Au-Sb and Au-Ag-Sb alloys as low-voltage contact materials

A recent investigation has shown that the increase in contact resistance of low-voltage noble-metal electrical contacts with the number of on-off switch cycles is primarily due to carbon build-up on the contact surfaces. Moreover, when the contact electrodes are made of base metals, such as Ni, Fe, Ti and Sb, carbon formation can be delayed, if not eliminated. Among these metals, Sb has been found to be the best contact material against carbon formation. Because of the comparatively higher electrical resistivity and the potential for oxidation, however, Sb cannot be used as a contact material. Therefore, it has been decided to alloy noble metals, such as Au and Ag, with Sb. In this study, Au-Sb and Au-Ag-Sb alloys of various compositions were prepared and tested in air-benzene mixture at room temperature. An impact tester was used for conducting tests that simulate the operation of relay contacts with electrical load. Of all the alloys tested for discouraging carbon formation, the Au-7 Ag-30 Sb alloy was found to be the best.