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