Chapter 12: Ceramics

Question 1

Ceramics

Answer 1

Metal–nonmetal compound with covalent and/or ionic bonding. Usually a metallic oxide, carbide, nitride, fluoride, boride, or sulfide.

Question 2

Ceramic properties ()

Answer 2

Stiff and brittle, hard (wear resistant), lightweight, corrosion resistant (chemically inert), high melting point (strong primary bonds). Electrical insulators. Creep at higher temperatures than metals and only under compression.

Question 3

Sintering

Answer 3

Densification of powder at a high temperature (lower than Tm) by reducing the surface area. Part becomes densified and has higher strength and very little porosity.

Question 4

Powder processing steps for crystalline or glass ceramics (6)

Answer 4

1. Grinding
2. Consolidation
3. Green forming
4. Binder removal
5. Sintering
6. Hot isostatic pressing

Question 5

Grinding

Answer 5

Grind raw materials to produce a fine particle size. This is raw powder.

Question 6

Consolidation

Answer 6

Mixing powder with polymeric binders.

Question 7

Green forming

Answer 7

Pressing, extruding, injection molding powder into a desired shape. The added polymers liquefy and hold the ceramic particles close together.

Question 8

Green compact

Answer 8

Low strength and low density shaped powder.

Question 9

Binder removal

Answer 9

Slowly heating a green compact to burn out the binder

Question 10

Hot isostatic pressing

Answer 10

Heat treatments to remove internal closed porosity. Heated at a high pressure temperature to deform the grain structure and close pores.

Question 11

Cementation

Answer 11

Chemical reaction to form a hard ceramic.

Question 12

Portland cement

Answer 12

Mix of clay and lime bearing calcinated to 1400°C. Primary constituents: tri-calcium silicate and di-calcium silicate.

Question 13

Hydration of cement

Answer 13

Produces a paste which sets and hardens (forms).

Question 14

Packing of ceramics

Answer 14

Less dense than metals, because neither covalent nor ionic bonds produce close packing.

Question 15

Brittleness of ceramics

Answer 15

Brittle in tension since there is no dislocation motion to accompany stress increases around flaws (with ionic or covalent bonding dislocation motion is very difficult). Strong in compression.

Question 16

Corrosion of ceramics

Answer 16

Resist oxidation and be more chemically stable and have high melting point.

Question 17

Hardness of ceramics

Answer 17

Often hard, since ionic and covalent bonds tend to be slightly stronger than metallic

Question 18

Brittle fracture rule

Answer 18

The larger the volume of sample being tested, the lower its flexural strength. There is a greater probability of finding a critical flaw in a larger volume of material.

Question 19

Ion exchange

Answer 19

Process by which large ions are placed into the surface structure of a glass by immersing the glass in a chemical solution at elevated temperature; resulting in a stronger, thinner, tougher, higher damage tolerant glass.