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The work is devoted to the study of the novel process of catalytic decomposition of light hydrocarbons on a catalyst at temperatures of 550 °С and 600 °C at various pressures. The CVD process is a new COx-free approach for hydrogen production. A glass fiber fabric was used as a catalyst, which was preliminarily modified by the application of additional outer layers of NiO and porous silica. A technical mixture of propane and butane was used as feedstock. The main purpose is to investigate the effects of pressure and temperature on the production of hydrogen and carbon nanofibers over a glass-based catalyst. As a result of the decomposition of the mixture, the yield of hydrogen was 266–848 L/gcat, and that of carbon nanofibers was 3–10 g/gcat. Increasing the pressure of propane-butane mixture decomposition led to an increase of the catalyst lifetime. The highest yield of hydrogen and carbon nanofibers was achieved at 1 bar and 600 °C.

The process of thermolysis of barium hydroxostannate BaSn(OH)6 as a precursor for preparing barium stannate BaSnO3 has been investigated using the method of differential thermal analysis. Thermal decomposition products of the precursor were characterized using X-ray diffraction, IR spectroscopy, low-temperature nitrogen adsorption, and scanning electron microscopy. It was shown that dehydration at nearly 270 °C resulted in the formation of an X-ray amorphous multiphase product, from which single-phase barium stannate crystallized at temperatures above 600 °C. The synthesized barium stannate was used as a functional additive to prepare composite proton electrolytes in the CsHSO4-BaSnO3 system. The structural and transport properties of the obtained system were investigated. It is shown that the highly conductive state of the salt is stabilized in a wide range of temperatures. High conductivity values of composite solid electrolytes in the medium temperature range create the possibility of their use as solid electrolyte membrane materials.

The relevance of the research is conditioned by great dependence of uninterrupted operation of critical mechanisms driven by high-voltage induction motor, providing operation of oil and gas and chemical industry, metallurgy, electric power industry and other strategically important branches of the country. The issue of reliability of continuous operation is particularly acute in the operation of thermal power plants. Almost all electric drives of critical auxiliary mechanisms of thermal power plants are based on powerful high-voltage induction motors with squirrel-cage rotor. As a rule, specifics of operation of these motors are severe conditions of starting under load at increased temperatures and environmental pollution. Emergency stops of induction motors together with the responsible mechanisms at thermal power plants eventually cause power unit shutdown or lead to under-release of electricity and revision of the operating mode of the power system. Despite such consequences, in particular from damage to the short-circuited rotor winding of a high-voltage induction motor, a protection with sensitivity capable of detecting this defect has not yet been developed or introduced. Damage of rotor circuit has latent character, can exist for a long enough time, not critically affecting the operation of the machine, nevertheless, the fact of presence of breakage can be considered as an emergency condition of the machine in complex with the mechanism. According to the data of repairs and revisions of high-voltage induction motors, there are cases when up to 30 % of bars of the whole rotor were damaged simultaneously. When the integrity of the connection between the bar and the short-circuiting ring is broken, its deformation can occur only in the direction of the air gap, irreversibly damaging the active part of the stator. Operation of inductions motor with a broken core is accompanied by a number of additional negative side effects, such as increased power consumption, general reduction of machine performance and efficiency, generation of additional heat, increased wear of bearings. In case of diagnosing a short-circuited winding defect at an early stage of its development, it is possible to repair the rotor by the company itself. Early diagnosis of rotor core breaks of high-voltage auxiliary motors of thermal power plants is a difficult and at the same time extremely relevant purpose. The main aim of the research is the development and experimental testing of a method for diagnosing broken rotor bar in a high-voltage induction motor based on mathematical processing of signals from stator current sensors. Methods: theory of electrical machines, methods of digital signal processing, statistical methods of data processing, methods of approximation of experimental data, method of regression analysis. Presented studies were carried out on the experimental workbench, specially created for the purpose of diagnostics of broken rotor bars. Results. The paper introduces the method of diagnostics of broken rotor bars based on approximation of stator current signals. The criterion of rotor circuit damageability was revealed and the dependence of this criterion on the degree of damage to the «squirrel cage» of an induction motor was obtained.

The article studies the effect of polynorbornene (PNB) in the composition of PNB with Norman 747 LV plasticizer (RC) on the curing characteristics of the rubber compound and the physico-mechanical, dynamic, dielectric properties and the thermal behavior of vulcanizates based on a combination of isoprene, α-methylstyrene-butadiene, and nitrile-butadiene rubbers. It is shown that vulcanizates containing PNB in the composition of the RC had lower conditional tensile strength, hardness, and tear resistance compared to the vulcanizate of the base version of the rubber compound. Studies of dynamic mechanical analysis indicate that an increase in the content of RC, and hence PNB, in the rubber compound contributes to an increase in the mechanical loss factor (tanδ) and a decrease in the storage modulus of vulcanizates. It was found that vulcanized rubber, containing 24.0 parts per hundred of rubber (phr) (8.98 wt. %) PNB as part of the RC, is characterized by stable physico-mechanical, improved vibration-absorbing properties, as well as increased dielectric parameters. This rubber compound can be used as a base for rail fasteners for railroad tracks.

This work is dedicated to the study of the treatment of multi-walled carbon nanotubes (MWCNTs) with dichromic acid. The dichromic acid was formed by dissolving different concentrations of CrO3 in water. The effect of the concentration of dichromic acid on the change in texture characteristics, elemental composition, defectiveness, graphitization degree, and surface chemistry of MWCNTs was investigated using various analytical techniques, such as transmission electron microscopy, energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). Testing of MWCNTs as electrodes for supercapacitors in 3.5 M H2SO4 solution was carried out using cyclic voltammetry. A decrease in the average diameter of CNTs after treatment was found. The EDX and XPS showed that the oxygen content on the surface of MWCNTs increased after treatment with dichromic acid. The formation of Cr2O3 after treatment with dichromic acid was detected by XPS. High angle annular dark field scanning transmission electron microscopy was used to confirm the intercalation of the chromium-containing compound between graphene layers of MWCNTs after treatment with dichromic acid. It was found that two different types of MWCNTs showed diverse behavior after treatment. The highest specific capacitance of the MWCNTs after treatment was 141 F g−1 (at 2 mV s−1) compared to 0.3 F g−1 for the untreated sample.

Relevance of the study is caused by an urgent need in theoretical justification and practical development of selective methods of diagnosing complex internal damages of powerful high-voltage squirrel-cage induction motors, which are one of the main elements of responsible mechanisms of all technological processes in fuel and energy complex. As a rule, specificity of work of high-voltage squirrel-cage motors in fuel and energy complex, both at a stage of extraction and transportation of georesources, and at a stage of their processing, are heavy conditions of start-up, especially it is expressed for critical mechanisms of thermal power plants (feed pumps, mills, crushers, smoke exhausters, blowers, etc.). Failures of squirrel-cage induction motors of critical mechanisms at thermal power plants lead to either shutdown of a power unit or at least to reduction of a level of electric power generation. At the same time, despite the gravest and, as a rule, irreversible consequences, there are no protections against such damage as defects in short-circuited winding of squirrel-cage induction motor rotor and such damage is detected only during overhaul. Broken-rotor-bar in the initial stage is latent and is a trigger for the development of more dangerous emergency modes. Lack of tested technical means for diagnostics of this type of damage is first of all related to insufficient formalization of mathematical description of processes in squirrel-cage induction motor when defects in rotor winding occur. Object: high voltage squirrel-cage induction AC motors. The aim of the research is to perform modeling of induction machine with electrical asymmetry rotor, adequately reflecting physical processes in the machine when damage occurs in the rotor cage. Methods. Theoretical research methods were used to solve the problem. They include: the theory of electrical machines, numerical methods. Simulation modeling was performed in MatLab environment, and mathematical data processing in MathCad package. Results. An n-phase simulation model of an induction motor has been developed, which allows us to investigate the broken rotor bar in a squirrel-cage. Proposed analytical expressions, which describe the motor operation when the rotor is stationary.

This article is devoted to the investigation of the influence of the solvent on sensing properties, such as response and recovery rate, of chemiresistive gas sensors. Multi-walled carbon nanotubes were used as an active material for the sensors. The initial material was investigated by scanning electron spectroscopy and transmission electron microscopy, low-temperature nitrogen adsorption, Raman spectroscopy, and X-ray diffraction. The active material was produced by drop casting. Different polar solvents (acetone and ethanol) were used for suspension preparation. Textolite with copper contacts on the edges of one side was used as a sensor substrate. The gas sensing properties (the response and the recovery time) were investigated in the range of 100–500 ppm NO2 at room temperature. The films made using different solvent suspensions showed high sensitivity and rapid recovery rate to nitrogen dioxide. It was found that the method of film preparation has an effect on the measured sensing properties. The films prepared using different suspensions possessed different properties: the film made from the acetone suspension had the response values from 8.49% to 20.26%, and the recovery values from 0.06%/min to 0.16%/min. The response of the film made from the ethanol suspension increased , being from 12.25% to 23.63%; the recovery rate were also increased (from 0.19%/min to 0.39%/min).

To date, the research on carbon nanomaterials has progressed rapidly. More than 400 papers were written in 2021 on the application of carbon nanomaterials in various fields. The high demand for the use of such materials has increased due to a sharp increase in the demand for semiconductor materials and materials for supercapacitor electrodes and other electrical devices. Despite the unique physical properties of carbon nanomaterials, there are limitations to their use. To solve this problem, various methods of modifying the surface, both through chemical interactions and physical adsorption, were proposed. One of these methods is chemical modification. The evaluation of effect of chemical treatment parameters on the properties of carbon nanomaterials is an urgent task due to the fact that the chemistry of the processes is poorly understood. In this work, the effect of concentrated sulfuric and nitric acids on the change of specific surface area, elemental composition, composition of functional groups, and also on the change of specific capacitance was considered. It is believed that both the porosity and the functional groups formed during oxidation contribute to the change in specific capacitance. The specific surface area of all samples decreased on average by a factor of 1.5–3 after the chemical treatment. Different oxygen and sulfur-containing functional groups are observed after the chemical treatment. The highest specific capacitance of the treated carbon nanofibers was 114 F/g.

In this paper, room-temperature chemiresistive gas sensors for NO2 detection based on CVD-grown carbon nanofibers (CNFs) were investigated. Transmission electron microscopy, low-temperature nitrogen adsorption, and X-ray diffraction were used to investigate the carbon nanomaterials. CNFs were synthesized in a wide range of pressure (1–5 bar) by COx-free decomposition of methane over the Ni/Al2O3 catalyst. It was found that the increase in pressure during the synthesis of CNFs induced the later deactivation of the catalyst, and the yield of CNFs decreased when increasing pressure. Sensing properties were determined in a dynamic flow-through installation at NO2 concentrations ranging from 1 to 400 ppm. Ammonia detection was tested for comparison in a range of 100–500 ppm. The obtained sensors based on CNFs synthesized at 1 bar showed high responses of 1.7%, 5.0%, and 10.0% to 1 ppm, 5 ppm, and 10 ppm NO2 at 25 ± 2 °C, respectively. It was shown that the obtained non-modified carbon nanomaterials can be used successfully used for room temperature detection of nitrogen dioxide. It was found that the increase in relative humidity (RH) of air induced growth of response, and this effect was facilitated after reaching RH ~35% for CNFs synthesized at elevated pressures.

The proton conductivity and structural properties of (1–x)CsH2PO4–xZnSnO3 composites with compositions of x = 0.2–0.8 were studied. Zinc stannate ZnSnO3 was prepared by the thermal decomposition of zinc hydroxostannate ZnSn(OH)6, which was synthesized by hydrolytic codeposition. To optimize the microstructure of ZnSnO3, thermal decomposition products of ZnSn(OH)6 were characterized by thermal analysis and X-ray diffraction, Fourier transform infrared spectroscopy, low-temperature nitrogen adsorption, and electron microscopy. The study reveals that the thermolysis of ZnSn(OH)6 at temperatures of 300–520 °C formed an X-ray amorphous zinc stannate with a high surface area of 85 m2/g possessing increased water retention, which was used as a matrix for the formation of the composite electrolytes CsH2PO4–ZnSnO3. The CsH2PO4 crystal structure remained in the composite systems, but dispersion and partial salt amorphization were observed due to the interface interaction with the ZnSnO3 matrix. It was shown that the proton conductivity of composites in the low-temperature region increased up to 2.5 orders of magnitude, went through a smooth maximum at x = 0.2, and then decreased due to the percolation effect. The measurement of the proton conductivity of the ZnSnO3–CsH2PO4 composites revealed that zinc stannate can be used as a heterogeneous additive in other composite solid electrolytes. Therefore, such materials can be applied in hydrogen production membrane reactors.

The synthesis of a 90% Ni/Al2O3 catalyst via solution combustion synthesis with various fuels was studied in this work. Catalysts with a high content of the active component (i.e., nickel) were obtained as a result of the combustion of Ni(NO3)2·6H2O and Al(NO3)3·9H2O mixtures with fuel. The fuels, such as hexamethylenetetramine, glycine, urea, starch, citric acid, and oxalic acid, were investigated. The synthesis was carried out in a furnace, with the temperature being raised from room temperature to 450 °C at a rate of 1 °C per min. The paper evaluates the efficiency of fuels and their effect on the structure and properties of catalysts, as well as their catalytic activity. The catalyst was used for the synthesis of hydrogen and carbon nanofibers by methane decomposition at 1 bar and 550 °C. The catalysts were tested in a vertical flow reactor without preliminary reduction. The obtained samples of catalysts and carbon nanomaterials were studied by transmission electron microscopy, low-temperature nitrogen adsorption, and X-ray diffraction. The highest activity of the catalyst was obtained when citric acid was used as a fuel. The specific yields of hydrogen and carbon nanofibers were 17.1 mol/gcat and 171.3 g/gcat, respectively. Catalytic decomposition of methane led to the formation of cup-stacked carbon nanofibers.

The relevance. The share of electricity generated by installations based on renewable energy is constantly growing, and therefore the need for the development of power supply systems and automatic control of electrical machines underlying wind and hydro generators is still relevant. As part of such alternating current generator sets, synchronous electric machines, induction generator with phase and squirrel-cage rotor are used. Frequency converters installed in the stator and rotor circuits of induction motor make it possible to control their excitation, however, to start generation, additional external power sources must be used. Due to the residual magnetization in the magnetic circuit, it is possible to ensure the process of guaranteed self-excitation of the induction generator by connecting the capacitor banks to the electrical circuit of its stator without using an additional external power source. The proposed method of non-stationary capacitor excitation makes it possible to ensure the adaptation of the generator set to the change in operating modes under conditions of decentralized power supply. The main aim of the research is to study the proposed voltage stabilization system of induction generator with a short-circuit rotor with variable capacitor excitation as part of a renewable energy source. Methods. To achieve the goal of the research, theoretical and experimental research methods were used. Theoretical research methods include the theory of differential equations, methods for the numerical solution of ordinary differential equations, the theory of electric drives, the theory of electrical machines, numerical methods for approximating data. The basis of experimental research is testing an induction generator with non-stationary capacitor excitation on a developed test bench in order to obtain load characteristics and oscillograms of voltages on the stator windings of an induction generator with a short-circuit rotor in different operating modes. Results. An original experimental setup with a unit imitating the operation of a turbine, an electromechanical energy converter in the form of an induction generator with a short circuit with non-stationary capacitor excitation has been developed and manufactured. The control system is made in the form of a galvanically isolated module integrated with the power unit in a moisture-resistant design using a wireless Bluetooth communication interface. A method for switching capacitor banks using thyristors as a controlled switch with two-way conduction is described and tested. The analysis of the obtained load characteristics shows the fundamental possibility of ensuring a guaranteed generation of electricity with voltage stabilization within the limits of load power variation. The system of automatic switching of capacitors with a capacitance varying depending on the power consumption applied as part of the experimental setup made it possible to provide an acceptable time for dynamic response to a disturbing effect under nonstationary load.

The article concentrates on the topical issue connected with the detection of defects in the rotor winding of electric machines. The experimental sampling and digital processing of electrical signals from controlled windings is in the basis. The authors conducted the research using two experimental units for asynchronous motor and synchronous generator, respectively. A distinctive feature of the proposed research stands is in solving the problems of digital processing and data analysis on the basis of the application of microprocessor relay protection unit BMRZ developed in Russia. The authors applied method of wavelet decomposition to select the detailing component. They also presented the results of experiments for the breakage in the short-circuit rotor of an asynchronous motor and proved that the microprocessor-based BMRZ device is capable of digitizing at a sampling rate that meets the requirements, and in conjunction with the data processing algorithms that carry out the selective determination of hard-to-detect defects, is applicable in the diagnosis of electrical machines.

Room-temperature gas sensors based on granulated carbon nanofiber material were investigated for the detection of NO2. The granulated material consisting of intertwined carbon nanofibers was synthesized by the decomposition of CH4 over the Ni/Al2O3 catalyst in a vibro-fluidized bed reactor. Carbon material was investigated using transmission electron microscopy, Raman spectroscopy, low-temperature nitrogen adsorption, and X-ray photoelectron spectroscopy. Investigation of the gas sensors towards NO2 at room temperature (25 ± 2 °C) was carried out in a dynamic flow-through setup in the range from 1 to 500 ppm. A comparison of the sensitivity gas sensor to NH3 and CH4 was also given. The sensor based on non-treated carbon nanofiber material showed the response ΔR/R0 of 5.1 % to 10 ppm of NO2. It was found that the sensor response to NO2 decreased when increasing the relative humidity. The effect of the relative humidity was more pronounced for low concentrations of nitrogen dioxide and decreases with a further increase in them.

The role of plasma functionalization of multi-walled carbon nanotubes (MWCNTs) for room-temperature ammonia gas sensors was investigated. Plasma functionalization of MWCNTs with maleic anhydride was carried out at various durations. The active material of the gas sensor was investigated by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. It was shown that the formation of functional groups on the surface of carbon nanotubes led to an increase in the ammonia sensor response by two to four times. The increase in functionalization duration induced the rise of O/C from 0.28 to 0.335, an increase in sensor resistance, and the distortion of the shape of the I-V curves.

Every year the problem of water purification becomes more relevant. This is due to the continuous increase in the level of pollution of natural water sources, an increase in the population, and sharp climatic changes. The growth in demand for affordable and clean water is not always comparable to the supply that exists in the water treatment market. In addition, the amount of water pollution increases with the increase in production capacity, the purification of which cannot be fully handled by conventional processes. However, the application of novel nanomaterials will enhance the characteristics of water treatment processes which are one of the most important technological problems. In this review, we considered the application of carbon nanomaterials in membrane water purification. Carbon nanofibers, carbon nanotubes, graphite, graphene oxide, and activated carbon were analyzed as promising materials for membranes. The problems associated with the application of carbon nanomaterials in membrane processes and ways to solve them were discussed. Their efficiency, properties, and characteristics as a modifier for membranes were analyzed. The potential directions, opportunities and challenges for application of various carbon nanomaterials were suggested.

This article is devoted to the investigation of the sensing behavior of chemically treated multi-walled carbon nanotubes (MWNTs) at room temperature. Chemical treatment of MWNTs was carried out with a solution of either sulfuric or chromic acids. The materials obtained were investigated by transmission electron microscopy, scanning electron microscopy, Raman-spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The active layer of chemiresistive gas sensors was obtained by cold pressing (compaction) at 11 MPa of powders of bare and treated multi-walled carbon nanotubes. The sensing properties of pellets were investigated using a custom dynamic type of station at room temperature (25 ± 2 °C). Detection of NO2 was performed in synthetic air (79 vol% N2, 21 vol% O2). It was found that the chemical treatment significantly affects the sensing properties of multi-walled carbon nanotubes, which is indicated by increasing the response of the sensors toward 100–500 ppm NO2 and lower concentrations.

The article discusses the role of economic and social development of the region in achieving economic growth, identified the key concepts in strategic planning, strategy and shows the role of strategic planning in the holistic development of the region.

Highly porous expanded graphite was synthesized by the programmable heating technique using heating with a constant rate (20 °C/min) from room temperature to 400–700 °C. The samples obtained were analyzed by scanning electron microscopy, energy-dispersive spectroscopy, low-temperature nitrogen adsorption, X-ray photoelectron spectroscopy, Raman spectroscopy, thermogravimetry, and differential scanning calorimetry. A comparison between programmable heating and thermal shock as methods of producing expanded graphite showed efficiency of the first one at a temperature 400 °C, and the surface area reached 699 and 184 m2/g, respectively. The proposed technique made it possible to obtain a relatively higher yield of expanded graphite (78–90%) from intercalated graphite. The experiments showed the advantages of programmable heating in terms of its flexibility and the possibility to manage the textural properties, yield, disorder degree, and bulk density of expanded graphite.