CERAMICS MATERIALS
CERAMICS MATERIALS
Ceramic materials are inorganic materials consisting of metallic
and non-metallic elements chemically bonded together to form
complex compounds.
Ceramic materials are usually ionic or covalently-bonded
materials, and can be crystalline or amorphous.
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
CERAMICS MATERIALS
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Properties and applications of Ceramics
Traditional Ceramics
New Ceramics
Glass
Some Important Elements Related to Ceramics
Guide to Processing Ceramics
1. Traditional ceramics - clay products such as pottery and
bricks, common abrasives, and cement
2. New ceramics - more recently developed ceramics based
on oxides, carbides, etc., and generally possessing
mechanical or physical properties superior or unique
compared to traditional ceramics
3. Glasses - based primarily on silica and distinguished by
their noncrystalline structure
» In addition, glass ceramics - glasses transformed into
a largely crystalline structure by heat treatment
CERAMICS MATERIALS
Ceramics properties
 High hardness, (high strength, stiffness, wear resistance)
 Brittle, Low ductility or malleability i.e. low plasticity,
 Electrical and thermal insulating,
 Chemical stability, and high melting temperatures
 Some ceramics are translucent, window glass (based on silica).
 Lower density than most metals,
 Low resistance to fracture, highly resistant to compressive loads.
 Corrosion resistance
 Ceramics are hard, brittle, totally elastic and are heat resistant.
At extremely low temperature, exhibit superconductivity.
 Due to high resistance to heat, application in furnace linings.
 Ceramics are often used as protective coatings to other materials.
CERAMICS MATERIALS
Applications of Ceramics
 Electrical Ceramics, insulators, electrical devices, Superconductors.
 Coatings, Biocompatible coatings (fusion to bone), Self-lubricating bearings
 Abrasives
 Piezoelectric materials are lead zirconate titanate and barium titanate.
 Design of high-frequency loudspeakers, Transducers for sonar, and
 Actuators for atomic force and scanning tunneling microscopes.
 Semiconducting ceramics are also employed as gas sensors.
 Corrosion resistant applications, Windows, Television screens,
 Magnetic materials (audio/video tapes, disks, etc.), Magnets.
 Ceramic fibers, graphite and aluminum oxide, fiber-reinforced composites
 Pottery, clay, glasses, vitreous enamels, and Cutting tools.
 Chemically Bonded Ceramics (e.g. cement and concrete)
 Structural Ceramics, Whitewares (e.g. porcelains),
 Engineering ceramics
1- Oxides (SiO2, Al2O3, Fe 2O3, MgO, SrTiO3, MgAl2O4, YBa2Cu3O7-x)
2- Carbides (SiC, WC, TiC), Borides, Nitrides (Si3N4, TiN, AlN, GaN, BN),
3- Composites: Particulate reinforced
CERAMICS MATERIALS
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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
Ceramic insulators - applications include electrical transmission
components, spark plugs, and microelectronic chip substrates
Magnetic ceramics – example: computer memories
Nuclear fuels based on uranium oxide (UO2)
Bioceramics - artificial teeth and bones
CERAMICS MATERIALS
Advanced Ceramics: Sensors, Valves, Dielectrics, Space shuttle, Spark plugs,
Magnetic recording media,
Glasses: Optical Composite, Porous ceramic tiles
Cements: Composites structural Clay: Whiteware Bricks
Refractories: Bricks for high T
Abrasives: Sandpaper Polishing
Heat Engines
Excellent wear &
corrosion resistance
Low frictional losses
Heat resistant
Low density
Brittle, Difficult to
Machine
Si3N4, SiC, & ZrO2
Ceramic Armor
Electronic Packaging
Al2O3, B4C, SiC & Boron nitride (BN)
TiB2
Silicon Carbide (SiC)
Hard materials
Aluminum nitride (AlN
Good expansion
Good heat transfer
coefficient
Poor electrical
Conductivity
CERAMICS MATERIALS
Traditional Ceramics
 Primary products are fired clay (pottery, tableware, brick,
and tile), cement, and natural abrasives such as alumina
 Glass is also a silicate ceramic material and is sometimes
included among traditional ceramics
Raw Materials for Traditional Ceramics
 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
CERAMICS MATERIALS
Clay and Silica as a Ceramic Raw Material
 Clays consist of fine particles of hydrous aluminum silicate,
Most common clays are based on the mineral kaolinite,
(Al2Si2O5(OH)4)
 When mixed with water, clay becomes a plastic substance that
is formable and moldable. When heated to a sufficiently
elevated temperature (firing ), clay fuses into a dense, strong
material. Thus, clay can be shaped while wet and soft, and
then fired to obtain the final hard product
 Silica is available naturally in various forms, most important is
quartz, the main source of quartz is sandstone, Low in cost;
also hard and chemically stable
 Principal component in glass, and an important ingredient in
other ceramic products including whiteware, refractories, and
abrasives
CERAMICS MATERIALS
Alumina as a Ceramic Raw Material
 Bauxite - most alumina is processed from this mineral, which is
an impure mixture of hydrous aluminum oxide and aluminum
hydroxide plus similar compounds of iron or manganese.
Bauxite is also the principal source of metallic aluminum
 Corundum - a more pure but less common form of Al2O3, which
contains alumina in massive amounts
 Alumina ceramic is used as an abrasive in grinding wheels and
as a refractory brick in furnaces
Traditional Ceramic Products
 Pottery and Tableware
 Brick and tile
 Refractories
 Abrasives
CERAMICS MATERIALS
New Ceramics
Ceramic materials developed synthetically over the last several
decades
 The term also refers to improvements in processing techniques
that provide greater control over structures and properties of
ceramic materials
 In general, new ceramics are based on compounds other than
variations of aluminum silicate, which form most of the
traditional ceramic materials
 New ceramics are usually simpler chemically than traditional
ceramics; for example, oxides, carbides, nitrides, and borides
 Thin films of many complex and multi-component ceramics are
produced using different techniques such as sputtering, sol-gel,
and chemical-vapor deposition (CVD).
 Fibers are produced from ceramic materials for several uses: as
a reinforcement in composite materials, for weaving into
fabrics, or for use in fiber-optic systems.
CERAMICS MATERIALS
Oxides
Ex.
Properties
Aluminum oxide
Al2O3
high strength and hardness, high stiffness, high thermal stability
magnesium oxide
MgO
high thermal stability
Mullite
Al6Si2O13
Low coefficient of thermal expansion, high thermal stability
silicon dioxide
SiO2
Low density, transparency
Zirconium
dioxide
ZrO2
high toughness when transformation toughened
Carbides
Ex.
Diamond
C
high strength, stiffness, low coefficient of thermal expansion,
Graphite
C
high strength, stiffness, low coefficient of thermal expansion
silicon carbide
SiC
high strength and hardness, high stiffness
tungsten carbide
WC
high strength and hardness
Nitrides
Properties
Ex.
Properties
Boron nitride
BN
very high strength and hardness, very high stiffness
silicon nitride
Si3N4
high strength, hardness, stiffness and high thermal stability
CERAMICS MATERIALS
Oxide Ceramics
 Most important oxide new ceramic is alumina
 Although also included as a traditional ceramic, alumina is today produced
synthetically from bauxite, using an electric furnace method
 Through control of particle size and impurities, refinements in processing
methods, and blending with small amounts of other ceramic ingredients,
strength and toughness of alumina are improved substantially compared to
its natural counterpart
 Alumina also has good hot hardness, low thermal conductivity, and good
corrosion resistance
Products of Oxide Ceramics
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Abrasives (grinding wheel grit)
Bioceramics (artificial bones and teeth)
Electrical insulators and electronic components
Refractory brick
Cutting tool inserts
Spark plug barrels
Engineering components
CERAMICS MATERIALS
Carbides
 Silicon carbide (SiC), tungsten carbide (WC), titanium carbide (TiC),
tantalum carbide (TaC), and chromium carbide (Cr3C2)
 Although SiC is a man-made ceramic, its production methods were
developed a century ago, and it is generally included in traditional
ceramics group
 WC, TiC, and TaC are valued for their hardness and wear resistance in
cutting tools and other applications requiring these properties
 WC, TiC, and TaC must be combined with a metallic binder such as
cobalt or nickel in order to fabricate a useful solid product
Nitrides
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The important nitride ceramics are silicon nitride (Si3N4), boron nitride
(BN), and titanium nitride (TiN)
Properties: hard, brittle, high melting temperatures, usually electrically
insulating, TiN being an exception
Applications:
– Silicon nitride: components for gas turbines, rocket engines, and
melting crucibles
– Boron nitride and titanium nitride: cutting tool material and coatings
CERAMICS MATERIALS
Functional Classification of Ceramics
CERAMICS MATERIALS
Functional Classification of Ceramics
CERAMICS MATERIALS
Strength Properties of Ceramics
 Theoretically, the strength of ceramics should be higher than metals because
their covalent and ionic bonding types are stronger than metallic bonding
 However, metallic bonding allows for slip, the basic mechanism by which
metals deform plastically when subjected to high stresses
 Bonding in ceramics is more rigid and does not permit slip under stress
 The inability to slip makes it much more difficult for ceramics to absorb
stresses
Imperfections in Crystal Structure of Ceramics
 Ceramics contain the same imperfections in their crystal structure as
metals - vacancies, displaced atoms, interstitialcies, and microscopic cracks
 Internal flaws tend to concentrate stresses, especially tensile, bending, or
impact
– Hence, ceramics fail by brittle fracture much more readily than metals
– Performance is much less predictable due to random imperfections and
processing variations
CERAMICS MATERIALS
Compressive Strength of Ceramics
 Ceramics are substantially stronger in compression than in
tension
 For engineering and structural applications, designers have
learned to use ceramic components so that they are loaded in
compression rather than tension or bending
Methods to Strengthen Ceramic Materials
 Make starting materials more uniform
 Decrease grain size in polycrystalline ceramic products
 Minimize porosity
 Introduce compressive surface stresses
 Use fiber reinforcement
 Heat treat
CERAMICS MATERIALS
Physical Properties of Ceramics
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Density – in general, ceramics are lighter than metals and
heavier than polymers
Melting temperatures - higher than for most metals
– Some ceramics decompose rather than melt
Electrical and thermal conductivities - lower than for metals;
but the range of values is greater, so some ceramics are
insulators while others are conductors
Thermal expansion - somewhat less than for metals, but
effects are more damaging because of brittleness
CERAMICS MATERIALS
Properties of Ceramics
CERAMICS MATERIALS
Classification of ceramics into micro-structural terms
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Single crystals of appreciable size (e.g. ruby laser crystals).
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Glass (non-crystalline) of appreciable size (e.g. sheets of float glass).
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Crystalline or glassy filaments.
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Polycrystalline aggregates bonded by a glassy matrix (e.g. porcelain
pottery).
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Glass free polycrystalline aggregates (e.g. ultra pure, fine grained, zero
porosity forms of alumina, magnesia, and beryllia).
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Polycrystalline aggregates produced by heating glasses of special
composition (e.g. glass-ceramics).
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Composites (e.g. silicon carbide or carbon filaments in a matrix of glass
or glass-ceramic; magnesia graphite refractories, concrete).
CERAMICS MATERIALS
Glass
 As a state of matter, the term refers to an amorphous (noncrystalline)
structure of a solid material
– The glassy state occurs in a material when insufficient time is
allowed during cooling from the molten state for the crystalline
structure to form
 As a type of ceramic, glass is an inorganic, nonmetallic compound (or
mixture of compounds) that cools to a rigid condition without
crystallizing
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Because SiO2 is the best glass former
– Silica is the main component in glass products, usually comprising
50% to 75% of total chemistry
– It naturally transforms into a glassy state upon cooling from the
liquid, whereas most ceramics crystallize upon solidification
CERAMICS MATERIALS
Glass temperature - The temperature below which an undercooled
liquid becomes a glass.
Glass formers - Oxides with a high-bond strength that easily produce a
glass during processing.
Intermediates - Oxides that, when added to a glass, help to extend the
glassy network; although the oxides normally do not form a glass
themselves.
Glass modifier –
• Glasses:
-- do not crystallize
-- change in slope in spec. vol. curve at
glass transition temperature, Tg
-- transparent
Crystalline materials:
-- crystallize at melting temp, Tm
-- have abrupt change in spec. vol. at Tm
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CERAMICS MATERIALS
Specific volume
Liquid
(disordered)
Supercooled
Liquid
Glass
(amorphous solid)
Crystalline
(i.e., ordered)
Tg
When silica crystallizes on cooling, an abrupt
change in the density is observed. For glassy silica,
however, the change in slope at the glass
temperature indicates the formation of a glass from
the undercooled liquid. Glass does not have a fixed
Tm or Tg. Crystalline materials have a fixed Tm and
they do not have a Tg.
Tm
solid
T
Adapted from Fig. 13.6, Callister, 7e.
Specific volume (1/r) vs Temperature (T)
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CERAMICS MATERIALS
The effect of temperature and composition on the viscosity of glass.
CERAMICS MATERIALS
CERAMICS MATERIALS
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Sheet forming – continuous draw
– originally sheet glass was made by “floating” glass on a pool of
mercury
Adapted from Fig. 13.9, Callister 7e.
CERAMICS MATERIALS
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Techniques for forming lass products: (a) pressing, (b) press and blow process, and (c)
drawing of fibers.
Glass Products
Window glass, Containers – cups, jars, bottles, Light bulbs,
Laboratory glassware – flasks, beakers, glass tubing, Glass fibers –
insulation, fiber optics, Optical glasses - lenses
CERAMICS MATERIALS
Glass-Ceramics is a ceramic material produced by conversion of glass into a
polycrystalline structure through heat treatment
 Proportion of crystalline phase range = 90% to 98%, remainder being
unconverted vitreous material
 Grain size - usually between 0.1 - 1.0 m (4 and 40 -in), significantly
smaller than the grain size of conventional ceramics
– This fine crystal structure makes glass-ceramics much stronger than the
glasses from which they are derived
 Also, due to their crystal structure, glass-ceramics are opaque (usually grey
or white) rather than clear
Processing of Glass Ceramics
 Heating and forming operations used in glass working create product shape
 Product is cooled and then reheated to cause a dense network of crystal
nuclei to form throughout
– High density of nucleation sites inhibits grain growth, leading to fine
grain size
 Nucleation results from small amounts of nucleating agents in the glass
composition, such as TiO2, P2O5, and ZrO2
 Once nucleation is started, heat treatment is continued at a higher
temperature to cause growth of crystalline phases
CERAMICS MATERIALS
Advantages of Glass-Ceramics
 Efficiency of processing in the glassy state
 Close dimensional control over final product shape
 Good mechanical and physical properties
– High strength (stronger than glass)
– Absence of porosity; low thermal expansion
– High resistance to thermal shock
 Applications:
– Cooking ware
– Heat exchangers
– Missile radomes
CERAMICS MATERIALS
Elements Related to Ceramics
 Carbon
– Two alternative forms of engineering and commercial importance:
graphite and diamond
 Silicon
 Boron
 Carbon, silicon, and boron are not ceramic materials, but they sometimes
– Compete for applications with ceramics
– Have important applications of their own
Graphite
Form of carbon with a high content of crystalline C in the form of layers
 Bonding between atoms in the layers is covalent and therefore strong, but
the parallel layers are bonded to each other by weak van der Waals forces
 This structure makes graphite anisotropic; strength and other properties
vary significantly with direction
– As a powder it is a lubricant, but in traditional solid form it is a
refractory
– When formed into graphite fibers, it is a high strength structural
material
CERAMICS MATERIALS
Diamond is a carbon with a cubic crystalline structure with covalent
bonding between atoms
– This accounts for high hardness
 Industrial applications: cutting tools and grinding wheels for
machining hard, brittle materials, or materials that are very abrasive;
also used in dressing tools to sharpen grinding wheels that consist of
other abrasives
 Industrial or synthetic diamonds date back to 1950s and are fabricated
by heating graphite to around 3000C (5400F) under very high
pressures
Boron is semi-metallic element in same periodic group as aluminum
 Comprises only about 0.001% of Earth's crust by weight, commonly
occurring as minerals borax (Na2B4O7- 10H2O) and kernite
(Na2B4O7-4H2O)
 Properties: lightweight, semiconducting properties, and very stiff (high
modulus of elasticity) in fiber form
 Applications: B2O3 used in certain glasses, as a nitride (cBN) for cutting
tools, and in nearly pure form as a fiber in polymer matrix composites
CERAMICS MATERIALS
Silicon is a semi-metallic element in the same periodic table group as carbon
 One of the most abundant elements in Earth's crust, comprising  26% by
weight
 Occurs naturally only as chemical compound - in rocks, sand, clay, and
soil - either as silicon dioxide or as more complex silicate compounds
 Properties: hard, brittle, lightweight, chemically inactive at room
temperature, and classified as a semiconductor
Applications and Importance of Silicon
 Greatest amounts in manufacturing are in ceramic compounds (SiO2 in
glass and silicates in clays) and alloying elements in steel, aluminum, and
copper
 Also used as a reducing agent in certain metallurgical processes
 Of significant technological importance is pure silicon as the base material
in semiconductor manufacturing in electronics
 The vast majority of integrated circuits produced today are made from
silicon
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CERAMICS MATERIALS
Processing of Advanced Ceramics
Different techniques for processing of advanced ceramics.
CERAMICS MATERIALS
Schematic of the jaw, rotary, crushing rollers, and hammermill crushing equipment and
ball mill (grinding) equipment. (Jaw, rotary, crushing, and hammermill: Source: From
Principles of Ceramics Processing, Second Edition, by J.S. Reed, p. 314, Figs. 17-1 and 172. Copyright © 1995 John Wiley & Sons, Inc. Reprinted by permission. Ball mill grinding:
Source: From Modern Ceramic Engineering, by D.W. Richerson, p. 387, Fig. 9-3.
Copyright © 1992 Marcel Dekker, Inc.)
CERAMICS MATERIALS
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Processes for shaping crystalline ceramics: (a) pressing, (b) isostatic pressing,
(c) extrusion, (d) jiggering, and (e) slip casting.
CERAMICS MATERIALS
Guide to Processing Ceramics
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Processing of ceramics can be divided into two basic
categories:
1. Molten ceramics - major category of molten
ceramics is glassworking (solidification processes)
2. Particulate ceramics - traditional and new
ceramics (particulate processing)
CERAMICS MATERIALS
Tape Casting
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Thin sheets of green ceramic cast as flexible tape
used for integrated circuits and capacitors
cast from liquid slip (ceramic + organic solvent)
Adapted from Fig. 13.18, Callister 7e.
CERAMICS MATERIALS
Hot pressing: Diffusion Processes during Sintering
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5
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Diffusion processes during sintering and powder metallurgy. Atoms diffuse to
points of contact, creating bridges and reducing the pore size
CERAMICS MATERIALS
Hot pressing: Diffusion Processes during Sintering
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5
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2
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The steps in diffusion bonding: (a) Initially the contact area is small; (b) application
of pressure deforms the surface, increasing the bonded area; (c) grain boundary
diffusion permits voids to shrink; and (d) final elimination of the voids requires
volume diffusion
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CERAMICS MATERIALS
The change in the volume of a ceramic body as moisture is removed during
drying. Dimensional changes cease after the interparticle water is gone.
CERAMICS MATERIALS
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During firing, clay and other fluxing materials react with coarser particles to produce a
glassy bond and reduce porosity.