THE CHEMISTRY OF ANTIWEAR FILMS GENERATED BY THE COMBINATION OF ZDDP AND MODTC EXAMINED BY X-RAY-ABSORPTION SPECTROSCOPY

In order to obtain a better understanding of the decomposition mechani sms of antiwear and antioxidant engine oil additives such as zinc dial kyldithiophosphate (ZDDP) and molybdenum dithiocarbamate (MoDTC), trib ochemical and thermally deposited films were prepared from oil solutio ns containing varying concentrations of these two additives. The chemi stry of these films was studied by using X-ray absorption (XANES) spec troscopy and X-ray photoelectron (XPS). The antiwear properties were e xamined on a Plint rubbing machine by measuring the amount of wear as a function of time and the concentrations of the additives. The XANES and XPS spectra indicate that the dominant species from MoDTC in the a ntiwear films resembles that of a MoS2-like film, and in the thermal f ilms, the dominant species are those of a sulphate and MoO3. The spect ra also indicate that the phosphorus from ZDDP forms polyphosphate cha ins of varying lengths. The combined use of organo-Mo compounds and Zn alkyl dithiophosphates showed a synergistic effect by reducing both f riction and wear.