Russian Physics Journal最新文献

The issues of accelerating the synthesis of oxide compounds are solved by improving certain stages of the ceramic manufacturing process. A new method is advanced, involving a short-term heating of the reaction agents to the melting temperature, which is aimed at manufacturing ceramic materials that are difficult or even impossible to be produced by other processes. In view of this circumstance, it is critical to optimize the initial states of the oxides of the reaction mixture to ensure their most effective melting under the electron-beam treatment. Using an aluminum oxide as an example, it is shown how important it is to control its initial phase state. It is demonstrated that in the cases where aluminum oxide consists of a few phases, specifically monoclinic and corundum, then during the electron-beam treatment the electron energy is primarily spent on a monoclinic-to-corundum phase transition. Only following this, the aluminum oxide powder undergoes melting. This makes the electron beam treatment less effective.

In this work, Tm³⁺- and Yb³⁺-doped SrBi₄Ti₄O₁₅ phosphor was successfully synthesized through the high-temperature solid-state reaction. The phosphor composition was characterized by X‑ray diffraction, revealing a reduction in the lattice parameters and volume due to a successful substitution of Sr³⁺ by Tm³⁺ and Yb³⁺. Under the excitation of a 980 nm diode laser, weak green emission centered at 476 nm and strong red emission centered at 696 and 801 nm were observed, which originated from Tm^{3+ 1}G₄→³H₆, ¹G₄→³F₄, ³F_2,3→³H₅ and ³H₄→³H₆ transitions. The best doping concentration for Tm³⁺ and Yb³⁺ was 1 and 20 mol%, respectively. Extensive studies were conducted on the Tm³⁺/Yb³⁺ co-doping effect on the pump power. The absolute sensitivity of non-thermal coupling levels for doped Tm³⁺/Yb³⁺ calculated at different wavelengths, was 0.4504 and 0.0359 K⁻¹, respectively. These results indicated that SrBi₄Ti₄O₁₅:Tm³⁺/Yb³⁺ is an effective candidate for red up-conversion luminescent materials and can be used as a high-efficiency temperature sensing material.

In this paper, γ‑ray with varied energies of 60, 186, 242, 295, 352, 609, 662 keV, emitted from radioactive sources ¹²⁴Am, ²²⁶Ra, ¹³⁷Cs, are used to determinate the attenuation coefficient for eight samples of different composition prepared from organic compounds (epoxy) and sodium chloride. Measurements are conducted using a γ-ray spectrometer connected to sodium iodide detector (NaI(Tl)). The results are compared with the ICRU-44 report values. It is found that there is good agreement between the obtained results and results from ICRU-44, and the difference is less than 3%. In comparison to ICRU-44, it is confirmed that the materials used in this study, are good alternatives for dosimetry and potentially for tissues to make tissue phantoms for biological tissues under study.

Electron beam 3D printing is a method of modern high-performance additive manufacturing of titanium alloy products. There are well-known problems with the formation of equiaxed primary grains suitable for providing the required level of mechanical characteristics that call for searching technological approaches to improve the quality of printing products used in critical industries. Machine Hammer Peening (MHP) has proven itself as the most effective method of interlayer material work hardening in additive manufacturing. The article examines the possibility of controlling the structural-phase state and mechanical properties of Ti–6Al–4V titanium alloy by using the interlayer machine hammer peening with different intertreatment intervals. The data obtained during experimental studies indicate that the greatest improvement in strength and microhardness is provided by machine hammer peening after depositing each 4 layers. Machine hammer peening contributes to the formation of a more uniform structure, the columnar prior grain refinement, elimination of columnar grains, and a decrease in the thickness of the α‑lath width. The results of the research confirm the effectiveness of using machine hammer peening in layer-by-layer electron beam additive manufacturing of the Ti–6Al–4V alloy for improving mechanical properties.

The present study focuses on the mechanism by which the Nd: YAG laser energy affects the properties of plasma produced from locally manufactured copper and zinc alloys at the ratio of 80 to 20%. Five different laser energies (500–900 mJ) are used to study the apparent effects on the plasma at every energy value. The fundamental wavelength of the laser directed perpendicular to the alloy surface (target) is 1064 nm. Through the results obtained on the electron temperature and its density, it is shown that there is a clear and gradual increase in both of them with the increasing laser energy in addition to an increase in the intensity of spectral emissions at high energies. The electron temperature is calculated by the Boltzmann method, while the Stark expansion method is used to calculate the electron density. To deepen the understanding of the plasma behavior, the additional basic parameters are calculated, which include the plasma frequency (f_p), the Debye length (λ_D), and the number of charged particles in the Debye sphere (ND). The results show a clear increase in the plasma frequency and Debye length at high energies. On the other hand, there is a clear decrease in the Debye length when the laser energy increases. This study provides a deeper insight into the mechanisms of laser interaction with different materials, especially copper and zinc alloys, as it opens the way to improving many applications such as laser cutting and engraving using lasers, as well as spectral analysis of materials in the industrial field, in addition to many environmental and technological applications.

In the present study, AA7075-based metal matrix composites were fabricated using the powder metallurgy technique followed by microwave sintering to investigate the influence of ceramic reinforcements on mechanical properties. Silicon carbide (SiC) was used as a single reinforcement in varying weight percentages (0–9 wt.%), and further enhancement was studied using a hybrid combination of SiC (fixed at 7 wt.%) and silicon dioxide (SiO₂) in varying amounts (0–5 wt.%). The mechanical behavior was characterized through compression strength and hardness measurements. Among the single-reinforced composites, the highest compression strength of 221 MPa and hardness of 97 Hv were achieved at 7 wt.% SiC. In the case of hybrid reinforcement, the composite containing 7 wt.% SiC + 3 wt.% SiO₂ exhibited the maximum compression strength of 302 MPa and hardness of 112 Hv, demonstrating a significant enhancement over the base alloy and the single-reinforced systems. These findings reveal that microwave sintering, combined with optimal hybrid reinforcement, is highly effective in improving the mechanical performance of aluminum matrix composites, making them suitable for advanced structural and aerospace applications.

The paper proposes a four-level model which includes deep and shallow acceptors and donors, allowing to predict characteristics for the HR GaAs:Cr material and sensors. It is shown that the best agreement between the simulated values and experimental data of the non-equilibrium charge carrier lifetime, Hall mobility, and resistivity of the HR GaAs:Cr material, is achieved at the EL2 center concentration in the range of (1 to 3)∙10¹⁵ cm^–3, the Cr concentration of about 1∙10¹⁷ cm^–3, and the concentration of thermal acceptors in the range of (1 to 4)∙10¹⁶ cm^–3. It is shown that EL2⁺ and Cr ionized centers are the dominant deep levels that determine the lifetime of respectively non-equilibrium electrons and holes in LEC HR GaAs:Cr.

Method of calculating the effective permeability of a particle encapsulated within multiwall carbon nanotubes (MWCNTs) is considered in the present work. The method is based on finding the potentials and then using these potentials to determine the resulting magnetic fields of a two-layer cylinder in an infinite medium. The effective magnetic permeability is calculated for the proposed model depending on its value and particle size. It is shown that the effective magnetic permeability starts to decrease more rapidly compared to that of the massive material as its size is reduced to the nanometer scale.

The physical concept of structural and phase states of water and aqueous solutions low-stable to external impacts is presented. The concept allows one to understand physics of various effects observed in water and super-highly diluted aqueous solutions. In particular, the approach allows one to estimate the effect of mechanical action (stirring) on these solutions in Epstein’s effect. An analysis of thermodynamic and phase low-stable states of a physical system allows the adequate mechanism of system transition to a new structure-phase state to be proposed under a weak external impact. In this case, in spite of the fact that the external impact is weak, it can lead to considerable structure phase changes of the system state, since the structural units in the initial and final states, though close thermodynamically, can differ significantly in symmetry. Physical reasons for weak reproducibility of the results of investigations of the characteristics of water and aqueous solution structure at ultra-high dilution are discussed together with the importance of the small external effect for the transition to a new structure-phase state.

Concerning the existence and non-existence of the magnetic field, the laser-induced breakdown spectroscopy of cadmium oxide plasma is investigated in the current study. Accordingly, an Nd:YAG laser (1064 nm, 9 ns), in addition to the pulse laser intensity varying from 300 to 600 mJ, is employed to produce the plasma in a vacuum environment at the operating pressure ranging between 0.5 and 2 Torr. Any increase in the laser energy leads to a gradual increase in the electron density and temperature. It is well-known that the electron density and temperature increase when a magnetic field is added to cadmium oxide plasma. Thus, the magnetic field impact is approved with the existence of beta values less than 1 in the plasma parameter. The study highlights how adjusting the laser intensity and operating pressure can directly affect the plasma properties, providing a deeper understanding of the matter interaction under different conditions. This knowledge can be used to improve spectroscopy techniques and develop new applications in scientific research and industry, as understanding of relationships between pressure, energy, and magnetic fields opens up vast possibilities for the plasma property control with greater precision.