DEPENDENT-VARIABLE TRANSFORMATION FOR THE TREATMENT OF DIFFUSION, MIGRATION, AND HOMOGENEOUS REACTIONS - APPLICATION TO A CORRODING PIT

The anodic dissolution of nickel in chloride medium is treated for a s tagnant solution and the hemispherical cavity geometry common to the d issolution of passivating, corrosion-resistant metals. A new coordinat e system developed recently by the authors again proves to be useful i n dealing with the problem numerically, particularly with regard to th e singularity at the pit lip. The quasipotential transformation allows us to reduce the coupled, nonlinear partial differential equations go verning the concentrations and the potential to a single linear equati on, Laplace's equation, with a great reduction in computation time ard an increase in the accuracy attainable. The method thus treats couple d diffusion and migration with an arbitrary number of facile homogeneo us reactions and the participation of an arbitrary number of species i n the heterogeneous electrode reaction. Numerical calculations for the dissolution of nickel in chloride solutions are compared with publish ed experimental results.