Mechanism of Hydrogen Generation by Decomposition of Lubricating Oils: Effect of Lubricating Oils on Hydrogen Brittle Flaking

Abstract

In the rolling bearings used in automotive electrical instruments and auxiliary devices such as alternators, it is well-known that brittle flaking occurs earlier than expected due to hydrogen embrittlement. Despite this, in the flaking mechanism, the generation process of hydrogen atoms in lubricating oils has not been clarified microscopically. In this study, we theoretically elucidated the reaction processes of poly-α-olefin (PAO) and alkyl diphenyl ether (ADE) molecules using quantum mechanical (QM) calculations. The basic and important mechanism for the generation of hydrogen molecules was clarified for the first time at the atomic level. Upon considering the generation mechanism on ceramics and nascent steel surfaces, it was found that the reason why the amount of hydrogen generation is similar regardless of the type of lubricant is because the energy required for hydrogen generation is almost the same. Furthermore, it was suggested that the suppression of hydrogen brittle flaking by ADE was due to the low exposure frequency of the nascent steel surface.

Keywords

• rolling bearing
• flaking
• hydrogen embrittlement
• hydrogen generation mechanism
• quantum mechanical calculation
• nascent steel surface