Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2024 number 5

A boundary value problem is considered for a nonlinear mass transfer model that generalizes the classical Boussinesq approximation under inhomogeneous Dirichlet boundary conditions for velocity and mixed boundary conditions conditions for the concentration of the substance. It is assumed that the viscosity and diffusion coefficients and the buoyancy force in the model equations depend on the concentration. A mathematical apparatus for studying the problem is developed and used. to prove the theorem on the global existence of a weak solution. Sufficient conditions for similar problems that ensure the local uniqueness of weak solutions are given.

A problem is posed on a joint unsteady unidirectional motion of two immiscible fluids in a cylindrical tube with a constant temperature difference on the solid surface of the tube. From the mathematical viewpoint, this is an adjoint and inverse problem with respect to the pressure gradient of one of the fluids along the tube. The condition of problem overdetermination is a specified unsteady total flow rate of both fluids. A steady solution is found. A priori estimates of the solution of the unsteady problem in a uniform metric are obtained. Based on these estimates, sufficient conditions for input data are formulated at which the steady solution is exponentially stable.

This paper describes a multidimensional initial-boundary-value problem for Kelvin-Voigt equations for a viscoelastic fluid with a nonlinear convective term and a linear impulse term, which is a regular junior term describing impulsive phenomena. The impulse term depends on an integer positive parameter n , and, as n → +∞, weakly converges to an expression that includes the Dirac delta function that simulates impulse phenomena at the initial time. It is proven that, as n → +∞ an infinitesimal initial layer associated with the Dirac delta function is formed and the family of regular weak solutions of the initial-boundary value problem converges to a strong solution of a two-scale micro- and macroscopic model.

The characteristics of combined flows of evaporating liquid and laminar gas flow in a flat horizontal channel are studied based on the exact partially invariant solution of thermoconcentration convection equations. The influence of the liquid layer thickness and the conditions for the temperature function on the upper wall of the channel on the rate of evaporation caused by gas pumping is investigated. The exact solution is verified by comparison with experimental data. The linear stability of the exact solutions is studied. It is established that regardless of the type of boundary thermal regime, the system always experiences oscillatory instability in the in the form of cellular convection. Thermal insulation of the upper wall does not lead to a change in the structure of the most dangerous perturbations, slightly destabilizes the flow in the case of long-wave perturbations, and has a stabilizing effect in the case of short-wave perturbations.

One possible formulation of the inverse problem of identification of the vortex structure based on the flow velocity vectors at a set of points is considered, and an algorithmic method of its solution is proposed. The approach is based on the vortex structure presentation by a combination of the Rankine vortices. Identification is understood as determination of the number of model vortices, their intensities, centers, and radii. The method implies minimization in space of the parameters of the model system of the objective functional estimating the closeness of the known and modeled velocity vectors. The algorithm includes the following stages: search for the initial approximation for the vortex structure, refinement of the model vortex parameters, and correction of the resultant structure. Solving the direct problem of the flow development prediction is based on solving the initial-boundary value problem for the Euler equation for the ideal fluid dynamics by the spectral-vortex method. Results of test computations performed by the proposed approach are presented. It is demonstrated that the model system in all test computations ensures a sufficiently accurate description of the topology of streamlines during identification. Predictions at times corresponding to changes in the flow topology are obtained.

A nonlinear problem of unsteady motion of a circular cylinder in an ideal infinitely deep fluid under the action of arising hydrodynamic loads is considered. A method of reducing the solution of the initial mathematical problem to the solution of an equivalent integrodifferential system of equations for the function determining the shape of the sought free surface for the normal and tangential components of the fluid velocity on the free surface, and for the unknown trajectory of cylinder motion is used. The initial (in terms of time) asymptotic curve of the solution, which describes the cylinder motion from the state at rest is constructed.

This paper describes a study based on a three-dimensional Ostroumov-Birikha solution and pertaining to two-layer flows of liquid and gas-vapor mixture with account for diffusion-type evaporation on a thermocapillary interface. The results of analytical and numerical simulation of convective flows in a channel with solid impermeable walls arising under different temperature conditions are presented. The values of the mass evaporation rate and thermocapillary stresses calculated on the basis of the exact solution and obtained experimentally are compared.

Linear model equations in partial derivatives with two independent variables are considered. The highest operator symmetries and general solutions for a series of hyperbolic equations are found. Equivalence transformations are constructed for some equations.

Heat exchange in a liquid film moving along the bottom of a microchannel is calculated on the basis of a developed three-dimensional nonstationary model of motion. The liquid moves under the action of a cocurrent gas flow in the channel, with a square heater located at its bottom. In this case, the action of all the main physical factors during their interaction is taken into account: diffusive and convective heat transfer, dependence of liquid properties on temperature, thermocapillary effect, occurrence and evolution of surface deformations, and evaporation and condensation of liquid. It is revealed that the heater size significantly affects temperature fields, surface deformations, and temperature extremes. A formula for calculating the greatest excess of the average temperature achieved on the substrate is derived.

This paper considers hyperbolic systems of equations of a certain type that describe one-dimensional nonlinear waves propagating in the same way in both x directions. Each system of this type can be set in correspondence to a hyperbolic system of equations with a halved order, constructed on the basis of the initial system of equations. The similarity of the solutions of this system of equations and the original one is studied.

Unsteady one-dimensional shear flows of a viscoelastic medium are considered. A general approach is formulated for media with several relaxation times, which allows the known models of viscoelastic flows to be presented as evolutionary systems of first-order equations. Conditions of hyperbolicity of flow classes considered are found for the Johnson-Segalman, Giesekus, and Rolie-Poly models. The equations of motion of the viscoelastic medium are presented in the form of a full nonlinear system of conservation laws. A method of calculating unsteady discontinuous flows within the framework of the models under consideration is proposed. The class of unsteady Couette flows in the gap between the cylinders used in rheological tests is studied numerically. The process of shear lamination of its influence on the structure of steady flows are investigated. The numerical results obtained are compared with experimental data.

This paper presents a mathematical model of a medium consisting of active particles capable of adjusting their movement depending on so-called signals or stimuli. Such models are used, for example, in studying the growth of living tissues, colonies of microorganisms and more highly organized populations. The interaction between two types of particles, one of which (predator) pursues the other (prey) is investigated. The predator's movement is described by the Cattaneo heat equation, and the prey is only capable of diffusing. In view of the hyperbolicity of the Cattaneo model, in the case of sufficiently weak diffusion of preys, the presence of long-lived short-wave structures can be assumed. However, the mechanism of instability and failure of such structures is found. The relations for the transport coefficients of the predator that block this mechanism are derived explicitly.

The normal coordinates method is used in conservative mechanical systems to reduce two quadratic forms to a sum of squares. In this case, a system of differential equations is split into a system of independent oscillators. A linear dissipative mechanical system with a finite number of degrees of freedom is determined by three quadratic forms: kinetic and potential energy of the system, as well as the Rayleigh dissipative function, which, generally speaking, cannot be reduced to a sum of squares. Conditions are considered under which all three quadratic forms are reduced to a sum of squares by a single transformation exactly or approximately. It is shown that, for such systems, normal coordinates can be introduced in which the system is split into independent second-order systems. This allows one to construct exact or approximate analytical solutions in general form and with an estimated relative error in the case of an approximate solution. The advantages of this approach are shown for problems of theoretical mechanics and electrical engineering, in which analytical solutions are constructed and optimization analysis is carried out. In this case, traditional methods allow only numerical calculations to be performed for given parameter values.

Asymptotic behavior of solutions of initial-boundary-value problems arising in simulation of motion of incompressible viscoelastic fluids is studied in the case of various combinations of small relaxation parameters (stress relaxation time at constant strain and strain relaxation time at constant stress), one of which can be equal to zero.

Publications dealing with investigations of corkscrew fluid flows with collinear velocity and vortex vectors are reviewed. New solutions are presented for the Navier-Stokes equations for an incompressible fluid and second-order fluid equations, which are two-dimensional analogs of corkscrew flows.

The existence of a classical solution was established for a one-phase radial viscous fingering problem in a Hele-Shaw cell under surface tension (original problem) by means of parabolic regularization for a certain subsequence {ε_n}_n∈N, ε_n > 0. In this paper, we prove the uniqueness of the classical solution to the original problem with the use of parabolic regularization for the full sequence of the parameter {ε}, ε > 0.

It is shown that the wave of flameless spotty combustion of ballasted RDX can propagate in a stable manner in a granulated initial mixture. Under certain conditions, flameless combustion of RDX-containing granulated mixtures can proceed in a vibrational or gushing mode. Based on the process of flameless RDX combustion, a method of single-stage synthesis of high-porosity granules containing nano-sized cobalt or iron particles is developed. The synthesized granulated composite material reveals a comparable catalytic activity in hydrocarbon synthesis by the Fischer-Tropsch method. This material differs from the existing analogs by the absence of pyrophoric properties.

Experiments are conducted to study the instability of detonation waves in mixtures of nitromethane, tetranitromethane, and FIFO with inert diluents by recording the detonation front glow with a NANOGATE-22/16 high-speed eight-channel sixteen-frame electron-optical camera. In the detonation instability region, the detonation front exhibits a nonuniform glow, which is associated with a turbulent flow in the reaction region. The formation of cellular structures with the reaction of the explosive in oblique and transverse waves is not observed in the compositions studied.

This paper presents the results of experimental and computational studies of the influence of a number of factors on the detonation velocity of model mixed explosive compositions: type of explosive and polymer binder, content and particle size of components (explosives, aluminum powder, oxidizer), and charge diameter. It has been found that the detonation velocities of the explosive okfol and mixed compositions based on an active binder with an explosive content of 60-80 % (CL-20, HMX) are close to each other. The most marked decrease in detonation velocity is observed for mixed compositions with a mass content of aluminum higher than 20% with increasing oxidizer concentration from 6 to 30%. An increase in the particle size of the explosive and oxidizer leads to an increase in the experimental detonation velocity of the explosive composition. The critical detonation diameter of mixed compositions based on the active binder is 40-80 mm depending on the content of components.

A simple method of predictive estimation of the yield of detonation nanodiamonds is described, which takes into account the mass fractions of elements in the carbon-containing explosive with a general formula C_aH_bN_cO_d . An empirical dependence of the content of detonation nanodiamonds in the semi-product of nanodiamond synthesis (diamond charge mixture) on the fraction of carbon in molecules of explosives is derived. The yield of detonation nanodiamonds is presented as a function of the fractions of chemical elements in the initial system, which makes it possible to give quantitative predictions of the yield of detonation nanodiamonds.

Results of experimental investigations of the polymorphic transformation β → δ of various fractions of HMX are reported; the studies are performed by methods of differential thermal and thermogravimetric analysis, as well as by picnometer tests. With an increase in the crystal size, it is found that the temperature of the beginning of the polymorphic transformation of HMX decreases, and the HMX density also decreases. It is hypothesized that the change in the polymorphic transformation temperature is associated with the dependence of the enthalpy jump on the polymorphic transformation on structural defects.

The model of a source of shock-induced ejection based on the Richtmyer-Meshkov instability physics and developed for calculating the ejected mass of metal particles and its velocity distribution in the flow is applied to calculate the particle size distribution. The model is developed form metals transforming to a liquid state after the shock wave impact. It is shown that one has to know not only the density and surface tension of the liquid medium, but also the initial amplitude and wavelength of disturbances, as well as the shock wave profile for predicting the particle size spectrum in the case of liquid medium ejection. According to the theory developed, the particle size in the flow is largely determined by the disturbance wavelength than by the initial amplitude. The results are compared with experimental data on the size of nanoparticles ejected from narrow bands with initial disturbances on the free surface on tin and lead samples.

When studying the process of shock-induced dusting, especially when particle fluxes move in a gas or are caused by several shock waves, it is necessary to obtain experimental data on the time history of density in these fluxes starting from the arrival of the shock wave at the free surface of the sample. In this work, such measurements were performed using high-speed radiography with synchrotron radiation. In the experiments, one or two successive shock waves with a pressure of ≈40 GPa arrived at the free surface of tin samples with a roughness Rz 5, 20 and 60. Shock-wave unloading occurred in vacuum or gas (air, helium, nitrogen) at initial pressures 1-8 atm. The paper presents the experimental setups and experimental data on the density dynamics in dust fluxes formed upon exposure to one and two successive shock waves after their arrival at the free surface of samples in vacuum and gas media.

A scheme of registration of displacements of reflecting surfaces by the method of laser ranging with the use of a device developed for measuring the delay of optical signal propagation is considered. Results of test experiments aimed at studying the dusting parameters and spallation fracture of metals under shock wave loading with simultaneous applications of photonic Doppler velocimetry and laser ranging methods are reported.

An approach is proposed that allows for the construction of shock adiabats of molecular crystals of nitro compounds based on data on their isothermal compression. Equations of state for PETN and TATB crystals are constructed for this purpose. The comparative analysis of experimental data on shock-wave compression of a simple PETN crystal and computational results is performed using the proposed approach to converting isothermal compression pressures to a shock adiabat and the constructed equation of state for PETN, presented in the work. As shown by the analysis, the experimental and calculated pressures lie within the limits of experimental error.

This paper presents a semi-empirical multiphase equation of state (EOS) of copper for two solid FCC and BCC phases, as well as a liquid phase with account for vaporization is presented. A wide range of experimental and theoretical data is used to parameterize the EOS. In the field of plasma states of matter, calculations are performed using the RESEOS average atom model and are also applied to develop the EOS. Curves are plotted for FCC-BCC phase transition, for melting, and for liquid-vapor transition. In general, the EOS-based calculations are in good agreement with the experimental data and the results of theoretical calculations in a wide range of temperatures and pressures.

This paper presents the results of an experimental study of dusting and dispersion of a lead sample in vacuum after shock-wave loading and isentropic unloading using optoelectronic microscopy and photonic Doppler velocimetry. The dynamics and spectrum of predominantly dispersed particles are studied. Optical visualization is ensured by cutting out an 0.5-mm wide stream from the dispersed cloud using a diaphragm with a slit. The experiments are carried out in a sealed armored chamber. A 1- or 2.5-mm thick sample is loaded with a solid explosive through a metal substrate 1 and 2 mm in thickness. The shock wave intensity varies from about 23 to 38 GPa, and the pressure gradient behind the wave front ranges from 80 to 157 GPa/cm. After the loading, the lead is either in a liquid phase, in a solid phase, or in a mixture of both. It is shown that the particle size distributions of dispersed lead are different at different phase states.

The currently used shaped charges with combined hemisphere-cylinder liners allows obtaining compact steel elements with velocities of about 6 km/s. In this work, the possibility of modifying hemisphere-cylinder liners to expand the velocity range of the resulting compact elements was investigated by numerical simulation within the framework of the two-dimensional axisymmetric problem of solid mechanics. The simulation was carried out for a 100 mm diameter shaped-charge charge with a copper liner. The jet-forming part of the liner had a degressive (decreasing from top to bottom) thickness, a hemispherical or semi-ellipsoidal shape outer surface, and a semi-ellipsoidal or semi-superellipsoidal inner surface. As a result of the calculations, the geometric parameters of combined liners to form compact elements of maximally possible mass with velocities of 5-9.5 km/s were selected. For an element with a velocity of about 9.5 km/s, the mass was about 5 g.

According to Lavrentiev's hydrodynamic theory, the penetration depth of a shaped-charge jet is determined by its total length. However, experience of practical application of shaped charges has shown that the penetration usually ceases before the jet is completely used up. For a reliable description of experimental results, the effective length and the effective (critical) velocity of the shaped-charge jet are introduced to exclude from consideration the closing section of the jet, which various reasons is not involved in penetration. Effective velocity values are introduced into calculation methods as constants for a specific pair of jet and target materials or in the form of an empirical dependence on the focal length. The possibility of separating the jet into effective and ineffective sections based on physically justified reasons without the need to construct empirical dependences is considered.

This paper presents the results of numerical simulation of the operation of rotating shaped charges. The results show the that the velocity of radial expansion of high-speed hollow cylindrical projectiles simulating shaped-charge jet elements has no influence on their penetration depth. Numerical analysis was performed to study the stretching of a rotating stretchable metal cylinder (jet) with a harmonic lateral surface profile. The influence of various parameters, including the angular velocity of the jet, on its continuity in the axial and radial directions was evaluated. A relation for estimating the ultimate elongation coefficient of a rotating shaped-charge jet is proposed. Comparison of calculation results with experimental data shows that they are in satisfactory agreement with each other.

This paper presents the results of a series of studies to determine the dynamic strength characteristics of samples manufactured using selective laser melting technology of 12Kh18N10T steel powders and compares them with the properties of 12Kh18N10T steel obtained by traditional hot rolling under shock-wave loading in a compression pressure range of 3-7 GPa. It is shown that the steel samples manufactured using selective laser melting technology have greater resistance to short-term tension resulting from the interaction of counter-current unloading waves compared to the hot-rolled 12Kh18N10T steel.

Dynamic properties of volume-structured samples with different topology of mesh structures made of AK6 aluminum and synthesized by selective laser melting are considered. Tests are carried out at quasistatic strain rates of 10²÷10³с^-1 by the Kolsky method using a split Hopkinson bar. Strain diagrams are constructed, and the values of the conditional yield strength and tensile strength are determined. The results of measuring the properties of samples with different topology of mesh structures of FCC and BCC types and triply periodic surfaces of minimum energy of the gyroid type. The effect of the geometric characteristics of gyroids (cell size and wall thickness) on the strength properties of the samples is described. It is shown that gyroids have improved characteristics at the same material density. Mesh metal materials obtained by additive technology can be used in engineering to reduce structural mass and destructive high-energy mechanical effects.

The article is concerned with the preparation of medium-temperature highly conductive composite proton electrolytes of the new type by introducing a nanodiamond (ND) additive to cesium dihydrogen phosphate, and investigation of their properties. The data on changes in the structural properties of the salt in the composite, morphology, mechanical strength and proton conductivity depending on the composition (1- x )CsH₂PO₄- x ND (where x = 0-0.98, the molar fraction of ND) are considered. Valuable information explaining the mechanism of nanocomposite formation was obtained: the salt protons are partially bound to OH nanodiamond groups, which results in the arrangement of a weaker hydrogen bond system of the salt. It has been shown that there is no chemical interaction between the components in the composites, and the structure of CsH₂PO₄ ( P 2₁/ m ) is preserved during dispersion and partial amorphisation of the salt with an increase in the mole fraction of ND. The composites are characterised by the uniform particle distribution. The introduction of small ND concentrations leads to the stabilization of the size of salt particles (250±20 nm) in nanocomposites, as a result of the interfacial surface interaction of the components. Based on the change in the enthalpy of the superionic phase transition and X-ray diffraction data, the proportion of the amorphous phase in the composites was estimated to increase substantially with an increase in ND molar fraction, reaching 50 % at x = 0.8. A significant increase in the proton conductivity of the low-temperature phase of CsH₂PO₄ is observed, up to 3.5 orders of magnitude with a maximum at x = 0.9, and a decrease at x > 0.95 due to the conductor-insulator percolation effect. The superionic conductivity of the composites does not change up to x = 0.7 (11.7 vol% ND) and remains close to the value characteristic of initial salt CsH₂PO₄ (~10^-2 S/cm). An assessment of the strength characteristics of nanocomposites using the Vickers method shows that, due to the high hardness of nanodiamonds, the microhardness of the composites is significantly higher than that of initial CsH₂PO₄ even with a small content of ND additives ( x = 0.3, which corresponds to 2.64 vol%). The studied composite electrolytes have high proton conductivity, chemical stability and mechanical strength required for medium-temperature proton membranes of the new type for fuel cells.

The results of studying high-temperature oxygen desorption from an YBaCo₂O_6-δ oxide in the quasi-equilibrium regime are presented. The solid-phase synthesis of the oxide, ways and methods of its characterisation are described. The data obtained by quasi-equilibrium oxygen release technique allowed us to provide a reliable description of oxygen desorption from the oxide and to calculate the change in oxygen content in the oxide. Oxygen content in YBaCo₂O_6-δ is determined as a continuous function of temperature and the partial pressure of oxygen within the ranges of 600-900 °C and 0.2-10^-5 atm, respectively. The data obtained make it possible to identify the conditions of phase transitions in the oxide and determine the stability regions of the conductive phase, which is necessary for the development of cathode materials for solid oxide fuel cells.

The aim of this work was to develop a simple method to prepare silver micro- and nanoparticles that can be used to fabricate electroconductive compositions, including pastes, inks, and adhesives. To achieve this goal, the reduction of silver alkyl carboxylates (SAC) with different lengths and structures of the methylene chain by ethylene and propylene glycol was studied. The possibility of preparing monodisperse silver nanoparticles without using polymers as dispersants and stabilisers was shown. The particles obtained were characterized by X-ray diffraction analysis and electron microscopy. It was found that complete reduction of the straight short-chain alkyl SAC occurred at lower temperature (100-130 °C) than long-chain ones (130-170 °C). The particles synthesised under these conditions were spherical, and their average size decreased from 70 to 16 nm with an increase in the length of methylene chain. In the case of branched SAC structure, the reduction with polyols started at lower temperatures and was accompanied by the formation of larger silver particles 150 to 450 nm in size. It was shown that the characteristics of particles obtained by the reduction of linear SAC were almost independent of the synthesis conditions, whereas in the case of branched analogues the temperature, synthesis time and polyol type affected the size of the particles formed. Based on the data obtained, a mechanism for the formation of silver nanoparticles was proposed. Silver particles synthesised according to the developed procedure can find application as metal fillers in 2D and 3D printing inks and pastes for the manufacture of functional components and devices, in conductive adhesive compounds, in polymer composites, in medicine and biology.

High-temperature ceramic materials C_f/ZrB₂-SiC consisting of a refractory ZrB₂-SiC matrix reinforced with continuous carbon fibres (C_f) are of intense interest as candidates for the development of next-generation thermal protection for propulsion systems designed to operate under extreme conditions of temperature, mechanical load, and aggressive gas flows. The focus of these studies is on the oxidative and ablative stability, which is crucial for the practical application of high-temperature materials. In the present work, high-temperature C_f/ZrB₂-SiC composites were prepared by the ceramic prepreg method based on carbon fibre tow impregnation with ceramic slurry, formation of unidirectional ceramic ribbons, followed by their lay-up, pyrolysis, and silicon melt infiltration. The morphology and phase distribution over the volume of ceramic C_f/ZrB₂-SiC composites have been studied by electron microscopy with energy-dispersive spectroscopy performed at different accelerating voltages. For the first time, the behaviour of such materials under the conditions of exposure to high-speed plasma flow at temperatures as high as 2100 °С has been investigated. Air pressure was 0.35 MPa, air flow rate was 6 m³/h. The composite demonstrates rather stable behaviour up to 2000 °С for 300 s. A comparative analysis of the composite microstructure before and after gas dynamic tests has been carried out. The phase and elemental composition, as well as the cross-sectional morphology of the composite, are determined. It is shown that the ablative stability of the composite is due to the formation of complex microstructure, in which several sublayers can be distinguished, and each of them prevents oxygen diffusion inside the composite. Temperature increase up to 2100 °С leads to a significant degradation of the composite. The obtained data can be used for further improvement of the composition of high-temperature composites suitable for the stable functioning of power system parts and units under extreme conditions.

An efficient procedure for sample preparation and determination of rare earth elements (REE) in the brown coals of the Azeysk by a highly sensitive method, mass spectrometry with inductively coupled argon plasma, has been developed. The relative standard deviations in REE determination by the semi-quantitative and quantitative methods do not exceed 15 and 8 wt%, respectively. The total content of rare earth elements is 0.92 ± 0.07 kg/t of coal, which was verified by an independent spectrophotometric method with аrsenazo III.

Cocrystals of betulin with dicarboxylic acids were obtained using mechanochemical treatment with the addition of small amounts of organic solvents. The formation of cocrystals was confirmed by powder X-ray diffraction, thermal analysis, and IR spectroscopy methods. The presence of a solvent, the optimal components ratio, and the duration of mechanical processing are important for the formation of cocrystals. In order to choose a solvent for preparing betulin cocrystals, the solvents of different polarity were compared. It has been shown that cocrystals are formed if solvents that can effectively dissolve dicarboxylic acid are used during mechanical processing. For comparison with the mechanochemical method, betulin cocrystals were obtained by heating a mixture of starting reagents. Morphological changes observed by scanning electron microscopy upon heating the reaction mixtures also indicate the formation of cocrystals. It has been shown that when cocrystals are dissolved in water, solutions with an increased concentration of betulin are formed, and an increase in the length of the aliphatic chain of the acid leads to a decrease in the rate of betulin release into the solution.

The process of metal bismuth dissolution in nitric acid was studied, and a comparison was made over environmentally friendly methods of obtaining bismuth nitrate solutions by the preliminary oxidation of bismuth, as well as by its dissolution in the presence of urea or ammonium nitrate. It has been shown that the dissolution of bismuth in the presence of ammonium nitrate at a molar ratio of ammonium nitrate to bismuth equal to 1.5-3.5 and a temperature of 70±5 °C allows eliminating the release of nitrogen oxides into the gas phase and obtaining a solution with a high concentration of bismuth. The feasibility of two-stage hydrolytic processing of a bismuth-containing nitrate solution in order to purify bismuth from impurity metals is shown. The first stage is the aqueous hydrolysis of a bismuth-containing solution by adding a bismuth nitrate solution to water heated to 60 °C at a volume ratio of water to bismuth-containing solution 9 : 1, and the second stage is additional precipitation of bismuth from the mother solution after aqueous hydrolysis by adding ammonium carbonate solution to reach pH 1 at a temperature of 55±5 °C. Based on the research carried out, ecologically safe technologies have been developed for the production of bismuth oxohydroxonitrate [Bi₆O₅(OH)₃](NO₃)₅∙3H₂O and bismuth nitrate pentahydrate Bi(NO₃)₃∙5H₂O, as well as specially pure bismuth(III) oxide. As a result of the reduction of bismuth(III) oxide in molten sodium hydroxide containing sulphur at a temperature of 500 °C and at a ratio of bismuth(III) oxide/sodium hydroxide/sulphur equal to 1: 1.31: 0.20, high-purity metallic bismuth was obtained.

Physicochemical and pharmacological properties of mechanochemically synthesised supramolecular systems/complexes of the guest-host type have been studied at the institutes of the Siberian Branch of the Russian Academy of Sciences in cooperation with Chinese Zhejiang University of Technology. The guest is a molecule of a medicinal substance, and the host is a carrier particle - a macromolecule of polysaccharide, saponine micelle, silicon dioxide particle, etc. The strengthening of the pharmacological effect of such structures is achieved by increasing the water-solubility and trans-membrane permeability of drug molecules. The most effective hosts among the studied carriers are plant metabolites - glycyrrhizic acid and its salts, as well as polysaccharide arabinogalactan from Larix Siberica wood. An original solid-phase mechanochemical technology has been developed to obtain water-soluble supramolecular systems from the solid dispersions of components. In this case, supramolecular systems are formed in the process of solid-phase synthesis, or by dissolving the obtained dispersions in aqueous media. As a result of studies of a large number of widely used drugs of various pharmacological classes, it has been shown that the inclusion of drug molecules in these supramolecular systems can significantly increase the bioavailability, effectiveness and safety of their action and reduce the effective therapeutic dose of drugs significantly (by a factor of 2-150), and decrease (down to complete disappearance in some cases) harmful side effects. In this paper we give a brief overview of the studies carried out mainly over the last 10 years.