Corrosion mechanisms for nickel exposed to the atmosphere

Physical and chemical information on nickel corrosion layer formation, evol ution, morphology, and chemical makeup is organized and presented, together with information on nickel-containing minerals and other crystalline struc tures that might be expected to be present. The chemical reactions involved in the formation of these constituents during the corrosion process are th en surveyed. By far the most abundant of the typical corrosion products are various forms of nickel sulfates, including hydroxysulfates and the minera l retgersite (alpha-NiSO4. 6H(2)O). The presence of these species is shown to be a natural consequence of the thin aqueous layer chemistry involving a tmospheric SO2 and SO42- that occurs on nickel in humid environments. Forma tion pathways for retgersite and gaspeite are shown in schematic diagrams. Comprehensive kinetic simulations of the corrosion processes have begun to provide insight into the corrosion chemistry but-are limited by a shortage of laboratory determinations of the rates of dissolution, precipitation, an d transformation of nickel-containing chemical species. (C) 2000 The Electr ochemical Society. S0013-4651(99)08-034-9. All rights reserved.