Pitting corrosion of Aluminum alloy in chloride solution cantaining sulfate and sulfite ion

Abstract

The effects of sulfate and sulfite ion on pitting corrosion for Al alloy in chloride solution were investigated by potentiodynamic polarization measurements. If the concentration of sulfate and sulfite ion was equal to each other, the oxygen diffusion ^－limited current density in the sulfate ion solution was higher than that in the sulfite ion solution and hydrogen ion diffusion ^－limited current density in the sulfite ion solution was higher than that in the sulfate ion solution. The pitting potential became more noble with an increase in sulfate and sulfite ion concentration. The open circuit potential was independent of sulfate ion concentration and increased with sulfite ion concentration. These results indicated that the difference between the pitting and the open circuit potential became larger with sulfate ion concentration and smaller with sulfite ion concentration. Upon the above results, it was concluded that sulfate acted as an inhibitor and sulfite acted as an accelerator.