No abstract

No abstract

No abstract

Results of experimental studies of adhesion between goldigold, platinum/ platinum and gold/platinum-group metal contacts, over the load range 1 mg to 10 g, are interpreted on the basis of simultaneous measurements of contact resistances. The relationship established between coefficient of adhesion and contact resistance demonstrates the importance of surface films in preventing adhesion. Adhesion between gold/gold contacts was significantly higher than between gold/platinuni-group metal contacts. In goldigold contacts adhesion increased markedly above 90°c, but with platinum/platinum contacts temperatures above 550'c are required before adhesion is accentuated.

Established materials for light-duty electrical-contact applications are based on the platinum-group metals and gold; silver, copper, tungsten, and their alloys are employed for heavy-duty contacts. The main features of the operation of heavy-duty contacts are arcing and welding, which become important when the power being switched exceeds ∼ 100 W or the current ∼ 1.0 A. In the light-duty field, erosion transfer, mechanical wear, and contact resistance are the phenomena of contact operation that have to be considered. With light-duty contacts, surfaces must be free from tarnish films to ensure low contact resistance: hence the use of the platinum metals and gold. Silver can be used only in restricted light-duty applications where the electrical and mechanical conditions permit rupture of sulphide films.