Magnetic field effects in electrochemistry

R. Aogaki

National Research Laboratory for Magnetic Science JST, 1-1-56, Shibashimo, Kawaguchi, 333-0848, Japan Department of Product Design, Polytechnic University 4-1-1, Hashimotodai, Sagamihara, 229-1196, Japan

Abstract
As a magnetic field effect in electrochemistry, the MHD effect is a well-known phenomenon. It arises from the Lorentz force yielded by the interaction between electrolytic current and magnetic field, so that the mass transfer is enhanced by the induced macroscopic liquid flow. The same kind of effect, i. e., the micro-MHD effect has also been found in the electrocrystallization and the corrosion of copper in a high magnetic field. In the case of copper corrosion by nitric acid, the localized Lorentz force and resultant local convection are characteristic of this effect, which are formed by the currents circulating in electrochemical cells on the copper surface. Consequently, numerous minute vortexes and a pair of macroscopic rotations emerge in a magnetic field vertical to the copper surface. At high acid concentration, these microscopic vortexes usually suppress the dissolution rate, whereas at low concentration, the copper corrosion is contrarily promoted by the magnetic field. When the magnetic field does not retain a uniform distribution, the magnetic force is newly generated by the magnetic field gradient, so that the magneto-convection is induced. Sometimes, since the velocity becomes compatible with that of the MHD flow, in the heterogeneous magnetic field, it is thus necessary to consider the contribution of this flow to the MHD effect. Figs 9, Refs 24.