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Powder Synthesis

Powder Synthesis. Che5700 陶瓷粉末處理. 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 :

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Powder Synthesis

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  1. Powder Synthesis Che5700 陶瓷粉末處理 • 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

  2. Ideal Powder Che5700 陶瓷粉末處理 • Ideal powder: • spherical, submicron (or nanometer) • Narrow size distribution • No agglomerate • Uniform composition, high purity

  3. Many examples

  4. 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

  5. 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

  6. From bauxite (鋁礬土): Bayer process to produce alumina; feedgrindingadd alkaline & mixng digester thickener  filter  precipitation  crystallization + classification  filtration  drying and calcination  product

  7. 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

  8. Magnesium zinc ferrite

  9. Preparation of high purity alumina Che5700 陶瓷粉末處理 • High purity: > 99.5%; • 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 • Distillation method: Al metal as source, reaction to get AlR3 or alkoxide Al(OR)3, then remove impurity by distillation, calcination to get oxides. • Spark discharge: high purity Al as electrode, under high electrical voltage, spark discharge to get oxide

  10. 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;

  11. 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

  12. 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)

  13.  Different method: competitive in terms of quality and cost

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