Effects of Magnetic Field on Uneven Dissolution of Iron in Sulfuric Acid Solution with Chlorides

The effects of magnetic field on anodic dissolution and passivation of iron in a sulfuric acid solution with chlorides are investigated by electrochemical measurements and surface observations. In the anodic potentiodynamic polarization curve, the potential for the drastic current drop is not significantly affected by the potential sweep rate under 0 T, which moves in the negative direction with increasing potential sweep rate under 0.4 T magnetic field that is parallel to the working electrode surface. The uneven surface produced during the potentiodynamic polarization hinders the transition from active dissolution to passivation. The area fraction of the locally accelerated dissolution increases with prolonging polarization time at high potentials where the surface film precipitation-dissolution process is the rate-determining step for metal dissolution. Pretreatment under potentiostatic polarization at 0.4 T magnetic field produces an uneven surface that would result in unrecoverable electrochemical states after switching from 0.4 T to 0 T, depending on the applied potential. The positive-feedback mechanism for the magnetic field effect and the surface morphological effect is proposed. The results demonstrate the direct magnetohydrodynamic effect and its resultant uneven surface on the anodic behavior of iron.