Magnetic fields would affect electrochemical reactions for metallic materials in aqueous solutions. The main effect of a magnetic field applied on an electrochemical system is the introduction of additional forces on the ions in the electrolyte, such as Lorentz-force driven magnetohydrodynamics (MHD) effect and Kelvin-force-driven magnetic field gradient force (MFGF) effect. There are some published reports on the influence of magnetic fields on the pitting corrosion, and apparently contradictory results have been reported. In this work, we focused on the effect of magnetic field on anodic dissolution of iron in a molybdenum nitrate solution with chloride ions.

The typical potentiodynamic polarization curves of iron in a 0.2 mol L^-1 Na₂MoO₄ +0.2 mol L^-1 NaCl solution at a potential sweep rates of 0.833 mV/s and under 0 T and 0.4 T magnetic field are shown in Fig. 1. Magnetic field decreased the limiting current densities at high potentials. The results in Fig. 1 were confirmed by potentiostatic polarization measurements, which were used to study the effect of magnetic field on the anodic corrosion of iron. After a relatively long period of polarization at 0.4V(SCE) at 0T, imposing a magnetic field will result in a sudden increase and then a slowly decrease of the current density, as shown in Fig. 2(a). The electrode surface morphologies after potentiostatic polarization at 0.4V for 200s under 0T are shown in Fig. 2(b), which are corresponded to the conditions in Fig. 2(a). The pits have propagated deeply. The mass transfer process between occluded pit bottom and the pit mouth would became difficult with the deepening of the pits. The retarding effect of magnetic field on anodic dissolution of iron in a molybdenum nitrate solution with chloride is ascribed to its effect on the mass-transport process between the occluded pit bottom and the pit mouth and finally the resultant disturbance of the autocatalysis process involved in pitting