ABSTRACT
This chapter discusses the subject of contact corrosion. The observation and analysis of the tarnish films gives the contact designer knowledge of how the surface of the contact can change under different classes of ambient atmospheres. The closed electrical contact has to perform its function of passing electric current reliably and with no change in its contact resistance for the entire duration of its life. The contacts have to perform this function even though the ambient atmosphere in which they reside contains pollutants which can cause the contacts to tarnish or corrode. Clean surfaces of many metals exposed to air oxidize quickly. The usual tarnish films formed in air at ambient temperatures are mostly composed of mixtures of oxides, sulphides, and chlorides, as well as carbonates and sulphates. The rate of reaction of metals with formation of corrosion product coatings depends in most instances on the relative permeability of the coating to the reactants.
