The Influence of Velocity and Dissolved Oxygen on the Initial Corrosion Behavior of Iron in High Purity Water

The electrochemical “polarization resistance” method (also known as “linear polarization” method) was used in conjunction with a rotating iron electrode to investigate the effect of velocity and dissolved oxygen on the initial corrosion behavior of iron in high purity water. In low concentration, dissolved oxygen is cathodically reduced on iron surface sites and thereby accelerates corrosion. In moderate concentrations, the accelerating effect of oxygen on corrosion is considerably diminished via formation of a porous surface film, probably Fe(OH)2, which reduces the number of active surface sites for iron dissolution. In much higher dissolved oxygen concentrations, the corrosion potential becomes more active and corrosion rate again increases. This effect is attributed to partial oxidation of the Fe(OH)2 film by the diffusing oxygen to gelatinous ferric hydroxide film, which is more resistant to oxygen diffusion thereby resulting in a lower corrosion potential where active iron dissolution accelerates.