Thermal formation of corundum from aluminum hydroxides prepared from various aluminum salts

Abstract

Aluminum hydroxides have been precipitated from various aluminum salts and the differences in their thermal behaviour have been investigated. Pseudoboehmite derived from the nitrate, sulfate and chloride all form γ-Al2O3 at approximately 400 °C but the formation of α-Al2O3 at 1200 °C occurs more readily in the material derived from the sulfate. This contains a higher concentration of anionic impurities related to differences in the solubility of the original aluminum salts. The sulfate is retained in the gel to higher temperatures at which its eventual decomposition may lead to the formation of a reactive pore structure which facilitates the nucleation of α-Al2O3.