Ceramics

1. Ceramics • Mixture of metallic and non-metallic elements (clay products). • Traditional: whiteware, tiles, brick, sewer pipe, pottery, and abrasive wheels. • Industrial (fine ceramics): turbine, automotive, aerospace components, heat exchangers, semiconductors, seals, cutting tools.

2. Ceramic Applications • Electronic insulators • Engine components • Machining tools • Porcelain • Bioceramics for prosthetics

3. Structure of Ceramics • The structure of ceramic crystals is among the most complex of all materials. • Contain various elements. • Covalent bonding (electron sharing), stronger than metals. • Hardness, thermal, and electrical resistance higher than metals. • Finer the grain size, higher strength and toughness.

4. Ceramic Materials • Clay (kaolin): silicate of aluminum. • Flint: fine-grained silica. • Feldspar: aluminum silicates, potassium, calcium/sodium.

5. General Properties of Ceramics • Mechanical Properties • Much stronger in compression vs. tension (one magnitude difference) • Sensitive to cracks, impurities, porosity • Lack toughness, ductility, are brittle and strong • static fatigue failure (load over a period of time)- similar to stress-corrosion cracking. • pre-stressing (compressing) increases resistance to breakdown from tensile stress.

6. General Properties of Ceramics • Physical Properties • low specific gravity/density. • low thermal conductivity (porosity – air is poor conductor). • low thermal expansion. • resistance to wear. • Alloying With metallic elements can cause ceramics to conduct

7. Types of Ceramics • Oxide Ceramics • Alumina • most widely used • high temperature applications • Electrical, thermal insulation, cutting tools • Zirconia • high toughness/strength • resistance to thermal shock, wear, and corrosion. • low thermal conductivity, friction coefficient. • Engine components

8. Ceramic Knife (Zirconia) (global.kyocera.com)

9. Other Types of Ceramics • Carbides • tungsten, titanium, and silicon carbide. • Silicon is an abrasive • Grinding wheels, cutting tools • Nitrides • cubic boron nitride, titanium nitride, and silicon nitride. • Grinding and cutting tools, turbine engines, bearings, sand-blast nozzles

10. Other Types of Ceramics (Cont.) • Sialon • silicon nitride and aluminum oxide, yttrium oxide, titanium carbide. • Higher strength and thermal-shock resistance than silicon nitride • Cutting tools • Cermets • ceramics bonded with metallic elements. • cutting tools/high temperature applications.

11. Silica • Polymorphic material (different crystal structures) • Quartz • Most glasses are 50% silica • Silicates- reaction of silica and oxides of al, mg, fe, etc. (clay, asbestos, mica, and silicate glasses)

12. Glasses • Amorphous solid (structure of a liquid) • No specific freezing or melting point • Cooled at a rate too high for crystals to form (supercooled). • All glasses contain at least 50% silica.

13. Glass Applications • Containers • Windows • Cookware • Fiber Optics • Monitors • Lighting

14. Glass Properties • Brittle, hard • Resistant to chemicals and corrosion • Low thermal conductivity and expansion. • Dielectric properties. • Reflection, refraction, absorption. • Static Fatigue

15. Glass Ceramics • High crystalline structure • Stronger than glass • Shaped first and heat treated • devitrification or recrystallization of glass.

16. Graphite • Crystalline form of carbon, having a layered structure. • solid lubricant, low friction properties. • brittle in nature. • strength and stiffness increases with temperature.

17. Diamond • Hardest substance known • Synthetic (or industrial) • lacks impurities which natural diamonds might have. • electrical conductivity is 50 times higher than natural diamonds (heat sinks)

18. Topic Support • Kyocera- http://americas.kyocera.com/kicc/index.cfm • http://kyoceraadvancedceramics.com/index.html • http://www.ceramics.org/