Alteration of the Acid-Base Properties of the Oxidized Surface of Disperse Aluminum during the Adsorption of Ammonium Compounds and the Antifriction Effect

Abstract

The number of active centers of disperse aluminum powder is determined by the spectrophotometric method using the Hammett indicators in the range of pK_a values of 0.3 to 14.2; alteration of the distribution of the donor-acceptor sites on the surface as a result of the adsorption of quaternary ammonium compounds (QACs) from the gas phase is studied. The curves of the distribution of adsorption sites of aluminum-based powders are built depending on the ionization constant pK_a of the indicators. A sharp decrease in the number of active sites in the Lewis acid sites region is detected for Al/(A + T) sample, where alkamon (A) and triamon (T) are jointly adsorbed. The number of sites is halved at pK_a =–0.3, 5, and 9.5. We reveal that the antifriction effect of a lubricant is enhanced as the acidity of the surface of the powder with the adsorbed quaternary ammonium compounds is decreased.