Reactivity of Aluminum Nitride Powder in Dilute Inorganic Acids

The reactivity of AlN powder in diluted inorganic acids was studied by measuring the pH and temperature during its hydrolysis. At very low starting pH (pH ∼1) no reaction was observed, regardless of the acid used. In contrast, in a less acidic environment, i.e., at higher pH values (pH ∼3), the reaction was fast enough to reveal the influence of different acids on the hydrolysis reaction. Monoprotonic acids which are completely dissociated (HCl, HF, HNO 3 ), and form water‐soluble salts with aluminum, did not influence the hydrolysis reactions. In the presence of incompletely dissociated diprotonic H 2 SO 4 and H 2 CO 3 acids which form water‐soluble salts with aluminum, the reaction was hindered but not prevented. In the presence of phosphoric acid the hydrolysis was prevented at room temperature, presumably because of the formation of insoluble phosphates on the powder surface. At elevated temperatures their solubility was substantial, and the reactivity of AlN powder in a diluted hot phosphoric acid was reestablished. In the presence of silicic acid the reaction was suppressed at both room and elevated temperatures, which was also ascribed to the formation of insoluble silicates. The adsorption of silicate anions onto the powder surface was confirmed by chemical analysis and zeta potential measurement. Using DRIFT measurements, however, the presence of Si–O bonds on the powder could not be unambiguously confirmed, since the characteristic wavelengths for these bonds are in the region of very strong Al–N stretching frequencies.