Bulletin of the Russian Academy of Sciences: Physics最新文献

The dependences of the breakdown voltage U_br on the parameter p × d—the product of the working gas pressure p and the interelectrode distance d (Paschen curve) in helium (p × d = 1.1–300 Torr cm), neon (p × d = 0.25–30 Torr cm) and argon (p × d = 0.09–570 Torr cm) were investigated. It is shown that the right branch of the Paschen curve (p × d) > (p × d)_min for all investigated gases demonstrates lower breakdown voltage values than the known results, which is associated with a change in the emission properties of cold cathodes operating in pure gases with the effect of impurities influence minimization on current generation processes.

The results of using two generators with an operating voltage of about 50 kV for high voltage electric pulse crushing of quartz raw are presented. A comparison with previously obtained results of quartz raw crushing on a generator with an operating voltage of 250 kV is performed. Reducing the operating voltage of the generator allows improving its operating qualities and simplifying the generator design due to the exclusion of a step-up pulse transformer from the circuit. It is shown that while maintaining the energy level in the high-voltage storage and reducing the operating voltage from 250 to 50 kV, the crushing efficiency remains at the same level. An increase in the stored energy while other parameters constant does not lead to an increase in the crushing efficiency, since energy consumption and the proportion of overgrinding fraction increase.

We examined the influence of pulsed ultraviolet (UV) laser radiation on the microstructure, phase composition, and functional characteristics of surface layers of Ti–6Al–4V alloy. Laser treatment leads to significant changes in the phase composition of the alloy surface, where newly formed oxide phases (TiO₂, TiO) are detected in addition to the main initial α- and β-phases of Ti. It is shown that UV laser treatment leads to an increase of nanohardness by 25–30%, an increase of roughness, and a significant increase in hydrophilicity. In the initial state, the average value of wetting contact angle is 80°, and it decreases to 9°–13° after UV laser treatment. It is shown that the observed changes are due to the saturation of surface layer with oxygen, the concentration of which increses to 12–20%. This saturation leads to the formation of oxide phases and with an increase in free surface energy. Futhermore, it alters the ratio of the surface energy components, resulting in a decrease in a dispersity and a significant increase in the polar component. Based on the research conducted, it is concluded that UV laser treatment is an effective method to change the surface structure of Ti–6Al–4V alloy, its morphology and properties.

We presented the results of numerical simulation of plasma formation in a traditional discharge scheme for vacuum arc plasma-assisted deposition and compares them with experimental measurements. It was found that the average electron temperature is 1.00 eV without arc-activated evaporators. In the case of all plasma sources operating, the average electron temperature can achieve 1.35 eV, while plasma concentration is at the level of 10¹⁶–10¹⁷ 1/m³. In addition, the coefficient of unevenness of plasma concentration is 82% when metal plasma evaporators are not activated, and it decreases to 125% when they are active. A decrease in this coefficient was also observed as the radius decreased due to a reduction in the influence of gas and metal plasma generators. The agreement between the results of computer simulation and experiment provides grounds for using the hydrodynamic representation when solving the problem of reducing the degree of plasma distribution unevenness in large-sized discharge systems in the hollow anode mode (more than 0.1 m³) and optimizing installations for generating gas-metal beam-plasma formations.

We present the results of probe measurements of plasma parameters and ion mass-to-charge state of a DC magnetron sputtering system (MSS) in gas and vacuum (gasless) operating modes at operating pressures from 2 down to 0.05 mTorr. It is shown that, in comparison with the gas operating mode, the discharge plasma of the vacuum magnetron is characterized by higher values of electron temperature and plasma potential, along with the generation of multiply charged metal ions of the target material. This mode is also characterized by a higher degree of ionization of sputtered material and enhanced ion current density onto the substrate. The revealed differences may be useful for improving quality and properties of formed coatings.

The work is devoted to the study of the structure of plasma jets formed by a high-current vacuum arc discharge. The experiments were conducted on the high-current generator IMRI-5 with a current amplitude of 250 KA. The plasma jet was formed while burning a vacuum arc discharge between coaxial aluminum electrodes with initiation on the surface of a capropolon dielectric. The following were registered in the experiments: a current flowing along the plasma jet at different distances from the plasma gun cathode; visible image of a plasma jet at different moments in time with an exposure of 10 ns; the propagation speed of the plasma jet. Numerical simulation of the evolution of the plasma jet was carried out. The results of the simulation are compared with the experiments.

High-entropy borides (HEB) are a new class of unique materials characterized by outstanding properties. In this paper, a comprehensive study of the oxidation properties of a high-entropy boride of the composition (Ti_0.2Zr_0.2Nb_0.2Hf_0.2Ta_0.2)B₂ is carried out for the first time. HEB was synthesized by a vacuum-free electric arc method by a direct current arc discharge of 100 A for 90 s. The oxidation stability of the obtained powder (Ti_0.2Zr_0.2Nb_0.2Hf_0.2Ta_0.2)B₂ was studied by two approaches. In the first case, it was found that the (Ti_0.2Zr_0.2Nb_0.2Hf_0.2Ta_0.2)B₂ sample is characterized by an oxidation temperature of ~800°С based on the assessment of phase transformations in situ during heating of the powder in the temperature range from 0 to 1200°С in air. In the second case, it was determined that the (Ti_0.2Zr_0.2Nb_0.2Hf_0.2Ta_0.2)B₂ powder can withstand temperatures up to ~700°С according to the results of the analysis of the composition of HEB during oxidation in an atmospheric furnace. The formation of oxides is confirmed by the results of scanning electron microscopy. The characteristics of HEB obtained in the work are consistent with the currently known literature data.

A mathematical model is developed that describes the process of the initial stage of electrical explosion of cylindrical conductors in the skin current mode. The model describes: nonlinear diffusion of the magnetic field; Joule heating; dynamics of the conducting material under the action of the Ampere force and thermoelastic stresses; phase transitions “solid–liquid” (melting) and “liquid–vapor” (evaporation). The influence of a non-uniform initial spatial profile of specific electrical resistance ({{rho }_{e}}(r)) near the conductor surface on the processes under study is analyzed. Profiles ({{rho }_{e}}(r)) with different abruptness of transition from surface to volume values, and with different effective thickness of the modified layer are considered. The possibility of delaying plasma formation on the surface due to the use of initial profiles ({{rho }_{e}}(r)) with increased values of specific resistance on the surface is discovered.

One of the trigger systems for the pseudospark switches is based on a usage of the low-current auxiliary glow discharge with hollow cathode and hollow anode. The electrodes of the auxiliary discharge are often placed inside the grounded cathode cavity of the main high-voltage electrode gap. The space of the auxiliary discharge communicates with the space of the main cathode cavity via the aperture in the flat part of one of the trigger electrodes. Then the characteristic feature of such an arrangement is the availability of the so-called parasitic current, which flows via the aperture to the grounded cathode. This paper deals with the investigation of the features of the formation of the parasitic current at different electric circuits for powering the auxiliary discharge.

We investigated the effect of the beam plasma parameters on the modification of the polypropylene surface properties in argon and air atmospheres. This beam plasma was generated by a ribbon electron beam at a pressure of 0.1–10 Pa. The results show a non-monotonic increase in plasma concentration (up to 3 × 10¹⁵ m^–3) at a pressure of 1 Pa for argon plasma. This increase might be associated with the ignition of a beam-plasma discharge. However, this dependence of plasma parameters on pressure is monotonous for air plasma. The study shows that air plasma treatment provides a more pronounced reduction in the wetting edge angle compared to argon plasma. This decrease might be explained by the combined physical and chemical effects of the air active components. The use of electric potential had made it possible to enhance surface modification, especially at low pressures. The highest processing efficiency was achieved in the 1–5 Pa range, where an optimal balance is maintained between plasma density and particle energy. In addition, the air plasma ensures a longer retention of hydrophilic properties compared to argon plasma treatment. The obtained results can be important for the processing polymer materials technologies development.