Том 9, № 5 (2018)

Bilayer composite membranes (CMs) are prepared by depositing a polymer layer onto track-etched polypropylene (PP) membrane by using plasma polymerization of hexamethyldisilazane (HMDSN). The chemical structure, wetting properties, and morphological characteristics of the prepared CMs are investigated. By depositing the plasma-polymerized polymer, we obtain CMs with two hydrophobic layers, of which one is the initial PP membrane, serving as a matrix. This layer has a water contact angle of 120°. The other layer, which was formed during plasma polymerization of HMDSN, contains nitrogen-containing functional groups, along with minor amounts of oxygen-containing, mainly carboxylic, groups. The water contact angle of this layer is ~98°. Deposition of a polymer film by plasma-assisted polymerization results in smoothing surface asperities of the initial (matrix) membrane, a considerable decrease in pore diameter, and alteration of pore shape; namely, the pores acquire an asymmetric (conical) profile.

Transparent conducting films based on graphene particles are obtained via ultrasonic-assisted liquid-phase exfoliation of natural graphite. For the first time, the Langmuir–Blodgett technique is reported to be utilized for the deposition of transparent conducting thin films based on directly exfoliated graphene on dielectric substrates (glass and lithium niobate). It is shown that centrifugation of graphene suspensions prior to the film deposition enables the formation of conducting coatings with high transparency (higher than 90%). A number of film parameters (sheet conductance, transmission coefficient in the optical domain) are investigated; the achieved level of properties (the sheet resistance of 143 Ω/sq at the optical transmission coefficient of 90% and the weak dependence of absorption on the wavelength) makes these films an attractive material for transparent electrodes in photovoltaic devices, light emitting diodes, and advanced sensor technologies. The samples of graphene-based films deposited on a transparent piezoelectric substrate (lithium niobate) showed themselves as candidates for application as a part of primary transducers for electronic devices and sensing technologies as a possible substitute for ceramic materials based on indium-tin oxide.

The effects of paired substitution of 3d¹⁰ cations (\(\rm{Zn{_{0.5}^{2+}}Ge{_{0.5}^{4+}}}\)) or 2p⁶ and 3p⁶ cations (\(\rm{Mg{_{0.5}^{2+}}Ti{_{0.5}^{4+}}}\)) for manganese in polycrystalline manganites of specifically designed systems \(\text{L}{\text{a}_{0.8 - x}}\text{S}{\text{r}_{0.2 + x}}\text{Mn}_{0.8 - 2x -2\gamma}^{3 +}\text{Mn}_{0.2 + x + 2\gamma}^{4 +} \times {\left( {\text{Me}_{0.5}^{2 +}\text{Me}_{0.5}^{4 +}} \right)_x}{\text{O}_{3 + \gamma}}\) on their electromagnetic parameters are studied and compared. Temperature dependences of the resistance, magnetoresistance and magnetostriction constant are measured. In the proposed systems, the linear rise of strontium concentration simultaneously with increasing number of substituents allows high characteristics of manganites to be maintained owing to the increase in the concentration of free charge carriers, through which ferromagnetic double exchange interaction is carried out. The data obtained are also compared with the properties of Ga³⁺(3d¹⁰)-substituted manganites as peculiar standards. All sintered (Zn,Ge)-containing manganites in the temperature range from 100 to 293 K have metallic type of conductivity, while (Mg,Ti)-substituted samples exhibit semiconducting features, and Ga-containing compositions reveal a “metal-semiconductor” transition point (T_ms). The annealing under conditions ensuring stoichiometric oxygen content leads to the shift of this transition toward lower temperatures in manganites with 3d¹⁰ substituents and to the increase in T_ms in compositions with substituting p⁶ cations. In the investigated systems, the absolute values of negative magnetoresistance up to ~90–200% at 120–150 K in the field of 9.2 kOe are obtained, and the linear magnetostriction constant reaches record values of about 10^–3 in the field of 4.6 kOe. Manganite La_0.65Sr_0.35Mn_0.85Ga_0.15O₃ with a weak temperature dependence of magnetoresistance of ~20% at room temperatures is of particular service for magnetic field sensors. Possible approaches to the interpretation of established regularities demonstrating the role of electronic configurations of substituents for manganese in the formation of the properties of manganites and interesting for the development of new materials for electronics are discussed.

The chemical interaction in the Li₂CO₃–Nb₂O₅ and Li₂O–B₂O₃–Nb₂O₅ systems and crystallization features of LiNbO₃ crystals from the melts containing boron impurity are considered. Raman spectra of LiNbO₃:B crystals grown from a congruent melt containing ~0.55–1.24 mol % of B₂O₃ are studied. There are noticeable changes in the entire Raman spectrum upon doping with boron, which indicates a change in alternation of the main cations and vacancies along the polar axis of the LiNbO₃:B crystal and “perturbation” of oxygen octahedra. Moreover, expansion of oxygen octahedra is anisotropic with an increase in boron concentration in the melt. Boron, hardly entering the structure of the lithium niobate crystal, significantly changes the structure of the melt and thus has a significant effect on structure and physical characteristics of the LiNbO₃:B crystals. The results obtained for the LiNbO₃:B crystals are compared with those obtained for nominally pure stoichiometric (LiNbO_3stoich) and congruent (LiNbO_3cong) lithium niobate crystals.

Structural features of mineral crystal phases and defectiveness of bismuth organosiliconate crystals are inspected at various temperatures of treatment (from 100 to 500°C). X-ray diffraction enables evaluation of crystal lattice periods from spectrograms recorded in СuK_α radiation. The approximation analysis of the broadening of the most intense diffraction lines in crystals from (hkl) crystallographic indices allows one to determine the coherent domain sizes and microdistortions Δа/а of a crystal lattice. It is found that exposure of the Na₂O–Bi₂O₃–SiO₂ system (NBS material) to temperatures of 300–500°C leads to a decrease in amorphism, microdistortions, and the density of dislocations in a crystal lattice of Bi₁₂SiO₂0 sillenite. The formation of a denser structure of sillenite crystal with higher X-ray density (9.210 g/cm³) and greater cubic crystal lattice parameter (a = 10.1335 Å) is detected. The presented Bi₁₂SiO₂₀ material can be used as a gamma and protective filler of radiation protective polymers and in the design of electro-and magneto-optical laser radiation modulators.

Light-emitting diodes (LEDs) operate under conditions of ionizing irradiation. The purpose of this work is to research the action of preliminary irradiation with fast neutrons on the reliability of LEDs. The objects of research are LEDs based on double AlGaAs heterostructures. The control of the forward-bias region of the current–voltage characteristic of the LED allows detecting the parallel-connected dislocations to the p–n junction of the LED. Moreover, it makes possible to determine the resistance of ohmic contacts. The LEDs have an s-shaped form of the current–voltage characteristic, which is due to the connection of dislocations parallel to the p–n junction of its active layer. Long-term operating conditions are simulated by accelerated step-by-step tests. Analysis of the current–voltage characteristic shape makes it possible to mark several distinctive areas that are defined by the electron injection level in the active region of the LED. The marked areas can be characterized by corresponding threshold currents. The threshold currents go up when the step number increase is accompanied by an increase in resistance of ohmic contacts during step-by-step tests and under irradiation with fast neutrons. Preliminary irradiation with fast neutrons leads to a shift in the threshold currents depending on the fluence of fast neutrons. Preliminary irradiation with fast neutrons with fluence in the region of radiation-stimulated reconstruction of the initial defect structure makes it possible to increase the resistance of ohmic contacts during operation and, therefore, to increase their reliability. Preliminary irradiation with fast neutrons in the region of only radiation defects leads to the accelerated increase in resistance of ohmic contacts during operation, which decreases their reliability. Preliminary irradiation with fast neutrons can be used in the manufacturing technology of LEDs with the purpose of increasing the reliability.

Analysis of the combination of the “titanium implant–bone tissue” using the model of the composite material “cylindrical titanium implant–plastic,” where plastic with the shear strength of 62.3 MPa simulates the bone tissue, was performed. The shear strength of the “cylindrical titanium implant–plastic” system increases with the increase of the macro- and microrelief of the titanium surface in the series smooth surface, processed by abrasive, with three-dimensional capillary-porous (TCP) titanium coating, with TCP Ti coating and microplasma oxidation—2.9, 29, 44.65, and 52.27 MPa respectively. In this case, the shear strength of plastic in this combination increases from 3 to 92%. Analysis of the shear strength of coatings during microplasma oxidation in phosphate and silicate electrolytes with the addition of hydroxyapatite, calcium gluconate, or citrate was conducted. The best result of 57.27 MPa was obtained using the phosphate electrolyte containing synthetic hydroxyapatite (HA). In this case, when samples were subjected to shear, the destruction of samples occurred with plastic simulating the bone tissue. In samples with three-dimensional capillary-porous titanium coating at the average shear strength of 44.65 MPa, the fracture surface passes along the top of the coating.

Composite NiO–30 wt % Ag–40 wt % Bi₂O₃ material was synthesized and studied. The microstructure of this material cooled from 800°C was studied, and the presence of a percolative network of silver in the bulk of composite was shown. The transport properties of this composite (electrical conductivity, oxygen ion transport number, and oxygen fluxes) in the temperature range of 725–800°C were investigated. The oxygen permeability of a membrane based on the NiO–30 wt % Ag–40 wt % Bi₂O₃ material was calculated and the selectivity of transferred oxygen over nitrogen in the process of separation from air was evaluated. At 800°C, the electrical conductivity was ~50 Ω^–1 cm^–1, the oxygen ion transport number was 0.02, the oxygen permeability was 2.1 × 10^–8 mol cm^–1 s^–1, and the selectivity of oxygen (over nitrogen) was above 1000. The oxygen permeabilities of some ceramic and cermet membranes and the membrane material fabricated in this work were compared. Composite NiO–30 wt % Ag–40 wt % Bi²O³ shows a high selective oxygen permeability compared to the state-of-the-art analogs and can be used as an ion transport membrane for separation of oxygen from air.

Carbonated hydroxyapatite (CHA) owing to its chemical and phase composition that is similar to that of the inorganic component of native bone tissue is a promising material for reconstructive surgery to heal bone defects that are caused by trauma and extensive surgery. An original method for obtaining porous CHA ceramic granules was developed. To obtain a system of interconnected pores, a protein foam with sucrose was used. The optimum ratio of the protein foam to the ceramic CHA powder was found to be 3: 1 for production of porous ceramics with a homogeneous structure. The mechanical properties of the porous CHA ceramics that we obtained at different ratios between the protein foam and ceramic CHA powder were studied: as the concentration of the ceramic CHA powder increased in the mixture, the compressive strength of the CHA ceramics decreased from 6–7 to 2–3 MPa. The microstructure of the CHA ceramics is characterized by the presence of pores that are different in size, from fractions to tens of microns. In vitro studies of the porous CHA ceramics were performed. The evaluation of the influence of the granules on the growth of rat MMSCs in vitro revealed a decrease in the cell viability with an increase in the concentration of the granules. The reduced viability of the MMSCs in the presence of the granules can be associated with alkalization of the environment by the sintering additive.

The effect of the graphitization conditions at 3000°C on the crystal structure and properties of high-modulus polyacrylonitrile-based carbon fibers (CFs) is studied. It is shown that an increase in the temperature of CF processing from 1400 to 3000°C leads to a decrease in the tensile strength and an increase in Young’s modulus. However, an increase in the winding rate from 10 to 300 m/h during the synthesis of CFs at a fixed graphitization temperature of 3000°C leads to decreases in both the tensile strength and Young’s modulus. The crystal structure of the synthesized CFs is studied by the X-ray diffraction and Raman spectroscopy methods. It is shown that an increase in the thermal processing temperature from 1400 to 3000°C leads to a decrease in the d₀₀₂ interlayer spacing and an increase in the crystallite size L_c. It is established by the Raman spectroscopy method that the I_D/I_G parameter (the ratio of the integral intensities of the D and G spectral bands) decreases at the same time, which is also characteristic of an increase in the degree of perfection of the CF crystal structure. On the contrary, an insignificant increase in the d₀₀₂ interlayer spacing and a decrease in the L_c value are observed with an increase in the winding rate for CFs synthesized at a fixed graphitization temperature of 3000°C, while the I_D/I_G parameter in this case hardly changes. A detailed analysis of the shape of the (002) diffraction peak shows that, unlike CFs obtained at a winding rate of 10 m/h, CFs obtained at higher winding rates consist of at least two distinct structures of different degrees of graphitization. Further thermal treatment of these CFs at 2650°C under steady-state conditions leads to a significant decrease in the d₀₀₂ spacing parameter and an increase in the L_c value. It is established from the measurements of the I_D/I_G ratio that radial inhomogeneity of the CF crystal structure over the cross section increases at higher winding rates, which is associated with inhomogeneous heat transfer in the filaments. It is concluded that high rates of heating to 3000°C have a negative effect on the structural and mechanical properties of CFs.

In this work, we tested experimentally refractory porous aluminosilicate ceramic materials as protective energy-absorbing design elements of naturalistic large-scale layouts of explosion-proof thin-walled metal containers. We showed that lightweight refractory porous aluminosilicate materials can be effectively used for an efficient (two or more times) increase in explosion-proof characteristics of the containers simultaneously with minimization of their mass and dimensions. These materials significantly reduce the impact of a shock wave and other damaging factors of explosives and explosive devices on the metal shell of the containers. We developed full-size models of explosion-proof containers with a diameter of 1.2 m that are capable of withstanding an explosion of explosive charge (TNT) with a weight of not less than 3.5 kg without being beyond the range of elastic deformation of the metal shell. The obtained results allow designing similar explosion-proof containers in a wide mass-scale range with predetermined explosion-proof characteristics without costly research and development. Solid refractory porous materials are promising for the development of nonstationary transported explosion-proof containers for the storage, transportation, and destruction of explosive materials and devices, since their application makes it possible to reduce the material consumption, weight, and dimensions of containers.

Interaction of the structure of the composite alloy (Al–12 Si)–40 Sn with its mechanical and tribological properties was studied. The alloy was obtained by the liquid-phase sintering of powder briquettes made of the powder mix of tin PO-2 and an atomized aluminum alloy of the eutectic composition Al–12 Si. Sintering was carried out at a temperature below the melting point of the eutectic; otherwise, the sample melted and lost its shape. It was found that the given sintering temperature does not make it possible to obtain samples with high density; their residual porosity was 6–8% and it almost was not decreased with the increase in the sintering time. The obtained material had low mechanical properties, which slightly improved with the increase in the sintering time to two hours. At the same time, the amount of exuded and evaporated tin noticeably increased. Taking into account the undesirable phenomena that occurred during a long exposure of sintered samples at high temperature, the hot densification was carried out after the short-term sintering. Densification of the sintered samples aiming at removal of the residual porosity was carried out in a closed mold under pressure above the ultimate strength of the alloy. It was established that such operation contributed both to significant improvement of strength and ductility of the studied material. In addition, the obtained nonporous material had high wear resistance under dry friction against a steel counterbody; it was especially noticeable during friction under high pressure. The wear rate of samples with a matrix made of the aluminum-silicon alloy was 30% lower as compared with the alloy with the matrix made of pure aluminum at all other conditions being equal.

Two methods for transition metal carbide nanopowder production such as plasma chemical synthesis and high-energy ball milling are considered. The control of the chemical, phase, and dispersed composition of carbides produced from oxide and halogenide raw materials is studied by an electric arc plasma plant with a power of 20 kW. A study of the grinding time effect of micron-sized carbide powders on a Retsch PM-400 mill tool in hard-alloy containers is carried out to obtain nanosized powders, as well as to determine fractional composition and particle shapes. It is shown that powders obtained by plasma chemical synthesis have a grain size of 20–80 nm and are subjected to a spheroidized or equiaxed shape. The process allows one to tune the phase composition and the content of common and free carbon. Polydispersed carbide powders with a specific surface area of 3–25 m²/g and predominately bimodal particle size distribution in a range from less than 0.1 μm to dozens of microns are thus obtained by high-energy ball milling.

The features of the dehydration and recrystallization processes were studied on samples of aluminum hydroxide obtained by carbonization of an aluminate solution at 40°C and isolated by Bayer’s decomposition. The main differences in the structural transformations of these samples consist in the individual sequence of the formation of polymorphic modifications of oxides in the dehydration of each aluminum hydroxide. The structural transformations of these types of hydroxide and the dynamics of the polymorphism of the decomposition products were studied in the temperature range of 100–1000°С. Data from crystallooptical, X-ray phase, and thermogravimetric methods of analysis showed that the recrystallization of the structure occurs more slowly when calcining the carbonized aluminum hydroxide than in the decomposition method. It is determined that, with the dehydration of the hydroxide, sodium aluminosilicate and carbon reduce the rate of formation of high-temperature modifications of alumina. The reactivity of aluminum oxide obtained by thermal decomposition of chemically pure sulfuric, hydrochloric, and nitric acid crystalline salts of aluminum salts is determined not only by the phase composition but also by the nature of the starting material. Despite the general morphology of the process of formation of aluminum oxide during the decomposition of the investigated crystalline hydrates, the formation of the phase composition of Al₂O₃ occurs at different temperatures and at different rates. Structural rearrangements during the decomposition of salts occur in the solid phase, which determines the total porosity and the specific surface area of each type of aluminum oxide. A study of the polymorphism of black alumina containing iron and silicon impurities was also carried out on samples obtained after leaching of the mineral part of the carbonaceous rocks with sulfuric, hydrochloric, and nitric acids in the temperature range of 100–1000°C. An inhibitory effect of impurities and a reducing agent on the formation of high-temperature structural modifications of aluminum oxide in the process of heat treatment of sulfuric, hydrochloric, and nitric acid crystalline hydrates of aluminum salts was revealed.

Composite materials (CMs) based on activated carbon fiber material (ACFM) modified with oxygen-containing transition metal compounds (MnO₂, Ni(OH)₂, and Co(OH)₂) by using colloid electrophoresis are studied. All prepared CMs have higher capacitance than the individual parental materials, with the CM ACFM–Ni(OH)₂ exhibiting the maximum capacitance (~380 F g^–1). Changes in the capacitances of ACFM and prepared ACFM-based CMs induced by potential cycling, the time of exposure to electrolyte solution, and potential scan rate are investigated. The capacitances of all CMs are found to increase with the number of cycles, but tend to decrease at higher potential scan rates.

The phase and elemental composition and microhardness of instrumental steel U9 with zirconium and silicon coatings subjected to compression plasma flows and air thermal annealing are investigated. It is found that plasma impact leads to the formation of a surface layer with the thickness of up to ~8.5 μm alloyed with zirconium and silicon atoms and containing Fe₂Zr intermetallic. Formation on the surface of the oxide γ-ZrO₂ and carbonitride Zr(C, N) as a result of interaction with the residual atmosphere of the vacuum chamber is found. Change in the phase composition and dispersion of the structure leads to a twofold increase in microhardness. The alloyed layer retains the stability of the structure and phase composition (excluding polymorphic transition in ZrO₂) up to 400°C. Annealing at 600°C leads to the internal oxidation accompanied by formation of a surface iron oxide scale and penetration of the oxygen atoms to the whole depth. The increase in the annealing temperature leads to the decrease in microhardness throughout the alloyed layer.

The liquid-phase method for synthesis of disperse mesoporous powders from the Al₂O₃–ZrO₂ (Y₂O₃) system is developed. It is shown that cryotreatment makes possible to constrain particle agglomeration and obtain the precursors with the specific surface area of higher than 100 m²/g and pore volume ranging from 0.18–0.51 cm³/g. Influence of the aluminum oxide source (AlOOH, Al[(CH₃)₂CHO]₃ and Al(NO₃)₃) on the powder dispersivity and pore structure is found, and this makes it possible to control their textural characteristics. It is found that the components obtained are two-phase (γ-Al₂O₃ + t-ZrO₂); the size of the phases is not greater than 45 nm. Thermal treatment of nanocompositions within the Al₂O₃–ZrO₂ (Y₂O₃) system at 700°C for 50 h keeps the nanosize of phases (<60 nm) and hardly changes the crystal structure. The experimental results described in this work make possible to recommend the materials obtained as precursor powders for catalyst supports in methane conversion to synthesis gas.

Disperse precipitates in high-strength high-chromium martensite-ferrite steel of 0.15C–12Cr–Ni–Mo–W–V composition after various modes simulating the after-forging annealing were investigated. The investigated metal after holding at 1050°С for 1 h and quenching in oil was heat treated (HT) in two modes: HT 1—the after-forging annealing at 700°С for 6 h to relieve stresses; HT 2—HT 1 with the following isothermal annealing, heating to 1000°С, short holding, cooling to 700°С, and holding for 16 h. On the basis of the combined research, including optical metallography, X-ray phase analysis, transmission electron microscopy, and small-angle X-ray scattering, it was found that the tempered martensite structure with the ferrite phase of less than 1% was formed in the steel after HT 1; and after HT 2, transition from the martensiteferrite to ferrite-pearlite state took place; significant growth of carbides of the (Fe Cr)₂₃C₆ type and substructural components (coherent scattering areas, electron density inhomogeneity) was found; and finely dispersed particles of vanadium carbide V₂C about 30 nm in size were formed.