Search

The comparative analysis of the kinetics of the bulk crystallization of AsSe1.5Bix glasses (х = 0, 0.01, and 0.05) in the temperature range 210–260°C is conducted by the data of density measurement using the generalized Kolmogorov–Avrami equation and the results of phase and differential thermal analysis. The kinetics of the surface crystallization of As2Se3 glass containing 0.4 at % Bi at 270 and 310°C and the parameters of the specific electrical conductivity and microhardness of the quenched semiconducting glass-ceramics at different stages of thermal treatment are studied.

Gas-filled neutron tubes generating pulses with specified parameters are needed for neutron well-logging. These parameters are affected most by the ion-pulse shape. The results of numerical modeling of the dynamics of the electron beam, secondary ions, and electrons generated in the volume of the Penning ion source with an electron emitter and their effect on the ion-pulse parameters are examined. The calculation was performed in an axisymmetric geometry with the aid of the KARAT software package. The physical processes occurring in the ion source and their influence on the growth of the ion current extracted from the plasma as a function of the maximum current of the injected electrons and the geometry of their source were analyzed. It was found that the steady-state ion current is independent of the electron current and is mostly due to the geometry and radius of the electron beam.

A comparative study of the kinetics of massive bulk crystallization of As2Se3, As1.9Se3, and As2.1Se3 bulk glasses at 240°C is performed using the Kolmogorov–Avrami model. A theoretical analysis of the experimental dependences of the linear growth rate of As2Se3 crystals on temperature and viscosity of the As2Se3 glass is performed. It is shown that the dislocation growth of crystals in the form of spherulites appears to be probable in the As2Se3 glass under overcooling at ∆T = 30–135°С. For individual lamellar crystals As2Se3 with dislocation-free faces inside the spherulites, a growth mechanism with surface two-dimensional nucleation (2Dsg model) appears to be probable at ∆T = 75–135°С.

A model is proposed for intensification of the process of high-temperature vacuum removal of iron impurities from microporous aluminum oxide via purging of the particle layer with argon. In the temperature range characteristic of this process, the pressure of saturating vapors above pure iron is on the order of 0.1 mm Hg. For an impurity with a concentration of several particles per million, the figure is proportionally smaller, and this creates problems with evacuation of the chamber. The use of argon as a carrier gas destroys the rigid connection between the partial vapor pressure of the impurity and the pressure in the vacuum chamber. Calculations show that the argon flow under moderate vacuum 10–5 mm Hg with a mass flow rate on the order of 10–7 kg/(m2 s) provides a very deep purification.

The parameters of the specific electroconductivity and electrode properties of massive glass and amorphous films of PbS–AgI–As2S3 and PbS–Ag2S–As2S3 are studied. It is established that the lower detection limit of Pb2+ cations is 10–7 mol/L for most of the studied membranes, while the Nernst region of the electrode function is 10–6–10–1 mol/L. The response time of the best film membranes Pb-ISE is 30–40 s in diluted solutions and 5–10 s in 0.01–0.1 M stirred solutions of Pb(NO3)2.

The authors present the results of numerical simulation of the kinetic processes in deuterium microwave-resonator plasmas with electron–cyclotron resonance at a nonuniform distribution of the magnetic and electric fields. For the actual configuration of the resonator module, the authors show the optimal magnetic field distribution in terms of energy efficiency. The solution of the kinetic scheme of the microwave discharge in deuterium plasmas makes it possible to relate the gas-discharge plasma properties with the parameters of the deuterium-ion source: the residual gas pressure, the gas flow into the microwave resonator, the charged particle flows on the wall and into the ion-optical system, the electrical and magnetic field strength and distribution in the resonator, and the power input into it. The results make it possible to reveal and implement generator operation modes with the highest characteristics ever recorded.

We have examined the feasibility of preparing high-purity aluminum oxide by oxidizing granulated aluminum in a 0.1 M potassium hydroxide solution, followed by heat and acid treatments of the oxidation products. The aluminum oxidation product, consisting of two phases of Al(OH)3 (bayerite and gibbsite), was first heat-treated at temperatures of 300, 600, 900, and 1200°C; then treated with hydrochloric acid; and calcined at a temperature of 1450°C. It has been shown that raising the preheat treatment temperature increases the total concentration of impurities, including Fe impurities, but reduces the concentration of alkali metals (K, Na, and Li). Using 99.7%-pure aluminum, we have prepared aluminum oxide with a purity at a level of 99.886%. Using 99.98%-pure aluminum, we have obtained aluminum oxide with a purity at a level of 99.993%.

The chemical purity of fused corundum was demonstrated experimentally to improve after high-temperature (~1750°C) vacuum (~10–5 mm Hg) roasting. Three industrial fused corundum samples with different particle-size and impurity profiles were heat treated, after which the impurity contents decreased by an order of magnitude. The samples were practically completely purified of Na, Mg, K, Mn, Cu, and Zn whereas the Fe content decreased by 8 – 10 times. Samples were found to consist of porous granules 16 – 60 μm in size that consisted of solid microparticles of characteristic size 0.4 – 0.7 μm. The specific surface area of the granules lay in the range 2.8 – 3.3 cm2/g.

Methods of measuring the density, microhardness, temperature dependence of conductivity, X‑ray analysis, and optical microscopy of the quenched samples are used to explore the kinetics and the mechanism of transformations during the bulk isothermal crystallization of AsSe1.5Рbx semiconducting glasses (х = 0, 0.025, 0.13) in the temperature range 210–340°С. The kinetics of the total bulk crystallization of glasses is analyzed according to the data of density measurements using the Kolmogorov–Avrami equation generalized for the stepwise and incomplete isothermal transformations.

The experiments were carried out to show that it was possible to raise the chemical purity of the electrically fused alumina powders by means of the high-temperature (about 1750 °C) vacuum (about 10–5 mm Hg) roasting. Three samples of the commercial fused corundum were heat-treated, the samples having different size grading and impurity composition, after the treatment the impurity level turned out to be ten times as less: the samples were almost completely cleared off Na, Mg, K, Mn, Cu and Zn impurities, the iron content decreased by the factor of 8‒10. It was determined that the samples were built up of the porous pellets of the size of 16‒60 microns, formed out of the solid micro-particles of the size of 0,4‒0,7 microns. The pellets' specific surface area was within the 2,8 and 3,3 cm/gram.

The results of numerical simulation of the microwave discharge kinetics in molecular deuterium in electron-cyclotron resonance mode are presented for a description of the physical processes in the resonator of a neutron generator. The calculations have been carried out in an approximation of homogeneous electric and magnetic fields, as well as the Maxwellian electron energy distribution function. In the kinetic scheme, the reactions of excitation, dissociation, ionization, and recombination of deuterium atoms and molecules, as well as elastic collisions, were taken into account. As a result, the time dependences of the number density and temperature of the plasma components at different electric and magnetic field intensities and the initial number density of molecular deuterium are obtained. The values of the fields corresponding to the minimum ionization time are determined, and the maximum ion current extracted from the microwave discharge is estimated.

The stability of double-layer supercapacitors with organic electrolyte and electrodes of activated charcoal is improved by optimizing the activation parameters of the material and also by its additional thermal treatment after the activation. The optimized modes of such pretreatment are shown.

Processes accompanying the electrodynamic acceleration of a thin plate liner at a high accelerating current density are investigated. In addition to determining the electrical characteristics, shadow filming of the plate profile was carried out during the acceleration and the deformation of the profile in the region of fixed attachment to the current leads was monitored. A new experimentally reproducible effect in which the plate splits into three separate fragments, which is explained by nonuniform overheating by the current of the plate’s cross section and the electrodynamics of the process, was found. It was detected that, on the acceleration of copper liners, the current sheath is separated from the metal body of the liner and diverges in two directions. The nature of this phenomenon has not yet been determined.

The kinetics and mechanism of stepwise transformations underlying the isothermal bulk crystallization of As2Se3Sn x (x = 0.26, 0.40, 0.55) semiconductor glasses in the temperature range 210–310°C have been studied using 119Sn Mossbauer spectroscopy, X-ray diffraction, density and electrical conductivity measurements, and microhardness tests. The results demonstrate that small particles of the primary phase SnSe initiate heterogeneous nucleation and two-dimensional growth of crystals of the secondary, major phase As2Se3.

Results of the numerical simulation of the formation of the ion beam in the accelerating gap of a vacuum neutron tube are presented. Calculations are performed with the KARAT code in a two-dimensional nonstationary formulation for plasma formed in arc discharge and inflowing into an accelerating gap with the given time dependences of parameters (density, expansion velocity). The small duration of the vacuum arc leads to a considerable change of parameters of inflowing plasma during the accelerating pulse. Two geometries are considered: the conventional and sectioned diode, in which the total voltage is divided between the anode, intermediate electrode, and cathode.

For supercapacitors with sulfuric acid electrolyte, a promising carbon material was suggested, namely, activated carbon from waste wood. It was shown how the synthesis conditions of activated carbon affect its porous structure and electrochemical characteristics of supercapacitors on its basis. The changes in the porous material under different synthesis conditions were controlled using the highly informative limited evaporation method, which allows us to obtain complete information about the porous structure of the micro- and mesopores of the material within a relatively short period of time. The negative effect of the excess volume of macropores in the electrode on the capacity and energy based on the dry mass of electrodes was shown experimentally and analyzed. The properties of the synthesized material were compared with those of other carbon materials. The best samples of the developed material possess a specific electric capacity of over 390 F/g.

The process of advanced aluminum-alumina powders production for selective laser melting was studied. The economically effective method of obtaining aluminum&ndash, alumina powdery composites for further selective laser melting was comprehensively studied. The aluminum powders with 10&ndash, 20 wt. % alumina content were obtained by oxidation of aluminum in water. Aluminum oxidation was carried out at &le, 200 &deg, C. The oxidized powders were further dried at 120 &deg, C and calcined at 600 &deg, C. Four oxidation modes with different process temperatures (120&ndash, C) and pressures (0.15&ndash, 1.80 MPa) were investigated. Parameters of aluminum powders oxidation to obtain composites with 10.0, 14.5, 17.4, and 20.0 wt. % alumina have been determined. The alumina content, particle morphology, and particle size distribution for the obtained aluminum&ndash, alumina powdery composites were studied by XRD, SEM, laser diffraction, and volumetric methods. According to the obtained characteristics of aluminum&ndash, alumina powdery composites, they are suitable for the SLM process.

The results of experimental studies of discharge generation regimes in ion sources of gas-filled neutron tubes are presented. The objects of investigation are neutron tubes developed at the Dukhov All-Russia Research Institute of Automatics (VNIIA) for portable pulsed neutron generators. The experiments showed that the conditions for igniting a discharge depend on the pulse-periodic powering system of the ion source and the conditions for heating the gas generator of the neutron tubes. The obtained data show that the efficiency and stability of gas-filled neutron tubes can be increased by optimizing the operating regimes of the powering systems and creating the appropriate ignition conditions for a discharge.

The kinetics of stepwise transformations during bulk isothermal crystallization of semiconducting AsSe1.5Sn x (x = 0.13, 0.20, 0.28) glasses has been studied in the temperature range of 210−310°С using 119Sn Mossbauer spectroscopy, XPA, and the density and microhardness measurements of the quenched specimens. The kinetics of the gross bulk crystallization of glasses have been analyzed according to the data on density measurement using the Kolmogorov–Avrami equation, which was generalized on stepwise and incomplete isothermal transformations.

Dynamic characteristics of compact vacuum gaps are studied. Experiments are performed in the microsecond range of current pulses with amplitudes ranging from 50 A to 5 kA and rates of rise ranging from 109 to 1010 A/s at switching voltages ranging from 2 to 10 kV. The most stable operation of the gaps is reached when the cathode is triggered using positive pulses. The instability of the initial stage of burning of vacuum arc leads to an increase in the stabilization time of the main discharge. Electrical valve-like properties of compact gaps are manifested in the stable quenching of vacuum arc at a current attenuation rate of 0.5 kA/μs.

An experimental setup developed in cooperation between the Institute for Energy Problems of Chemical Physics and the Joint Institute for High Temperatures for studying processes that occur during laser sublimation and for modeling thermophysical and chemical processes in situ at high temperatures in large-scale facilities is described.

The vibrational IR spectra of polymer-chain glasses and single crystals of TlAsX2 (X = S, Se) have been studied. The results of the kinetic study of the surface isothermal crystallization of glasses are theoretically anlayzed in different ways, taking into account the peculiarities of their structure. The semiempirical calculation of the temperature dependence of nonreconstructive crystal growth rate is performed. It is shown that the layered stationary growth of crystals in the TlAsS2 glass occurs on screw dislocations. In the TlAsSe2 glass the transition from a dislocation mechanism to two-dimensional nucleation and the layered growth of crystals is possible at supercooling of more than 120°C.

We demonstrate the possibility of obtaining high-purity aluminum oxide by successive processes of hydrothermal oxidation of aluminum and vacuum heat treatment of the solid oxidation product (boehmite). The results of studies of changes in the structural properties and chemical purity of alumina samples obtained in the different modes of vacuum heat treatment of boehmite are presented. Experiments have shown the ability to produce alumina with a purity of 99.997% (the total content of all impurities is approximately 30 ppm) of aluminum with a purity of 99.8%. It was shown that the chemical purity of the final product depends on not only the temperature and time of heat treatment but also a number of other parameters of the process.

Simple and potentially energy efficient way for synthesis of Al/Al2O3 composites is described. Synthesis method is based on aluminum powder oxidation in water at 100-200 °C and following drying and calcination at 600 °C. Aluminum powder with average size of about 40 urn that is currently applied in additive manufacturing was used. Present work was devoted to the study of oxidation degree of aluminum and so the propagation depth and structure of Al2O3 shell in composite’s matrix. AI/Al2O3 composites were produced in different regimes with different maximum temperature and duration of the process of aluminium oxidation in water. Aluminum oxidation degree and aluminium content in obtained Al/Al2O3 were changed in the range from 5.5 % and 90.1 % to 21.3 % and 66.2 % respectively. The size of single crystals of Al2O3 in shell was changed from about 6 nm to 200 nm and the thickness of Al2O3 shell was changed from about 400 nm to 1000 nm by changing the regime for Al/Al2O3 composite production. Experimental results showed that Al2O3 shell was well clutched with aluminum core. Shell structure had cracks aroused by calcination process. Size distribution for obtained composites was very close for that of initial aluminum powder. All of these characteristics recommend the obtained Al/Al2O3 composites for additive manufacturing.

The present study is devoted to hydrogen generation at temperatures down to −40°C by aluminum and magnesium oxidation in various aqueous solutions. At −40°C the highest conversion degrees (180 min.) are 17% for aluminum powder in KOH aqueous solution and 43.4% for aluminum granules in HCl solution containing CuCl 2 . At −30 °C for MgCl 2 solution magnesium powder samples ball-milled with Ni, Ga and without additives yielded 82.8, 73 and 67.2% respectively.

This article considers modeling of the gas-filled neutron tube's ion source with discharge initiated by the non-recombined plasma from the previous pulse. The simulation was carried out with a homogeneous distribution of the non-recombined plasma with a concentration of 5.108 cm−3. In the case of filling the neutron tube volume by atomic hydrogen with pressure of 10-3 Torr, the slew rate of the extracted atomic hydrogen ion current equals only 10 mkA/mks. For increasing this value gas mixture of atomic hydrogen and xenon at a pressure of 0.5.10−3 Torr or molecular hydrogen at a pressure of 10−3 Torr to the atomic hydrogen were utilized. This led to increasing of the slew rate of the extracted atomic hydrogen ion current to 100 mkA/mks with xenon and 20 mkA/mks with molecular hydrogen.

The paper presents results of physical processes modeling in the gas-filled neutron tube's Pennnig-type ion source with an electron emitter. The latter is a ring-shaped thermocathode of two different configurations: an internal radius of 2 mm and external radius of 3 mm and 5 mm. The features of the discharge dynamics depending on emitted electrons currents equal to 1 mA, 10 mA and 50 mA were investigated. At a current of 1 mA for a thin and wide ring, the value of the extracted ion current and front time do not exceed 200 ¼A and 3 ¼s respectively. In the case of currents of 10 mA and 50 mA for a thin emitter ring, the ion current maximum value does not exceed 700 ¼A and front time is less than 1 ¼s. For a wide ring, the maximum value of the extracted current reaches 900 ¼A, and the front time varies from 1 μs to 3 μs.

This article considers opportunity of the gas-filled neutron tube's ion source modeling by the KARAT code. To increase the efficiency of registration equipment in oil and gas logging, it is necessary to significantly reduce the duration of the neutron pulse front. To verify the adequacy of the numerical model, the experimental oscillograms of the extracted ion current and the discharge current was compared with the oscillograms obtained by simulating the work of gas-filled neutron tube GNT1-32 by the KARAT code under the same conditions. Despite the fact that the experimental oscillograms had a wide spread from pulse to pulse, the comparison showed a satisfactory agreement with the calculated data for such key parameters as the front time and pulse amplitude for both the extracted and the discharge current.

Activated carbons on the basis of wood are obtained; the carbons are characterized by the optimal characteristics necessary to apply in supercapacitors with a sulfuric acid-based electrolyte. The properties of activated carbon including detailed study of the porous structure by the limited evaporation technique, as well as their electrochemical parameters in the supercapacitor structure, are investigated comprehensively. For material synthesis, correlations between the regime factors, the porous structure, and the functional characteristics of the supercapacitors on that basis are found. Suppositions concerning the peculiarities of formation of the porous structure of activated carbons obtained by the thermochemical synthesis method with use of an alkali as the activator, as well as the influence of the synthesis parameters on the electrochemical characteristics of the supercapacitors, are proposed.

Optimization of the operating regime of power supply circuits of vacuum neutron tubes by inserting additional elements eliminates the instability of current flow, matches the acceleration and discharge pulses, and makes it possible to decrease significantly the current and neutron load on the ion source. In addition, the neutron yield does not decrease, as experiments confirm.

The thermocatalytical synthesis conditions required for the activation of wood charcoal with NaOH in terms of the formation of pores in its structure were investigated. The present study was conducted to explore the potential application of activated carbons as electrodes in supercapacitors with organic electrolyte. The total pore volume and micro- and mesopore ratio were controlled by the activation temperature and alkali addition rate. The working characteristics of carbon electrodes (e.g., specific capacity and ohmic losses) in supercapacitors are strongly influenced by the properties of the pores in their structures. Herein, the optimal ratio of raw material to activator and activation temperature are established: an increase in the ratio of NaOH to carbonizate rate by a factor of 2 and setting the synthesis temperature at 700°C positively influence the electrochemical characteristics of supercapacitors and provide them with specific capacities of up to 160 F g-1.

Porous multilayer graphenes have been synthesized by decomposition of hydrocarbons in a thermal plasma jet. Products of synthesis were characterized by electron microscopy, thermogravimetry, Raman spectroscopy, and X-ray diffraction. Possibility of producing a wide range of graphene materials with different morphology and structure has been shown. Influence of the experimental conditions on mesopores structure of the synthesis products has been investigated using the method of “limited evaporation.”

Glasses were synthesized by the vacuum melting method from highly pure elemental substances at a temperature of 700 °C followed by quenching of the ampoules with melts in air ranging from 500 °C, and from Tl2X and As2X3 compounds at 500 °C for 5 hours with quenching in air. X-ray amorphism, the lack of crystalline microinclusions when thin sections are viewed in the MIM-8and MIK-1 microscopes showed the glassy state and homogeneity of the obtained glasses. According to the molecular model, the correct trigonal pyramid AsX3has C3v symmetry with four vibrational modes: two symmetrical modes of stretching ν1(А1) and bond bending ν2(А1), as well as two asymmetric double-degenerate modes of stretching ν3(Е) and bond bending ν4(Е). The improper pyramid XtAsX2 with two identical bridge As–X bonds and one unbridged (terminal) short bond has lower symmetry Cs. Moreover,the degeneration of vibrations ν3(Е) and ν4(Е) is removed, and all six vibrational modes become active in the infrared spectra. Then, it can be expected that due to the lowering of symmetry С3v → Cs during the transition from the trigonal-pyramidal AsX3/2 structural units (s.u.) with the three bridge As–X bonds in the As2X3 crystals to the chained s.u. Tlq+Xq–AsX2/2(X = S, Se) with two bridge bonds and the short unbridged As–Xt bond, the absorption bands ν3(Е) and ν4(Е) in the vibrational IR spectrum of the TlAsX2 crystals are split into two bands: ν2(А', νs) and ν5(А'', νa) of the corresponding symmetric and asymmetric stretching vibrations of the As–X bonds inside theXtAsX2 pyramids with symmetry Сs,ν4(А', δs), and ν6(А'', δa) of the symmetric X–As–X and asymmetrical X–As–Xt bending vibrations(for single crystal TlAsS2 ν1 = 334, ν2 = 312, ν3 = 141, ν4 = 190, ν5 = 287, ν6 = 178 cm–1). The high frequency bands νcb and νca in the spectra of the crystals and broad absorption bands at 370–395 and 240–270 cm–1 in the spectra of glass of the corresponding TlAsSe2 and TlAsS2 can be related to the stretching vibrations of the As–Х–As bridges between the two АsХ3 pyramids, which arise during the removal of the degeneration of the intermolecular coupling mode (c) and differ in frequency(a ,b). In the IR vibrational spectra of TlAsX2 glasses, due to the disappearance of the long-range order and the presence of the dispersion of the lengths of the As–X chemical bonds, characteristic also for monoclinic crystals of TlAsX2, there are only four broad absorption bands in the wave number range of 60–400 cm–1.These bands are a superposition of 2–3 intense absorption bands in the spectra of the crystals and indicate the persistence of chained s.u. Tlq+Xq–AsX2/2 (X = S, Se) in the glass. Based on the results of DTA and thermodynamic calculations, the soft mode of synthesis of TlAsS2 and TlAsSe2 glasses uniform in composition and structure is proposed from thallium and arsenic chalcogenides. The vibrational IR spectra of polymer-chain glasses and TlAsX2 crystals are studied, the probable assignment of the observed absorption bands is performed, and the presence of a pyramidal structural unit Tlq+Xq–AsX2/2 in glasses and crystals with two bridge bonds and a shorter As–X unbridged bond is established., Стекла синтезировали методом вакуумной плавки из особо чистых элементных веществ при температуре 700 °С с последующей закалкой ампул с расплавами в воздухе от 500 °С, а также из соединений Tl2X и As2X3 при 500 °С в течение 5 ч с закалкой в воздухе. Рентгеноаморфность, отсутствие кристаллических микровключений при просмотре шлифов в микроскопах МИМ-8 и МИК-1 свидетельствовали о стеклообразном состоянии и однородности полученных стекол. В соответствии с молекулярной моделью правильная тригональная пирамида AsX3 имеет симметрию C3v с 4 колебательными модами: две симметричные моды растяжения ν1(А1) и изгиба связи ν2(А1), две асимметричные, дважды вырожденные моды растяжения ν3(Е) и изгиба связи ν4(Е). Неправильная пирамида XtAsX2 с двумя одинаковыми мостиковыми связями As−X и одной немостиковой короткой связью имеет более низкую симметрию Cs. При этом вырождение колебаний ν3(Е) и ν4(Е) снимается, и все 6 колебательных мод становятся активными в инфракрасных спектрах. С учетом вышеизложенного можно ожидать, что из-за понижения симметрии С3v → Cs при переходе от тригонально-пирамидальных структурных единиц (с.е.) AsX3/2 с тремя мостиковыми связями As−X в кристалле As2X3 к цепочечным с.е. Tlq+Xq−AsX2/2(X− S,Se) с двумя мостиковыми и короткой немостиковой связью As−Xt полосы поглощения ν3(Е) и ν4(Е) в колебательном ИК-спектре кристаллов TlAsX2 расщепляются на две полосы соответственно ν2(А', νs) и ν5(А'', νa) симметричных и асимметричных валентных колебаний связей As−X внутри пирамид XtAsX2 с симметрией Сs, ν4(А', s) и ν6(А'', a) симметричных X−As−X и асимметричных X−As−Xt деформационных колебаний (для монокристалла TlAsS2 ν1=334, ν2=312, ν3=141, ν4=190, ν5=287, ν6= 178 см−1). Высокочастотные полосы νcb и νca в спектрах кристаллов TlAsS2 (403 и 383 см−1) и TlAsSе2 (277 и 260 см−1) и широкие полосы поглощения при 370−395 и 240−270 см−1 в спектрах стекол соответственно TlAsS2 и TlAsSе2 можно отнести к колебаниям растяжения мостиков As−Х−As между двумя пирамидами АsХ3, которые возникают при снятии вырождения моды межмолекулярного сцепления (с) и различаются по частоте (а, b). В ИК колебательных спектрах стекол TlAsХ2 из-за исчезновения дальнего порядка и наличия дисперсии длины химических связей As−X, характерной также для моноклинных кристаллов TlAsX, наблюдаются лишь четыре широкие полосы поглощения в диапазоне волновых чисел 60−400 см−1. Эти полосы являются наложением 2–3 интенсивных полос поглощения в спектрах кристаллов и свидетельствуют о сохранении в стеклах цепочечных с.е. Tlq+Xq−AsX2/2(X−S,Se). На основании результатов ДТА и термодинамических расчетов предложен мягкий режим синтеза однородных по составу и структуре стекол TlAsS2 и TlAsSe2 из халькогенидов таллия и мышьяка. Исследованы колебательные ИК-спектры полимерно-цепочечных стекол и кристаллов TlAsХ2, впервые выполнено вероятное отнесение наблюдаемых полос поглощения и установлено наличие в стеклах и кристаллах пирамидальной структурной единицы Tlq+Xq−AsX2/2 с двумя мостиковыми и одной концевой более короткой связью As−X., Известия СПбЛТА, №219 (2017)

The aim of present study was the investigation of purification efficiency of industrial white fused alumina at high-temperature calcinations, in vacuum. Three powder samples of alumina with different initial purity and particle size distribution were studied. The impurities amount in the white fused alumina powder decreased by factor 10 after vacuum calcinations. White fused alumina samples were almost completely cleared of Na, Mg, K, Mn, Cu and Zn. The iron content in the studied samples decreased by factor 8–10. Comparison of the granulometric composition and specific surface area of samples, showed that samples look like sets of porous grains with the average sizes between 16–60 μm. In turn, porous grains are composed of dense micro-particles with a characteristic size of 0.4–0.7 μm. The specific surface area of grains lies in the range 2.8–3.3 cm2/g. Relatively high rate of purification takes place due to porous structure and high surface area of the samples.

Three different types of current-collecting plates for air-hydrogen PEM fuel cell were manufactured and tested: unmodified titanium plates; gold-plated titanium plates and titanium plates treated by carbon ions implantation. It was shown that the applied surface modifications reduce contact resistance between titanium plate and carbon gas diffusion layer. Total ohmic resistance of fuel cell is reduced by 1.8 and 1.4 times in case of gold-plated titanium and carbon-implanted titanium, respectively, in comparison with uncoated titanium. Although gold plating turned out to be more profitable than carbon ion implantation in terms of electrical characteristics, in the last case, the performance enhancement was reached without using precious metals, which at mass production must play more important role. This technology promises to reduce the cost of bipolar plates manufacturing, while maintaining high electrical performance of PEM fuel cells.

Different operating regimes of a source of ions for vacuum neutron tubes developed at the All-Russia Research Institute of Automatics (VNIIA) for portable pulse neutron generators are examined. Experiments demonstrate unstable reproduction of the time dependences of the current in the primary discharge gap of the ion source. The oscillograms of the current and voltage pulses of the arc discharge show the presence of instabilities in the vacuum arc. It is also found that during the first half of the current the burn regime of the arc is strongly nonstationary.

The local surrounding of copper, antimony, and iodine atoms in multicomponent chalcogenide films CuI-PbI2-As2Se3 and CuI-SbI3-PbI2-As2Se3 deposited from solutions of chalcogenide glass in n-butylamine has been studied by the Mossbauer spectroscopy method on 121Sb and 129I isotopes. It was established that antimony atoms are in the Sb (III) state, where each antimony atom is surrounded by three selenium atoms. Copper atoms are in the Cu (I) state and are surrounded by iodine atoms. The local surrounding of copper, antimony, and iodine atoms in chemically deposited chalcogenide films is analogous to the local surrounding of atoms in the initial chalcogenide glass.

Highly developed nanoporous carbon materials have been prepared by a two-stage thermocatalytic process. In the first step, alder (Alnus rhombifolia) and birchwood (Betula pendula) were carbonized with and without a dehydration catalyst (H3PO4); in the second step, the material was activated by means of NaOH. The dependence of the porous structure of activated carbons from process parameters was characterized by the novel limited evaporation technique. Specific surface areas, pore volumes, and radii were calculated according to the Derjaguin-Broekhoff-de Boer theory. The tests of activated carbons as electrodes in supercapacitors demonstrated their high potential for this application.

The goal of this work is to show the possibility of practical usage of the environmentally pure oxidation process of preliminarily dispersed aluminum (aluminum powders of the ASD or PAD grade according to TU (Technical Specifications) 48-5-226-87, which are serially produced in industry) with liquid water in order to obtain gaseous hydrogen in volumes sufficient to provide the operation of energizers based on airhydrogen fuel cells (AHFC) for portable and stationary devices (up to 3 kW). It is shown that the synthesis of aluminum oxides-hydroxides with the specified phase and chemical compositions as well as the particle shape and size can be provided simultaneously with producing commercial hydrogen.

We report on the basic electrical characteristics of the volume nanosecond pulsed discharges in air at atmospheric pressure. The measurements of temperature were performed using spectral methods, whereas the electron density of plasma was measured using a multibeam Fabry-Perot interferometer. It is shown that, subject to maintaining the form of the volume discharge, the maximum electron density is 1.5 × 1013 cm−3, which is comparable to the critical value in streamer discharges.

An experimental facility for studying the kinetics of molecular association formation from atoms produced by evaporation of the target material by powerful CO2 laser pulses is described. First experimental results are presented for the spectral and spatial-temporal characteristics of the spread of Al atoms produced in interactions of laser radiation with aluminum oxide Al2O3, followed by AlO formation in various low-pressure (0.1–0.3 Torr) atmospheres. Images of structurally similar forms condensed on a glass surface have been observed with an atomic-force microscope.

The nanoporous structures of activated carbons and carbide derived carbons are investigated via the adsorption limited-evaporation method. Electrochemical properties of these structures used in the models of supercapacitors are analyzed. It has been found that porous structure parameters correlate with the specific characteristics of supercapacitors based on the mentioned materials.

Structural formation of plastic greases, which are essentially colloidal systems, during their fabrication and the factors that affect aging of lubricants during storage in containers and use in friction units are examined. The results of an analysis of the quality of the greases after prolonged use in friction units in different types of engineering are reported.

The electrical conductivity of chalcogenide semiconductor films in the CuI-AsI3-As2Se3 and CuI-SbI3-As2Se3 systems, which have been prepared by chemical deposition from mono-n-butylamine, has been studied as a function of the temperature and film composition. It has been established that the electrical conductivity of the CuI-AsI3-As2Se3 and CuI-SbI3-As2Se3 films is predominantly determined by the copper iodide content. It has been demonstrated that the electrical properties of the chalcogenide glasses and the related films are characterized by the same values to within the experimental error, which is explained by the same model of dissolution of vitreous semiconductors in amines with the retention of the electrical properties of chalcogenide glasses after the deposition of films from their solutions.

The electrical conductivity of CuI-Cu2Se-As2Se3 chalcogenide semiconductor films prepared through the chemical deposition from an organic solvent has been investigated as a function of the temperature and composition of the films. It has been established that the electrical properties of the chalcogenide glasses and related films are characterized by the same values within the limits of the experimental error. This result is in agreement with the model of dissolution of vitreous semiconductors in organic bases (amines), according to which the main properties of bulk (cast) chalcogenide glasses are retained in films prepared from these glasses.

A high-voltage nanosecond pulse generator intended for studying diffuse discharges in gases at pressures close or equal to atmospheric pressure is described. The generator produces pulses with an ∼50-ns (at half-height) duration, a >50-kV voltage amplitude, a 10- to 12-ns rise time, and a pulse repetition rate of up to 1 kHz across an equivalent load (1.3 kΩ, 15 pF). The generator is based on available cheap components, and the amplitude (energy) of output pulses and their repetition rate can be promptly regulated in a wide range. The generator is immune to noise and reliable.