Evolution of Aluminum Hydroxides in Diluted Aqueous Aluminum Nitride Powder Suspensions

Abstract

The evolution of aluminum hydroxides in diluted aqueous aluminum nitride (AlN) powder suspensions in the temperature range 22–90 °C was studied in order to set up a general mechanistic model over a broad temperature range, uniting previously observed hydrolysis reactions at room temperature and at elevated temperatures into a single scheme. It is shown that dispersing the AlN powder in the water results in the temperature-dependent formation of various aluminum hydroxides in the following sequence: amorphous aluminum hydroxide gel, aluminum monohydroxide (boehmite), and aluminum trihydroxides (bayerite, nordstrandite, and gibbsite). The unique interdependency between the temperature and the pH of the hydrolyzing AlN powder suspension, governed by the ammonia's solubility and the exothermic hydrolysis reactions producing Al(OH)4– species, is the driving force for several evolution paths of these aluminum hydroxides exhibiting numerous morphologies.