EFFECTS ON CONTACT RESISTANCE OF PASSING ELECTRICAL-CURRENT THROUGH WIPING PALLADIUM CONTACTS

A study has been carried out to evaluate the effect of passing electri cal current through wiping palladium contacts, Different magnitudes of de current, from 0 to 4 A, are used, and at 0 A the wipe amplitudes c hange from 50 mu m to 1 mm. Two types of contact resistance are examin ed: one is dynamic contact resistance monitored and stored during wipi ng by a digital oscilloscope, and the other is static contact resistan ce measured at the start of sliding by a digital voltmeter, In light o f dynamic contact resistance measurements we propose a tentative mecha nism for explaining the contact resistance degrading process; the comp arison of static contact resistance during wiping with and without cur rent demonstrates that passing electrical current through the wiping c ontacts can restrict the contact resistance degradation. This occurs b y 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 the rmal expansion, The evidence demonstrates that the critical wiping num ber, (N-c), where the contact resistance begins to increase rapidly, i s strongly dependent on the wipe amplitude at 0 A, but slightly affect ed by current, AES analysis results show that oxides mainly exist with in the wear track, while polymers concentrate at the ends of the wear track.