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Ceramic, Polymer and Composite Materials

What is Ceramic Materials?

Inorganic and non-metallicmaterials (mostly oxide ofvarious metals)

Bonding is either ionic orcovalent

Brittle in nature, goodcorrosion and wearresistance.

Widely used for householditems, electronics, electrical,communication, tools, aswell as in many otherindustrial uses.

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Crystal Structures of Ceramic Materials

Compared to metallic materials, crystal structures ofceramic materials are more complex. Anions give

main structure, cations sit at convenient positions.

Other Examples: MgO, MnS, LiF, FeO Other Examples: ZnTe, SiC, etc 2


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Phase Diagrams: Ternary Phase Diagrams

SS: Solid solution, Mullite: Intermediate compound of silica and alumina

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Glasses

Non-crystalline ceramics

Composed of various types of metallic oxides (mainly)Used for household containers, window, lenses, fibre glass, etc.

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Better mechanical properties, low thermal expansion andshocks, high temperature properties, better biocompatability.

Good dielectric properties.

Widely used as ovenware, tableware, oven window, electrnicpackaging industries.

As substrate for printed circuit boards, heat exchangers, etc.

Properties and Uses of Glass-Ceramics

Ceramics: Clay Products

Main ingredient is natural clay. It is mixed with water and otheringredients to have a good plastic mass easy for shaping.

After shaping, the product is dried, fired, glazed and so on.

Main product groups are structural products (bricks, tiles,sewer pipes) and whitewares (uses ???). 7


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Ceramics: Refractory Products

High melting point materials inert to decoposition at hightemperature, good thermal insulating property.

Mostly inert at severe environment at high temperature.

Wide variety of product, but main product is brick.

Mainly used as furnace lining in steel and power generationindustries, glass factories, heat treatment furnaces, etc.

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Special Refractories

Very high purity oxide with very little porosity.

Main groups are alumina (tube furnace), magnesia (tubefurnace and other engineering products), beryllia, zirconia,silicon carbide (heating elements in furnaces), carbon andgraphites (crucible for furnace), etc.

Ceramics: Abrasive Products

Abrasive ceramics are used to wear or cut away of othermaterials. Diamond, alumina, SiC, WC, silica sand, etc.

Uses: Grinding, polishing or lapping wheels.

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Cements: Mixture of Ceramic Materials

Cements: Several commercial products as cement, plaster ofparis, lime, etc.

Special behaviours: When mixed with water they form paste,subsequently set and harden to form a rigid load bearingcomponent. Here no firing is needed.

Might be mixed with other component as bricks, sand, stone,etc. as per requirements.

Very common cement is the portland cement, which is amixture of clay and lime bearing component (lime stone). Themixture is calcined and then ground.

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Advanced Ceramics

Microelectromechanical System (MEMS)

It is mechanical device composed of several electricalcomponents on silicon substrate. All components are inmicrometer dimensions.

Mechanical Components: Microsensors and microactuator.Microsensors collect mechanical, thermal, chemical, opticaland magnetic information.

Microactuator then responses as positioning, moving, filtering,pumping, etc.

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Optical Fibre

Made of high purity silica, free from minute levels of contaminants.

Fully defect free that can absorb, scatter or attenuate light beam.

Needs very advanced and high quality processing technique.

Optical Fibre in Communication

In metallic wire signal transfer is electronic, whereas in OF it iseletromagnetic or light radiation.

For simultaneous 24,000 telephone calls if we need 33 tons ofcopper, then optical fibre it is possible from 0.1kg of OFmaterials.

Diameter of OF is 5 to 100 micrometer.12


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Ceramic Ball Bearing

In past beraing metals which are hard, strong, corrosion

resistant were used to make ball and race components.

Recently, Si3N4 has replaced many metallic components.

Silicon nitride is inferior interms of tensile strength, so in manycases ceramic balls and steel races are used in combination.This combination is known as hybrid bearing.

Silicon nitride is lighter (density 3.3) compared to steel (7.84).So, hybride ball-bearing is lighter.

The modulus of elasticity of silicon nitride is 320 GPa, which is200 GPa for steel. So, hybrid ball bearing is resistant to 30-40%higher speed compared to that of steel ball bearing system.

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Polymeric Materials

It is one type of hydrocarbon. Two gross categories: Natural andsynthetic.

Natural: Wood, rubber, wool, cotton, leather, silk, etc.

Synthetic: Synthetically produced, wide varieties, superior tonatural one.

Saturated Polymer: Where double or triple covalent bond exists.

Saturated: When elements have single bond. For further entry ofatom, one bonded atom must be replaced, as methane, ethane.

Ethylene Acetylene

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Isomerism

Same composition with different atomic arrangement, butane.

Isobutane

Normal Butane

Molecular Structures of Polymers

Linear Polymers: Here repeat unitis joined together end to end.Extensive Van der Waals bond iseffective, very flexible, e.g. PE,PVC, PS, nylon, etc.

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Branched Polymers

Besides end to end chains, side chains are also formed due tochange in synthesis parameters.

Side chain formation reduces the density. Example: LDPE.

Crosslinked Polymers

Adjacent linear chains are joined by covalent bonds at variouslocations.

This is done by adding foreign atoms or molecules. Example:Most of rubber is crosslinked in this way called vulcanization.

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Network Polymers

Heavily crosslinked polymer is called network polymer.High temperature and good mechanical properties. Epoxy,phenol-formaldehyde, etc.

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Thermoplastic and Thermoset Polymers

Thermoplastic Polymers

Polymers which soften and liquefy on heating and solidify andharden on cooling.

Most linear and branched polymers are thermoplastic. Generallysoft and recyclable. PE, PVC, PS, PP, etc.

Thermosetting Polymers

Becomes permanently hard during processing and do notsoften on heating Epoxy, phenol-formaldehyde, polyester, etc.

10-50% bonds are branched. Stronger than thermoplasticpolymers, better thermal and dimensional stability.

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Copolymers

For better service properties two or more polymers aresynthesized together.

May be various types, in general four types.

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Applications of Various Polymeric Materials (Plastic)

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Elastomers

It has ability to be deformed to a large extent and can elasticallyspring back during unloading because of crosslink driving force.

To be elastomers polymers must be amorphous, chain bondrotation must be of free movement type, delayed onset ofplasticity.

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Composite Materials

Composite is a multi-phase material, where each constituentphases contribute for required combination of unusualproperties.

Examples: 1. Pearlite composed of very hard and brittlecementite and very soft and ductile ferrite. TS of cementite is5000psi and for ferrite it is 40000psi. TS of peralite is 120,000psi,

where a synergism is operative which difficult to explain.

In the present state composite is artificially made.

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Matrix phase is continuous and surrounds the filler/reinforcingphase(s).

Depending on required properties, reinforcing phases might be ofdifferent shape, size, spatial distribution to fulfill the target.

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Classification of Composites

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Large Particle Reinforced Composites

Fiber Reinforced Composites

For better property combination criticallength of fiber is important.

Critical length depends on diameter, tensileand shear strength of the fiber.

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Deformation Pattern in Fiber Reinforced Composites

Continuous Fiber : When L = 15Lc

Continuous, discontinuos andrandomly oriented fibers

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Importance of Critical Length of Fiber in Composite

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Stress-strain Curves of Composite with DuctileMatrix and Brittle Fiber

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Elastic Behaviour in Longitudinal Loading

In the longitudinal direction

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Fiber and Matrix Phases of Composite

Various materials of different shape, size, distribution andconcentration.

Matrix Phases might be metallic, ceramic or polymeric. Dependingon matrix phases composites are named as MMC, CMC or PMC.

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