No 7 (2025)

Electrical discharge machining of molybdenum surfaces used to increase hardness, heat resistance and corrosion resistance of machine parts, units and assemblies has been studied. It has been found that electrical discharge machining of molybdenum surfaces allows obtaining durable functional coatings of parts by using high-voltage electric arc in hydrogen atmosphere at a pressure of 0.1 MPa and fixed gap between anode made of graphite and processed surface of the part, cathode, at a rigid current-voltage characteristic of pulsed current source with voltage of 2000 V. The pulse duty cycle has been varied depending on required roughness of the molybdenum carbide Mo₂C coating. Depending on the supplied power two carbide phases in different percentage ratio α-Mo₂C:β-Mo₂C were formed on the surface.

The reflective and structural characteristics of a multilayer Ni(80)Mo(20)/C system, which is promising for the manufacture of Goebel mirrors and suppression of the CuK_β emission line (λ = 0.139 nm), have been studied for the first time. The optimal ratio of Ni(80)Mo(20) and C materials has been determined to achieve the best reflectivity at a wavelength of λ = 0.154 nm (CuK_α1 emission line). The reflection coefficient for periods d = 41.5 and 33.5 Å was R ≥ 69%. The positive effect of vacuum annealing of the Ni(80)Mo(20)/C structure, consisting in an increase in the first-order reflection coefficient, has been shown. The increase in reflectivity could be due to a decrease in the thickness of the transition regions and the “decompression” of the carbon layers, which is accompanied by an increase in the thickness of these layers, and an increase in the X-ray optical contrast at the interfaces. It has been found that vacuum annealing of the multilayer Ni(80)Mo(20)/C structure at temperatures up to 320°C does not significantly affect the distribution of local radiation grazing angles over the substrate area.

The results of a study on the quantum yield of various photocathodes designed to detect X-ray radiation with an energy above 40 keV are presented. Experiments have been conducted with photocathode samples made of CsI, LaB₆, CdWO₄ and ZnWO₄ using synchrotron radiation from the wiggler at the VEPP-4M accelerator. These materials have been chosen due to their high atomic numbers Z, which ensures effective interaction with X-rays through the photoelectric effect. The study has been carried out in the energy range 40–100 keV, which corresponds to the conditions of experiments on fast-flowing physical processes requiring high temporal and spatial resolution. The data obtained allow us to determine the most suitable materials for creating effective photocathodes in electron-optical converters for recording fast physical processes.

An approach to rapid (in less than 1 h) prototyping of X-ray microlenses from silica with an aperture of about 50 μm and a radius of curvature of 10 μm is presented. The formation of a concave microlens surface is achieved by using focused ion beam systems and isotropic etching in hydrofluoric acid. The presented approach allows obtaining a gain in the fabrication time by about 10 times compared to ion-beam lithography. Furthermore, the fabrication of a series of lenses will lead to a reduction in time costs proportional to the number of simultaneously processed lenses in an acid solution.

The article presents the results of a study on the effect of ultrasonic exposure on the process of photocatalytic decomposition of metronidazole using ZnO microtetrapods under simultaneous irradiation with artificial sunlight. The synthesized zinc oxide microtetrapods had pronounced sharp tips, clear facets, and edges, indicating their high crystalline perfection. This unique morphology of ZnO microtetrapods provides the material with high catalytic activity in both photocatalytic and piezocatalytic processes. The Raman spectrum of ZnO microtetrapods showed distinct peaks corresponding to the transverse E₁ and high-frequency E_2h modes. The high intensity of the E_2h mode indicates the crystalline perfection of ZnO microtetrapods. The enhancement of the intensity of the transverse optical mode A₁ is observed at the tip of the tetrapod and is absent at the base. It has been shown that the use of ZnO microtetrapods achieves significant efficiency in the decomposition of metronidazole due to the combined effect of light and ultrasound, creating a piezoelectric field on the surface of ZnO. This piezoelectric field promotes the spatial separation of photogenerated charges and reduces the likelihood of their recombination, significantly increasing the rate of decomposition of the target pollutant. The rate constant for the decomposition of metronidazole in piezophotocatalysis is higher than the rate constants for photolysis, sonolysis, sonophotolysis, piezocatalysis, and photocatalysis by 1254, 35, 17, 8, and 4 times, respectively.

The spacecraft passive protection of a monolithic and a screen types has been considered. The screen passive protection includes one additional protective shield placed in front of the protected wall. The penetration length of particles for various types of passive protection has been estimated. Based on the simulation results and experimental data presented in the literature, the applicability ranges of various types of spacecraft passive protection are formulated.

Electrostatic ion sources with different methods of plasma excitation are widely used in the production of high-tech products, the modification of the surfaces of which allows providing predetermined properties. These properties essentially depend on the parameters of the generated ion beams, which are determined by the correspondence of the ion-extraction system to the problem to be solved, in particular, the optimal design of the ion source as a whole, including the propellant consumption parameters. This work is devoted to solving the problem of optimizing the flow rate of the ion source. It is proposed to consider the integral discharge parameters of a radio-frequency ion source operating as part of a vacuum process facility. This approach makes it possible to ignore spatial distributions of discharge plasma parameters and to propose a simple model for determining the optimal coefficient of the source mass efficiency. An example of a calculation is shown, which allows preliminary estimation of the parameters of the process facility.

An increasing rate of the near-Earth space contamination with man-made debris hinders the long-term sustainable development of space activities, including those in the actively used geostationary earth orbit. Space debris is understood as the non-functioning objects of space technology and their fragments. To solve this problem, an ion source has been developed that forms a weakly diverging ion beam, under the contactless impact of which a space debris object should move in the direction of the disposal orbit. Minimizing the ion beam divergence angle increases the range of impact on space debris object. However, there is a problem of the IS stable operation, which is associated with the functioning of the ion-extraction system that is responsible for the configuration of a weakly diverging ion beam. The ion-extraction system is the most critical and complicated unit of the ion source in terms of design and technology. The peculiarity of operation of the ion-extraction system electrodes is related to their non-uniform heating and deformation, which result in degradation of the ion source performance (ion beam divergence half-angle, ion current density, and thrust) and in the high-voltage breakdown. The electrodes have different thicknesses, can be made of different materials and their heating is characterized by different thermal profiles. For the ion-extraction system reliable operation, it is necessary to ensure the stability of gap between the emission electrode and the accelerating electrode in operating modes. Non-uniform heating leads to additional deflections of electrodes. Thus, it is important to be able to calculate the initial shape of electrodes and their deformation when heated up to operational temperatures, at which stable operation of the ion-extraction systems hold be ensured. The importance of not only using the developed mechanical-mathematical model of ion-extraction system electrodes, but also of performing numerical modeling for the deformed state of the ion-extraction system electrodes using a simplified algorithm. It allows the assessment of the deformed state with a significant reduction in modeling time.