Erosion Phenomena of Silver-Base Contacts (Part I)

Abstract

The erosion manner of Ag, Ag-W (6500) and Ag-CdO (100') contacts under large current (D. C.) was examined mainly from the view point of the micro-structural changes of their contact surface layers. In the first place the result of a single making operation of large current on each virgin contact surface shows more spreaded arc-foot and shallower erosion-depth in the case of Ag-matrix containing W or CdO than in the case of pure Ag-contact. Then as to the structural changes due to the repeated operations, it is found that in the case of Ag-W contact the composition of the surface layer is converted into the mixture of W and W-oxide by the dissipation of Ag, while in the case of Ag-CdO contact into Ag-rich by the dissipation of CdO.In view of the fact that the micro-structure has an important function in contact operation, the Ag-CdO contacts of uniform composition (10% CdO) but of different micro-structures were compared. From these experiments it is found that properly minute distribution of CdO tends to leave the contact at but slight rate of erosion, but expra-ordinarily minute distribution increases the dissipation amount of CdO.The operating condition in this experiment included in addition to the normal swi-tching on-off test, other loading systems such as exclusively to make and exclusively to break the circuit.