Powder Synthesis

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    13-Jan-2016

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Powder Synthesis. Che5700 . 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 : - PowerPoint PPT Presentation

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  • Powder SynthesisSolid state method: Solid-solid reaction; decomposition of solid; oxidation or reduction of solidLiquid phase method:Chemical precipitation, co-precipitation, evaporative salting out, hydrothermal, etc. Gas phase method:Gas phase reaction, gas-solid reaction, evaporative condensationOthers:Solvent removal (spray drying, freeze drying), sol-gel , etcChe5700

  • Ideal PowderIdeal powder:spherical, submicron (or nanometer)Narrow size distributionNo agglomerateUniform composition, high purity

    Che5700

  • Many examples

  • Some examplesSi3N4: from Si nitridation; or SiO2 reduction + nitridationPLZT: precipitation + spray dryingZrO2: hydrolysis of metal saltsY2O3: emulsion precipitationSiC: plasma synthesis, vapor phase reactionYttria: homogeneous precipitationTiN, AlN: combustion synthesis

    Che5700

  • 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 (): Bayer process to produce alumina; feedgrindingadd alkaline & mixng digester thickener filter precipitation crystallization + classification filtration drying and calcination product

  • Extract zirconium from zirconZircon: ZrO2.SiO2Method one: high temperature melting and decomposition (use arc furnace or plasma arc) > 1750oC; quench use acid to dissolve ZrO2 or alkaline for SiO2Method 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 zirconiaChe5700

  • Magnesium zinc ferrite

  • Preparation of high purity aluminaHigh 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 H2ODistillation 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 oxideChe5700

  • Preparation of high purity alumina(2)(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;Che5700

  • Transparent AluminaOne 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 m, 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