Synthesis of Ultrafine β”-Alumina Powders via Flame Spray Pyrolysis of Polymeric Precursors

Richard Laine

S.S. NTHRBDTRRL A.C. Sutorik (1998)

J. Am. Ceram. Soc., 81:1477-86.

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.

flame spray pyrolysis