Physical and chemical aspects of the study of clusters, nanostructures and nanomaterials

In this paper, a study of a graphite intercalation compound by potassium was carried out using Raman spectroscopy. The purpose of the study was to determine the intercalation stage and study the influence of intercalated atoms on the vibrational properties of highly oriented pyrolytic graphite lattice. The intercalation of highly oriented pyrolytic graphite by potassium was performed using a two-zone method. Raman spectra were obtained for both pure and intercalated highly oriented pyrolytic graphite. The experiments carried out to identify the synthesized structures showed the formation of sixth stage graphite intercalation compound. Knowledge of the stage of the intercalated graphite compounds is important for its use as a superconducting material, as well as in supercapacitors. In addition, the intercalation stage is a key factor in obtaining graphene by chemical exfoliation of graphite intercalation compound, since the number of graphene layers will directly depend on the intercalation stage. In the obtained Raman spectra, the effect of G -peak splitting is observed, indicating a change in the vibrational properties of the graphite lattice during its intercalation due to the charge transfer from the intercalate to the carbon layers. The value of the transferred charge is determined using first-principles calculations.

As a part of the research work, inorganic lead-containing halide perovskite nanocrystals with the CsPbX ₃ structure were obtained by the hot injection. The alloying of single crystals of perovskites was carried out by solution methods, zinc and indium ions acted as dopants. The photoluminescence spectra and optical density spectra of the obtained colloidal solutions were studied. Our studies have shown that doping of perovskite nanocrystals with metal ions leads to an increase in photoluminescence as well as to a shift in the maximum of photoluminescence relative to the reference composition by 4 and 12 nm for bromides and iodides, respectively. Also, it has been shown that the magnitude of the shift does not depend on the type of dopant. It is noted that within the framework of this work, doping does not lead to a change in the position of the edge of its own absorption.

A comparative analysis of the photoluminescent properties, concentration of OH^- -groups and optical quality of double-doped crystals obtained from charges of different genesis has been performed. In a LiNbO₃:Er (0,53 mol.%): Zn (4,02 mol.%) crystal obtained by solid-phase doping, the content of OH^- -groups is higher than in a LiNbO₃:Er (0,75 mol.%): Zn (3,82 mol.%) crystal obtained by homogeneous doping. These changes occur as a result of the simultaneous formation of two types of complex defects in the LiNbO₃:Er (0,53 mol.%): Zn (4,02 mol.%) crystal structure: Zn_Nb^3--OH and V_Li-OH . It has been established that photoluminescence in the visible region is caused by radiative transitions of Er ³⁺ without the manifestation of the host’s own luminescence in the studied crystals. For the LiNbO₃:Er:Zn crystal obtained by solid-phase doping, the luminescence intensity is 77% higher than in the crystal obtained by homogeneous doping. This may be due to the participation of OH^- -groups in the energy transfer between the host and the Er ³⁺ ions.

The results of an experimental study of the magnetic domain structure on the basal plane of RFe ₁₁ Ti single crystals ( R=Y, Gd, Ho, Er ) by magnetic force microscopy are presented. At room temperature, the compounds are characterized by magnetocrystalline anisotropy of the «easy axis» type. Based on the magnetic force microscopy data, the sizes of domains on the basal plane of the samples were determined. Using the Bodenberger-Hubert method, the surface energy density of domain walls g was determined for all compounds based on the magnetic force microscopy data: YFe ₁₁ Ti - 4,05 mJ/m², GdFe ₁₁ Ti - 5,93 mJ/m², HoFe ₁₁ Ti - 4,97 mJ/m², ErFe ₁₁ Ti - 2,98 mJ/m². The cube counting method was used to calculate the fractal dimension D_L of the stray fields of the domain structure at different heights from the surface (0,1 - 9 μm). D_L on the surface of the z(0) sections has values of 2,62 for compounds with R = Y, Gd, Ho and 2,72 for R=Er . For all samples, D_L has a maximum near the surface.

The article presents the results of studying the microstructure of rapidly solidified foil of Sn _{55,18 Zn 44,50 Si 0,23 Al 0,09} alloy. The phase composition of rapidly solidified foil was studied. A uniform distribution of alloying silicon and aluminum in tin in the form of a solid solution was established. The formation of the (100) texture of tin and (101 0) of zinc was revealed, associated with the predominant growth of crystallites, in which the close-packed planes of tin and zinc are perpendicular to the direction of heat removal during crystallization. An analysis of the structure and properties of the foil during isothermal annealing and natural aging was performed, with a description of the processes occurring. Formation of a dispersed structure due to high degree of supercooling of liquid phase with increase of degree of dispersion of zinc during isothermal annealing (average chord d on sections of zinc phases is 1,24 μm before heat treatment and 0,42 μm after isothermal annealing for 170 min at 150°C) along with invariance of texture during heat treatment is established. Change of the microhardness of foil during natural aging, noticeable formation of large number of clusters of precipitations of tin and zinc phases due to their supersaturation, as well as reinforcing action of alloying elements ( Si , Al ) are explained. During heat treatment zinc dissolves in the matrix phase, with decrease of its volume, while share of softening phase of tin increases which leads to a decrease in the microhardness.

The efficiency of the recording dynamic holograms in dispersed liquid-phase media with a high concentration of nanoparticles is analyzed. The optical nonlinearity of the medium is due to the electrostriction forces acting on the particles of the dispersed phase in a gradient light field. Mass transfer is considered in the case of suprathermal radiation intensities, when the light-induced change in the concentration of nanoparticles is greater than the initial one and reaches saturation. It is shown that at high levels of the radiation intensity, the recording of a dynamic hologram is carried out in a significantly nonlinear mode, when the phase lattice becomes non-sinusoidal. At the same time, the amplitude of the first harmonic increases sharply with increasing intensity, which makes it possible to achieve a significant increase in the efficiency of the hologram recording. The results obtained are relevant for dynamic holography of dispersed liquid-phase media, as well as for optical diagnostics of such media.

High-entropy alloys based on refractory metals, possessing an unusual combination of physical, mechanical, tribological, electrophysical, etc. properties, can be recommended for use in various fields of industry and medicine. The aim of the work is to study the growth process of high-entropy alloys films of the Ti-Nb-Zr-Ta-Hf-Cu system in real time by X-ray phase analysis using synchrotron radiation. Experiments on the deposition of multielement metal films were carried out on the VEIPS-1 setup developed at the Institute of high current electronics Siberian branch of the Russian academy of sciences for studying the processes of the film and coating formation on a synchrotron radiation source. The process of in situ thin film structure formation with high time resolution was studied using a synchrotron radiation source - the VEPP-3 electron storage ring, The Institute of nuclear physics, Siberian branch of the Russian academy of sciences. It is shown that the deposition of Ti-Nb-Zr-Ta-Hf-Cu plasma on a HG40 substrate is accompanied by the formation of an amorphous-crystalline state represented by phases of the composition (presumably) Ti-Nb-Zr-Ta-Hf-Cu , TiZr, NbZr , and CuTiZr , formed at different stages of film deposition. The main phase is the Ti-Nb-Zr-Ta-Hf-Cu composition.

The paper studies the dependence of the magnetoresistance and Seebeck coefficient of the composite magnetoresistive composition near the percolation threshold of 80% La _{0,7 Sr 0,3 MnO 3}/20% GeO ₂ on the constant magnetic field strength up to 3,8 kOe and temperature in the range from 25°C to 150°C. The 80% La _{0,7 Sr 0,3 MnO 3}/20% GeO ₂ samples have the p -type conductivity, a the positive sign of the Seebeck coefficient and a dielectric character of the change in the electrical resistance with temperature. The activation energy of such compositions is of about 0,35 eV. The magnetoresistance of such a composition decreases with an increase in the temperature difference between the hot and cold edges and disappears in the region of the phase transition temperatures of 90°C. It was found that in a constant external magnetic field of 3,8 kOe, a decrease in the Seebeck coefficient of the 80% La _0,7 Sr _0,3 MnO ₃/20% GeO ₂ compositions by 11% is observed at a temperature difference of 10 K. The dependence of the Seebeck coefficient on the magnetic field decreases with an increase in the hot edge temperature and also disappears in the temperature range of 90°C, which is associated with the ferromagnetic-paramagnetic phase transition of lanthanum manganite La _0,7 Sr _0,3 MnO ₃ and the suppression of spin-dependent electron tunneling.

The article discusses the possibility of obtaining functional composite materials with pronounced photocatalytic properties. A hybrid composite material based on nanoscale cadmium sulfide fixed on a matrix of hydroxyapatite obtained by precipitation from solution has been developed. The initial components and synthesized samples were certified using some modern physico-chemical analysis methods: X-ray phase analysis, energy dispersive X-ray analysis, Raman spectroscopy, scanning electron microscopy, the Brunauer-Emmett-Teller method. The functional characteristics of the developed composite material Ca ₁₀( PO ₄)₆( OH )₂- CdS , in particular, the photocatalytic activity under the action of ultraviolet or visible radiation, are investigated. The efficiency of using the developed composite material as a photocatalyst was evaluated by the rate of oxidation of p-dihydroxybenzene (hydroquinone). Based on experimental data obtained, the values of the constants of the reaction rate of photocatalytic oxidation of hydroquinone and the time of its half-conversion under various conditions (radiation, the presence of a catalyst) are calculated. It is proved that the developed composite material, which is a hydroxyapatite modified with colloidal CdS particles, has pronounced catalytic properties and is a promising material for use as a photocatalyst. A patent application has been filed for the developed composite material.

For the first time, the adsorption of barium atoms on the surface of the (0001) face of GaN was calculated using the density functional method. The 2D GaN layer was modeled using a GaN (0001) 2×2 supercell containing 10 GaN bilayers. The electron density of state and the adsorption energy of the Ba atom were calculated for five adsorption sites of the Ba atom: in the hollow position, in the bridge position between the surface Ga ( N ) atoms, and above the surface Ga ( N ) atom. There was one Ba atom per 4 surface Ga atoms in the first GaN bilayer. The adsorption of the barium atom above the surface N atom was most preferable. The adsorption energy was 2,96 eV. The adsorption of Ba atoms resulted in an insignificant reconstruction of the GaN surface: the maximum shift of the Ga ( N ) atoms did not exceed 0,11 Å. The adsorption of Ba resulted in the formation of a surface band below the Fermi level.

In this work, ceramic samples based on lutetium-aluminum garnet doped with erbium (content 1 at.%) were manufactured. In the manufacture of ceramic material, the chemical precipitation method was chosen. The influence of two types of sintering additives, MgO and CaO , on the microstructure and optical properties of ceramic samples obtained at vacuum sintering temperatures of 1800, 1850, 1875°C was studied. The article discusses in detail how the microstructure and optical transmission of ceramics with sintering additives MgO and CaO change at different vacuum sintering temperatures. It was found that magnesium oxide allows to achieve a higher optical transparency of ceramics (about 80%), while calcium oxide more effectively inhibits the grain growth. An increase in the sintering temperature for samples with MgO from 1800 to 1850°C contributed to an increase in the light transmission of samples from 10 to 80% and an increase in grain size from 1,80 to 3,03 microns. Earlier no such a phenomenon was not observed for samples with CaO , samples obtained at sintering temperatures of 1850 and 1875°C had approximately the same microstructure, containing some residual microporosity.

The results of experimental studies of magnetic properties and magnetization reversal processes of a series of alloys Sm-Gd-Zr-Co-Cu-Fe are presented. The studied samples were subjected to prolonged isothermal annealing for 24 hours, which made it possible to achieve the formation of a certain nanostructure that affects the hysteresis properties of the material and allows to achieve a high coercivity state. According to the magnetic measurements data obtained by the method of a vibrating magnetometer, the hysteresis loops are constructed, the dependence of the saturation magnetization, and the coercive force on chemical composition, and the values of the temperature coefficient of magnetization change depending on the relative content of Sm and Gd are determined. It is shown that the substitution of a part of samarium atoms for gadolinium atoms increases the effect of the mechanism of irreversible rotation of the spontaneous magnetization vector on the remagnetization of samples. Application of the studied samples in various devices puts serious demands on the stability of their magnetic properties at high temperatures. Our researches allow us to conclude that compounds with gadolinium concentration x= 0,5 have the greatest coercive force, and compounds with gadolinium concentration in the range x= 0,5-0,6 have the highest temperature stability.

LiNbO ₃: Cu (0,005 wt.%), LiNbO ₃: Cu (0,015 wt.%), LiNbO ₃: Cu (0,022 wt.%), LiNbO ₃: Cu (0,042 wt.%), LiNbO ₃: Cu (0,46 wt.%) crystals were studied by IR absorption spectroscopy in the region of stretching vibrations of OH ^--groups. These crystals were grown by the Czochralski method using the technology of direct doping of a charge of congruent composition. It has been established that the recorded absorption bands in the infrared spectrum in the frequency range 3469-3490 cm^-1 are associated with a deviation in the composition of the LiNbO ₃: Cu crystal from the stoichiometric one. Such changes occur due to a deficiency of Li ⁺ cations in the crystal structure. The incorporation of Cu ²⁺ dopant leads to disordering of the cation sublattice and noticeable deformation of oxygen octahedra. This occurs due to an increase in the O-O bond lengths. In this case, a new absorption band with a frequency of 3487 cm^-1, corresponding to the V_Li-OH complex defect, is recorded in the IR spectrum. Calculation of the volume concentration of OH^- - groups showed the highest value for crystals of LiNbO ₃: Cu (0,005 wt.%), LiNbO ₃: Cu (0,015 wt.%), LiNbO ₃: Cu (0,022 wt.%). These changes occur due to the simultaneous formation of two types of complex defects in the crystal structure: Cu ⁺- OH - Cu ^3- and V_Li-OH . A change in the mechanism of entry of a doping impurity into the structure of a LiNbO ₃: Cu crystal (0,042 wt.%) leads to a decrease in the concentration of OH ^-- groups.

This work examines the main reasons for the appearance of an «extra» band with a frequency of ~737 cm^-1 in the Raman spectra of lithium niobate crystals. The following stand out among the reasons: the presence of clusters (microstructures); the presence of microinclusions of impurity phases of other lithium niobates ( LiNb ₃ O ₈ and Li ₃ NbO ₄); strong anharmonicity of some fundamental vibrations of the Raman spectrum. The structure of clusters differs from the structure of the crystalline matrix. It has been shown that the appearance of a line with a frequency of ~737 cm^-1 in the Raman spectrum cannot be unambiguously associated with the existence of regions with reduced symmetry in the structure of doped crystals. These regions are the result of uneven incorporation of dopants into the crystal. The existence of these areas is also not explained in terms of the photorefractive effect. The results of studying the features of the defect structure, stoichiometry, optical uniformity and photorefractive effect confirm a correlation between the band with a frequency of ~737 cm^-1 and Nb_Lidefects in the structure of the lithium niobate crystal.

The results of our research of the surface of steel disks before and after friction are presented. Problems of the friction couple contact area estimation were under consideration. The results of searching a universal criterion of the friction couple contact area quantitative estimation are discussed. Using optical and scanning tunneling microscopy allows studying the surface profile at the micro- and nanoscales. An approach for determination of the contact area between bodies is proposed on the basis of the fractals theory. Such an approach allows to describe the heat transfer between bodies (conductive at contacts and radiant in pores heat exchange), to define the dependence of the friction force on the applied external force. The offered technique for the quantitative estimation of the surface structure at the micro- and nanoscales by means of the fractal theory will allow improving the accuracy of the spacecrafts thermal modes calculation as well as parameters of the knots of friction in them. This, in turn, will positively affect reliability and durability of the future spacecrafts. Improvement of methods in our further work will be aimed at studying tribological properties of the robotic products under the influence of the space factors and validation of the numerical modeling of the friction and heat exchange between mobile knots using results of experiments.

In the last decade, variational quantum algorithms implemented on modern quantum computers have successfully solved practical problems of optimization, quantum chemistry, and machine learning. We propose new variational quantum algorithm based on a Monte Carlo scheme that uses a random selection of the generators for a unitary transformation, and also uses optimization of the objective functional employing the annealing or Metropolis-Hastings algorithm. The states of the quantum system in the form of a density operator and its model Hamiltonian are represented by expansions in the Pauli basis. In the algorithm, the state of the system is changed by means of a random choice of the Pauli generator that determines the unitary transformation of the state. The efficiency of the annealing algorithm directly depends on the equiprobable choice of the transition from one state to the second, so the work uses a compromise version of the uniform distribution of operators on the SU (2 ⁿ ) group - the direct product of the SU (2) group, where n is the number of qubits in the system. The random choice of a single-qubit operator (consistent with the Haar measure on SU (2)) is implemented in Hopf coordinates on the group manifold (the three-sphere). The results of testing the algorithm show that it can be effective for low-dimensional systems.

The four-component Au-Cu-Pd-Pt nanosystems of different sizes with the stoichiometric composition Au ₃ CuPd ₁₂ Pt ₄ were studied. The molecular dynamics method was used as a simulation method, the interatomic interaction was described by the tight-binding potential. Based on the results of a series of computer experiments, it was found that the four-component Au-Cu-Pd-Pt nanoparticles do not have a tendency to form a core-shell structure, even though gold atoms demonstrate an increased segregation to the surface. Melting and crystallization temperatures were determined for the studied Au-Cu-Pd-Pt nanoparticles. The dependence of the crystallization temperature on the cooling rate was also established. With an increase in the cooling rate, the crystallization temperature decreases, and the temperature range in which crystallization occurs increases, while the heating rate does not significantly affect the melting temperature. It is shown that the size effect and the effect of the temperature-changing rate make it possible to control the dominant presence of the fcc or hcp local structure, and also affect the temperature stability of the resulting crystalline phases.

We study the asymptotic behavior of the maximum degree in the geometric graph model with a preferential attachment choice-based edge step. Geometric graphs are natural models that describe some nanoscale systems, while preferential attachment provides a good description of complex networks, particularly different neural networks. The model is a recursively built sequence of graphs. We start with the initial graph on a single vertex and we add a new vertex and draw a few edges on each step. Each vertex is assigned a parameter that represents its location. The recursion step consists of two parts. First, we introduce a new vertex and draw edges to close enough vertices. This step represents the geometric part of the model. Then, we draw edges between vertices by preferential attachment with the choice rule. We prove that dependent on model parameters, the maximum degree could exhibit sublinear (similar to the standard preferential attachment) and linear (representing concentration effect) behavior.

The reliability of the atomistic simulation is determined in terms of the correctness of the problem statement, including the choice of the interatomic interaction potential and its parameterization. In this paper, a detailed testing of the tight-binding potential parameters was carried out by means of studying the influence of the ratio between pair and many-body interactions on the process of the structure formation in binary Pd-Pt nanoparticles. Three parameterizations of the tight-binding potential for the cross parameters were selected: set (I) corresponded to the use of the Lorentz-Berthelot rule, sets (II) and (III) specified the scaling laws for the pair interaction parameters and the many-body interaction parameters, respectively. For sets (I) and (III), the surface segregation of palladium atoms was established, while the use of set (II) led to the formation of the Janus structure. In addition, differences in the formation of the local structure in binary Pd-Pt nanoparticles were established. Set (III) predicts the dominance of the local bcc structure. Radial distributions of the local density of Pd and Pt atoms in the Pd-Pt nanoparticles at a final temperature of 300 K were also calculated.

Despite intensive development of adsorption science, there are still many unresolved issues. In this regard, at least one of them can be highlighted in the present paper. As early as 1927 [1], it was established that solids change their dimensions during adsorption of gases and vapors. However, the development of research in this area was hampered for a long time by the lack of theoretical concepts and great experimental and methodological difficulties. Meanwhile, the study of the deformation of solids during adsorption is of great importance both for the development of adsorption thermodynamics and for practical purposes. In the theory of adsorption, a method for describing adsorption equilibrium is widely used, in which the role of a solid is reduced only to the creation of an adsorption force field in which the adsorbate is located. The adsorbent itself is considered thermodynamically inert. It is obvious that the analysis of a two-component system is replaced by consideration of only one component - the adsorbate. However, the very fact of the existence of deformation of a solid during adsorption directly indicates the insufficient rigor of the description of adsorption equilibrium in the language of concepts of the one-component system, as was accepted in deriving, for example, the classical Henry, Langmuir or BET (Brunauer-Emmett-Teller) equations. Therefore, the greatest value is represented by those works in which attempts are made to construct a general theory of adsorption (and absorption), including phenomena on deformable adsorbents (absorbents). From such a general equation, as special cases, at least the known classical adsorption equations should follow. In work [2], such an equation was proposed and it was shown that from it, as special cases, follow the classical Henry, Langmuir and BET equations with constants that have a clear physical meaning. Thus, the constant in the Henry equation is determined by temperature, the specific surface area adsorbent, size of adsorbate molecules, molar mass of adsorbate, and the isosteric heat of adsorption (the energy of interaction of the adsorbate molecules with the adsorbent surface). In the derived particular BET equation, in contrast to the classical version, a clear dependence of the equation constant on specific physical characteristics of the adsorption system is indicated for the first time. It is determined by the concentration of adsorbate molecules in the liquid phase at temperature under consideration, concentration of adsorbate molecules during the formation of a dense monolayer on the adsorbent surface, the energy of interaction of adsorbate molecules with the adsorbent surface, and the heat of condensation. The approach presented in this work can serve as a basis for modeling a wide variety of adsorption and absorption phenomena, including adsorption on microporous adsorbents and deformable bodies. The present work continues the studies conducted. It is shown that particular cases of the equation presented in [2] are the well-known classical Fowler-Guggenheim, Temkin equations.

The application of 3D nanocrystalline materials obtained using the liquid-phase and solid-phase powder metallurgy technologies is one of the basic approaches to designing high-efficiency and low-cost thermoelectric energy converters. Nanostructured alloys of the Si_x - Ge _{1- x} system represent one of the most efficient high-temperature thermoelectric materials. Features of the equilibrium phase composition of Si_x - Ge _{1- x} nanoparticles with a core-shell structure and various fractions of Si have been simulated using the thermodynamic approach in the interval between the liquidus and solidus temperatures. It has been demonstrated that the temperature dependences of the equilibrium phase composition of co-existing liquid and solid phases in the heterogeneous region significantly depend on the mutual arrangement of these phases in the core-shell structure. The results are accompanied by analysis of the initial composition effect which consists in the fact that not only the volume fractions of co-existing phases but also their composition depend on the Si fraction of the parent particle. The «hysteresis effect» has been shown. A thermodynamic interpretation of the obtained results has also been given based on three mechanisms of reducing the free energy of the system.

The main objective of the study was to find the size limit at which silver nanoclusters with different initial morphology spontaneously change their structure to the fcc structure inherent to the bulk silver. For this purpose, we have examined the data of high-resolution electron microscopy of the initial and annealed silver nanoparticles formed on a carbon substrate by vacuum-thermal evaporation. It was found that as a result of annealing, the number of small nanoparticles (D<3,5 nm) approximately twice decreased, and the proportion of nanoparticles with icosahedral and decahedral facets increased approximately 1,5 times. To evaluate the obtained results by the molecular dynamics method based on the second moment approximation of the tight-binding potential, an additional study of the stability limits of structural modifications of silver nanoclusters of similar diameters (D=2-10 nm) was carried out in order to determine the size limit of a possible thermally induced structural transition from the initial amorphous morphology to the fcc phase. The obtained data were compared with the results for Ag nanoparticles with the initial fcc structure. It was shown that the size limit at which the nanoclusters changed their initial amorphous structure to the fcc structure corresponds to a particle diameter of 8-10 nm.

The dependence of the adhesion energy of the polyacrylonitrile oligomeric chain on the surfaces of carbon nanoparticles such as carbon nanotubes and graphene is studied in the framework of full atomistic molecular mechanics simulation using the polymer consistent force field and the open part of the condensed-phase optimized molecular potentials for atomistic simulation studies force field. The length of the polyacrylonitrile oligomer chain, the number of layers in the graphene nanoparticle, the diameter of the carbon nanotube, and the type and density of the modifier molecules on the surface of the graphene are the main parameters of the calculations. The graphene nanoparticle is taken as a limiting case corresponding to the large-diameter carbon nanotube. N-(2-aminoethyl) carbamoyl, nitrocyclohexane, benzamide, and dinitrobiphenyl are selected as surface modifiers. It is shown that with an increase in the number of layers and diameter of carbon nanotubes, the adhesion energy of the polyacrylonitrile oligomer chain increases, which allows us to consider multiwalled carbon nanotube with large diameters as a preferred filler for polyacrylonitrile. The estimates obtained also show that when surface modifiers are used, it is possible to increase the adhesion energy of polyacrylonitrile only in the case of low surface modifier densities.

The adsorption of gold atoms on the surface of the (100) tungsten face was calculated using the density functional method. A 2 D layer of W atoms was used as a tungsten substrate. The 2 D layer of W was modeled by a W (100) 2×2×2 supercell. The calculation was carried out for three sites of adsorption of the Au atom on the W (100) surface: in the hollow position, in the bridge position between the surface W atoms and on top the surface W atom. There was one Au atom per 8 surface W atoms. Adsorption of the Au atom in the bridge position is most preferable. The adsorption energy is 4,18 eV. Adsorption of Au atoms leads to the following reconstruction of the W surface: the shift of W atoms in the surface plane does not exceed 0,18 Å, and the shift of the upper layer of W atoms is 0,022 Å towards the volume of W . The valence band of the 2 D W (100) layer is formed mainly W 5 d electrons, with a minor contribution from W 6 s electrons. Adsorption of gold leads to a change in the spectrum of the valence band of the tungsten surface layer.

The article is devoted to the study of stability of ternary Cu-Fe-Ni nanoparticles (consisting of 5400 atoms) with a core-shell structure and its relationship with the surface segregation. The main focus is on modeling their structural formation using the LAMMPS software. The authors test the hypothesis that stability of nanoparticles depends on the spontaneous segregation of one of the components to the surface. Three configurations with different atomic distributions (configuration Cu ₄₅ Fe ₄₅ Ni ₁₀ with random distribution of atoms, as well as configurations - Cu ₂₅ Fe ₂₅@ Ni ₅₀ and Fe ₂₅ Ni ₂₅ @Cu ₅₀) are considered, and numerical modeling is performed for each of them using molecular dynamics methods and applying the tight-binding and embedded atom method potentials. The analysis showed that copper tends to segregate to the surface, while nickel concentrates in the core, significantly affecting mechanical properties of the nanoparticles. Patterns of the defect formation and their impact on the strength of nanostructures were identified. The article emphasizes that the correct choice of shell and core can both stabilize and destabilize the nanoparticles, providing prospects for the practical application of these materials.

The problem of the thermal stability of mono- and binary metallic nanocages consisting of gold and silver atoms with the same nuclearity of 3000 atoms is considered. The initial configurations of nanocages were obtained in the ClusterEvolution software by cutting them out of a larger icosahedron. The heating process for studying the thermal stability/instability was simulated in the Metropolis software using the Monte Carlo method and the Metropolis scheme. The interatomic interaction was described by the tight-binding potential. The influence of the composition, characteristic dimensions (inner and outer radii), and the shape of the inner surface in the initial configuration on the thermal stability of nanocages was studied. The temperature of complete collapse of the internal cavity of nanocages was determined. The results of calculations of the temperature dependence of the average local density and the local density profiles at different temperatures corresponding to different initial configurations, as well as the temperature evolution of the fractions of crystalline structures in them, are presented and analyzed.

Reducing the cost of the materials and technologies used to form functional films is one of the most pressing issues in the rapidly developing transparent electronics industry. In this regard, ZnO-based films deposited by magnetron sputtering are of particular interest, being considered as a real alternative to more expensive indium oxide films when forming transparent electrodes in various optoelectronic applications. However, the choice of optimal film's compositions and formation modes for each specific application is complicated by the lack of systematic comparative data on these systems obtained under identical conditions. In this work, ZnO films doped with Al, Ga, and In at a level of 1 to 20 at.% were obtained under identical conditions by the magnetron sputtering method. The dependence of the structure and electrical characteristics of ZnO films on the dopant content and deposition temperature was studied. It has been established that the key factors determining the behavior of an impurity in a ZnO matrix are its chemical activity, solubility in the matrix, the ionic radius of the impurity metal in a given coordination, and the electrical characteristics of additional oxide phases of the doping element formed at grain boundaries.

Based on magnetic fluids, new effective technical devices have been implemented, such as magnetic fluid bearings, seals, and dampers. The magnetic-viscous effect inherent in magnetic fluids can not only improve the properties of magnetic fluid units, but significantly complicate their operation after a long stop. This refers to the so-called «stop effect», which occurs due to an abnormally high limiting shear stress in a structured liquid. It is shown that, based on the existing ideas about the thixotropic properties of a magnetic fluid, it is not possible to convincingly explain the experimental value of the yield strength. Estimations according to the known formulas obtained for the chain model give a significantly underestimated value of the yield strength of a real magnetic fluid. A hypothesis is proposed according to which the rheological properties of the carrier medium change in the process of structure formation in the magnetic fluid under the action of compressive stresses created by a network of dispersed particles. Experiments have confirmed an increase in the density of the magnetic fluid in the magnetic field under the influence of such stresses. It can be assumed that high values of the yield strength are due to the presence of the intrinsic yield strength of the dispersion medium, which is in a quasi-solid state.

Experimental results on the synthesis of nanoparticles of Ge₂Sb₂Te₅ phase-change material by the direct laser-induced transfer method are presented. Thin films obtained by the thermal vacuum deposition were used as a donor material and silicon wafers as an acceptor. The laser-induced forward transfer was carried out using the sub-nanosecond pulsed laser irradiation. The morphology, topology, and size of the obtained nanoparticles were analyzed by scanning electron microscopy. Structural studies were performed by Raman scattering. A quasi-uniform distribution of nanoparticles on the substrate and a quasi-uniform size distribution were achieved. It was shown that it is possible to achieve a nanoparticle diameter of less than 100 nm. Raman spectra show that the nanoparticles obtained are in the crystalline state. The results show the possibility of creating an element based on nanoparticles with a specific distribution in size as a technological alternative to devices based on thin films. The use of nanoparticles will make it possible to achieve the energy efficiency, greater flexibility, and smoothness of switching as well as to realize neuromorphic and stochastic computation.

The review discusses the most effective methods for reducing droplet density on the surface of thin films during pulsed laser deposition. This review highlights pulsed laser deposition as a promising technique for producing thin films from a wide range of materials. However, a significant challenge to its industrial application is the formation of droplets on the thin film surface. The primary causes of the droplet formation are identified, and a classification of methods to reduce the droplet density during pulsed laser deposition is provided. Completely eliminating droplets without compromising the quality or altering the stoichiometric composition of the thin films is exceedingly difficult, and no researchers have achieved this to date. The most effective strategy for reducing the droplet density involves optimizing the pulsed laser deposition parameters for specific material groups. Techniques such as using a segmented crystalline target, periodically rotating it at a specific speed, and employing excimer lasers at the energy densities slightly above the ablation threshold have been shown to reduce the droplet density on the thin film surface to as low as 10³ cm^-2. The physical and chemical processes occurring on the target surface have the greatest impact on the droplet formation. Among active methods, high-speed filtration is the most effective, capable of reducing droplet density to approximately 2 × 10³ cm^-2.

The paper presents the results of modelling the phase shift of a passing optical beam caused by the formation of a layered structure in a controllable cell made of the phase-change material Ge₂Sb₂Te₅ induced by the controlling influence of pulsed laser radiation of short and ultrashort duration. The crystallization of a thin film of Ge₂Sb₂Te₅ is analyzed on the basis of the thermokinetic approach, taking into account the kinetic properties of the material, the energy and duration of the applied laser radiation, the amorphization of the upper layers of the film during rapid heating and the temperature dependence of the kinetic properties. Graphs of the thickness of the crystalline layer in the film material were plotted for each influencing pulsed radiation. From the data on the position of the crystalline layer, the phase shift of the transmitted optical radiation is calculated. Based on the modelling data of the investigated cell, a phase shifter can be constructed to transform an optical beam of arbitrary aperture. The proposed method of controlling the optical beam front by changing the structural state of a thin film can be very promising when accurate and fast tuning of the optical phase transparency is required.

A mathematical model of the internal friction in a polycrystalline material with the nanoscale grain size is considered. Their boundaries contain pores, both in the triple joints of the grains and between them. Under the influence of the alternating normal boundary stresses, flat sections of the boundary are periodically active sources and sinks for vacancies. Due to the presence of these flows, the mutual displacement of adjacent grains is carried out. Depending on temperature, the diffusion length of the vacancies is smaller or compared with the distance between the pores. In the graph of the dependence of the internal friction on temperature, there is a break between the rectilinear sections. From the position of the fracture, the average size of the flat sections of the border can be estimated. The effective activation energy of the process in these cases depends on temperature and differs twice. At temperatures when the concentration of thermal vacancies in the boundary exceeds the geometrically necessary value of the concentration of structural vacancies, the activation energy increases even more. The transition temperature to this value is determined by the degree of imbalance of the boundary structure.

The problems associated with the global warming due to greenhouse gas emissions from human activities are driving the search for new technologies to reduce CO ₂ emissions from the fossil fuel combustion. Hydrogen is a clean and efficient energy carrier, so the hydrogen energy is considered as one of the strategic directions for the development of the energy security and sustainability. Although hydrogen can be produced by electrolysis of water, most of the hydrogen produced worldwide currently comes from steam reforming of natural gas, which must be purified to ultra-high purity for economic reasons. Traditional methods based on pressure swing absorption-desorption using cryogenic distillation are energy intensive, which motivates the development of new highly selective and energy efficient H ₂ purification technologies. Such technologies include rapidly developing membrane technology, which at the moment has not yet reached the level required for its widespread industrial application. In this review article, we analyze the main aspects of current research in the field of hydrogen purification technology using dense metal membranes, with an emphasis on their technological stability due to the selection of their chemical composition (including multicomponent) and optimization of the structural state. We also considered the prospects for further development and use of this technology for economic needs.

In this work, films of polyvinylidene fluoride, copolymer of vinylidene fluoride and trifluoroethylene have been studied. The samples were made by direct ink writing technology. Some of the produced films were polarized in the corona discharge field. The dependences of the relative permittivity on temperature were studied for the films. The study showed that for polyvinylidene fluoride films, no maximum is observed in the dependences of the permittivity on temperature, since the assumed temperature of the ferroelectric phase transition is higher than the melting temperature. The maximum in the temperature dependence of permittivity for polarized copolymer of vinylidene fluoride and trifluoroethylene films is shifted by 10℃ toward higher temperatures compared to the maximum for non-polarized films. In this case, the permittivity of non-polarized films has higher values compared to the corresponding value for polarized samples. This is due to an increase in the proportion of the β -phase after polarization, as well as to the internal electric field caused by the space charge formed during the polarization process at the phase boundaries.

Experimental results on the silicon wafers irradiation by a low-frequency giant nanosecond pulses neodymium-doped yttrium-aluminum garnet laser with a wavelength of 1,064 μm are presented. The pulse duration at the half-height was 170 ns, and the pulse repetition frequency was 2 Hz. The experiments were carried out for the cases of silicon wafers placements in air and in bidistilled water. For the case of irradiation in air, a nanostructured region with a uniform distribution of particles was succeeded to form on the surface of the silicon wafer. The exposure time was 2 minutes, which corresponded to 240 laser pulses. In this case, the particles were formed mainly from silicon dioxide as a result of the thermal oxidation during ablation in air. When the exposure time was doubled, this effect was not achieved, and destruction areas of wafer were formed. For the case of irradiation in bidistilled water within two and four minutes, the mechanical and thermal destructions prevail on the surface of the silicon wafer, which manifest themselves in cracking along the edges of the crystal structure and in the form of the surface solidified melted regions.

As a result of the work performed, a method for synthesizing selenium nanoparticles stabilized with methylcellulose was developed and optimized. Selenious acid was used as a selenium-containing precursor, ascorbic acid as a reducing agent, and methylcellulose as a stabilizer. A multifactorial experiment was conducted to optimize the method for synthesizing selenium nanoparticles stabilized with methylcellulose. It was found that for the synthesis of selenium nanoparticles with the smallest average hydrodynamic radius, the molar concentration of selenious acid in the solution should be in the range from 0,0036 to 0,1033 mol/l, the mass of methylcellulose - from 3,0 to 3,985 g, the molar concentration of ascorbic acid - from 1,52 to 2,12 mol/l. It is shown that pH of the medium, charge and concentration of sodium and barium ions do not affect the average hydrodynamic radius of selenium nanoparticles stabilized with methylcellulose. However, when exposed to iron ions, the radius increases from 150 to 270 nm. It is established that an increase in the concentration and charge of anions has a significant effect on the average hydrodynamic radius of selenium nanoparticles stabilized with methylcellulose. With an increase in the concentration of chlorine ions from 0,1 to 1 mol/l, an increase in the average hydrodynamic radius of particles occurred from 143 to 156 nm, with an increase in the concentration of sulfate ions from 0,1 to 1 mol/l, an increase in the average hydrodynamic radius of particles - from 165 to 6129 nm, with an increase in the concentration of phosphate ions from 0,1 to 1 mol/l, an increase in the average hydrodynamic radius of particles - from 149 to 17000 nm.

The article discusses the possibility of obtaining a hardened composite material with a porous structure based on nanostructured hydroxyapatite (HAP) synthesized by precipitation from a solution. The new material by the mechanochemical synthesis of hydroxyapatite with aluminum, silicon, nickel, hafnium and titanium was obtained. The synthesized samples are certified using modern physical and chemical methods of analysis. The influence of the qualitative and quantitative composition of the composite on the sintering processes and the strength characteristics of the studied samples is shown. It has been experimentally established that the Ca ₁₀( PO ₄)₆( OH )₂ - 15% CaF ₂-15% TiO_x . system is the most promising for the development of biocomposites based on it. Composite materials of this composition have a dense uniform structure with a high degree of crystallinity, with developed porosity, and are a promising material for further research in order to introduce it into medical practice. The possibility of practical application of the obtained composite material as a component of a bioactive coating is evaluated. A patent application has been filed for the developed composite material.

Composites based on hydroxyapatite and natural biopolymers are promising materials for bone grafting. In this work, samples of hydroxyapatite were synthesized by chemical precipitation from aqueous solutions in the presence of high molecular weight hyaluronic acid (0,4-0,8 wt.%). The resulting powders are represented by carbonate-containing nanohydroxyapatite and contain 89-98 wt.% of polysaccharide. A correlation has been established between the content of hyaluronic acid in the mother solution and the crystal chemical, structural and morphological characteristics of the samples. It was revealed that, in comparison with the hydroxyapatite sample, in viscoelastic media of the polysaccharide, powders are formed that have a smaller parameter a of the hydroxyapatite crystal lattice, close in value to the stoichiometric phase. With an increase in the content of hyaluronic acid in the mother solution, the crystallinity, crystallite sizes and specific surface area of the composites decrease; their average value is 16 nm and 47 m²/g. Samples based on nanohydroxyapatite and polysaccharide consist of oval-lamellar agglomerated particles. At the maximum content of hyaluronic acid in the model solution, amorphized round conglomerates, dense in structure, are formed. The synthesized composites can be used in medical practice as osteoconductive implants, as well as to create nanoencapsulated drug delivery systems.

Currently, the global demand for orthopedic implants exceeds 6 million units per year and continues to increase. It is known that human bone is a composite material, the inorganic part of which is formed by calcium phosphates, mainly in the form of hydroxyapatite of non-stoichiometric composition. This fact determines the interest in studying the possibility of using hydroxyapatite-based materials for biomedical purposes, which are similar to the chemical composition of the bone and dental tissues and have high biocompatibility. Research in this area is necessary from both the fundamental perspective for expanding the scope of the method, and in view of development of new materials and studying biological fluids in health and pathology. The work shows that the presence of organic and inorganic additives in the synthesis of hydroxyapatite affects the composition and morphology of the crystals of the resulting compound. The results of analysis, presented in the form of diagrams, allow us to judge the inversely proportional relationship between the crystallization time and the value of the morphological dimension of the hydroxyapatite structures, regardless of the nature of the additive. The results obtained confirm the possibility of using morphological analysis to establish the patterns of formation of hydroxyapatite-based materials and to perform an express assessment of their properties (composition, morphology, degree of crystallinity, nature and concentration of impurities).

The presence of impurities of other metals in titanium alloys affects the composition of the oxide film after heat treatment: in addition to rutile, the VT 00 alloy contains Ti ₆ O oxide, which in the VT 1-0 and VT 6 alloys is transformed into Ti ₃ O oxide, which affects the corrosion resistance and mechanical strength. Calcium phosphate coatings containing brushite, calcite and apatite were obtained by electrochemical deposition on titanium plates at room temperature, pH 5, and a constant current density of 30 mA/cm² from a suspension electrolyte CaCO ₃ / Ca ( H ₂ PO ₄)₂. A layer of amorphized apatite was applied to the coatings using the biomimetic method in a 3-fold concentrated model solution of Simulated Body Fluid to improve biocompatibility. After heat treatment at 800°C, calcium phosphate coatings obtained on titanium VT 00 have greater biocompatibility, but lower resorbability, due to the presence of a larger amount of crystalline hydroxyapatite in the coating.

One of the ways to develop methods for effective and economical synthesis of carbon nanostructures from the plant raw materials is to use the energy of the microwave electromagnetic field for pyrolytic transformations of biomass. Combining microwave irradiation and pyrolysis process is a new solution with several advantages that increase the efficiency of the biomass processing and determine the prospects of the microwave pyrolysis in obtaining carbon nanoproducts. In this work, the conditions for catalytic synthesis of carbon nanotubes through the microwave pyrolysis of cellulose, a major component of biomass, were studied. The objective of the present investigation is to evaluate the effect of a binary nickel-iron catalyst supported on a carbon substrate on synthesis of carbon nanostructures. This process involves the use of organic additives, such as glucose and thiourea, which are intended to prevent oxidative reactions in the system and maintain the activity of the catalyst. Experiments were carried out by treating the mixture of reagents with the microwave radiation with a frequency of 2450 MHz and a power of 1000 W for 10-12 minutes. The synthesis samples were characterized by X-ray phase analysis and transmission electron microscopy. In all experiments, the formation of multi-walled carbon nanotubes and few-layer graphene particles was observed. It was experimentally found that the used catalyst showed great activity in the microwave synthesis of carbon nanotubes in the presence of glucose.

The paper presents the results of a study on the sensitivity of gas-sensing zinc oxide ZnO film nanostructures at room temperature. The aim of the research was to investigate the effect of ambient humidity on the conductivity of ZnO samples and their response to ethanol vapor in the presence of water vapor. It has been discovered that zinc oxide films are responsive to both water and ethanol vapor at room temperature, across a broad range of concentrations (5% to 50% saturated vapor). The study found that repeated exposure to water vapor can lead to changes in the conductivity of zinc oxide samples when they are exposed to dry air. Additionally, pre-annealing the samples at 400°C can help to replicate the concentration-dependent response of gas-sensitive structures to water vapor. Hysteresis was observed in the relationship between concentration and response to water vapor, in the range of 5% to 90% of the relative humidity. This can be explained by the capillary condensation of water vapor within the mesopores of zinc oxide layers. As the humidity of a gas sample containing ethanol increased, the response values and detection limit for ethanol decreased in the gas-air mixture for ZnO samples. Statistical analysis using the principal component method showed the potential for classifying dry and humid gas samples with ethanol vapor in air. Data processing was used to eliminate the influence of the background humidity on the calibration curve for gas-sensitive ZnO samples, demonstrating the effectiveness of this method.

The dynamics of cisplatin release and its mixture with hydroxyapatite from bioinert templates based on carbon felt and polyethylene were studied. Changing the polyethylene and carbon felt layer ratio in the templates influenced the volumetric concentration of cisplatin and the duration of its release. The diffusion of cisplatin from the samples was limited by the number of polyethylene layers. After crystallization at 800°C, the phase composition of hydroxyapatite- α is 65% hydroxyapatite and 35% α -tricalcium phosphate, and hydroxyapatite- αβ consists of 50% hydroxyapatite, 35% α - and 15% β - tricalcium phosphate. Long-term (44 days) release was observed in templates with 2-3 layers of carbon felt and 3-4 layers of polyethylene, and it was slowed when using mixtures with hydroxyapatite (58 days). The appending of hydroxyapatite/cisplatin mixtures into the template with varying amounts of hydroxyapatite phases and α -/ β -tricalcium phosphates slowed the release of cisplatin by 14 days, totaling 58 days, due to the sorption and/or binding of cisplatin to calcium phosphates.

In aqueous solutions of magnesium chloride and sodium dihydrogen phosphate at Mg / P molar ratios of 1,0-1,5 and pH of 5-7 in the presence of gallic acid, crystalline hydrates of magnesium hydrophosphate (newberyte - MgHPO ₄·3 H ₂ O ) and orthophosphate ( Mg ₃( PO ₄)₂·22 H ₂ O ) were obtained, which after heating at 800°C transformed into pyrophosphates ( Mg ₂ P ₂ O ₇). X-ray phase and thermal analysis methods, as well as infared spectroscopy, showed that the presence of an organic additive in the liquid-phase synthesis of magnesium phosphates does not lead to a noticeable change in the phase composition of the reaction products. It was revealed that gallic acid affects the formation of the structure of crystalline hydrates depending on the Mg / P molar ratio. It was found that with prolonged maturation of the sediments (over 6 months), the size of the unit cell of magnesium phosphates decreases. The obtained magnesium phosphate powders modified with gallic acid exhibit redox activity and are promising for use in biomaterials as resorbable components with antioxidant properties.

It is shown that the sorption of lanthanum cations by synthetic aluminosilicate zeolite, unlike natural ones, increases both in acidic and neutral conditions by 4 times (from 8 to 26%) and 8 times (from 4 to 33%), and the sorption capacity increases by 3-8 times to 145 and 184 mg/g, respectively. A comparative analysis of the applicability of the adsorption of Langmuir, Freundlich, Temkin, Dubinin-Radushkevich models to describe experimental isotherms of adsorption of lanthanum cations on synthetic zeolite is made. It is shown that the Langmuir model is best suited in aqueous media ( R ² = 0,9996). This indicates that a homogeneous monolayer surface is formed as a result of sorption. Based on the pseudo-first, pseudo-second order models and the intraparticle diffusion model, an assumption is made about the ion-exchange nature of sorption. It has been shown that zeolites can almost quantitatively extract La ³⁺ cations from aqueous solutions and are of interest as sorbents with a high sorption capacity.

The article discusses the possibility of dispersion strengthening of nanostructured hydroxyapatite synthesized by precipitation from solution introducing reinforcing additives of non-stoichiometric titanium oxide and zirconium dioxide. The reinforced composite material: hydroxyapatite - non-stoichiometric titanium oxide - zirconium dioxide was obtained by mechanochemical synthesis of hydroxyapatite with doping components followed by annealing at 1000°C. The initial components and synthesized samples were certified using modern physicochemical methods of analysis: X-ray phase analysis, differential thermal analysis, scanning electron microscopy, surface area and porosity analysis, dispersion analysis. The influence of the qualitative and quantitative composition of the composite on the sintering processes and strength characteristics of the studied samples in a wide temperature range of 25-1200°C is shown. It has been experimentally established that the most promising system for developing biocomposites based on it is hydroxyapatite - 15% non-stoichiometric titanium oxide - 5% zirconium dioxide. Composite materials of this composition have a dense, uniform, strong structure with a high degree of crystallinity and a developed surface. They seem to be promising materials for further research with the aim of introducing it into medical practice.

The hardened composite material with a porous structure was obtained by mechanochemical synthesis of nanostructured hydroxyapatite synthesized by precipitation from an aqueous solution with reinforcing additives of zirconium dioxide and silicic acid. Food gelatin is used as a binder. The influence of the phase composition on physico-chemical properties of coatings (adhesive strength, microhardness, specific surface area, microstructure) is estimated. It has been established that the use of composite material together with gelatin as a part of a bioactive coating makes it possible to increase its hardness and adhesive strength. A patent application has been filed for the developed bioactive coatings based on nanoscale hydroxyapatite and biogenic elements with a binding agent. The composition of the dry mixture based on hydroxyapatite has been developed, which ensures a long shelf life without negative consequences and creates simple transportation conditions. Dilution of the dry mixture with distilled water gives a suspension that is convenient to use for coating implants of any configuration.

The use of proteins to create the targeted drug delivery systems is a promising approach in medicine and has many advantages. The formation of hybrid drug carriers based on proteins and polyoxometalates has a number of additional benefits. Polyoxometalates are able to bind both proteins and molecules of certain drugs to obtain water-soluble products without the use of toxic reagents and organic solvents. The regulation of the experimental conditions allows to control the size of the particles formed in solution. The gradual destruction of polyoxometalate { Mo₇₂Fe₃₀ } at blood pH provides a pH -dependent mechanism for drug release from the carrier structure. In our research, we obtained bovine serum albumin associated with coordination complexes { Mo₇₂Fe₃₀ }-doxorubicin and { Mo₇₂Fe₃₀ }-tetracycline in aqueous solution. A decrease in the rate of the drug release in a phosphate buffer solution at pH 7.4 (blood pH ) from the obtained materials compared to systems not containing albumin was observed. The data obtained in this study shed light on the formation patterns of multicomponent supramolecular systems, consisting of polyoxometalates, proteins, and drugs. The results indicate the possibility of creating hybrid carriers for targeted drug delivery based on polyoxometalates and albumin using non-covalent binding.

In this article, the features of synthesis and physicochemical properties of a composite material based on precipitated hydroxyapatite and synthetic aluminosilicate zeolites are investigated. Using modern methods of analysis, both the obtained composite material and individual components included in its composition are certified. The material was synthesized by mixing with simultaneous grinding in a vibration mill of synthetic zeolite and hydroxyapatite, followed by annealing of the resulting mixture. The characteristics of the initial aluminosilicate zeolites and hydroxyapatite were clarified by infared spectroscopy, their interaction during mechanochemical synthesis and subsequent heat treatment of composites obtained on their basis was assessed. X-ray phase analysis of the initial synthetic zeolites indicates the loss of adsorbed and crystallization water and decomposition to complex aluminosilicate oxides of calcium and sodium during heat treatment at 1000 °C. It was also found that although precipitated hydroxyapatite is structurally unstable and its phase composition depends on temperature, the behavior of the composite material obtained on its basis differs significantly during high-temperature treatment. It was proven that thermal annealing of the composite obtained by mechanosynthesis during heat treatment at 1000 °C does not lead to chemical modification of the hydroxyapatite structure and the formation of a new compound due to the introduction of zeolite. Differential thermal analysis showed an increase in the stability of the composite material relative to its individual components. The morphology of the original materials and those subjected to heat treatment was studied using scanning electron microscopy; a change in morphology during sintering was shown. Along with the study of the thermal stability of the materials, an assessment of the linear shrinkage of the samples and their microhardness was carried out. The conducted comprehensive studies made it possible to recommend composites based on precipitated hydroxyapatite, containing 15 wt.% aluminosilicate zeolites in their composition, as promising materials for further study, possessing the best functional characteristics, including strength.

This article describes the features of determining the enthalpy characteristics of the hydrate formation process. Aspects of forming hydrate structures from hydrate-forming agent molecules and water are described. It is shown that the processes of the hydrate formation and dissociation have different natures, which are determined by the interaction of the hydrate former with water in one phase state or another: hydrate former - solid phase of water - ice, hydrate former - liquid phase of water, hydrate former in a critical (pseudocritical) state - liquid phase of water. The dependence of the water crystallization temperature on the pressure and nature of the hydrate former is analyzed. The energy processes occurring during the formation of clusters and unit cells of the crystal lattices of hydrate structures due to the release and absorption of the thermal energy are described. Dependences are proposed for calculating the heat of formation of the crystal lattice from ice-like associates of water molecules. It is shown that the process of restructuring the ice lattice into a hydrate lattice can be both exothermic and endothermic.