Synthesis of Ultrafine β"-Alumina Powders via Flame Spray Pyrolysis of Polymeric Precursors |
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Authors: | Anthony C Sutorik Siew Siang Neo David R Treadwell Richard M Laine |
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Affiliation: | Departments of Materials Science and Engineering, and Chemistry, Macromolecular Science and Engineering Center, University of Michigan, Ann Arbor, Michigan 48109–2136 |
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Abstract: | Flame spray pyrolysis of a polymeric precursor is used to prepare ultrafine powders that, when sintered, convert to essentially pure phase lithium-doped sodium β"-alumina. The precursor Na1.67 Al10.67 Li0.33 N(CH2CH2O)3]10.67-OCH2CH2O]·x(HOCH2CH2OH) has been synthesized from stoichiometric amounts of metal hydroxides and tri-ethanolamine (N(CH2CH2OH)3, TEA) in excess ethylene glycol. The precursor is dissolved in ethanol, and an atom-ized spray of the solution is combusted in a specially con-structed flame spray apparatus. Combustion occurs at ~2000°C, followed by immediate quenching. This proce-dure provides for a measure of kinetic control over the process. The resulting nanopowder particles are 50–150 nm in diameter and exhibit powder X-ray diffractometry pat-terns similar to β"-alumina. Heating the nanopowder at 30°C/min to 1200°C with a 1 hisotherm converts it to pure β"-alumina. In preliminary sintering studies, green powder compacts (~65% theoretical density) sintered at 1600°C for 12 min densify to 3.0 ± 0.1 g/cm 3 (~92% theoretical density) with minimal loss of Na2O. This procedure offers several processing and cost advantages over conventional β"-alumina syntheses. |
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