Electrochemical Reduction of Zirconia in Melts Based on Mixture of Calcium Chloride and Calcium Oxide

Abstract

It has been found that the reduction of zirconium dioxide from the CaCl2-NaCl-CaO and CaCl2-LiCl-CaO melts involves calcium and gallium intermetallics, which are formed during the cathodic polarization of the gallium cathode, calcium being not consumed for reduction, and evolved oxygen being discharged at the anode. Zirconium deposits on the gallium cathode as a fine powder, whose specific surface area decreases with increasing current density. Calcium is discharged at the gallium cathode irreversibly with considerable depolarization. The degree of zirconium reduction is the higher, the lower the acid strength of the oxide-chloride melt.

Review—Preparation of Hafnium Metal by Electrolysis

“…Although thermodynamic calculations indicate that HfO 2 cannot be electrodeoxidized in NaCl molten salt, several metals and alloys such as Ti, Nb, Ge, Zr, Ti-Fe and Ta-Nb can still be obtained through the electrodeoxidation process in the CaCl 2 -NaCl molten salt. [65][66][67][68][69][70][71] Since the binding ability between O 2− and Ca 2+ is stronger than that of Na + in the molten salt, and thus the generated Na 2 O will preferentially combine with CaCl 2 to form CaO and NaCl, which will not affect the electrolysis process. Meanwhile, the addition of NaCl into the molten salt can not only lower the melting point, but also reduce the concentration of oxygen ions in the CaCl 2 -CaO molten salt by reducing the proportion of CaO.…”

Review—Preparation of Zirconium Metal by Electrolysis

“…98 The addition of NaCl can not only decrease the melting point of electrolyte, but also lower the activity of CaO in molten CaCl 2 -CaO melt. 96 In 2016, Gritsai 99 reported that Zr was obtained by electrodeoxidation of ZrO 2 in CaCl 2 -CaO-NaCl melt.…”