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

摘要

Aluminium hydroxides have been precipitated from various aluminium salts and the differences in their thermal behaviour have been investigated. Pseudoboehmite derived from the nitrate, sulfate and chloride all form #gamma#-Al_2O_3 at approx 400 deg C but the formation of #alpha#-Al_2O_3 at 1200 deg 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 aluminium 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 #alpha#-A1203.