Presentation on theme: "Chapter 13: Applications and Processing of Ceramics"— Presentation transcript:
1 Chapter 13: Applications and Processing of Ceramics ISSUES TO ADDRESS...• How do we classify ceramics?• What are some applications of ceramics?• How is processing of ceramics different than for metals?
2 Classification of Ceramics Ceramic MaterialsGlassesClayproductsRefractoriesAbrasivesCementsAdvancedceramics-optical-compositereinforcecontainers/household-whitewarestructural-bricks forhigh T(furnaces)-sandpapercuttingpolishing-composites-enginerotorsvalvesbearings-sensorsAdapted from Fig and discussion in Section , Callister & Rethwisch 8e.
3 Ceramics Application: Die Blanks -- Need wear resistant properties!tensileforceAoddie• Die surface:-- 4 mm polycrystalline diamondparticles that are sintered onto acemented tungsten carbidesubstrate.-- polycrystalline diamond gives uniformhardness in all directions to reduce wear.Adapted from Fig. 11.8(d), Callister & Rethwisch 8e.Courtesy Martin Deakins, GE Superabrasives, Worthington, OH. Used with permission.
4 Ceramics Application: Cutting Tools -- for grinding glass, tungsten,carbide, ceramics-- for cutting Si wafers-- for oil drilling• Materials:-- manufactured single crystal or polycrystalline diamondsin a metal or resin matrix.oil drill bitsbladesSingle crystal diamonds-- polycrystalline diamondsresharpen by microfracturingalong cleavage planes.polycrystallinediamonds in a resinmatrix.Photos courtesy Martin Deakins,GE Superabrasives, Worthington,OH. Used with permission.
5 Ceramics Application: Sensors A substituting Ca2+ ionremoves a Zr 4+ ion andan O2- ion.Ca2+• Example: ZrO2 as an oxygen sensor• Principle: Increase diffusion rate of oxygen to produce rapid response of sensor signal to change in oxygen concentration• Approach:Add Ca impurity to ZrO2:-- increases O2- vacancies-- increases O2- diffusion rate• Operation:-- voltage difference produced when O2- ions diffuse from the external surface through the sensor to the reference gas surface magnitude of voltage difference partial pressure of oxygen at the external surfacereferencegas at fixedoxygen contentO2-diffusiongas with anunknown, higher-+voltage difference produced!sensor
6 Refractories• Materials to be used at high temperatures (e.g., in high temperature furnaces).• Consider the Silica (SiO2) - Alumina (Al2O3) system.• Silica refractories - silica rich - small additions of alumina depress melting temperature (phase diagram):Composition (wt% alumina)T(ºC)1400160018002000220020406080100alumina+mullite+ LLiquid(L)crystobalitealumina + L3Al2O3-2SiO2Fig , Callister & Rethwisch 8e. (Fig adapted from F.J. Klug and R.H. Doremus, J. Am. Cer. Soc. 70(10), p. 758, 1987.)
7 Advanced Ceramics: Materials for Automobile Engines Disadvantages:Ceramic materials are brittleDifficult to remove internal voids (that weaken structures)Ceramic parts are difficult to form and machineAdvantages:Operate at high temperatures – high efficienciesLow frictional lossesOperate without a cooling systemLower weights than current enginesPotential candidate materials: Si3N4, SiC, & ZrO2Possible engine parts: engine block & piston coatings
8 Advanced Ceramics: Materials for Ceramic Armor Components:-- Outer facing plates-- Backing sheetProperties/Materials:-- Facing plates -- hard and brittle— fracture high-velocity projectile — Al2O3, B4C, SiC, TiB2-- Backing sheets -- soft and ductile — deform and absorb remaining energy — aluminum, synthetic fiber laminates
9 Ceramic Fabrication Methods (i) PARTICULATE FORMINGCEMENTATIONGLASSFORMING• Blowing of Glass Bottles:-- glass formed by application of pressure -- mold is steel with graphite lining• Pressing:plates, cheap glassesGobParisonmoldPressingoperation• Fiber drawing:wind upSuspendedparisonFinishingmoldCompressedairAdapted from Fig. 13.8, Callister & Rethwisch 8e. (Fig is adapted from C.J. Phillips, Glass: The Miracle Maker, Pittman Publishing Ltd., London.)
10 Sheet Glass Forming Sheet forming – continuous casting sheets are formed by floating the molten glass on a pool of molten tinAdapted from Fig. 13.9, Callister & Rethwisch 8e.
11 Glass Structure • Basic Unit: Glass is noncrystalline (amorphous) • Fused silica is SiO2 to which no impurities have been added• Other common glasses contain impurity ions such as Na+, Ca2+, Al3+, and B3+Si04tetrahedron4-Si4+O2-• Quartz is crystallineSiO2:Si4+Na+O2-(soda glass)Adapted from Fig , Callister & Rethwisch 8e.
12 Glass Properties • Specific volume (1/r) vs Temperature (T): • Crystalline materials:-- crystallize at melting temp, Tm-- have abrupt change in spec.vol. at TmSpecific volumeSupercooledLiquidLiquid(disordered)• Glasses:-- do not crystallize-- change in slope in spec. vol. curve at glass transition temperature, Tg transparent - no grain boundaries to scatter lightGlass(amorphous solid)Crystalline(i.e., ordered)solidTTgTmAdapted from Fig. 13.6, Callister & Rethwisch 8e.
13 Glass Properties: Viscosity • Viscosity, h:-- relates shear stress () and velocity gradient (dv/dy):velocity gradientdvdytglassh has units of (Pa-s)
14 Log Glass Viscosity vs. Temperature soda-lime glass: 70% SiO balance Na2O (soda) & CaO (lime)• Viscosity decreases with Tborosilicate (Pyrex): % B2O3, 3.5% Na2O, 2.5% Al2O3fused silicasoda-limeglass96% silicaVycor: 96% SiO2, 4% B2O3Pyrexfused silica: > 99.5 wt% SiO2Viscosity [Pa-s]1102614200600100014001800T(ºC)Working range: glass-forming carried outannealing pointTmeltstrain pointAdapted from Fig. 13.7, Callister & Rethwisch 8e. (Fig is from E.B. Shand, Engineering Glass, Modern Materials, Vol. 6, Academic Press, New York, 1968, p. 262.)
15 Heat Treating Glass • Annealing: • Tempering: -- removes internal stresses caused by uneven cooling.• Tempering:-- puts surface of glass part into compression-- suppresses growth of cracks from surface scratches.-- sequence:before coolinghotinitial coolinghotcoolerat room temp.tensioncompression-- Result: surface crack growth is suppressed.
17 Ceramic Fabrication Methods (iia) GLASS FORMINGPARTICULATEFORMINGCEMENTATIONHydroplastic forming:• Mill (grind) and screen constituents: desired particle size• Extrude this mass (e.g., into a brick)rambilletcontainerforcedie holderdieAodextrusionAdapted from Fig. 12.8(c), Callister & Rethwisch 8e.• Dry and fire the formed piece
18 Ceramic Fabrication Methods (iia) GLASS FORMINGPARTICULATEFORMINGCEMENTATIONSlip casting:• Mill (grind) and screen constituents: desired particle size• Mix with water and other constituents to form slip• Slip casting operationsolid componentAdapted from Fig , Callister & Rethwisch 8e. (Fig is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.)hollow componentpour slipinto molddrainmold“greenceramic”absorb water• Dry and fire the cast piece
19 Typical Porcelain Composition (50%) 1. Clay(25%) 2. Filler – e.g. quartz (finely ground)(25%) 3. Fluxing agent (Feldspar) aluminosilicates plus K+, Na+, Ca+-- upon firing - forms low-melting-temp. glass
20 Hydroplasticity of Clay • Clay is inexpensive• When water is added to clay-- water molecules fit in between layered sheets-- reduces degree of van der Waals bonding-- when external forces applied – clay particles free to move past one another – becomes hydroplasticweak vander WaalsbondingchargeneutralSi4+Al3+-OHO2-Shear• Structure ofKaolinite Clay:Adapted from Fig , Callister & Rethwisch 8e. (Fig is adapted from W.E. Hauth, "Crystal Chemistry of Ceramics", American Ceramic Society Bulletin, Vol. 30 (4), 1951, p. 140.)
21 Drying and Firing• Drying: as water is removed - interparticle spacings decrease – shrinkage .Adapted from Fig , Callister & Rethwisch 8e. (Fig is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.)wet bodypartially drycompletely dryDrying too fast causes sample to warp or crack due to non-uniform shrinkage• Firing:-- heat treatment between ºC-- vitrification: liquid glass forms from clay and flux – flows between SiO2 particles. (Flux lowers melting temperature).Adapted from Fig , Callister & Rethwisch 8e. (Fig is courtesy H.G. Brinkies, Swinburne University of Technology, Hawthorn Campus, Hawthorn, Victoria, Australia.)Si02 particle(quartz)glass formedaroundthe particlemicrograph of porcelain70 mm
22 Ceramic Fabrication Methods (iib) GLASS FORMINGPARTICULATEFORMINGCEMENTATIONPowder Pressing: used for both clay and non-clay compositions.• Powder (plus binder) compacted by pressure in a mold-- Uniaxial compression - compacted in single direction-- Isostatic (hydrostatic) compression - pressure applied by fluid - powder in rubber envelope-- Hot pressing - pressure + heat (
23 Sintering Sintering occurs during firing of a piece that has been powder pressed-- powder particles coalesce and reduction of pore sizeAdapted from Fig , Callister & Rethwisch 8e.Aluminum oxide powder:-- sintered at 1700ºCfor 6 minutes.15 mAdapted from Fig , Callister & Rethwisch 8e. (Fig is from W.D. Kingery, H.K. Bowen, and D.R. Uhlmann, Introduction to Ceramics, 2nd ed., John Wiley and Sons, Inc., 1976, p. 483.)
24 Tape Casting Thin sheets of green ceramic cast as flexible tape Used for integrated circuits and capacitorsSlip = suspended ceramic particles + organic liquid (contains binders, plasticizers)Fig , Callister & Rethwisch 8e.
25 Ceramic Fabrication Methods (iii) GLASS FORMINGPARTICULATEFORMINGCEMENTATION• Hardening of a paste – paste formed by mixing cement material with water• Formation of rigid structures having varied and complex shapes• Hardening process – hydration (complex chemical reactions involving water and cement particles)• Portland cement – production of:-- mix clay and lime-bearing minerals-- calcine (heat to 1400ºC)-- grind into fine powder