A method of obtaining highly dispersed tin (II) oxide (SnO) powder by the evaporation-condensation method was investigated when the initial material was heated by focused radiation of a subterahertz gyrotron with a frequency of 0.26 THz and a power of 1 kW. The process was carried out with a purge with nitrogen inert with respect to SnO. A powder with a SnO weight content of 92% was obtained. The specific surface was 7.20 m2/g, which corresponds to an average particle size of 130 nm. The characteristics of the obtained powder are analyzed. The applicability of the experimental setup for the production of nanopowders from compounds requiring special gas conditions during the evaporation-condensation process has been demonstrated.

A method for the preparation of a highly dispersed powder of tin monoxide (SnO) by the evaporation/condensation method under heating the initial material with focused radiation of a subterahertz gyrotron with a frequency of 0.26 THz and a power of 1 kW is investigated. The process is carried out with a purge with nitrogen that is inert with respect to SnO. A powder with a SnO content of 92 wt % is obtained. The specific surface area of the powder is 7.20 m 2 /g, which corresponds to an average particle size of 130 nm. The characteristics of the obtained powder are analyzed. The applicability of the experimental setup for the production of highly dispersed powders from compounds that require special gas conditions in the evaporation/condensation process is demonstrated.

Spheroidization of micropowders of a heat-resistant alloy based on nickel aluminide with a particle size of 20 to 45 μm was studied. The alloy was produced by calcium hydride reduction (CHR) and elemental synthesis (SHS). The spheroidization was carried out in a flow of argon–hydrogen thermal plasma generated by a direct-current (DC) plasma torch. The degree of spheroidization of the micropowders reached 98.5%, and the flowability was 20 s/50 g.

Spherical Nb-Si powder alloy is a perspective material to manufacture products for the aerospace industry by additive technologies. Nb-16Si (at.%) powder alloy was prepared by mechanical alloying from pure elemental powders using planetary ball mill Fritsch Pulverisette 4. Spheroidization was carried out on plasma generator based on thermal plasma arc generator with vortex discharge stabilization. Experimental results show that plasma spheroidizing of Nb-16Si powders obtained by mechanical alloying is possible. It is shown that after the spheroidization the particle surface is rough which indicates the cast structure of the material. Three phases having different optical contrast are revealed on microsections: Nb5Si3, Nb3Si and Nbss, which is confirmed by X-ray diffraction. It is shown that the main peaks in the X-ray graph after MA correspond to a solid solution of niobium with a cubic lattice and the parameter a = 0.333 nm, as well as niobium silicide Nb5Si3 with a hexagonal lattice (P63/m) a = 0.7536 nm and c = 0.5249 nm. After spheroidization the hexagonal lattice of niobium silicide Nb5Si3 is transformed into a tetragonal lattice (I4/m) with the parameter a = 0.6557 nm and c = 1.186 nm. The other phase components remain unchanged.

The development of new, more refractory heat-resistant materials for gas-turbine engines is one of most important problems of modern materials science. This is associated with the fact that nickel superalloys currently used for this purpose have a lower melting point of ~1400°C, which limits their own maximal working temperature by a range of 1100–1150°C. The Ni alloys can be replaced by natural composites, in which refractory metals are a matrix, while their silicides are intermetallic hardeners. Only three “refractory metal–silicon” binary systems manifest stability to the Me5Si3 silicide, notably, Nb5Si3, Re5Si3, and W5Si3. From the viewpoint of a combination of a high melting point and a low density, the Nb5Si3 compound is optimal among other silicides. The use of alloys of the Nb–Si system in additive manufacturing machines is of considerable interest. This work presents the results of experimental investigations into the treatment of the Nb–16 at % Si powder fabricated using mechanical alloying of elemental Nb and Si powders in the thermal plasma flux. The Nb–16Si alloy powder is fabricated by the mechanical alloying of powders of pure elements in a Fritsch Pulverisette 4 planetary mill. The powder spheroidization is performed in a plasma installation based on a discharge vortex-stabilized electric-arc thermal plasma generator. Based on the results of experimental investigations, the principal possibility to perform the plasma spheroidization of particles of the Nb–16Si alloy prepared by mechanical alloying is shown. It is shown that the surface of spheroidized particles is rough and reflects the cast material structure. Three phase components Nb5Si3, Nb3Si, and Nbss having different optical contrast are revealed in microslices, which is confirmed by X-ray phase analysis.

The creation of new higher melting temperature materials for gas turbine engines is one of the most important tasks of modern materials. This is due to the fact that nickel superalloys currently used for these purposes have a low melting point about 1400 °C which limits their own maximum working temperature to 1100–1150 °C. Ni alloys can be replaced by natural composites with refractory metals as a matrix and their silicides as intermetallic hardeners. Only three of refractory metal – silicon binary systems exhibit stability to the Me5Si3 silicide, namely Nb5Si3, Re5Si3 and W5Si3, Nb5Si3 is the best compound among other silicides with regard to the combination of high melting point and low density. The use of Nb–Si alloys in additive manufacturing machines is of considerable interest. The paper presents the results of experimental studies on the thermal plasma processing of Nb–16Si alloy powder prepared by mechanical alloying of Nb and Si elemental powders. Nb–16Si (at.%) alloy powder was prepared by mechanical alloying of pure element powders using the Fritsch Pulverisette 4 planetary mill. Spheroidization was carried out on a plasma unit based on vortex-stabilized arc thermal plasma generator. The results of experimental studies conducted confirmed the possibility to perform plasma spheroidization of Nb–16Si alloy powder particles obtained by mechanical alloying. It is shown that the particle surface after spheroidization is rough and reflects the cast structure of the material. Three phase components having different optical contrast are revealed on microsections: Nb5Si3, Nb3Si and Nbss, which is confirmed by X-ray diffraction.

With the help of a complex of methods of disperse-structure analysis of nanopowders of plasmachemical synthesis, the function of particle-size distribution and its main characteristics—the average size and dispersion—are studied. A generalization of results of disperse characteristics for nanoparticles formed with the participation of various mechanisms—“vapor–solid” and “vapor–liquid–solid”—is carried out. It is shown that the formation of titanium nitride and carbonitride nanoparticles proceed on the vapor–solid mechanism without the participation of coagulative-particle growth. For the nanopowders under study, it is established that the variation range of standard deviation for the distribution function is in the interval of 30–60% of the average diameter; the index of aggregation is defined in the range of 1.5–3.0. It is revealed that the logarithmically normal function of particle-size distribution most authentically (with a correlation coefficient of more than 0.95) describes all studied objects for all mechanisms of particle formation in a wide range of dispersion of the received nanopowders independently of process parameters and organization of gas-disperse stream in the plasma reactor. Hypothetically, the established lognormal particle-size distribution is determined by the lognormal distribution of nanoparticles by residence time in the growth zone.

WinFit software is used to determine using the profile of a single diffraction peak the sizes of coherent scattering domains and microstrains for tungsten powders obtained through plasma chemical synthesis and hydrogen reduction from tungstic acid. It is shown that the use of the (110), (200) or (211) diffraction peaks is the most expedient for the calculations. At the same time, it should be noted that, in the case of significant microstrains, the sizes of coherent scattering domains calculated using the second and the third peaks are underestimated.

Fabrication of WO3 tungsten oxide nanoparticles by evaporation of the initial oxide material with a focused beam of 24-GHz electromagnetic radiation generated in a 5-kW gyrotron complex at a design microwave power density of 10 kW/cm2 has been experimentally studied. Tungsten oxide powders consisting of particles, which sizes are in range of 20 nm up to 1 μm, have been obtained. The particles have different shapes, close to spherical or octahedral, suggesting their formation via both the “vapor-liquid-crystal” and the “vapor-crystal” mechanism. The maximal evaporation rate was 100 g/h. The feasibility of powder dispersity controlling by varying the flow rate of cooling air has been revealed.

Приведены результаты экспериментальных исследований получения частиц оксида вольфрама WO3 из паров, образующихся при испарении исходного материала сфокусированным потоком электромагнитного излучения с частотой 24 ГГц, генерируемом в гиротронном комплексе мощностью 5 кВт с расчетной плотностью потока СВЧ энергии 10 кВт/см2. Получены порошки WO3, состоящие из частиц, размеры которых находятся в диапазоне 20 нм до 1 мкм. Частицы имеют различную форму – как близкую к сферической, так и форму октаэдров, что свидетельствует о протекании формирования частиц по механизмам “пар–жидкость–кристалл”, так и “пар–кристалл”. Максимальная скорость испарения составила 100 г/ч. Установлена возможность управления дисперсностью получаемого порошка при изменении расхода охлаждающего воздуха.

Microstructural characteristics of tungsten nanopowders were determined by the Williams-Hall method from the experimental data obtained using an Ultima IV diffractometer with high-speed detector. The effect of the change in the slit size limiting the divergence of the incident beam on the tungsten diffraction peak profiles was investigated. It was shown that insignificant changes in the profile characteristics affect only slightly the results of microstructural analysis.

Air–methane and nitrogen–hydrogen DC thermal plasma confined flows were used to synthesize tungsten carbide and vanadium carbide nanopowders. The influence of input process parameters such as C/W and C/V molar ratio, plasma jet chemical composition, plasma jet enthalpy, and reactants flow rates on the average nanoparticle size, chemical and crystallographic phase compositions were investigated. During post heat treatment, the synthesized MeC1−x nanopowders were fully carburized to monocarbides WC and VC with particles size less than 80 and 40 nm correspondently.

We present X-ray diffraction data for Al2O3 nanopowders prepared by oxidizing aluminum powder in an air plasma, followed by size separation via centrifugation and heat treatment.