EFFECT OF SURFACE REACTIVITY OF LUBRICANTS ON THE PROPERTIES OF ALUMINUM ELECTRICAL CONTACTS

Lubricants are used in electrical contacts to minimize friction and me chanical wear and protect electrical interfaces against corrosion. Thi s paper provides an example of the importance of differentiating betwe en the lubrication and ''electrical-contact protection'' properties of lubricants. The paper reports on the frictional properties and the ef fect on contact resistance of stearic acid boundary films on aluminum. Stearic acid is an effective lubricant for aluminum because the long- chained acid molecules are chemically attached to the native aluminum oxide surface film. In an electrical contact, mechanical disruption of this native oxide film during sliding exposes the underlying aluminum metal to the stearic acid. The ensuing chemical reaction of the acid with the exposed metal leads to chemical breakdown of the lubricant an d immediate surface oxidation of the aluminum. This reaction engenders a large increase in contact resistance. These observations provide un ambiguous evidence that stearic acid is unacceptable as a lubricant fo r aluminum electrical contacts, although it is effective as a conventi onal lubricant for aluminum.