Potential Distribution, Shape Evolution, and Modeling of Pit Growth for Ni in Sulfuric Acid

Growth of artificial pits in the Ni/sulfuric acid system was investigated using a microprobe technique for the potential monitoring and pH measurements within the pits, as well as routine electrochemical, solution analysis, and metallographic techniques. The measured data and the observed changes in shape of the pit with time demonstrate that the IR voltage drop mechanism of localized corrosion operates for this system. Experimental results are in good agreement with the results of mathematical modeling. It is also found that the increase in Ni ++ ions and in pH within the pit have a destabilizing effect on the pit growth process and that this effect can be explained within the framework of the IR voltage drop mechanism.