Silver Migration in Electrical Insulation

Silver or silver plated metals, because of the favorable electrical and chemical properties of silver, have application in communications systems and throughout the electrical industry. When fabricating apparatus component assemblies, it is frequently expedient to assemble the silver parts in a manner such that they are in intimate contact with insulating materials such as phenol fiber. When standing electrical unipolar potential and atmospheric moisture are present, the silver may migrate. Silver migration may be defined as a process by which silver, when in contact with insulating materials under electrical potential, is removed ionically from its initial location, and is redeposited as metal at some other location. The redeposition occurs in two principal ways, namely; 1115 1118 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1 9 5 5 FIG. 2 -- Step-by-step bank phenol fiber separators illustrating silver migration.