Contact resistance variations of tungsten contacts operated in air and silver-tungsten carbide contacts operated in vacuum

Two experiments were conducted to determine the effects of W and oxide formation on the variations of contact resistance (R_c) of Ag-W contacts. The first consisted of switching pure W contacts in air in a 20-A circuit for 500 operations and then observing the variations of R_c while they passed a 20-A steady-state current. In the second experiment, Ag-WC contacts were operated in vacuum and then subjected to a series of steady-state currents up to 5000 A. The pure W contacts exhibited a wide variation in R_c. The Ag-WC contacts showed a consistent steady R_c value. These results are discussed with reference to previous data on Ag-W and Ag-WC contacts operated in air and on the formation and dissociation of W oxides and silver tungstates