non metallic particles

8/10/2019 non metallic particles

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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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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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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



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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.



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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)



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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.


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


attacked by basic slags.

Examples: Magnesite, Dolomite,

Chrome magnesite, etc


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REFRACTORIES

Neutral refractories


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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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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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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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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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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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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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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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.

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non metallic particles