Reactivity of aluminum nitride powder in dilute inorganic acids

The reactivity of AIN powder in diluted inorganic acids was studied by meas uring the pH and temperature during its hydrolysis, At very low starting pH I (pH similar to 1) no reaction was observed, regardless of the acid used. In contrast, in a less acidic environment, i.e., at higher pH values (pH si milar to 3), the reaction was fast enough to reveal the influence of differ ent acids on the hydrolysis reaction. Monoprotonic acids which are complete ly dissociated (HCl, HF, HNO3), and form water-soluble salts with aluminum, did not influence the hydrolysis reactions. In the presence of incompletel y dissociated diprotonic H2SO4 and H2CO3 acids which form water-soluble sal ts with aluminum, the reaction was hindered but not prevented. In the prese nce of phosphoric acid the hydrolysis was prevented at room temperature, pr esumably because of the formation of insoluble phosphates on the powder sur face. At elevated temperatures their solubility was substantial, and the re activity of AIN powder in a diluted hot phosphoric acid was reestablished. In the presence of silicic acid the reaction was suppressed at both room an d elevated temperatures, which was also ascribed to the formation of insolu ble silicates, The adsorption of silicate anions onto the powder surface wa s confirmed by chemical analysis and zeta potential measurement. Using DRIF T 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.