Gelation of Aluminum Hydroxide Sols

The gelation of aluminum hydroxide sols obtained from aluminum sec -butoxide has been studied as a function of the conditions of preparation, including pH, temperature, and time of aging. The preceding studies of Yoldas have been extended in more acidic conditions, up to a molar proportion of 1.12 HNO₃ per Al(OC₄H₉)₃. It has been found that stable sols can easily be obtained by processing at any temperature between 20° and 90°C beyond a molar proportion of 0.28 HNO₃. The corresponding gels are suggested to have a boehmite-like structure in which there is a metastable folding of the (020) layers at 20°C, and a stable unfolding at 80°C, the two structures coexisting at intermediate processing temperatures.