Role of nascent metallic surfaces on the tribochemistry of phosphite lubricant additives

The role of the nascent surface on the decomposition of phosphite additives has been investigated. An environmentally controlled tribometer was used to conduct tribotest in UHV and gas. Sliding test in UHV was performed to tribo-activate steel surfaces. Adsorption of trimethylphosphite on tribo-activated surface was made to investigate its decomposition on freshly scratched surfaces. In situ XPS analyses have shown that tribofilm of iron phosphide is poorly formed on the tribo-activated surface. This observation confirms that iron phosphide tribofilm is mainly formed under tribological condition. The role of the contact pressure and tribo-emission process is highlighted.