CONTACT RESISTANCE INCREASE IN PALLADIUM MATERIAL AS A RESULT OF MECHANOCHEMICAL REACTION

In small-size relays used under low current, mechanical actions of con tacts at make-break, such as impact and wipe, can affect contact deter ioration more than electric factors such as arcing and Joule heat. In this article, the effects of vertical impact and horizontal wipe were studied in separate experiments in order to clarify the mechanism by w hich a palladium oxide film is formed on the contact area and the cont act resistance is rapidly increased by make-break operations under no load in air. The experiments show that the main factor of contact resi stance increase is the formation of an accumulated layer made of insul ation powders by wipe action. Based on this fact, models of contact su rface condition during operations are suggested to explain the variati on of contact resistance. In addition, the effect of passing current t hrough the contacts is also explained by the models. (C) 1997 Scripta Technica, Inc.