Formation of palladium-oxides by mechanochemical reaction on Pd and Ag-Pd alloy contacts

The authors have previously reported (see Proc. 14th Int. Conf. on Electric Contacts, p.233-7, 1988) that, when Pd contacts are operated using mechanical break-make actions without switching load current in the air, palladium-oxides are formed on the contact surfaces by mechanochemical reaction caused by mechanical actions, and they cause serious deterioration of contact resistance. In the present work, the formation of the same products is reported on Ag-Pd70% and Ag-Pd50% contacts after tests involving operation 100000 times. Significant increase of contact resistance, however, was not observed. On the other hand, it is also found that the products show nonlinearity of contact resistance according to measuring current in both dynamic and static measurement. Temperature calculation shows that softening of the electrodes is not the main cause of the observed phenomenon. Thermal dissolution of the products is proposed as a possible cause