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Heat exchange of silicon carbide samples in subsonic air, nitrogen and carbon dioxide plasma jets of the VGU-4 HF-plasmatron has been investigated. A significant influence of the chemical composition of the dissociated gas flow on the material behavior was revealed. The macro- and microstructure of the samples surface was analyzed, the phase composition before and after exposure was studied. The emissivity of the samples surface was investigated. Numerical modeling of the experimental modes using author's codes based on Navier–Stokes equations was carried out. The values of the effective recombination coefficient of atoms and molecules γw on the material surface were obtained. Probe measurements of heat fluxes and dynamic pressures for the modes of the experiments were performed. [ABSTRACT FROM AUTHOR]

The effects of subsonic plasma flows of carbon dioxide and pure nitrogen combined with additional laser irradiation on silicon carbide material were investigated. Silicon carbide samples were exposed to temperatures from 1480 to 1620°C (in the carbon dioxide plasma flow) and from 1600 to 1960°C (in the pure nitrogen plasma flow) at a constant pressure in the test chamber of 1 × 104 Pa and gas mass flow rate of 2.4 g/s. Significant differences in the heat transfer and behavior of the samples were observed depending on the plasma composition. The microstructure and surface profiles of the samples before and after different exposures were compared. Surface peculiarities were detected in the areas where the maximum laser irradiation intensity was applied. [ABSTRACT FROM AUTHOR]

The adsorption, temperature-programmed desorption, and carbonylation of dimethyl ether (DME) in the presence of mordenite and ferrierite (SiO2/Al2O3 ≈ 20, Zeolyst International) is studied. The effect of introducing Cu, Co, and Mg cations by ion exchange is discussed. Dimethyl ether carbonylation is conducted at 200°С, a pressure of 3 MPa, and a space velocity of 8000 mL g–1 h–1 in the following mixture (vol %): DME, ⁓2.2; CO, 92.8–95.5; and the rest, N2. After an induction period, the methyl acetate content in the presence of mordenite is about 4–5 times higher than that in the presence of ferrierite. Water, methanol, and hydrocarbons are formed in trace amounts. The introduction of Cu, Co, and Mg cations into mordenite by ion exchange (single ion-exchange run, cation/Al ratio of no more than 35%) leads to an increase not only in stability, but also in activity in the DME carbonylation reaction. It is found that an increase in the content of copper (from 1.19 to 2.23 wt %) and magnesium (from 0.62 to 1.8 wt %) has different effects on activity. It increases in the case of copper and decreases in the case of magnesium. The prereduction of a copper-exchanged mordenite leads to the appearance of metallic copper particles on the surface of the mordenite crystallites and a decrease in activity. According to in situ diffuse reflectance infrared spectroscopy, the introduction of magnesium cations by three ion-exchange runs leads to a significant decrease in the number of Brønsted acid sites (BASes) in both the 12-MR and 8-MR channels of the mordenite. The catalytic characteristics of ferrierite hardly change upon the introduction of copper and magnesium by ion exchange. [ABSTRACT FROM AUTHOR]

The heat transfer to a cylindrical water-cooled copper model was experimentally investigated in an induction VGU-4 high-frequency (HF) plasmatron of the Institute for Problems in Mechanics of the Russian Academy of Sciences. The model, 30 mm in diameter, equipped with a calorimetric transducer with a heat-adsorbing graphite surface, 13.8 mm in diameter, was exposed to the surface heating in the combined regime by nitrogen plasma and laser radiation and in the cases of the heating with only laser radiation or a nitrogen plasma jet. The experiments in the HF-plasmatron jets were performed at the pressure in the setup low-pressure chamber p = 1 × 104 Pa, nitrogen mass flow rate G = 2.4 g/s, and the plasmatron HF-generator anode power Na.p. = 22 kW. It is established that in the chosen experimental regimes the dissociated-nitrogen jet and the high-frequency induction discharge do not produce a considerable effect on the laser beam passing through them. The values of the heat flux density are obtained as functions of the laser radiation power delivered. The subsonic nitrogen plasma flow in the quartz discharge channel and in the low-pressure chamber of the VGU-4 setup is numerically modeled under the experimental conditions basing on the solution of the complete Navier–Stokes equations using the Patankar–Spalding method. [ABSTRACT FROM AUTHOR]

The existing ideas on the status of the Navier-Stokes equations are changed in taking into account the following facts: generally speaking, the terms of these equations neglected in the boundary layer equations are of the order of certain Burnett terms in the conservation equations; the Navier-Stokes equations cannot be used to describe slow nonisothermal gas flows since in this case it is necessary to take the Burnett temperature stresses into account; and in the transport relations the Burnett terms determine certain effects (for example, the mechanocaloric effect). [ABSTRACT FROM AUTHOR]

The physicochemical and catalytic (CO2 hydrogenation) characteristics of Mo-containing catalysts were studied. The catalysts containing 8 and 15 wt % Mo oxide were prepared by impregnation of γ‑Al2O3 with ammonium paramolybdate, followed by drying and calcination at 500°C. The introduction of Mo oxide reduced the pore volume of the support and increased the average pore size, indicating that molybdenum oxide was distributed in the support pores. According to the X-ray diffraction analysis, the calcinated catalyst did not contain the crystalline MoO3 phase. According to the Raman spectra, oxygen-containing formations were present on the catalyst surface, with Mo atoms tetrahedrally and octahedrally coordinated to the oxygen atoms. The impregnated MoO3 was partially reduced with hydrogen during linear heating, starting from 320°C. The hydrogenation of CO2 (gas composition, vol %: 30.7 CO2, 68 H2, the rest was N2; 0.5 g sample) was studied under conditions of linear heating to 400°C. The main reaction was the reverse reaction of CO steam reforming. The contribution of methanation to CO2 hydrogenation was small. An increase in the temperature and pressure had a positive effect on CO2 conversion. When the pressure increased from 1 to 5 MPa, the CO content was approximately doubled. In the CO2 hydrogenation, appreciable activity (although significantly lower compared to that of Mo-containing catalysts) was also exhibited by γ-Al2O3, preliminarily heated to 400°C in an H2 flow. The activity of alumina also increased with pressure. [ABSTRACT FROM AUTHOR]

The results of calculating the shock wave structure in Ne–Ar, He–Ar, He–Ne, and He–Xe mixtures by means of the relaxation method on the basis of the system of Navier-Stokes equations and complete and modified systems of Burnett equations are compared with the results of direct statistical simulation (Monte-Carlo method). The domain of applicability of these systems of equations for calculating gas dynamic variable profiles is analyzed as a function of both the molecular mass ratio and the initialconcentrations. [ABSTRACT FROM AUTHOR]

Reduction of neutral metal clusters (Co4(CO)12, Ru3(CO)12, Fe3(CO)12, Ir4(CO)12, Rh6(CO)16, {CpMo(CO)3}2, {Mn(CO)5}2) by decamethylchromocene (Cp*2Cr) or sodium fluorenone ketyl in the presence of cryptand[2.2.2] and DB‐18‐crown‐6 was studied. Nine new salts with paramagnetic Cp*2Cr+, cryptand[2.2.2](Na+), and DB‐18‐crown‐6(Na+) cations and [Co6(CO)15]2– (1, 2), [Ru6(CO)18]2– (3–4) dianions, [Rh11(CO)23]3– (6) trianions, and new [Ir8(CO)18]2– (5) dianions were obtained and structurally characterized. The increase of nuclearity of clusters under reduction was shown. Fe3(CO)12 preserves the Fe3 core under reduction forming the [Fe3(CO)11]2– dianions in 7. The [CpMo(CO)3]2 and [Mn(CO)5]2 dimers dissociate under reduction forming mononuclear [CpMo(CO)3]– (8) and [Mn(CO)5]– (9) anions. In all anions the increase of negative charge on metal atoms shifts the bands attributed to carbonyl C–O stretching vibrations to smaller wavenumbers in agreement with the elongation of the C–O bonds in 1–9. In contrast, the M–C(CO) bonds are noticeably shortened at the reduction. Magnetic susceptibility of the salts with Cp*2Cr+ is defined by high spin Cp*2Cr+ (S = 3/2) species, whereas all obtained anionic metal clusters and mononuclear anions are diamagnetic. Rather weak magnetic coupling between S = 3/2 spins is observed with Weiss temperature from –1 to –11 K. That is explained by rather long distances between Cp*2Cr+ and the absence of effective π–π interaction between them except compound 7 showing the largest Weiss temperature of –11 K. The {DB‐18‐crown‐6(Na+)}2[Co6(CO)15]2– units in 2 are organized in infinite 1D chains through the coordination of carbonyl groups of the Co6 clusters to the Na+ ions and π–π stacking between benzo groups of the DB‐18‐crown‐6(Na+) cations. [ABSTRACT FROM AUTHOR]

The features of oxidation of ultra-high-temperature ceramic material HfB2-30 vol.%SiC modified with 1 vol.% graphene as a result of supersonic flow of dissociated CO2 (generated with the use of high-frequency induction plasmatron), as well as under the influence of combined heating by high-speed CO2 jets and ytterbium laser radiation, were studied for the first time. It was found that the addition of laser radiation leads to local heating of the central region from ~1750 to ~2000–2200 °C; the observed temperature difference between the central region and the periphery of ~300–550 °C did not lead to cracking and destruction of the sample. Oxidized surfaces and cross sections of HfB2-SiC-CG ceramics with and without laser heating were investigated using X-ray phase analysis, Raman spectroscopy and scanning electron microscopy with local elemental analysis. During oxidation by supersonic flow of dissociated CO2, a multilayer near-surface region similar to that formed under the influence of high-speed dissociated air flows was formed. An increase in surface temperature with the addition of laser heating from 1750–1790 to 2000–2200 °C (short term, within 2 min) led to a two to threefold increase in the thickness of the degraded near-surface area of ceramics from 165 to 380 microns. The experimental results indicate promising applications of ceramic materials based on HfB2-SiC as part of high-speed flying vehicles in planetary atmospheres predominantly composed of CO2 (e.g., Venus and Mars). [ABSTRACT FROM AUTHOR]

The nitrogen‐vacancy color center in diamond is one of the important systems in the fast‐growing field of sensing. This color center is used in both high‐resolution and high‐sensitivity sensors. However, techniques for the quick and efficient formation of NV centers are still in the development stage. Herein, a study on the influence of the electron irradiation dose on the conversion of substitutional nitrogen into NV− centers is presented. The study is done on diamonds that are highly enriched with nitrogen (≈100 ppm), which, on one hand, should maximize the effect of irradiation, and, on other hand, be of interest for high‐sensitivity magnetometers. The maximum achieved conversion efficiency is as high as 37% ± 3.7%, with no observed saturation on the electron dose even with the simplest annealing procedure. The measurements of the corresponding dephasing time made it possible to make a theoretical estimate for the shot‐noise‐limited magnetic field sensitivity per unit volume of diamond to be roughly ≈1×10−13T [Hz⋅mm−3]−1. [ABSTRACT FROM AUTHOR]

The necessary conditions of local simulation of the aerodynamic heating in subsonic high-enthalpy air jets on the megawatt VGU-3 HF-plasmatron are determined. The domain in the "enthalpy-stagnation pressure" coordinates and, respectively, the boundaries of the velocity and the altitude of entry into the atmosphere are found for a body with the nose bluntness radius of 1 m for which these conditions can be implemented when using models with the effective radius of 10–45 mm. The experimental data confirming the conclusions of theory that the range of heat fluxes to the catalytic surface of a standard water-cooled model on the VGU-3 facility is significantly extended as compared with the VGU-4 100 kW HF-plasmatron are given. [ABSTRACT FROM AUTHOR]

Chemical vapor deposition (CVD) along with thermal decomposition of monosilane (SiH4) in a fluidized bed of multiwalled carbon nanotubes (MWCNTs) is used to prepare MWCNT-Si composites containing silicon nanoparticles deposited on the nanotube surfaces. The structure of obtained Si nanoparticles in composites based on MWCNTs with different average diameters is studied by TEM, SEM, XRD, Raman spectroscopy, and FTIR spectroscopy of diffuse reflection. The size of Si particles varies from 3 nm to 45 nm and increases together with the MWCNT diameter. The major part of precipitated silica in the nanoparticles occurs in the amorphous state with small (below 3 nm in size) inclusions of nanocrystalline silicon. Specific discharge capacity of prepared composites used as the anode material for lithium-ion batteries is estimated. [ABSTRACT FROM AUTHOR]