KINETICS AND MECHANISM OF THE MAGNESIUM ELECTRODE-REACTION IN MOLTEN MGCL2-NACL BINARY-MIXTURES

Using electrochemical impedance spectroscopy and a relaxation method w ith galvanostatic perturbation the kinetics and mechanism of the magne sium electrode reaction in six melts oi the binary MgCl2 - NaCl system were determined at several temperatures. A three-step electrode proce ss was found. the high frequency one being pure charge-transfer wherea s the low frequency one showing mixed charge transfer-diffusion charac ter. The exchange current density for the high frequency step is in th e range from 20 to 50 A cm(-2) whereas for the low frequency step it v aries from 3 to 10 a cm(-2). On the basis of the corresponding exchang e current densities and structural and thermodynamic data, a mechanism of the overall electrode reaction in these melts is proposed. The cou rse of the low frequency exchange current density with the composition , corresponds to the change of the MgCl2 thermodynamic activity in the more dilute solutions of MgCl2 in the melt.