Electrochemical Study of a Pendant Molten Alumina Droplet and Its Application for Thermodynamic Property Measurements of Al-Ir

Abstract

Limited knowledge of the thermodynamic and transport properties of refractory materials in the liquid state remains a key challenge limiting their application. Using alternating current (AC) and direct current (DC) techniques, the electrochemical kinetics of oxygen evolution and metal deposition was investigated in a pendant droplet of molten alumina (Al2O3) with three iridium (Ir) electrodes in a thermal imaging furnace. For the first time, the direct electrolytic decomposition of molten Al2O3 to oxygen gas and aluminum (Al) metal (alloyed with Ir) was observed, confirming the ionic nature of molten Al2O3. The decomposition potential of molten Al2O3 was measured with high precision using AC voltammetry, and the results demonstrated remarkable sensitivity to variation in temperature enabling measurement of chemical potential and entropy of Al at the Ir-rich solid-liquid phase boundary for the first time. The results were in remarkably close agreement with the most recent thermodynamic assessment of the Al-Ir system. ©The Author(s) 2017. Published by ECS. All rights reserved.