Che5700 陶瓷粉末處理
Powder Synthesis
Solid state method: Solid-solid reaction; decomposition of solid; oxidation or
reduction of solid Liquid phase method:
Chemical precipitation, co-precipitation, evaporative salting out, hydrothermal, etc.
Gas phase method: Gas phase reaction, gas-solid reaction, evaporative
condensation Others:
Solvent removal (spray drying, freeze drying), sol-gel , etc
Ideal Powder
Che5700 陶瓷粉末處理
• Ideal powder: spherical,
submicron (or nanometer)
Narrow size distribution
No agglomerate Uniform
composition, high purity
Many examples
Some examples
Che5700 陶瓷粉末處理
Si3N4: from Si nitridation; or SiO2 reduction + nitridation
PLZT: precipitation + spray drying ZrO2: hydrolysis of metal salts
Y2O3: emulsion precipitation SiC: plasma synthesis, vapor phase reaction Yttria: homogeneous precipitation TiN, AlN: combustion synthesis
•One way to get powder of desired composition: from minerals, simple physical separation, + chemical purification to get products.•Purity: often not very high; used in conventional ceramic industry
From bauxite (鋁礬土 ): Bayer process to produce alumina; feedgrindingadd alkaline & mixng digester thickener filter precipitation crystallization + classification filtration drying and calcination product
Extract zirconium from zircon
Che5700 陶瓷粉末處理
Zircon: ZrO2.SiO2 Method one: high temperature melting and
decomposition (use arc furnace or plasma arc) > 1750oC; quench use acid to dissolve ZrO2 or alkaline for SiO2
Method two: zircon + NaOH high temperature reaction Na2ZrO3 + Na2SiO3 + water filtration to remove Na2SiO3.nH2O crude sodium zirconate + HCl filtration to remove SiO2 colloids get ZrOCl2 – HCl solution evaporative concentration crystallization filtration to remove impurities (Fe, Ti, Na, Al, HCl etc) get ZrOCl2 8 H2O repeat and secondary crystallization high purity ZrOCl2 8 H2O calcination zirconia
Magnesium zinc ferrite
Preparation of high purity alumina
Che5700 陶瓷粉末處理
• High purity: > 99.5%; (1) Selective crystallization: get ammonium alum or
ammonium alum carbonate hydrate (AACH) first, repeated dissolution-crystallization, to remove impurities, e.g. Na, Mg, Ca, Fe, Ti, SiO2; NH4Al(SO4)2 12 H2O
(2) Distillation method: Al metal as source, reaction to get AlR3 or alkoxide Al(OR)3, then remove impurity by distillation, calcination to get oxides.
(3) Spark discharge: high purity Al as electrode, under high electrical voltage, spark discharge to get oxide
Preparation of high purity alumina(2)
Che5700 陶瓷粉末處理
(4)Chemical reaction: ethylene chlorohydrin process, sodium aluminate solution as source, add organic acid ClCH2CH2OH, slow neutralization reaction to get Al(OH)3, impurity such as Na, Si, Fe difficult to enter oxide lattice; by-product ethylene oxide, may react with HCl to get ethylene hydrin to save money
(5) Modified Bayer process : add large silica particle during calcination, to trap evaporated Na2O to remove it; or flowing HCl to form soluble NaCl to remove it;
Transparent Alumina
•One potential application: to be used in HID (high-intensity discharge) lamp; for projectors, etc.• anti-corrosive, heat resistant, good strength (better than fused silica)
•HID lamp: greater light output/watt electrical input
Opaque alumina: purity > 99.5%; grain size ~ 0.55 μm, residual porosity 0.3%; transparent alumina: residual porosity < 0.03%(taken from J. Am. Cer. Soc., 89(6), 1985-1992, 2006)
Different method: competitive in terms of quality and cost