Ag(40 wt%)-Pd(60 wt%) alloy has been widely applied to contact materials installed in various electromechanical devices. However, in application to the down sized relays, failure due to contact resistance is caused easily by both growth of oxide film on the contact surface and low contact force. To solve the increase in contact resistance, an overlay of thin Au or thin Au-Ag (8-10 wt%) has been used on the alloy. Despite this, cleanliness and low hardness of these overlays cause adhesion, or sticking, at contact interface. Increase in contact resistance and sticking are contrary to each other. In order to eliminate these contrary properties, the author studied improving the Ag-Pd alloy with a dopant. Low level of contact resistance for both static and dynamic contacts of Ag-Pd with Mg doping was found even if the contact surface was covered with an oxide contaminant film. This paper presents the excellent contact resistance and adhesion behaviors of Ag-Pd-Mg alloy and their mechanisms, and also presents in the later part, surface contamination behaviors for organic gases.

On account of its superior electrical contact performance, Ag (40wt%)-Pd(60wt%) alloy has been widely used to the electrical contacts of electromechanical devices. However, regarding small devices, some important difficulties arise due to the small size such as the degradation of the contact resistance caused by the oxide film grown on the surface. To solve these problems, it was reported previously that doping Mg and Cr into the Ag-Pd alloy was tried to improve the oxide film. As a result, the oxide film grown on the Ag-Pd-Mg surface exhibited a remarkably low contact resistance. However, for the oxide film on Ag-Pd-Cr, no improvement of the contact resistance was observed. In this study, to clarify the cause of the low contact resistance for Ag-Pd-Mg, the effect of the doping with a third element on the composition and formation of the oxide film was analyzed using electron diffractometry, XPS and STM. As a result, Ag was found to be distributed on the outermost surface and inside the oxide film formed on Ag-Pd-Mg. However, Ag was not found on the surface of and inside the oxide film formed on Ag-Pd-Cr. Therefore, it was concluded that the presence of Ag on the surface of and inside the oxide film reduces the resistivity of the film.