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A method for improving the tactical and technical characteristics of ion thrusters while maintaining the specified electrical characteristics of the power source is proposed. This method is considered on the example of increasing the accelerating voltage on the electrodes of the ion-optical system of the prototype ion thruster. The method is based on the creation of a dielectric layer on the electrodes of an ion-optical system. Experimental and theoretical studies of the operation of the ion-optical system as part of the ion thruster have shown that the presence of a layer of dielectric coating on the electrodes allows you to achieve a steady-state voltage of up to 740 V, and in the absence of this layer-no more than 570 V. The calculated values of the thrust for the prototypes of ion thrusters were 14 μN with an ion-optical system having a dielectric layer and 8.4 μN a dielectric on the electrodes. The presence of dielectric coatings on the electrodes of the ion-optical system makes it possible to improve the characteristics of ion thrusters without significant design changes.

The microstructure and phase composition of 03Kh12N10MTR-VD steel after heat treatment and their effect on the mechanical properties and impact toughness KCV–196 have been studied by scanning electron microscopy, X-ray spectral analysis (EDS), and electron backscatter diffraction (EBSD).

Yb:CaWO4 and Yb, Nb:CaWO4 single crystals have been grown by the Czochralski method in air and in protective atmospheres and subjected to additional annealing in air, in CO/CO2 atmosphere, and in forevacuum. The optical absorption spectra in the range from 250 to 1500 nm and the luminescence spectra of these crystals in the visible and near-IR spectral regions upon UV excitation have been investigated. It is shown that additional introduction of Nb5+ ions into Yb:CaWO4 crystal increases by an order of magnitude (almost to unity) the Yb3+ distribution coefficient between CaWO4 crystal and melt. It is found that optical excitation of the crystals in the range of 260–355 nm induces down-conversion luminescence of Yb3+ ions from the 2F5/2 level in the vicinity of 1 µm. An increase in the oxidative potential of synthesis atmosphere, as well as the introduction of niobium into the crystal composition, weakens this luminescence. A consistent pattern explaining the nature of the donor centers involved in down-conversion population of excited state 2F5/2 of Yb3+ in the crystals is proposed. Within this pattern, Yb2+ ions play the role of these donor centers. Another (much less efficient) mechanism of population of the 2F5/2 level is intracenter relaxation from the higher-lying charge transfer excited state within Yb3+ ions. At the same time, it is confirmed that color centers based on oxygen vacancies and partially reduced tungsten ions, as well as self-trapped excitons on tungstate complexes, are not involved in population of the excited state 2F5/2 of Yb3+ ions, and the optical centers formed in Yb:CaWO4 crystals as a result of vacuum annealing suppress ytterbium luminescence.

Introduction of the exothermic mixture into the flux-cored electrode core filler and its’ influence to the deposited metal composition and recovery factors of alloying elements were investigated in the article. An influence of FCAW-S core filler composition with exothermal mixture implemented for recovery hardfacing by wear-resistant alloys was investigated in this article. An influence of oxidizing agent to reducing agent ratio (CuO/Al) in the composition of exothermic mixture, on the recovery factors of the alloying system components was considered. As well as the ratio of exothermic mixture oxidizing agent to graphite (CuO/C) and the amount of exothermic mixture (TM) in the flux-cored wire filler composition. Some mathematical models of the recovery factors dependence on the studied factors were received as a result of the investigation. An analysis of the results of the study showed that the ratio of the oxidizing agent to the reducing agent in the exothermic mixture (CuO/Al) had the greatest influence on the recovery factors of alloying elements. Received mathematical dependences of the alloying elements recovery rates allowed to optimize the calculation of composition of the FCAW-S core filler mixture with exothermic mixture and the deposited metal composition. To receive the high values of the elements recovery factors, the parameters subject to investigation should have the following values:CuO/C = 3.75 … 5.25, CuO/Al = 3.75 … 5.25, CuO + Al = 33 … 45 wt.%.

The physico-mechanical properties of ceramic-matrix Al2O3-based composites are strongly influenced by the particle size of Al2O3, the presence of carbon nanotubes (CNTs), and the temperature regimes of sintering. In order to obtain the very low porosity ceramic composites with high rates of flexural strength and crack resistance, mathematical models were developed for grinding the particles of Al2O3 and spark plasma sintering of the composite. Mathematical models were based on the equations of the balance of the number of particles by size taking into account their grinding (for the grinding stage), the balance of pores in the composite by the size (for the sintering stage). The kinetic parameters of mathematical models were determined and a good agreement was reached between the calculated and experimental results. The developed models were used to determine the optimal modes of grinding and sintering stages, which made it possible to obtain, in particular, the composite Al2O3 - CNT (20 vol. %) with bending strength 540 MPa, and crack resistance 6.3 MPa·m1/2.

A concentration series of sodium–gadolinium molybdate single crystals have been grown by the Czochralski method from melts of stoichiometric and some nonstoichiometric compositions in atmospheres with different oxygen contents. The actual compositions, microhardness, and crack resistance of the grown crystals have been investigated. All crystals are characterized by a significant sodium deficit with respect to stoichiometry and a large number of vacancies in the (Na + Gd) sublattice. The range of congruent melting is determined for this compound, and its homogeneity range is estimated to extend (on the scale of atomic concentration ratios Gd/Na) at least from 1.10 to 1.75. It is found that the microhardness of sodium– gadolinium molybdate crystals is significantly anisotropic, whereas the degree of crack resistance anisotropy does not exceed the measurement error. At the same time, neither microhardness nor crack resistance exhibit any significant dependence on the growth charge composition and the synthesis conditions in the investigated range of variation in these parameters.

Samples of a SiC composite with an oxide additive of eutectic composition produced from the organomagnesiumoxane-yttriumoxane-alumoxane oligomer (OMYA) and multi-walled carbon nanotubes (MWCNTs) were prepared by the spark plasma sintering (SPS). It is shown that the combined introduction of an oxide additive derived from OMYA together with MWCNTs significantly increases the fracture toughness and strength of the composite.

In the framework of the large hadron collider (LHC) upgrade project, new materials are proposed for the vacuum. Amorphous carbon deposited onto the vacuum-chamber wall is examined as a coating with a low secondary electron emission rate for superconducting systems designed to upgrade the LHC, i.e., to increase the luminosity of the machine (HL-LHC). Since protons will generate synchrotron radiation with a critical energy of ~10 eV and a flux of 1016 photon m–1 s–1, it is important to study the effect of photons on a surface covered with amorphous carbon at room and cryogenic temperatures. The construction and parameters of the setup on the new synchrotron beamline of the VEPP-2000 booster are described. The first results of measuring the photodesorption coefficient are also presented.

Metal–polymer nanocomposite polyvinyltriazole–silver nanoparticles were obtained using one-pot synthesis in irradiated aqueous solutions of 1-vinyl-1,2,4-triazole (VT) and silver ions. Gel permeation chromatography data show that upon radiation initiation, the molecular weight of poly(1-vinyl-1,2,4-triazole) increases with increasing monomer concentration. To study the kinetics of polymerization and the features of the radiation–chemical formation of nanoparticles, UV-Vis spectroscopy was used. TEM images show a relatively small average size of the forming nanoparticles (2–3 nm) and a narrow size distribution, which shows the effective stabilization of nanoparticles by triazole substituents at a molar ratio of VT and silver ions of 25/1. The addition of ethyl alcohol was used to increase the efficiency of synthesis and suppress the crosslinking of macromolecules in solution. The results of the work show that aqueous–alcoholic solutions of 1 wt.% VT can be used to obtain soluble nanocomposite materials. 10 wt.% monomer solutions have prospects for use in the preparation of polymer gels filled with nanoparticles.

Three NaGd(WO4)2 single crystals were grown by the Czochralski method using charges of different chemical purity. The impurity compositions of the grown crystals were analyzed by inductively coupled plasma mass spectrometry. The optical absorption spectra of the crystals were measured, and the effect of uncontrollable impurities on their optical properties and color was analyzed. The green color encountered in NaGd(WO4)2 crystals in some cases was shown to be due to the uncontrollable impurities of d elements, among which the chromium impurity had the most significant effect.

The features of obtaining coatings on carbon steel, structural steel St3 are studied during diffusion metallization – simultaneous saturation of steel with boron, chromium and aluminum (boron chromium aluminizing), without the use of special heat treatment. The basic compositions of powder mixtures are established using the simplex lattice method, which make it possible to obtain boride structures of increased hardness, phases of a solid solution of boron, chromium and aluminum in Feα and the predicted depth of the surface layer on the surface of carbon steel. The characteristic features of the microhardness formation of the surface layer of coatings are established depending on the composition of the saturating mixture. An important factor is established for the effect of aluminum on the microhardness of the surface layer in multicomponent systems. Its presence contributes to the formation of solid solutions. New data are obtained on the formation of surface layers during steel saturation with boron, chromium and aluminum, and the conditions for obtaining layers of high hardness and high ductility are determined. The optimal areas for the formation of coatings of various structures and depths by the simplex planning method are found. As optimization factors, let’s use the relative planes occupied by borides and solid solution, as well as the depth of the surface layers. It is clearly shown how the structure of surface layers changes depending on the quantitative relations between the components of saturating mixtures. The graphical dependences of the boride phase, the phase of the solid solution and the depth of the layer, on the composition of the saturating mixture during diffusion metallization (boron chromium aluminizing) allow to improve the process in order to obtain coatings with increased wear resistance on the surface of carbon steel

High-resolution low-temperature absorption spectra in the region of the 5I8 → 5I7, 6, 5, 4, 5F5 transitions in impurity Ho3+ ions in synthetic forsterite crystals (Mg2SiO4) are recorded. Comparison of the observed shape of the spectral lines with the hyperfine structure calculated using crystal-field theory makes it possible to attribute the spectral lines to single centers and dimers for the first time.

The process of outflow of a vapor–gas mixture (pressurization gas and vapors of fuel components) into an underpressure medium has been considered by using the ideal gas model. Basic assumptions and limitations for theoretical and experimental modeling are given, in particular, for the gas temperature and pressure in the course of experiments. A mathematical and a physical models have been developed, and closely coinciding numerical and experimental results have been obtained within the framework of the introduced assumptions and limitations. The results obtained confirm the validity of the models developed.

A structural computer simulation of ytterbium-containing forsterite crystals has been carried out. Atomistic simulation is performed using the GULP 4.1 software package (General Utility Lattice Program). Different mechanisms of ytterbium dissolution in forsterite crystals are considered, and the dissolution energies of isolated defects, as well as charged and neutral clusters of various configurations, are calculated. The results of the calculation manifest that the formation of ytterbium clusters with a magnesium vacancy gives a significant gain in the dissolution energy. The formation of neutral clusters (dimers) in the M1 site (YbMg1νMg1YbMg1) leads to an energy reduction by 1.7 eV compared with the statistical distribution of defects. As a result of simulation, it is shown the energetic substantiation of the formation of ytterbium dimers in forsterite crystals. A model of the most energetically favorable center in the M1 site is proposed—a dimer, consisting of a pair of trivalent ytterbium ions with a magnesium vacancy between them, forming a chain parallel to the crystallographic axis c.

Simulation of the solid solutions in the system of double sodium–gadolinium and sodium–europium molybdates, which are promising matrices for solid state lasers and phosphors has been carried out by the method of interatomic potentials. Two types of solid solutions have been studied, one of which contains finite components corresponding to the stoichiometric NaGd(MoO4)2–NaEu(MoO4)2 compositions with statistical distribution of cations in the crystal lattice. Another object is a cation-deficient Na2Gd4(MoO4)7–Na2Eu4(MoO4)7 system, in which we have examined the variants of statistical distribution and partial ordering of cations over structural positions. Atomistic simulation has been performed using the GULP 4.0.1 software package (General Utility Lattice Program). It is shown that when we pass from sodium-gadolinium molybdate to sodium-europium molybdate, both of stoichiometric and cation-deficient compositions, an increase in the unit cell volume is observed, while the density of the crystal, the energy of interatomic interactions in the structure, the vibrational entropy and the heat capacity decrease along with increasing europium content. The energy of interatomic interactions in the structure for cation-deficient solid solutions is less than for stoichiometric ones. Other aforementioned characteristics for cation-deficient solid solutions have greater values than for stoichiometric ones. The role of cluster europium centers in concentration quenching in NaGd(MoO4)2–NaEu(MoO4)2 solid solutions has been examined.

A well-resolved hyperfine structure in optical spectra of holmium-doped synthetic forsterite Mg2SiO4 has been detected for the first time. Crystal-field calculations have been performed for single centers of impurity Ho3+ ions and dimers in forsterite Mg2SiO4.

The electron paramagnetic resonance spectra of impurity trivalent erbium ions in synthetic forsterite single crystals (Mg2SiO4) have been studied by the electron paramagnetic resonance method in the X and Q frequency bands. It is found that erbium ions predominantly substitute for magnesium ions in crystallographic position M1 that is characterized by the inversion symmetry of the crystal field. In this case, a pronounced effect of dimer self-organization of erbium ions during the crystal growth takes place; the effect is manifested in the fact that the concentration of erbium dimer associates consisting of two closely spaced ions bound by the spin– spin interaction is several orders of magnitude higher than the concentration of dimer associates that form randomly at a statistical distribution of impurity ions in the forsterite crystal lattice. The directions of the main magnetic axes and the parameters of the effective spin Hamiltonian describing the magnetic characteristics of impurity erbium centers have been determined.

Different versions of quantum cutting mechanisms in Yb doped Scheelite-like molybdate and tungstate single crystals were studied, with participation of various schemes of donor-acceptor interaction (various kinds of donor centres: self-trapped excitons at molybdate/tungstate complexes; high-lying excited states of Yb3+ ion; Yb2+ ion; traps based on cation and oxygen vacancies; accidental impurities.). All the versions were rejected.

Monoclinic Yb3+,Li+:ZnWO 4 crystals were grown by Czochralski and their structure is refined. The spectroscopic properties of Yb3+ ions were studied with polarized light and the scheme of Stark splitting of Yb3+ manifolds in these crystals was determined. The Raman spectra were measured. A diode-pumped 2.90 W laser action at 1059 nm in the crystals was demonstrated

The content of all matrix elements, including oxygen, was determined by X-ray spectral microanalysis in series of single crystals of sodium-gadolinium molybdates (NGM) grown from melt by Czochralski technique. All grown NGM crystals, including those grown from stoichiometric charge, are non-stoichiometric and contain a molybdenum deficiency of about 3% in average. The NGM congruently melting composition has been determined. For crystals grown from melt of equimolar (stoichiometric) composition, the content of cationic vacancies in the (Gd + Na) sublattice is close to zero, while the composition of crystal differs from the initial melt. As the Gd excess increases, the content of cationic vacancies in the (Gd + Na) sublattice increases up to 10%. It has been found that cation-deficient NGM crystals are also anion-deficient. The concentration of oxygen vacancies varies from 0.5 to 5% of the amount of anion sites. Possible mechanisms responsible for the formation of cationic and anionic vacancies in NGM crystals are discussed.

A conceptual approach to improve the safety of rocket-space activity is presented, including minimization of space debris returning from space. The main idea is to eliminate hazards of uncontrolled re-entry of detachable rocket design elements after finishing their mission with the use of the energy of pyrotechnic thermite reaction to disrupt these parts made of composite polymeric material, i.e., carbon fiber reinforced polymer. As an example, the payload fairing half is considered, the conditions for its descent in dense layers of the atmosphere are calculated. Results reveal that depending on the entrance velocity, the target object or completely burn out, or the additional heat source is required for its full destruction. It is proposed that pyrotechnic composition to be installed on the object could serve as additional heat source to provide its combustion or fine dispersion during the atmospheric re-entry phase of the descent trajectory. The possible pyrotechnic compositions to be used are presented and discussed.

Crystals of ferroelectric‒ferroelastic gadolinium molybdate Gd2(MoO4)3, calcium molybdate CaMoO4, and double sodium‒gadolinium molybdates of stoichiometric (Na1/2Gd1/2MoO4) and cationdeficient (Na2/7Gd4/7MoO4) compositions, which are used to design solid-state lasers, phosphors, and white LEDs, have been simulated by the interatomic potential method. Their structural, mechanical, and thermodynamic properties are calculated using a unified system of interatomic potentials and effective ion charges, which demonstrated transferability and made it possible not only to describe the existing experimental data but also to predict some important physical and thermodynamic properties of molybdate crystals. The influence of the deviation from stoichiometry and partial ordering of cations on sites in nonstoichiometric crystals on the properties and local structure of sodium‒gadolinium molybdates is discussed.

Thermal conductivities of MWO4 (M = Ca, Cd, or Ba), NaGd(WO4)2:1 at % Er, NaGd(WO4)2:2 at % Yb, and NaLa0.5Gd0.5(WO4)2:2 at % Nd single crystals have been experimentally investigated in the temperature range of 50–300 K.

Concentration series of disordered scheelitelike Yb:NaGd(MoO4)2 and Yb:NaLa(MoO4)2 single crystals are grown by the Czochralski method. The actual concentrations of Yb3+ ions in the crystals are determined by optical-absorption spectroscopy. The luminescence of Yb3+ ions in these crystals in the region of 1 μm is studied under UV and IR excitation. In the case of UV excitation, this luminescence appears as a result of nonradiative excited state energy transfer from donor centers of unknown nature to ytterbium. The character of the concentration dependence of Yb3+ luminescence indicates that the energy transfer at high Yb concentrations occurs with active participation of a cooperative mechanism, according to which the excitation energy of one donor center is transferred simultaneously to two Yb3+ ions. In other words, the quantum yield of this transfer exceeds unity, which can be used to increase the efficiency of crystalline silicon (c-Si) solar cells.

Paramagnetic centers formed by impurity Yb3+ ions in synthetic forsterite (Mg2SiO4) grown by the Czochralski technique are studied by X-band CW and pulsed EPR spectroscopy. These centers are single ions substituting magnesium in two different crystallographic positions denoted М1 and М2, and dimer associates formed by two Yb3+ ions in nearby positions М1. It is established that there is a pronounced mechanism favoring self-organization of ytterbium ions in dimer associates during the crystal growth, and the mechanism of the spin–spin coupling between ytterbium ions in the associate has predominantly a dipole–dipole character, which makes it possible to control the energy of the spin–spin interaction by changing the orientation of the external magnetic field. The structural computer simulation of cluster ytterbium centers in forsterite crystals is carried out by the method of interatomic potentials using the GULP 4.0.1 code (General Utility Lattice Program). It is established that the formation of dimer associates in the form of a chain parallel to the crystallographic axis consisting of two ytterbium ions with a magnesium vacancy between them is the most energetically favorable for ytterbium ions substituting magnesium in the position М1.

The evolution dynamics of Cr 4+ , Cr 3+ and Cr 2+ contents in chromium doped forsterite (Cr: Mg 2 SiO 4 ) laser crystals during their prolonged high-temperature multi-stage oxidizing annealing have been investigated for the samples grown by Czochralski in ‘standard’ slightly oxidizing atmosphere (Ar +2,2 vol% O 2 ), as well as in inert atmosphere (argon, the residual O 2 content is 0,01 vol%). The contents of Cr 4+ increase by factor of 1,5–3 during the first 800–1000 h of the annealing and then do not change substantially. Cr 2+ practically disappears from the crystals within 800–900 h of the annealing. The content of Cr 3+ passes through a maximum during the annealing. Therefore, this content is determined by two parallel reactions: Cr 2+ →Cr 3+ and Cr 3+ →Cr 4+ .

Crystals of sodium–gadolinium molybdates of two compositions: stoichiometric (Na1/2Gd1/2MoO4) and cation-deficient (Na2/7Gd4/7MoO4) composition in which 1/7 of the corresponding cation positions are not occupied are simulated by the method of interatomic potentials. For cation-deficient crystals, two kinds of cation position distribution are considered: the statistical distribution of sodium, gadolinium, and unoccupied cation positions in the I41/a structure and their partial ordering in the I space group. As a result of the simulation, structural characteristics of sodium–gadolinium molybdates agreeing well with the known experimental data are obtained. In addition, a number of important elastic and thermodynamic properties of these compounds are predicted. The results obtained in the partial-occupancy approximation and by constructing a 7 × 2 × 2 supercell are compared. The local structure of sodium–gadolinium molybdates are analyzed in detail. The influence of the deviation from the stoichiometry as well as cation ordering on the properties of these crystals is discussed.

Gadolinium molybdate Gd2(MoO4)3 orthorhombic ferroelectric ferroelastic (β'-phase) is simulated by the method of interatomic potentials. The simulation is performed using the GULP 4.0.1 code (General Utility Lattice Program), which is based on the minimization of the energy of the crystal structure. Parameters of the gadolinium–oxygen interatomic interaction potentials are determined by fitting to the experimental structural data and elastic constants by a procedure available in the GULP code. Atomistic modeling using the effective atomic charges and the system of interatomic potentials made it possible to obtain reasonable estimates of structural parameters, atomic coordinates, and the most important physical, mechanical, and thermodynamic properties of these crystals. Temperature dependences of the heat capacity and vibrational entropy of the crystal are obtained. The calculated parameters of gadolinium–oxygen interaction potentials can be used to simulate more complex gadolinium-containing compounds.

Articles for technical use made from twisted aluminum oxide yarns are promising for application in various areas of industry. With the aim of improving the characteristics of the mechanical properties, multifilament yarns are twisted with the needed number of plies. We used a full factorial experimental design to obtain a regression equation reflecting the dependence of the yarn elongation under tension up to break vs. twists for yarns of linear density 10 tex into two plies and then five plies. The study results show that by varying the degree of the first and subsequent twists, we can change the elongation under tension up to break of twisted aluminum oxide yarns in certain ranges.

Three NaGd(WO 4 ) 2 single crystals have been grown by Czochralski technique using the initial chemicals with different purity. The optical absorption spectra of the crystals, as well as their impurity compositions have been measured. The possible reasons of the addition coloration of these crystals have been analyzed.

The paper discusses the potential of several Yb-doped scheelite-like double tungstate crystals for sunlight down-conversion. Four hosts NaY(WO4)2, NaY1/2Gd1/2(WO4)2, NaY2/3Gd1/3(WO4)2, and NaY(Mo1/2W1/2O4)2 with the same 10% at. Yb doping level were comparatively investigated. Besides that, the effect of increase the Yb concentration from 10 at.% to 15 at.% was checked in case of NaY(WO4)2 crystal host. The efficient ytterbium 900-nm broadband emission was obtained under ultraviolet excitation, despite the absence of Yb absorption lines in this range. This happens due to non-radiative energy transfer from donor centers of the hosts to Yb active ions. This absorption wavelengths range of the host can be tuned by changing the crystal chemical composition. The obtained results indicate that the family of Yb-doped scheelite-like double tungstates is a suitable candidate for developing down-converter materials for solar energy applications.

This paper presents the results of an experimental study of the parameters of nitrogen, argon and helium plasma obtained in high-frequency capacitive ring discharge at a pressure of 35 Pa. The parameters were determined by a single Langmuir probe. Work is being carried out as part of a project to develop a backlash ion microwave plasma generator. The object of study is ionized gas formed in the ring capacitance gap of a microwave solid-state generator emitter on the MOSFET transistor MRF284. The power consumed by the microwave generator in the study is no more than 5 W. The work resulted in getting the volt-ampere characteristics of a high-frequency discharge in low-pressure gas and determining the main plasma parameters.

The specific features of the EPR spectra of Tm3+ impurity ions in synthetic forsterite have been studied by continuous-wave EPR spectroscopy in the frequency range of 270–310 GHz at a temperature of 4.2 K in weak magnetic fields. Narrow resonance signals unrelated to the modulation of the resonance conditions of EPR under the modulation of the external magnetic field have been discovered in measurements at frequencies corresponding to the zero field splitting between the ground and first excited singlet electron states of Tm3+ ions in zero magnetic field. The origin of these narrow lines is discussed.

Cathode catalysts for a hydrogen–oxygen fuel cell (FC) with proton-conducting (acidic) and anion-conducting (alkaline) electrolytes are synthesized via the pyrolysis of nitrogen-containing iron and cobalt complexes on the surfaces of highly disperse carbon materials. The catalysts are characterized by X-ray photoelectron spectroscopy (XPS) and tested under model conditions on a thin-layer disk electrode and as a part of a membrane electrode assembly of hydrogen–oxygen FCs. The properties of the CoFe/C system formed via the pyrolysis of macroheterocyclic cobalt and iron compounds on carbon materials (XC-72 soot and multiwall nanotubes (MNTs)) are described for the first time. According to XPS data, the surface of the CoFe/C catalytic systems is enriched with carbon (95.5 at %) and contains nitrogen (2 at %), oxygen (2 at %), and metals (0.5 at %). According to the results from electrochemical measurements under model conditions, the CoFe/MNT catalytic systems approaches 60% Pt/C (HiSPEC9100) commercial platinum catalyst according to their activity in the oxygen reduction reaction in an alkaline medium (0.5 M KOH). The half-wave potentials are 0.85 and 0.88 V for CoFe/MNT and 60% Pt/C (HiSPEC9100) catalysts, respectively. The maximum specific powers of hydrogen–oxygen FCs with anion-conducting electrolytes are 210 mW/cm2 (60% Pt/C (HiSPEC9100) based cathode) and 180 mW/cm2 (CoFe/MNT based cathode). The characteristics of a membrane electrode assembly with a non-platinum cathode correspond to the best analogs described in the literature. The results of this work show the prospects for further studies on scaling this technology for the synthesis of the proposed non-platinum cathode catalysts and optimizing the architecture of the membrane electrode assembly of FCs based on them.

The method of spark plasma sintering is used to obtain an α-Al2O3-based nanocomposite reinforced with many-walled carbon nanotubes in amounts up to 50 vol.%. A mathematical model is constructed to describe the change in porosity during the sintering operation. The model accounts for the physico-chemical essence of the processes which take place during spark plasma sintering. Results obtained from experimental studies and mathematical modeling are used to determine the optimum sintering regime, which makes it possible to obtain a composite that has zero porosity and a carbon-nanotube content up to 50 vol.%.

Composite materials based on the Al2O3–MgO system reinforced with multiwalled carbon nanotubes (MWCNTs) were fabricated by vacuum sintering and hot pressing. The ceramic matrices were represented by corundum Al2O3 ceramic with the addition of 0.25 wt % MgO and magnesium aluminate spinel MgAl2O4. The prepared composites based on corundum and magnesium aluminate spinel containing MWCNTs were investigated by optical microscopy and scanning electron microscopy, and their microhardness and fracture toughness were studied. The samples are a densely sintered matrix with the average crystallite size of 3–5 μm with MWCNTs distributed uniformly on grain boundaries forming a reticular carcass. The samples of the Al2O3–MgO composite with 8 vol % MWCNTs demonstrated the flexural strength and fracture toughness two times higher as compared to the initial ceramic material (Al2O3 + 0.25% MgO).

The composition of microparts of sodium-gadolinium molybdate crystals, grown by the Czochralski method in different atmospheres from stoichiometric ((Na0.5Gd0.5)MoO4; group I) and nonstoichiometric ((Na2/7Gd4/71/7)MoO4 (II.1) and (Na6/15Gd8/151/15)MoO4 (II.2); group II) initial charge compositions (where = vacancies), was refined by X-ray diffraction analysis. All the crystals under investigation were found to crystallize in the space group I41/a without any signs of structural modulation and the refined crystal compositions were different from the initial charge compositions. Crystals from group I had a gadolinium excess and sodium deficiency without vacancies in the dodecahedral site. Vacancies were found in the Mo and O sites of the structure of the dark-gray micropart of the crystal grown in an Ar atmosphere, with the composition of the near-colorless micropart of the same crystal being close to stoichiometry. Microparts of the crystals from group II contain vacancies in both cation sites in (Na0.348(8)Gd0.5280.124)(Mo6+0.996(3)0.004)O4 (II.1) and in the dodecahedral and oxygen sites in (Na0.300(8)Gd0.5760.124)Mo6+(O3.880(10)0.120) (II.2). It was revealed that an additional annealing in air of the crystals grown in a slightly oxidizing atmosphere reduces the oxygen vacancies content. The possibility of growing crystals with an ordered structure depending on the ratio of the formula coefficients of components in the dodecahedral site of scheelite structure is thus discussed herein.

A regression equation that takes account of the dependence of imbalance of yarns with a 100 tex linear density on the first and second twist into two and then five strands, respectively, was derived by full factorial experiment. The optimum twists were obtained by evolutionary planning.

Atomistic modeling of europium-containing scheelite-like molybdates promising for use in solid-state lighting is performed. The analysis of local structure of the nearest environment of europium ion in the powellite-based solid solutions, namely Ca2(MoO4)2 – Eu2(MoO4)3 and Ca2(MoO4)2 – NaEu(MoO4)2, has been accomplished. The similar analysis was also performed for solid solutions based on double molybdates of both stoichiometric NaGd(MoO4)2 – NaEu(MoO4)2 and cation-deficient Na2Gd4(MoO4)7 – Na2Eu4(MoO4)7 compositions. The comparison of the local structures has been implemented at equal content of europium replaced ∼ 5% of “calcium” sites. It is shown that the symmetry of the cation site occupied by europium in all the studied solid solutions decreases compared to the symmetry of this site in the scheelite structure. The nearest distance between the europium ions is 3.90–4.01 A. It is shown that the multivariate environment of the activator ion in the double molybdates causes a strong dispersion of interatomic distances Eu-O. It is found that these changes lead to a strong distortion of the oxygen polyhedra EuO8 holding the relative proximity of their average size. The latter circumstance may explain the observed by spectroscopic studies the existence of single center of europium in these complex systems.

This paper presents the results of an experimental study of the velocity of ionized nitrogen flowing from the working chamber of an experimental sample of the primary accelerating system of the ion engine into the vacuum space. The main method of research was chosen calorimetric method. The design of a small spacecraft jet propulsion system with ionized gas acceleration in the high-frequency gap of a microwave generator is proposed. The object of the study is a prototype of the primary ion engine accelerator system with a solid-state microwave plasma generator and an accelerating gap. The study showed that a 3-watt microwave generator together with a pulsed voltage source of an accelerating potential difference of 1 W at a nitrogen consumption of 2.5 mg/s creates an ion jet whose speed reaches 30 km/s.the Current of the ion jet was 2-2.5 mkA. The field strength of the accelerating potential difference was 4450 V / m.

Downconversion properties of a number of Ybdoped Scheelite-like molybdate and tungstate single crystals have been investigated. The efficient non-radiative excited state energy transfer from donor centres to Yb ions was observed. At high Yb concentrations a substantial part of this transfer runs by cooperative mechanism, that can be used for increase the efficiency of solar cells based on crystalline silicon.

The series of Cr:Mg 2 SiO 4 laser crystals grown from non-stoichiometric melts has been studied. According to the polarized optical absorption spectra, the content of Cr4+ ions in the crystals increases with increment of MgO excess in the melt, whereas the concentration of parasitic Cr3+ ions passes through a maximum in this series.

A series of NaGd(MoO4)2 single crystals doped with various Yb3+ concentrations (from 0.5 to 30 at %) is grown. The optical absorption spectra of the crystals are measured within the range from 800 to 1200 nm and used to calculate the actual concentrations of Yb in the samples. The luminescence of crystals is studied under UV excitation. It is found that there exist two types of active centers that are not directly related to Yb3+ ions and exhibit broadband luminescence in the visible spectral region. In addition, UV excitation of crystal gives rise to Yb3+ luminescence in the region of 1 μm owing to nonradiative excited-state energy transfer from, probably, donor centers of the host to ytterbium. The character of the dependence of the UV-excited luminescence of Yb on its concentration in the samples, in comparison with the corresponding dependence measured under IR excitation, points to the occurrence of cooperative down-conversion in crystals with high ytterbium concentrations, which means that the excited-state energy of donors is simultaneously transferred to two Yb3+ ions. In other words, excitations are multiplied; i.e., the quantum yield of this down-conversion exceeds unity.

The melt structure evolution under the action of the low-frequency axial vibration control (AVC) technique was studied in situ by Raman spectroscopy for several complex chemical compound melts: sodium nitrate, margarine acid, paraffin mixture (C 17 -C 20 ). The measurements were conducted in the temperature range from the melting point up to 60 °C above. Comparison of crystallization heats for AVC activated and steady melts with melting heats of AVC-CZ and conventional CZ produced powders allowed to propose the energy diagram of NaNO 3 states for activated and non-activated melts and crystals based on DTA, XRD, DSC and Raman experimental data.

A nanocomposite based on corundum ceramic containing multiwall carbon nanotubes (to 50% by volume) as reinforcement was obtained by spark plasma sintering. The structure of the obtained material was investigated by means of optical and electronic microscopy. The elastic modulus and cracking resistance were measured and found to be three times greater than the corresponding values for pure aluminum oxide.