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.

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.

The spectrum of inelastic collisions of low-energy protons in the field of molecular excitations of water is obtained in terms of the complex refractive index of water determined from optical measurements in the infrared, visible, and ultraviolet regions. In the range of atomic frequencies (energies), the inelastic collision spectrum is determined from the integrated absorption cross section of X and gamma rays. The resulting spectra will extend the range of applicability of the photoionization model, which is of interest for improving dosimetry planning of the exposure of patients in proton (ion) therapy.

Gold, nickel and platinum nanoparticles (NPs) have been synthesized by impregnating single-crystalline silicon surface with precursors (aqueous solutions of corresponding salts). The morphologies of the formed nanostructured coatings have been studied, and the electronic structures of the synthesized NPs, as well as their adsorption properties with respect to H2, O2, and H2O, have been determined. It has been found that oxidized nickel NPs are reduced by molecular hydrogen, while pure platinum NPs are oxidized by molecular oxygen already at room temperature. This phenomenon has not been observed for particles deposited in a similar way onto highly oriented pyrolytic graphite. In addition, it has been revealed that water molecules are formed on gold NPs as a result of the interaction between H2 and O2 in two stages, in contrast to the three-stage process (sequential exposure in H2, O2, and H2), which is inherent in NPs deposited onto graphite. Differences in the adsorption properties of NPs of the same type deposited onto graphite and silicon are associated with the adsorption of a significant amount of the test gases on the latter.

Quantum chemical calculations of the heats of reduction with carbon monoxide of the simplest electrically neutral or electrically charged oxides and oxides of nickel Ni2O2 and Ni2O, as well as of copper oxides and oxides of Cu2O2 and Cu2O, are performed. The heats of transformation of neutral or charged oxides and oxides of copper into active isomers with an O-radical are also calculated. Based on the calculation results, an explanation is proposed for the experimental results on the change in the rate of reduction of oxidized nickel and copper nanoparticles by carbon monoxide when an electric voltage is applied to them.

Five resonant states of long-lived negative molecular ions were defined during the gas-phase resonant electron capture by perylene. Three states are the ground state (0.05 eV) and two shape resonances (0.4 eV and 0.7 eV). Core-excited Feshbach resonance (1.4 eV) transits into a quartet state, which delays the autodetachment of additional electron and causes the negative differential conductance in tunneling transition due to the spin prohibition. Inter-shell resonance (2.5 eV) is mixed with the ground state with the same symmetry and is likely to be stabilized through the light emission with simultaneous transition to a quartet state.

Calculations showed that hydrogen adsorption into subsurface sites is most likely to occur on Au (110) and (211) faces. The presence of low-coordinated Au atoms on significantly reduces the barrier of subsurface adsorption of H. The barriers of H surface diffusion increase in the following Au series: (110) < (111) < (100) < (211). An analysis of the dependence of the surface diffusion barriers on the electronic structure of gold atoms on the respective faces revealed a U-shaped dependence of the centers of the s- and d-bands. This dependence is the result of the filling of the s- and d-bands on different faces of the gold. The results obtained suggest that it is possible to use band centers to determine surface diffusion barriers.

С помощью моделирования в рамках теории функционала плотности адсорбции атомарных кислорода и водорода на поверхности наночастиц палладия на подложках графита с различными дефектами были рассчитаны энергии связи адатомов и изменения плотности состояний атомов металла при взаимодействии с адатомами. Установлено, что энергетическая стабильность адсорбции кислорода и водорода не зависит от места адсорбции адатома на поверхности наночастицы (интерфейс или вершина), что согласуется с результатами СТМ/СТС-экспериментов.

A correlation is shown between the negative differential conductance of single molecules recorded using scanning tunneling microscopes and gas-phase long-lived negative ions formed upon resonant electron capture by the same molecules with a multiplicity of four (4TNI#) and a spin prohibition on the rapid autodetachment of an additional electron. It is assumed that negative differential conductance in the studied compounds is associated with the formation of 4TNI# ions in scanning tunneling microscopes, which suppress the tunneling current due to a similar spin prohibition. Remarks are made about a possible mechanism for the formation of 4TNI# ions in scanning tunneling microscopes.

Density functional theory (DFT) modeling of the adsorption of atomic oxygen and hydrogen on the surface of palladium nanoparticles on graphite substrates with various defects is used to calculate the binding energies of adatoms and changes in the density of states of metal atoms upon interaction with adatoms. It is established that the adsorption of oxygen and hydrogen does not have more energetically favorable or stable adsorption sites on the surface of the nanoparticle, such as the interface with the substrate or the top, which is consistent with the results of the scanning tunneling microscopy and spectroscopy (STM/STS) experiments.

— A nanostructured gold–nickel coating has been synthesized on the surface of pyrolytic graphite. Its physicochemical properties have been studied by scanning tunneling microscopy and spectroscopy, Auger spectroscopy, mass spectrometry, and other methods. It has been found that the coating consists of clusters formed by gold and nickel nanoparticles. It has been shown that an electric field can inhibit or stimulate the adsorption of hydrogen on gold and the reduction of the oxidized surface of nickel nanoparticles with carbon monoxide. The mechanisms of the influence of the field on the chemical processes involving H 2 and CO are different. Quantum-chemical simulation has made it possible to determine the values of the energy barriers for CO adsorption on nickel nanoparticles.

In this work, we studied the local adsorption properties of gold, nickel, and platinum nanoparticles. A correlation was established between the chemical properties of massive and nanosized particles of these metals. The formation of a stable adsorption complex M-A(ads) on the nanoparticles' surface was described. It was shown that the difference in local adsorption properties is caused by specific contributions of nanoparticle charging, the deformation of its atomic lattice near the M-C interface, and the hybridization of the surface s- and p-states. The contribution of each factor to the formation of the M-A(ads) chemical bond was described in terms of the Newns-Anderson chemisorption model.

Application of a potential to a gas phase reaction catalyst is one of the possible methods of catalytic activity control. Since this approach is not popular, there are few publications about the effect of applied potential and some aspects of this phenomenon have not been considered at all. However, it is of great interest to identify the factors that increase the activity of the reaction under conditions of applied potential. In this study, the activity of copper oxide reduction by carbon monoxide at an applied potential was analyzed by quantum-chemical calculations. According to the estimates, the highest activity should be observed for Cu2O; the activity of CuO allotropes should be substantially lower. Low potentials of about one volt affect the binding energies of CO with oxides and the energy of the oxide reduction reaction, which eventually determines the activity of oxide reduction. A detailed analysis of the electronic structure of oxides does not allow us to draw clear conclusions about the activity. The electric field is assumed to be able to affect reduction when the oxides reach potentials of & SIM;& PLUSMN;2 V. In the case of Cu2O and CuO allotropes, the negative potential promotes the reduction reaction, which is consistent with the experiment. Calculations also showed that the differences in the reduction reaction energies of CuO allotropes at different potentials are due to the local changes in the interatomic bonding in these systems. The negative potential promotes the reduction reaction of copper oxides by carbon monoxide in the gas phase.

Measurements are reported of the increase in catalytic CO oxidation rate on gold nanocoatings obtained by applying a positive or negative electrical voltage of variable magnitude to a coating. In experiments on an initial mixture of 1.8

— Heterogeneous catalytic reactions involving nitrous oxide (N 2 O) are of great interest for medicine, technology, and ecology. The goal of this work is to determine the features of adsorption of N 2 O molecules followed by their interaction with a catalytic system based on metal nanoparticles at room temperature. Scanning tunneling microscopy and spectroscopy, as well as Auger spectroscopy, have been employed to identify the results and products of the adsorption of nitrous oxide on the surface of individual Pt nanoparticles synthesized on highly oriented pyrolytic graphite. It has been shown that, at short exposures, oxygen atoms resulting from dissociative adsorption oxidize the surface of nanoparticles only near the platinum–graphite interface. As the exposure increases, the entire surface of the nanoparticles is covered with oxide. Thus, it has been shown that the adsorption properties of the surface of the platinum nanoparticles on graphite are not the same, and this fact provides the possibility to carry out different chemical reactions on different surface regions, thereby increasing the efficiency of the catalytic system as a whole.

Экспериментально определено увеличение скорости каталитического окисления СО на покрытиях из наночастиц золота при подаче на них электрического напряжения различной полярности и величины от внешнего источника. В условиях эксперимента при 430 °С, атмосферном давлении, начальном составе смеси 1.8% СО + 10.2% О 2 + Ar и начальном размере частиц покрытия 0.2–3 нм последовательное увеличение подаваемого положительного напряжения U вначале приводит к росту скорости окисления СО на 28% при U = +10 В, плавно снижающемуся до 20% при U = +30 В. Подача отрицательного напряжения менее эффективна: вначале скорость окисления растет на 12% при U = –10 В, а затем снижается до 7% при U = –30 В. Выполнены квантовохимические расчеты теплот ассоциации СО и О 2 с простейшим электронейтральным или электрически заряженным кластером золота Au 3 , а также теплот реакций Au 3 CO + O → Au 3 CO 2 и Au 3 CO 2 → Au 3 + CO 2 для различных зарядов Au 3 -содержащих комплексов. По результатам расчетов предложено объяснение увеличения скорости каталитического окисления СО на покрытиях из наночастиц золота, электрически заряженных с помощью внешнего источника напряжения.

The oxidation of Ni nanoparticles supported on highly oriented pyrolytic graphite was investigated under conditions of low exposure to oxygen by methods of scanning tunneling microscopy and spectroscopy. It was found that charge transfer effects at the Ni-C interface influenced the surface activity of the nanoparticles. The O2 dissociation and the Ni oxidation were shown to occur only at the top of the nanoparticle, while the border of the Ni-C interface was the less preferable area for these processes. The O2 dissociation was inhibited, and atomic oxygen diffusion was suppressed in the given nanosystem, due to the decrease in holes concentration.

A simple descriptor based on electron density within the modified embedded atom model (MEAM) is proposed to describe the adsorption and dissociation of hydrogen on gold. The correlations of the electron density calculated in the MEAM model are shown at various active centers of the gold cluster on the atomic and molecular hydrogen adsorption energies and H2 dissociation barrier. The algorithm for the MEAM electron density calculation is taken in the form of a program code. The change in the surface activity of gold nanoparticles of various diameters was studied with a descriptor. A sharp increase in the nanoparticles activity was observed at diameters <4.2 nm. A temperature rise is shown to increase the surface activity because of surface morphology changes.

The interaction of CO and H-2 with single clusters of gold and copper-based nanoparticles in the presence of an electric field has been studied. It is shown that depending on the direction of the electric field vector, the adsorption of molecules from the gas phase is stimulated or inhibited. Mechanisms of influence of the field on chemical processes are proposed.

Quartz crystal microbalances (QCMs) are devices that have been proven to function as sensors for detecting specific chemical species; this usually requires that the QCM is modified with a material that is capable to interact with the desired compound. Zeolites are an example of materials used as sensitive layer. This due to their capacity for selective adsorption and large surface area; moreover, they can grow directly on the QCM surface. After, the interaction between sensitive layer and analyte, there is a mass change on the QCM surface, which induces a frequency shift in the frequency generated by the QCM. However, the application of QCMs requires that some factors are considered, such as QCM functioning, wiring and surface functionalization. Even when there are commercial devices for QCM operation, a literature revision shows that some concepts are not understood, or some misconceptions are observed. In this work, the basics of QCM are discussed, from principles of operation to an application where a QCM was functionalized to work as sensor for water vapor.