Hydrogen Evolution during Friction from Chemisorbed Water on Metals and Alloys

In this study, hydrogen formation was investigated during lubrication tests, which were carried out with synthetic hydrocarbon oil under high-vacuum conditions using disks made of Fe, Cr, SUS304, SUS440C, and SUJ2. The evolved gases were detected using a quadrupole mass spectrometer. Hydrogen evolution was observed at the beginning of the sliding. Hydrogen and hydrocarbons were formed simultaneously after 1 km of sliding distance. The hydrocarbon oil was decomposed tribochemically by the same point. When SUS304 was used as the specimen, a higher rate of hydrogen evolution was observed at the beginning of the sliding action compared to the other metals. X-ray photoelectron spectroscopy of the disk surface revealed that there was a thicker oxide film and large amount of chemisorbed water on SUS304. These results suggest that the chemisorbed water on SUS304 could be a source of hydrogen. When the SUS304 specimen was pretreated with heavy water, hydrogen deuteride ion was detected during the lubrication test. It can be concluded that chemisorbed water on metal surfaces is a source of tribochemically-formed hydrogen during lubrication tests. The sharp decrease in hydrogen evolution at the beginning of sliding is related to the destruction and removal of the oxide film