Silver whiskers growth on power contacts in corrosive industrial atmospheres

Systematic and accelerating growth of silver whiskers was found on power contacts of low voltage breakers at a recycle pulp plant in Minnesota. Hazardous phenomenon led to strong overheating and caused a number of failures of circuit breakers in 1999-2000. The major corrosive component at the plant is hydrogen sulfide (0.2-2 ppm in control room). Using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) we have determined morphology and chemical composition of the whiskers, which grow from heavily corroded silver-plated copper surfaces of the power contacts virtually everywhere but mostly from the edges and corners. The filaments growing only for two months are up to several inches (5-10 cm) long and up to 0.04 in (~1 mm) thick. Most of the whiskers are made of 97-99% silver with 1-3% of copper. The surface of most of the whiskers is covered with silver sulfide. The major factors initiating and accelerating the mechanism of whisker growth have been thoroughly investigated to determine the means to control and minimize the hazardous phenomenon