Effects of the Lorentz force and the gradient magnetic force on the anodic dissolution of nickel in HNO3 + NaCl solution

Abstract

In this paper, the magnetic field perturbation method is used to study the effects of the Lorentz force and the gradient magnetic force on the anodic dissolution of Ni in 0.50mol dm-3 HNO3+5.0mmol dm-3 NaCl solution. During the anodic dissolution process, magnetic fields are applied in two directions: parallel (B//) and perpendicular (B⊥) to the surface of the electrode. Thus, the effects of different magnetic forces on the anodic dissolution can be analyzed. After the application of B//, the current may increase, decrease or remain stable under different potentials, while the peak potential, the oscillatory region and the passive potential shift positively. These are always caused by the Lorentz force, which enhances the mass-transport processes. However, after the application of B⊥, the peak potential, the oscillatory region and the passive potential shift negatively. The currents always tend to decrease under the different potentials, which can be explained as follows: the gradient magnetic force suppresses convection to increase the concentration of corrosion products, such as the paramagnetic Ni(II) species, in local positions at the electrode|electrolyte interface. However, neither B// nor B⊥ affects the anodic dissolution in the passive region for the oxide film on the electrode surface inhibits the MF effects. If Ni dissolves in 0.50mol dm-3 HNO3 with different chloride ions containing solution at the same potential, the effects caused by B// are different for it is in different regions and the rate-determining steps are different, however, the currents still tend to decrease with application of B⊥.