Studies on Direct Electrochemical De-Oxidation of Solid ThO₂ in Calcium Chloride Based Melts

Abstract

Molten salt based direct electrochemical de-oxidation methods were investigated for the conversion of ThO2 to Th metal in CaCl2 melts at 900 °C. A Fray-Farthing-Chen (FFC) Cambridge process was performed at a constant cell voltage of 3.1 V wherein a cathode of porous ThO2 pellet and a graphite anode were used. The study also explored the feasibility of electro-calciothermic reduction of ThO2 in CaCl2–0.5 wt.% CaO melt. Electrochemical experiments were carried out for different intervals of time to elucidate the reduction mechanism. The cathode products were characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray analysis. No Ca-Th-O intermediate phases were observed during the reduction experiments in either process. This indicates that the reduction might occur in a single step viz. ThO2 to Th. The direct electrochemical reduction of ThO2 in CaCl2 based melts at 900 °C was found to be feasible.

Understanding the behaviour of a niobium oxide cathode in a molten chloride bath using different DC voltammetric techniques

“…The oxide ions then migrate through the molten salt electrolyte towards a graphite anode, where they are discharged in the form of carbon oxide gases [1]. A significant number of laboratory studies have since concentrated on the electrolytic production of numerous metals such as Ti, Th, Gr, Si, Nb, Cr, Hf, Zr; binary alloys and intermetallics such as Co-Cr, W-Ti, NdCo 5 ; ternary alloys such as Nb-Hf-Ti, Ti-6Al-4V; and quaternary alloys such as Ti-29Nb-13Ta-4.6Zr and CoCrFeNi [2][3][4][5][6]. The method has also been used to create nano and micro-sized particles of mono and binary carbides and oxycarbides [7][8][9][10][11].…”

Studies on Preparation of Thorium-Based Intermetallics in CaCl2 Melt by Electrochemical De-Oxidation Process

“…Recently, electro-reduction of solid ThO 2 has been attempted in our laboratory in CaCl 2 melt at 900 °C using the FFC Cambridge process. 33 The process was found to be feasible for Th metal preparation. However, the reduction process was observed to be kinetically sluggish.…”

“…However, the reduction process was observed to be kinetically sluggish. The extent of conversion of ThO 2 to Th during the electro-reduction experiment in CaCl 2 melt was found to be ∼(93-95)% even after conducting the electrolysis run for 96 h. 33 Similarly, MgO exhibits significantly less electrical conductivity 10…”

“…[16][17][18][19][20][21][22][23][24][25] Several important metals and alloys, including actinide metals and their alloys, e.g., U, Th, U-Pu, Pu-Fe, U-Ti, U-Mo, U-Nb alloys, etc, have been prepared using this method from their respective oxides. [26][27][28][29][30][31][32][33][34][35][36][37] Fray-Farthing-Chen (FFC) Cambridge process is one such process, wherein the reduction of metal oxide cathode is effected by electrons (electro-reduction), and the process is conventionally conducted in CaCl 2 melt at 900 °C. 38,39 A cell voltage less than the decomposition potential of CaCl 2 melt is applied between the metal oxide cathode and graphite anode.…”

“…8 The electro-reduction of ThO 2 requires a relatively high potential. 32,33 It is also considered an electrical insulator and has an electrical conductivity of 10…”