It has been demonstrated that the formation of insulating material by mechanochemical reaction during make-break operations can lead to a rapid increase of electrical contact resistance in Pd contacts. To further examine this phenomenon the changes at contact surfaces during make-break were observed and the effects of impact and wipe, which exist at the closure of contacts, were studied separately. Observation shows the wear track spreads from a circle to an ellipse, and the frictional powder is scraped from wear track and gathers from particles to clusters. Additionally the results of impact and wipe experiments indicate that the formation of insulating material depends on wipe rather than impact. Frictional powder strongly affects the increase of contact resistance.
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