Electrical contacts in electromechanical devices must maintain low contact loop resistance to avoid power losses at the interfaces. Contamination and corrosion of exposed contact surfaces can occur through outgassing of volatile species from surrounding materials. Modification of surface layers can also occur through oxidation or segregation of contact alloy constituents. Low contact resistance values are obtained by using bare metal surfaces, which are easily degraded by reaction with adsorbed species.
Clean electrical contacts are generally maintained by controlling the atmosphere in hermetically sealed devices, a method that is not totally effective for extended life applications. Production processes themselves often leave behind sources of contamination for the electrical contact surfaces, such as the solder on the circuit board surface seen in the figure shown here. (reference)
Sulfur rich environments are common at industrial facilities such as petroleum and chemical plants, refineries, paper and pulp recycling plants, sewer and wastewater plants. Such atmosphere produced by various chemical technologies causes a serious corrosion problem for many metals used in electrical apparatus.