Russian Physics Journal最新文献

In this paper, the effect of ultrasound on the microhardness and microstructure of friction stir welding joints is investigated. It has been found that the area with minimum microhardness is located in the thermomechanically affected zone on the retreating side. An ultrasonic impact resulted in an increase in the size of this area. The weakening of the region is attributed primarily to the low content of hardening particles due to overaging. It was also found that the ultrasonic impact during welding resulted in a 5 times reduction of residual stresses.

Orbital evolution of model near-Earth space (NES) objects moving in orbits with semi-major axes in the range from 8 000 to 100 000 km is analyzed to reveal the dynamic structure features of this NES region to choose a disposal strategy for spent spacecrafts or deployment of new satellite systems. The areas possessing the greatest stability and keeping preset orbital elements and hence the most suitable for placing new satellites and disposal of spent satellites are shown. The areas in which the deployment of satellites is inexpedient are highlighted.

The physical and chemical characteristics of hydrophobic protection of cement rock and concrete surfaces, using the binders based on polyurethane, elemental sulfur, and nanodimensional fillers of Tarkosil and thermally modified peat, are discussed. It is shown that a combined use of the physical texture-formation methods and an optimal selection of the protective coating chemical composition results in a significant increase of the wetting angle and the solid phase surface energy. It is found out that a directional orientation of the magnetically sensitive particles in the magnetorheological composites in a magnetic field is among the most effective methods for improving the protective coating properties.

The synthesis and the structural and luminescence studies of samarium-doped calcium aluminate phosphors are reported. These phosphors are synthesized by the solid-state reaction method with a variable concentration of doping ions (0.5–3.0 mol%). The synthesized phosphors are characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) techniques. The XRD studies show that the doped phosphors have a cubic structure. The SEM images reveal that the Sm³⁺- doped Ca₃Al₂O₆ phosphor represents a combination of some rod-like and flower-like structures. The FTIR studies confirm the formation of a Ca₃Al₂O₆:Sm³⁺ phosphor. The photoluminescence (PL) emission measurements upon excitation by 273 nm (ultraviolet light) show the characteristic emission peaks of Sm³⁺ at 579, 589, 600 and 619 nm. The characteristic orange-red emission is observed for samarium ion. The excitation spectra of the Ca₃Al₂O₆:Sm³⁺ phosphor mainly consist of a more intense charge transfer band (CTB) of Sm³⁺ located at 273 and 395 nm with some peaks centred at 319 and 362 nm. The CIE coordinates are calculated by the spectrophotometric method using the spectral energy distribution of the Ca₃Al₂O₆:Sm³⁺ sample. The prepared phosphors can act as a single host for orange-red light emission in display devices.

The paper presents the comprehensive analysis of the structure, properties, and corrosion of micro-arc coatings with ZrO₂ and TiO₂ particles after the low-energy high-current electron beam (LEHCEB) treatment. The coating morphology, microstructure, phase and elemental compositions are investigated by the scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray powder diffraction. After the LEHCEB treatment, the coating structure with ZrO₂ particles changes from friable and porous to denser with closed spheroidal pores. It is shown that the adhesive strength of the coating with ZrO₂ particles increases with the critical load growth from 10 to 18 N. Moreover, the treatment enhances its corrosion resistance, as evidenced by a reduction in the corrosion current from 7.48∙10^–7 to 1.05∙10^–8 A/cm² and an increase in polarization resistance from 0.9·10⁴ to 5.77∙10⁶ Ω·cm². In contrast, the coatings with TiO₂ particles exhibit a more porous structure due to the volatilization of low-melting components (sodium silicates), as evidenced by a reduction in the concentration of Na and Si elements in their composition. The adhesive strength and corrosion resistance of the coatings with TiO₂ particles deteriorate after the treatment.

In this work, deformation behavior of porous ceramics ZrO₂ – 5.5 wt.% Y₂O₃ with a different morphology of the pore space under axial quasi-static compression is studied by the method of digital image correlation (DIC). Two stages of the deformation behavior of ceramics have been identified, namely, the controlled accumulation of microcracks and the formation of block structures. It has been found that an increase in the average pore size leads to the decrease of the tensile strength and the effective elasticity modulus and the increase of the ultimate deformation, while the nature of the deformation macrolocalization changes from ordered to chaotic one. It is shown that the rate of accumulation of local deformations in the central part of the deformable sample with a pore size of 68 μm is several times higher than in the sample with a pore size of 29 μm.

Orbital evolution of model circumlunar objects moving in circular orbits is analyzed to determine areas optimal for the deployment of new satellite systems moving in orbits of this kind. The areas are determined in which the objects not only remain in their orbits for a long time, but also keep preset initial parameters and hence are the most suitable for the deployment of long-living satellite systems.

The paper deals with two problems. The main problem is the parameter calculation for the Yarkovsky effect using analytic formulas and their comparison with that obtained through its inclusion in the number of parameters to be detected. Unknown physical parameters of asteroids are varied to obtain the boundary values from analytic formulas. Numerical calculations imply that acceleration driven by the Yarkovsky effect, is inversely proportional to the degree of the heliocentric distance. It is shown that numerical calculations for objects with a well-defined orbit are in good agreement with analytic boundaries. The second problem concerns the numerical calculation of the best degree value for the distance to the Sun. It is demonstrated that the best results are obtained at the degree value of 2.

Thermoelectric materials are of growing interest to renewable energy technologies and applications. Because of the work progress of thermoelectric materials, experimental and theoretical methods in evaluating thermodynamic behavior and properties of these materials play a significant role. As is known, heat capacity is one of the fundamental thermodynamic properties of thermoelectric materials that should be foreseen accurately. The Debye–Einstein approximation is one of the efficient methods for calculating the heat capacity of materials without any restriction in their use. For this purpose, this work aims at the heat capacity calculation of PbTe, PbS and PbSe thermoelectric materials using the Debye–Einstein approximation.

Lithium manganese nanoferrites (Li_xMn_1–2xFe_2+xO₄, x = 0.0, 0.1, 0.2, 0.3, 0.4) are prepared by the chemical coprecipitation method. Magnetic properties of as-synthesized samples are investigated at room temperature using a vibrating-sample magnetometer. The superparamagnetic behavior of the samples is observed on the recorded M-H curves. From the hysteresis curve, saturation magnetization, coercivity, and retentivity are obtained. The squareness ratio, anisotropy constant and magnetic moment of the samples are calculated and compared. The cyclic voltammetry analysis is performed for different scan rates to determine the specific capacitance. The energy density and power density are calculated from the charge-discharge curve. The resistance to selected bacteria is analyzed using the antimicrobial activity test.