Solid Oxide Membrane for Reduction of Ce0.8Gd0.2O2 and TiO2 in LiCl-Li2O

Thursday, 9 October 2014: 17:20
Expo Center, 1st Floor, Universal 3 (Moon Palace Resort)
L. C. Olson, B. L. Garcia-Diaz (Savannah River National Laboratory), and K. Brinkman (Clemson University)
A solid oxide membrane was used in a three electrode electrochemical cell to separately reduce, both Ce0.8Gd0.2O2 and TiO2 in molten solution of LiCl-Li2O.  The Ce0.8Gd0.2O2 was used as a surrogate for UO2, with the goal of using a similar technique during potential nuclear fuel reprocessing scenarios. The solid oxide membrane was a closed-end yttria stabilized zirconia tube inserted in an electrochemical cell with an argon cover gas.  A tungsten electrode was used as a quasi reference, and a graphite basket was used to separately hold both Ce0.8Gd0.2O2 and TiO2 powders. One end of the YSZ tube was held at room temperature, while the closed end was submerged in the molten salt at 650 °C. A platinum bearing paint coated the inside of the SOM and facilitated electrical contact from the nonconductive cold region to the conductive hot region.  Argon gas was swept through the solid oxide membrane and an oxygen detector, where the oxygen pumped through the membrane during reduction was monitored.  Initial oxygen evolution was measured using the oxygen meter and readings were observed to correlate to reduction of the Ce0.8Gd0.2O2 and TiO2 as determined from electrochemical data.  The reduced Ce and Ti oxides were examined post experiment via SEM, EDS, and XRD.  EDS and XRD were used to prove partial reduction in both the Ce0.8Gd0.2O2 and TiO2, but complete reduction to the metallic state was not observed for either oxide to date.  EDS analysis found reduction of the TiO2 to as low as Ti­0.8O0.2 (with trace Cl, Li could not be detected).  EDS analysis of the Ce0.8Gd0.2O2 found evidence of reduction to Ce0.8Gd0.2O (with trace Cl, Li not detected).  XRD found evidence of LiTiO2, LiTi2O4, and (Li0.54Ti2.86)O6 from the TiO2 basket/electrode.  Analysis of reduced products may have been impacted from air exposure during analysis.  Fragility of the electrode basket used for the TiO2 experiment was believed to be the limiting factor in achieving reduction, and further experiments are ongoing using a more robust metallic basket/electrode design.