High Temperature Electrochemistry III: Materials Electrochemistry I
Sponsored by: TMS Extraction and Processing Division, TMS: Pyrometallurgy Committee, TMS: Hydrometallurgy and Electrometallurgy Committee
Program Organizers: Prabhat Tripathy, Idaho National Laboratory; Guy Fredrickson, Idaho National Lab; Boyd Davis, Kingston Process Metallurgy Inc.
Wednesday 2:00 PM
March 1, 2017
Location: San Diego Convention Ctr
Session Chair: Uday Pal, Boston University; Steven Herrmann, Idaho National Laboratory
Molten Flux Design for Solid Oxide Membrane Based Electrolysis of Si from Silica: Thomas Villalon1; Uday Pal1; Soumendra Basu1; 1Boston University
A one-end-closed oxygen-ion-conducting stabilized zirconia (SOM) tube is used to separate pure silica (SiO2) dissolved in an appropriately engineered molten flux from an inert anode placed inside the SOM tube. To ensure product purity, a pre-reduction step using a secondary cathode at lower applied potentials is employed to remove impurities that are more electronegative than Si. The impurity-laden secondary cathode is removed, and then employing a liquid tin cathode in the molten flux the applied potential is increased to reduce the dissolved silica. The reduced Si go into solution in the liquid tin cathode. Less electronegative impurity ions compared to Si remain in the flux. Thus impurity oxides of both more and less electronegative impurities are not reduced along with silica.
Electrochemical Deposition of Barium into Liquid Bismuth from BaCl2-LiCl-CaCl2-NaCl Electrolyte: Hojong Kim1; Nathan Smith1; Timothy Lichtenstein1; Kuldeep Kumar1; 1The Pennsylvania State University
Using liquid bismuth metal that possesses strong chemical interactions with barium, we demonstrate that electrochemical separation of barium into a liquid bismuth electrode is possible from BaCl2-LiCl-CaCl2-NaCl (16-29-35-20 mol%) electrolyte at 600 °C. While the standard emf analysis suggests Na as the first species to deposit in this electrolyte, barium was found to be the first species to be reduced into the bismuth electrode followed by Ca. The exceptional barium deposition was ascribed to extremely low activity values of barium in bismuth (as low as 10-15), shifting the deposition potential of barium to the most positive potentials and resulting in barium deposition into bismuth. By exploiting the chemical interactions between barium and bismuth, this study suggests that liquid bismuth can potentially be employed in separating out alkali/alkaline-earth fission products such as Ba, Sr, and Cs from the molten salt electrolytes in the pyrochemical processes for used nuclear fuels recycling.
Electrochemical Behavior of Sn/SnCl2 Cathode in Na | NaCl-AlCl3-SnCl2 | Sn Cell: Takanari Ouchi1; Raku Watari2; Donald Sadoway2; 1Massachusetts Institute of Technology ; 2Massachusetts Institute of Technology
A key area of research in molten salt batteries is to reduce the operating temperature. One molten salt system known to operate at low temperatures is the ZEBRA battery utilizing Na as the anode, Ni/NiCl2 as the cathode, and beta-alumina and molten NaCl-AlCl3 as the electrolyte. In this cell, the formation of solid NiCl2 upon charging inhibits the mass transport, hence limits the kinetics of charge/discharge processes and the utilization of active components. To address this issue, we investigated the validity of a liquid Sn/SnCl2 as the cathode. In this work, the diffusion coefficient of Sn ion and the exchange current density of Sn/Sn2+ redox reaction in a molten NaCl-AlCl3-SnCl2 electrolyte were evaluated. As a result, the liquid Sn/SnCl2 cathode is found to have suitably fast kinetics, which potentially enables a hypothetical Na | NaCl-AlCl3-SnCl2 | Sn cell with high power and energy densities at low operating temperature.
3:30 PM Break
Impurity Removal from Titanium Oxycarbide: Farzin Fatollahi-Fard1; Petrus Pistorius1; 1Carnegie Mellon University
A process to remove impurities from titanium oxycarbide – the feedstock used to make titanium via the MER electrochemical process – from impure oxycarbide produced from low-grade feedstocks such as ilmenite is described. Titanium oxycarbide produced by carbothermal reduction from a natural ilmenite concentrate will contain many metallic impurities, such as iron, manganese, and silicon. If these impurities are not removed, then these metallic impurities will contaminate the titanium product. The MER process can be modified into a two-step process to first remove the contaminating metallic impurities before titanium production begins. The titanium oxycarbide produced by this first electrochemical step has been characterized to determine its impurity content, and should meet the required specifications to produce commercially pure titanium.
Thermal Imaging Furnace Technique for Ultra-high Temperature Electrochemical Measurements: Bradley Nakanishi1; Erick Hernandez1; Antoine Allanore1; 1Massachusetts Institute of Technology
Refractory oxides are essential to applications ranging from lasers to aerospace. In particular, their properties at high temperature are of importance, including in the molten state. Demonstrating that these melts are amenable to direct electrochemical probing remains a frontier. If available, such an approach would allow direct access to the constituents' thermodynamic and transport properties. Herein we report a novel technique coupling alternating current electrochemical measurements with a thermal imaging furnace using Al2O3, La2O3 and Y2O3 components. This containerless approach provides access to ultra-high temperatures in excess of 2000K and continuous visual observation of the melt and electrodes during measurements. Furthermore, we have observed for the first time the electrolytic decomposition of these melts using this approach, and established a viable pathway towards thermodynamic property measurements. These findings are foreseen to accelerate the pace of discovery of novel, oxide solvents for reactive metal recovery, e.g. aluminum or rare earth elements.