Investigation of decomposition of hydrocarbon oil on the nascent surface of steel

Hydrocarbon oil with low vapor pressure has been used as a lubricant in high-vacuum conditions. Decomposition of the oil under boundary lubrication conditions was studied by investigating desorption of hydrogen and hydrocarbons, generated by tribochemical reaction occurred on nascent surface of 52100 steel during the sliding process in a ball-on-disk type sliding tester. Gaseous products by tribochemical decomposition were monitored by a quadrupole mass spectrometer (Q-MS), which would reveal the decomposition mechanism of hydrocarbon oil. It is found that tribochemical reactions of hydrocarbon oil occurred on active sites on steel generated by sliding, the desorption amount of hydrogen and gaseous hydrocarbons increased linearly with sliding velocity, and parabolically with load. A critical load for the activation of decomposition of the hydrocarbon oil on bearing steel was found to be about 1.1 N. In this paper, the decomposition mechanism of hydrocarbon oil was also explored.