Seminar on Ceramics

1. CERAMICS
1
Persian Guard. Iran, from Persepolis, Audience Hall (Apadana) of the Palace.
Achaemenid Period, reign of Xerxes, 486–480 B.C. Limestone, 10 1/2 x 9 x 1
7/8 in. (26.6 x 22.8 x 4.7 cm).

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An inorganic compound consisting of a metal (or semi-metal) and one or more
nonmetals for which the interatomic bonds are ionic or predominantly ionic with
some covalent character.
The term ceramics comes from the Greek word ‘keramikos’ ,which means
“Burnt stuff”, indicating that desirable properties of these materials are normally
achieved through high temperature heat treatment process called Firing.
They may be amorphous, partly crystalline or fully crystalline.
They are either formed from a molten mass that solidifies on cooling and matured
by the action of heat, or chemically synthesized at low temperature using for
example hydrothermal or sol-gel synthesis.
A wide-ranging group of materials whose ingredients are clays, sand and feldspar.
Ceramics Defined

3. EXAMPLES
Important examples:
 Silica - silicon dioxide (SiO2), the main ingredient in most glass
products
 Alumina - aluminum oxide (Al2O3), used in various applications
from abrasives to artificial bones
 More complex compounds such as hydrous aluminum silicate
(Al2Si2O5(OH)4), the main ingredient in most clay products
3

4. PROPERTIES OF CERAMICS
 Extreme hardness:
High wear resistance
Extreme hardness can reduce wear caused by friction.
 Corrosion Resistance
 Heat resistance
Low electrical conductivity
Low thermal conductivity
Low thermal expansion
Poor thermal shock resistance
 Brittle, virtually no ductility - can cause problems in both processing and
performance of ceramic products , Low fracture toughness.
 Some ceramics are translucent, window glass (based on silica) being the
clearest example
 Low density 4

5. COMPARISON: METALS VS CERAMICS
5
CeramicsMetals

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Taxonomy of Ceramics
Glasses Clay
products
Refractories Abrasives Cements Advanced
ceramics
-optical
-composite
reinforce
-containers/
household
-whitewares
-bricks
-bricks for
high T
(furnaces)
-sandpaper
-cutting
-polishing
-composites
-structural
engine
-rotors
-valves
-bearings
-sensors
Adapted from Fig. 13.1 and discussion in
Section 13.2-6, Callister 7e.
Types of Ceramics

7. Oxide Ceramics Non-Oxide Ceramics Composites
 Oxidation Resistant  Low Oxidation resistance  Variable Oxidation
resistance
 Electricaly Insulating  Extreme hardness  Toughness
 Low thermal conductivity  High thermal conductivity  Variable thermal and
electrical conductivity
 Slightly complex
manufacturing and high
 Difficult energy dependent
manufacturing and high
 Complex manufacturing
process and high cost
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Oxide and Non-Oxide Ceramics
 Zirconia(ZrO3),
Alumina(Al2O3)
 Carbides,Borides,Nitrides,
Silicides
 Particulate reinforced
combinations of oxide and
non-oxide(Silicon
Aluminium Oxynitride
{Al6N6O2Si} )

8. Amorphous Ceramics Crystalline Ceramics
 Atoms exhibit only short range Order  Atoms are arranged in a regular
repeating pattern in three dimensions
long range order
 No distinct melting temperature(Tm) for
these materials as there with crystalline
material
 Crystalline materials are “Engineering”
ceramics:
 High melting point
 Strong
 Hard
 Brittle
 Good Corrosion Resistance
 Na2O,CaO,K2O  Silicon Nitride(Si3N4),Silicon
Carbide(SiC),Zirconia(ZrO2),Alumina
(Al2O3)
Amorphous and Crystalline Ceramics

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AMORPHOUS CERAMICS (GLASSES)
 Main ingredient is Silica (SiO2)
 If cooled very slowly will form crystalline structure.
 If cooled more quickly will form amorphous structure consisting
of disordered and linked chains of Silicon and Oxygen atoms.
 This accounts for its transparency as it is the crystal boundaries
that scatter the light, causing reflection.
 Glass can be tempered to increase its toughness and resistance
to cracking.

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GLASS
TYPES
Three common types of glass:
 Soda-lime glass - 95% of all glass, windows
containers etc.
 Lead glass - contains lead oxide to improve refractive
index
 Borosilicate - contains Boron oxide, known as Pyrex.
Based On Its Application
 Flat glass (windows)
 Container glass (bottles)
 Pressed and blown glass (dinnerware)
 Glass fibres (home insulation)
 Advanced/specialty glass (optical fibres)
Glass Containers

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PRESSED GLASS PROCESSING
Softened
Gob

12. Based on mineral silicates, silica, and mineral oxides found in nature
 Primary products are fired clay (pottery, tableware, brick, and tile),
cement, and natural abrasives such as alumina
 Products and the processes to make them date back thousands of years
 Glass is also a silicate ceramic material and is sometimes included among
traditional ceramics
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Traditional Ceramics

13.  Advanced ceramic materials have been developed over the past
half century
 Applied as thermal barrier coatings to protect metal structures,
wearing surfaces, or as integral components by themselves.
 Engine applications are very common for this class of material
which includes silicon nitride (Si3N4), silicon carbide (SiC),
Zirconia (ZrO2) and Alumina (Al2O3)
 Heat resistance and other desirable properties have lead to the
development of methods to toughen the material by
reinforcement with fibers and whiskers opening up more
applications for ceramics 13
Advanced Ceramics

14. Traditional Ceramics
White wares
Abrasives
Refractories
Cement
Bricks and Tile
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15.  Mineral silicates, such as clays of various compositions, and silica, such as
quartz, are among the most abundant substances in nature and
constitute the principal raw materials for traditional ceramics
 Another important raw material for traditional ceramics is alumina
 These solid crystalline compounds have been formed and mixed in
the earth’s crust over billions of years by complex geological processes
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Raw Materials For Traditional Ceramics
Alumina ceramic components

16. CERAMIC PRODUCTS
 Clay construction products - bricks, clay pipe, and building tile
 Refractory ceramics - ceramics capable of high temperature
applications such as furnace walls, crucibles, and molds
 Cement used in concrete - used for construction and roads
 Whiteware products - pottery, stoneware, fine china, porcelain, and
other tableware, based on mixtures of clay and other minerals
 Glass - bottles, glasses, lenses, window pane, and light bulbs
 Glass fibers - thermal insulating wool, reinforced plastics (fiberglass),
and fiber optics communications lines
 Abrasives - aluminum oxide and silicon carbide
 Cutting tool materials - tungsten carbide, aluminum oxide, and cubic
boron nitride 16

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tensile
force
Ao
Addie
die
• Die blanks:
-- Need wear resistant properties!
• Die surface:
-- 4 mm polycrystalline diamond
particles that are sintered onto a
cemented tungsten carbide
substrate.
-- polycrystalline diamond helps control
fracture and gives uniform hardness
in all directions.
Courtesy Martin Deakins, GE
Super abrasives,
Worthington, OH. Used with
permission.
Adapted from Fig. 11.8 (d),
Callister 7e.
APPLICATION: DIE
BLANKS

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• Example: Oxygen sensor ZrO2
• Principle: Make diffusion of ions
fast for rapid response.
APPLICATION: SENSORS
A Ca2+ impurity
removes a Zr4+ and a
O2- ion.
Ca2+
• Approach:
Add Ca impurity to ZrO2:
-- increases O2- vacancies
-- increases O2- diffusion rate
reference
gas at fixed
oxygen content
O
2-diffusion
gas with an
unknown, higher
oxygen content
-+
voltage difference produced!
sensor
• Operation:
-- voltage difference
produced when
O2- ions diffuse
from the external
surface of the sensor
to the reference gas.

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• Tools:
-- for grinding glass, tungsten,
carbide, ceramics
-- for cutting Si wafers
-- for oil drilling
blades
oil drill bits• Solutions:
coated single
crystal diamonds
polycrystalline
diamonds in a resin
matrix.
Photos courtesy Martin Deakins,
GE Superabrasives, Worthington,
OH. Used with permission.
APPLICATION: CUTTING TOOLS
-- 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.

21.  Ceramic armor systems are used to protect military personnel
and equipment.
 Advantage: low density of the material can lead to weight-
efficient armor systems.
 Typical ceramic materials used in armor systems include
alumina, boron carbide, silicon carbide, and titanium diboride.
 The ceramic material is discontinuous and is sandwiched
between a more ductile outer and inner skin.
 Alumina ceramic/Kevlar composite system in sheets about
20mm thick are used to protect key areas of Hercules aircraft
(cockpit crew/instruments and loadmaster station).
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Applications: Advanced Ceramics
Ceramic Armour

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Projectile
Outer hard
skin
Ceramic-
Discontinuous
Inner
ductile
skin
Personnel
and
Equipment
Ceramic Armor
System
Ceramic - Composite Armor

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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
Heat Engines
Advantages:
 Run at higher temperature
 Excellent wear &
corrosion resistance
 Low frictional losses
 Ability to operate without
a cooling system
 Low density
• Disadvantages:
– Brittle
– Too easy to have voids-
weaken the engine
– Difficult to machine
• Possible parts – engine block, piston coatings, jet engines
Ex: Si3N4, SiC, & ZrO2
Gears (Alumina)
Rotor (Alumina)

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TURBOCHARGE
R
Ceramic
Rotor

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Ceramic Brake Discs

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