Том 10, № 5 (2019)

A method making it possible to calculate the density and matrix volume fraction of two-component and hybrid composites reinforced with unidirectional rovings of carbon fibers (CF) and ultrahigh-molecular-weight polyethylene (UHMWPE) fibers is presented. Experimentally found constants of the rovings were used in calculation. The values of calculated density and matrix volume fraction were compared with an actual data of samples. The samples were obtained by resin impregnation of the rovings at free air. The impregnation was implemented simultaneously with laying of the rovings. This procedure does not permit saving the prespecified sample volume without volume control. The effects of volume deviations on the actual density of sample and the actual volume fraction of matrix were investigated on the samples with uncontrolled and controlled volume. The roving volume fractions and concentrations of hybrid and two-component composites were specified as the basic data of calculations. The actual densities of samples, as well as the value of matrix volume fractions, were compared with the calculated ones. The experimental data are in good agreement with the calculated data.

The dimensionless thermoelectric figure of merit and magnetic field production ability of “natural” nanostructures–layered ternary alloys (TA) of the family [(Ge, Sn, Pb)(Te, Se)]_m [(Bi,Sb)₂(Te,Se)3]_n, with non-isovalent cationic substitution (Ge, Sn, Pb ↔ Bi, Sb) are investigated. In the transition from binary alloys (BA) to TA, we observed the formation of the phase “phonon glass–electronic crystal” (PGEC) and its subsequent degeneracy, accompanied by sharp increase in the carrier densities in the samples. As a result, the size ZT of samples went down, and the size X substantially increased, which speaks in the work to formation of a degenerated PGEC phase under non-isovalent cationic substitution in the samples. Comparison with known thermoelectric materials (ТEMs) (metals, semimetals, and semiconductors) used for production of magnetic fields H in contours of short-circuited ТC has shown that the investigated TA forms a new class of TEMs for magnetic field production with raised values of parameters X and Y.

The effect of reducing agents and reduction conditions on the electrophysical characteristics of thin transparent conductive films obtained from an alcohol dispersion of graphene oxide (GO) by spin coating at different rotation speeds of the substrate (from 5000 to 7000 rpm) is investigated. Surface morphology of the films, light transmittance, structure of chemical bonds in the films, specific surface electrical resistance, and thickness of the films are determined. Films of multilayer reduced graphene oxide (RGO) with a thickness of 10 to 60 nm and a specific surface electrical resistance of 7.7 to 26.77 kΩ/cm² and light transmission of 74 to 88%, which can be widely used in photovoltaics and sensor electronics, are obtained. It is established that the treatment of the samples under study in saturated ammonia vapor most effectively contributes to the reduction of the specific surface electrical resistance of the films.

Specimens of ChS-139 steel (0.2 С–12 Cr–Ni–Mo–W–Nb–V–N–B) were irradiated up to 6 displacements per atom (dpa) with Fe ions at 250, 300, and 400°C. The radiation-induced clusters and Cottrell atmospheres enriched in Ni, Si, and Mn were revealed in irradiated samples by atom probe tomography. The typical sizes of the radiation-induced clusters were about 2–7 nm, and their number density was about (2–20) × 10²³ m^–3. It was shown that the highest irradiation temperature (400°C) is compliant with the lowest enrichment of clusters in Ni, Si, and Mn as well as with the largest average size of clusters (~5 nm) and the least number density (~2 × 10²³ m^–3). A noticeable decrease in the number density of radiation-induced clusters with an increase in the damage dose to 4 dpa at 300°C was found. At the same time, it was shown that the Cr–V–Nb–N clusters found in the initial state dissolve with the increase in the irradiation dose at all considered temperatures. The value of detected radiation-induced effects is indicative of their significant role in the low temperature radiation embrittlement of ChS-139 steel.

Undoubted leadership among catalytic materials for the purification of exhaust gases is occupied by composite cermets. Creation of catalytic materials for gas purification indicates that the main problem is partial or complete replacement of rare earth metals in their composition. In this regard, the creation of new permeable catalytic materials with partial or complete replacement of rare earth metals is relevant. Selection of composition and manufacturing technology is of great importance for the production of porous materials. The basis of charge for the production of porous materials is industrial waste such as metal oxides, metal powders, and polymetal ores (bastnaesite) containing rare earth cerium. Charge composition for the production of porous permeable metal-ceramic materials based on metal oxides with the addition of ground bastnaesite is proposed. The influence of bastnaesite on the physicomechanical and functional properties of materials obtained by self-propagating high-temperature synthesis is studied. It is shown that the neutralizer filters from materials with additives of bastnaesite have catalytic properties and can be successfully used in the purification of exhaust gases of internal combustion engines.

The results of tensile and compression tests performed for a layered carbon-carbon material in the range of 20–3000°C are presented. The material has been developed using chopped high-modulus VPR-19C fiber and coke obtained by repeatable thermomechanical treatment of bakelite lacquer LBS-1 and subsequent pyropacking resulting from carbon saturation from the gas phase at 1000°C. The production technology provides a transverse anisotropy of the material structure and, accordingly, the mechanical properties. In the course of compression tests in the direction parallel to the pressing axis at room temperature, it has been found that, when the sample height increases by a factor of 6, the material elastic modulus increases by a factor of 1.4, which is accompanied by a 2.4-fold decrease in the compression strength. The material hardens with the increase in the test temperature: its tensile strength in the circumferential direction increases by a factor of 3 at a temperature of 3000°C, and the elastic modulus increases by a factor of 1.2 in the range of 1000–2000°C; however, with a further increase in the test temperature, it begins to decrease, and at a temperature of 3000°C, it is 0.3 of its value at room temperature.

The structure, phase composition, and C, O, and N content in two cermet coatings sprayed from powders of the initial composition of 30SiC–NiCr and 30SiC–TiNi are studied. The change in the chemical and phase composition is monitored at the stage of obtaining powders and plasma spraying of the coatings. The powder is obtained by mechanical alloying and subsequent sintering of the compact. With mechanical alloying, the content of oxygen and nitrogen increases. When sintering, the content of silicon carbide is reduced by 10 times, silicides are formed, and the content of light elements at this stage changes insignificantly. After plasma deposition, the phase composition of the coatings does not qualitatively change with respect to the powder to be sprayed, but nonequilibrium crystalline and amorphous phases are formed and the content of carbon and oxygen decreases. The microhardness of coatings of 10 GPa at load on an indenter of 10 g is determined by 50% of the volume fraction of SiC in the initial powder.

We investigate the structure and properties of ceramic based on tetragonal zirconia (Y-TZP) containing low-modulus inclusions of hexagonal boron nitride (h-BN). (Y-TZP)(h-BN) ceramic samples with low h-BN content exhibit increased fracture toughness (K_1C). The highest fracture toughness was observed for (Y-TZP)(0.5 wt % h-BN) ceramic: K_1C = 12 ± 0.53 MPa m^1/2. The increase in failure viscosity caused by incorporation of low-modulus inclusions (i.e., h-BN) is due to two dissipative mechanisms: the martensite transformation of the ZrO₂ matrix and crack arrest at relatively weak interfaces between the matrix and low-modulus inclusions of h-BN. As the proportion of h-BN increases, the contribution of martensite transformation to the fracture toughness diminishes, a consequence of the grain size of tetragonal zirconia diminishing, which makes this phase stable.

Compact ceramic long-dimensional materials based on titanium monoboride modified with aluminum nitride dopants (3 and 5 wt %) were obtained via SHS extrusion. Titanium monoboride was produced using azide technology of self-propagating high-temperature synthesis (SHS-Az). Small dopants of nanoscaled aluminum nitride powder exert a strong influence on the phase composition, structure, and physicomechanical properties of samples prepared by SHS extrusion. Scanning electron microscopy data reveal the refinement of the main titanium monoboride phase grains in modified samples. The most pronounced refinement of titanium monoboride grains is observed as the AlN nanopowder content is increased to 5 wt %. The combustion characteristics (temperature and combustion rate) are measured in an installation simulating the real SHS extrusion conditions. It is established that AlN at its content of 3 wt % in the initial charge interacts with the titanium matrix during combustion with the formation of the Ti₂AlN and Ti₄AlN₃ MAX phases. AlN at a concentration of 5 wt % undergoes decomposition during combustion with release of titanium nitrides and pure aluminum, as well as the TiB, TiB₂ and Ti₂AlN phases. Modified compact ceramic materials are shown to exhibit higher microhardness in comparison with samples without using nanomodified AlN dopants.

The processing of electric arc furnace dust by the Waelz process forms the iron-containing residue called Waelz slag. In the paper, best practices for recycling of Waelz slag from electric arc furnace dust processing have been analyzed and physicochemical characteristics and microstructure of the Waelz slag obtained from JSC Chelyabinsk zinc plant have been investigated. Chemical analysis of the Waelz slag composition has shown that it contains 26.4 wt % of iron with a metallization degree of 47 and 18.7 wt % carbon. It also contains about 1 wt % of zinc unevaporated during Waelz process. It has a complex multicomponent mineralogical composition. Analysis of papers has shown that currently Waelz slag recycles mainly in the construction industry in the production of cement, concrete, bricks and for road making. There is a limited number of papers devoted to recycling of Waelz slag in metallurgy because it contains too high values of contaminants such as zinc, lead, sulfur, phosphorus and copper. It is expedient to apply for recycling of Waelz slag the reduction smelting with obtaining of pig iron, slag suitable for construction industry and zinc-lead fume.

The ability to apply granulated materials with cellulose as sorbents for silver extraction from thiocyanate solutions in industrial technological schemes is studied. Samples extracted from sulfite unbleached pulp from coniferous wood via preactivation, dilution, chemical modification, and extraction with successive curing of granules formed are studied. The granule surface is shown to possess a developed pore system with diameter of 2–5 μm. The optimum time of silver sorption from a potassium thiocyanate solution by a cellulose-containing sorbent with a weight of 500 ± 2 mg is found to be 120 min. The silver anion complexes can be completely extracted from thiocyanate solutions with a silver content of not higher than 1 g/L. The experimentally evaluated sorption capacity of a cellulose-containing material in relation to silver is 20 mg/g.

The technique of cohesive zones makes it possible to evaluate the stability of the material, both at the beginning of the crack propagation and to the appearance and development of defects in the places of stress concentration. The ability to reliably determine the parameters of fracture of polymer composite materials and to predict the behavior of structural elements from them under loading is an urgent task for the aerospace industry. It is proposed to use the length of the cohesive zone in the finite-element 3D model for mode I of interfacial delamination of the carbon fiber composite laminates in the form of a double cantilever beam (DCB). The length of the cohesive zone is calculated from the experimentally determined parameters such as the local interlayer cohesive strength of the material and the critical strain energy release rate. The determined length of the cohesive zone is used in the model to select the minimum number of finite elements at their optimum size, which ensures a higher accuracy of calculations of the main parameters of fracture toughness of carbon fiber composite laminates. As a result of the research, the main parameters of crack resistance are determined and the optimal length of the interface elements is chosen. The obtained model accurately describes the process of crack growth along the entire length of the cohesive zone, and the results of its application correlate well with the results of the experiments.