Nº 6 (2024)

The corrosion behavior of EP-823 steel was studied during high-temperature treatment (HTT) with nitrogen. It was found that in nitrogen at temperatures of 650–800°C, the steel is subject to only slight surface corrosion. It is shown that there is a slight change in the surface composition and structure of steel, which does not have a significant effect on the reprocessing of model SNF. It is shown that on the surface of the material, processes of interaction of some electronegative components of ferritic-martensitic steel with components of the gas phase – nitrogen and impurity oxygen – occur with the formation of inclusions of nitride and oxide compounds of chromium and manganese of different stoichiometric compositions. The process is limited by the diffusion of these components from the volume of the alloy to the surface. The corrosion rates of EP-823 steel at temperatures of 650 and 800 ° C were 0.104 and 0.241 mm / year for 12 hours of exposure, and 0.013 and 0.02 mm/year for 84 hours of exposure, respectively. The nature of the destruction of the surface of the samples is continuous and uneven, localization of corrosion at the boundaries of steel grains is clearly observed, which is associated with the formation of secondary phases along the grain boundaries. At the temperature of the treatment, significant sensitization of steel occurs, chain-like precipitation of secondary phases is observed along the grain boundaries, which leads to the development of intercrystalline corrosion. Conclusions are made about the change in the structure of the material during high-temperature exposure and the nature of the corrosion damage of the material is determined; based on the results of X-ray fluorescence analysis, conclusions are made about the composition of the corrosion products of EP-823 steel.

The article defines the dependence type of the cathode polarization of an aluminum-ion battery based on chlorinated graphite of the initial EC-02 type in a low-temperature melt of aluminum chloride with 1-ethyl-3-methylimidazole chloride on the geometric characteristics of the electrode and the current density. It is determined that for the chlorinated graphite material the polarization values are slightly reduced compared to the initial non-chlorinated graphite of the same brand in a similar melt and are 25–50 mV at 1 mA/cm². The dependence of polarization on the current density does not have a break between the values of 1 and 1.2 mA/cm², observed for initial graphite, which characterizes the maximum rate of the current-generating reaction, which means an increase in the rate of the main process on the chlorinated graphite. Using a reference experiment on a glassy carbon electrode, the surficial density of chloroaluminate complexes intercalation sites was estimated as about 15%. Accordingly, the maximum degree of intercalation for such materials is 6. Since graphite chlorination does not lead to distortions geometric parameters of its interlayer gaps, the sorption density of chloroaluminate ions is found to increase after chlorination; in the case of non-chlorinated graphite, the degree of intercalation varies with current density from 9 to 18.

The results of an experimental study of the temperature dependences of the kinematic viscosity and specific electrical resistance of wear-resistant cast irons ИЧХ28Н2 and ICh300Kh25F4 in the liquid state are presented. The kinematic viscosity was determined by the method of damped torsional oscillations of a crucible with a melt. Specific electrical resistance was measured by the rotating magnetic field method. The measurements were carried out in the mode of two successive heatings of the samples from 1300 to 1650°C. After the first measurement, the sample was crystallized and cooled to a temperature of 25 °C at a rate of 1 °C/s. The second measurement was carried out without removing the sample from the laboratory setup and changing the atmosphere. The results of measuring the temperature dependences of kinematic viscosity and specific electrical resistance are discussed in the context of the concept of the microheterogeneous structure of liquid cast irons. Hysteresis of the temperature dependences of viscosity and electrical resistance obtained during the first heating of the samples to 1550°С was detected, which serves as indirect evidence of the destruction of microheterogeneities. The absence of hysteresis during the second heating of the sample after crystallization confirms the irreversible nature of the destruction of microheterogeneities. A conclusion is made on the recommended mode of high-temperature melt treatment (HTMT) of wear-resistant cast irons, which involves heating the melt to 1550°С. Heating of liquid wear-resistant cast irons IChKh28N2 and ICh300Kh25F4 to 1550°С leads to the destruction of micro-inhomogeneities, as a result of which, upon subsequent cooling and crystallization, an improved microstructure of the ingot is formed.

Aluminum alloys with zirconium additives are increasingly used in the aerospace industry, instrument making and power engineering, due to the combination of increased corrosion and thermal resistance without compromising density and electrical conductivity. A promising method for producing such alloys is synthesis in molten fluorides of alkali and alkaline earth metals, using oxides as a consumable metal-containing component. According to existing scientific and technical data, the use of electrolysis can contribute to an increase in the efficiency of reducing zirconium oxide to metallic oxide, in connection with which, the study of the electrochemical behavior of zirconium ions in fluoride melts is relevant. The method of cyclic chronovoltammetry was used to study the main regularities of cathodic electroreduction of zirconium and aluminum ions from melts based on KF–AlF3 with additives of zirconium and aluminum oxides at a temperature of 750°C on a tungsten cathode. A series of polarization curves were obtained both in a pure melt and with additives of zirconium and aluminum oxides at potential scan rates from 0.1 to 2 V. It was shown that the discharge of aluminum ions is observed more negative than the potential of –1.6 V, and at a potential of –1.8 to –1.9 V, the Al peak corresponding to the reduction of aluminum ions is formed. In the region of potentials more positive than –1.6 V, the cathodic process AlxWy is also observed, presumably associated with the reduction of aluminum ions and the formation of its intermetallic compounds with tungsten. When ZrO2 is added to the melt under study, the voltammograms additionally show a Zr platform and an Al+Zr peak at potentials of –1.3 and –1.6 V, associated with the discharge of zirconium ions and the combined discharge of zirconium and aluminum ions, respectively. When scanning the potential to the anodic region, the Al’ peak is observed at a potential of about –1.6 V and the Al’ and Zr’ waves, associated with the oxidation of metallic aluminum and aluminum with zirconium from the intermetallic compound, respectively. For the tungsten electrode, an increase in the current densities of the Al+Zr peak and a potential shift with an increase in the potential scanning rate are expectedly observed, which indicates the electrochemical irreversibility of the process under study.

This paper presents a review of data on the solubility of rare earth oxides in halide melts of alkali and alkaline earth metals. The highest solubility of rare earth oxides is observed in fluoride melts, the lowest – in chloride melts. There are very few works devoted to the study of the solubility of rare earth oxides in mixed chloride-fluoride melts. The solubility of rare earth oxides decreases in the series La-Ce-Pr-Nd-Gd. The greatest number of works are devoted to the study of the solubility of neodymium, lanthanum and cerium oxides. There are practically no data on the solubility of “heavy” rare earth oxides (from Tb to Lu) in halide melts.