Organophosphorus chemistry structure and performance relationships in FZG gear tests

A model investigation was conducted involving several different molecular weight phosphorus compounds prepared in base stocks of various polarities. The study involves two different parts. In one part, the same phosphorus compound was blended into several base stocks of differing polarities and was observed to give differing FZG gear test results. In part two, several different phosphorus compounds of various molecular weights were blended into the same base fluid and were observed to give differing FZG gear test results. Solution properties were studied by dielectric thermal analysis and afforded data as to mobility and surface reactivity. X-ray photoelectron spectroscopy was performed on sectioned gear teeth and provided elemental composition as well as thickness of the reacted surface layer. This data was correlated with the recorded FZG gear test results. A surface interaction mechanism is proposed that accounts for the relative phosphorus content and thickness of the wear protection films. The mechanism is based on correlating the additive molecular weight and base stock polarity as it relates to the FZG gear stage test pass result.