Taxonomy of Ceramics Glasses Clay Refractories products optical whiteware bricks for high T composite bricks furnaces reinforce containers household Abrasives Cements Advanced ceramics sandpaper composites engine cutting structural rotors polishing valves bearings sensors 1 Application Refractories Need a material to use in high temperature furnaces Consider the Silica SiO2 Alumina Al2O3 system Phase diagram shows mullite alumina and crystobalite as candidate refractories 2200 T C 3Al2O3 2SiO2 2000 Liquid L 1800 mullite alumina L mullite L crystobalite L 1600 1400 mullite crystobalite 0 20 alumina mullite 40 60 80 100 Composition wt alumina 2 Application Cutting Tools Tools for grinding glass tungsten carbide ceramics for cutting Si wafers for oil drilling Solutions oil drill bits blades coated single crystal diamonds polycrystalline diamonds in a resin matrix 3 Application Sensors Example Oxygen sensor ZrO2 Principle Make diffusion of ions Ca 2 fast for rapid response Approach Add Ca impurity to ZrO2 A Ca 2 impurity removes a Zr 4 and a O2 ion increases O2 vacancies increases O2 diffusion rate Operation voltage difference produced when O2 ions diffuse from the external surface of the sensor to the reference gas sensor gas with an unknown higher oxygen content O2diffusion reference gas at fixed oxygen content voltage difference produced 4 Ceramic Fabrication Methods I PARTICULATE FORMING GLASS FORMING CEMENTATION Pressing Gob Pressing operation Parison mold Fiber drawing Compressed air Blowing suspended Parison Finishing mold wind up 5 Sheet Glass Forming Sheet forming continuous draw originally sheet glass was made by floating glass on a pool of mercury 6 Glass Structure Basic Unit 4Si0 4 tetrahedron Si 4 O2 Quartz is crystalline SiO2 Glass is amorphous Amorphous structure occurs by adding impurities Na Mg2 Ca2 Al3 Impurities interfere with formation of crystalline structure Na Si 4 O2 soda glass 7 Glass Properties Specific volume 1 r vs Temperature T Crystalline materials Specific volume Liquid disordered Supercooled Liquid Glasses Glass amorphous solid Crystalline i e ordered Tg crystallize at melting temp Tm have abrupt change in spec vol at Tm Tm solid T do not crystallize change in slope in spec vol curve at glass transition temperature Tg transparent no crystals to scatter light 8 Glass Viscosity vs T and Impurities Viscosity decreases with T Impurities lower Tdeform soda lime glass 70 SiO2 balance Na2O soda CaO lime borosilicate Pyrex 13 B2O3 3 5 Na2O 2 5 Al2O3 Viscosity Pa s Vycor 96 SiO2 4 B2O3 fused silica 99 5 wt SiO2 10 14 10 10 10 6 10 2 1 200 strain point annealing range Tdeform soft enough to deform or work Tmelt 600 1000 1400 1800 T C 9 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 further cooled cooler hot cooler compression tension compression Result surface crack growth is suppressed 10 Ceramic Fabrication Methods IIA GLASS FORMING PARTICULATE FORMING CEMENTATION Milling and screening desired particle size Mixing particles water produces a slip Ao Form a green component container Hydroplastic forming force extrude the slip e g into a pipe Slip casting pour slip into mold absorb water into mold green ceramic pour slip into mold solid component Dry and fire the component ram bille t container drain mold die holder extrusion Ad die green ceramic hollow component 11 Drying and Firing Drying layer size and spacing decrease wet slip partially dry green ceramic Drying too fast causes sample to warp or crack due to non uniform shrinkage Firing T raised to 900 1400 C vitrification liquid glass forms from clay and flows between SiO2 particles Flux melts at lower T Si02 particle quartz micrograph of porcelain glass formed around the particle 70mm 12 Ceramic Fabrication Methods IIB GLASS PARTICULATE CEMENTATION FORMING FORMING Sintering useful for both clay and non clay compositions Procedure produce ceramic and or glass particles by grinding place particles in mold press at elevated T to reduce pore size Aluminum oxide powder sintered at 1700 C for 6 minutes 15 mm 13 Powder Pressing Sintering powder touches forms neck gradually neck thickens add processing aids to help form neck little or no plastic deformation Uniaxial compression compacted in single direction Isostatic hydrostatic compression pressure applied by fluid powder in rubber envelope Hot pressing pressure heat Adapted from Fig 13 16 Callister 7e 14 Tape Casting thin sheets of green ceramic cast as flexible tape used for integrated circuits and capacitors cast from liquid slip ceramic organic solvent 15 Ceramic Fabrication Methods III GLASS PARTICULATE CEMENTATION FORMING FORMING Produced in extremely large quantities Portland cement mix clay and lime bearing materials calcinate heat to 1400 C primary constituents tri calcium silicate di calcium silicate Adding water produces a paste which hardens hardening occurs due to hydration chemical reactions with the water Forming done usually minutes after hydration begins 16 Applications Advanced Ceramics 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 Si3N4 SiC ZrO2 17 Applications Advanced Ceramics Ceramic Armor Al2O3 B4C SiC TiB2 Extremely hard materials shatter the incoming projectile energy absorbent material underneath 18
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