Search

The investigations of (Ti + Al)-SiO2 surfacing by magnetron deposition are presented in this article. The correlation between film`s thickness deposited on the particles by mechanocomposites and magnetron sputtering time was established. It was determined that the rational time for surfacing by Ti-Al mechanocomposites system is about 40 minutes. According that deposition time the thickness of deposited SiO2 films were obtained as 5.2 microns.

The computation methods of the thermodynamic properties are used for theoretical studies of multicomponent refrigerant blends (MRBs) for low-temperature throttling refrigeration units, providing cryostatting modes for cooled objects in the temperature range of –90 – –160 °С. The article presents the comparative analysis of the state equations for calculating thermodynamic properties of multicomponent refrigerant mixtures. Quantitative and qualitative differences in the results of calculations in the lowtemperature region are determined.

Theoretical studies of refrigerant blends in closed-loop throttling low-temperature refrigeration machines, which provide the specified cryostatting mode for cooled objects in the temperature range of – 90 to – 160°С, require computation of thermodynamic properties and phase equilibria. A method of computation of the phase equilibria and thermodynamic properties of multi-component refrigerant blends is presented based on the use of the two-parameter Redlich–Kwong equation of state in the Soave modification.

This paper presents a detailed experimental study of phase formation processes in a mechanically activated Ti + Al powder mixture. High-temperature synthesis has been performed in thermal explosion mode using induction heating of the mixture. We present the first evidence that, during a continuous transition from rapid heating to high-temperature annealing, the composition of the synthesis products depends on the secondary structuring time. Early stages of annealing involve structural relaxation processes, which make the phase composition more uniform and lead to the formation of an essentially single-phase TiAl compound. In later stages, the system undergoes a transition to thermodynamic equilibrium, which is accompanied by the formation of compounds that are in equilibrium at the annealing temperature.

In situ synchrotron studies of structure and phase formation dynamics in mechanically activated (t = 7 min, power density 40 g) and mechanically activated with subsequent irradiation by γ-quanta 60Co powder mixture (Ti 64 wt% + Al) during high-temperature synthesis by the method of thermal explosion using induction heating are described. In situ high-temperature synthesis was carried out on the created experimental complex adapted for synchrotron X-ray diffraction methods. The sequence of formation and time–temperature interval of the metastable and main phases were determined. The impact of preliminary mechanical activation and of γ-irradiation on the macrokinetic parameters of the synthesis were studied experimentally in situ. It has been established that the impact of γ-irradiation on the mechanically activated powder mixture of the composition Ti 64 wt% + Al leads to a change in the thermal parameters of combustion: the maximum synthesis temperature and the burning rate decrease. The heating rate for the non-irradiated mixture is 204.8 K s−1 and that for the irradiated mixture is 81.6 K s−1. The dependences of mass fractions of the synthesized compounds on time and temperature were calculated from the stage of preheating until completion of the thermal explosion. A single-phase equilibrium product of the composition γ-(TiAl) is formed in γ-irradiated mechanically activated mixture when the system reaches maximum temperature. The synthesized product of the mechanically activated mixture without γ-irradiation contains 72% γ-(TiAl); TiAl3 (26%) and residual Ti (2%) are also observed.

The results of numerical modeling of laser energy supply in a supersonic flow are presented. In contrast to the common approach, in the new calculation model, not only the absorbed power is taken into account, but also the plasma breakdown impulse in the domain of emission focusing does. The value of the impulse is determined using the model of radiation absorption behind the front of the laser-supported detonation wave. An analysis of the results is presented.

In the present work, the experimental study of the features of phase formation processes in preliminary mechanically activated powder mixture Ti+Al was conducted. The synthesis was realized...

The paper presents the results of an experimental study of an optical discharge plasma obtained by absorbing radiation from a pulsed-periodic radiation of a CO2 laser with a pulse repetition rate of 40 kHz and an average power of 1.6 kW. In order to increase the length of the breakdown plasma the laser beam (diameter 25 mm) was focused in the in an argon subsonic flow by a lens with a focal length f = 254 mm. To visualize the process, we used a FASTCAM SA-Z video camera (Type 480K), exposure time (1.0 µs), and shooting speed of up to 200,000 fps. The conditions for registering an optical scheme varied by using a Foucault knife, diaphragms, and light filters in order to develop optimal methods for obtaining data. The experimental results showed that the plasma dynamics has two successive stages: from the high-speed optical discharge propagation with absorption of radiation behind the laser supported detonation (LSD) wave front to the next less speed stage.

The purpose of the work presented is to study the processes of phase formation in mechanically activated Ti + Al powder mixture which was exposed to low doses of gamma radiation. A two-stage treatment of the initial powder mixture of the specified composition was conducted. At the first stage, the mixture was mechanically activated in order to achieve a high quality of contact between the reactants. At the second stage, the mixture was subjected to gamma irradiation in order to form a wide transition zone in the contact area. The irradiated mixture was heated by the external heating source. To study the processes of phase formation, the technique of time-resolved X-Ray diffraction was used. The comparative analysis of intermetallic phases formation sequences for irradiated and non-irradiated mixtures was carried out. It was found that the heterogeneous reactions pathways are significantly different for these cases. The detailed analysis of parallel and consecutives reactions was carried out at various stages of high-temperature synthesis taking into account the structure of the Ti–Al equilibrium diagram. It was found that the most probable mechanism of heterogeneous reaction in unirradiated mixture is the predominant dissolution of titanium with the formation of intermetallic phases TiAl, TiAl3. In the irradiated mixture, on the contrary, the flow of aluminum atoms dominates, which leads to the formation of the only synthesis product of the TiAl composition. In the case of forced cooling of the mixture after thermal explosion (TE), a uniform distribution of reactants is observed in the whole volume of the sample of the irradiated mixture which is similar in composition to the TiAl compound.

This paper is aimed at finding the primary cause and mechanisms of flow structure rearrangement (stable/unstable) behind the front of strong shock waves (SW) in gases. Results of experimental and calculated investigations of strong shock waves in atomic gases obtained by the authors of this work and other researchers for the last several decades are analyzed. A unique analytical approach, referred to by the authors as the source of electrons method, is used, which makes it possible to determine the relationship between the kinetic processes of ionization of particles and the energy exchange in a non-equilibrium flow (avalanche ionization region) behind a shock wave in argon in a wide range of flow conditions: M = 10–30, pressure ahead of the shock wave front p1 = 1–25 torr. In addition to the basic processes, the following additional mechanisms are considered: (a) associative ionization in interatomic collisions with participation of highly excited atoms, (b) integral radiation losses, (c) convective energy transfer, and (d) electrons heating in the polarization electric field. It is found that the primary cause of flow structure instability in shock waves is the presence of flow boundaries responsible for (i) weak gas-dynamic perturbations and (ii) local (near-wall) inhomogeneity of the medium ahead of the shock wave front and behind it. The mechanism of structural instability of the shock wave in atomic gases at low Mach numbers is caused by a cardinal change in the relationship of the basic and additional kinetic and energy exchange processes between the ionized flow components behind the front, even in the case of a weak perturbation of the atomic–ionic component temperature. In the range of high Mach numbers, the instability mechanism is due to the thermal effect induced by wall and near-wall gas layers heating ahead of the SW front by precursor radiation and also due to possible energy release initiated by polarization of the electric field near the wall behind the shock wave front.

There are considered ecologically harmless technologies for nano-structural material obtaining by methods of mechanochemistry with carrying out a reaction of high-temperature synthesis in a metal matrix for the application of the powder material obtained in the course of gas-detonation coating processes which may substitute electroplate chromium coating. As a sputtered powder there was used SVS- mechanocomposite having Ti-C-NiCr in its composition. It is determined that the wear of piston rings with the developed coating is lower by 27%, than in similar rings with an electroplate chromium coating.

The influence of absorbed γ-quantum irradiation doses Dγ (60Co isotope) on the structural parameters of Ti3Al single-phase compounds is experimentally investigated. The structural characteristics are defined more accurately using X-ray diffractometry. On account of the results of structural studies, it is found that exposure to low γ-radiation doses (e.g., Dγ = 1 × 103 Gy) generates the nonequilibrium state of the Ti3Al structure. An increase in the absorbed dose (to Dγ = 1 × 105 Gy) stimulates the formation of a metastable radiation-induced state, which is identified by diffraction-reflection splitting, an increase in the crystal-lattice volume, and changes in the parameters of the fine structure (the coherent-scattering-region size decreases to 13 nm, and the defect concentration increases).

The influence of a thermal wake due to gas injection and due to a pulsating optical discharge (POD) on the aero-dynamic-drag force of a body in a supersonic air flow with Mach number M = 1.45 are experimentally examined. With the help of a single-component aerodynamic balance, the influence of the injected subsonic jet and the thermal wake produced by POD on the aerodynamic drag of a hemisphere-on-cylinder model was studied. It is shown that the observed aerodynamic-force reduction phenomenon can be made more pronounced by increasing the laser power and pulse repetition frequency, or by decreasing the distance between the model and the pulsating optical discharge. The maximum aerodynamic-force reduction (up to 15%) due to the thermal-wake action was observed at a maximum laser-radiation power of W = 2.3 kW and at a pulse rate of f = 90 kHz. The joint effect due to the argon jet and due to the POD caused an aerodynamic-drag force reduction reaching 30%.

We have studied the effect of sintering temperature on the structural and phase transformations of alloys produced by the spark plasma sintering of Ti + 23.5 at % Al + 21 at % Nb powder mixtures at temperatures in the range 1100–1550°C. The sintered alloys have been characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy (elemental X-ray mapping). The alloys sintered at temperatures of 1100 and 1200°C have been shown to have a nonuniform microstructure. According to electron microscopy results, the alloys consist of grains of the α2 and Nb2Al phases and small precipitates of the O-phase (intermetallic compound Ti2AlNb). In addition, there are particles of unreacted niobium and titanium. The alloys sintered at a temperature of 1300°C have a uniform lamellar structure.

Structural peculiarities of a powder composite mixture on the basis of aluminum and dispersion carbon structures intended for gas-detonation sputtering for an anti-friction purpose are investigated in the paper. As initial materials there was used an aluminum powder, carbon powder, boron carbide powder, powder slurry consisting of fullerenes C60 and ultra-dispersion diamonds in a certain ratio. The powder mixture obtained was subjected to a mechanical activation with the aid of a planetary ball mill of AGO-2S type. According to the results of the morphological analysis it was established that a composite mixture possesses a layer structure characteristic for powder mixtures subjected to a mechanical activation in the course of a long period of time. A mean size of obtained mechano-composite particles makes about 100…150 mkm. An X-ray structural investigation of a composite powder mixture formulations 70% Al+30%C+B4C and 70%Al + 30%C60 (total %) + B4C after mechanical activation revealed that boron carbide contributes well to the amorphization of a composite powder mixture. It is also established that after mechano-activation of the “Al+C+B4C” powder mixture during 4 min carbon transforms to an X-ray amorphous state to which testifies the presence of amorphous “halo” at small angles and carbon peaks disappeared completely. There is no carbon dissolution in aluminum and chemical compounds are not formed.

The structural and phase state of powder samples of compounds Ti3Al and TiAl has been investigated experimentally before and after the action of small doses of gamma irradiation. To study phase and structure parameters, the X-ray diffractometry has been used. It has been established experimentally that after the same conditions of gamma irradiation structural states of these compounds differ. It has been revealed that for compound Ti3Al small doses of gamma irradiation serve stimulators to form radiation-induced states. In the irradiated TiAl sample, a crystal-lattice distortion was observed with the retention of a high crystallinity of the structure and no signs of a special radiation-induced state were revealed.

Effects of gamma-irradiation on the process of SHS of mechanoactivated mixtures Ti-Al-C and Ti-Al-Nb were studied. Mechanical activation was performed for 7 minutes in planetary ball mill at energy intensity 40 g. SHS was initiated by induction heating with varying time of annealing. Gamma-irradiation was performed on 60Co isotope to absorbed dose 3·104 Gy. Structural parameters of cells of components were calculated. Gamma-irradiation affects components of triple systems in different ways, leading to unsystematic changes in elementary cells. After SHS in powder mixture 80% Ti + 12% Al + 8% C without gamma-irradiation, it was found that product contains Ti2AlC, Ti3AlC2, TiC and unreacted C. Irradiated mixture react fully - diffractogram identifies Ti2AlC, Ti3AlC2 and TiC. Annealing for 2 minutes produces a product with dominant Ti2AlC. SHS in mixture 45% Ti + 12% Al + 43% Nb revealed that product consists of Ti2AlNb, B2-phase, α2-phase and residual Nb and Ti. During synthesis in irradiated mixture without annealing, diffractograms show decrease in level of diffuse background and increase in values of reflection intensities, structural state of products is stabilized. Effect of gamma-irradiation contributes to growth of phases and stabilization of structure synthesized product.

In this paper, we consider the solution of the problem of the theory of piezoelectricity. The effective elastic, piezoelectric, and dielectric characteristics are calculated for a two-layer composite with a volume concentration of layers of 50%. The corresponding characteristics are calculated for a two-layer material with an orthogonal-reinforced structure. For the numerical solution of the problem, the conjugate gradient method for solving systems of algebraic equations was used. The results were visualized using a software package developed at Bauman Moscow state technical University. The paper presents the distribution of the stress field σij and the vector d ¯ i in problems Lr and Lpq .

Аbstract With the use of time-resolved X-Ray diffraction, the analysis of the phase formation dynamics processes in mechanically activated powder mixture of Ti + Al composition in the thermal explosion mode was carried out. The synthesis was conducted under conditions of heating by an external source of constant power. It was found that at the stage of low-temperature heating (preheating stage), a significant amount of reaction products (intermetallic phases) is formed. A possible reason for this is the presence of disordered transition zones that form at the interface between the reactants in the process of preliminary mechanical activation. However, in the process of nonequilibrium synthesis (thermal explosion), the formation of the only compound γ -TiAl occurs. It was established that the structural changes continue after completion of the chemical reaction. At the first stage of high-temperature annealing, the processes of structural relaxation (which are not accompanied by the appearance of new compounds) are realized. At the second stage, the processes of transition to a thermodynamically equilibrium state occur. It was shown that the forced cooling of the system at various stages of the synthesis can be a way of controlling the structure, composition and, as a consequence, properties of the synthesis product.

The aim of the work was to study the effectiveness of enzyme preparations in the composition of animal feed on the increase in live weight and meat productivity of goslings. Amylosubtilin and protosubtilin were introduced into the feed for goslings of the first experimental group; amylosubtilin and celloviridin were added into the feed for goslings of the second experimental group. It was found that the absolute increase in live weight in the control group was 6366.9 g in gander and 5734.43 g in geese. In the first experimental group this indicator was exceeded: for gander by 7.51%, in geese - by 7.24%; in the second experimental group - by 10.35% and 9.07%, respectively. The slaughter yield of half-hulled carcasses of gander in the control group was 79.27%; in the first group this indicator was higher by 1.34% and in the second group higher by 3.03%. The geese in the control group amounted to 81.80%. In the first experimental group it was higher by 1.2% and in the second experimental group higher by 1.96%. The slaughter yield of gutted carcasses of gander in the control group was 60.78%, in the first experimental group - 61.16% (+1.6%) and in the second experimental group - 62.76% (+1.98%); in geese - 62.76%, 63.17% (+1.69%) and 64.86% (+2.1%) respectively.

An in situ synchrotron study of the specific features of the phase formation dynamics in mechanically activated 16 wt% Al + Ti powder composition is described, the high-temperature synthesis being carried out under the condition of high volume inflammation by means of inductive heating. The kinetics of the phase formation were registered with an experimental complex, especially designed, constructed and adjusted for the method of dynamic diffraction analysis in synchrotron radiation beams. It has been experimentally in situ shown that increasing the time of mechanical activation of the initial powder mixture reduces the temperature at which components start to react and the time of realization of the high-temperature synthesis. With the latter set at 1 min of mechanical activation, the temperature of the reaction in the mixture is T = 603°C; at 3 min of mechanical activation, T = 442°C; and at 7 min, T = 359°C. The maximum burning temperatures are: for 1 min of mechanical activation, T max = 1080°C; for 3 min, T max = 1003°C; and for 7 min, T max = 820°C. It was found that formation of both stable compounds Ti3Al, TiAl3, TiAl2, TiAl and metastable phases Ti9Al23, Ti5Al11, Ti2Al5, Ti3Al5 occurs at the stage of primary structure formation, before the system goes to thermal explosion. High-temperature synthesis of a mixture of the studied composition takes place without formation of a liquid phase, in the solid-phase combustion mode. It was found that the increase in the time of mechanical activation of the initial powder mixture contributes to the formation of a product with a dominant content of intermetallic compound Ti3Al. By synthesis of the powder mixture of composition 16 wt% Al + Ti, mechanically activated for 7 min, the content of Ti3Al in the final product was found to be 68%.

The influence of basic high-temperature synthesis parameters on the process of structure formation in the mechanically activated powder mixture 3Ti+Al was investigated in the study. The synthesis was realized by the method of induction heating in the thermal explosion mode. The heating temperature of the mixture reached 1500°C during the solid state reaction. This temperature exceeded the adiabatic combustion temperature. The investigations of the phase structure formation processes were conducted by XRD methods. In order to obtain a Ti3Al single-phase compound, the optimal time-temperature parameters of the synthesis were determined.

At present the development of methods of layer-by-layer and line-by-line synthesis of finished prototypes and functional products made of powder materials furthers introduction of these technologies into different areas of human activities from light to heavy industry and medicine. The research has been carried out to describe how gamma radiation of the Co60radioactive isotope and the mechanical activation makes an impact on the copper powder, as well as the nature of sintering by the layer-by-layer laser synthesis. The changes of the structure and properties of the powder, which generally affects the layer-by-layer laser process of products sintering, have been detected.

The effect of an optical pulsed discharge created by CO2-laser with an average power of up to 2.2 kW on the aerodynamic drag of a model in a supersonic air flow is experimentally investigated. Experiments were carried out in a supersonic wind tunnel MAU-M (diameter of the nozzle outlet dc = 50 mm) on the modes M = 1.36, Re1 = 1.4– 3.8*107 1/m. To ensure a stable optical breakdown, a jet of argon gas was introduced into the focusing region of the laser beam. As a result, a decrease in the aerodynamic force acting on the model was obtained. This decrease was 15% when a subsonic flow of argon was introduced into the main flow and another 15% when optical pulsed discharge was organized.

The paper presents the results of the experiment, describing the effect of mechanical activation of powder Cu and Ni on the nature of their SLS-sintering method. The changes in structure and bulk density of powders after mechanical activation are revealed, which generally has a positive effect on the synthesis process of a product.Intorduction

We report a study of the wave structure formed by an optical discharge plasma upon the absorption of repetitively pulsed CO{sub 2} laser radiation in a supersonic (M = 1.36) air flow. Experimental data are presented on the configuration of the head shock wave and the geometry and characteristic dimensions of breakdown regions behind a laser plasma pulsating in the flow at a frequency of up to 150 kHz. The data are compared to calculation in a point explosion model with allowance for counterpressure, which makes it possible to identify the relationship between laser radiation and supersonic flow parameters that ensures quasisteady- state energy delivery and is necessary for extending the possibilities of controlling the structure of supersonic flows. (interaction of laser radiation with matter)

The experimental investigation of structure formation processes in preliminary mechanically activated powder mixture 3Ti + Al was carried out. The synthesis was realized in the thermal explosion mode with the use of high-frequency induction heating. The characteristic features of structure and phase formation in this system by quenching of the mixture at different annealing times were installed. It was shown, that the processes of structure-phase formation occur in the following sequence: chemical reaction - structural relaxation - thermal relaxation - thermal equilibrium. The time-temperature intervals of Ti3Al strictly single-phase compound existence with various concentrationsof non-equilibrium defects of the structure were established.

MW-assisted combustion synthesis in mechanically activated 3Ti+Al powder mixtures in a thermal explosion mode was explored by thermography and XRD with special emphasis on the influence of mode/rate of MW heating. The main stages of the process were outlined as well as optimal conditions for preparation of single-phase Ti3Al.

In this article, the approach to evaluate the probability of estimating the range of the beacon with a given accuracy is proposed. To determine the range to the beacon, a set of Kalman filters is applied to the beacon bearing measurements according to the given hypotheses about its motion parameters. The calculation of the probability of the correct choice of a hypothesis is presented. The hypothesis with the minimum sum of squared residuals is considered without prediction errors, its expectation and standard deviation, respectively, are. The time, required to determine the range with the probability 0.9..0.95 is calculated according to the proposed method agrees with the results obtained by statistical analysis, performed over multiple data sets. The results of the simulation of the “frequency” graph are shown.

The granulometric composition of a hydroxyapatite powder has been investigated. The initial powder has been classified into particle size ranges (0.1–10, 10–20, 20–30, and 50–300 μm). Coatings prepared from a hydroxyapatite powder of different size have been deposited by the detonation gas spraying technique. The structure and phase composition of the coatings have been studied. Changing the initial granulometric composition of the powder mixture is shown to provide control over the sprayed surface roughness.

Double extensive air showers were studied at the Tien Shan high-mountain scientific station of the Lebedev Physical Institute using two different installations. One measured the electron-photon shower component, the other measured Cherenkov radiation. Double showers separated by a time interval of ∼100 ns were detected by both setups. The frequency of the occurrence of such showers in each setup is analyzed. It is shown that these frequencies are identical when observing vertical showers (the zenith angle ϑ < 60°).

As a result of optical and pneumometric measurements is defined the flow shock wave structure that is formed by the optical breakdown, due to focused repetitively pulsed CO2 laser radiation when entering perpendicular to a supersonic (M = 1.36, 1.9) air flow direction. The dynamics of the bow shock formation in front of the energy input area is shown, depending on the frequency of energy impulse sequence. A flow structure is defined in the thermal wake behind pulsing laser plasma as well as wake’s length with low thermal heterogeneity. A three-dimensional configuration of the energy area is defined in accordance with pneumometric and optical measuring results. It is shown that Pitot pressure decreases in thermal wake at a substantially constant static pressure, averaged flow parameters weakly depend on the energy impulse’s frequency in range of 45-150 kHz.

We present the features of macrokinetics of phase formation during the solid-state synthesis in the mechanically milled 3Ni + Al mixtures. It was found that with milling time, the activation energy decreases down to anomalously low values, which is related to structural changes in the powder mixtures. A method was proposed to process thermograms of the synthesis in the thermal explosion mode and was used to study the kinetic function structure and its parameters in the system. The numerical processing of the experimental data shows that the kinetic function most adequately corresponds to the law of homogeneous kinetics of phase formation with the reaction order close to unity.

The results obtained by studying double-front extensive air showers in which more than 107 particles are contained and in which the fronts are separated by a time interval of Δt ∼ 100 ns are presented. Serious difficulties in explaining “delayed” showers are revealed. In this connection, a hypothesis that the “leading” showers are initiated by tachyons produced in the first interaction of primary particles is proposed.

New heterogeneous catalysts for synthesis of a biodiesel fuel, modified with strongly acidic groups, were developed. The catalysts are produced by pyrolysis and subsequent sulfation of fruit kernels and granulated porous copolymers and resins. The structural-sorption and catalytic properties of the materials obtained were studied in the reaction of catalytic re-esterification of rapeseed oil by methanol and ethanol. The conditions in which carbon materials with high content of surface acid groups are obtained were optimized.

Conditions of a static thermal explosion in mechanically activated Ti-C-Ni mixtures are studied. Mechanical activation of the mixtures in a planetary ball mill during 30–180 sec is found to reduce the reaction-initiation temperature by 1000–600°C, as compared with traditional self-propagating high-temperature synthesis. Results of x-ray diffraction analysis and electron microscopy of activated mixtures and thermal explosion products are described. The result of the synthesis is a TiC compound in a solid nickel matrix.