Vol 9, No 2 (2018)

Theoretical research is performed on isolated nanoparticles (NPs) and NP-containing composite films with establishing analytically the concentration of nonequilibrium charge carriers and luminescence intensity as functions of surface recombination rate s, radius, diffusion length, lifetime of minority charge carriers, and other parameters. A hyperbolic dependence of the photoluminescence intensity (PL) on the parameter s is found. It is shown theoretically and experimentally that the photostimulated rise of s of NPs brings about quenching, while its decline favors amplification of PL. The microphotoluminescence PL intensity is established as a function of exciting laser exposure time for powdered carbon nanoparticles (CNPs), solutions of CNPs, and composite films based on PVOH polymers and CNPs with average particle diameters of 1.3 and 1.7 nm. Furthermore, the PL signal intensity of films processed at temperatures of 100–200°C decreases upon their exposure to a high-power-density 532-nm excitation radiation and rises in the case of films treated at 220–340°C. Almost always, the PL intensity of exposed dry CNP powders abruptly drops. The study allows putting forward a new method for contactless and rapid measurement of the parameters of luminescent NPs.

Currently, the prospects for replacing traditional materials with quasi-two-dimensional compounds based on transition metal dichalcogenides are actively being studied. The quasi-two-dimensional molybdenum disulfide MoS₂, a semiconductor with a finite band gap, can be used either as a standalone material or as a part of layered heterostructures. When creating nanosized electronics elements based on such ultrathin materials, the application of an atomic layer etching technology is of key importance. In this paper, a brief description of the properties of MoS₂ monolayers in comparison with graphene and the monolayers of hexagonal boron nitride is considered. On the basis of the results of computer simulation by means of a DFT (density functional theory) method, effects caused in the MoS₂ monolayer by chlorine atoms and molecules widely used in the state-of-the-art of atomic layer etching applied to silicon materials are demonstrated.

Specimens of Al–Mg alloy 1560 of ultrafine-grained structure were obtained by the method of severe plastic deformation based on multiple equal-channel angular pressing. Impact on physical and mechanical properties of the processed material and fracture pattern of specimens was studied. Tensile tests showed an increase of the offset yield strength and resistance to rupture with decrease in the ultimate deformation. The obtained specimens have increased microhardness values compared to the initial ones. It was established that the last cycle of pressing determines the structural orientation of macroscopic shear bands occurring at an angle to the specimen longitudinal axis while passing connection of channels. It affects the physical and mechanical properties of the material and fracture pattern. The quality control of the obtained specimens by the method of ultrasonic defectoscopy and X-ray tomography confirmed the absence of macroand microdefects when following the matched optimal regime of processing.

Experimental data on structural, magnetic, and electrical features of manganites of the system La_0.65Sr_0.35–cCecMn_{1 – x}Zn_xO_{3 + γ} (c = 0, 0.05; x = 0, 0.05, 0.10), synthesized by ceramic processing, are reported. Part of the samples were annealed under conditions that yield stoichiometric oxygen content. The samples obtained are of rhombohedral structure, but contain the impurity of the CeO₂ phase. The introduction of cerium and zinc leads to a decrease in the unit cell volume of the rhombohedral phase. Cerium does not substantially affect the magnetization and Curie point of the initial samples. The width of the “ferromagnetic–paramagnetic” transition temperature interval rises after annealing, especially in manganite with high zinc content. Initial and annealed samples of composition with c = 0.05, x = 0.10 exhibit the phase transition “metal–semiconductor” at temperatures of about 219 K and 200 K, respectively. All other manganites possess a metallic character of conductivity in the range of 100–300 K. The maximum absolute value of magnetoresistance reaches 52%. The approaches to the interpretation of experimental results are discussed.

Static and fatigue strength at room temperature under conditions of repeated stretching of lowactivated ferrite-martensite 12% chromium steels EK-181 (Fe–12Cr–2W–V–Ta heat treatment + aging in lead at 600°C, 3000 h), EP-823 (Fe–12Cr–W–V–Ni–Mo–Nb, annealed condition), and alloy V–4Ti–4Cr (heat treatment + aging in lead at 600°C, 3000 h) were studied. It was shown that for materials there is straight-line dependence between the level of rupture resistance values and fatigue strength. The maximum fatigue limit of 600 MPa appears in steel EK-181 after a standard heat treatment and aging in lead at 600°C, 3000 h, and the minimal one of 300 MPa is observed in vanadium and V–4Ti–4Cr alloys. The fatigue failure mechanism is predominately of ductile character for all materials studied. The fatigue cracking originates near the surface and in some cases clustering of nonmetallic inclusions is the place of origin. The fatigue crack propagation is related to formation of a typical striation relief. Significant distinctions in the fracture surface relief of specimens after standard heat treatment and aging in liquid lead are not observed.

Indentation tests are used to investigate the effect of high-power nanosecond deuterium ion pulses (~100 keV, ~10¹⁰ W/cm²) and dense deuterium plasma (~100 eV, ~10⁷ W/cm²) generated by a Plasma Focus machine on the mechanical properties of vanadium-based alloys such as V–5Ti–5Cr, V–5Ga–5Cr, V–5Ga, and V–5Ga–0.1Ce. It is established that the V–Ga–Cr alloys have a higher resistance to embrittlement during radiation-thermal exposure than that of V–Ti–Cr alloys. X-ray diffraction analysis shows that the structure of solid solution is retained in all investigated alloys after pulsed ion and plasma irradiation. No signs of solid solution decomposition and the precipitation of second phases are found. It is established that pulsed ion-plasma irradiation suppresses the rolling texture that is typical of the alloys in the initial state and decreases the lattice parameter of the alloys, which in the case of the V–Ga alloy can be explained by the escape of gallium from the recast surface layer. Doping with a rare earth element (cerium) increases the radiation resistance of the V–Ga alloy, which results in the stability of the mechanical properties and the lattice parameter after irradiation.

Catalysts where the support was a nanodisperse solid solution of Gd_0.1Ti_0.1Zr_0.1Ce_0.7O₂ and the active component was Pd, Pt, or Pd–Pt were obtained. The support was synthesized by co-precipitation with sonication. Palladium and platinum acetylacetonates were used as the precursors. The samples were studied by X-ray powder diffraction (XRD), X-ray fluorescence (XRF), transmission electron microscopy (TEM), and low-temperature nitrogen adsorption. The catalytic activity of the resulting samples in CO oxidation was measured by the flow method. Palladium-containing sample was the most active. The temperature of complete CO oxidation increases in the order Pd > Pd–Pt > Pt. The synthesized catalysts are of interest in detoxification of gas emissions.

We investigated antimicrobial properties of polyester fabrics with photochemical activity that they gained owing to modification by small amounts of undoped and metal-doped titanium dioxide nanoparticles. We showed that the polyester fabric modified by undoped titanium dioxide leads to decolorization of colored impurities, but does not exhibit antimicrobial properties. We found that the use of nanosized silver-doped titanium dioxide particles with a higher photocatalytic activity as a modifier provides the polyester fabric with the ability to suppress the vital activity of bacteria. We analyzed the mechanism of the antimicrobial activity of nanosized silver-doped titanium dioxide. We showed that ions that are released by silver nanoparticles inhibit the activity of Gram-positive bacteria S. aureus in the absence of UV irradiation. We found that the polyester fabric with a coating that is formed by silver-doped titanium dioxide nanoparticles in the presence of UV irradiation acquires the ability to inactivate Gram-negative bacteria E. coli via a photocatalytic mechanism. This mechanism requires a contact between the modified polyester fabric with bacteria, which makes it possible for them to be sorbed by the titanium dioxide coating.

The microstructure and phase composition of the Mo-Si alloy doped with Sc, Y or Nd were investigated. The methods of X-ray diffraction analysis (XRD), electron microscopy, and electron probe microanalysis (EPMA) were used to determine the main phase components and their volume fractions as well as to assess the speciation and interphase distributions of doping rare earth elements (REE). It was shown that, when introducing up to 3.0 at % Si, Y, or Nd into the Mo–15.3 at % Si hypoeutectic alloy, the structure intrinsic to naturally occurring (in situ) composites was formed. This structure was composed of an α-Mo based solid solution and a strengthening silicide phase including Mo3Si and the particles of complex composition enriched in REE. Doping additives contributed significantly to the microstructure dispersity and modified the morphology of particles of both the metallic and silicide phases, and increased the Mo_ss/Mo₃Si volume ratio. The microhardness of structural components was determined and the parameters of lattice elementary cells of the main phases were evaluated for the REE-doped alloys under study. The observed regularities of their variations generally conformed to the conclusions about the influence of REE on the structural-phase state of the Mo-Si hypoeutectic composites.

Composite materials on the basis of A5 aluminum containing 0.01–0.1 wt % of carbon nanotubes (CNT) were obtained. The composite materials were fabricated by sand casting. Carbon nanotubes were added to the aluminum melt in the form of powdered mixture preliminarily produced using an AGO2S planetary ball mill. It was demonstrated that the CNT additions improved the ultimate tensile strength and yield strength of cast metal by 9 and 32%, respectively. The improvement of metal strength properties even at such a minor amount of nanotubes is determined not only by the inoculating effect but also by dispersion, dislocation, and, to a lesser extent, by reinforcing mechanisms of strengthening. For CNT content in aluminum equal to 0.01 wt %, the calculated yield strength agrees well with experimental values, whereas for CNT content equal to 0.05 and 0.1 wt %, the obtained strengthening is significantly lower than calculations, which can be attributed to agglomeration of nanotubes. The degree of conversion of carbon nanotubes into aluminum carbide as a consequence of interaction with aluminum melt is analyzed. It is demonstrated that less than 50% of carbon nanotubes are transformed into aluminum carbide during melting at 700–800°C. The fact that CNTs are not completely converted into carbide can be attributed to the fact that CNTs are arranged into bundles and only top layer of CNTs is in contact with the melt.

On the basis of broken glass, clay, and organic additives, granular insulating glass crystalline material and technology of its production is developed. The regularities of the effect of composition and firing temperature on the properties of the granules are specified. The resulting granular thermally insulating material is produced with a bulk density of 200–290 kg/m³, pellet strength of 0.82–2.5 MPa, thermal conductivity of 0.067–0.087 W/(m °C), and water absorption of 2.6–3.2% by weight. The effect of the basic physical characteristics of the components of the charge on the process of pore formation is studied. According to the results of investigations, the basic parameters affecting the sustainability of the swelling glass are specified. The rational charge composition and thermal and gas synthesis mode are chosen so that the partial pressure of gases is below the surface tension of the melt. This enables the formation of granules with small closed pores and vitrified surface. The article presents the results of studies on the use of foamed glass ceramic materials for pipe insulation of heating mains.

To fabricate an electrocatalyst containing nanostructured layers of WOy and MoS_x, a sequential formation of tungsten oxide and molybdenum sulfide thin films is performed by means of the pulsed laser deposition of W and Mo in low-pressure air and hydrogen sulfide media, respectively. The reactive medium pressure and the substrate (glassy carbon) temperature are varied during and after the deposition. WOy thin films of various morphologies and structures determining certain differences in their catalytic properties in the reaction of hydrogen evolution in acidic solutions are obtained. However, the catalytic efficiency of the obtained WO_y nanoelements (spheres, needles, and sheets) with amorphous and crystalline structures appears to be insufficient. Additional deposition of MoS_x with an amorphous structure results in a significant improvement of the catalytic properties. Sulfur atoms in the MoSx amorphous matrix cause the formation of catalytically active sites, while the developed surface of the WO_y stimulates an increase in the catalyst total active area. Penetration of hydrogen effectively formed on MoS_x into the bulk of thin films of WO_y provides a crucial electrocatalysis condition—low current resistance in the support layer with a large exposed surface area.

Cu–W composite alloys are obtained using the liquid-phase impregnation method of noncompacted W powders and sintered porous W and W + Cu specimens. The structure of the alloys and its influence of pre-crystallization processing by low-frequency oscillation (LFO) on the “Cu melt–W powder” compositions are investigated. The technological parameters of obtaining low-porosity (1–2%) alloys are defined. It is proved that varying the thermo-time LFO exposure makes it possible to modify the W concentration in the matrix, creating the composite layers with high tungsten content (80–90%). The LFO treatment of the “copper melt + noncompacted W powders” compositions has a number of advantages compared to the routine (liquid-phase impregnation of compacted tungsten powder) industrial technology of production of Cu–W alloys. There are significant reduction of stages (up to 1–2), the possibility of replacement of working atmospheres (hydrogen, vacuum) by cheaper “Ar + CO,” and the dispersion of W phase.

The influence of synthesis parameters on peculiar features of the forming crystalline phases of copper oxide nanoparticles is inspected via electron microscopy, IR spectroscopy, X-ray diffraction, and differential thermal analysis. The nanopowders are produced through the evaporation of a bulk copper cathode by a low-pressure arc discharge with successive condensation of plasma-chemical reaction products on the substrate. The partial pressure of oxygen in the feeding Ar/O₂ gas mixture is varied in a range of 3–30 Pa. The aforementioned methods reveal that particles are formed with controllable dispersion, phase composition, and structural features. The control of characteristics of nanodispersed oxides is based on their formation mechanisms that are brought by the competing impact of coagulation and diffusion processes. The synthesis products are spherical powders of copper oxides comprising a mixture of crystalline phases with the prevalence of CuO, whose average particle sizes are 10–20 nm. The qualitative differences in samples for the opposite partial pressures of oxygen (\({P_{{O_2}}} = 3\) and 30 Pa) are confirmed through the interpretation of IR and DTA spectra. The transmission bands over a wavenumber range of 440–530 cm^–1, being intrinsic of CuO, are distinguished from those of Cu₂O at 1130, 2923, and 2970 cm^–1. The discrepancy of the DTA curves is due to the diversity in thermal stability of CuO/Cu₂O oxides at their different proportion in samples.

Magnetic colloids which exist in a nonflowing pasty form at room temperature and are transformed into a liquid state during heating are described for the first time. Magnetic fluids (MFs) are obtained in a hydrocarbon medium after introduction of a nanosize magnetite into kerosene in the presence of stabilizers. Fatty acids with different lengths of a hydrocarbon fragment, from C₁₂ to C₂₂, were used as stabilizers. Magnetic granulometry data showed that the average diameter of particles is 8.3 nm. The MF samples are studied by differential scanning calorimetry. The geometric parameters of adsorption layers are calculated taking into account the geometric parameters of nanoparticles and stabilizer molecules. The models of liquid and solid states of the adsorption and overlapping layers of two particles are constructed from calorimetric measurements, calculation data, and observations of the phase state of MFs. The experimental and theoretical data prove that transition of the adsorption layer from the liquid phase to the solid one for particles ~8 nm in size is possible if the length of the hydrocarbon moiety in the stabilizer is C₁₄ and higher. The length of the stabilizer molecule and its melting point are the main parameters which determine the structure and properties of MFs. Moreover, when the length of the hydrocarbon fragment in the stabilizer is C₁₂ and higher, magnetic and van der Waals interactions between solid particles may be neglected.

The present work is aimed at solving an important problem: premature failure of a critical element of downhole equipment, such as the pump-compressor pipe. For performance improvement, we propose to clad the inner part of the steel pipe with stainless steel. We experimentally test three schemes of explosive cladding by stainless steel of the inner part of one-meter steel pipe billets. For the production of high-quality twolayer pipes by explosion welding, we also propose to use either solid (a metal rod) or solid-liquid (shots with water) internal fillers. The use of these types of fillers makes it possible to avoid damage to the inner cladding layer and minimize the transverse deformation of the bimetallic pipe. Microstructural analysis of the joint boundary shows that the proposed explosion cladding produces an acceptable joining of the 37Mn2V structural steel with the 08Cr18Ni10Ti corrosion-resistant steel. The shock-compressed gas in the welding gap with no lateral outflows is found to lead to the formation of large fusion zones on the final sections of bimetallic cylindrical billets that may result in delamination of the layer joint. The quality of the welded two-layer tube blanks is ultrasonically controlled to check the bond continuity. Verification indicates that the adhesion of layers of good quality occurs over the entire length of samples, except for small initial and final segments.