Molecularly-engineered lubricants: Synthesis, activation, and tribological characterization of silver complexes as lubricant additives

Many machines operate in harsh environments where elevated temperatures require careful consideration of the lubricant for optimal performance. Lubricant additives can be designed to improve properties of base oil at specific temperature ranges. In the present work, two [tris(phosphino)borate]AgL (La =a PEt₃; NHC) complexes are synthesized and added to engine oil at various concentrations. The complexes thermolyze between 200 and 300a °C, yielding metallic Ag. A mixture of engine oil and the silver-based nanoparticles provides fully flooded lubrication for pin-on-disk friction tests. A thermo-elastohydrodynamic model for point contact is utilized to predict the pin loads at which flash temperatures between 200 and 300a °C occur, thus inducing thermal decomposition of the complexes. Results of the friction tests and wear measurements indicate a significant reduction in wear at 0.5-1.0% Ag complex weight concentrations and little change in friction. The improved wear performance is attributed to the thermolysis and deposition of the silver-based complexes in the wear scar, as confirmed by energy-dispersive X-ray analysis.