s ( 세라믹 ) Associate Professor Su-Jin Kim School of Mechanical Engineering Gyeongsang National University
OCW Ionic crystal structures https://youtu.be/a3cphn_ogvq?list=pl8eaogbez9xiwgbmcihctmo4bxsb4v8hm Crystal Structures https://youtu.be/jilo8ippzis s high temperature, hardness, chemical stable > brittle https://youtu.be/9dopxiv4css Space Shuttle Heat Protection https://youtu.be/ozg3x7yy80o
OCW Cement and Concrete https://youtu.be/woaus5xnjuo Glass (MIT kids 5min) brittle, crack, rapid cooling, compressive stress on surface https://youtu.be/1vrduybhvyo
KOCW 세라믹결정구조 http://www.kocw.net/home/cview.do?lid=0f4393f1fb61cdd3 세라믹, 유리, 탄소, 강도시험 http://www.kocw.net/home/cview.do?lid=2f87428d88f9a817 세라믹스의분류및활용 http://www.kocw.net/home/cview.do?lid=a0d249cb4b34f91b
s are compounds of metallic and nonmetallic(o, N, C) elements. Bonding between atoms is ionic or covalent. Pottery Aerospace Medical Cutting IC Glass
Bonding Ionic bonding, Covalent bonding. CaF 2 : Ionic SiC: Covalent
Ionic Bonding & Structure Ionic bonding + - e - Ionic radius - stable structures ZnS - - + - - - - + - - - - + - - NaCl CsCl unstable stable stable
General properties of ceramics High melting temperature High hardness (wear resistance) Chemical stability Electrical & thermal insulator Brittle (linear elastic) Compression strength >> Tension (sensitive to crack) Low thermal expansion
Stress (Mpa) Stress-Strain ( 응력 - 변형율 ) Room T behavior is usually elastic, with brittle failure 250 Aluminum oxide 50 Glass Strain 0.0008
Modulus of elasticity (GPa) Flexural strength (Mpa) Porosity ( 기공 ) Strneggth ( 강도 ) Porosity decreases modulus of elasticity and fracture strengths. 200 100 0 0.1 0.2 0.3 0.4 0.5 0.6 Volume fraction porosity
Flexural strength( 굴곡강도 ) 3-point bend test to measure flexural strength & elastic modulus. cross section b rect. d R circ. F L/2 L/2 location of max tension d = midpoint deflection Flexural strength: s fs s fs 3 2bd F f F f R L 3 L 2 (rect. cross section) (circ. cross section) Material Typical values: s fs (MPa) E(GPa) Si nitride 250-1000 Si carbide 100-820 Al oxide 275-700 glass (soda-lime) 69 304 345 393 69
Ex) 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 voidsweaken the engine Difficult to machine Possible parts engine block, piston coatings, jet engines Ex: Si 3 N 4, SiC, & ZrO 2
Classification of s Various types of ceramics are: Silicon Si: Silica SiO 2 Oxids O: Alumina Al 2 O 3, Zirconia ZrO 2 Carbides C: Tungstem carbides WC, Silicon carbide SiC Nitrides N: Cubic boron nitride cbn, Titanium nitride TiN, Sialon
Silicate s( 규산염세라믹 ) Most common elements on earth are Si & O SiO 2 (silica) : The strong Si-O bonds lead to a high melting temperature (1710 C) for this material Quarz( 석영 ), Glass( 유리 ), Clay( 점토 ) 4- SiO 4 tetrahedron Si 4+ O 2 -
Silica, SiO2 Crystalline: Quartz send( 규사 ), Rock crystal( 수정 ) Non-crystalline (amorphous): Glass ( 유리 )
Alumina Silicate( 규산알미늄 ) Al 2 O 3 SiO 2 H 2 O Refractories( 내화벽돌 ) used in high temperature furnaces. Clay( 점토 ) adjacent layers are bound by van der Waal s forces. T( C) 2000 Liquid (L) alumina+l 1800 1600 crystobalite+l 1400 0 SiO 2 mullite + L 3Al 2 O 3-2SiO 2 mullite + crystobalite alumina +mullite 20 40 60 80 100 Al 2 O 3 %
Oxides ( 산화물 ), O Excellent wear resistance (Vickers hardness 10 GPa) High rigidity (Young s ratio 300GPa) High electric resistance (>10 15 Ωcm) White color tone Ex) Alumina(Al 2 O 3 ) Zirconia(ZrO 2 )
Alumina, Al 2 O 3 Powder Sintering Bauxite(Al 2 O 3 H 2 O) Aluminum ingot https://youtu.be/h7tuweuahai
Zirconia, ZrO 2 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 ) CaCO 3 Application: Cement, Glass, Tile, Gypsum( 석고 CaSO 4 H 2 O) board for insulation & soundproofing
Products 1. Structural: bricks, floor and roof tiles 2. Refractories: iron making crucible 3. Whitewares: tableware, pottery, bathroom 4. Special: implants, disk brake, bearing
Porcelain ( 도자기 ) Fine particle(quartz, Clay, Feldspar) + wet state plasticity form dry state Sintering( 소결 ) by fire Porcelain
Powder Sintering ( 분말소결 ) 15 m
Glass ( 유리 ) Glass is non-crystalline (amorphous) NaO 2 CaO6SiO 2 Some elements replaced by MgO, Al 2 O 3 and K 2 O They are resistant to chemical attacks and ranked by their resistance to acid, alkali or water corrosion. Na + Si 4+ O 2 -
Glass vs. Glass-ceramic
Glass Properties Easy processing (medium melting temperature) Transparent High hardness Corrosion resistance Fragile(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.
Specific volume vs Temperature Specific volume Supercooled Liquid Glass (amorphous solid) Liquid (disordered) Glasses: - do not crystallize - change in slope in spec. vol. curve at glass transition temperature, Tg - transparent - no crystals to scatter light Crystalline (i.e., ordered) T g T m solid T Crystalline materials: - crystallize at melting temp, Tm - have abrupt change in spec. vol. at Tm
Glass Viscosity( 점도 ) vs. T and Impurities Viscosity decreases with T Impurities lower Tdeform soda-lime glass: 70% SiO 2 balance Na 2 O (soda) & CaO (lime) borosilicate (Pyrex): 13% B 2 O 3, 3.5% Na 2 O, 2.5% Al 2 O 3 Vycor: 96% SiO 2, 4% B 2 O 3 Viscosity [Pa s] 10 14 10 10 fused silica: > 99.5 wt% SiO 2 strain point annealing range 10 6 10 2 1 T melt 200 600 1000 1400 1800 T( C) T deform : soft enough to deform or work
Brittle Fracture ( 취성파괴 ) Micro cracks amplify tensile stress Low fractural strength & tensile strength. Fracture surface of glass rod
Heat Treating Glass Annealing: --removes internal stress caused by uneven cooling. Tempering: --puts surface of glass part into compression --suppresses growth of cracks from surface scratches. --sequence: before cooling hot surface cooling cooler hot cooler --Result: surface crack growth is suppressed. further cooled compression tension compression
Products Beaker Display cover Green house glass