In situ attenuated total reflection (ATR) spectroscopic analysis of tribological phenomena

Abstract

A new method based on Attenuated Total Reflection (ATR) Fourier Transform Infrared (FT-IR) spectroscopy has been applied to the in situ characterization of tribofilms formed from antiwear extreme-pressure lubricant additives under tribological conditions in the boundary lubrication regime. ATR spectroscopy has the advantage that a sample in tribological experiments can be analyzed in situ , through a thin metallic film representing one of the rubbing surfaces. ATR tribological tests were performed with a tribometer in which a fixed steel cylinder slides against an ironcoated germanium ATR crystal. Changes in the ATR spectrum of a zinc dialkyldithiophosphate (ZnDTP) solution in poly-α-olefin (PAO) due to thermal and/or tribochemical reactions occurring between the lubricant additive and the iron surface have been investigated as a function of time. ATR analysis has been performed in situ on the tribofilms formed from the ZnDTP, both under purely thermal and tribological conditions. The results reported in this study show that iron is not involved in the thermal reaction of ZnDTP, while the rate of the tribofilm formation seems to be enhanced by the presence of iron. Different mechanisms and kinetics have been found for the thermal and tribochemical reactions between the ZnDTP and the iron surface under these experimental conditions.