Direct electrolytic reduction of solid alumina using molten calcium chloride-alkali chloride electrolytes

Abstract

Solid alumina was reduced by electro-deoxidation to aluminium metal containing 1.8 and 5.4 at% Ca in molten CaCl2-NaCl and CaCl 2-LiCl electrolytes at 900 °C, respectively. The potential-pO2- diagrams for the Al-O-M-Cl (M = Na or Li, or/and Ca) system were constructed to predict equilibrium phase relationships in the electrolytes at 700 and 900 °C. It was found that calcium aluminates were formed as the main intermediate reaction products and were subsequently reduced to form the Al-rich Al-Ca alloys during electro-deoxidation. Calcium and/or lithium, at reduced activities, were created at the cathode especially at 700 °C at the same time as the ionization of the oxygen from the cathode, which resulted in Al2Ca formation. The experimental results were consistent with the thermodynamic predictions. © 2009 Springer Science+Business Media B.V.