Abstract
The results of the electrochemical reduction of zirconium dioxide in molten electrolytes based on calcium or magnesium chloride on a liquid gallium cathode, bypassing the stage of granulation and sintering with carbohydrates, are presented. The liquid gallium cathode provides not only reliable contact with zirconium dioxide, but also favourable conditions for its reduction. The contact area of the gallium cathode with fine oxide powder is much larger than the contact area of the granulated and sintered zirconium dioxide with a solid conductor. This ensures a more uniform cathode polarization. Due to the lower specific mass, zirconium dioxide is located on the surface of gallium cathode, the convective movement of which provides more intense mass transfer at the interface of the phases and removal of recovery products from the zone of electrode reaction. Products of electrolysis under such conditions do not block neither the surface of zirconium dioxide nor the surface of the cathode. Zirconium, which is formed during the renewal, due to a larger specific mass, precipitates to the bottom of the electrolyser, and the layer of gallium protects it from interaction with the components of the molten electrolyte. In addition, due to the formation of alloys, the reduction of metal cations on liquid cathodes proceeds at more positive potentials than on solid indifferent cathodes, which reduces the specific energy consumption by electrolysis. The results of voltammetric studies confirm this conclusion.
The reduction product is fine-grained zirconium powder with an average particle size of 1—3 microns, and purity of 99.9 %. As the density of the current increases, the value of the specific surface of the powder, the specific volume of the micropore and their average radius decrease. The degree of extraction depends on the composition of the electrolyte mixture and naturally decreases when replacing cations in the melts both on the basis of calcium chloride and on the basis of magnesium chloride in the following sequence Na+ > K+ > Li+. The melt based on compounds of calcium and sodium chloride provides the best performance. The removal degree of zirconium from such melt reaches 77 %.