In situ auger electron spectroscopy characterization of wet-CO 2-lubricated sliding copper electrical contact

Abstract

The electrical contact resistance, elemental surface composition and friction of an OFHC copper slip ring rotating in contact with two high purity copper wire brushes on different tracks were investigated in situ for heavy and light normal contact forces under a wet CO 2 environment at atmospheric pressure. Scanning electron microscopy was also used to characterize the slip ring and brush surfaces. Previous work in ultrahigh vacuum showed that, as rotation proceeded, interfacial impurities were almost totally removed and the electrical contact resistance decreased until cold welding occurred. In the present work, the slip ring surface was sputter cleaned (more than 95% Cu) before contact rotation and was only slightly contaminated after rotating in wet CO 2. Both the contact resistance and the friction decreased quickly and reached steady state values almost simultaneously in the early stages of rotation. Also, cold welding phenomena did not occur. Scanning electron micrographs taken after each experiment showed that the surfaces of the slip ring tracks and the brush wire ends were much rougher when heavy normal contact forces were used than in the light normal force condition. All these results confirm that wet CO 2 is an effective lubricant for Cu-Cu electrical sliding contacts.