AbstractThe rheological features of the melt flow of the initial low-density polyethylene and its filled composites with aluminum powder are studied. The effect the filler concentration, temperature, and shear rate on the composite rheology is explored. To improve the compatibility of metal-polymer systems, a compatibilizer representing a graft copolymer of low-density polyethylene with content of 5.8 wt % maleic anhydride is used. The values of the melt flow index (MFI) of low-density polyethylene are determined depending on the concentration of aluminum powder. The filler concentration is varied in the range of 0.5–30 wt %. It is shown that 0.5 wt % of aluminum powder leads to the maximum MFI of the composites. The flow curves and the dependence of the effective viscosity on the shear rate of the initial low-density polyethylene and composites with content of 0.5 and 5.0 wt % aluminum powder are determined. A theoretical justification of the regularities of changes in rheological properties is proposed. The dependence of the change in the effective viscosity of the melt on temperature in Arrhenius coordinates is established. On the basis of the curves obtained, the values of the apparent activation energy of the viscous flow are determined. It is determined that the introduction of the filler results in an increase in the activation energy of the viscous flow. A temperature-invariant characteristic of the viscosity properties of composites is constructed, allowing one to predict the change in the value of this indicator at high shear rates, close to their processing by extrusion and injection molding.

AbstractA technology has been developed for obtaining and evaluating in model studies in vitro a chemically fixed xenogenic bone matrix structurally resistant to osteoclastic resorption. The parameters of demineralization of the fragmented bone matrix have been selected in which the complete removal of the mineral component is carried out with the preservation of collagen in its native state. Optimal technological parameters of chemical fixation with epoxy compounds make it possible to obtain a stable material with free epoxy groups which can serve as a carrier for recombinant protein growth factors (rhBMP) in conditions of a pronounced regenerative process.

AbstractA method is developed for the synthesis of ZnSb and β-Zn4Sb3 compounds using fast melt crystallization on a rotating disk (melt spinning) to obtain powders. The microstructure and thermoelectric properties of samples obtained by hot pressing of powders prepared by this method are studied. The microstructure, chips, and composition of the samples are studied using optical and scanning electron microscopy. The nanosized grain structure of the obtained materials is established. The thermoelectric parameters of the samples, the Seebeck coefficient, electrical conductivity, and thermal conductivity, are measured in the temperature range from 300 to 700 K. The coefficient of thermoelectric figure of merit is calculated. The highest quality factor (ZТ = 0.8 at 600 K) is observed for hot-pressed samples of β-Zn4Sb3.

AbstractThe analysis of the literature on bioactive surfaces of volume implants and plasma coatings on their surface is performed. The influence of the porous sizes on the process of growing new bone in an implant surface is described. The traditional porous structure of a plasma titanic coating, which is formed owing to a decrease in extent of deformation of spraying particles on a substrate, is not optimum for growing of a new bone tissue. Modern dense hydroxyapatite (HA)-titanium coatings do not have the necessary porous structure, and transfer of cyclic loading through an external layer is not reliable. At the same time, comparative studies of 17 surfaces of implants indicate obvious advantages of plasma HA coatings during implantation, which are not dependent on the degree of their crystallinity. Three-dimensional capillary-porous (TCP) titanium coatings in the form of ridges and cavities with additional HA plasma and microplasma coatings are prospective for medical application owing to division of dense and porous volumes of a coating, increase in the area of the border with a new bone tissue, higher shear, and the possibility of spraying of the HA coating with equilibrium structure at a temperature of the surface of titanium of 550°C. The analysis of HA coating content phase is made depending on the modes of plasma spraying.

AbstractThe paper presents a comparative analysis of the structure and elastic properties of industrial nonwoven perchlorovinyl, chlorinated polyethylene, and polysulfone materials used for the production of nonwoven separation materials for chemical current sources. The replacement of perchlorovinyl with chlorinated polyethylene and polysulfone provides materials having poorer physical and mechanical properties.

AbstractThe results of studying the mechanical properties of the Ti–4.25Al–2V titanium alloy produced by direct metal deposition with use of the equipment developed by the St. Petersburg State Marine Technical University are described. The mechanical properties of the deposited metal are compared with those of the cast and forged metal blanks. It is shown that the superior properties of the former in comparison with cast metal are associated with differences in the structure (in particular, with a high degree of dispersity).

Abstract—The method of mathematical modeling was used to determine the rate of cooling of the heat-affected zone upon assembling the weld joints of reactor plants for nuclear icebreakers by preweld depositions. The effect of thermal cycles in various sections of deposited metal welded using three types of welding consumables, namely, carbon steel, silicon-manganese steel, and steel alloyed with nickel, was simulated using a quenching deformation dilatometer. The structure and hardness of the samples after simulated exposure to thermal welding cycles were studied. The deposited metal in using a Sv-06AA carbon wire was found to have a ferrite-pearlite structure throughout the range of cooling rates. An Sv-08GS manganese silicon wire forms an acicular ferrite structure in a wide range of cooling rates, while an Sv-10GN steel wire alloyed with nickel forms an acicular and quasi-polygonal ferrite structure.

AbstractA description of the developed nanosecond high-voltage generator of low-temperature plasma based on a volume streamer discharge is given. Plasma is formed in a high-voltage three-electrode gap, one of which is at a floating potential. Plasma is formed when a special switch is triggered, which connects a floating potential electrode, pre-charged with positive streamers, to a grounded electrode. The operation of the generator in a pulse-periodic mode greatly simplifies its application in experimental studies. Its design and electrical circuit are described. The main electrical characteristics and parameters of streamer plasma radiation in the optical and ultraviolet ranges are presented. An example of a specific application of a generator plasma for solving problems of water purification from metal ions (by the example of manganese) using electric discharge technology is given. The use of a low-temperature plasma of a streamer discharge for experimental research in the field of propagation of an ultrahigh-frequency (microwave) signal in an ionized region of the atmosphere (thunderstorm cell) is described.

AbstractTechnology for the formation of composite materials with a magnesium matrix and a filler based on lead alloys has been proposed, which makes it possible to increase the tribotechnical properties of plain bearings. According to the proposed technology, a porous magnesium matrix with open porosity is obtained by filtration of a magnesium melt through water-soluble granules, which, after solidification of the melt, are leached into a solution of acetic acid. To obtain a composite casting, a porous magnesium matrix is impregnated with lead or lead alloys. The conducted studies of the formation processes of a composite material with a magnesium matrix and babbitt filler show that the proposed technology makes it possible to obtain composite materials with satisfactory filling of porous magnesium with babbitt without discontinuities and visible defects. The filling temperature is 500–550°C and the preliminary heating temperature of porous magnesium is 200–350°С. The properties of the obtained composite with a magnesium matrix and babbitt filler show that the material has a lower (by almost 2 times), density, higher thermal conductivity, and better performance properties than lead-based alloys.

AbstractThe possibility of obtaining highly porous hydrogel composite materials for biomedical applications based on tricalcium phosphate in a polyethylene glycol diacrylate matrix, aimed at repairing bone defects, has been studied. The effect of different content of inorganic filler particles exerted on the mechanical characteristics of highly porous hydrogel composites β-Ca3(PO4)2/polyethylene glycol diacrylate has been studied. It is demonstrated that the preparation of highly porous composite materials with specified elastic properties is quite possible. The viscoelastic properties of the obtained materials are shown to depend on the preset pore size. Varying the tricalcium phosphate fraction in the highly porous hydrogel material makes it possible to control the relative stiffness of the composite.

Abstract—The effect of sulfur and oxygen concentrations on the formation of chemical bonds in films based on the ternary Mo–S–O compound has been studied. The compound is of interest with respect to the creation of efficient thin-film catalysts for electrochemical and, especially, photoactivated water splitting reaction. The films have been created by pulsed laser deposition in a mixture of gases (argon and oxygen) at room temperature of the substrate. The factors that greatly affect the position of the Fermi level in the band gap of the triple compound have been determined, which is mainly responsible for the choice of components in hybrid and heterostructures for photoelectrodes. The change in the chemical state of Mo–S–O films in the electrochemical process of hydrogen production in an acidic solution has been investigated. Indicators of changes in the local packing of atoms (self-organization) have been revealed: they consist in a decrease in the concentration of metal oxide clusters and an increase in the concentration of Mo–S clusters on the surface of the films. According to the thermodynamic analysis performed using the density functional theory, when oxygen is removed from the surface of Mo–S–O films, and, consequently, a hybrid MoSx/(Mo–S–O) structure is formed, the efficiency of hydrogen formation can be controlled by the quantum-chemical interaction of various clusters. Here, only certain combinations of clusters can provide sufficiently high catalytic activity.

AbstractSystematization of available information on the results achieved in the field of development of promising materials based on two-, three-, and four-component compounds of the (Si–B–C–N) system such as nitrides, carbides, borides, silicon and boron carbonitrides, and silicon borocarbonitride is carried out on the basis of the analysis of domestic and foreign scientific publications. Information about their structure, properties, and methods of obtaining is given. The dependence of the properties of fibers, monoliths, and composite materials on the chemical composition and structure of Si–B–C–N compounds is considered. The results of testing finished products at high temperatures in an oxidizing environment are presented. The prospects of using the materials of the (Si–C–N–B) system in industry and engineering for the manufacture of parts and assemblies designed to work at high temperatures under mechanical loading in aggressive environments are described.

AbstractThis paper addresses the question of an evaluation of damage accumulation in a steel structure during operation. The fracture criterion of the structure is defined as the highest value of uniform deformation in tensile testing of steel. This paper presents a method to allow the calculation of the damage from the change in the coercive force with regard to the value of the maximum uniform deformation of steel in tension and the value of the initial coercive force.

AbstractThe second part of the review of the boundary friction tribology of solid carbon coatings gives special priority to the effects of generating modified layers and the tribochemical interaction of alloying additives with liquid lubricant components used for improving antifriction and antiwear properties. The possibilities of improving the lubricity of several full-formula oils and model lubricant compositions used in friction units are considered. Recommendations on the structure and alloying of diamond-like carbon coatings developed for use in lubricated heavy-duty friction units are provided.

AbstractThe appearance of ZhS6K grade alloy granules, the surface and internal structure, and the chemical composition thereof have been analyzed. It is shown that one can control the formation of a preset state of interfaces (tracks, crystallization cells, hatch block boundaries, grains, phases, and discontinuities such as pores and cracks) through the fractional composition, packing density upon filling, and scanning speed in order to obtain a better material quality. The initial structural state of the samples has been studied. An interrelation between the structure of crystallization cell boundaries, dispersed particles, and the structure of fragments has been established. It is shown that all the studied samples have different structural features at the same power and scanning strategy. The analysis has been performed using the methods of optical metallography and scanning electron microscopy (SEM).

Abstract—We present the results on the influence of parameters of the thermochemical treatment process in selenium vapor during production of solid lubricant coatings from molybdenum diselenide on the construction steel specimens with a plasma Mo coating. We propose an empirical mathematical model of the temperature–time parameters of the Mo selenization process making it possible to control the quality of the resulting coatings depending on the requirements for their tribotechnical properties. Their tribotechnical characteristics in air and in vacuum are evaluated within the temperature range of 20–600°C.

AbstractThe profiles of individual tracks were experimentally studied with consideration of the powder flow rate, nozzle speed, and temperature when creating a coating from a monometallic aluminum powder, a mixture of two monometallic powders of the aluminum–nickel and nickel–titanium systems, as well as composite powder from a mixture of monometallic powder of aluminum and corundum. Aluminum and nickel powders were chosen for investigation, since they are the basis for most functional coatings. The dependence of the track profile on the scanning speed is established; the step between the tracks ensuring uniform coverage is determined.

AbstractStructural and magnetic characteristics of La0.7Sr0.3Mn0.9Fe0.05Zn0.05O3 + γ and La0.7Sr0.3Mn0.9Fe0.05Mg0.05O3 + γ manganites, in which the iron is Mössbauer isotope 57Fe, are investigated and compared. Ceramic samples were sintered in air at 1473 K. They were then exposed to heat treatments at 1223 K and various partial pressure of oxygen in the gas phase, which ensured the production of manganites with following values of non-stoichiometry index: γ = −0.005; 0; 0.007; 0.008 for Zn-containing manganites (ZnM), and γ = −0.022; 0; 0.002; 0.005 for Mg-containing manganites (MgM). All synthesized manganites have rhombohedral crystal structure. Mössbauer spectroscopy data correspond to Fe3+ (3d5) ions. Curie point and magnetization depend on γ nonmonotonically. ZnM have essentially higher values of magnetic parameters and narrowest temperature interval of “ferromagnetic–paramagnetic” transition as compared with MgM. Their structure is considered as more homogeneous, which corresponds to lower value of quadrupole splitting of Mössbauer spectra. The results obtained indicate that different effect of Zn2+ and Mg2+ ions on electromagnetic characteristics of manganites is mainly determined by the configuration of their electron shells (3d10 and 2p6, correspondingly).

AbstractTwo variants of the generalized three-component mathematical model of external sliding friction are proposed. This approach involves the Deryagin molecular friction theory and allows describing the dependence of friction force on load under one or more changes in friction modes caused by complex physicochemical and mechanical processes in the friction contact area. The change in friction is shown to have a piecewise linear character, whereas such parameters of frictional interaction as the differential coefficient of friction, the equilibrium force of molecular attraction, and the molecular component of friction force change in a sigmoid manner.

AbstractGadolinium hafnate (Gd2HfO5) powders are obtained by mechanochemical synthesis from hafnium and gadolinium oxides. XRD, chemical analysis, and scanning and transmission electron microscopy show the transition of initial oxides into single-phase nanodisperse gadolinium hafnate after 30 min of mechanochemical synthesis. This powder is studied for its compactibility and sintering.