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.

Ceramic Applications

• Electronic insulators

• Engine components

• Machining tools

• Porcelain

• Bioceramics for prosthetics

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.

Ceramic Materials

• Clay (kaolin): silicate of aluminum.

• Flint: fine-grained silica.

• Feldspar: aluminum silicates, potassium,

calcium/sodium.

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.

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

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

Ceramic Knife (Zirconia)

(global.kyocera.com)

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

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.

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)

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.

Glass Applications• Containers

• Windows

• Cookware

• Fiber Optics

• Monitors

• Lighting

Glass Properties

• Brittle, hard

• Resistant to chemicals and corrosion

• Low thermal conductivity and expansion.

• Dielectric properties.

• Reflection, refraction, absorption.

• Static Fatigue

Glass Ceramics

• High crystalline structure

• Stronger than glass

• Shaped first and heat treated

• devitrification or recrystallization of glass.

Graphite

• Crystalline form of carbon, having a

layered structure.

• solid lubricant, low friction properties.

• brittle in nature.

• strength and stiffness increases with

temperature.

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)

Topic Support• Kyocera-

http://americas.kyocera.com/kicc/index.cfm

• http://kyoceraadvancedceramics.com/index.html

• http://www.ceramics.org/