CERAMICS

Taxonomy of Ceramics

Glasse Clay Refractorie Abrasives s product s -optical s -whiteware -bricks for -sandpaper -composite -bricks high T -cutting reinforce (furnaces -polishin ) -containers/ Adapted from Fig. 13.1 and discussion in Section 13.2-6, Callister 7e. g household

Cements Advanced ceramic

-composites engine -structura -rotors s l -valves -bearings

• Properties: -sensors -- T for glass is moderate, but large for other ceramics. m -- Small toughness, ductility; large moduli & creep resist. • Applications: -- High T, wear resistant, novel uses from charge neutrality. • Fabrication -- some glasses can be easily formed -- other ceramics can not be formed or cast. Ceramic Bonding

• Bonding: -- Mostly ionic, some covalent. -- % ionic character increases with difference in electronegativity (remember!?!).

• Large vs small ionic bond character: CaF2: large SiC: small Characteristics of Ceramics Low density compared to metals High melting point or decomposition temperature High hardness and very brittle High elastic modulus and moderate strength Low toughness High electrical resistivity Low thermal conductivity High temperature wear resistance Thermal Shock resistance High corrosion resistance In crystalline ceramics the crack propagation is usually through the grains (transgranular) and along specific crystallographic (or cleavage) planes, which are planes of high atomic density

Main drawback is brittleness and low toughness SPECTRUM OF CERAMICS USES

8 CLASSIFICATION OF CERAMICS

Oxides

CERAMICS Nonoxides

Composite

• Oxides: Alumina, zirconia

• Non-oxides: Carbides, borides, nitrides, silicides

• Composites: Particulate reinforced, combinations of oxides and non-oxides

9 CLASSIFICATION OF CERAMICS

• Oxide Ceramics:

Oxidation resistant

chemically inert

electrically insulating

generally low thermal conductivity

slightly complex manufacturing

low cost for alumina

more complex manufacturing

higher cost for zirconia. zirconia 10 CLASSIFICATION OF CERAMICS

• Non-Oxide Ceramics:

Low oxidation resistance

extreme hardness

chemically inert

high thermal conductivity

electrically conducting

difficult energy dependent Silicon carbide cermic foam filter (CFS) manufacturing and high cost.

11 CLASSIFICATION OF CERAMICS •Ceramic-Based Composites: Toughness

low and high oxidation resistance (type related)

variable thermal and electrical conductivity

complex manufacturing processes

high cost. Ceramic Matrix Composite (CMC) rotor

12 CLASSIFICATION OF CERAMICS

13

CLASSIFICATIONS OF CERAMICS

amorphous

CERAMICS crystalline

• Amorphous

the atoms exhibit only short-range order

no distinct melting temperature (Tm) for these materials as there is

with the crystalline materials

Na20, Ca0, K2O, etc

Amorphous silicon and thin film PV cells

53 CLASSIFICATIONS OF CERAMICS • Crystalline

atoms (or ions) are arranged in a regularly repeating pattern in three dimensions (i.e., they have long-range order)

Crystalline ceramics are the

“Engineering” ceramics

– High melting points

a ceramic (crystalline) and a glass (non-crystalline)

– Strong

– Hard

– Brittle 54 GENERAL COMPARISON OF MATERIALS

Property

Hardness

Elastic modulus

Ceramic

Very High

Very High

Metal Polymer

Low Very Low

High Low

Thermal expansion High

Wear resistance High

Corrosion resistance High

Low Very Low

Low Low

Low Low

55 GENERAL COMPARISON OF MATERIALS

Property

Ductility

Density

Ceramic

Low

Low

Metal Polymer

High High

High Very Low

Electrical conductivity Depends High Low on material

Thermal conductivity Depends High Low on material

Magnetic Depends High Very Low on material

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