Classification of ceramics
What a ceramic is ?
From Greek word “keramos” (pottery, potter’s clay)
Inorganic nonmetallic materials obtained by the action of heat and subsequent
cooling
Polycrystalline materials, single phase or multiphase (composites), sometimes with
an amorphous component (glass)
Traditional ceramics
•Whitewares: tableware, cookware, sanitary ware, etc.
•Refractories (kiln and furnace linings for steel and glass industry)
•Structural clay products (floor & roof tiles, bricks, etc.)
Fabricated from clay, quartz, feldspar (earthenware) and kaolin (porcelain)
Technical/advanced ceramics
•Structural ceramics (mechanical properties: strength, toughness, hardness, creep
resistance)
•Functional ceramics (electric, magnetic, optical properties)
Structural ceramics
•Si3N4: bearing balls, cutting tools, heat exchangers, turbocharger rotors, parts of
gas turbines
•SiC: abrasives, disk brakes, pipes for corrosive liquids, ballistic armors
•WC, Ti(C,N): cermets, inserts for cutting tools
•B4C: neutron absorber in nuclear plants, ballistic armors, nozzles, abrasives
•Al2O3 (alumina): spark plugs, substrates, crucibles, furnace tubes, ballistic armors,
thermal insulation
•3Al2O3•2SiO2 (mullite) & Mg2Al3(Si5AlO18) (cordierite): catalytic converters, ceramic
filters
•ZrO2 (zirconia): knifes, watch cases, orthopedic implants, grinding media, thermal
barrier coatings
•UO2: nuclear fuel
•Ca10(PO4)6(OH)2 (hydroxyapatite): biomedical implants, artificial bone
Two Kyocera ceramic knives
Ceramic body armour plates
The Porsche Carrera GT's
silicon carbide disk brake
Ceramic Si3N4 bearing parts
Radial rotor made from Si3N4
for a gas turbine engine
Functional ceramics
Functionality
Material
Applications
Resistors
SiC, MoSi2, LaCrO3
Heating elements for high temperature
furnaces
Thermistors
(NTCR & PTCR)
Spinels
BaTiO3
Temperature sensors, self-regulating
heating elements
Dielectrics with very low
losses (r = 3 -10)
Al2O3, AlN,
cordierite
Substrates for electronic circuits and
chip packaging
Dielectrics for microwave
applications (r = 30-80)
BaTi4O9,
Zr(Ti,Sn)O4,
BaMg1/3Ta2/3O3,
(Ba,Sr)TiO3,
MW resonators, filters and antennas for
mobile communications and GPS
devices, tunable MW devices
Temperature stable dielectrics
(r  100)
CaTiO3, BaONd2O3-TiO2
Capacitors with temperatureindependent capacitance
Dielectrics with very high
dielectric constant (r  3000)
BaTiO3
Multilayer ceramic capacitors
Piezoelectric ceramics
Pb(Zr,Ti)O3 (PZT)
Transducers, actuators and resonators
Pyroelectric ceramics
Pb(Zr,Ti)O3
IR radiation detection and imaging
Functional ceramics
Functionality
Material
Applications
Ferroelectric
ceramics
Pb(Zr,Ti)O3
SrBi2Ta2O9
Ferroelectric memories (FeRAMs)
Electrostrictive
ceramics
PbMg1/3Nb2/3O3 -PbTiO3
(PMN-PT)
Actuators
Magnetic ceramics
Spinels (Ni,Zn)Fe2O4
BaFe12O19
Y3Fe5O12 (YIG)
Inductors
Permanent magnets
Microwave devices (radars)
Ionic conductors
Y:ZrO2 (YSZ)
Gd:CeO2
β-alumina
Electrolytes for solid-oxide fuel cells
(SOFCs), oxygen sensors
Na-Batteries
Superconductors
YBa2Cu3O7-x (YBCO)
MgB2
Superconducting cables for magnets
Transparent
ceramics
Al2O3, MgAl2O4, Y3Al5O12
(YAG)
Phosphors, optical materials for lenses
and laser systems, nose cones for heatseeking missiles, high-pressure sodium
street lamps
Optoelectronic
materials
LiNbO3
PLZT
Waveguides, frequency doublers,
voltage-controlled optical switches,
modulators
Thick (left) and thick (right) substrates (alumina)
Pressed and extruded parts (alumina, mullite, zirconia)
Ferrites cores
Microwave dielectric components
Microstructure of ceramics
Ceramic microstructures
SSS 99% Al2O3 – transparent fully dense (“ideal”) ceramic: grains
+ grain boundaries
SSS 99% Al2O3 - ceramic with residual porosity: grains + g.b. + pores
LPS 96% Al2O3 - dense ceramic with grain boundary glass phase: grains +
glassy phase (CaO*SiO2) + 2 types of g.b.
Microstructural variables
Density
- crystallographic (from unit cell parameters)
- theoretical (zero porosity, takes into account real composition)
- apparent (geometrical) density (< theoretical)
- relative density = (apparent/theoretical)*100
 Porosity
- closed (only closed above 93% r.d.)
- open (pore networks connected to the surface)
- intragranular
- intergranular
 Grain size (simplest method: mean intercept length)
 Grain size distribution (monomodal, bimodal, abnormal grain growth)
 Grain shape (equiaxed, elongated, prismatic, columnar, tabular, platelets)
- aspect ratio (ratio longest/shortest size dimensions)
Extended defects (dislocations, stacking faults, twins, domain walls)
 Second phase composition, shape and distribution
 Texture (grains oriented in a preferential direction)
Types of porosity
Intergranular
porosity
Intragranular
porosity
Y2O3:ZrO2 (PSZ) ceramic
Intra- and intergranular porosity
Ba(Ti,Ce)O3 ceramic
Closed (intragranular) and open
(itergranular channels) porosity
Shape of grains and pores
gb
120°
gb
gb
Equilibrium shape of grains. Hexagons (2D) and truncated octahedron (3D)
Concave pore
Convex pore
Irregular pore
associated with a
hard agglomerate
Grain size distributions and abnormal grain growth
Mg0.1Al1.8Ti1.1O5 ceramics
1450°C/2 h
Equiaxed grains with
monomodal distribution
1500°C/2 h
Some large elongated grains
appear: onset of AGG
1550°C/2 h
Bimodal distribution related to
AGG
Revealing microstructure
Polished surface
Fractography
Grain pull-out
Cross-sections of Ba(Ti,Zr)O3 ceramics
Revealing microstructure
Chemical etching
Thermal etching
Vapour
Solid grain
Solid grain
After polishing
Si3N4
Fully-dense alumina
After thermal treatment
SiC
Er-doped BaTiO3
Revealing microstructure
Optical microscopy in polarized light
Coated Co:WC:Ti(C,N) cermets
Revealing microstructure
Scanning electron microscopy using backscattered electrons (BEI)
Al2O3-(Zr,Y)O2 composite
The darker phase is alumina
Ba(Ti,Ce)O3 ceramic containing
Ce-rich inclusions
Spectrum
In stats.
O
Ti
Ba
Ce
Total
1
2
Yes
Yes
23.43
22.41
9.37
2.77
58.72
41.71
8.48
33.11
100.00
100.00
Secondary phases in Er-doped BaTiO3
White phase: Er2Ti2O7
Dark gray phase: Ba6Ti17O40