Island growth of corroded products on various plated surfaces after long-term indoor air exposure in China

The environmental effects on several contact platings including gold, silver, nickel and tin were studied after investigating the morphology, composition and fretting behavior of natural corroded products, which were formed in Shanghai, China after long-term indoor air exposure. Corrosion formed on all of the testing coupons are found as discrete islands rather than continuous layers as predicted. Not only the protrusive core product but also one or more dark rings centrically surrounding the core are seen on gold plated coupons. Micro-observation on the ring shows that it is formed by accumulated and discrete islands similar to that of the core. The height of corroded products on the ring is much lower than that of the core. The composition of corroded product on the ring is similar to that of the core. Fretting across the dark ring also causes high contact resistance. Preliminary investigation shows that this may cause sudden and rapid high impedance and error codes in telecommunication systems.