Transcript Applications and Processing of Ceramics Short review of glass/ceramics 13.3,13.8,13.10)

Introduction to Materials Science, Chapter 13, 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 (13.113.3,13.8,13.10)
University of Virginia, Dept. of Materials Science and Engineering
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Introduction to Materials Science, Chapter 13, Applications and Processing of Ceramics
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
University of Virginia, Dept. of Materials Science and Engineering
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Introduction to Materials Science, Chapter 13, Applications and Processing of Ceramics
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.
University of Virginia, Dept. of Materials Science and Engineering
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Introduction to Materials Science, Chapter 13, Applications and Processing of Ceramics
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
University of Virginia, Dept. of Materials Science and Engineering
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Introduction to Materials Science, Chapter 13, Applications and Processing of Ceramics
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
University of Virginia, Dept. of Materials Science and Engineering
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Introduction to Materials Science, Chapter 13, Applications and Processing of Ceramics
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

FA


dv dy dv dy
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Introduction to Materials Science, Chapter 13, Applications and Processing of Ceramics
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
University of Virginia, Dept. of Materials Science and Engineering
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Introduction to Materials Science, Chapter 13, Applications and Processing of Ceramics
Properties of Glasses (II)
Important temperatures in glasses
can be defined by viscosity
University of Virginia, Dept. of Materials Science and Engineering
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Introduction to Materials Science, Chapter 13, Applications and Processing of Ceramics
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.
University of Virginia, Dept. of Materials Science and Engineering
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Introduction to Materials Science, Chapter 13, Applications and Processing of Ceramics
Summary
Make sure you understand language and
concepts:
 Glass tempering
 Glass transition temperature
 Melting point (glass)
University of Virginia, Dept. of Materials Science and Engineering
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