The Corrosion Mechanism in Low Conductivity Media with Water Traces: Studies in Wet Bromine

Experimental and theoretical investigations are combined to evaluate the critical dependence of corrosion rates in a low conductivity medium on the presence of traces of water. Although this study concentrates on the intense corrosive properties of wet bromine, the results are expected to be applicable to other low conductivity media. It is found that local electrochemical cells are mainly responsible for the relatively intense corrosion currents in spite of the high electrical resistivity of the medium. The phenomenon is explained by the formation of a thin conductive layer at the metal-bromine interface. This layer may consist of an aqueous phase built up mainly by the hygroscbpicity of the bromides present as corrosion products. Characterization of corrosion products and analyses of the corrosion potentials of various alloys in wet bromine indicate that the cathodic reaction consists of the reduction of Br₂ to Br⁻. It is also found that the corrosion of passive metals, such as Ni, occurs through breakdown of passivity facilitated by a combination of high redox potential and sufficient Br⁻ concentration.