Surface-modified Pd nanoparticles as a superior additive for lubrication

The tribological performance of lubricants is favourably altered by adding small amounts of nanoparticles which provide reduced wear and low friction. However, one of the main difficulties of using nanoparticles as additives is their dispersion or dissolution in lubricant oils, typically of hydrocarbon nature. With the surface modification of nanoparticles through long chain high molecular weight hydrocarbons, stable dispersions in lubricant oils become feasible. Here we show that using surface-modified Pd nanoparticles (2 nm size) with tetraalkylammonium chains, stable dispersions in lubricant oils become feasible with excellent tribological properties (friction similar to 0.07, wear resistance similar to 10(-10) mm(3)/Nm). Electrical contact measurements were also used to monitor the conductivity of the contact during sliding. The use of these nanoparticles made decrease the electrical resistance of the contact a percentage of 97 to 99.5% in comparison with the initial value measured for the base oil alone. To understand these phenomena the contact surfaces and Pd nanoparticles were studied after friction by scanning electron microscopy (SEM) combined with energy dispersive X-ray analysis (EDX) and transmission electron microscopy (TEM), respectively. The outstanding performance is attributed to a combination of factors as metallic character of palladium, nanometric size, and replenishment of Pd nanoparticles onto the contact forming a transfer layer. This discovery opens new perspectives of using metallic nanoparticles as lubricant additives for small contacts and connectors applications.