Fe²⁺の溶存酸素による酸化反応

抄録

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.