CHAPTER 13: APPLICATIONS AND PROCESSING OF CERAMICS

CHAPTER 13: APPLICATIONS AND
PROCESSING OF CERAMICS

ISSUES TO ADDRESS...

• How do we classify ceramics?
• What are some applications of ceramics?
• How is processing different than for metals?

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TYPES AND APPLICATIONS OF
CERAMICS

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TYPES AND APPLICATIONS OF
CERAMICS

Glass and Glass Ceramics: easy production, transparent, available in
amorphous and crystalline form (devitrification - transition ot crystalline by heat
treatment), additives are Na2O, B2O3 etc.

Clay Products: easy to shape at room temperature, loss of water initiated by
firing, then hardening

Refractories: contain Aluminum, Magnesium, Titanium, Iron and other oxides in
various concentrations. Highly corrosion resistant.

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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

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FABRICATION AND PROCESSING
OF CERAMICS

Many of the fabrication process known for metals cannot be applied in general due
to the brittleness and high melting point of ceramics
Alternative: e.g powder pressing, drying and firing, sintering (powder pressing and
firing below melting point)

The melting of glasses
Solidification is gradual and proceeds with
increasing viscosity as the glass is cooled.

No sharp and well defined melting point
exists.

This can be seen when observing the
volume change upon cooling:

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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,

Cements formed from a fluid paste that hardens by chemical reactions

Glasses produced by complete melting of raw ingredients

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APPLICATION: GLASS

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

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THE VISCOSITY-TEMPERATURE RELATION

IMPORTANT TEMPERATURES IN GLASSES CAN BE DEFINED BY VISCOSITY

Stages of melting: Glass forming operations occur between
softening and working points
Melting point: viscosity is 10 Pa-s, the glass is
liquidlike 8

Working point: viscosity is 103 Pa-s, the glass
can be deformed (glass blower)

Softening point: viscosity = 4×107 P, maximum
T at which a glass piece maintains shape for
a long time

Annealing point: viscosity 1012 Pa-s, atomic
diffusion is sufficient to remove residual
stresses in a short period (about 15 minute)

Strain point: viscosity 3×1013 Pa-s, if the
temperature falls below the strain point no
plastic deformation occurs prior to fracture.

The glass composition determines the
temperature for passing the critical viscosity
levels.

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HEAT TREATMENT OF GLASSES

TEMPERED GLASS

The surface cools more rapidly and
becomes rigid below the strain point,
while the interior is still soft and
plastically deformable.

With further cooling the solid surface layer
is subjected to compressive stress as
the interior shrinks. The core is now
under tensile the surface under
compressive stress.

A crack induced by tensile loads form the
outside has now first to overcome the
compressive stress of the surface
before it can propagate.

This treatment is used for glass tables,
lenses, windshields

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CERAMIC FABRICATION METHODS

GLASS PARTICULATE CEMENTATION
FORMING FORMING

Pressing: Fiber drawing:

Blowing: wind up

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SHEET GLASS FORMING

Sheet forming – continuous draw

Originally sheet glass was made by “floating” glass on a pool of mercury

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APPLICATION: CLAY PRODUCTS

Construction Materials: Clay and 12
shale are used in making strong,
durable bricks and drainpipes for
homes and other buildings. Tiles are
made of clay and talc. Cement
consists chiefly of calcium silicates
and is used primarily in making
concrete. Gypsum is used to
produce plaster for the surfaces of
walls and ceilings. Bathtubs, sinks,
and toilets are made of porcelain,
which consists chiefly of clay,
feldspar, and quartz.

Dinnerware: Ceramics make excellent
containers for food and drinks. They
do not absorb liquids, and they resist
acids, salts, detergents, and
changes in temperature.

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CERAMIC FABRICATION METHODS

GLASS PARTICULATE CEMENTATION
FORMING FORMING

• Milling and screening: desired particle size

• Mixing particles & water: produces a "slip"

• Form a "green" component Ao die holder

container

--Hydroplastic forming: force ram bille extrusion Ad

extrude the slip (e.g., into a pipe) conttainer die

--Slip Casting

pour slip absorb water pour slip Drain Trim “green
into mold into mold “green into mold Mold Neck ceramic”

ceramic”

Solid component Hollow component

• Dry and fire the component 13

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FEATURES OF A SLIP

Shear

Clay is inexpensive charge
Adding water to clay neutral

allows material to shear easily along
weak van der Waals bonds enables
extrusion enables slip casting

Structure of charge weak van
Kaolinite Clay: neutral der Waals
bonding
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Al 3+
OH-
O2-

Shear 14

DRYING AND FIRING

• Drying: layer size and spacing decrease.

wet slip partially dry “green” ceramic

Drying too fast causes sample to warp or crack due to non-uniform shrinkage

• Firing:

--T raised to (900-1400°C)
--vitrification: liquid glass forms from clay and flows between

SiO2 particles. Flux melts at lower T.

micrograph of Si02 particle
porcelain (quartz)

glass formed
around
the particle

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CERAMIC FABRICATION METHODS

GLASS PARTICULATE CEMENTATION
FORMING FORMING

Powder Pressing: Compaction of a powder mass, which usually

contains some water as a binder, by pressure
to desired shape.

The microstructure of the material
changes by reduction of the pore
size and shrinking of the
individual grains during firing
(heating to 900 1400 C)

Engineering Materials Engineering M12 During firing the glass
Moorpark College components might become liquid
(vitrification) and a number of
other complex reactions and
phase transitions can occur.

16

CERAMIC FABRICATION METHODS

GLASS PARTICULATE CEMENTATION
FORMING FORMING

Sintering: useful for both clay and non-clay compositions.
Procedure:

grind to produce ceramic and/or glass particles
inject into mold
press at elevated T to reduce pore size.

Aluminum oxide powder:

sintered at 1700C
for 6 minutes.

15µm

Sintering: powder pressing + firing below melting T 17

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APPLICATION: REFRACTORIES

Need a material to use in high temperature furnaces.
Consider Silica (SiO2) - Alumina (Al2O3) system.
Phase diagram shows:

mullite, alumina, and crystobalite (made up of SiO2)
tetrahedra as candidate refractories.

2200 3Al2O3-2SiO2 alumina + L
T(°C)
mullite
2000 Liquid

1800 (L)

crystobalite mullite alumina
+L +L +

1600 mullite mullite
+ crystobalite
1400
0 20 40 60 80 100
Composition (wt% alumina)
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APPLICATION: ABRASIVES

CUTTING TOOLS

Tools: oil drill bits blades
coated single
for grinding glass, tungsten, crystal diamonds
carbide, ceramics
for cutting Si wafers polycrystalline
for oil drilling diamonds in a resin
matrix.
Solutions:
19
manufactured single crystal or
polycrystalline diamonds in a
metal or resin matrix. optional
coatings (e.g., Ti to help
diamonds bond to a Co matrix
via alloying) polycrystalline
diamonds resharpen by
microfracturing along
crystalline planes.

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APPLICATIONS: CEMENTS

PORTLAND CEMENT

Construction Materials: cement,
plaster of paris, and lime, which,
as a group, are produced in
extremely large quantities. Used
to produce concrete bricks,
pavers, and stucco.

Stucco: the common term for
portland cement plaster, is a
popular exterior finish for
buildings.

Cement Pavers: Are used for drive
ways, city streets, county roads,
state routes, and interstate
highways, to parking lots,
industrial storage facilities, and
airports.

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CERAMIC FABRICATION METHODS

GLASS PARTICULATE CEMENTATION
FORMING FORMING

Produced in extremely large quantities.

Portland cement:

mix clay and lime bearing materials
calcinate (heat to 1400C)
primary constituents:

tri-calcium silicate
di-calcium silicate

Adding water

produces a paste which hardens
hardening occurs due to hydration (chemical reactions

with the water).

Forming: done usually minutes after hydration begins.

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APPLICATIONS: ADVANCED CERAMICS

HEAT ENGINES

Advantages: Disadvantages:

– Run at higher temperature – Brittle

– Excellent wear & corrosion – Too easy to have voids-
resistance weaken the engine

– Low frictional losses – Difficult to machine

– Ability to operate without a
cooling system

– Low density

• Possible parts – engine block, piston coatings, jet engines
Ex: Si3N4, SiC, & ZrO2

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APPLICATIONS: ADVANCED CERAMICS

ELECTRONIC PACKAGING

Chosen to securely hold microelectronics & provide
heat transfer

Must match the thermal expansion coefficient of the
microelectronic chip & the electronic packaging
material. Additional requirements include:

good heat transfer coefficient
poor electrical conductivity

Materials currently used include:

Boron nitride (BN)
Silicon Carbide (SiC)
Aluminum nitride (AlN)

thermal conductivity 10x that for Alumina
good expansion match with Si

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APPLICATIONS: ADVANCED CERAMICS

SENSORS

Ex: Oxygen sensor: ZrO2 Ca2+
Principle: Make diffusion of ions
A Ca2+ impurity
fast for rapid response. removes a Zr4+ and a

Approach: O2- ion.

Add Ca impurity to: sensor

increase O2- vacancies gas with an reference

increase O2- diffusion unknown, higher O2- gas at fixed
oxygen content diffus oxygen content
Operation:
ion
Voltage difference produced
when O2- ions diffuse between

external and references gases.

+-

voltage difference produced!

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APPLICATION: DIE BLANKS

Die blanks: Ao die Ad tensile
force
Need wear resistant properties!

die

Die surface: 25

4 mm polycrystalline diamond
particles that are sintered on to a
cemented tungsten carbide
substrate.

polycrystalline diamond helps control
fracture and gives uniform hardness
in all directions.

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SUMMARY 26

Basic categories of ceramics:

glasses
clay products
refractories
cements
advanced ceramics

Fabrication Techniques:

glass forming (impurities affect forming temp).
particulate forming (needed if ductility is limited)
cementation (large volume, room T process)

Heat treating: Used to

alleviate residual stress from cooling,
produce fracture resistant components by putting

surface into compression.

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Summary

Make sure you understand language and concepts:

Abrasive ceramics Firing
Green Refractory ceramics
Softening point Vitrification
Annealing point Glass transition temperature
Hydroplastic forming Sintering
Strain point Whitewares
Calcination Glass–ceramic
Melting point Slip casting
Structural clay products Working point
Cements
Microelectromechanical systems
Thermal shock
Crystallization
Optical fiber
Thermal tempering

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Announcements

Reading

Chapter # 14

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