Effect of Spatial Distribution of Electronic and Ionic Currents on the Magnetic Field Induced by Galvanic Corrosion

Abstract

Magnetic fields induced by galvanic coupling between zinc and gold in an acidic media have been evaluated using a superconducting quantum interference device which operates at liquid nitrogen temperature. The goal was to study whether magnetic fields induced by electronic current from cathode to anode within a metal could be canceled by that induced by ionic currents from anode to cathode within a solution. A line scan over a zinc plate was made to evaluate the vertical component of the magnetic field. The present study shows one case in which the magnetic field gradient was not very clear over the zinc plate coupled to gold in 0.1 mol dm-3 Na2SO4 (pH 3) solution. This could be attributed to the fact that two components of the fields happened to be almost same in magnitude but opposite in direction. An artificial obstacle set in a solution to modify the path of ions enabled clear detection of the field gradient caused by electronic current. In separate experiments, the field gradients were evaluated as a function of ionic and electronic currents, respectively. The magnitudes of the field gradient were proportional to both electronic and ionic currents. The slopes for both gradients were found to be almost same for the present configuration of electrodes. The results indicate in general that magnetic fields caused by practical corrosion do not always disappear but can be canceled partly depending on the configuration of electrodes.