Effect of precursors and preparation methods on the properties of lithium aluminate

Abstract

Lithium aluminate is a potential candidate for both tritium breeding material in fusion reactor and electrolyte matrix in molten carbonate fuel cell (MCFC). Effect of precursors and preparation methods on the properties of lithium aluminate powders was investigated to establish the optimum precursor system and preparation method. Sol- gel method, solid state reaction method and polymeric precursor method were used to prepare gamma lithium aluminate powders. The method using hydrothermal treatment was proposed to control the morphology of the lithium aluminate powders and the effect of precursors on the morphology of the product powders was studied. The intermediates and final products were characterized by XRD, IR, BET, TG- DTA, and SEM analysis. Six kinds of lithium salt/ alkoxide- aluminum alkoxide systems were used for the starting mixtures of the sol- gel method to prepare lithium aluminate powders. Gel prepared from each lithium alkoxide- aluminum alkoxide system was a mixture of $LiOHㆍxH_2O$ and $LiAl_2(OH)_7ㆍxH_2O$. When the gel was heated, gamma lithium aluminate began to be formed about 600-700℃. However, the temperature at which gamma lithium aluminate was completely formed and phase purity of gamma lithium aluminate were dependent on the size of alkoxy group. Phase pure gamma lithium aluminate was obtained at low temperature from the butoxide- butoxide system. Lithium and aluminum alkoxides reacted each other to form double metal alkoxide in the propoxide- propoxide or butoxide- butoxide system. When bulky alkoxides were used, lithium and aluminum alkoxides reacted easily due to low molecular association of aluminum alkoxides. It was found that the homogeneity of gel increased with the size of alkoxy group because of low molecular association of aluminum alkoxides. The homogeneous gel resulted in phase pure gamma lithium aluminate. It was found that the alcohol- alkoxide exchange reaction was appreciable during the mixing of alkoxides, and the alcoho...