Kinetic Model for Aluminum Dissolution in Corrosion Pits
The kinetics of aluminum dissolution in etch pits and tunnels, in a 1 M HCl-3 M H2SO4 solution at 70°C, were investigated. Dissolution current densities during growth of tunnels and pits, at potentials of roughly −0.8 and 1 V vs.Ag/AgCl respectively, were found to be approximately 6 A/cm2. Transient experiments using current step reductions during pitting, or anodic current pulses during tunnel growth, revealed strongly potential-dependent current densities up to 300 A/cm2. The results suggested that the dissolution rate is potential-dependent when measured on times scales of ∼1 ms after potential disturbances, but insensitive to potential in quasi-stationary experiments. A kinetic model was presented assuming a monolayer or multilayer chloride layer on the aluminum surface, including kinetic expressions for transfer of Al+3 and Cl− ions at the film/solution interface, and ionic conduction in the film. In agreement with experiments, the model yields constant or potential-dependent dissolution rates following a Butler-Volmer relation, depending on the time scale of experimental measurements. The large current densities in anodic transient experiments derived from high rates of Cl− incorporation during film growth.
This article is from Journal of the Electrochemical Society 151 (2004): B45–B52, doi:10.1149/1.1635386. Posted with permission.