A. V. Samokhin

Plasma-Assisted Processes for Manufacturing Nanosized Powder Materials

Theoretical analysis is given to one of the promising processes for the preparation of nanosized metal powders, namely, plasma chemical synthesis by the action of thermal plasma on a material distributed in the plasma. Special attention is given to the methodology of investigation of such plasma jet processes, which may ensure the prediction of results of experimental studies; qualified data processing; and, ultimately, preparation of powders with a prescribed composition and required nanoscale dimensions by means of controlled plasma-chemical synthesis.

Composite coatings formed by plasma electrolytic oxidation

The prospects of using organic and inorganic nanosized materials are shown in the process of the formation of surface multifunctional composite protective layers obtained using plasma electrolytic oxidation on metals and alloys.

Magnetic properties of surface layers formed on titanium by plasma electrolytic oxidation

The magnetic properties of the coatings formed by plasma electrolytic oxidation on titanium and modified by nanoparticles of cobalt were studied. The coercitivity of the obtained magnetoactive layer were equal to 514 Oe at room temperature and to 1024 Oe at 2 K. The high coercitivity is the result of the nanosize effects of particles embedded in the coating. The structure of the nanoparticles, which consist of a Co ferromagnetic core and a CoO antiferromagnetic shell, determines the magnetic properties of the coatings on the whole.

Production of titanium nitride nanopowder from titanium hydride based on synthesis in thermal plasma

The synthesis of TiN nanopowder from titanium hydride in thermal plasma generated in DC arc plasmatron is investigated experimentally. It is shown that a single-phase TiN nanopowder can be produced within a two-stage process consisting of plasma synthesis and separation of powdered product by means of sedimentation. The yield of nanopowder is up to 90%.

Metal Oxide Nanopowder Production by Evaporation–Condensation Using a Focused Microwave Radiation at a Frequency of 24 GHz

The new method for metal oxide nanopowder production is proposed. It is the evaporation–condensation using a focused microwave radiation. The source of microwaves is technological gyrotron with frequency of 24 GHz and power up to 7 kW with the energy density flux of 13 kW/cm2. Radiation was focused on the layer of powder of the treated material to ensure its evaporation, subsequent condensation of vapor in the gas stream, and deposition of particles on the water-cooled surface. Deposited powders consist of particles whose sizes are in the range of 20 nm to 1 μm. The powder consists of particles having different shapes—close to spherical shape as well as octahedral, which indicates that the mechanism of particles formation is “vapor–liquid–crystal” as well as “vapor–crystal.” The maximum evaporation rate was 100 g/hr. The proposed approach is original and extends the possible methods of producing nanoparticles.

Fabrication of coatings on the surface of magnesium alloy by plasma electrolytic oxidation using ZrO 2 and SiO 2 nanoparticles

Reverse osmosis (RO) membranes modified with SnO2 nanoparticles of varied concentrations (0.001-0.1 wt.%) were developed via in situ interfacial polymerization (IP) of trimesoyl chloride (TMC) and m-phenylenediamine (MPD) on nanoporous polysulfone supports. The nanoparticles dispersed in the dense nodular polyamide on the polysulfone side. The effects of IP reaction time and SnO2 loading on membrane separation performance were studied. The modified reverse osmosis membranes were characterized by scanning electron microscopy (SEM), X-ray diffractometer (XRD), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), contact angle measurement, and atomic force microscopy (AFM). The synthesized SnO2 nanoparticles size varies between 10 and 30 nm. The results exhibited a smooth membrane surface and average surface roughness from 31 to 68 nm. Moreover, hydrophilicity was enhanced and contact angle decreased. The outcomes showed that an IP reaction time was essential to form a denser SnO2-polyamide layer for higher salt rejection, the developed reverse osmosis membranes with the incorporation of the SnO2 nanoparticles were examined by measuring permeate fluxes and salt rejection, and the permeate flux increased from 26 to 43.4 L/m2ċh, while salt rejection was high at 98% (2000 ppm NaCl solution at 225 psi (1.55 MPa), 25°C).Structural modifications and their impact upon magnetic properties are studied in amorphous and nanocrystalline NANOPERM-type 57Fe75Mo8Cu1B16 alloy. They are introduced by irradiation with 130 keVN+ ions to the total fluencies of up to 2.5 × 1017 ions/cm2 under different cooling conditions. Increased temperature during the irradiation triggers formation of nanocrystallites of bcc-Fe in those subsurface regions that are affected by bombarding ions. No crystallization occurs when good thermal contact between the irradiated sample and a sample holder is assured. Instead, structural rearrangement which favours development of magnetically active regions was determined by the local probe methods of Mossbauer spectrometry. Dipole magnetic interactions dominate in subsurface regions on that side of the ribbons which was exposed to ion irradiation. Nevertheless, structural modifications demonstrate themselves also via macroscopic magnetic parameters such as temperature dependence of magnetization, Curie temperature, and hysteresis loops. Impact of only the temperature itself to the observed effects is assessed by the help of samples that were subjected just to heat treatment, that is, without ion irradiation.Results of investigation of the incorporation of zirconia and silica nanoparticles into the coatings formed on magnesium alloy by plasma electrolytic oxidation are presented. Comprehensive research of electrochemical and mechanical properties of obtained coatings was carried out. It was established that the polarization resistance of the samples with a coating containing zirconia nanoparticles is two times higher than that for the sample with base PEO layer. One of the important reasons for improving the protective properties of coatings formed in electrolytes containing nanoparticles consists in enhanced morphological characteristics, in particular, the porosity decrease and increase of thickness and resistivity (up to two orders of magnitude for ZrO2- containing coating) of porousless sublayer in comparison with base PEO layer. Incorporation of silica and zirconia particles into the coating increases the mechanical performances. The layers containing nanoparticles have greater hardness and are more wear resistant in comparison with the coatings formed in the base electrolyte.

Synthesis of nanoscale zirconium dioxide powders and composites on their basis in thermal DC Plasma

ZrO2, ZrO2–MgO, and ZrO2–Al2O3 nanopowders are obtained via oxidation of disperse ZrCl4 and its blends with (Mg, Al) metals by oxygen in a plasma reactor with confined plasma jet flow on the basis of an dc arc plasma generator. The change in the ZrCl4 rate and plasma jet enthalpy allows one to synthesize nanopowders with the specific surface area of 18–32 m2/g (Dav = 33–58 nm). The obtained nanopowders are polydisperse, consist of uniaxial spherical particles, and contain 0.25–0.75 wt % of chlorine. The dependence of the chlorine content in powders on the zirconium chloride output exhibits an extreme behavior. The ZrO2 nanopowders represent a mixture of monoclinic and tetragonal zirconium dioxide modifications with approximately equal contents. The ZrO2–MgO nanopowders (10 mol %) with the cubic structure identified as Zr0.875Mg0.125O1.875 are obtained in oxidation of the ZrCl4–Mg mixture in an oxygen–argon plasma stream. The ZrO2–Al2O3 nanopowders (30 wt %) are synthesized by oxidation of the ZrCl4–Al blend, whose phase composition is represented by tetragonal ZrO2 structure with monoclinic phase impurity in the absence of any Al2O3 phases, which can be explained by the formation of nonequilibrium Zr–Al–O solid solution with tetragonal structure as a result of the size effect.

Structure formation and properties of weld alloys with addition of refractory compound nanoparticles

The structure and properties of Fe and Ni3Al weld metals doped with TiCN and WC nanoparticles are investigated via optical and scanning electron microscopy, X-ray spectroscopic microanalysis, and fatigue life and abrasive wear tests.

Interaction of exogenous refractory nanophases with tin dissolved in liquid iron

The interaction of refractory phase nanoparticles (Al2O3 and TiN as an example) 30–100 nm in size with a surface-active substance in the Fe-Sn melt and the subsequent removal of nanoparticle + Sn ensembles to the M/ceramics and M/gas interfaces is studied. A technique for choosing nanoparticles is developed and grounded, and a technique for the introduction of nanoparticles in the melt in the form of nanoparticles-Fe composite material is developed. The dependences of the degree of tin removal during heterophase interaction on the time of holding of nanoparticles in a liquid metal (5–20 min) and the size and the fraction of nanoparticles in the melt are investigated. The changes of the surface tension and the density of the Fe, Fe-Sn, Fe-Sn-Al2O3, and Fe-Sn-TiN melts are analyzed, and the influence of the nature and size of refractory nanoparticles on these properties when temperature changes is revealed.

Production of spherical powders on the basis of group IV metals for additive manufacturing

The method of production of group IV powders for additive manufacturing is presented. Powders are produced in the hydrogenation-dehydrogenation process followed by plasma spheroidization of prepared polygonal powders. The dependence of composition of hydrides on amount of absorbed hydrogen is established for the group IV metals; it allows optimizing the technological parameters of processes for hydrogenation and grinding. It is shown that spherical powders of titanium, Ti–6Al–4V, and Zr–10% Ti of mass fractions of 40–70 μm and not less than 40 μm with calculated spheroidization level achieving 96% may be produced in Ar + 8 vol % H2 thermal plasma flow generated by an arc-jet plasma generator. The average roundness factor is 1.01.