Influence of acid-base and adsorptive characteristics of disperse aluminum modified by ammonium compounds on antifriction effect in lubricant

The article analyses the acid-base and adsorptive characteristics of the metal samples obtained using method of layering of different-sized molecules of quaternary ammonium compounds (QAC). The method allows to vary the hydrophilic-lipophilic, antifriction and other properties of commonly used disperse metals. The method includes the process of adsorption of reagents such as QAC based triamon (C₁-C₂) and alkamon (C₁₆-C₁₈), which have very different in length hydrocarbon radical at nitrogen atom. The acid-base properties of modified disperse aluminum were studied using Hammett indicator method and it has been established that there is a change in the quantity of the donor-acceptor centers of the powder caused by the adsorption of QAC. Spectrophotometric analysis of surface centers was performed using the Hammett indicators within the range of pKa values from -0.3 to 14.2. The distribution curves of the active adsorption centers of aluminum-based powders were plotted against the acid dissociation constant (acid strength - pK_a) of the indicators. A sharp decrease is observed in the number of centers in the Lewis acid sites region for the Al/(A+T) sample with co-adsorbed alkamone (A) and triamon (T). In addition, significant decrease in antifriction and water-repellent properties of the sample Al/T/A (consistent treatment of metal in vapor of T and A) in comparison with sample Al/(A+T) is explained by the increase of Bronsted base centers with pK_a = 9.5 and less intense interaction of QAC with Lewis acid centers with pK_a = 14.2.The following pattern was revealed: increase in the antifriction effect of oil based lubricants is accompanied by reduction of the Bronsted centers content and as a rule by the decrease of acidity function (H) of the surface of the QAC-modified Al-powder which was added to the lubricant.