Growth of Tribological Films: In Situ Characterization Based on Attenuated Total Reflection Infrared Spectroscopy

In this paper we describe the development of a new technique based on attenuated total reflection (ATR) Fourier transform infrared (FT-IR) spectroscopy and its application to the in situ study of lubricant system behavior under tribological conditions. The lubricated tribological system consisted of a fixed steel cylinder, sliding across the surface of a germanium ATR crystal, coated with a thin iron film in the presence of the well-studied secondary zinc dialkyl dithiophosphate (ZnDTP) lubricant additive. Using this approach, changes in the additive chemistry due to adsorption, as well as reaction film growth, can be studied as a function of sliding time and temperature. The ATR FT-IR spectra reported in this work are fully consistent with the existing ZnDTP literature and show the decomposition of ZnDTP with the formation of P−O−P species following thermal testing at 150 °C, while a simple phosphate film has been detected on the iron surface following tribological testing at the same temperature.