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NON-METALLIC
MATERIALS
MATERIALS SCIENCE
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NON-METALLIC MATERIALS
1. CERAMICS
2. REFRACTORIES
3. GLASSES
4. POLYMERS
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CERAMICS
DEFINITION
Ceramic materials are complex
compounds and solutions containingboth metallic and non-metallicelements, which are having ionic orcovalent bonds.
Examples: Bricks, Refractories,Glass, Tableware, etc.
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CERAMICS
Bonding and structure
Properties of ceramic materials
Ceramic processing
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BONDING AND STRUCTURE
Completely ionic,
Completely covalentand
Combination of both ionic and
covalent bonding.
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BONDING AND STRUCTURE
For ionic crystals the crystal
structure is influenced by two
factors:
i. The magnitude of the electrical
charge on each of the componention (because the crystal to be
neutral all the +ive charge should
balance the no. of ivecharge)
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BONDING AND STRUCTURE
ii. The ionic radius ratio (rc/ra) of cat-
ion(rc)and anion(ra) (because eachcation prefer to have as many
nearest neighbor anion as
possible)
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2 0 0
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6 0.414 0.414 rc/ra< 0.732
8 0.732 0.732 rc/ra< 1
( octahedral)
( cubic)
12 1.0 rc/ra= 1 FCC or HCP
BONDING AND STRUCTURE
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Examples for ionic bonded
structures: Sodium chloride, Cesium
Chloride, Perovskite, etc
For covalent crystals the crystal
structure is influenced by thedirectionality of bonding.
BONDING AND STRUCTURE
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Example for covalently bondedstructure: Diamond cubic
Compare to covalently bondedmaterials Ionic bonded materials
have closed packed structures (because of the directionality ofcovalent bonding)
BONDING AND STRUCTURE
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Example of combined bonding
structure: Zircon (ZrSiO4)
Here there is a covalent bond
between Si and O ( ) and a
ionic bond between this unit and Zrion.
BONDING AND STRUCTURE
4
4SiO
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PROPERTIES
Lower density
High melting temperature
Lower thermal conductivity
Low thermal expansion
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PROPERTIES
Poor electrical conductivity
Good dielectrics
High hardness and brittle
Good inertness towards chemicals
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PROCESSING
Powder preparation
Shape forming process
Densification or sintering
Final machining
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FORMINGPROCESS
1. Die pressing
2. Isostatic pressing
3. Extrusion
4. Slip casting
5. Injection moulding
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DIE PRESSING
Power mixed with organic binders
Filled into the die
Pressure is applied unidirectional
Inexpensive method
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DIE PRESSING
Plunger
Powder
Die
Typical Die pressing setupNEXT
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ISOSTATICPRESSING
Powder mix is loaded into the rubber
mould
Pressed in a hydrostatic moulding
chamber
Density variation is avoided
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EXTRUSION
Stiff plastic mix (powder+binder) is
extruded through an orifice
Used for making materials having an
axis normal to a fixed cross section
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EXTRUSION
Piston
Orifice
Extruded
Component
Powder
mix
Typical setup for ExtrusionNEXT
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SLIP CASTING
Slip (is a suspension of particle in a liquidmedium) is poured into a plaster - of -parries mould
After the drying process the mould isreleased
Slip casting is a simple method and usedto produce complex shapes
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SLIP CASTING
SlipSolid Mass
Plaster Mould
Typical slip casting processNEXT
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INJECTION MOULDING
Plastic mix ( power+ thermoplastic
polymer)is preheated in the barrel of
the injection moulding machine.
The viscous material is forced
through an orifice into a shaped toolcavity.
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INJECTION MOULDING
Piston
Tool Cavity
Orifice
Powder
mix
Typical Injection moulding process
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REFRACTORIES
DEFINITION
Refractories are heat resistant
materials with high meltingtemperature, they are oxides,carbides of Si, Al, Zr, Mg, etc
Examples: SiO2, MgO, CaO, ZrO2,SiC.
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REFRACTORIES
Acid refractories
Basic refractories
Neutral refractories
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REFRACTORIES
Acid refractories
The refractories which are not
attacked by acid slags.
Examples: silica, silicates such as
fire clay, kyanite etc
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REFRACTORIES
Basic refractories
The refractories which are not
attacked by basic slags.
Examples: Magnesite, Dolomite,
Chrome magnesite, etc
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REFRACTORIES
Neutral refractories
The refractories which are not
attacked by acid or basic slags.
Examples: Graphite, Zirconia, Silicon
carbide, etc
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REFRACTORIES
FIRE CLAY REFRACTORIES
Raw material is fire clay (grayish orblackish in colour)
Chemical composition is Al2O3. 2SiO2.2H2O
It should have refractoriness at least1650C and be plastic enough tomanufacture bricks.
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FIRE CLAY REFRACTORIES
USES
Used in all places of ordinary
furnaces.
Also used in glass melting furnaces,
pottery kilns, blast furnaces, etc.
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GLASSES(INORGANIC)
DEFINITION
Glass is a noncrystalline,
metastable material, lacks long rangeorder, which has hardened andbecome rigid without crystallizing.
Example of inorganic glasses: Sodalime glass, fused silica, etc.
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GLASSES(INORGANIC)
Glass transition temperature
Glass composition
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GLASS TRANSITION TEMPERATURE
For any amorphous materials the critical
temperature which separates glassy
behavior from rubbery behavior is calledglass transition temperature (Tg).
Tg can be defined using the volume
change associated with heating orcooling.
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GLASS TRANSITION TEMPERATURE
If the cooling rate is slower enough for
crystallization there will be a volume
change associated with melting point(Tm).
If the cooling rate is fast to prevent
crystallization the volume of the material
follows the slope characteristics of liquideven below melting point(Tm).
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GLASS TRANSITION TEMPERATURE
The liquid present below Tmis calledsuper cooled liquid.
On further cooling of this liquid, at aparticular temperature the slope ofthe curve decreases, and thistemperature is called glasstransition temperature(Tg).
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GLASS TRANSITION TEMPERATURE
Liquid
Crystal
Glass
Super Cooled
Liquid
Tg Tm
SpecificVolume
Temperature
Volume change as a function of temperature
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GLASS COMPOSITIONS
Most of the glasses have:
Silica (SiO2)( major constituent)
Lime (CaO)
Soda (Na2
O)and
Other Oxides like PbO, B2O3, etc.
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GLASS COMPOSITIONS
According to properties oxides aredivided into three types:
Glass (Network) formers
Network modifiers
intermediates
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GLASS COMPOSITIONS
GLASS FORMERS
These oxides forms threedimensional network using itstriangular or tetrahedral units.
Example: SiO2, B2O3, P2O5, V2O3,G2O,etc.
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GLASS COMPOSITIONS
NETWORK MODIFIERS
Oxides incapable of forming a threedimensional network, but break upthe network structure, thus lowers Tmand T
g
.
Example:Na2O, CaO, Y2O3, etc.
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GLASS COMPOSITIONS
INTERMEDIATES
Oxides doesn't form glass by itself
but incorporated in the network
structure of the glass formers.
Example: Pb2O, Al2O3, BeO, TiO2, etc.
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GLASS COMPOSITIONS
TYPICAL GLASS COMPOSITION
1. Fused silica( 99%SiO2)
2. Window glass ( 72%SiO2, 1%Al2O3,10% CaO, 14%Na2O, 2%MgO)
3. Optical flint (50%SiO2, 1%Na2O,19%PbO, 8%K2O, 13%BaO)
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POLYMERS
DEFINITION
POLYMERIZATION MECHANISMS
DEGREE OF POLYMERIZATION
TYPES OF POLYMERS
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POLYMERS
DEFINITION
Polymers are organic materials,
with long chain molecules, having
carbon as the common element in
their makeup.
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POLYMERS
POLYMERIZATION MECHANISMS
Addition polymerization
Condensation polymerization
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ADDITION POLYMERIZATION
Addition polymerization is produced
by covalently joining the individualmolecules, producing chainswithout changing the chemistry ofthe reactants.
No byproduct is produced.
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ADDITION POLYMERIZATION
Reaction is initiated by heat,pressure or a catalyst.
Polymerization is terminated bycollision between the active ends oftwo chains or by addition ofterminator (i.e, free radicals fromcatalyst)
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ADDITION POLYMERIZATION
Chain length is controlled by theamount of initiator(for small amount
of initiator longer chain length due toless amount of terminator)
Example:Production of polyethylenefromethylene ( C2H4)
initiator is Hydrogen peroxide(H2O2)
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ADDITION POLYMERIZATION
H O O H + Ethylene Molecule
H O + H O + Mer
C =C
H H
H H
CC
H H
H H
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ADDITION POLYMERIZATION
H O + H O Initiation of
reaction
Polyethylene
CC
H H
H H
CCH H
H H
CCH H
H H
CCH H
H H
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CONDENSATION POLY
Two or more molecules joined by a
chemical reaction that releases a bi-
product such as water, alcohol, etc.
This mechanism often involves
different monomers as startingmolecules.
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CONDENSATION POLY
Example: Dimethyl terephtalate and
ethylene glycol to producePolyethylene terephthalate (PETpolymer).
By product is methyl alcohol(CH3OH)
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CONDENSATION POLY
H CO C
H
H
O O
C O C
H
H
H
n
C
H
H
C
H
H
O
HH
O
n
+
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CONDENSATION POLY
+
H C
H
H
O
O C
O
C O C
H
H
C
H
H
O H
n
H C
H
H
O H
n
PETPolymer
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CONDENSATION POLY
The length of the polymer chain
depends on the ease with which the
monomers can diffuse to the end andundergo condensation reaction.
Chain growth ceases when no moremonomer reach the end of the chain.
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DEGREE OF POLY
Polymers do not have a fixedmolecular weight, instead have a
range.
The average length of a linearpolymer, or average number ofrepeat unit in the chain is calleddegree of polymerization.
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DEGREE OF POLY
Degree of polymerization
Weight average molecular weight
unitrepeatofweightMolecularpolymerofweightmolecularAverage
iiw MfM
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DEGREE OF POLY
Numberaverage molecular weight
Mi mean molecular weight of ith
range.
fi
weight fraction of the polymer
having chains within ith range.
Xi fraction of the total number of
chains within ith
range.
iin MXM
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TYPES OF POLYMERS
THERMO PLASTICS
THERMOSETTING PLASTICS
ELASTOMERS
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THERMOPLASTICS
Composed of long chains, may or
may not have branches.
Bonded together by weak Vander
walls bonds between chains.
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THERMOPLASTICS
They can be amorphous orcrystalline.
Behave in a plastic, ductile manner.
Processed into shapes by heating toelevated temperatures and can berecycled.
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THERMOSETTINGPLASTICS
Composed of long chains moleculesthat are strongly cross linked.
Stronger, but brittle thanthermoplastics.
They do not melt upon heating butbegins to decompose, hencerecycling is difficult.
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ELASTOMERS
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ELASTOMERS
They are known as rubbers.
Have elastic deformation > 200%
They can be thermoplastics or lightly
cross linked thermosets.
Polymer has coil-like molecules that can
reversibly stretch by applying force.