Corrosion rates of binary alloys of nickel and iron measured by polarization methods

Abstract

Specimens of ten binary alloys of nickel and iron containing 3, 5, 10, 16, 20, 30, 36, 50, 57, and 81 percent Ni and of the metals nickel and iron were immersed for 7 months in 265 gallons of city water to which had been added 3 percent by weight of sodium chloride. Cathodic and anodic polarization curves of the specimens were obtained at about 22 periodic intervals throughout the exposure period. Corrosion currents, calculated from currents at breaks in the curves, were converted to corrosion rates expressed as weight losses by applying Faraday's law. The calculated weight losses were in reasonable agreement with the actual weight losses. The polarization rates, DeltaV/DeltaI, of the specimens calculated from cathodic polarization curves (cathodic control prevailed) at several intervals throughout the exposure period were plotted on logarithmic coordinates with respect to the corrosion current densities calculated from breaks in the same curves. Similarly, the averages of these DeltaV/DeltaI values were also plotted on logarithmic coordinates versus the actual corrosion rates expressed as weight losses. Both plots conformed to the theoretical slope of -1.