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Chapter Outline: Applications and Processing of Ceramics Chapter 13: Applications and Processing of Ceramics Short review of glass/ceramics applications and processing (13.1-13.3,13.8,13.10) Formation and processing of Ceramics

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Chapter Outline:

Applications and Processing of Ceramics

Chapter 13:Applications and Processing of Ceramics

  • Short review of glass/ceramics applications and processing (13.1-13.3,13.8,13.10)

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

Applications of Ceramics

  • Compressive strength is typically tentimestensile 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.

Silicate Glasses

Non-crystalline silicates (SiO2) containing other oxides (CaO, NaO2, K2O, Al2O3)

Containers, windows, lenses, fiberglass, etc.


Container/window glasses contain

~ 30 wt% oxides (CaO, Na2O)

whose cations are incorporated within SiO4 network: network modifiers.

Quartz sand + soda ash or limestone


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

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


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

Properties of Glasses (II)

Important temperatures in glasses

can be defined by viscosity


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.



Make sure you understand language and concepts:

  • Glass tempering
  • Glass transition temperature
  • Melting point (glass)