No 1 (2024)

A method has been proposed and implemented for experimentally measuring the effective conductivity of a limited volume of a metal melt with an admixture of solid well-conducting particles depending on the volume fraction of the impurity in the range from zero to seven percent. A comparison is made with known theoretical dependencies for effective conductivity. It is shown that none of the considered models provides even qualitative agreement with experiment. On the experimental curve, several sections can be distinguished with different dependences of conductivity on the volume fraction of the impurity. The experimental data are approximated by analytical functions, which make it possible to use the results obtained for numerical modeling of MHD processes.

One of the ways to obtain high-quality products and meet ever-increasing requirements on properties of steel is microalloying it with rare earth elements such as cerium. Cerium can significantly affect mechanical properties of steel even at low concentrations. To reduce the cost of steel, it is rational to add cerium into steel not with ferroalloys but by direct reduction from oxide systems. In order to study this process, thermodynamic modeling of the reduction of cerium from slags of the CaO–SiO₂–Ce₂O₃ system, containing 15% Al₂O₃ and 8% MgO, with aluminum and calcium carbide at temperatures of 1 550 and 1 650°C is carried out. The simulation is performed using the HSC 6.12 Chemistry software package (Outokumpu) based on Gibbs energy minimization and using the simplex planning lattice method. The results of thermodynamic modeling are presented in the form of composition-property (equilibrium cerium content in the metal) diagrams for temperatures of 1 550 and 1 650°С. When using metallic aluminum as a reducing agent, increasing the basicity of the slag (CaO/SiO₂) from 2 to 5 at a temperature of 1 550°C leads to an increase in the equilibrium cerium content in the metal from 2 to 20 ppm in the concentration range of 0–15٪ Ce₂O₃, i.e. an increase in the basicity of the slag is beneficial for the development of the cerium reduction process. An metal temperature increase also has a positive effect on the process of reduction of cerium with aluminum. With an increase in temperature to 1 650°С, the equilibrium content of cerium in the metal increases from 4 ppm to 30 ppm in the concentration range of 0–15٪ Ce₂O₃. The use of calcium carbide as a reducing agent leads to an increase in the concentration of cerium in the metal to 30 and 40 ppm at temperatures of 1 550 and 1 650°C, respectively, at a basicity of 5. The decisive role of slag basicity, cerium oxide concentration and temperature in the development of the process of cerium reduction with aluminum and calcium carbide is confirmed.

Molten mixtures of chlorides of alkali and polyvalent metals have found wide application in the electrolytic refining of a number of metals, such as plutonium. The current efficiency in such processes depends on many factors, among which the most significant are the corrosion resistance of products made of ceramic materials in contact with melts, as well as the solubility of the metal to be purified in melts containing its chloride. Thus, when carrying out refining electrolysis to purify liquid cerium in a molten equimolar mixture of sodium and potassium chlorides with an initial concentration of cerium trichloride of 3 mol. %, it was possible to obtain a maximum current efficiency of 63%. It was shown that a significant part of the losses is due to the release of alkali metal and the dissolution of metallic cerium. There are no data on the solubility of a (polyvalent) metal in molten salt compositions containing its chloride in the literature. Therefore, the purpose of this work was to determine the solubility of metallic cerium in the (NaCl–KCl)–CeCl₃ melt at an electrolysis temperature of 850°C. An installation was created to determine the solubility of cerium with sampling of the salt melt without access to oxidizers. This was achieved by pouring the salt melt from the beaker, where the melt was saturated with cerium, into an external beaker without opening the device. It is shown that the solubility of cerium drops sharply with a decrease in the concentration of cerium trichloride and can be approximated by the equation: N_Ce = 1.67∙10^–5∙x³–9.62∙10^–4∙x² + 4.50∙10^–2∙x, N_Ce in mol. %, and x is the concentration of cerium trichloride in the melt in mol. %.

The article presents the results of studies of an experimental coating obtained in the process of plasma synthesis of tungsten borides and the reduction of metallic tungsten, from a mixture obtained on the basis of a scheelite concentrate and a boron-containing material. The coating was formed on an Al₂O₃ substrate. The paper describes a step-by-step process of formation of tungsten borides on the substrate surface and reduction of metallic tungsten from oxide, using a high-temperature synthesis unit — a plasma generator. The formation of a coating on a substrate consisting of reduced metallic tungsten and borides of the W–B system proceeds in one technological stage in the process of condensation from the vapor-drop phase. To conduct a series of experiments, a prototype of an indirect plasma torch was developed with the generation of an electric arc plasma flow with a specific power g > 10⁴–10⁵ W/cm². In the process of high-temperature plasma flow exposure to the complex structures of the mineral concentrate and tungsten oxide included in its composition, destructurization and subsequent sublimation of the mixture material in the form of a vapor-drop phase occur. The synthesis of tungsten borides occurs in the process of chemical transformations, when the dispersed material is removed from the heated plasma flow, the formation of nucleating phases and condensation from the vapor droplet phase on the substrate surface. The synthesis process is also accompanied by a significant sublimation of boron from the compounds, which leads to the reduction of metallic tungsten. The material obtained in the course of plasma synthesis forms the W–B system and structures, the physicochemical properties of which depend on the mixture composition, flux density, plasma pressure and temperature. The results of a chemical analysis of particles forming a W–B coating on the surface of an Al₂O₃ substrate in the form of a solid solution of dendrite crystals are presented. In the course of X-ray spectral microanalysis, the phase composition of coating samples was determined, the presence of tungsten borides W₂B₅, WB₂, W₂B, WB and metallic tungsten were revealed. The results of research work on obtaining coatings or films based on the W–B system, using mineral multi-component raw materials, can be useful in various science-intensive industries, in the hydrometallurgical or chemical industries.

The paper considers the possibility of coating Al–Zr–V–Nb in the form of a powder with a fraction of 0.063 mm and a humidity of 0.33%, measured using the AND MX-50 device, on a substrate made of 08Cr18Ni10 steel. The deposition was carried out using a laser complex consisting of a laser radiation source LS-5 and a robot KUKA KR-60 ha in a protective argon atmosphere. Gas purging was carried out before the deposition process of 0.3 s and after 1 s. For reliable bonding of the coating powder (Al–Zr–V–Nb) with the surface of the base material (Steel 08Cr18Ni10), a mixture of powder with polyvinyl alcohol was applied to the steel before deposition. According to the data obtained on the Carl Zeiss EVO 40 scanning electron microscope, the optimal mode of deposition of Al–Zr–V–Nb powder on the base material corresponds to a power of 250 Watts at a processing speed of 0.5 m/s and a coating thickness of 0.6 mm. At a lower power of 230 W, the coating cannot melt qualitatively and, in this regard, insufficient penetration of the base metal by the coating metal (adhesion) occurs, resulting in partial detachment. If the power is increased to 270 W, then the base metal and the substrate interact with each other just as well and create a strong monolayer of the coating, as in the optimal mode, but when cooling, due to a significant difference in cooling speeds (the 08Cr18Ni10 steel plate does not have time to cool at the speed of the coating material), cracking occurs and the appearance of microcracks. Thus, there is a need to further increase the number of passes or an additional melting process to create a reliable coating with no discontinuities and islands. At the same time, measurements of Vickers microhardness (HV) during surfacing of the Al–Zr–V–Nb coating showed an increase in HV values by more than two times compared to the base material, which is a sufficient reason for using Al–Zr-V-Nb powder as a strengthening coating for 08Cr18Ni10 steel).