GALVANIC INTERACTIONS BETWEEN ALLOYS AND MINERALS IN SULFURIC-ACID

Many semiconducting minerals have sufficient conductivity to permit electrochemical reactions on their surfaces. Consequently, galvanic interactions will occur when such minerals are coupled to metals or other conducting minerals. Accelerated galvanic corrosion of metals coupled to minerals is likely because most minerals exhibit potentials in solution that are noble to the corrosion potentials (E(corr)) of typical metal alloys. Anodic and cathodic polarization diagrams can be used to predict galvanic corrosion rates expected from any given galvanic couple in a particular corrosive electrolyte. Polarization diagrams were presented for numerous minerals and alloys in sulfuric acid (H2SO4). Examples demonstrated how the curves could be used to estimate the likelihood of galvanic corrosion and the reaction rates to be expected in metal-metal, metal-mineral, and mineral-mineral couples. The effects of relative cathode-to-anode surface area, application to initiation of pitting corrosion, and limitations of the method also were reviewed.