Hydration phenomena of aluminum oxides

Abstract

The hydration of amorphous and crystalline aluminas (γ and η) has been investigated by the dipping treatment in water at the temperatures of room to 95°C. Amorphous aluminum hydroxide, pseudoboehmlte, bayerite, hydrargillite and nordstrandite are formed by the hydration of amorphous alhmina. By the dipping at low temperatures, although the formation of amorphous aluminum hydroxide or pseudoboehmite is observed in the beginning of hydration, alumina trihydrates such as bayerite, and hydrargillite and/or nordstrandite appear in the dipping for about ten days and their formed amounts increase with increasing the period of dipping. With rising the dipping temperature, however, the rate of hydration is promoted, and pseudoboemite is formed at frst and then bayerite and nordstrandite are formed, afterwards the amount of nordstrandite formed increases when the period of dipping is extended more longer. Accordingly it is inferred that the hydration of amorphous alumina proceeds in the following sequence:
amorphous alumina→amorphous aluminum hydroxide pseudoboehmite→alumina trihydrate
On the other hand, the hydration of crystalline aluminas is little caused by the dipping treatment in water at room temperature, but η- and γ-aluminas are hydrated to alumina trihydrates and pseudoboehmite, respectively, when the dipping temperature is rised.