Friction reduction mechanism of glycerol monooleate-containing lubricants at elevated temperature - transition from physisorption to chemisorption.

The friction reduction mechanism of glycerol monooleate (GMO) was investigated under boundary lubrication with elevated temperature. Tribological performances were tested using reciprocating test rig by adding 5 wt.% GMO into Poly-alpha Olefin (PAO) base oil. Friction coefficient and wear were recorded during experiments. The used oil was evaluated by infrared detection after experiments. Results show that GMO could reduce friction coefficient at both low and high temperature. At elevated temperature, the friction coefficient of PAO-GMO blend climb up gradually, followed by a decrease tendency, and the wear increase gradually with temperature. The results of Quartz Crystal Microbalance show that the physical adsorption film plays the main role in friction reduction at low temperature. While at high temperature, the Infrared Spectrum and X-Ray Photoelectron Spectrum show that the GMO involves into the chemisorption with friction surface, producing Fe(OH)O and Fe3O4. The friction reduction mechanism of GMO transferred from physisorption to chemisorption, which reduced friction coefficient at both low and high temperature.