Russian Physics Journal最新文献

The results of a study on the sensitivity of sensors fabricated from single-crystal sapphire and bulk undoped silicon carbide to X‑ray radiation with photon energies in the range of 10–80 keV are presented. The photocurrent is measured experimentally and the carrier lifetime is estimated. The photocurrent dependence on the X‑ray intensity and the sensor voltage is determined experimentally and via modeling.

Physicochemical properties of silver nanoparticles (AgNPs) produced in this work by the plasma jet assisted method without reducing agents or chemical stabilizers using distilled water as a medium are studied in the present work. The UV-Vis AgNP surface plasmon resonance (SPR) characteristics, confirmed by spectroscopy and FTIR spectra, show the presence of functional groups coming from the breakdown of a water molecule. The crystalline structure of nanoparticles is confirmed by results of XRD analysis, while SEM studies reveal their external spherical shapes. Using tests for the zone of inhibition (ZOI), the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and antibacterial activity of the produced nanoparticles are assessed. The effectiveness of the AgNPs against pathogenic bacteria is evaluated. The results obtained demonstrate a relationship between the antibacterial efficacy and plasma exposure time. After 20 min of exposure, the ZOI reached 22.5 mm, the MIC decreased to 25 µg/mL, and the MBC reached 40 µg/mL. Our findings indicate that plasma jet assisted manufacturing is a controllable, efficient, and environmentally benign method for creating the bioactive silver nanoparticles with potent antibacterial activity promising for future biological and pharmaceutical applications.

The structure and properties of alloy 2024 formed during friction stir welding, assisted with three different water cooling techniques: (i) underwater welding with extra cooling of the tool by a water jet, (ii) cooling by still water, and (iii) water jet cooling, are explored. The structural changes due to extra cooling are studied. A number of various cooling techniques are assessed, including the water-filled bath, continuous-flow cooling, and their combinations. The results indicate that the combined cooling method yields the strongest joint.

The physical concept of structure-phase states of water and aqueous solutions low stable to external impacts is developed. The concept allows one to understand physics of various observable effects in water and aqueous solutions. In particular, the concept allows the role of external impacts (temperature, mechanical shaking, etc.) in the Epstein effect to be explained. Our analysis of thermodynamic and phase low stable states of physical system allows us to propose an adequate mechanism of system transition to a new structure-phase state under a weak external impact (temperature, pressure, or dynamic loading in the form of shaking or intensive mixing). 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 are close thermodynamically, can essentially differ in structure-phase features and symmetry.

An Al-Mg composite containing the Fe, Ni, and Ti powders added by the method of friction stir processing (FSP) is studied. An application of the friction stir processing to engineering the wear-resistant composites based on an aluminum matrix is demonstrated to be highly effective, depending on the selected system of strengthening phases. The addition of Fe, Ni, and Ti powder particles in the course of friction stir processing is shown to decrease the friction coefficient during the dry friction contact. It is shown that the effective method for fabricating wear-resistant materials is to introduce an iron powder into the aluminum matrix, thereby forming iron aluminides of various compositions during processing. The tribological behavior of composite materials differs from that of the initial aluminum alloys in two primary aspects: first, a smaller role of adhesive wear, and, second, a larger contribution from the normal mechanochemical wear.

The mechanical and inelastic properties of a TiNi thin wire with a diameter of ~950 µm are studied after the synthesis of a surface alloy (SA) based on the Ti-Ni-Ta system with an amorphous structure and a thickness of ≤ 1 µm. The SA is synthesized by a 2-fold alternation of deposition of the alloying film (Ti₆₀Ta₄₀ (at.%), with a thickness of ~100 nm) and liquid-phase mixing of the [film/substrate] system using a low-energy high-current electron-beam. The deformation behavior of the samples is examined in torsion tests before and after thermal cycling (TC) of the [SA/TiNi-substrate] system within the temperature range of a B2 ⇄ B19′ martensitic transformation. The cyclic tests reveal that the presence of SA does not lead to an increase in martensitic shear stress τ_M and stress hysteresis loop ∆τ, but it affects the material ability to accumulate and recover superelastic strain γ_SE. It is found out that the TC of the initial and modified samples does not significantly affect the deformation behavior of the wire. It is noted that the amorphous SA does not crack after TC and does not peel off from the surface after torsion tests. As a result of testing to failure at an accumulation shear strain of γ ≥ 25%, the presence of an SA leads to a decrease in the shear fracture strength τ_max by ~200 MPa and in the fracture strain γ_max by ~15% compared to the values for the initial TiNi samples.

The paper investigates the influence of discharge pulse duration t_on (7 and 100 µs) on the composition, structure, and mechanical properties of TiBₓ coatings deposited by the dual high-power impulse magnetron sputtering method using Ti and TiB₂ targets. X‑ray photoelectron spectroscopy revealed that reducing the pulse duration increased the titanium content in the coatings, lowering the B/Ti ratio from 2.3 to 1.3. X‑ray diffraction and transmission electron microscopy analyses revealed a structural transformation from a polycrystalline coating deposited at t_on = 100 µs to an amorphous/nanocrystalline state for the coating deposited at t_on = 7 µs. While the hardness values were similar for both coatings (~41 GPa), the friction coefficient decreased from 0.94 to 0.83 with the shorter pulse duration. This study demonstrates that adjusting the magnetron power supply parameters, specifically the pulse duration, is an effective tool for tailoring the properties of TiB_x coatings, showing great promise for applications requiring high hardness and improved wear resistance.

The paper studies the effect of friction stir processing (FSP) on the structure and properties of a bronze-steel composite material fabricated by wire-feed electron beam additive manufacturing (EBAM). The efficiency of the hybrid approach is demonstrated, allowing the formation of gradient structures with a hardened surface layer and a high degree of homogenization. FSP leads to significant grain refinement, increased microhardness, and an increase in the yield strength, while maintaining plasticity. The obtained results confirm promise for using EBAM in combination with FSP for creating wear-resistant surface structures in copper alloys. The method has high potential for practical application in mechanical engineering and the transport industry.

This paper presents the development and empirical evidence of magnetic resonance electrotechnique aimed at scaliness reduction on heat exchange surfaces and in pipelines of thermal power plant cooling systems. The paper proposes the design of an electromagnetic device capable of generating current pulses affecting the water flow and hardness. The technique promotes the formation of crystallization centers outside the heat exchanger surface, thereby preventing the scaliness deposition. Research results confirm the effectiveness of the proposed technique. It is environmentally friendly, eliminates the need for chemical reagents and reduces operational costs. The proposed technique has the potential for broad application in the energy and industrial sectors.

The paper proposes the accelerated method for reconstructing radio images based on monostatic ultra-wideband sounding data from a set of distributed scatterers. The method is based on reducing the reconstruction points of the studied medium by detecting the areas with scatterers. In a homogeneous medium, scatterers are not needed in reconstruction, allowing to significantly reduce the amount of calculation. In order to effectively isolate the areas of the scatterer location, it is proposed to reconstruct the scatterer image at several spatial resolutions: first, low and a successive two-fold increase in resolution. Low-resolution images are constructed from signals with a reduced frequency band. Such images approximately show the presence or absence of scatterers in a particular area. A further increase in resolution is performed only in areas where the level of the reconstructed signal exceeds the specified threshold. Numerical simulation results show a several times decrease in the amount of calculation for the proposed method than the migration method.