats over the molten matte of copper.
4. BESSEMERIZATION
Copper metal is extracted from molten matte through bessemerization
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Copper metal is extracted from molten matte through bessemerization .
The matte is introduced into Bessemer converter which uphold by tuyers.
The air is blown through the molten matte. Blast of air converts Cu2S partly
into Cu2O which reacts with remaining Cu2S to give molten copper.
2Cu2S + 3O2 2Cu2O + 2SO2
2Cu2O + Cu2S 6Cu + SO2The copper so obtained is called "Blister copper" because, as it solidifies,
SO2 hidden in it escapes out producing blister on its surface.
IMPURITIES IN BLISTER COPPER
AND THEIR EFFECTS
Blister copper is 99% pure. It contains
impurities mainly iron but little amount
of As, Zn, Pb, Ag and Au may also be
present. These impurities adverselyaffect the electrical as well as
mechanical properties of copper.
Therefore, they must be removed.
EXTRACTION OF ZINC Lecture Notes By Dr Tanweer Hussain
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ZINC Ores are found in the forms of
1) Zinc sulphide2) Smithsonite (ZnCO3) 67% Zn3) Hemimorphite or (Zn4Si2O7(OH)2.H2O). 54.2% Zn
4) Zincite (ZnO)5) Willemite (Zn2SiO4) 58.5%.
EXTRACTION OF ZINC FROM SULPHIDE ORE
There are two methods of zinc extraction1) Pyrometallurgy2) Hydrometallurgy
EXTRACTION OF ZINC & ALUMINIUM BY SMELTING PROCESS
Following steps are involved in the extraction of zinc .
1. CONCENTRATION
The finely crushed ore is concentrated by Froth-Floatation process. Froth
flotation is a process for separating minerals from gangue by taking
advantage of differences in their hydrophobicity. The finely crushed ore is
suspended in water containing a little amount of oil. A blast of air is passed
through the suspension. The particles get wetted by the oil and float as a
froth which is skimmed. The gangue sinks to the bottom.
2. ROASTING
Th d i h d i f i h f
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The concentrated ore is then roasted in a furnace in the presence of a
current of air.
3. SMELTING
The roasted ore is mixed with coke and silica (sand) SiO2 and is introduced
in to a blast furnace, where the hot air is blasted.
H i h d d ib h ll d h i d li f l
HEAT TREATMENT Lecture Notes By Dr Tanweer Hussain
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Heat treatment is the term used to describe the controlled heating and cooling of metals
and alloys for the purpose of altering their structures and properties.
Heat treatment is the process of combination of heating and cooling operations, timed
and applied to metals and alloys in their solid state to obtain desired properties.
AIM OF HEAT TREATMENT
The aim is to obtain a desired microstructure to achieve certain predetermined
properties (physical, mechanical, magnetic or electrical).
The same metal or alloy can be
made weak and ductile for easein manufacture, and then
retreated to provide high strength
and good fracture resistance for
use and application
SOFTENING HEAT TREATMENTLecture Notes By Dr Tanweer Hussain
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Annealing Full Annealing
Process Annealing
Stress-relief Annealing
Spheroidization Annealing
Normalizing
Tempering
The term annealing refers to a heat treatment in which a material is exposed to anANNEALING Lecture Notes By Dr Tanweer Hussain
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The term annealing refers to a heat treatment in which a material is exposed to an
elevated temperature for an extended time period and then slowly cooled. Annealing is
carried out to (1) relieve stresses; (2) increase softness, ductility, and toughness; and/or
(3) produce a specific microstructure.
Annealing is a heat treatment used to eliminate some or all of the effects of cold working.Annealing at a low temperature may be used to eliminate the residual stresses produced
during cold working without affecting the mechanical properties of the finished part.Any
annealing process consists of three stages: (1) heating to the desired temperature, (2)
holding or soaking at that temperature, and (3) cooling, usually to room temperature.
Time is an important parameter in these procedures. During heating and cooling,temperature gradients exist between the outside and interior portions of the piece; their
magnitudes depend on the size and geometry of the piece. If the rate of temperature
change is too great, temperature gradients and internal stresses may be induced that
may lead to warping or even cracking.
PROCESS ANNEALING is a heat treatment that is used to negate the effects of cold
work that is, to soften and increase the ductility of a previously strain-hardened metal.Process annealing is applied to low carbon steels (
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products. Parts are heated to temperatures below the A1(between 550 and 650C or
1000 and 1200F), held for a period of time, and then slow cooled to prevent the
creation of additional stresses. Times and temperatures vary with the condition of the
component, but the basic microstructure and associated mechanical properties generally
remain unchanged.
SPHEROIDIZATION ANNEALING:When high-carbon steels are to undergo extensive
machining or cold forming, a process known as spheroidization is often employed. Here
the objective is to produce a structure in which all of the cementite is in the form of small
spheroids or globules dispersed throughout a ferrite matrix. This can be accomplished
by a variety of techniques, including (1) prolonged heating at a temperature just belowthe A1followed by relatively slow cooling, (2) prolonged cycling between temperatures
slightly above and slightly below the or (3) in the case of tool or high-alloy steels, heating
to 750 to 800C (1400 to 1500F) or higher and holding at this temperature for several
hours, followed by slow cooling.
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NORMALIZING: In plastically deformed metals (for example, by rolling operation),the grains are irregularly shaped and relatively large, but vary substantially in size. An
annealing heat treatment called normalizing is used to refine the grains (i.e., to
decrease the average grain size) and produce a more uniform and desirable size
distribution; fine-grained pearlitic steels are tougher than coarse-grained ones.
One should note a key difference between full annealing and normalizing. In the full
anneal, the furnace imposes identical cooling conditions at all locations within the metal,
which results in identical structures and properties. With normalizing, the cooling will be
different at different locations. Properties will vary between surface and interior, and
different thickness regions will also have different properties. When subsequent
processing involves a substantial amount of machining that may be automated, the
added cost of a full anneal may be justified, since it produces a product with uniform
machining characteristics at all locations.
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TEMPERINGis a process of heat treating, which is used to increase the toughnessof iron-based alloys. It is also a technique used to increase the toughness of glass. For
metals, tempering is usually performed after hardening, to reduce some of the excesshardness, and is done by heating the metal to a temperature below its "lower critical
temperature. Tempering is usually performed after quenching, which is rapid cooling of
the metal to put it in its hardest state.
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HARDENING HEAT TREATMENTLecture Notes By Dr Tanweer Hussain
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To harden by quenching, a metal (usually steel or cast iron) must be heated above the
upper critical temperature and then quickly cooled. Depending on the alloy and other
considerations (such as concern for maximum hardness vs. cracking and distortion),
cooling may be done with forced air or other gases, (such as nitrogen). Liquids may beused, due to their better thermal conductivity, such as water, oil, a polymer dissolved in
water, or a brine. Upon being rapidly cooled, a portion of austenite (dependent on alloy
composition) will transform to martensite, a hard, brittle crystalline structure. The
quenched hardness of a metal depends on its chemical composition and quenching
method.
QUENCHING
Overall Hardening Heat Treatment
Surface hardening by changing the surface chemistry
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HARDENING
Hardening of steels is done to increase
the strength and wear properties.
Carbon steel is heated 30 & 50degrees C above the upper critical point
and then quenched quickly
The quicker the steel is cooled theharder it will be.
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POLYMERS (Poly=many+ Mers=unit )Lecture Notes By Dr Tanweer Hussain
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Polymers consist of chains of molecules.
Polmolecules consisting of one unit (known as a monomer) or a few units (known as
oligomers) that are chemically joined (by covalent bonding) to create these giant
molecules. Most polymers are organic, meaning that they are carbon-based; however, polymers
can be inorganic (e.g., silicones based on a Si-O network).
What is Polymerization?
Polymerization is the process by which small molecules consisting of one unit (known as
a monomer) or a few units (known as oligomers) are chemically joined to create thesegiant molecules. Polymerization normally begins with the production of long chains in
which the atoms are strongly joined by covalent bonding.
Classification of PolymersThere are several ways of classification of polymers based on some special
id ti Th f ll i f th l ifi ti f l
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considerations. The following are some of the common classifications of polymers:
Classification Based on Source
Under this type of classification, there are three sub categories.
1. Natural polymersThese polymers are found in plants and animals. Examples are proteins, cellulose,
starch, resins and rubber.
Naturally occurring polymers are derived from plants and animals, these materials
include wood, rubber, cotton, wool, leather, and silk.
2. Semi-synthetic polymers
Cellulose derivatives as cellulose acetate (rayon) and cellulose nitrate, etc. are the usualexamples of this sub category.
3. Synthetic polymers
A variety of synthetic polymers as plastic (polythene), synthetic fibres (nylon) and
synthetic rubbers (Buna S) are examples of man-made polymers extensively used in
daily life as well as in industry.
The synthetics can be produced inexpensively, and their properties may be managedto the degree that many are superior to their natural counterparts.
Plastics are materials that are composed principally of naturally occurring and
modified or artificially made polymers often containing additives such as fibers,
fillers, pigments, and the like that further enhance their properties.
Classification Based on Structure
1 Linear polymers
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1. Linear polymers
These polymers consist of long and straight chains. The examples of Polymers are high
density polythene, polyvinyl chloride, etc. These are represented as:
2. Branched chain polymers
These polymers contain linear chains having some branches, e.g., low density
polythene. These are depicted as above:
3. Cross linked or Network polymers
These are usually formed from bi-functional and tri-functional monomers and contain
strong covalent bonds between various linear polymer chains, e.g. bakelite, melamine,etc. These polymers are depicted as above:
Classification Based on Molecular ForcesUnder this category, the polymers are classified into the following four sub groups on the
basis of magnitude of intermolecular forces present in them
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basis of magnitude of intermolecular forces present in them.
1. Elastomers: These are rubber like solids with elastic properties. In these
elastomeric polymers, the polymer chains are held together by the weakest
intermolecular forces. These weak binding forces permit the polymer to be stretched.A few crosslinksare introduced in between the chains, which help the polymer to
retract to its original position after the force is released as in vulcanised rubber.
Fibres: Fibres are the thread forming solids which possess high tensile strength and
high modulus. These characteristics can be attributed to the strong intermolecular forces
like hydrogen bonding. These strong forces also lead to close packing of chains and
thus impart crystalline nature. The examples are polyamides (nylon 6, 6), polyesters
(terylene), etc.
2. Thermoplastic polymers
These are the linear or slightly branched long chain molecules capable of repeatedly
softening on heating and hardening on cooling. These polymers possessintermolecular forces of attraction intermediate between elastomers and fibres.
Some common thermoplastics are polythene, polystyrene, polyvinyls, etc
3. Thermosetting polymers
These polymers are cross linked or heavily branched molecules, which on heating
undergo extensive cross linking in moulds and again become infusible. These cannot
be reused. Some common examples are bakelite, urea-formaldehyde resins, etc.
Polymers of Commercial Importance
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y p
The fracture strengths of polymeric materials are low relative to those of metals and
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ceramics. As a general rule, the mode of fracture in thermosetting polymers (heavily
cross linked networks) is brittle (curve B). The behaviour for a plastic material, curve B, is
similar to that for many metallic materials; the initial deformation is elastic, which is
followed by yielding and a region of plastic deformation. Finally, the deformation displayedby curve C is totally elastic; this elasticity is displayed by a class of polymers termed the
elastomers.
The influence of temperature on the
stressstrain characteristics of
poly(methyl methacrylate)
The stressstrain behaviour for brittle,
plastic, and highly elastic polymers.
CERAMICS
The word Ceramic is derived from a Greek word keramikos which means burnt
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The word Ceramic is derived from a Greek word keramikos which means burnt
earth. In traditional ceramics (untill mid of 21st century), the primary raw material was
clay. The products considered in traditional ceramics are china-ware, porcelain, bricks,
tiles, and, in addition, glasses and high-temperature ceramics. But industrial ceramics
(or advanced ceramics ) are non-metallic inorganic materials, including metal oxides,borides, carbides, and nitrides as well as complex mixture of these materials.
Because most of the ceramics are composed of at least two elements, and often more,
their crystal structures are generally more complex than those for metals.
Ceramics can be crystalline, amorphous or mixture of both. Crystalline ceramics
have a characteristically brittle behaviour.
The atomic bonding in ceramics ranges from purely ionic to totally covalent; many
ceramics exhibit a combination of these two bonding types, the degree of ionic
character being dependent on the electro-negativities of the atoms.
For those ceramic materials for which the atomic bonding is predominantly ionic, the
crystal structures may be thought of as being composed of electrically charged ionsinstead of atoms.
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GENERAL PROPERTIES OF CERAMICS
High Youngs Modulus and high melting points(Strong bonds (covalent and /or ionic))
Limited electrical and thermal conductivity Low thermal shock resistance (Coefficients of thermal expansion and thermal
conductivity are low)
Refractory (Stability at high temperature (NO CREEP))
Resistance to oxidation/corrosion (Chemical stability)
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Glass
1. Based on SiO2 + additives
Traditional Ceramics
1. Porous ceramics (bricks, pottery, china)
2. Compact ceramics (porcelain, earthware)
3. Refractory ceramics (SiC, Al2O3, ZrO2, BeO, MgO).
Industrial / Advanced Ceramics
1. Magnetic Ceramics
2. Electronics (Piezoelectric, capacitor dielectric, spark plugs and Ferroelectrics)
3. Electro-optics: LiNbO3
4. Abrasive ceramics: nitrides and carbides Si3N4, SiC
5. Superconductive ceramics ( yttrium barium copper oxide ceramic, YBa2Cu3O7)6. Biomaterials : Hydroxyapatite
7. Automotive ceramics
8. Nuclear Ceramics
9. Tribological ceramics (resistant to wear and friction)
Alumina (Al2O3) is used in applications where a material must operate at hightemperatures with high strength. Alumina is also used as a low dielectric constant
substrate for electronic packaging that houses silicon chips One classic application is
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substrate for electronic packaging that houses silicon chips. One classic application is
insulators in spark plugs. Some unique applications are being found in dental and
medical use.
Diamond (C) is the hardest naturally occurring material. Industrial diamonds are used
as abrasives for grinding and polishing. It is, of course, also used in jewelry.
Silica (SiO2) is probably the most widely used ceramic material. Silica is an essential
ingredient in glasses and many glass-ceramics. Silica-based materials are used in
thermal insulation, refractories, abrasives, as fiber-reinforced composites, and laboratory
glassware. In the form of long continuous fibers, silica is used to make optical fibers for
communications. Powders made using fine particles of silica are used in tires, paints,
and many other applications.
Silicon carbide (SiC)provides outstanding oxidation resistance at temperatures even
above the melting point of steel. SiC often is used as a coating for metals, carbon-
carbon composites, and other ceramics to provide protection at these extreme
temperatures. SiC is also used as an abrasive in grinding wheels and as particulate and
fibrous reinforcement in both metal matrix and ceramic matrix composites. It is also usedto make heating elements for furnaces.
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Silicon nitride (Si3N4) has properties similar to those of SiC, although its oxidation
resistance and high temperature strength are somewhat lower. Both silicon nitride and
silicon carbide are likely candidates for components for automotive and gas turbineengines, permitting higher operating temperatures and better fuel efficiencies with less
weight than traditional metals and alloys.
Titanium dioxide (TiO2) is used to make electronic ceramics such as BaTiO3. Fine
particles of TiO2 are used to make suntan lotions that provide protection against
ultraviolet rays.
Zirconia (ZrO2) is used to make many other ceramics such as zircon. Zirconia is alsoused to make oxygen gas sensors that are used in automotives and to measure
dissolved oxygen in molten steels. Zirconia is used as an additive in many electronic
ceramics as well as a refractory material. The cubic form of zirconia single crystals is
used to make jewelry items.
Boron Nitride (BN)Because of excellent thermal and chemical stability, boron nitride
ceramics are traditionally used as parts of high-temperature equipment. Boron nitride
has a great potential in nanotechnology. Nanotubes of BN can be produced that have a
structure similar to that of carbon nanotubes. The carbon nanotubes can be metallic or
semiconducting, whereas a BN nano-tube is an electrical insulator. BN nanotubes are
more thermally and chemically stable than carbon nanotubes which favors them for
some applications.
COMPOSITE MATERIALS
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Composites are produced to give a combination of properties that cannot be attained by
a single material but when two or more materials or phases are used together. A
composite material is a microscopic or macroscopic combination of two or more distinctmaterials with a recognizable interface between them. A common example of a
composite is concrete. It consists of a binder (cement) and a reinforcement (gravel).
Composite materials may be selected to give unusual combinations of stiffness,
strength, weight, high-temperature performance, corrosion resistance, hardness, or
conductivity. Composites highlight how different materials can work in synergy. Materials
that have specific and unusual properties are needed for a host of high-technology
applications such as those found in the aerospace, underwater, bioengineering, and
transportation industries.
The individual materials that make up composites are called constituents. Most
composites have two constituent materials: a binder or matrix, and a reinforcement. The
reinforcement is usually much stronger and stiffer than the matrix, and gives thecomposite its good properties. The matrix holds the reinforcements in an orderly pattern.
Because the reinforcements are usually discontinuous, the matrix also helps to transfer
load among the reinforcements.
In composites , the constituent materials must be chemically dissimilar and separated by
a distinct interface.
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1STCLASSIFICATION OF COMPOSITE MATERIALSComposite materials can be classified in different ways. One of the classification systemfor composite materials is based on the matrix phase. We list the classes here:
1. Metal Matrix Composites (MMCs) include mixtures of ceramics and metals, such as
cemented carbides and other cermets, as well as aluminium or magnesium
reinforced by strong, high stiffness fibers.
2. Ceramic Matrix Composites (CMCs) are the least common category. Aluminum oxide
and silicon carbide are materials that can be imbedded with fibers for improved
properties, especially in high temperature applications.
3. Polymer Matrix Composites (PMCs). Thermosetting resins are the most widely used
polymers in PMCs. Epoxy and polyester are commonly mixed with fiberreinforcement, and phenolic is mixed with powders. Thermoplastic moulding
compounds are often reinforced, usually with powders
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Composites can also be placed into following three categories based on reinforcing
materials: particle-reinforced, fiber-reinforced, and structural composites based on theshapes of the materials. Concrete, a mixture of cement and gravel, is a particulate
composite; fibreglass, containing glass fibres embedded in a polymer, is a fibre-
reinforced composite; and plywood, having alternating layers of wood veneer, is a
laminar composite.
2 CLASSIFICATION OF COMPOSITE MATERIALS
PARTICLE-REINFORCED COMPOSITES
In particle-reinforced composites, particles of distinct materials are embedded together
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to form the composite. The particulates can be large particles (such as gravels, as in
case of concrete) or very small particles (< 0.25 microns). Thus large-particle
composites and dispersion-strengthened composites are the two sub classifications of
particle-reinforced composites.
Large-Particle Composites: In large particle composites, particlematrix interactions is
not treated on the atomic or molecular level. Here the matrix refers to the bonding
medium which is continuous and surrounds the other phase. The degree of
reinforcement or improvement of mechanical behaviour depends on strong bonding at
the matrixparticle interface. A very common large-particle composite is concrete, which
is composed of cement (the matrix) and sand and gravel (the particulates).
Dispersion-Strengthened Composites: For dispersion-strengthened composites,
particles are normally much smaller, with diameters between 0.01 and 0.1 mm (10
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