Application of soft X-ray absorption spectroscopy in chemical characterization of antiwear films generated by ZDDP Part II: the effect of detergents and dispersants

Abstract

X-ray absorption near edge structure (XANES) spectroscopy has been used to study the chemical nature of the antiwear films generated on steel surfaces using zinc dialkyldithiophosphates (ZDDPs), in the presence of detergents and dispersants. The spectra were recorded both in total electron yield (TEY) and fluorescence yield (FY) modes, to investigate the chemical nature of P,S, Ca and O on the surface and in the bulk, respectively. The interaction of a commercial secondary ZDDP with a calcium sulphonate (neutral) detergent, a calcium phenate (basic) detergent and a polyisobutylene succinic anhydride polyamide dispersant has been examined. Using a range of concentrations, it has been found that calcium sulphonate interacts with ZDDP only at high concentration (≥2%), whereas calcium phenate affects the film formation even at low concentrations. The strongest interaction has been found for the polyisobutylene succinic anhydride polyamide dispersant. The polyphosphate films formed in the presence of the these additive have shorter chain length compared with ZDDP alone and contain less unchanged ZDDP. These finding are discussed in the framework of a mechanism for the film formation presented in Part 1 of this study.