Paper IX (ii) The Removal of Substrate Material through Thick Zinc Dithiophosphate Anti-Wear Films

The composition and structure of well-developed zinc dialkyldithiophosphate (ZDTP) anti-wear films, formed under factional conditions, has been examined by scanning electron microscopy/electron probe microanalysis (SEM/EPMA) and secondary ion mass spectrometry (SIMS), without solvent washing. The presence of the molecular groups identified by SIMS was confirmed to depths of at least 100 nm by X-ray photoelectron spectroscopy (XPS) depth profiling. The main constituent of the film approximated closely to P2O5, with varying amounts of organic material, and sulphides and oxides of zinc and iron. A model is proposed for a glassy polyphosphate film whose physical properties vary with depth as a result of varying modifier contents. The consequences of such a structure for film adhesion and for the physical and chemical processes of removal of substrate material are discussed.