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 %.

The paper presents a quantum-chemical model and experimental confirmation of cation catalysis mechanism during the cathodic discharge of carbonate anion in chloride melt. The model of cationized carbonate complex, which describes the effect of the acid-base properties of the melt on the electronic, energetic, structural, and electrochemical properties of the carbonate anion, was proposed. Cation-anion interaction between CO3 2- anion and the strongly polarizing cations (Li+, Ca2+, Mg2+) result either in the formation of cationized anions (metal complexes) or in anion dissociation. Dissociation of CO3 2- anions can occur directly or through an intermediate stage of formation of "short-lived" metal complexes. The changes in the electrochemical behavior of CO3 2- anion were studied by voltammetry by the sequential addition of cations with different polarizing (electrostatic) force to the Na,K,Rb|Cl eutectic. The potentiostatic electrolyses carried out in three electrolytes Na,K,Rb|Cl–Na2CO3–LiCl(CaCl2,MgCl2) at a same potential of -1.1 V against Ag/AgCl reference electrode gave a carbon powder.

A method for the refining of gallium, using bipolar gallium electrodes, in molten electrolytes containing its compounds with lower oxidation states has been developed. A gallium (I) - β –alumina membrane was used to separate the electrodes and bipolar electrodes. The effect of the electrolysis conditions on gallium transfer from the anode to the cathode through the gallium (I) - β –alumina membrane has been studied. It has been show that gallium refining in molten electrolytes allows one to obtain high-purity gallium with high current efficiency.

In the recent years, much attention has been focused on the synthesis of various carbon nanomaterials (CNMs) because of their wide range of potential applications. These materials have been fabricated by different methods such as the laser and arc evaporation of graphite, catalytic pyrolysis of hydrocarbons, disproportionation of CO on metal-catalysts etc. Promising method for synthesis of CNMs is high-temperature electrochemical synthesis (HTES) in molten salts. Although much research has been devoted to this subject, little is known about the mechanism of HTES and which fundamental reactions taking place during this process. In this work an attempt to confirm the mechanism of cation-anion interaction between the CO3 2- anion and the strongly polarizing cations (Li+, Ca2+, Mg2+) is made. The mechanism of these interactions has a complex nature. Cation-anion interaction can result either in the formation of cationized anions (metal complexes) or in anion dissociation both under the direct influence of cations and through the intermediate stage of formation of "short-lived" metal complexes. To test this hypothesis, the quantum chemistry modeling and the cyclic voltammetry experiments were done. It has been shown by the quantum chemistry method that by changing the cationic composition of the electrolyte, one can transform anionic carbonate complexes into a new active state – cationized carbonate complexes. Experimental confirmation of cation-anion interaction was studied in the chloride melts Na,K,Cs|Cl, Na,K,Rb|Cl, Na,K|Cl by the cyclic voltammetry method at temperature ranges of 550–580 °C and of 700–800 °C, which are much lower than the thermal decomposition temperature. The electrolyses was carried out in electrolytes under potentiostatic conditions at a potential of -1.1 V at the concentrations of lithium, calcium and magnesium chlorides, corresponding to the clear observation of cathodic waves. According to the data of a chemical and an X-ray phase analysis a black powder of the cathodic product was carbon. The morphology of electrolytical carbon is presented in the figure below. Based on the obtained results the following conclusions can be done: In the Na,K,Rb|Cl melt containing weakly polarizing Na+, K+, Rb+ cations, the CO3 2- anion shows no electrochemical activity in the temperature range of 570–700 °C. This is accounted for by the large values of the activation barriers to the two- and four-electron reduction of CO3 2-. The addition of strongly polarizing cations (cations with high specific charge) results in the activation of the carbonate ion, which is caused by a large excess of Li+ and Ca2+ cations. In the case of Mg2+ cations, the carbonate ion shows electroactivity at much lower concentrations. Independent of the polarizing power of the cation (melt acidity), the CO3 2- reduction process in molten chlorides occurs in the same potential range of -0.7 to -0.9 V versus a silver reference electrode. The CO3 2- electroreduction process under the action of strongly polarizing cations occurs at temperatures much lower than the thermal decomposition temperature of the corresponding carbonate. This suggests that the formation of CO2 is not the result of thermal decomposition, but is a consequence of the polarizing action of cations. Figure 1