material engineering all slides me

8/13/2019 Material Engineering All Slides ME

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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 nontoxic and un-reactive with

beverages. In addition, each material has its pros and cons.

WHAT IS MATERIALS ENGINEERING?Lecture Notes By Dr Tanweer Hussain


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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.


L t N t B D T H i


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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


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


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.


OLecture Notes By Dr Tanweer Hussain


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Wrought

IronPig Iron

Iron OreLecture Notes By Dr Tanweer Hussain



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Conventional Blast Furnace


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.

Crucible ProcessLecture Notes By Dr Tanweer Hussain


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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.

Electric FurnaceLecture Notes By Dr Tanweer Hussain


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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.

Kaldo Process: Lecture Notes By Dr Tanweer Hussain


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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.

2. ROASTINGLecture Notes By Dr Tanweer Hussain


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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

Stress-Strain Behaviour of PolymersLecture Notes By Dr Tanweer Hussain


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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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