Corrosion of braze joints by hydrogen sulfide

The early field failure of some motor control contactors due to the separation of the contacts from the copper arms to which they had been brazed was investigated. All of the failed devices were from geographical areas where the temperature and humidity were high and where there was a local source of sulfurous gases. Corrosion of the contact assemblies in the area of their braze joints by sulfur was identified as the cause of the premature failures. A laboratory test was used to evaluate the effectiveness of different assembly modifications in minimizing the corrosive attack by hydrogen sulfide. Silver plating was ineffective in protecting the braze joint from corrosion. Changing the braze alloy to one having a substantial zinc content was found to effectively impede the corrosive attack of the braze joint area and thus would be expected to increase the life of the devices in corrosive sulfurous environments