Tribological characteristics and mechanisms of boronitrogenated methyl epoxyoleate as bio-based additive in petroleum lubricant

In this work, boronitrogenated methyl epoxyoleate (BNMEO) was prepared by boronization and nitrogenation of methyl epoxyoleate (MEO). The tribological properties of BNMEO and MEO as bio-based lubricating additives in a petroleum oil were determined on a four-ball tribometer. The topographies, element compositions, and tribochemical species of the worn surfaces were analyzed by a scanning electron microscope, an energy dispersive X-ray spectrometer, and an X-ray photoelectron spectroscope, respectively. Results showed that both BNMEO and MEO, especially the former, were excellent in fortifying load-carrying capacities and friction-reducing and antiwear abilities of the oil under mild loads. However, their abilities in improving extreme pressure property of the oil under severe loads were very limited. The prominent ability of BNMEO in reducing friction and wear was characterized by well-increased maximum nonseizure loads and decreased wear scar diameters and friction coefficients and was attributed to generation of a dense and robust boundary lubrication film which consisted of a matrix of BNMEO with inclusions of aminic compounds, boron oxide, iron oxide, and hydrocarbons, thanks to strong adsorptions and tribo-oxidations of BNMEO on the metallic surfaces in the tribological processes.