Hydrogen Evolution during Friction from Chemisorbed Water on Metals and Alloys

Abstract

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.

Chemical Activity of Nascent Surfaces for Tribochemical Reactions of Lubricant Components

“…Nevertheless, hydrogen evolution was observed during sliding as a tribochemical decomposition product of water at the beginning of sliding, because water adsorbs on natural metal oxides covered on steel. 35 As mentioned above, it is clear that the adsorption activity of molecules on nascent steel surfaces closely depends on their molecular structure. Electron rich compounds, such as benzene, olefins, and sulfides have πand lone pair electrons and exhibit higher adsorption activity than that of polar compounds such as acids, amines and water.…”

“…Although it is known that water adsorbs on metal oxides easily through polar interactions, it is notable that the chemical affinity of water for nascent steel surfaces is weak. Nevertheless, hydrogen evolution was observed during sliding as a tribochemical decomposition product of water at the beginning of sliding, because water adsorbs on natural metal oxides covered on steel …”

Operando exploration of tribochemical decomposition in synthetic FeS2 thin film and mineral iron pyrite

“…22,23 Among these techniques, Mechanically Stimulated Gas Emission Mass Spectrometry (MSGE-MS) has emerged as a powerful method over the last two decades. [24][25][26] By employing tribological action such as rubbing or scratching, MSGE-MS allows for precise and controlled mechanical activation of materials and coatings on a micrometre to nanometre scale under wellcontrolled load, speed, and environmental conditions. By integrating this technique with mass spectrometry, it becomes possible to accurately detect and quantify volatile products that swily propagate in vacuum from buried mechanical interfaces, thereby facilitating the real-time characterization of tribochemical reactions.…”