A. K. Gatin’s research while affiliated with Russian Academy of Sciences and other places

Using quantum chemical modelling, in this work, we considered the structure effects determining the adsorption of H and O atoms on (111), (100), (110) and (211) surfaces of gold, nickel and platinum nanoparticles. Surface deformation enhanced the adatom bonding to active sites with a large coordination number on flat (111) and (100) surfaces, while no distinct tendency was observed on kinked (110) and (211) surfaces. The effect of the neighboring atoms depends on the coupling matrix element Vad2. For metals with a considerable matrix element, the adsorption energy decreases with the rise in coordination number, and vice versa.

A new method of producing metal powders for additive manufacturing by the atomization of free-falling melt streams using pulsed cross-flow gaseous shock or detonation waves is proposed. The method allows the control of shock/detonation wave intensity (from Mach number 4 to about 7), as well as the composition and temperature of the detonation products by choosing proper fuels and oxidizers. The method is implemented in laboratory and industrial setups and preliminarily tested for melts of three materials, namely zinc, aluminum alloy AlMg5, and stainless steel AISI 304, possessing significantly different properties in terms of density, surface tension, and viscosity. Pulsed shock and detonation waves used for the atomization of free-falling melt streams are generated by the pulsed detonation gun (PDG) operating on the stoichiometric mixture of liquid hydrocarbon fuel and gaseous oxygen. The analysis of solidified particles and particle size distribution in the powder is studied by sifting on sieves, optical microscopy, laser diffraction wet dispersion method (WDM), and atomic force microscopy (AFM). The operation process is visualized by a video camera. The minimal size of the powders obtained by the method is shown to be as low as 0.1 to 1 μm, while the maximum size of particles exceeds 400–800 μm. The latter is explained by the deficit of energy in the shock-induced cross-flow for the complete atomization of the melt stream, in particular dense and thick (8 mm) streams of the stainless-steel melt. The mass share of particles with a fraction of 0–10 μm can be at least 20%. The shape of the particles of the finest fractions (0–30 and 30–70 μm) is close to spherical (zinc, aluminum) or perfectly spherical (stainless steel). The shape of particles of coarser fractions (70–140 μm and larger) is more irregular. Zinc and aluminum powders contain agglomerates in the form of particles with fine satellites. The content of agglomerates in stainless-steel powders is very low. In general, the preliminary experiments show that the proposed method for the production of finely dispersed metal powders demonstrates potential in terms of powder characteristics.

The effect of low-pressure direct current discharge on polyphenylene oxide films was studied. Filtered atmospheric air was used as the working gas. It was shown that plasma treatment leads to significant hydrophilization of the polymer surface during treatment at the cathode and anode. The storage of modified films in air leads to a decrease in hydrophilicity, which is more characteristic of films treated at the anode. The change in the chemical structure of plasma-modified samples was studied by X-ray photoelectron spectroscopy and the formation of a significant amount of oxygen-containing groups was shown during plasma treatment of films. The atomic content of oxygen increased to a greater extent after treatment at the anode. Using atomic force microscopy, the change in film morphology after exposure by plasma was studied and a significant increase in their roughness was established. The modified films had significantly higher selectivity of gas permeability for CO2/CH4, CO2/N2 and O2/N2 vapors without reducing the flow of CO2 and O2 relative to the initial values.

The results of a comprehensive investigation into the structure and properties of nanodiamond soot (NDS), obtained from the detonation of various explosive precursors (trinitrotoluene, a trinitrotoluene/hexogen mixture, and tetryl), are presented. The colloidal behavior of the NDS particles in different liquid media was studied. The results of the scanning electron microscopy, dynamic light scattering, zeta potential measurements, and laser diffraction analysis suggested a similarity in the morphology of the NDS particle aggregates and agglomerates. The phase composition of the NDS nanoparticles was studied using X-ray diffraction, Raman spectroscopy, electron diffraction, transmission electron microscopy, atomic force microscopy, and scanning tunneling microscopy. The NDS particles were found to comprise both diamond and graphite phases. The ratio of diamond to graphite phase content varied depending on the NDS explosive precursor, while the graphite phase content had a significant impact on the electrical conductivity of NDS. The study of the mechanical and tribological characteristics of polymer nanocomposites, modified with the selected NDS particles, indicated that NDS of various types can serve as a viable set of model nanofillers.

The magnetic effects (ME) of a moderate magnetic field (MF, 600 mT) on the rate of radical generation (Wi) in mixed micellar systems of quaternary ammonium compounds with hydroperoxides (QAC-ROOH), measured by the inhibitor method, and the effect of magnetic field on the rate of radical polymerization initiated by radicals, generated from the surface by QAC chemisorbed on a solid carrier upon interaction with hydroperoxide dissolved in the monomer are compared. It has been established that in micellar solutions MF reduces Wi, ME ≈ –0.45. In the case of radical polymerization of styrene containing cumyl hydroperoxide on the surface of mica plates with a chemisorbed monolayer of QAC (CTAB or ACh), the polymerization rate increases in MF.

A new method of producing metal powders for additive manufacturing by the atomization of free-falling melt streams using pulsed cross-flow gaseous shock or detonation waves is proposed. The method allows the control of shock/detonation wave intensity (from the Mach number of 4 to about 7), as well as the composition and temperature of the detonation products by choosing proper fuels and oxidizers. The method is implemented in laboratory and industrial setups and preliminarily tested for melts of three materials, namely, Zinc, Aluminum alloy AlMg5, and stainless steel AISI 304 possessing significantly different properties in terms of density, surface tension, and viscosity. Pulsed shock and detonation waves used for the atomization of free-falling melt streams are generated by the pulsed detonation gun operating on the stoichiometric mixture of liquid hydrocarbon fuel and gaseous oxygen. The analysis of solidified particles and particle size distribution in the powder is studied by microscopy, fraction separation by sifting on sieves, laser diffraction wet dispersion method (WDM), and atomic force microscopy (AFM). The operation process is visualized by a video camera. The minimal size of the powders obtained by the method is shown to be as low as 0.1 to 1 mm, while the maximum size of particles exceeds 400–800 mm. The latter is explained by the deficit of energy in the shock-induced cross-flow for the complete atomization of the melt stream, in particular dense and thick (8 mm) streams of the stainless-steel melt. The mass share of particles with a fraction of 0–10 μm can be at least 20%. The shape of the particles of the finest fractions (0–30 and 30–70 μm) is close to spherical (zinc, aluminum) or perfectly spherical (stainless steel). The shape of particles of coarser fractions (70–140 μm and larger) is getting more irregular. Zinc and aluminum powders contain agglomerates in the form of particles with fine satellites. The content of agglomerates in stainless-steel powders is very low. In general, the preliminary experiments show that the proposed method for the production of finely dispersed metal powders looks promising in terms of powder characteristics and cost.

Gold, nickel and platinum nanoparticles were synthesized by impregnating the monocrystalline silicon surface with precursors (an aqueous solution of the corresponding salt). The morphology of formed nanostructured coatings has been studied, the electronic structure and adsorption properties of synthesized nanoparticles with respect to H2, O2, and H2O have been determined. It was found that oxidized nickel nanoparticles are reduced by molecular hydrogen, and unalloyed platinum nanoparticles are oxidized by molecular oxygen already at room temperature, which is not observed for particles deposited in a similar way on highly oriented pyrolytic graphite. We also found that the formation of water molecules on gold nanoparticles in interaction with H2 and O2 proceeds in two stages, unlike the three-stage process (sequential exposure in H2, O2, H2) which is characteristic of nanoparticles deposited on graphite. Differences in the adsorption properties of nanoparticles of the same type deposited on graphite and silicon are associated with the adsorption of a significant amount of test gases on the latter.