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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.

Activated carbons (ACs) based on wood charcoal were synthesized via sodium hydroxide activation and studied as electrode material in supercapacitors (sulfuric acid electrolyte). In focus were the porous structure of the ACs and their electrochemical properties as a function of the synthesis conditions. The data of surface area and pore volume and pore size dimensions (determined by N2 adsorption and evaluated based on three theories) of the ACs activated at 700°C and with NaOH/carbonizate ratios of 2 and 3.7 are reported, such as the specific capacitance (F g−1), specific resistance (Ohm cm), electrolyte volume (mm3 g−1) and the specific power capacity of a cell (Wh kg−1) of the supercapacitors made of various ACs. It was established that the porosity is increasing with increasing activation temperature and activator rate while the specific capacitance of the device increased up to 390 F g−1 based on elementary cell mass.

Simple, safe, scalable and low-cost method of hydrogen production via aluminum-water reaction was proposed. Hydrogen generation method is based on oxidation of coarse aluminum of centimetric scale in alkali aqueous solution with alkali concentration of no more than 0.1 M under intensive mixing of reaction medium. In presented work aluminum conversion (hydrogen yield) was studied depending on the aluminum to solution mass ratio (α changed from 30.1 to 2.7), the concentration of alkali in aqueous solution, the mixing rate, the form of aluminum particles (granules or chips) and chemical purity of aluminum. It was shown that under implemented experimental conditions alkali is continuously regenerated during oxidation reaction and synergistic effect of low content alkali aqueous solution and intensive mixing works. Aluminum conversion degree after 5 h oxidation of aluminum chips at 90 °C in 0.1 M KOH aqueous solution with α = 4 and mixing rate of 400 rpm was 75.4%. With alkali concentration increasing from 0.01 M to 0.3 M the conversion of aluminum increases from 20.7 to 95.7% (after 5 h at 90 °C, α = 4). Proposed method was strongly affected by mixing of reaction medium inside the reactor while it didn't feel the difference between aluminum chips and granules having specific surface area of 22 and 5.5 cm2/g respectively. Chemical purity of aluminum had little effect on aluminum conversion as well. Generally, proposed method can be used for hydrogen generation, aluminum waste utilization and special-grade alumina production.

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.

Hydrogen forming by aluminium oxidation with liquid water of water solutions at low temperatures is complicated by the following reasons. Firstly, on an aluminium surface a film of oxide is formed effectively preventing further oxidation. Secondly, the rate of aluminium oxidation considerably decreases as the temperature of the system decreases. However, in this study the methods are given which enable one to overcome the above difficulties. The experiments on the oxidation of powdered activated aluminium in different water solutions have been carried out. The data obtained have been used to plot a number of curves characterizing hydrogen flow rates depending on the solution composition and the temperature of the process (the original weight of the powder was 0.25 g, solution volume - 300 ml, measuring time - 180 min). At −40 °C for KOH solution the yield of hydrogen was 50 ml, for CaCl 2 – about 5 ml, and for ZnCl 2 – approximately 2 ml. At −10 °C H 2 yield for NaOH was 264 ml, for KOH – 260 ml; at −20 °C: 100 ml for NaOH, and 225 ml for KOH. For KOH solution at temperatures of −30 °C and −40 °C the yields were equal to 192 and 49 ml respectively. Oxidation of granulated non-activated aluminium (2.5 g of aluminium per 300 ml of solution) with hydrochloric acid solution in the presence of CuCl 2 (2.5 g per 300 ml of solution) resulted in generation of more than 2000 ml of hydrogen during 300 min. For FeCl 3 solution the total value of hydrogen obtained during 180 min was equal to 70 ml, it also has been observed partial freezing of this solution.

Activated carbons produced from two wood species, birch and alder, were compared. For both carbons identical dependences of the porous structure and electrochemical parameters of the carbons on activation conditions were determined in a wide range of activation parameters (temperature, alkali/carbon mass ratio). In addition, an inverse dependence of the specific capacitance of the samples on the specific surface area was found.

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.

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.

Consider solution of equation, which describe motion of microwave discharge plasma components, and take into account microwave field, magnetic field of permanent magnets and elastic scattering on hydrogen atoms and ions. This solution has a resonant character, moreover, it shows that average energy of electrons in exact resonance on several orders greater than the energy corresponding to the maximum ionization cress section. Also, shows solution of equations of electron motion between two elastic collisions. Electron trajectories may be very different from the elliptic orbits and from each other depending on closeness to exact resonance.

Stationary magnetic field which necessary to electron cyclotron resonance formed by permanent magnets from alloy NeFeB. Computer simulation by code ANSYS allows us to find such configuration of permanent magnets that gives magnetic field strength equal 875 mT at input and output hole. Regulation of magnetic field distribution provides by special iron bars. Also, computer simulation shows that even slight change of position of the bars results to significant changes of ionization rate in resonators volume. This provides necessary conditions for effective ionization of gas in volume of the resonator. Ions highest production rate corresponds to resonance amplification coefficient equal 105.

Determine complex conductivity of the microwave discharge plasma in resonator of the ion source. Using CST Microwave Studio allowed us to calculate dimensions of the resonance microwave window providing necessary reflection coefficient and to find effective amount of microwave discharge plasma from condition of resonance preservation. This makes it possible to determine value of electromagnetic filed in plasma and get it relation with power of electromagnetic wave. Computations show that fulfillment of the condition electron cyclotron resonance results to large reduction of electromagnetic field amplitude.

Дана термодинамическая характеристика истинной растворимости при 25 °С аморфной и кристаллических наноразмерных модификаций TiO2 в зависимости от рН водной среды в интервале 0–14,7 с учетом образования гидроксокомплексов Ti(1V) и дисперсности твердой фазы. Средний эффективный радиус твердых частиц (r ? 25 нм для TiO2) следует учитывать в качестве термодинамического параметра при определении растворимости диоксида титана в наносостоянии. Растворимость модификаций TiО2 в водных слабокислых и слабощелочных средах при отсутствии фторид?ионов весьма низкая (10?9?10?5 моль/л) и определяется прочными нейтральными комплексами Ti(ОН)4, преобладающими при рН 3?10. Растворимость в водных средах заметно зависит от структуры кристаллов (рутил < брукит < анатаз), существенно возрастает с уменьшением размера частиц кристаллических нанопорошков и сильно (примерно на 3 порядка) при переходе от стабильного кристаллического рутила ??TiO2 (r >100 нм) к аморфной модификации. В сильнокислой среде (1 М HClO4) растворимость модификаций диоксида TiО2 на 4?5 порядков выше, чем в воде и определяется в основном комплексом Тi(OH)22+. В сильнощелочной среде (1 М NaOH) растворимость на 2?3 порядка выше, чем в воде и определяется комплексом Ti(ОН)5?. The thermodynamic characteristic of true solubility at 25 °C for amorphous and crystalline nanosized modifications of TiO2, depending on the pH of an aqueous medium in the range of 0–14.7 and allowing for the formation of Ti(IV) hydroxo complexes and the dispersity of the solid phase, was presented. The average effective radius of solid particles (r ? 25 nm for TiO2) must be considered as a thermodynamic parameter when determining the solubility of titanium dioxide in the nanostate. The solubility of polymorphic TiO2 modifications in aqueous weakly acid and weakly basic media with no fluoride ions is rather low (10?9–10?5 mol/L) and is determined by the strongly neutral Ti(OH)4 complexes that predominate at pH 3–10. Solubility in aqueous media depends substantially on the structure of the crystals (rutile < brookite < anatase), grows considerably as the particle size of crystalline nanopowders shrinks, and becomes stronger (by approximately three orders of magnitude) upon moving from stable crystalline rutile ?-TiO2 (r > 100 nm) to the amorphous modification. In a strongly acid medium(1M HClO4), the solubility of dioxide TiO2 modifications is 4–5 orders of magnitude higher than in water and is determined mainly by the Ti(OH)22+ complex. In a strongly alkaline medium (1M NaOH), the solubility is 2–3 orders of magnitude greater than in water, and is determined by the Ti(OH)5? complex.

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.

A recently developed dynamic desorption technique is used for obtaining vapor isotherms on porous materials. This gravimetric technique does not require any preliminary calibration and is based on analyzing the kinetics of liquid evaporation from a porous sample under quasi-steady state conditions. The crucial feature of the technique is concerned with the fact that no vapor pressure measurements are necessary. The technique is illustrated by desorption of benzene vapors from mesoporous silica MCM-41. To calculate the pore size distribution, the Derjaguin–Broekhoff–de Boer theory in its combination with the Wheeler model for capillary condensation is used. In the calculations, the reference data on benzene adsorption on a nonporous silica gel from two different sources (published by different authors) are applied. The mean mesopore sizes estimated from desorption isotherms are shown to be in a fair agreement with the calculations through the geometrical method based on the X-ray diffraction data. The dynamic desorption technique can serve as an additional tool for the characterization of a porous media.

An advanced method was investigated for production of ultrahigh-purity alumina α-Al2O3 (UHPA, 99.999%) with an oxidation of aluminum (purity 99.7%) granules in 0.1 g/mol aqueous solution of potassium hydroxide with a subsequent hydrochloric acid treatment and calcination of the oxidation product at 1450 °C. The evolution of impurities concentration after subsequent acid and thermal treatment was studied. The total concentration of impurities and especially iron impurity was decreased in UHPA while the concentration of alkali metals (K, Na, Li), on the contrary, was increased by the used production method (Al granules → reaction with alkali → acidic treatment + washing → thermal treatment). The proposed method allowed production of UHPA with purity 99.99% and 99.999% from pellets with the initial purity of aluminum 99.70% and 99.99% respectively. The advantage of the studied method of UHPA production is it's low cost and utility.