Abstract
It is well-known that the corrosion rate of iron and steel is affected by the Fe3+ concentration in acidified solutions. Experimental works on oxidation from Fe2+ to Fe3+ by the dissolved oxygen in various electrolytes have been carried out. Generally, the process is first order with respect to Fe2+, and it depends much on the pH. The reaction rate increased with decreasing pH in HCl, while the rate decreased with decreasing pH in other solutions such as phosphate, sulfate and citrate buffer solutions. The reaction rate was less than 10-3min-1 in solutions of pH<4, or the increment of Fe3+ was only 10-5M/min in solutions containing Fe2+ of 10-2M. The limiting current density for the cathodic process of those Fe3+ to Fe2+ would be 1.6×10-5ma/cm2, which is very small in comparison with the corrosion rate of Fe in aerated solutions. Therefore, it is concluded that the effect of oxidation of Fe2+ by the dissolved oxygen is negligible on corrosion of iron and steel.
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