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 stress12 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 Liquid￾glass 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