Traditional and engineering ceramicsTraditional and engineering ceramics
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Traditional ceramics Clay Silica Feldspar+ +
2322
2322
6..
6..
SiOOAlONa
SiOOAlOK2SiOOHSiOOAl 2232 2.2.
• Structural clay products : bricks,
sewer pipe, roofing tile
• EX: Triaxial bodies:Whiteware,
porcelain, chinaware, sanitary ware.
Reactions of a triaxial body
Traditional and engineering ceramicsTraditional and engineering ceramics
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Traditional ceramics
Triaxial whiteware chemical composition
Traditional and engineering ceramicsTraditional and engineering ceramics
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Traditional ceramics
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Electron micrograph of an electrical
insulator porcelain (etched 10 s, 0oC,
40% HF, silica replica)
quartz Mullite needles
High silica glass
Traditional and engineering ceramicsTraditional and engineering ceramics
Traditional ceramics
T. Udomphol
Chapter 1
Traditional and engineering ceramicsTraditional and engineering ceramics
Slip casting processMaster and plaster moulds
Fresh cast
Dry
Slip casting
Colour paintFire
Suranaree University of Technology October 2007
http://www.lindawilsonceramics.co.za/3.html
Pottery
T. Udomphol
Chapter 1
Traditional and engineering ceramicsTraditional and engineering ceramics
Slip casting processSlip casting process Sanitaryware
Slip casting in plaster moulds and demoulding
www.3emmegi.com
Suranaree University of Technology October 2007
Slip preparation
in ball millOHOHCaSOOHCaSO Co
223
221
4
150
24 .2. + →
Hemihydrate plaster – produced from gymsum
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Traditional and engineering ceramicsTraditional and engineering ceramics
Engineering ceramics • Contain more of pure compounds of oxides,
carbides, nitrides.
• Ex: Al2O3, Si3N4, SiC, ZrO2 , refractory
oxides
Mechanical properties of engineering ceramics
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Traditional and engineering ceramicsTraditional and engineering ceramics
Engineering ceramics Alumina
• Refractory tubing
• High purity crucibles for high temp
• High quality electrical applications
(low dielectric loss and high resistivity)
• Spark plug insulator
Microstructure of sintered, powdered aluminium
oxide doped with magnesium oxide
Alumina tubes
www.sentrotech.com
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Traditional and engineering ceramicsTraditional and engineering ceramics
Engineering ceramics Silicon nitride (Si3N4)
• Dissociate at T > 1800oC.
• Cannot be directly sintered � reaction bonding.
Silicon nitride for engineering applications
Silicon powder
N2 flow
nitriding
Microporous Si3N4
High strength
nonporous Si3N4
Hot pressing with
1-5%MgO
www.defazio-rotary.com
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Traditional and engineering ceramicsTraditional and engineering ceramics
Engineering ceramics Silicon carbide (SiC)
• Hard refractory carbide.
• Form skin of SiO2 at high temp.
• 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
www.stork.com
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Traditional and engineering ceramicsTraditional and engineering ceramics
Engineering ceramics Zirconia (ZrO2)
• Polymorphic: tetragonal � monoclinic.
• Mixed with CaO, MgO and Y2O3 � Partially stabilized zirconia (PSZ).
1170oC
Volume expansion
Heat treatment Cubic structure
www.azom.com
Zirconia
Mechanical properties of ceramicsMechanical properties of ceramics
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
• Brittle
• High strength (varying from 0.7 – 7000 MPa)
• Better compressive strength than tensile (5-10 times)
refractory; porous ceramics; glasses<50
porcelains; steatite, cordierite; magnesia, polished
glasses;
50-100
impure and/or porous alumina; mullite; high-alumina
porcelains; reaction bonded silicon nitride and
carbide; glass ceramics
100-200
sintered pure alumina and SiC; tempered glass200-600
Hot Pressed structural ceramics such as silicon
nitride, silicon carbide, alumina; sintered tetragonal
zirconia and sialon; cemented carbides
600-1000
polycrystalline long ceramic fibres (Al2O3, SiC): 1-2
GPa, single crystal short ceramic fibres (Al2O3, SiC
whiskers): 5-20 GPa,
> 1000
MaterialsLevel of strength
(MPa)
Mechanical properties of ceramicsMechanical properties of ceramics
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
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
• 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’
Mechanical properties of ceramicsMechanical properties of ceramics
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Factors affecting strength of ceramics
Depending on amount of defects
� giving stress concentration
• Surface cracks
• Porosity
• Inclusions
• Excessive grain sizes
No plastic deformation during crack
propagation from defects � very brittle.
Note:
Fabrication
Should control
• chemical composition
• microstructure
• surface condition
• temperature
• environment
Mechanical properties of ceramicsMechanical properties of ceramics
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Toughness of ceramics
• Low toughness due to covalent-ionic bonding.
• Using hot pressing, reaction bonding to improve toughness.
• Fibre-reinforced ceramic matrix composites.
Fracture toughness of ceramics
Mechanical properties of ceramicsMechanical properties of ceramics
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
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
( )( )
mma
MPa
mMPaKa
aYK
f
IC
fIC
µ
ππσ
πσ
8.451058.4
300
.6.3
5
2
2
2
2
=×=
==
=
−
Therefore the largest internal crack 2a = 91.6 µm
Mechanical properties of ceramicsMechanical properties of ceramics
T. Udomphol
Chapter 1
Transformation toughening of Partially Stabilized Zirconia (PSZ)
Zirconia
+ (CaO, MgO or Y2O3) PSZ (metal stable)
Sintering at 1800oC+rapid cooling to RT+
reheating at 1400oC to give fine precipitates
Suranaree University of Technology October 2007
Tetragonal ���� monoclinic
under stressing
Volume expansion
Mechanical properties of ceramicsMechanical properties of ceramics
Suranaree University of Technology October 2007
T. Udomphol
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Fatigue failure of ceramics
• Fatigue failure in ceramics is rare due to lack of
plastic deformation during cyclic loading.
Fatigue cracking of polycrystalline alumina under cyclic loading
Mechanical properties of ceramicsMechanical properties of ceramics
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Abrasive property of ceramics
• Hard and brittle
• Used as cutting, grinding and polishing tools.
www.moldmakingtechnology.com
Ceramic grinding wheelsCeramic cutting tools
• Aluminium oxide
• Silicon carbide
• Titanium nitride
• Tungsten carbide
• Boron nitride
Thermal properties of ceramicsThermal properties of ceramics
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
• Low thermal conductivity
due to ionic-covalent
bonding � insulator.
• Also used as refractories
in metal, chemical and
glass industries.
Thermal conductivity of
ceramic materials
Thermal properties of ceramicsThermal properties of ceramics
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Ceramic refractory materials
• A mixture of ceramic compounds
• Low-high temperature strength
• Low bulk density (2.1-3.3 g.cm-3)
• Porosity � insulating
Refractory bricks (60% Al2O3)
for hot blast furnace
img.alibaba.com
Basic refractory
Acidic refractory
Mainly based on SiO2 and Al2O3
Mainly based on magnesia (MgO),
lime (CaO) and Cr2O3
Thermal properties of ceramicsThermal properties of ceramics
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Thermal properties of ceramicsThermal properties of ceramics
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Acidic refractory Basic refractory
• Silica refractory has high
refractoriness, high mechanical
strength and rigidity at high
temperature.
• Fireclays (fine plastic clays +
flint + coarse clay or grog)
• High alumina refractories
contains 50-99% alumina,
giving higher fusion temperature
(more expensive than fireclay).
• Basic refractory consists of
mixtures of MgO, CaO and Cr2O3.
• High bulk density
• High melting point
• Good resistance to chemical
attack (basic slag, oxides)
• Ex 92-95% MgO used for lining
in basic-oxygen steelmaking
process
Thermal properties of ceramicsThermal properties of ceramics
T. Udomphol
Chapter 1
Ceramic tile insulation for the space shuttle orbiter
Suranaree University of Technology October 2007
• About 24,000 ceramic tiles (70%) of silica-fibre compound are
used for insulating external surface of space shuttle.
Thermal properties of ceramicsThermal properties of ceramics
T. Udomphol
Chapter 1
Ceramic tile insulation for the space shuttle orbiter
Suranaree University of Technology October 2007
Microstructure of LI900 high-temperature
reusable surface insulation (HTRS)
• High temperature reusable surface
(HTRS) made from 90% silica fibres
and 10% empty space.
• Density = 0.144 g.cm-3
• Temp ~ 1260oC
media.nasaexplores.com
upload.wikimedia.org
Borosilicate coating
GlassGlass
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
• Transparency
• Hardness and strength
• Corrosion/chemical resistance
• Vacuumtight enclosure
• Insulator
Properties of glass
Blown glass
www.geocities.com
Tinted or heat-absorbed glass
www.arch.tu.ac.th
Definition of glass
• An inorganic and noncrystalline
material which maintains its
amorphous microstructure below its
glass transition temperature.
GlassGlass
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Glass transition temperature (Tg)
• Unlike solidified metal, a glass
liquid does not crystallize but
follow an AD path.
Viscous Plastic Glassy
Temp (decrease)
• The faster cooling rate,
the higher values of Tg.Solidification of crystalline and amorphous
materials showing a change in specific volume
GlassGlass
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Structure of glass Glass forming oxide - SiO2
Si-O tetrahedron Ideal crystalline silica
(crystobalite)Simple silica glass with
no-long range order
GlassGlass
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Structure of glass Glass modifying oxides - Na2O, K2O, CaO, MgO
• Oxygen from Na2O breaks up
silica network, leaving oxygen
atoms with an unshared electron.
• Na+ or K+ ions fits into interstices
of network.
Network modified glass (soda-lime glass)
GlassGlass
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Structure of glass Intermediate oxides in glass - Al2O3 , Pb2O3
• Oxides such as Al2O3 or Pb2O3
cannot form glass network but
join into an existing network.
• Aluminosilicate glass
provides higher temperature than
common glass.
GlassGlass
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Glass composition
• Silica glass
• Soda-lime glass
• Borosilicate glass
(Pyrex glass)
• Lead glass
No radiation damage
Reduced Tm ~ 730 oC
Low thermal expansion
Shielding from high
energy radiation
GlassGlass
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Viscous deformation of glasses
• Glass remains its viscous
(supercooled) liquid above Tg.
Temp > Tg Viscosity
RTQ
oe+=ηη
η = viscosity of the glass
ηo = pre-exponential constant
Q = molar activation energy for
viscous flow
R = gas constant
T = absolute temperature
GlassGlass
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Viscosity reference points
Working point
Softening point
Annealing point
Strain point
Viscosity = 104 poise (103 Pa.s) � fabrication
Viscosity = 108 poise � glass flows at an appreciate
rate under its own weight (and surface tension).
Viscosity = 1013 poise � relieving internal stresses
Viscosity = 1014.5 poise � glass is rigid with slow
rate of stress relaxation.
Note: glass are usually melt at temp relating to viscosity = 102 poise
GlassGlass
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
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
Tsoftening = 1470+273 = 1743 K, ηap =108 P
RTQ
oe+=ηη
5
8
13
1010
1011exp ==
−=
spapsp
ap
TTR
Q
η
η
molkJQ
KK
Q
/382
1743
1
1213
1
314.8exp105
=
−=
GlassGlass
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Fabrications of glass
• Forming sheet and plate glass
• Blowing, pressing and casting of glass
• Float glass process � molten glass ribbon moves on the top of
molten tin in a reducing atmosphere.
• Remove glass sheet when the glass surface is hard enough �
then pass to annealing furnace called lehr to remove residual
stresses.
• 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.
GlassGlass
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Float glass process
GlassGlass
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
a) Reheat , b) final blow stage of a glass blowing machine process
GlassGlass
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Pyrex glass • Borosilicate glass
• Low thermal expansion
• Inert to almost all materials with the exception of
hydrofluoric acid, hot phosphoric acid and hot alkalies.
2.0%Al2O3
13.0%B2O3
0.5K2O
4.0%Na2O
81%SiO2
Approximate composition
GlassGlass
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
b) after centre has cooled.a) After surface has cooled from high
temperature near glass-softening temperature.
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.
Tempered glass
GlassGlass
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Distribution of residual stresses across the
sections of glass thermally tempered and
chemically strengthend
Tempered glass
• Tempering effect increases
the strength (4 x stronger than
annealed glass.
• Has higher impact resistance
than annealed glass.
• Ex: Auto side window, safety
glass for doors.
GlassGlass
Suranaree University of Technology October 2007
T. Udomphol
Chapter 1
Laminated glass
• Plastic interlayer (PVB-poly vinyle butyral)
is sandwiched with floated/annealed glass.
• Safety glass: Breaking like a spider web.
Laminated glass
www.dupont.com
Spider web breaking pattern
http://en.wikipedia.org/
GlassGlass
T. Udomphol
Chapter 1
Laminated glass
www.goodandquickglass.comSuranaree University of Technology October 2007
GlassGlass
T. Udomphol
Chapter 1
Chemical strengthened glass
Suranaree University of Technology October 2007
• Submerging sodium aluminosilicate glass in a bath containing a
potassium salt at T~ 450-500oC for 6-10 h.
• Replacing Na ions with
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
thermally tempered and chemically strengthened.
Used in supersonic aircraft glazing,
ophthalmic lenses.