Study of the Interaction of ZDDP and Dispersants Using X-ray Absorption Near Edge Structure Spectroscopy—Part 1: Thermal Chemical Reactions

The interactions of ZDDP and different dispersants have been investigated both in oil solutions and on steel substrates at 150–185 °C. X-ray absorption near edge structure (XANES) spectroscopy at P and S L-edge and K-edge has been used to identify the chemical species both in solution and on the surface of the steel. It was found that noticeable ZDDP decomposition in solution starts at 175 °C when no dispersant is present. In contrast, thermal oxidative films begin to form on the steel at 150 °C in the same solution. The products of decomposition in solution and in the film are phosphates and sulfides. N K-edge XANES spectroscopy has also been utilized to identify the reaction of the dispersant with the steel surface and ZDDP. The results show that dispersants enhance the decomposition of ZDDP in oil solutions as well on the steel surface. Dispersants, on their own, react/adsorb with the steel surface at 150–175 °C and also interact with ZDDP to form new products. Depending on the composition of the dispersants, the product is different.