1. Ceramics (세라믹) Associate Professor Su-Jin Kim
School of Mechanical Engineering
Gyeongsang National University

2. Ceramic
Memory
Pottery
Cutting
Aerospace
Medical

3. Ceramic Properties: Applications: Fabrication
- Tm for glass is moderate, but large for other ceramics.
- Small toughness, ductility; large moduli & creep resist.
Applications:
- High T, wear resistant, novel uses from charge neutrality.
Fabrication
- some glasses can be easily formed
- other ceramics can not be formed or cast.

4. Ceramics
Ceramics are compounds of metallic and non-metallic(O, N, C) elements.
Bonding between atoms is ionic or covalent .

5. Classification of Ceramics
Various types of ceramics are:
Silicon Si: Silica SiO2
Oxids O: Alumina Al2O3, Zirconia ZrO2
Carbides C: Tungstem carbides WC, Silicon carbide SiC
Nitrides N: Cubic boron nitride cBN, Titanium nitride TiN, Sialon

6. Silicate Ceramics(규산염 세라믹)
Most common elements on earth are Si & O
SiO2 (silica) : The strong Si-O bonds lead to a high melting temperature (1710°C) for this material
Quarz(석영), Glass(유리), Clay(점토) …
SiO 4
tetrahedron 4- Si 4+ O 2 - 6

7. Silica, SiO2
Crystalline: Quartz send(규사), Rock crystal(수정) Non-crystalline (amorphous): Glass (유리)

8. Alumina Silicate(규산알미늄) Al2O3 SiO2 H2O
Refractories(내화벽돌) used in high temperature furnaces.
Clay(점토) adjacent layers are bound by van der Waal’s forces.
Al2O3%
T(°C)
1400
1600
1800
2000 20 40 60 80
100
alumina
+mullite
mullite
3Al2O3-2SiO2
+ L
Liquid
(L) +
crystobalite
crystobalite+L
alumina+L

9. Oxides (산화물), O Excellent wear resistance (Vickers hardness 10 GPa)
High rigidity (Young’s ratio 300GPa)
High electric resistance (>1015Ωcm)
White color tone
Ex) Alumina(Al2O3) Zirconia(ZrO2)

10. Alumina, Al2O3
Powder  Sintering
Bauxite(Al2O3 H2O)  Aluminum ingot

11. Zirconia, ZrO2
High melting point (2700C), Low thermal conductivity (4.0 W/mK )
Refractories for iron casting

12. Nitrides (질화물) N Cutting materials and hard coatings: TiN, SiN
Hexagonal boron nitride, h-BN : a layered structure is a useful high-temperature (~900°C) lubricant
Gallium nitride (GaN) : blue light LED

13. Cubic boron nitride, CBN
CBN is widely used as an abrasive.
Insolubility in iron alloys at high temperatures. Tool for cutting or grinding steel alloy.
High thermal conductivity and electrical resistivity.

14. Carbides (탄화물) C Metal + Carbon C, Black color tone
Tungsten carbides WC (초경) : Cutting tools
Titanium carbide TiC : Cutting tools, CVD coating

15. Silicon Carbide, SiC Popular abrasive
Carbon-fiber-reinforced silicon carbide (C/SiC)is used for brake discs
Semiconductor: MOSFET

16. Diamond
SCD (Single Cristal Diamond) is covalent bonded single crystal of Carbon C
It is hardest in the world but decompose in air at 973 K.
PCD (Poly Crystal Diamond) is used to cut aluminum alloys, ceramics, and stone. But it is soluble in iron alloy to give carbides.

17. Graphite(흑연) Graphite is a layered structure of carbon C.
Weak van der Waal’s forces between layers
Planes slide easily over one another – low friction good solid lubricant

18. Carbon nanotubes
Sheet of graphite rolled into a tube, Ends capped with fullerene hemispheres
It has high strength and electrical current-carrying capability.

19. Limestone(석회암) CaCO3 Application: Cement, Glass, Tile, Ceramic
Gypsum(석고 CaSO4 H2O) board for insulation & soundproofing

20. Ceramic Products Structural: bricks, floor and roof tiles
Refractories: iron making crucible
Whitewares: tableware, pottery, bathroom
Special: implants, disk brake, bearing

21. figun_13_p501a Porcelain (도자기)
Fine particle(Quartz, Clay, Feldspar) + wet state  plasticity form  dry state  Sintering(소결) by fire  Porcelain

22. Powder Sintering (분말 소결)
15 m

23. General properties of ceramics
Ceramics are brittle, have high compressive strength and hardness at elevated temperatures, high elastic modulus, low toughness, low density, low thermal expansion, and low thermal and electrical conductivity.
1. Mechanical properties
Sensitivity to cracks, impurities and porosity
Strength in tension is lower than compressive strength.
2. Physical properties
Low specific gravity and have high melting temperatures.

24. Mechanical properties
Consider to be linearly elastic and brittle.
Bulk formed glass has low strength(<40 MPa) due to microcracks on the surface, but the strength of glass fiber is about 2 GPa stronger than steel.
Low thermal conductivity and high electric resistance.
Thermal expansion coefficient is lower than metals and plastics.
Optical properties can be modified by varying their composition and treatment.

25. Stress-Strain (응력-변형율)
fig_12_29
Stress-Strain (응력-변형율)
Room T behavior is usually elastic, with brittle failure
250 50
Stress (Mpa)
0.0008
Strain
Glass
Aluminum oxide

26. Porosity (기공)
Porosity decreases modulus of elasticity and fracture strengths.
Volume fraction porosity
Modulus of elasticity (GPa)
Flexural strength (Mpa)
200
100

27. Flexural strength(굴곡강도)
• 3-point bend test to measure flexural strength & elastic modulus. F
L/2
d = midpoint
deflection
cross section R b d
rect.
circ.
location of max tension
• Flexural strength:
• Typical values:
Si nitride
Si carbide
Al oxide
glass (soda-lime) 69
304
345
393
Material s fs
(MPa) E(GPa)
(rect. cross section)
(circ. cross section) 27

28. Ex) Ceramic for 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 28

29. Glass (유리) Glass is non-crystalline (amorphous) NaO2CaO6SiO2
Some elements replaced by MgO, Al2O3 and K2O
They are resistant to chemical attacks and ranked by their resistance to acid, alkali or water corrosion. Si 4+ Na + O 2 - 29

30. figun_13_p501a
Glasses
suspended
Parison
Compressed
air

31. Glass vs. Glass-ceramic

32. Glass Properties • Specific volume (1/r) vs Temperature (T):
• Glasses:
- do not crystallize
- change in slope in spec. vol. curve at glass transition temperature, Tg transparent
- no crystals to scatter light
Supercooled
Liquid
Liquid
(disordered)
Glass
(amorphous solid)
Crystalline
(i.e., ordered)
solid
• Crystalline materials:
- crystallize at melting temp, Tm
- have abrupt change in spec.
vol. at Tm T T g T m 32