Effect of seeding on α-Al₂O₃ powder formation from bayerite and bohemite

The influence of seeding on the production of α-Al₂O₃ powders from different hydroxides obtained by the precipitation method of AlCl₃ ·6H₂O with NH₄Cl was studied. A bayerite-bohemite mixture and single bayerite were obtained, depending on the process pH. The transformation sequence for each hydroxide and the transformation kinetics were characterized by thermal analysis and X-ray diffraction. The α-Al₂O₃ seeds lower the θ → α-Al₂O₃ transformation temperature and accelerate the transformation rate, but the transformation is more difficult when single bayerite is the precursor. It is suggested that the characteristics of the θ/α Al₂O₃ interface depend on the hydroxide precursor.