The coatings with a thickness more than 100μm were formed on Zr-1% Nb alloy and technical pure Zr by plasma electrolytic oxidation (PEO) in silicate–hypophosphite electrolyte at asymmetric electrical ...mode. It was found that the PEO coating thickness on Zr-1% Nb alloy is about 30% more than that on zirconium. The barrier layer for Zr-1% Nb alloy is not regular and has metallic inclusions. For zirconium, barrier layer is uniform and dense. The plasmatron high-temperature cycling (up to 2000K) has shown that the coatings surface keeps original microstructure but its morphology becomes some rougher. The thermal conductivity of PEO coatings is several times less than the one of reference sample of yttria-stabilized zirconia.
•The alloying of zirconium with niobium accelerates the formation of PEO coatings.•The barrier layer of PEO coatings for Zr-Nb alloy is unregular and has metallic inclusions.•The high-temperature cyclic tests demonstrate good thermal resistance of PEO coatings.
The heavy ion facility for technological applications is developed at the Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences. The booster synchrotron with electron ...cooling is one of the main parts of the facility. This work presents the beam dynamics simulation with betatron coupling and nonlinearities of the guided magnetic field. The transverse betatron coupling excited by electron cooling solenoid was compensated by the pair of skew quadrupole triplets with antisymmetric supply and located symmetrically relative to the solenoid center. The calculation of the vertical dispersion excited by the magnetic field of toroidal sections of the electron cooler was performed. The accelerator lattice was optimized for minimization of vertical dispersion. Another important factor of the beam dynamics is the tune dependence versus momentum deviation called chromaticity. To correct chromaticity, sextupole magnets are applied. On the other hand, sextupoles excite nonlinear resonances that can lead to significant limitation of the dynamic aperture. The dynamic aperture of the synchrotron was simulated by scanning of horizontal and vertical tunes in conditions of chromaticity and betatron coupling suppression. This method makes it possible to identify dangerous resonances. According to the calculations presented, a scheme with application of six sextupole families are developed. This scheme makes it possible to significantly reduce the influence of most dangerous resonances. The wide area of tunes with a fairly large dynamic aperture for particles with required momentum spread was found in simulations. Selection of the operating point in this particular area makes it possible to reduce the space charge effect on the dynamic aperture. At the chosen operating point, the influence of eddy currents and magnetic fields nonlinearities on the dynamic aperture was investigated.
In this study, we investigated distribution parameters such as particle size, of both powder and metalpowder composite (MPC) forms of steel 20X23H18 with a fraction of less than 63 microns after ...plasma melting and centrifugal spraying of a rapidly rotating cast billet using the plasma rotate electrode process method. We have discussed the morphology (appearance) of the MPC particles with a fraction of less than 63 microns. The flowability, angle of repose (looseness), and relative and bulk densities of the MPC were determined, and the yield ratio of the MPC was calculated. The quality of steel grade 20X23H18 MPC with a fraction of less than 63 microns and its application in the manufacture of parts by the method of selective laser sintering are discussed.
Bimetallic oxygen reduction reaction (ORR) catalysts based on multi-walled carbon nanotubes (MWCNTs) doped with cobalt, copper, and nickel phthalocyanines and modified with silver (MWCNT–CoPc–Ag, ...MWCNT–CuPc–Ag, and WMCNT–NiPc–Ag) were obtained using high-temperature synthesis. The synthesis was carried out at 900°C in a nitrogen atmosphere. Scanning electron microscopy (SEM), low-temperature nitrogen adsorption–desorption, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (XRD) were used to determine the physicochemical properties of the synthesized catalysts. The effect of high-temperature synthesis on the textural and morphological properties of materials was also studied. It was shown that the physicochemical parameters of materials largely depend on the nature of the metal in the composition of original phthalocyanine. The electrocatalytic activity of the materials was studied by linear voltammetry in a three-electrode cell with a rotating disk electrode and mercury oxide reference electrode. The MWCNT–CoPc–Ag catalyst showed high electrocatalytic activity in ORR, comparable to that of a commercial platinum catalyst, as well as high corrosion resistance.
The results of studying the dynamic adsorption of phenol by activated carbon (AC) in fluid media of liquid, subcritical, and supercritical water (26°C and 0.1 MPa, 24–400°C and 25 MPa) and the ...subsequent regeneration of AC under similar conditions are presented. It is shown that the adsorption–desorption isotherms are characterized by the presence of a hysteresis loop. An increase in the pressure at room temperature leads to an increase in the adsorption capacity, while an increase in the temperature at 25 MPa leads to a decrease of that. The amount of phenol remaining in AC after regeneration decreases with an increase in the temperature and does not depend on the pressure. The average relative rate of phenol desorption increases sharply at
T
≥ 200°C. It is found that the largest increases in the specific surface area and pore volume are achieved when AC is treated with supercritical water.
This paper presents the results of a study of the catalytic activity of bimetallic materials synthesized based on Vulcan XC-72 carbon black modified with nickel, cobalt, and molybdenum in the ...electrochemical oxygen reduction reaction. The studies of the synthesized catalysts by adsorption–desorption of nitrogen in vacuum show that they are mesoporous and possess low porosity and surface area. After modification with metals, the surface area of the catalyst and pore volume decrease. The Raman spectra of the samples evidence probable formation of intermetallics or mixed molybdenum oxides on the surface of the MoCo/C and NiMo/C catalysts, which is in agreement with the published data. Scanning electron microscopy shows the formation of spherical metal parties on amorphous Vulcan XC-72. All the studied bimetallic catalysts possess similar kinetic characteristics of the electrochemical oxygen reduction reaction; nevertheless, NiMo/C and NiNi/C catalysts manifest a higher activity. The verification of the robustness of operation of the synthesized catalysts shows their high corrosion resistance.
This article presents the results of study of dibenzothiophene (DBT, the fuel equivalence ratio
φ
=
0.94
–1.01) oxidation in a medium of dense water vapor or argon at uniform heating (1 K/min) to ...853 K of a tubular reactor made of stainless steel. The oxidation of DBT was found to proceed by the mechanisms of heterogeneous and homogeneous reactions. From the dynamics of the temperature of the reaction mixtures it follows that self-ignition of DBT in an environment of water vapor and argon occurs at 532 K. A Pt-Rh/Pt thermocouple introduced into the center of the reaction volume was found to have a catalytic effect on DBT oxidation. The results of mass spectrometry analysis of gas products show that the degree of carbon burnout exceeds 95% mol. The interaction of stainless steel and H
2
SO
4
formed in the DBT oxidation in water vapor causes steel corrosion, which is suppressed due to neutralization of the acid by calcium carbonate. The composition of the corrosion products was determined by the X-ray diffraction and energy-dispersive analysis methods.
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► A new technique for brown coal conversion in supercritical water is suggested. ► At coal conversion high-grade solid, liquid, and gaseous fuels are produced. ► Products composition ...and degree of desulfurization of coal residue are obtained.
The new technique of usage of supercritical water (SCW) for brown coals conversion into both liquid (condensed), and solid and gas (volatile) fuels is proposed. The method consists in cyclic filling of SCW up to the given pressure (pressurization) into the tubular reactor, filled with coal particles, and fast discharging of conversion products dissolved in SCW (depressurization). The dynamics and composition of conversion products in a mode of stepwise temperature (310–460°C) and pressure (9–31MPa) rise at cyclic filling and discharging of, first, the water vapor (T<374°C), and then of SCW have been investigated. The vapor stage of conversion has prevented agglomeration of coal particles at the stage of SCW conversion. The maximum yield of the condensed products is obtained at 390°C, 29.0MPa. High heating value of combustible products of conversion and solid residue appeared to be much more than that of initial coal because of removal of a great bulk (up to 85.2%) of native oxygen as CO2. H/C atomic ratio in the volatile combustible and condensed products is much higher than in the conversion residue because of redistribution of native hydrogen in coal organic matter (COM). It has been established that sulfur is mainly removed from COM as H2S (up to 77.2%) and nitrogen is concentrated (up to 67.2%) in the solid conversion residue.
The paper deals with the gasification of thiophene in supercritical water (SCW) at a molar ratio of H2O:C4H4S = 1:0.107, a temperature of 873-1023 K, a pressure of 30 MPa, and a holding time of ...150-600 s in a batch reactor. The gases of CO2, CO, H2, CH4, and H2S were detected in the composition of SCW gasification products. The maximum degree of thiophene gasification (>99.9%) was achieved at 1023 K and 600 s. The conversion of thiophene in SCW is described by a pseudo-first-order macro kinetic equation. It was revealed that the oxidation of thiophene in H2O/O2 mixture at uniform heating of the reactor (1 K·min−1) begins at T ≈ 400 K. The lack of O2 results in the formation of soot. It is shown that the formation of sulfuric acid during the oxidation of thiophene in the H2O/O2 mixture causes corrosion of stainless steel.
Slow resonant extraction from the synchrotron makes it possible to provide relatively stable beams for a long time. The principle of slow extraction is intentionally exciting the third-order ...resonance by controlling detuning and sextupole strength with the gradual release of particles from inside to outside a stable separatrix. The Budker Institute of Nuclear Physics (BINP) develops the ion synchrotron for a wide range of technological applications. This paper describes slow resonant extraction from an ion synchrotron with betatron oscillation excitation by a transverse RF field.
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