Effects on contact resistance of passing electrical current through wiping palladium contacts

A study has been carried out to evaluate the effect of passing electrical current through wiping palladium contacts. Different magnitudes of dc current, from 0 to 4 A, are used, and at 0 A the wipe amplitudes change from 50 μm to 1 mm. Two types of contact resistance are examined: one is dynamic contact resistance monitored and stored during wiping by a digital oscilloscope, and the other is static contact resistance measured at the start of sliding by a digital voltmeter. In light of dynamic contact resistance measurements we propose a tentative mechanism for explaining the contact resistance degrading process; the comparison of static contact resistance during wiping with and without current demonstrates that passing electrical current through the wiping contacts can restrict the contact resistance degradation. This occurs by a self-cleaning action which scrapes the wear debris accumulated at the end of the wear track far away from the contact spot caused by thermal expansion. The evidence demonstrates that the critical wiping number, (N _c), where the contact resistance begins to increase rapidly, is strongly dependent on the wipe amplitude at 0 A, but slightly affected by current. AES analysis results show that oxides mainly exist within the wear track, while polymers concentrate at the ends of the wear track