Applications of Ceramics 1. Structure and Properties tThe compressive strength is typically ten times the Structure: A crystalline material but more complex or n amorphous material tRansparency to light of some ceramics optical pplications(windows, photographic cameras, telescopes Mechanical Properties: .Slip does not occurs in ceramics: thus, brittle .Good thermal insulation use in ovens. the exterior tiles of the Shuttle orbiter etc. contains imperfection such as vacancies, interstitials, Good electrical isolation ceramics are used to isplaced atom and microcrack mIcrocracks make support conductors in electrical and electronic tension pplications. .Strengthening methods: uniform, smaller grains, Good chemical inertness applications in reactive minimizing porosity, inducing residual stress, reinforcement. heat treatment environments Plastic deformation in ceramics 2 Traditional ceramics CRystalline ceramics: Slip dislocation motion is fficult since ions of like charge have to be brought e Fired clay cement and natural abrasives based on silicates silica and mineral oxides. to close proximity large barrier for dislocation motion. Ceramics with covalent bonding slip is also Being able to fire the powder and water t easy: covalent bond strong ceramics brittle . Noncrystalline ceramie there is no regular Raw materials: kaolinite, silica (quartz is one form), bauxite (a pure form is corundum deform by viscous flow, i.e. by breaking and reforming silicon carbide other (like in a liquid) pOttery and Tableware viscosity is measure of glassy materials resistance to deformation 3 New Ceramics New Ceramics ISynthetic-Oxides, carbides, nitrides, borides and oxynitride (SiAlON) m Carbides OXides SiC, wC, TiC, TaC, Cr Cg- Alumina (Aluminum oxide)(AlO, w SiC- traditional ceramics used as abrasives powders from gOod hot hardness. Low thermal conductivity wolframite and scheelite corrosion resistance 9 TiC- Carburizing rutile or ilmenite aAbrasive electrical insulator bioceramics. cutting e TaC- Carburizing tantalum powders or tantalum +Zirconia(Zirconium oxide) t Chromium carbides-Carburizing chromium oxides Silica (SiO,)
11 The compressive strength is typically ten times the tensile strength. Transparency to light of some ceramics Þ optical applications (windows, photographic cameras, telescopes, etc) Good thermal insulation Þ use in ovens, the exterior tiles of the Shuttle orbiter, etc. Good electrical isolation Þ ceramics are used to support conductors in electrical and electronic applications. Good chemical inertness Þ applications in reactive environments. Applications of Ceramics 1. Structure and Properties Structure: A crystalline material but more complex or an amorphous material Mechanical Properties: Slip does not occurs in ceramics: thus, brittle. contains imperfection such as vacancies, interstitials, displaced atom and microcracks. Microcracks make ceramics weaker in tension. Strengthening methods: uniform, smaller grains, minimizing porosity, inducing residual stress, reinforcement, heat treatment Crystalline ceramics: Slip dislocation motion is difficult since ions of like charge have to be brought into close proximity ® large barrier for dislocation motion. Ceramics with covalent bonding slip is also not easy: covalent bond strong Þ ceramics brittle Non-crystalline ceramic: there is no regular crystalline structure ® no dislocations. Materials deform by viscous flow, i.e. by breaking and reforming atomic bonds, allowing ions/atoms to slide past each other (like in a liquid). Viscosity is measure of glassy material’s resistance to deformation. Plastic Deformation in Ceramics 2 Traditional Ceramics Fired clay, cement and natural abrasives based on silicates, silica and mineral oxides. Being able to fire the powder and water mixture. Raw materials: kaolinite, silica (quartz is one form), bauxite (a pure form is corundum), silicon carbide Types Pottery and Tableware Brick and tile Refractories Abrasives 3 New Ceramics Synthetic - Oxides, carbides, nitrides, borides and oxynitride (SiAlON) Oxides Alumina (Aluminum oxide) (Al2O3 ) Produced synthetically from bauxite Good hot hardness, Low thermal conductivity corrosion resistance Abrasive, electrical insulator, bioceramics , cutting tool, spark plug etc. Zirconia (Zirconium oxide) Silica (SiO2 ) New Ceramics Carbides SiC, WC, TiC, TaC, Cr3C2 . SiC –traditional ceramics, used as abrasives. WC –Carburizing tungsten powders from wolframite and scheelite TiC –Carburizing rutile or ilmenite TaC - Carburizing tantalum powders or tantalum pentoxide Chromium carbides - Carburizing chromium oxides
New ceramics 4 Glass Nitrides gLass n inorganic, nonmetallic compound that cools SIlicon Nitrides(SiaN) to a rigid condition without crystallizing (Amorphous glassy oC and decomposes at 1900C resistance to thermal shock and creep .Principal ingredient: Silica(SiO,) found in mineral quartz Corrosion resistance to molten nonferrous metal from sand Gas turbine, rocket engines and melting crucibles bOron Nitride (Bn) hermal shock commErcial glass products contain 50-75% silica .Form: Hexagonal or cubic(CBN) .Extremely high hardness .Cutting tools ity in a molten state rEtard devitrification eLectrical conductive materi .High hardness, low friction with ferrous materials, wea sAdd colors aAlter the index of refraction (for lense Silicate glass Properties of glasses des (Cao, NaO,K,O, ALO, Containers, windows, viscosity is increasing with decreasing T), without a clear melting temperature slope at the glass-transition temperature 30wt% oxides(CaO, Na0.“ Quartz sand+ soda ash or limestone Properties of gla Glass Formation at the Liquid- Melting point: viscosity 100P, below this viscosit (above this T) glass is liquid WOrking point: vise 10 P, glass is easily deformed Forming range Softening point: viscosity 4x10P, maximum Tat hich a glass piece maintains shape for a long time Annealing point: viscosity 1013P, relax internal resses(diffusion) Strain point viscosity =3 x 1014 P, above this viscosity a change in volume at fixed temperature fracture occurs before plastic deformation T: T bElow Tg, glass is a rigid brittle material lass forming operations occur between softening and orking points aracterized by continuous deformation (at a rate inversely related viscosity)rather than a fixed elastic strain in response to stress
12 New Ceramics Nitrides Silicon Nitrides (Si3N4 ) Oxidizes at 1200°C and decomposes at 1900°C. resistance to thermal shock and creep Corrosion resistance to molten nonferrous metals Gas turbine, rocket engines and melting crucibles Boron Nitride (BN) Form: Hexagonal or cubic (CBN) Extremely high hardness Cutting tools Titanium Nitride (TiN) Electrical conductive material High hardness, low friction with ferrous materials, wear resistance 4 Glass Glass ¾¾ an inorganic, nonmetallic compound that cools to a rigid condition without crystallizing. (Amorphous glassy ceramics dated back 4000 years) Principal ingredient: Silica(SiO2 ) found in mineral quartz from sandstone and sand Melted and cooled to form vitreous silica resistance to thermal shock Commercial glass products contain 50-75% silica. Compositions: Act as flux during heating Increase fluidity in a molten state Retard devitrification Reduce chemical attack Add colors Alter the index of refraction (for lenses) Silicate Glasses ¾ noncrystalline silicates (SiO2 ) containing other oxides (CaO, NaO2 , K2O, Al2O3 ) Containers, windows, lenses, fiberglass, etc. Silicate Glasses Example: Container/window glasses contain ~ 30 wt% oxides (CaO, Na 2O) whose cations are incorporated within SiO4 network: network modifiers. Quartz sand + soda ash or limestone Solidification is gradual, through a viscous stage (viscosity is increasing with decreasing T), without a clear melting temperature Specific volume (1/density) does not have abrupt transition at fixed temperature but shows a change in slope at the glass-transition temperature Properties of Glasses Important temperatures(viscosity) in glass: Melting point: viscosity = 100P, below this viscosity (above this T) glass is liquid Working point: viscosity = 104P, glass is easily deformed Softening point: viscosity = 4´107P, maximum T at which a glass piece maintains shape for a long time Annealing point: viscosity = 1013P, relax internal stresses (diffusion) Strain point: viscosity = 3 ´ 1014 P, above this viscosity, fracture occurs before plastic deformation Glass forming operations occur between softening and working points! Properties of Glasses Glass Formation at the Liquidglass Transition Temperature Below Tg, glass is a rigid brittle material Above Tg, glass behaves as a viscous liquid with behavior characterized by continuous deformation (at a rate inversely related to viscosity) rather than a fixed elastic strain in response to stress Tg: glass transition temperature Tm: Melting temperature (point) corresponds to a change in volume at fixed temperature