1. Ceramic and Polymer Materials
Chapter-7 (Unit III)
Ceramic and Polymer Materials
An overview of ceramic materials.
Mechanical and thermal properties of ceramics
An overview of polymeric materials, thermoplastics and thermosets, elastomers.
Engineering applications of ceramic and polymer materials.

2. Ceramic Materials
Ceramic materials are inorganic, nonmetallic materials that consist of metallic and nonmetallic elements bounded together primarily by ionic/or covalent bonds. The chemical compositions of ceramic materials vary considerably, from simple compounds to mixture of many complex phases bounded together.

3. Properties of ceramic materials
The properties of ceramic materials also vary greatly due to differences in bonding. In general, ceramics materials are typically hard and brittle with low toughness and ductility.
Ceramics are usually good electrical and thermal insulators because of the absence of conduction electrons.
Ceramic materials normally have relatively high melting temperatures and high chemical stability.

4. Engineering ceramic compounds (or Materials)
Formula
Melting point °C
Hafnium carbide
Hfc
4150
Titanium carbide
TiC
3120
Tungsten carbide WC
2850
Magnesium oxide
MgO
2798
Zirconium dioxide
ZrO2
2750
Silicon Carbide
SiC
2500
Boron Carbide
B4C3
2450
Aluminium oxide
Al2O3
2050
Silicon Nitride
Si3N4
1700

5. Processing of ceramics
Most engineering ceramic products are manufactured by compacting powders or particles into shapes that are subsequently heated to a high enough temperature to bond the particles together.
The basic steps in the processing of ceramics by agglomeration of particles are;
Material preparation
Forming or casting
Thermal treatment.

6. 1. Material preparation
The most ceramic products are made by the agglomeration of particles. The raw material for these products vary, depending on the required properties of finished ceramic part.
The particles and other ingredients such as binders and lubricants may be blended wet or dry.
For example: high alumina (Al2O3) blended with water and ‘wax’ as binders to form pallets.

7. 2. Forming
Ceramic products made by the agglomeration of particles may be a variety of methods in the dry, or liquid conditions. Forming, extrusion are commonly used methods for forming.

8. 3. Thermal Treatment
The thermal treatment is the essential step in the manufacture of most ceramic products. The following steps are followed in thermal treatment;
Drying and binder removal
Sintering : the process by which small particles of material are blended together by the solid-state diffusion is called sintering. In ceramic manufacturing this thermal treatment results in the transformation of porous material into dense, coherent product. In the sintering process, particles are coalesced by solid state diffusion at high temperature but below the melting point of compound being sintered.
Ex: The alumina spark plug insulator, is sintered at 1600°C ( the melting point of alumina is 2050°C). In sintering atomic diffusion takes place between the coating surfaces of the particles so’ that they become chemically bounded together.

10. Mechanism of plastic deformation in ceramic materials
The lack of plasticity in crystalline ceramics is due to their ionic and covalent chemical bonds. In metals, plastic flow takes place by the movement of dislocations in the crystal structure over special crystal slip planes.
In covalently bounded ceramics, the bonding between atoms is specific and directional, involving the exchange of electrons between pairs of electrons. Thus, when covalent crystals stressed to a high extent, they exhibit brittle fracture due to separation of electrons without subsequent deformation.

11. Factors affecting the strength of ceramic materials.
The mechanical failure of ceramic materials occurs mainly from structural defects, the principle sources of fracture in ceramic polycrystals include surface cracks produced during surface finishing, voids (porosity), inclusions, and large grains produced during processing.
Flaws in processed ceramics may also be critical in determining the fracture strength of ceramic material. A large flaw may be the major factor affecting the strength of a ceramic.

12. A Cermet is a composite material composed of ceramic (cer) and metallic (met) materials.
A cermet is ideally designed to have the optimal properties of both a ceramic, such as high temperature resistance and hardness, and those of a metal, such as the ability to undergo plastic deformation. The metal is used as a binder for an oxide, boride, or carbide. Generally, the metallic elements used are nickel, molybdenum, and cobalt. Depending on the physical structure of the material, cermets can also be metal matrix composites, but cermets are usually less than 20% metal by volume.

14. Applications SiAlON Ceramics – Uncoated and Coated
Silicon Nitride Ceramics –  Uncoated and Coated
The proven performance standard for efficient machining with indexable inserts made of ceramic cutting materials.
Inserts of ceramic cutting materials. Designed specifically for high-performance machining of cast iron materials.

15. Applications
CBN indexable inserts (polycrystalline cubic boron nitride) for efficient machining of cast iron materials and steels for turning, milling, boring and grooving.
Cermets Indexable inserts with very high hardness and wear resistance. An excellent cutting material for finishing in continuous cutting, for medium machining with minimally interrupted cutting and for grooving steel parts.

16. Thermoplastics
Thermoplastics - reversible in phase by heating and cooling. Solid phase at room temperature and liquid phase at elevated temperature.
Thermo plastics require heat to make them formable and after cooling, retain the shape they were formed into new shapes a number of times without significant change in properties. Most thermoplastics consists of very long main chains of carbon atoms covalently bonded together.
Ex; Polyethylene, Polypropylene, ABS, Nylon, PVC

17. Processing of Thermo plastics
Injection molding

18. 2. Extrusion Process

19. Injection orientation stretch blow molding (ISB)
Polyethylene Terephthalate (PET)
High density polyethylene (HDPE)
Polypropylene (PP)

20. Injection blow molding (Thermoforming)

21. Thermosetting plastics
Thermosetting plastics formed into a permanent shape and cured or set by chemical reaction cannot be reformed into another shape but degrade or decompose upon heating to a high temperature. Thus ,thermosetting plastics cannot be recycled.
Thermosets - irreversible in phase by heating and cooling. Change to liquid phase when heated, then follow with an irreversible exothermic chemical reaction. Remain in solid phase subsequently.
Epoxies;
Phenolics;
Polyesters;
Polyurethanes

22. Processing of Thermo setting plastics
Compression molding

23. 2. Transfer molding

24. Sheet molding compound (SMC)

25. Sheet molding compound (SMC) part

26. Elastomers: Elastomers or rubbers, are polymeric materials
Elastomers: Elastomers or rubbers, are polymeric materials. Whose dimensions can be changed greatly changed when stressed and which return to their original dimensions (or almost) when the deforming stress is removed.
Synthetic rubbers
butadiene rubber;
butyl rubber;
chloroprene rubber;
ethylene-propylene rubber;
isoprene rubber;
nitrile rubber;
polyurethanes;
silicones;
styrene-butadiene rubber;
thermoplastic elastomers.