The synthesis of beta alumina powders
Doctoral Thesis
1987
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University of Cape Town
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Abstract
Beta alumina solid electrolyte material is conventionally synthesized by the high temperature solid state reaction of α-Al₂O₃ with soda and a stabilizer ion such as lithia or magnesia. This reaction requires a reconstructive transformation of the α-Al₂O₃ oxygen sublattice and results in a two-phase mixture of β and β"-Al₂O. In order to maximize the preferred β"-Al₂O₃ phase an additional peak heat treatment schedule is required. This work investigated the replacement of the α-Al ₂O₃ component of the reaction mixture with a range of synthetic aluminium hydroxide precursor materials. Four different aluminium hydroxide precursors were synthesized by the controlled hydrolysis of a common aluminium isopropoxide parent material. The oxygen sublattice of each aluminium hydroxide precursor was engineered by varying the alkoxide hydrolysis conditions. These precursors were used to synthesize beta alumina powders by the high temperature solid state reaction with soda and lithia, resulting in powders with a nominal composition of Li₀.₃₈Na₁.₆₅Al₁₀.₆₆O₁₇. The solid state reactions were monitored by differential thermal analysis and thermogravimetric analysis. The structural development of the reaction products with increasing temperature, was monitored by powder X-ray diffraction. A significant observation was the direct formation of single phase β"-Al₂O₃ at 1200 °C by the solid state reaction of soda and lithia with certain aluminium hydroxides. The work concludes with the proposal of a generalized mechanism relating the aluminium hydroxide precursor oxygen sublattice to the nature of the beta alumina reaction product.
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Bibliography: pages 83-90.
Reference:
Van Zyl, A. 1987. The synthesis of beta alumina powders. University of Cape Town.