Synthesis of aluminum oxides from the products of the rapid thermal decomposition of hydrargillite in a centrifugal flash reactor: III. Properties of aluminum hydroxides and oxides obtained via the mild rehydration of the products of the centrifugal thermal activation of hydrargillite

The interaction between the amorphous product of the centrifugal thermal activation of hydrargillite (CTA HG) and aqueous electrolytes (pH 5–11) under mild conditions (15–35°C, atmospheric pressure) has been investigated by a variety of physicochemical methods. This interaction causes material morphologic and phase changes in CTA HG, and the product composition is governed by the pH of the electrolyte and by the hydration temperature and time. The product that forms in a basic medium or water in <24 h contains up to 50% pseudoboehmite. Raising the pH or temperature or extending the hydration time results in the formation of bayerite as the major phase (∼80%). An X-ray amorphous hydroxide forms in acid media. The heat treatment of this hydroxide at 550°C yields aluminum oxides differing from alumina prepared via hydroxide reprecipitation. Products with new, unusual properties can thus be obtained.