Friction and wear characteristics of acidic phosphate ester boundary layers analyzed by near-edge X-ray absorption fine structure

During friction at extremely low surface pressures, interesting phenomenon occurs in oleyl acid phosphate (OLAP) the friction coefficient exhibits a positive gradient in the velocity range of boundary lubrication, to mixed lubrication transitions, and the friction coefficient decreases as the running-in time increases. This phenomenon is presumed to be due to the action of the boundary layer<span style="text-decoration: line-through;">,</span>. <span style="text-decoration: line-through;">therefore</span> Therefore, in this study, we analyzed friction surfaces <span style="text-decoration: line-through;">with</span> containing residual friction test oil <span style="text-decoration: line-through;">still present using</span> by near edge X-ray absorption fine structure. The results were then combined with first-principles calculations<span style="text-decoration: line-through;">,</span> to investigate the chemical state of the boundary layer in a state <span style="text-decoration: line-through;">close</span> comparable to <span style="text-decoration: line-through;">that of</span> sliding. <span style="text-decoration: line-through;">As a result,</span> The results inferred <span style="text-decoration: line-through;">it was considered</span> that the iron salt of a phosphate ester and the coordination structure of an iron-centered phosphate ester were generated by OLAP-<span style="text-decoration: line-through;">added</span> containing oil and aggregated near the interface with the base material during friction. Furthermore, a boundary friction model that considers non-Newtonian characteristics was applied to an experimentally obtained friction diagram to verify the effect of the boundary layer on the friction characteristics. The maximum effective viscosity calculated <span style="text-decoration: line-through;">from a function obtained</span> by fitting the friction diagram was approximately 3000 Pa·s, <span style="text-decoration: line-through;">which was</span> equivalent to that of common greases. These results indicated that the characteristic frictional properties of OLAP are due to the action of its grease-like organic boundary layer.