Oxidation of Platinum Group Metal Contacts by the Mechanochemical Reaction

Abstract

When Pt, Pd and Rh contacts are operated in a make-and-break action under certain environments, some black powdery products other than the frictional polymer are sometimes generated at the contact spot and the contact resistance is increased. In order to investigate the origin of increase in the contact resistance, these contacts were operated in N₂-O₂-H₂O-C₆H₆, CH₃OH enviroments by the special tester, and then measurments of the contact resistance, observation of the contact surface and analysis by E.P.M.A. were conducted.
The results are as follows:
(1) Although the contact resistance of the metals operated in the atmosphere of the laboratory is low and stable, it operated in purified air is increased remarkably.
(2) The cause of the increase in the contact resistance in purified air is the oxidation of the metals by mechanochemical reaction.
(3) Water vapor and organic vapor such as C₆H₆ and CH₃OH act as the inhibitor of the oxidation by a mechanochemical reaction; it is a cause of the low contact resistance in air not purified.
(4) The cause of effect as the inhibitor is the adsorption of H₂O and organic vapor on the surface of the contact.