The sol-gel formation of Bayerite, Al(OH)3, precipitated from AlCl3·6H2O (13.6 g/l) and NH4OH (4N) at a basic pH 9 was studied. The resulting Bayerite was in the form of prisms ~3 μm in length. The transformation of this Bayerite to α-alumina was [Al(OH)3 ] → γ-Al2O3 → δ-Al2O3 → θ-Al2O3 → α-Al2O3. The slowest of these transitions, the one which controls the transformation by nucleation and growth kinetics, is the θ-Al2O3 to α-Al2O3. This rate-controlling transformation was studied by two different thermal treatments. One was isothermal and the other had two steps, the first of which created "in situ" nuclei, to enhance the transformation rate. The latter treatment reduced the time for the transformation at 1100oC from >80 h to only ~13 h and reduced the activation energy from 419.02 kJ mol−1 to 317.52 kJ mol−1. It produced a finer crystal size of α-alumina.

Keywords: Alumina, Sol-Gel Processing, Activation Energy, Thermal Treatments, and Nucleation