No 2 (2025)

This paper examines the main methods of chlorination of natural zirconium compounds, evaluates the efficiency of existing technologies and considers the most promising methods for the development of the industry. Currently, research and development of new, energy‒efficient methods for processing zirconium‒containing natural compounds and man‒made waste are being actively carried out throughout the world. The existing hydrometallurgical methods for processing zirconium‒containing materials have a number of significant disadvantages, such as: multi‒stage nature, low degree and intensity of zirconium extraction, high consumption of reagents, or the need for long‒term disposal in the case of processing nuclear waste. The most promising from a technical and economic point of view are pyrochemical methods of processing zirconium in molten salts due to the greater intensity of the process and the possibility of utilizing a wider range of compounds. Chlorine metallurgy methods are the basis for the production of most rare earth elements, and for elements such as titanium, zirconium, and hafnium, there are no acceptable alternatives and are the only way to obtain high‒purity metal. Most often, chlorination is carried out in melts based on chlorides of alkali and alkaline earth metals, within 1000 °C. Chlorination of oxides with pure chlorine, without the use of a reducing agent, is impossible up to a temperature of 827 °C and higher, due to the positive values of the Gibbs energy of the reaction, therefore, reducing agents are used to carry out the process, in particular various forms of carbon, however, this method makes it difficult to maintain the stoichiometry of the loaded reagents, which leads to the accumulation of carbon in the reaction zone. The main obstacles to the development of the idea of using carbon tetrachloride were its high cost, toxicity, and limited solubility in salt melts, which makes it more suitable for direct chlorination of oxides in CCl₄ vapors. Chlorination using elemental sulfur as a reducing agent seems more promising in terms of energy costs, technological effectiveness, and overall process efficiency. To increase the efficiency of chlorination, it is possible to use a combined method using a chlorine‒carbon‒sulfur system. The proposed method allows to reduce the process temperature and synthesize the necessary compounds directly in the reactor, which will reduce the number of technological operations and increase the profitability of the process.

In this work, a series of experiments were performed to study the effect of oxygen on the morphology of silicon obtained by electrodeposition from KCl‒K₂SiF₆ melt. SiO₂ was chosen as the oxygen carrier. The concentration of the additive was determined from the results of the study of the effect of SiO₂ additive on the concentration of free F‒ ions. According to the obtained dependence, assumptions about the nature of interaction between the components of the melt were made. The inflection points registered on the dependence ω(KF)‒ω(SiO₂) indicate a change in the character of interaction of SiO₂ with the investigated melt. Based on the results of the study of the kinetics of the cathodic process on glassy carbon, taking into account the theory of autocomplex structure, an assumption was made about the structure of discharging complex ions in KCl‒K₂SiF₆ and KCl‒K₂SiF₆‒SiO₂ melts. The kinetics was investigated by cyclic voltammetry. When SiO₂ was added, a broadening of the silicon discharge potential region was observed, as well as a disproportionate increase in the cathodic current with increasing SiO₂ concentration in the melt. One of the possible explanations for the obtained results is the change in the structure of the discharging complex ions. The obtained data on the kinetics of the cathodic process, as well as assumptions about the structure of the discharging complex, became the basis for the choice of parameters of potentiostatic electrolysis. A series of experiments on electrodeposition of silicon from the studied melts at varying the value of cathodic overvoltage from 0.10 to 0.25 V were carried out during the research. The morphology of cathodic precipitates was investigated by electron‒scanning microscopy. It is assumed that changes in the morphology of the obtained cathodic precipitates are associated with changes in the structure of the discharging complexes.

The main task of physicochemical analysis is the study of multicomponent systems. Knowledge of phase levels and their regularities in multicomponent systems is necessary for the development of optimal conditions for the search for compositions with given conditions. For this purpose, we studied the ternary system Cs₂O–V₂O₅–MoO₃. Based on the results of experimental studies, the first promising areas of the phase diagram for the synthesis of vanadium‒molybdenum bronzes of cesium were obtained. Compositions obtained on the basis of the system are promising in the development of new materials, in particular: anti‒corrosion coatings, ion‒electronic conductors with high activity. Theoretically, based on the results of the data obtained, it was proved that the synthesis of new materials from complex oxide phases by crystallization methods from a solid‒phase fusion melt can be used to break down a three‒component oxide system Cs₂O–V₂O₅–MoO₃, to identify topology patterns and phase formation in them. The topological image of the phase diagram constructed by a combination of data from its faceting elements is characterized by the presence of three congruent and four incongruently melting binary compounds on the faces, which divide it into four subsystems (I–IV), the most interesting, in our opinion, variants of triangulation of this system, according to which it was identified in triangulating sections, which divide it into 10 subsystems, which are quasi‒three‒component and triple systems, hence, they can be studied independently. For the convenience of performing extreme work both on the synthesis of individual compounds (D₁–D₃) and thermal analysis of systems, a set of methods of physical and chemical analysis was used. In particular, visual polythermic, differential thermal analysis. Finally, the main thing in this work is the prediction, modeling and experimental confirmation of phase formation in the system Cs₂O–V₂O₅–MoO₃ , its stable and metastable processes, which will make it possible to maximize the mechanism of the conditions for the formation and decay of the qualitative and quantitative composition of the phases.

The present paper presents an overview of the available experimental data (both our data and provided by other researchers) on the electrical conductivity of ZrCl₄–containing salt melts, for which the saturated vapor pressure of ZrCl₄ above them is P ⩽ 1 atm. These melts have a significant practical application potential. Such mixtures are divided into high‒temperature mixtures with a ZrCl₄ concentration of 0‒30 mol. %, and low‒temperature ones, with a narrower ZrCl₄ content range of 50‒75 mol. %. Based on the obtained experimental data it was found that the electrical conductivity of all molten ZrCl₄–containing mixtures increases as the temperature increases, zirconium tetrachloride concentration decreases, and the molten solvent salt is replaced in the row from CsCl to LiCl. The experimental data obtained are summarized and discussed taking into account the available information on the structure of the molten mixtures. Electrical conductivity of high–temperature MCl‒ZrCl₄ melts (0‒30 mol. % ZrCl₄; M is an alkali metal), is in the range of 0.6–3.1 Cm/cm, which is significantly higher than the electrical conductivity of low–melting molten mixtures of the same chlorides (0.1‒0.5 Cm/cm) with a high content of ZrCl₄ (55‒75 mol. %). It has been found that the use of low‒melting salt solvents, for example, LiCl–KCl eutectic, makes it possible to expand the range of existence of ZrCl₄‒containing melts by hundreds of degrees towards lower temperatures and saturated vapor pressures at sufficiently high values of electrical conductivity (0.9–2.8 Cm/cm). This provides additional advantages for the organization of various technological processes.