Eutectic Silver-Silicon Internally Oxidized Contacts

A new contact material for a sealed switch has been developed. The contact material is made by internally oxidizing an Ag-Si eutectic system alloy. The contact material shows very low contact resistance, like silver, but it does not stick even in ultrahigh vacuum due to the dispersed silicon oxide particles.'The internal oxidation mechanism of the newly developed material is quite different from that of a conventional one. Silicon oxide particles less than 2 tim in diameter are uniformly dispersed in the silver matrix throughout the specimen. This material is obtained by the following two processes. First, the melt of an Ag-Si alloy (Si:1-2.8 wt%) is cooled rapidly to obtain a finely dispersed eutectic matrix, and then the specimen is cold- or hot-worked. By this process, silicon particles are made fine and dispersed uniformly throughout the specimen. Second, the specimen is oxidized in an oxygen atmosphere at pressures from I to l0 atm. Conventional internally oxidized contact materials, such as Ag-CdO, are obtained by oxidizing a-type solid solution alloys under high pressure, so that segregated metallic oxides are large and not dispersed uniformly throughout the specimen. Sealed contact materials must have great resistance to sticking as well as stable contact resistance. Although the antisticking and contact resistance properties generally work against each other, the developed contact material has both properties.