A touch of gray [power contacts, silver corrosion, whiskers growth]

Sulfur-rich environments, such as those found in the paper and pulp industry, create a special problem with the silver plating in switchgear and motor control centers (MCCs). Silver plating is used throughout switchgear because of its superior conductivity and longevity. Silver is very sensitive to the presence of hydrogen sulfide (H₂S), which forms silver sulfide (Ag₂S), even at a very low concentration of corrosive gas. Nonuniform growth occurs in forms of "clumps," "dendrites," "nodules," and "whiskers". The decomposition of the contact surfaces leads to an increase of the contact resistance, hence, to a rise in temperature, and eventually to possible failure. This article analyzes the major factors initiating and accelerating the growth of the whiskers on silver plating in electrical apparatus.