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

Ceramic Memory Pottery Cutting Aerospace Medical

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.

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

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

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

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

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

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)

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

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

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

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.

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

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

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.

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

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

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

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

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

Powder Sintering (분말 소결) 15 m

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.

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.

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

Porosity (기공) Porosity decreases modulus of elasticity and fracture strengths. Volume fraction porosity Modulus of elasticity (GPa) Flexural strength (Mpa) 0 0.1 0.2 0.3 0.4 0.5 0.6 200 100

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) 250-1000 100-820 275-700 69 304 345 393 Material s fs (MPa) E(GPa) (rect. cross section) (circ. cross section) 27

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

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

figun_13_p501a Glasses suspended Parison Compressed air

Glass vs. Glass-ceramic

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