1. Applications and Processing of Ceramics
Chapter Outline:
Applications and Processing of Ceramics
Chapter 13: Applications and Processing of Ceramics
Short review of glass/ceramics applications and processing ( ,13.8,13.10)

2. Formation and processing of Ceramics
Ceramic materials have relatively high melting temperature and are brittle  strain hardening cannot be applied
Some ceramics formed by powder pressing. involve drying and firing,…
Sintering: powder pressing + firing below melting T
Cements formed from a fluid paste that hardens by chemical reactions
Glasses produced by complete melting of raw ingredients

3. Applications of Ceramics
Compressive strength is typically ten times tensile strength.
Transparency to light  optical applications (windows, photographic cameras, telescopes, etc)
Good thermal insulation  ovens, exterior tiles of the Shuttle orbiter, etc.
Good electrical isolation  used to support conductors in electrical and electronic applications.
Good chemical inertness  applications in reactive environments.

4. Silicate Glasses
Non-crystalline silicates (SiO2) containing other oxides (CaO, NaO2, K2O, Al2O3)
Containers, windows, lenses, fiberglass, etc.
Example:
Container/window glasses contain
~ 30 wt% oxides (CaO, Na2O)
whose cations are incorporated within SiO4 network: network modifiers.
Quartz sand + soda ash or limestone

5. Properties of Glasses (I)
Solidification is gradual, through a viscous stage (viscosity increasing with decreasing T) without a clear melting temperature
Specific volume (1/density) does not have abrupt transition at fixed temperature. Shows a change in slope at the glass-transition temperature

6. Viscosity (from Chapter 12)
Viscosity: a measure of non-crystalline (glass or liquid) material’s resistance to deformation
High-viscosity fluids resist flow;
low-viscosity fluids flow easily.
Viscosity: How readily a moving layer of fluid drags adjacent layers along with it.
Units are Pa-s: Poises (P) 1 P = 0.1 Pa-s
Viscosity of water at room temp is ~ 10-3 P
Viscosity of typical glass at room temp >> 1016 P

7. Properties of Glasses (II)
Important temperatures(viscosity) in glass
Melting point: viscosity = 100 P, below this viscosity (higher T) glass is liquid
Working point: viscosity = 104 P, glass is easily deformed
Softening point: viscosity = 4107 P, maximum T at which a glass piece maintains shape for a long time
Annealing point: viscosity = 1013 P, relax internal stresses (diffusion)
Strain point: viscosity = 3x1014 P, above this viscosity, fracture occurs before plastic deformation
Glass forming operations occur between softening and working points

8. Properties of Glasses (II) Important temperatures in glasses
can be defined by viscosity

9. Heat treatment of Glasses
Annealing: elevate temperature to remove thermal stresses resulting from inhomogeneous temperatures during cooling (similar to annealing of metals)
Tempering: heating glass above glass transition temperature but below softening point; then quench in an air jet or oil bath.
The interior: cools later than outside, tries to contract while in a plastic state after exterior has already become rigid. Causes residual compressive stresses on surface and tensile stresses inside.
In fracture: crack has to overcome residual compressive stress, making tempered glass less susceptible to fracture. Used in automobile windshields, glass doors, eyeglass lenses, etc.

10. Glass transition temperature Melting point (glass)
Summary
Make sure you understand language and concepts:
Glass tempering
Glass transition temperature
Melting point (glass)