The Formation of κ and κ′-Al2O3 from the Dehydration of Tohdite 5Al2O3·H2O

Abstract

Abstract The dehydration of tohdite 5Al2O3·H2O is well followed by means of the single-crystal electron-diffraction patterns, the X-ray powder patterns, differential thermal analysis, and the measurement of the density. Thermogravimetric measurements were also performed, both under a normal atmosphere and in a high vacuum. Just after the dehydration, an unstable intermediate phase was obtained; it was denoted as κ′-Al2O3(from tohdite). The mechanism of the transformation series: tohdite→κ′-Al2O3→κ-Al2O3→α-Al2O3 was discussed, and some basic data to serve as clues to elucidate the crystal structure of κ′- and κ-Al2O3 were obtained.