Anodic Polarization Behavior of Iron in Phosphoric Acid Solution Under the Action of Magnetic Field

Abstract

The effect of magentic field on anodic dissolution, passivation and dissolution-passivation transition of iron in sulfuric acid solutions have been investigated. The change of anodic dissolution in the dissolution-passivation transition region and the resultant shrinkage of the passive region due to applied magnetic field have been reported. Uneven dissolution of iron electrode after anodic dissolution in sulfuric acid solutions have been reported. In the represent work, the effect of magnetic field on anodic behavior of iron in 0.5 mol/L phosphoric acid is investigated. Potentiodynamic polarization curves and potentiostatic polarization measurements are conducted at 0T and 0.4T. The anodic polarization curves at 0T and 0.4T are shown in Fig. 1, and the electrode surfaces after the measurements are shown in Fig. 2. The anodic polarization curve at 0T exhibits typical anodic dissolution, dissolution-passivation transition, steady passivation and transpassivation behavior. There is no sgnificant effect of magentic field on the active dissolution at potentials lower than Emax, 0T. Magnetic field moves the dissolution-passivation transition potential to a more noble potential therefore narrows the steady passivation range. There is no passive range in the anodic polarizaiton curve at 0.4T, showing only the drastic drop of current at Emax, 0.4T and then an increase of current soon. There is a quasi-linear potential-current density relationship in a wide potential range, i.e. -0.45 to 0.90V(SCE) at 0T, and -0.45 to 1.85V (SCE). The electrode surfaces after the potentiodynamic polarization measurements up to 2.0V(SCE) at 100 mV/min are observed, indicating severe anodic dissolution. The uneven electrode surface shows the locally accelerated anodic dissolution at the left and right edges of the electrode. From the center of the electrode along the horizontal direction to the edge, the uneven dissolution of the electrode surface presents an aggravating tendency. The results are consistent with thoese observed for iron in sulfuric acid at 0.4T magnetic field. When potentiostatic polarization starts at 1.2V at 0T, passive state can be reached and the further applied 0.4T magnetic field decreased the measured current density, showing the potential-dependent rate determining step and the resultant magnetic field effect on selective electrochemical processes. Figure 1