TRANSPORT AND REACTION DURING PITTING CORROSION OF NI IN 0.5M NACL .1. STAGNANT FLUID

A two-dimensional model of a corrosion pit was developed with use of a finite-element method which accounted for multiple species in solution, reaction equilibria, migration, and surface kinetics. The model was used to simulate the dissolution of a hemispherical corrosion pit on nickel in 0.5M NaCl. Concentration profiles showed significant enrichment of ions inside the pit. Concentration gradients, however, extended well beyond the mouth of the cavity, indicating the importance of transport resistance outside the cavity. Pitting corrosion of nickel in chloride solution was also investigated experimentally by forming single corrosion pits under potentiostatic conditions. The dissolution current from single pits was found to be potential dependent. Current densities, measured experimentally in the range of 150-250 mV SCE, were in good agreement with values predicted theoretically with use of the mathematical model. Local dissolution rates calculated along the pit surface were also consistent with the shape evolution of pits observed experimentally.