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 (Al 2 O 3 ) with three iridium (Ir) electrodes in a thermal imaging furnace. For the first time, the direct electrolytic decomposition of molten Al 2 O 3 to oxygen gas and aluminum ( Structural materials developed for lasers, nuclear, aerospace or materials processing are required to sustain high temperature, and therefore often rely on solid refractory materials, e.g. iridium-based superalloys exhibiting exceptional corrosion and creep resistance.

Electrochemical Investigation of Molten Lanthanum-Yttrium Oxide for Selective Liquid Rare-Earth Metal Extraction

“…A similar description relates E * C and U (E * C ). Similarly to that described by Nakanishi et al, 12 the relative values of U (E * C ) and U (E * A ) were found to vary with cell geometry, i.e. the relative geometric surface areas of cathode and anode.…”

“…• The similarity of peak-splitting features across 2 nd and higher current harmonics with that observed for an Ir anode in molten Al 2 O 3 . 12 • The relative stability of the Ir anode during the short-duration electrolysis The features for the ACV voltammogram for an Ir anode were found to be consistent for all X La 2 O 3 investigated, permitting detection and measurement of the electrochemical reaction potential E * A coinciding with Reaction 6.…”

“…• The similarity of obtained 2 nd and higher current harmonic peaksplitting features to that observed for an Ir anode in molten Al 2 O 3 (compare I 2ω and I 3ω shown in Figure 2 with those shown in Nakanishi et al). 12 • The high REE content of the cathode products following electrolysis at E < E * C (Figures 6 and 7). • Electrolysis at E > E * C (less negative), shows no indication of REE-Ir alloy formation, with a content of REE in the Ir cathode below the detection limit of WDS.…”

“…Previously, we presented the thermodynamics evaluation of the unary-component, molten Al 2 O 3 investigated using decomposition voltage measurements combined with AC voltametry in a thermal imaging furnace, 12 showing the production of liquid aluminium. Such an approach allows for direct measurement of Gibbs energy and chemical potential in ionic molten oxide melts.…”

Electrochemical behaviour of titanium-bearing slag relevant for molten oxide electrolysis

“…In this work, a containerless approach with in situ, real-time visualization was used to study the electrochemical properties of molten TiO 2 − SiO 2 − Al 2 O 3 − MgO − CaO slag. Following the pioneering efforts of Nakanishi and Allanore [17], the pendant droplet technique was employed in a modified thermal imaging furnace. Cyclic voltammetry and potentiostatic electrolysis measurements were performed in a three-electrode configuration using iridium metal as working, pseudo-reference and counter electrodes.…”