Plasma-chemical Synthesis Research Articles

Plasma-Chemical Synthesis of Aluminum and Lead Silicate Glass Microspheres

Plasma-Chemical Synthesis of Aluminum and Lead Silicate Glass Microspheres

Исследование процесса гранулирования нанопорошка системы W – Ni – Fe методом распылительной сушки

A method for obtaining nanopowder microgranules of the W – Ni – Fe system (composition of the VNJ-90) of a micron size range by spray drying of a suspension based on composite nanoparticles obtained by plasma chemical synthesis is considered. The parameters of operation of the Buchi Mini Spray Dryer B-290 spray drying laboratory unit with an ultrasonic nozzle have been experimentally determined, providing for the production of nanopowder microgranules of VNJ-90 with an output of the target fraction of 25 – 63 µm at the level of 65 %. The dependence of the size and morphology of the obtained granules on the choice of the dispersion medium, the concentration of the dispersed phase and the organic binder in the suspension is established. The effect of the suspension flow rate during spray drying on the yield of granules of a fraction of 25 – 63 µm was evaluated. The test of the manufactured experimental sample of nanopowder microgranules in the process of plasma spheroidization was carried out.

Получение композитного порошка системы W – Ni – Fe со сферической формой частиц и исследование возможности его использования в технологии послойного лазерного сплавления

The powder of 93 W – 4.9 Ni – 2.1 Fe (VNZh-93) pseudo-alloy with a spherical particle shape in the size range of 15 – 50 μm with a grain size of 0.5 – 3 μm was obtained using plasma chemical synthesis, granulation and spheroidization technologies. The possibility of using spheroidized powder VNZh-93 in additive 3D-printing is demonstrated. Studies of the physical and mechanical characteristics and microstructure of VNZh-93 test samples made using the selective laser melting technology (SLM) have been carried out. It is shown that the parameters of the SLM significantly affect the formation of the microstructure of test samples. It is possible to form a homogeneous equiaxed microstructure with an average grain size of about 1 micron using optimal SLM modes. It is shown that maximum density and Vickers hardness of VNZh-93 obtained in optimal SLM modes are 16.8 g/cm3 and 480 HV, respectively. These values are not inferior to the values for VNZh-93 samples obtained using traditional liquid-phase sintering technology. At the same time, the main problem of selective laser melting of VNZh-93 powder is the heterogeneity of the bulk samples microstructure and the formation of microcracks and micropores in their structure.

Investigation of Plasma-Chemical Synthesis of Complex Oxide Compositions for Dispersed Uranium-Plutonium Mixed Fuel

Investigation of Plasma-Chemical Synthesis of Complex Oxide Compositions for Dispersed Uranium-Plutonium Mixed Fuel

Determining the influence of ultra-dispersed aluminum nitride impurities on the structure and physical-mechanical properties of tool ceramics

This paper considers features related to manufacturing the chromium oxide-based tool material. The process involved ultra-dispersed powders made of aluminum nitride. It has been established that the destruction of chromium oxide at high sintering temperatures is prevented through the reaction sintering of chromium oxide (Cr2O3) and aluminum nitride (AlN). It was established that the structure of the composite depends both on the temperature and the duration of hot pressing. Thermodynamic calculations of the interaction between Cr2O3 and AlN showed that this interaction begins at a temperature of 1,300 °C. In contrast to hot pressing in the air, no СrN and Сr2N compounds were formed in a vacuum. With increasing temperature, the content of Al2O3 in solid solution becomes maximum at a temperature of 1,700 °C in the case of hot pressing in the air while in vacuum the content of Al2O3 remains unchanged within the entire temperature range of 1,300–1,700 °C. When increasing the time of hot pressing to 30 minutes, the size of individual grains reaches 10 μm. It has been shown that in the sintering process involving Cr2O3 and AlN, the plasma-chemical synthesis produces the solid solution (Cr, Al)2O3 at the interphase boundary, which improves the mechanical properties of the material. The influence exerted on the quality of the machined surface of tempered hard steel when machining by the devised tool material based on chromium oxide with an optimal admixture of 15 wt % of ultra-dispersed aluminum nitride powder was investigated. It was determined that the quality of the machined hard steel surface improved compared to standard imported tool plates. It was established that the resulting tool material, in addition to relatively high strength and crack resistance, also demonstrates high thermal conductivity, which favorably affects the quality of the machined steel surface, given that lubricants and coolants are not used during the cutting process.

Influence of nanomodication on structure for-mation and properties of structural steel

The state of the problem of grinding the grain structure and improving the mechanical properties of low-alloy structural steels has been studied. The state of the problem of grain structure refinement and improving the mechanical properties of low-alloy structural steels has been studied. The role of nanodispersed additives is reduced to the creation of additional artificial crystallization centers in the melt. They must be consistent with the critical radiuses of the embryos. According to our calculations, for the grinding of primary austenite grains in castings, the size of the introduced particles should be 40–50 nm. Output and modified castings of 09G2 and 09G2S steels were subjected to severe plastic deformation by equal-channel angular pressing followed by low-temperature annealing at 350 °C. In the initial state, cast steels 09G2 and 09G2S had a ferrite-pearlite structure with an average primary austenite grain size of 30 μm; after modification and deformation, the grain size was 10 μm. After quenching and cooling in water, the structure has changed insignificantly - ferritic-reed, with an average grain size of ~ 8...10 microns. After cooling the quenched samples in a solution of 20 % NaCl in water, the structure of packet martensite was obtained. In the initial state, the studied steels have insufficiently high property values: microhardness Нμ up to 3000 MPa, yield point σ 0,2 up to 800 MPa. When quenching in water, the hardness somewhat increases, the most significant increase is observed when the samples are cooled in a NaCl solution. Due to the significant grinding of martensite crystals, accelerated cooling provides a greater increase in hardness. A nanodispersed powder of titanium carbonitride Ti (CN) with a fraction of 50...100 nm was obtained by the method of plasma-chemical synthesis, the process technology was developed. Intensive plastic deformation of 09G2 and 09G2S steel castings was carried out. The structure and properties of steels before and after treatments have been studied. As a result of the combination of hardening methods, the grain size of the steels was reduced by 3 times and the yield strength increased from 3000 to 4000 MPa. Nanodispersed powder of titanium carbonitride Ti (CN) with a fraction of 50...100 nm was obtained by the method of plasma chemical synthesis, and a process technology was developed. Intensive plastic deformation of castings of 09G2 and 09G2S steels was carried out. The structure and properties of steels before and after treatments were studied. As a result of a combination of hardening methods, grinding of steel grains by 3 times and increasing the yield strength from 3000 to 4000 MPa was achieved

Methods for obtaining a dispersed structure and increasing the strength of silicon-manganese steels

For high-strength structural steels, the problem of grinding grain and increasing strength is solved by the use of highly efficient technologies, the development of new steel compositions and the development of rational thermomechanical processing. Goal. The aim of the work is to transform the structure, study the methods of grain grinding and increase the strength properties of structural steels 09Г2, 09Г2С as a result of modification by nanodisperse compositions, heat treatment and intense plastic deformation. Methodology. The research material was structural low-carbon steels 09G2, 09G2S. The process of modifying the steel parameters of the geometric shape of the melts was carried out by smelting steels 09G2 and 09G2C in an induction furnace. The modified workpieces were subjected to intensive plastic deformation and heat-treating treatment according to the mode: heating temperature 1050 °C, exposure 5 min; cooled medium: water and 20 % solution of NaCl in water. Then – a rest at temperatures of 500 °C; 600 °C, exposure time – 30 minutes. Metallographic studies of the structure of steels before and after modification and mechanical testing of standard samples were performed. Results. The study of the structure grains of steels 09Г2 and 09Г2С in the initial state showed the presence of large grains up to 30 μm, reduced microhardness and yield strength. Originality. The substantiation of the choice of type and fraction of nanodisperse modifier was carried out. The use of plasma-chemical synthesis to obtain nanopowders based on titanium was substantiated. Nanopowders of titanium carbonitride Ti (CN) fraction 50 ... 100 nm were obtained by the method of plasma chemical synthesis. Practical value. The following methods were proposed for grinding grain and increasing the strength properties of steels: nanomodification, intensive plastic deformation in combination with heat-strengthening treatment.

Characterization of iron-doped crystalline silicon nanoparticles and their modification with citrate anions for in vivo applications

Objectives. This paper presents data on the development and study of the structural properties of iron-doped crystalline silicon (nc-Si/SiOx/Fe) nanoparticles obtained using the plasma-chemical method for application in magnetic resonance imaging diagnostics and treatment of oncological diseases. This work aimed to use a variety of analytical methods to study the structural properties of nc-Si/SiOx/Fe and their colloidal stabilization with citrate anions for in vivo applications.Methods. Silicon nanoparticles obtained via the plasma-chemical synthesis method were characterized by laser spark emission spectroscopy, atomic emission spectroscopy, Fouriertransform infrared spectroscopy, and X-ray photoelectron spectroscopy. The hydrodynamic diameter of the nanoparticles was estimated using dynamic light scattering. The toxicity of the nanoparticles was investigated using a colorimetric MTT test for the cell metabolic activity. Elemental iron with different Fe/Si atomic ratios was added to the feedstock during loading.Results. The particles were shown to have a large silicon core covered by a relatively thin layer of intermediate oxides (interface) and an amorphous oxide shell, which is silicon oxide with different oxidation states SiOx (0 ≤ x ≤ 2). The samples had an iron content of 0.8–1.8 at %. Colloidal solutions of the nanoparticles stabilized by citrate anions were obtained and characterized. According to the analysis of the cytotoxicity of the modified nanosilicon particles using monoclonal K562 human erythroleukemia cells, no toxicity was found for cells in culture at particle concentrations of up to 5 µg/mL.Conclusions. Since the obtained modified particles are nontoxic, they can be used in in vivo theranostic applications.

Morphological and magnetic features of columnar nanostructures CuO

Columnar nanostructures (CNS) were grown by plasma chemical synthesis at a gas mixture pressure of 90% He + 10% O2 200 Pa and substrate temperatures of 340K (sample 1) and 370K (sample 2). The effect of substrate temperature on the morphological, crystalline, magnetic, and impedance properties of CNS was studied. Scanning microscopy (SEM) showed that the morphology of CNS varies significantly from dendritic to wire structure. Energy dispersive X-ray spectroscopy (EDS) showed a change in the stoichiometry of the deficiency samples (Cu52O48) to an excess of oxygen (Cu42O58). X-ray diffraction analysis (XRD) and Rietveld fitting showed that samples 1 and 2 have a monoclinic crystal structure with a large proportion of the amorphous phase, the size of coherent scattering regions (CSR) was 26 nm (sample 1). Magnetic measurements showed that sample 1 exhibits ferromagnetic behavior, and at 6 K a magnetic hysteresis loop appears. Sample 2 from 250 K to room temperature exhibits diamagnetic behavior. A connection was found between the appearance of diamagnetism and a jump in the dielectric constant of sample 2. An assumption was made about the electron-ionic nature of the diamagnetism of sample 2.

Plasma-Chemical Synthesis and Investigation of Nano-Size Oxide Compositions Simulating Uranium-Thorium Dispersion Nuclear Fuel

Plasma-Chemical Synthesis and Investigation of Nano-Size Oxide Compositions Simulating Uranium-Thorium Dispersion Nuclear Fuel

Formation of titanium-cobalt nitride Ti0.7Co0.3N under plasma-chemical synthesis conditions in a low-temperature nitrogen plasma

Formation of titanium-cobalt nitride Ti0.7Co0.3N under plasma-chemical synthesis conditions in a low-temperature nitrogen plasma

Vacuum-arc synthesis of metal-organic framework structures based on ZrO2

The vacuum-arc synthesis of nanopowders based on zirconium oxide and metal-organic framework structures was carried out using a low-pressure arc discharge plasma. The obtained material was studied by several methods (XRF, IR, TEM, DTA). The TEM method showed that Zr-MOK is a highly agglomerated particle of an almost spherical shape. The image clearly shows the crystalline ordering of nanoparticles with a large (about 2 nm) lattice parameter. Particle sizes range from 5 to 30 nm. Average particle size 9.4 nm. XRD showed that the proportion of ZrO relative to Zr-MOK, calculated from the most intense lines of the diffractogram, is 65%. XRF results are in good agreement with IR studies. The DTA curve demonstrates a continuous exothermic process associated with a number of features of the plasma-chemical synthesis and morphology of the resulting nanoparticles, which is in full agreement with studies using transmission microscopy.

Plasmachemical synthesis of the binary hexafluorides of Mo, Os, Ir, Te, and U

Starting from the respective metal, we have synthesized the binary hexafluorides MF6 of M = Mo, Os, Ir, Te, and U by the use of a remote fluorine plasma source using a mixture of Ar and NF3 as the feed gas. The formation of the binary hexafluorides was confirmed by several different spectroscopic methods including IR, Raman, UV/VIS, and NMR spectroscopy.

Investigation of plasmachemical synthesis of oxide compositions for plutonium-thorium dispersion nuclear fuel

This paper presents the results of experimental studies on the process of plasmachemical synthesis of fuel oxide compositions for plutonium-thorium dispersion nuclear fuel. Precursors were simulated water-organic nitrate solutions, which have a lower calorific value near 8.4 MJ/kg. The precursors consisted of an organic component (acetone) and mixed water nitrate solutions including a matrix metal (magnesium, yttrium), samarium (instead of plutonium), and cerium (instead of thorium). The authors determined the compositions and modes of processing simulated solutions that provide plasmachemical synthesis of nanosized complex oxide powders imitating plutonium-thorium dispersion nuclear fuel.

Preparation of W-C-Co Composite Micropowder with Spherical Shaped Particles Using Plasma Technologies.

The possibility of obtaining composite micropowders of the W-C-Co system with a spherical particle shape having a submicron/nanoscale internal structure was experimentally confirmed. In the course of work carried out, W-C-Co system nanopowders with the average particle size of approximately 50 nm were produced by plasma-chemical synthesis. This method resulted in the uniform distribution of W, Co and C among the nanoparticles of the powder in the nanometer scale range. Dense microgranules with an average size of 40 microns were obtained from the nanopowders by spray drying. The spherical micropowders with an average particle size of 20 microns were received as a result of plasma treatment of 25.36 microns microgranule fraction. The spherical particles obtained in the experiments had a predominantly dense microstructure and had no internal cavities. The influence of plasma treatment process parameters on dispersity, phase, and chemical composition of spherical micropowders and powder particles microstructure has been established.

Plasma way to obtain ultrafine iron and aluminum oxides

The paper deals with two plasma-chemical synthesis installations based on alternating cur-rent plasma torches with power up to 30 kW, which can be used for production of ultrafine (nanosized) oxide and carbide materials. Some results obtained during experimental studies on the production of ultrafine powders of metal oxides (iron and aluminum) are presented.

Diborides of transition metals: Properties, application and production. review. Part 2. Chromium and zirconium diborides

The second part of the review considers properties, application and methods for producing chromium and zirconium diborides. These diborides are oxygen-free refractory metal-like compounds. As a result, they are characterized by high values of thermal and electrical conductivity. Their hardness is relatively high. Chromium and zirconium diborides exhibit significant chemical resistance in aggressive environments. They have found application in modern technology because of these reasons. Chromium diboride is used as a sintering additive to improve the properties of ceramics based on boron carbide and titanium diboride. Zirconium diboride is a component of advanced ultra-high temperature ceramics (UHTC) ZrB2–SiC used in supersonic aircrafts and in gas turbine assemblies. Ceramics B4C–CrB2and B4C–ZrB2have high-quality performance characteristics, in particular, increased crack resistance. The properties of refractory compounds depend on the content of impurities and dispersion. Therefore, to solve a specific problem associated with the use of refractory compounds, it is important to choose the method of their preparation correctly, to determine the admissible content of impurities in the starting components. This leads to the presence of different methods for the borides synthesis. The main methods for their preparation are:a) synthesis from elements;b) borothermal reduction of oxides;c) carbothermal reduction (reduction of mixtures of metal oxides and boron with carbon;d) metallothermal reduction of metal oxides and boron mixtures;e) boron-carbide reduction. Plasma-chemical synthesis (deposition from the vapor-gas phase) is also used to obtain diboride nanopowders. Each of these methods is described.

Microwave assisted synthesis of WC nanopowder from nanosized multicomponent system W-C produced in thermal plasma reactor

The effect of processing multicomponent nanopowders of the W-C system obtained by plasma-chemical synthesis in a microwave electromagnetic field with a frequency of 24 GHz, generated by continuous gyrotron, has been experimentally studied. It was found that the formation of nanosized particles of tungsten carbide WC occurs during microwave treatment. The influence of the processing time, microwave power and the composition of the gas atmosphere on the phase composition of nanopowders, their morphology and specific surface area was investigated.It has been found that processing in a microwave field can reduce the time of chemical transformations, leading to the formation of tungsten monocarbide, by an order of magnitude compared to traditional heating in an electric furnace in a hydrogen environment. At the same time, the particle size is preserved in the nanometer range.

Direct one-stage plasma-chemical synthesis of chalcogenide films doped with ytterbium

In this paper we descried the plasma-enhanced chemical vapor deposition (PECVD) approach for preparation of the arsenic sulfide thin films modified by ytterbium. Radio frequency (40.68 MHz) plasma discharge at low pressure (0.1 Torr) was used for the initiation of chemical interactions between precursors. Arsenic monosulfide (As4S4), elemental high-pure S and Yb were employed as the starting materials. The composition of the films was controlled by regulating of the temperature of the ytterbium source supplied with external heater. The Yb concentration in the Yb:AsxSy films was from 1 to 7 at%. The chalcogenide materials were also studied by Scanning Electron Microscopy (SEM), Optical spectroscopy in the range of 250-1000 nm, and Raman spectroscopy.

Physicochemical, optical, and photocatalytic properties of titanium dioxide modified with zinc oxide nanoparticles synthesized by a pulsed plasma chemical method

In this study, particles of titanium dioxide (TiO2) were modified with particles of zinc oxide (ZnO) using a pulsed plasma chemical method, with ZnO initially being obtained by an electrospark method. The particle size of the synthesized TiO2 powder modified with ZnO nanoparticles ranged from 30 to 100 nm. The morphology of the nanoparticles was found to be diverse, mainly represented by spheres, ovals, and parallelograms. The phase composition was a mixture of crystalline phases characteristic of TiO2 (rutile and anatase) and ZnO, with the predominant phase being anatase. The presence of Zn–O–Ti bond is typical for all samples of TiO2 powder modified with ZnO nanoparticles prepared using a pulsed plasma chemical synthesis, which indicates the formation of a solid solution. The optical and photocatalytic properties of the modified nanoparticles were also studied, as well as the band gap was determined. For some samples, a narrowing of the band gap was recorded. The samples showed high photocatalytic activity in the decomposition of methylene blue under the influence of ultraviolet and visible light in the wavelength range of 400–630 nm. Methylene blue degradation efficiency was 66% in visible light spectrum.