Physical and chemical aspects of the study of clusters, nanostructures and nanomaterials. Founded at 2009

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On the energetics of vacancy formation and diffusion in mesoporous materials

A.V. Shishulin, A.V. Shishulina
Nizhny Novgorod State Technical University named after R.E. Alekseev

Abstract: This paper examines the dependence of the vacancy formation energy and the activation energy of volume diffusion in the «skeleton» of a mesoporous material on the geometric characteristics (volume and shape) of the pores distributed within the material. The geometric features of the pores were defined within a fractal-geometric approach by their effective diameter and fractal dimension. The presented estimates indicate that the effect characteristic of nanoparticles, associated with the significant dependence of the vacancy formation energy and the activation energy of volume diffusion on the particle size and shape, can also occur in mesoporous materials (with a characteristic pore size from 5 to 50 nm), even though the mesoporous objects themselves can have macroscopic dimensions. Using porous gold as an example, it is shown that a decrease in the pore volume and a «complication» of their morphology lead to a noticeable reduction in the considered energy characteristics. The results were obtained within the framework of the cohesive energy-based model.
Keywords: vacancy formation energy, volume diffusion activation energy, mesoporous materials, fractal dimension, cohesion, size distribution, Hardy-Ramanujan-Rademacher formula

On the phase separation in nanoscale particle systems: the role of external environment (exemplified on W-Cr pseudo-alloy)

A.V. Shishulin, E.A. Vlyalkova, A.V. Shishulina
Nizhny Novgorod State Technical University named after R.E. Alekseev

Abstract: Due to their unique combination of physicochemical properties, heavy tungsten-based pseudo-alloys with an ultrafine-grained structure produced from nanoparticles by advanced powder metallurgy techniques have become a subject of considerable research interest. In this work, within the framework of a thermodynamic approach, we simulate the features of the phase composition in core-shell nanoparticles formed from a phase-separating solid solution, using the heavy W-Cr pseudo-alloy as a model system. For a binary system with limited solid-state solubility, a specific effect is demonstrated: in contrast to macroscopic systems, the equilibrium composition and volume fraction of the coexisting nanophases vary significantly depending on the chemical nature of the external environment. The environment dictates the surface energy of the outer interface. The set of considered modellin dispersion media includes argon (a common sintering atmosphere), hydrogen (an annealing atmosphere), and several others. For two distinct heterogeneous states of the core-shell structure, temperature dependences of the equilibrium phase composition in each state were obtained. A thermodynamic interpretation of the observed regularities is provided, based on three possible mechanisms for reducing the free energy of the system.
Keywords: nanoparticles, solution decomposition, chemical thermodynamics, solubility, core-shell, tungsten, chromium

Study of the parameters of carbon nanostructures synthesis in microwave co-pyrolysis of polystyrene and microcrystalline cellulose

A.N. Zaritovskii1, E.N. Kotenko1, S.V. Grishchuk1, V.A. Glazunova1, G.K. Volkova1
Galkin Donetsk Institute for Physics and Engineering
1 L.M. Litvinenko Institute of Physical Organic and Coal Chemistry

Abstract: The parameters of the synthesis of carbon nanostructures during microwave catalytic co-pyrolysis of polymer materials were studied. Polystyrene, which is a typical high-carbon synthetic polymer, and microcrystalline cellulose, a renewable environmentally friendly source of carbon of plant origin, were selected as carbon donors. The processes were carried out in the presence of a mixture of nickel and iron oxalates, which serve as metal catalysts precursors, using granulated activated carbon of AG-3 grade as a microwave absorber to convert electromagnetic energy into thermal energy. The effect of microwave acceptor concentration, treatment time and method of preparing the reaction mixture on the formation of multi-walled carbon nanotubes was investigated. It has been established that the optimal conditions for the synthesis process of the target product are achieved at a microwave acceptor concentration of 40% (wt.) and a cyclic exposure to microwave radiation with a power of 1000 W for 5-12 minutes. The results of studies were confirmed by the data of transmission electron microscopy and X-ray phase analysis.
Keywords: microwave co-pyrolysis, multi-walled carbon nanotubes, polystyrene, cellulose

Simulating the evaporation process of magnetic nanofluid to estimate the service life of magnetic fluid devices

A.N. Bolotov, O.O. Novikova
Tver State Technical University

Abstract: A generalized approach to calculating the service life of magnetic fluid tribological units operating in vacuum and gas environments is presented. The physical mechanisms of magnetic nanofluid degradation during dispersion medium evaporation and increasing solid phase concentration are examined. A statistical approach developed by Ya. I. Frenkel is used to estimate the rate of nanofluid liquid phase evaporation into a vacuum. An equation for the time dependence of the dispersed phase concentration in a magnetic fluid was obtained for calculating the durability of magnetic fluid devices in a vacuum. The dynamics of magnetic nanofluid mass loss upon contact with a gaseous medium was described using а diffusion mass transfer equation. An electrostatic analogy method was used to solve this equation. The time during which the volume content of the dispersed phase of the magnetic nanofluid increases to a limiting value was determined for magnetic fluid tribounits with an open fluid surface and those enclosed in a chamber with a small opening. Based on the obtained calculation relationships linking evaporation parameters with changes in the volume fraction of the dispersed phase and the maximum permissible viscosity criterion, an engineering methodology for assessing the service life of magnetic fluid bearings and seals has been developed. Recommendations for selecting magnetic fluid and operating modes that maximize its service life are provided.
Keywords: magnetic fluid, evaporation, dispersion medium, friction unit life, viscosity, plain bearing

Thermal desorption kinetics of titanium and titanium-vanadium gas absorbers

A.V. Parashchuk, E.P. Shehin
Moscow Institute of Physics and Technology (National Research University)

Abstract: The processes of gas release from titanium and titanium-vanadium getter materials used in electrovacuum devices were studied using thermodesorption spectroscopy. Two consecutive heating cycles were performed at a rate of 5°C/min, followed by an isothermal annealing at the end of the heating process. The activation energies of desorption for H2, H2O, CO2 and CH4 were calculated using the Redhead method. It has been shown that during secondary heating after 5 days of keeping in a vacuum, the hydrogen peaks are restored, some new high-temperature water peaks appear, and methane is formed, which was not present during the primary heating. For the Ti-V alloy, all desorption processes are shifted to lower temperatures (maximum of 550°C) with an activation energy of 2,52 eV compared to 3,62 eV for pure titanium. It has been established that during exposure at room temperature, getters sorb hydrogen, oxygen, and carbon-containing gases from the residual atmosphere, and the sorbated components enter into chemical interaction.
Keywords: thermodesorption spectroscopy, getter, titanium, titanium-vanadium alloy, activation energy, desorption, sorption, electrovacuum devices, Redhead method

Quantum-chemical calculation of the zinc(II) glycine complex: synthesis, structure, properties, determination of stability constants

D.V. Bespalov, O.A. Golovanova
Omsk State University named after F.M. Dostoevsky

Abstract: The combined application of quantum-chemical methods of density functional theory (DFT/B3LYP) with the 6‑31G(d,p) basis set and the semiempirical GFN2‑xTB method allowed to construct a reliable model of an isolated molecule of the zinc glycine complex. The structure was optimized, and the thermodynamic characteristics and infrared spectrum of the studied complex were calculated. Using potentiometric titration according to the Calvin-Melchior method, the stability constants of the complexes in the zinc–glycine system were determined. The ZnGly2 complex was synthesized. The 1:2 molar ratio was confirmed by complexometric and formol titration methods. The infrared spectra of the synthesized compound are presented. A comparison of the experimental and theoretical infrared spectra confirmed the reliability and consistency of the selected quantum-chemical methods. X‑ray phase analysis was used to determine the probable composition of the complex, and the unit cell parameters were calculated using the dichotomy method. The presence of a water molecule in the crystal lattice was confirmed by calculating the van der Waals volumes of atoms, and the average crystallite size was determined using the Scherrer method. The obtained data expand the understanding of the coordination chemistry of zinc and provide a basis for the rational design of bioactive compounds aimed at regulating homeostasis. These data can be used in medicine to prevent pathologies associated with impaired zinc metabolism and the formation of some nanoscale aggregates.
Keywords: synthesis, amino acids, zinc complexes, glycine, density functional method, molecular modeling

Model of the diffusion process in a nanostructured system as a generator of pseudorandom sequences

A.V. Shishulin, A.V. Shishulina
Nizhny Novgorod State Technical University n.a. R.E. Alekseev

Abstract: Complex random number generators that combine rapid pseudorandom sequence generation with hardware entropy sources have numerous practical applications in stochastic process modeling, machine learning, and information security. This paper presents a method for generating pseudorandom sequences based on a physical model of particle diffusion within a nanoscale periodic structure featuring a nonlinear potential and thermal noise, which serve as sources of dynamic chaos. The sequence of thermally activated transitions between potential minima exhibits irregular and chaotic behavior. The sequence generation is achieved through the digitalization of the particle’s stochastic motion along the energy landscape of the nanostructure. Particle diffusion in a nanostructured medium is described by the Langevin equation and is integrating by using the Verlet method. Additionally, a software implementation of the suggested algorithm is provided in the Ruby programming language. The obtained results demonstrate the potential for using a «pseudophysical» approach, which is based on nonlinear potentials of various physical natures, as a viable alternative to a «purely mathematical» methodology in the tasks involving the generation of random number sets.
Keywords: nanostructures, diffusion, nonlinear potential, dynamic chaos, pseudorandom numbers

A planar array of GST225-based memristor elements

V.A. Mikhalevsky1, A.A. Burtsev1, V.V. Ionin1, A.A. Nevzorov1,2, A.V. Kiselev1, N.N. Eliseev1, A.A. Lotin1,3
1 National Research Centre «Kurchatov Institute»
2 National University of Science and Technology MISIS
3 Mendeleev University of Chemical Technology

Abstract: This paper presents a modeling study of the electrical resistance in a memristor structure based on the phase-change Ge₂Sb₂Te₅ material. The changes in resistance are driven by some structural transformations in the active region of the memory cell under the influence of electrical control pulses. A novel planar architecture for memristor structures has been demonstrated. Using the simulation data for this architecture, temperature dynamics and phase transitions are analyzed within the framework of the classical Stefan problem. Optimal parameters for the electrical control pulses are identified. The results demonstrate that once the phase transition threshold is reached, the resistance switching time becomes essentially independent of the control parameters. The proposed memristor architecture exhibits advantages in both power efficiency and the capability for multilevel resistance states, positioning it as a key component for next-generation memristive technologies.
Keywords: memristor, chalcogenides, phase change materials, thin films, amorphization

Corrosion resistance of composite zinc-nanodiamond coatings

E.G. Korzh, V.E. Burlakova
Don State Technical University

Abstract: In the work, nanodiamonds were obtained by the method of hydrodynamic cavitation by LLC ICC «Sintez». The synthesized nanodiamonds were studied using atomic force microscopy and it was found that their particles have a shape close to spherical, and the particle size along the Z axis does not exceed 10 nm. The particles agglomerate and form larger structures up to 100 nm in size. The synthesized nanodiamonds in the form of colloidal solutions with a concentration of 0,5%, 1%, 3%, 5% and 7% were used in a galvanizing electrolyte to obtain composite zinc-nanodiamond coatings. The resulting coatings were studied using X-ray phase analysis and scanning electron microscopy. The presence of a carbon phase in the composition of the composite zinc coating corresponding to a diamond-like structure was proven. It was found that the morphological features of the zinc-nanodiamond coating surface differ significantly from the morphology of the zinc coating surface, which is expressed in the absence of a large number of depressions and irregularities. The corrosion activity of zinc-nanodiamond coatings was tested in a 3% sodium chloride (NaCl) solution. It was determined that composite zinc-nanodiamond coatings have increased corrosion resistance compared to zinc coatings, while the corrosion rate is reduced by 42%.
Keywords: nanodiamonds, zinc coating, composite coating, zinc-nanodiamond coating, corrosion

Metal oxide nanocomposites with plasmonic nanoparticles for photocatalysts and gas sensors

S.S. Nalimova1, Z.V. Shomakhov2
1 Saint Petersburg Electrotechnical University «LETI»
2 Kabardino-Balkarian State University named after H.M. Berbekov

Abstract: The increased absorption of light by metal oxide materials modified with plasmonic nanoparticles in the visible range makes them excellent candidates for use in photocatalysts and light activated gas sensors. The photocatalytic properties of these nanocomposite materials are studied. The main results of research on the decomposition of various organic dyes using these catalysts are analyzed. The effect of metallic nanoparticles on photocatalytic properties is explained by the formation of a Schottky barrier, as well as the effect of localized surface plasmon resonance (LPPR). The Schottky barrier at the metal-oxide interface efficiently separates and transfers charge carriers through an internal electric field, leading to an increase in photodegradation efficiency. This is achieved by separating electron-hole pairs and reducing the rate of charge carrier recombination. Due to the LPPR, the absorption of light increases, which leads to an increase in the generation of active charge carriers. Various authors have studied the response of composite structures composed of metal oxides and plasmonic nanoparticles to oxidizing and reducing gases under different experimental conditions, and their results have been summarized. The main reason for this increased response is an increase in the concentration of adsorbed oxygen ions due to transfer of photogenerated in plasmonic nanoparticles electrons. Mechanisms of the influence of the surface plasmon resonance effect on the properties of chemical gas sensors and photocatalysts involves the formation of a Schottky barrier when a noble metal contacts a semiconductor, the direct transfer of electrons, a local amplification of the electric field, and the transfer of the plasmon resonance energy.
Keywords: nanoparticles, metal oxide, photocatalysts, gas sensors, localized surface plasmon resonance