Silver corrosion and whiskers growth on power contacts in industrial atmosphere of pulp and paper plants

Extensive silver corrosion and growth of silver whiskers was found on power contacts of low voltage breakers at a recycle pulp plant in Minnesota. The phenomenon can be extremely hazardous. The plant experienced a number of failures of circuit breakers in 1999-2000 caused by strong overheating. Metallic whiskers were found growing from heavily corroded silver-plated copper surfaces of the power contacts virtually everywhere but mostly from the edges and corners. The length of the two-month old whisker reaches several inches (5-10 cm) and the thickness of the filament is up to 0.04" (/spl sim/1 mm). Using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) we have determined morphology and chemical composition of the whiskers. Most of the whiskers are made of 97-99% silver with 1-3% of copper. The surface of the larger whiskers is covered with silver sulfide. To determine the means of controlling and minimizing the hazardous phenomenon, the major factors initiating and accelerating the mechanism of whisker growths have been thoroughly investigated.