Effects of atmospheric corrosion on some materials used in electrical contacts (gold/nickel/brass, nickel/brass, brass, copper)

A quantitative and qualitative study of the contamination of different substrates in the presence of some polluting gas (H2S, SO2, NO2 and Cl-2) has been undertaken. Corroded samples are the copper, the brass, the brass covered with an electrochemical deposit of nickel (thickness approximate to 5 mu) and the brass covered with an electrochemical nickel coating (thickness approximate to 5 mu m) and with a gold coating (thickness approximate to 0.4 mu m). Tests of corrosion have been carried out in the humid synthetic air (HR=75%) containing either NO2 (0.2vpm), SO2 (0.2vpm), Cl-2 (0.01vpm), or NO2 (0.2vpm), H2S (0.2vpm), Cl-2 (0.01vpm). The corrosion rates and equally the nature and the morphology of the corrosion products have been compared in each corrosive atmosphere for the 4 different substrates. In all cases, the copper and the brass are covered with a continuous layer. For the brass with nickel coating or the brass with nickel and gold coating one observes the formation of germs These germs are generally constituted of salts of nickel sometimes equally salts of zinc and salts of copper (solely for samples with gold coating) identified by a process developed in our laboratory associating ionic chromatography, microgravimetry and atomic absorption. These studies have shown that the protection of the nickel by the gold requires a deposit of gold perfectly tight. The porosities in the layer of gold are probably connected to the crystalline structure of the gold deposit. The crystalline structure of the gold coating depends certainly on the crystalline structure of the deposit of nickel. Tests are now carried out to show the relation between the crystalline deposits structures and corrosion.