1. Chapter 1
Traditional and engineering ceramics
Traditional ceramics Clay + Silica + Feldspar
Al2O3 .2 SiO2 .2 H 2O SiO2 K 2O. Al2O3 .6 SiO2
Na2O. Al2O3 .6SiO2
• Structural clay products : bricks,
sewer pipe, roofing tile
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• EX: Triaxial bodies: Whiteware,
porcelain, chinaware, sanitary ware.
Suranaree University of Technology Reactions of a triaxial body October 2007

2. Chapter 1
Traditional and engineering ceramics
Traditional ceramics
Triaxial whiteware chemical composition
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Suranaree University of Technology October 2007

3. Chapter 1
Traditional and engineering ceramics
Traditional ceramics
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Suranaree University of Technology October 2007

4. Chapter 1
Traditional and engineering ceramics
Traditional ceramics
quartz Mullite needles
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High silica glass
Electron micrograph of an electrical
insulator porcelain (etched 10 s, 0oC,
40% HF, silica replica)
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5. Chapter 1
Traditional and engineering ceramics
Master and plaster moulds
Slip casting process Pottery
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Slip casting
Fire Colour paint Dry
http://www.lindawilsonceramics.co.za/3.html
Suranaree University of Technology Fresh cast October 2007

6. Chapter 1
Traditional and engineering ceramics
Slip casting process Sanitaryware
Hemihydrate plaster – produced from gymsum
150o C
CaSO4 .2 H 2O  → CaSO4 . 1 H 2O + 3 H 2O
 2 2
Slip preparation
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in ball mill
www.3emmegi.com
Suranaree University of Technology Slip casting in plaster moulds and demoulding October 2007

7. Chapter 1
Traditional and engineering ceramics
Engineering ceramics • Contain more of pure compounds of oxides,
carbides, nitrides.
• Ex: Al2O3, Si3N4, SiC, ZrO2 , refractory
oxides
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Mechanical properties of engineering ceramics
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8. Chapter 1
Traditional and engineering ceramics
Engineering ceramics Alumina
• Refractory tubing
• High purity crucibles for high temp
• High quality electrical applications
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(low dielectric loss and high resistivity)
• Spark plug insulator
www.sentrotech.com
Microstructure of sintered, powdered aluminium
oxide doped with magnesium oxide
Alumina tubes
Suranaree University of Technology October 2007

9. Chapter 1
Traditional and engineering ceramics
Engineering ceramics Silicon nitride (Si3N4)
• Dissociate at T > 1800oC.
N2 flow
• Cannot be directly sintered reaction bonding.
nitriding
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Silicon powder
Microporous Si3N4
Hot pressing with
1-5%MgO
High strength
nonporous Si3N4
www.defazio-rotary.com
Suranaree University of Technology Silicon nitride for engineering applications
October 2007

10. Chapter 1
Traditional and engineering ceramics
Engineering ceramics Silicon carbide (SiC)
• Hard refractory carbide. www.stork.com
• Form skin of SiO2 at high temp.
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• Resistance to oxidation at high temp.
• Can be sintered 2100oC with 0.5-1%B.
• Fibrous reinforcement in ceramic-
matrix composite material.
SiC fibre reinforced Titanium matrix
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11. Chapter 1
Traditional and engineering ceramics
www.azom.com
Engineering ceramics Zirconia (ZrO2)
1170oC
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• Polymorphic: tetragonal monoclinic.
Volume expansion Zirconia
Heat treatment Cubic structure
• Mixed with CaO, MgO and Y2O3 Partially stabilized zirconia (PSZ).
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12. Chapter 1
Mechanical properties of ceramics
• Brittle
• High strength (varying from 0.7 – 7000 MPa)
• Better compressive strength than tensile (5-10 times)
Level of strength Materials
(MPa)
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> 1000 polycrystalline long ceramic fibres (Al2O3 , SiC): 1-2
GPa, single crystal short ceramic fibres (Al2O3 , SiC
whiskers): 5-20 GPa,
600-1000 Hot Pressed structural ceramics such as silicon
nitride, silicon carbide, alumina; sintered tetragonal
zirconia and sialon; cemented carbides
200-600 sintered pure alumina and SiC; tempered glass
100-200 impure and/or porous alumina; mullite; high-alumina
porcelains; reaction bonded silicon nitride and
carbide; glass ceramics
50-100 porcelains; steatite, cordierite; magnesia, polished
glasses;
<50 refractory; porous ceramics; glasses
Suranaree University of Technology October 2007

13. Chapter 1
Mechanical properties of ceramics
Deformation mechanisms
• Lack of plasticity due to ionic and covalent bonding (directional).
• Stressing of covalent crystal separation of electron-pair
bonds without subsequent reformation brittle
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• Deforming of ionic single crystal (MgO or NaCl) shows
considering amount of plastic deformation under compressive
force. However ionic polycrystals are brittle due to crack formation
at grain boundaries.
NaCl structure showing slip on
the (110) plane [110] direction
or AA’ and on the (100) plane
[010] direction BB’
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14. Chapter 1
Mechanical properties of ceramics
Factors affecting strength of ceramics Should control
• chemical composition
Depending on amount of defects • microstructure
giving stress concentration • surface condition
• temperature
• environment
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• Surface cracks
• Porosity Fabrication
• Inclusions
• Excessive grain sizes
Note:
No plastic deformation during crack
propagation from defects very brittle.
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15. Chapter 1
Mechanical properties of ceramics
Toughness of ceramics
• Low toughness due to covalent-ionic bonding.
• Using hot pressing, reaction bonding to improve toughness.
• Fibre-reinforced ceramic matrix composites.
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Fracture toughness of ceramics
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16. Chapter 1
Mechanical properties of ceramics
Toughness of ceramics Example
A reaction-bonded silicon nitride has a strength of 300 MPa and a
fracture toughness of 3.6 MPa.m1/2, What is the largest-size internal
crack that this material can support without fracturing? Given Y = 1
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K IC = Yσ f πa
a=
K 2
IC
=
(3.6MPa. m ) 2
πσ 2
f π (300MPa )2
a = 4.58 ×10 −5 m = 45.8µm
Therefore the largest internal crack 2a = 91.6 µm
Suranaree University of Technology October 2007

17. Chapter 1
Mechanical properties of ceramics
Transformation toughening of Partially Stabilized Zirconia (PSZ)
Sintering at 1800oC+rapid cooling to RT+
Zirconia reheating at 1400oC to give fine precipitates
+ (CaO, MgO or Y2O3) PSZ (metal stable)
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Volume expansion
Tetragonal monoclinic
under stressing
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18. Chapter 1
Mechanical properties of ceramics
Fatigue failure of ceramics
• Fatigue failure in ceramics is rare due to lack of
plastic deformation during cyclic loading.
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Fatigue cracking of polycrystalline alumina under cyclic loading
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19. Chapter 1
Mechanical properties of ceramics
Abrasive property of ceramics
• Hard and brittle
• Used as cutting, grinding and polishing tools.
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• Aluminium oxide
• Silicon carbide
• Titanium nitride
• Tungsten carbide
• Boron nitride
www.moldmakingtechnology.com
Ceramic cutting tools
Ceramic grinding wheels
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20. Chapter 1
Thermal properties of ceramics
• Low thermal conductivity
due to ionic-covalent
bonding insulator.
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• Also used as refractories
in metal, chemical and
glass industries.
Thermal conductivity of
ceramic materials
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21. Chapter 1
Thermal properties of ceramics
Ceramic refractory materials
img.alibaba.com
• A mixture of ceramic compounds
• Low-high temperature strength
• Low bulk density (2.1-3.3 g.cm-3)
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• Porosity insulating
Acidic refractory
Mainly based on SiO2 and Al2O3
Basic refractory
Refractory bricks (60% Al2O3)
Mainly based on magnesia (MgO), for hot blast furnace
lime (CaO) and Cr2O3
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22. Chapter 1
Thermal properties of ceramics
T. Udomphol
Suranaree University of Technology October 2007

23. Chapter 1
Thermal properties of ceramics
Acidic refractory Basic refractory
• Silica refractory has high • Basic refractory consists of
refractoriness, high mechanical mixtures of MgO, CaO and Cr2O3.
strength and rigidity at high • High bulk density
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temperature.
• High melting point
• Fireclays (fine plastic clays +
• Good resistance to chemical
flint + coarse clay or grog)
attack (basic slag, oxides)
• High alumina refractories
• Ex 92-95% MgO used for lining
contains 50-99% alumina,
in basic-oxygen steelmaking
giving higher fusion temperature
process
(more expensive than fireclay).
Suranaree University of Technology October 2007

24. Chapter 1
Thermal properties of ceramics
Ceramic tile insulation for the space shuttle orbiter
• About 24,000 ceramic tiles (70%) of silica-fibre compound are
used for insulating external surface of space shuttle.
T. Udomphol
Suranaree University of Technology October 2007

25. Chapter 1
Thermal properties of ceramics
media.nasaexplores.com
Ceramic tile insulation for the space shuttle orbiter
• High temperature reusable surface
(HTRS) made from 90% silica fibres
and 10% empty space.
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• Density = 0.144 g.cm-3
• Temp ~ 1260oC
Borosilicate coating
Microstructure of LI900 high-temperature
upload.wikimedia.org reusable surface insulation (HTRS)
Suranaree University of Technology October 2007

26. Chapter 1
Glass www.geocities.com
Definition of glass
• An inorganic and noncrystalline
material which maintains its
amorphous microstructure below its
glass transition temperature.
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Blown glass
Properties of glass www.arch.tu.ac.th
• Transparency
• Hardness and strength
• Corrosion/chemical resistance
• Vacuumtight enclosure
• Insulator
Tinted or heat-absorbed glass
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27. Chapter 1
Glass
Glass transition temperature (Tg)
• Unlike solidified metal, a glass
liquid does not crystallize but
follow an AD path.
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Temp (decrease)
Viscous Plastic Glassy
• The faster cooling rate,
the higher values of Tg.
Solidification of crystalline and amorphous
materials showing a change in specific volume
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28. Chapter 1
Glass
Structure of glass Glass forming oxide - SiO2
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Si-O tetrahedron Ideal crystalline silica Simple silica glass with
(crystobalite) no-long range order
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29. Chapter 1
Glass
Structure of glass Glass modifying oxides - Na2O, K2O, CaO, MgO
• Oxygen from Na2O breaks up
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silica network, leaving oxygen
atoms with an unshared electron.
• Na+ or K+ ions fits into interstices
of network.
Network modified glass (soda-lime glass)
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30. Chapter 1
Glass
Structure of glass Intermediate oxides in glass - Al2O3 , Pb2O3
• Oxides such as Al2O3 or Pb2O3
cannot form glass network but
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join into an existing network.
• Aluminosilicate glass
provides higher temperature than
common glass.
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31. Chapter 1
Glass
Glass composition
• Silica glass
No radiation damage
• Soda-lime glass
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Reduced Tm ~ 730 oC
• Borosilicate glass
(Pyrex glass)
Low thermal expansion
• Lead glass
Shielding from high
energy radiation
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32. Chapter 1
Glass
Viscous deformation of glasses
• Glass remains its viscous
(supercooled) liquid above Tg.
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Temp > Tg Viscosity
η = ηo e + Q RT
η = viscosity of the glass
ηo = pre-exponential constant
Q = molar activation energy for
viscous flow
R = gas constant
T = absolute temperature
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33. Chapter 1
Glass
Viscosity reference points
Working point Viscosity = 104 poise (103 Pa.s) fabrication
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Softening point Viscosity = 108 poise glass flows at an appreciate
rate under its own weight (and surface tension).
Annealing point Viscosity = 1013 poise relieving internal stresses
Viscosity = 1014.5 poise glass is rigid with slow
Strain point
rate of stress relaxation.
Note: glass are usually melt at temp relating to viscosity = 102 poise
Suranaree University of Technology October 2007

34. Chapter 1
Glass
Example A 96 % silica glass has a viscosity of 1013 P at its annealing point of
940oC and a viscosity of 108 P at its softening point of 1470oC.
Calculate the activation energy in kJ/mol for the viscous flow of this
glass in this temperature range.
Tanneal = 940+273 = 1213 K, ηap =1013 P η = η o e + Q RT
T. Udomphol
Tsoftening = 1470+273 = 1743 K, ηap =108 P
η ap Q  1 1  1013
= exp   −  = = 105
η sp R  Tap Tsp  108
 
 
 Q  1 1 
10 = exp 
5
 − 
 8.314  1213K 1743K 
Q = 382kJ / mol
Suranaree University of Technology October 2007

35. Chapter 1
Glass
Fabrications of glass
• Forming sheet and plate glass
• Float glass process molten glass ribbon moves on the top of
molten tin in a reducing atmosphere.
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• Remove glass sheet when the glass surface is hard enough
then pass to annealing furnace called lehr to remove residual
stresses.
• Blowing, pressing and casting of glass
• For deep, hallow shapes like bottles, jars, light bulbs envelops.
• Blowing air to force molten glass into moulds.
• Pressing a plunger into a mold containing molten glass.
• Casting into open moulds.
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36. Chapter 1
Glass
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Float glass process
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37. Chapter 1
Glass
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a) Reheat , b) final blow stage of a glass blowing machine process
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38. Chapter 1
Glass
Pyrex glass • Borosilicate glass
• Low thermal expansion
• Inert to almost all materials with the exception of
hydrofluoric acid, hot phosphoric acid and hot alkalies.
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Approximate composition
SiO2 81%
Na2O 4.0%
K2O 0.5
B2O3 13.0%
Al2O3 2.0%
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39. Chapter 1
Glass
Tempered glass
The surface cools first (by rapid air cooling) and contract while
the interior is warm, developing compressive on the surface and
tensile in the middle.
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a) After surface has cooled from high b) after centre has cooled.
temperature near glass-softening temperature.
Suranaree University of Technology October 2007

40. Chapter 1
Glass
Tempered glass
• Tempering effect increases
the strength (4 x stronger than
annealed glass.
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• Has higher impact resistance
than annealed glass.
• Ex: Auto side window, safety
glass for doors.
Distribution of residual stresses across the
sections of glass thermally tempered and
chemically strengthend
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41. Chapter 1
Glass
Laminated glass www.dupont.com
• Plastic interlayer (PVB-poly vinyle butyral)
is sandwiched with floated/annealed glass.
• Safety glass: Breaking like a spider web.
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http://en.wikipedia.org/
Laminated glass
Spider web breaking pattern
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42. Chapter 1
Glass
Laminated glass
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www.goodandquickglass.com
Suranaree University of Technology October 2007

43. Chapter 1
Glass
Used in supersonic aircraft glazing,
Chemical strengthened glass ophthalmic lenses.
• Submerging sodium aluminosilicate glass in a bath containing a
potassium salt at T~ 450-500oC for 6-10 h.
• Replacing Na ions with
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larger K ions on the glass
surface.
Producing thin
compressive stresses at
the surface and tensile
stresses in the centre.
Distribution of residual stresses across the section of glass
Suranaree University of Technology thermally tempered and chemically strengthened. October 2007