Copper phosphate nanosheets as high-performance oil-based nanoadditives: Tribological properties and lubrication mechanism

Abstract

Geometric variables and surface chemistry of nanomaterials as lubricant additives both affect the details on the interacting frictional surface. Herein, copper phosphate nanosheets (CPNs) were synthesized by a simple and facile method, which exhibited extraordinary tribological properties as the novel lubricating oil nanoadditives. Compared with the base oil, the friction coefficient (COF) has been reduced by 77% by CPNs at a concentration of 20 wt%, which could also protect the titanium alloy surface from any measurable wear. But as the CPNs content increased to 25 wt%, the shear jamming caused by hydrogen bonding between crystal water in CPNs may interfere with lubrication. Besides, it is significantly effective in preventing the adhesions of titanium alloy on the surface of counterface at a suitable concentration. The extraordinary tribological performance is contributed to the nanosheets of copper phosphate but not the nanoparticles. Moreover, in the presence of CPNs, the tribo-film containing CPNs is formed during sliding contact, but this tribo-film can’t hold for a long time without CPNs, indicating that CPNs can well retain the tribo-film. However, the dominant factor for friction reduction and antiwear is not this tribo-film but the solid-liquid interface lubrication between nanosheets and lubricating oil. The Stribeck curves were used to explain how CPNs play a role in boundary lubrication and mixed lubrication.