A Mechanism of Vapor Effect on Friction Coefficient of Molybdenum Disulfide

Abstract
Molybdenum disulfide single crystals, compressed single crystals and pellets were friction tested in vacuum, air and water. The friction coefficient of MoS2 single crystal was hardly affected by air or water. In the case of the compressed MoS2 single crystals or MoS2 pellets, the friction coefficient became higher in the order of vacuum, air and water. When a large quantity of water was charged into compressed MoS2 single crystals or MoS2 pellets, the friction coefficient decreased to that obtained in a vacuum. These phenomena were explained by the surface tension of the condensed water in wedge-shaped cavities.