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

Transcription

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

2 OCW Ionic crystal structures Crystal Structures s high temperature, hardness, chemical stable > brittle Space Shuttle Heat Protection

3 OCW Cement and Concrete Glass (MIT kids 5min) brittle, crack, rapid cooling, compressive stress on surface

4 KOCW 세라믹결정구조 세라믹, 유리, 탄소, 강도시험 세라믹스의분류및활용

5 s are compounds of metallic and nonmetallic(o, N, C) elements. Bonding between atoms is ionic or covalent. Pottery Aerospace Medical Cutting IC Glass

6 Bonding Ionic bonding, Covalent bonding. CaF 2 : Ionic SiC: Covalent

7 Ionic Bonding & Structure Ionic bonding + - e - Ionic radius - stable structures ZnS NaCl CsCl unstable stable stable

8 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

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

10 Modulus of elasticity (GPa) Flexural strength (Mpa) Porosity ( 기공 ) Strneggth ( 강도 ) Porosity decreases modulus of elasticity and fracture strengths Volume fraction porosity

11 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 Si carbide Al oxide glass (soda-lime)

12 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

13 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

14 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 -

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

16 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 crystobalite+l SiO 2 mullite + L 3Al 2 O 3-2SiO 2 mullite + crystobalite alumina +mullite Al 2 O 3 %

17 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 )

18 Alumina, Al 2 O 3 Powder Sintering Bauxite(Al 2 O 3 H 2 O) Aluminum ingot

19 Zirconia, ZrO 2 High melting point (2700 C), Low thermal conductivity (4.0 W/mK ) Refractories for iron casting

20 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

21 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.

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

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

24 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.

25 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

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

27 Limestone( 석회암 ) CaCO 3 Application: Cement, Glass, Tile, Gypsum( 석고 CaSO 4 H 2 O) board for insulation & soundproofing

28 Products 1. Structural: bricks, floor and roof tiles 2. Refractories: iron making crucible 3. Whitewares: tableware, pottery, bathroom 4. Special: implants, disk brake, bearing

29 Porcelain ( 도자기 ) Fine particle(quartz, Clay, Feldspar) + wet state plasticity form dry state Sintering( 소결 ) by fire Porcelain

30 Powder Sintering ( 분말소결 ) 15 m

31 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 -

32 Glass vs. Glass-ceramic

33 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.

34 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

35 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] fused silica: > 99.5 wt% SiO 2 strain point annealing range T melt T( C) T deform : soft enough to deform or work

36 Brittle Fracture ( 취성파괴 ) Micro cracks amplify tensile stress Low fractural strength & tensile strength. Fracture surface of glass rod

37 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

38 Products Beaker Display cover Green house glass