The application of photoelectron spectroscopy to the study of e. p. films on lubricated surfaces

Abstract Photoelectron spectroscopy (ESCA) has been used to examine films formed on the surfaces of steel specimens by oil solutions of e.p. additives in immersion and rubbing tests. The additives used were elemental sulphur, dibenzyl disulphide, a commercial zinc dialkyldithiophosphate and pure zinc di-n-butyldithiophosphate. In the case of the two sulphur additives immersion specimens had films containing sulphate and free sulphur, whereas rubbed surfaces had patchy coatings of sulphide with lesser amounts of sulphate. The thiophosphate additives gave broadly similar films in rubbing and immersion tests. These contained the zinc, phosphorus and part of the sulphur in the original additive in films, possibly polymeric, of somewhat variable composition. Argon ion etching was used to explore the composition of a film from a thiophosphate additive. It showed that there were no large compositional variations through the thickness of the film and that it was of a discontinuous patchy nature.