Preparation and phase transformation behavior of χ-alumina via solvothermal synthesis

Solvothermal reaction of aluminum isopropoxide (AIP) in mineral oil at 250–300 °C over 2 h duration provides χ-alumina powder, which transforms directly to α-alumina after calcination at high temperature. The mechanism of the crystallization process appears to be the initial formation of a spherical complex which subsequently decomposes further to precipitate a solid. This mechanism is suggested by XRD, IR, TG/DTA, SEM and TEM characterization of the powder formed. χ-Alumina attains a critical crystallite size around 15 nm through accretion on calcination and then transforms directly to α-alumina through nucleation and growth process. Direct α-phase transformation of χ-alumina powders rather than passage through κ-alumina can be explained by the absence of the cation contamination and the higher crystallinity of χ-alumina in the AIP decomposition process.