04 powder synthesis2

04 powder synthesis2 - Co-Precipitatione.g. BaTiO3Ba- +...

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Unformatted text preview: Co-Precipitatione.g. BaTiO3Ba- + Ti-Salts + H2(C2O4) + H2OBaTiO(C2O4)24 H2ODewatering (200C) BaTiO(C2O4)2Heating in O2(400C) BaCO3+ TiO2(fine distributed)Heating (700C)BaTiO3(ultrafine)Sol-Gel Process for PowdersProcessing stepReactionHydrolyses of Alkoxide:Al(OR)3+ 2 H2O AlOOH + 3ROH(R = Alkyl group)Peptisation (Dispersing)AlOOH clear AlOOH-SolGelationAlOOH -H2O/gelling agentclear AlOOH-GelHeat treatmentAlOOH -Al2O3 -Al2O3-Al2O390243Ch HNO//400C1000C1200CDepending on the condition of the process the following can be formed:Particles, also submicron (spherical, mono sized)Fibers by extrusion/spinning of gelsThin filmsMonolithsAero gelsMonomodal Powders via Sol-Gel-Processinga) SEM-Picture of BaTiO3 b) TEM-Picture of Pb2Nb2O7Advantages of the sol-gel processfine powders, homogenous and pure educts possiblenarrow particle size distributionlow sintering temperaturessintering to high densities possibleDisadvantages:high raw material and processing cost (expensive educts, organic solvents)high shrinkage rates (Monoliths are difficult to achieve)Gas-Phase SynthesisGaseous compounds are released at high temperatures. The resulting powders are ultrafine. No comminution required.Properties of gas phase powders:Particle Size in submicron rangeLarge specific surface areaSpherical particles are typicalLow metallic impurity levelHomogeneously distributed sintering additivesSynthesis is done in high temperature streaming flow reactors and plasma reactorsHigh temperature streaming flow reactor...
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04 powder synthesis2 - Co-Precipitatione.g. BaTiO3Ba- +...

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