Metastable phases and macroheterogeneous composites

The way to control the interfacial reactions that processes during infiltration of macroheterogeneous composite materials is suggested. The idea is to combine the stable and metastable phases in the filler’s structure which dissolves at a different rate in the molten binder. To prove this approach, the structure and gas-abrasive wear of macroheterogeneous composite materials with Cu–20Ni–20Mn binder reinforced by Fe–(9.0–10.0)B–(0.01-0.2)C filler (in wt. %) cooled at 10–20 K/s or 103–104 K/s are studied. It is shown that the wear resistance of the investigated composite materials can be enhanced by accelerating interfacial reactions between the filler and the molten binder. Therefore, the composite materials produced from a rapidly cooled Fe–B–C filler show a higher resistance to gas-abrasive wear due to formation of Fe–Fe2(B,C) metastable eutectics in its structure. This eutectics crystallizes under metastable phase diagram due to the suppression of stable Fe2(B,C) phase formation and saturation of the rest of liquid by iron in the filler cooled at 103–104 K/s. As a result of rapid dissolution of the eutectics in the molten binder during infiltration, the strong adhesion at the interfaces of the composite materials is achieved which prevents the filler from spalling out under the impacts of abrasive.

Calculation of a non-reflective connection in a coaxial line

The calculation of the non-reflective connection in the coaxial line is performed by the integral equation method. The connection of coaxial lines with a significant difference in geometric dimensions is considered. A system of equations is obtained that allows calculating the reflection coefficient of the T-wave from such an inhomogeneity. This technique makes it possible to calculate a multistage coaxial waveguide in order to minimize the reflection coefficient from inhomogeneities.

Optical absorption of LiNaGe4O9:Mn crystal

The paper reports the results of optical absorption spectra studying in LiNaGe4O9 crystal doped with Mn. It is shown that Mn impurity causes the appearance of the additional absorption bands. The intensities of these bands change in different ways in the range of the ferroelectric phase transition. Semi-empirical version of the crystal field theory is used to discuss localization and charge state of Mn impurity ions in the LiNaGe4O9 structure.

On hydrodynamics in the presense of strong external potential field

On the base of the Boltzmann kinetic equation, hydrodynamics of a dilute gas in the presence of the strong external potential field is investigated. First of all, a gravitational field is meant, because the consistent development of hydrodynamics in this environment is of great practical importance. In the present paper it is assumed that it is possible to neglect the influence of the field on the particle collisions. The study is based on the Chapman–Enskog method in a Bogolyubov’s formulation, which uses the idea of the functional hypothesis. Consideration is limited to steady gas states, which are subjected to a simpler experimental study. Chemical potential μ0 of the gas at the point where the external field has zero value and its temperature T are selected as the reduced description parameters of the system. In equilibrium, in the presence of the field, these values do not depend on the coordinates. It is assumed that in thehydrodynamic states T and μ0 are weakly dependent on the coordinates and therefore their gradients, considered on the scale of the free path length of the gas, are small. The kinetic equation, accounting for the functional hypothesis, gives an integro-differential equation for a gas distribution function at the hydrodynamic stage of evolution. This equation is solved in perturbation theory in gradients of T and μ0. The main approximation is analyzed for possibility of the system to be in a local equilibrium by means of comparing it with an equilibrium distribution function. Next, the distribution function is calculated in the first approximation in gradients and it is expressed in terms of solutions Ap , Bp of some first kind integral Fredholm equations. An approach to the approximate solution of these equations is discussed. The found distribution function is used to calculate the fluxes of the number of gas particles and their energy in the first order in gradients T and μ0 . Kinetic coefficients, which describe the structure of these fluxes, are introduced. Matrix elements of the operator of the linearized collision integral (integral brackets) are used for their research. It is a question of validity of the principle of symmetry of kinetic coefficients and definition of their signs.

Phase diagram of the selfinteracting particle­-antiparticle boson system

A system of interacting relativistic bosons at finite temperatures and isospin densities is studied within the framework of the Skyrme­like mean­field model. The mean field contains both attractive and repulsive terms. The consideration is taken within the framework of the Canonical Ensemble and the isospin­density dependencies of thermodynamic quantities is obtained, in particular as the phase diagrams. It is shown that in such a system, in addition to the formation of a Bose­Einstein condensate, a liquid­gas phase transition is possible. We prove that the multi­boson system develops the Bose condensate for particles of high­density component only.

Volt-ampere characteristic of the double Schottky barrier

The volt-ampere characteristic (I-V characteristic) of the double Schottky barrier located in the contact region of ZnO grains of zinc oxide based varistor ceramics is calculated using the mechanism of the above-barrier electron emission. I-V characteristic is symmetric to the polarity of the voltage U. At U > 2kBT/e (kB is the Boltzmann constant, T is the absolute temperature, e is electron charge) the electric current is saturated. The contact of ZnO grains with a double Schottky barrier behaves like an electrical circuit consisting of two oppositely connected Schottky diodes. A small maximum possible decrease in the height of the double Schottky barrier in an electric field ~ 0.7kBT ≈ 0.018 eV does not allow explaining the high nonlinearity of I – V characteristic of varistor materials by the above-barrier electron emission. The most probable cause of nonlinearity is the tunnel emission of electrons and impact ionization.

Study of the influence of quick-hardened alloy on the properties of metal polymers

The article explores the effect of quick-hardened alloy PR-N65X25S3R3 based on nickel, (chemical composition – Ni64,6Cr25C1,2Si2,7B2,5Mn0,2Fe3,8) on the physical and mechanical properties of metal-containing polymers. Carried out tests and results have shown that the use of quick-hardened alloys, which are characterized by a set of unique properties, is appropriate. The developed metal-containing polymers that contain aromatic polyamide phenylone and 5 - 20 wt.% of self-fluxing amorphous alloys PR-N65X25S3R3 are characterized by 2 times greater abrasive wear resistance and better adhesive strength between the components. Due to the use of quick-hardened alloy it was possible to increase theeffective filler content from 15 wt.% to 20 wt.% that will increase the electromagnetic properties of metal-containing polymers.

Conditions for partial and complete crystallization suppression upon quenching from liquid state

For bulk-amorphizing alloys Мg65Сu25Y10 and Zr41,2 Тi13,8Сu12,5Ni10Ве22,5, the thickness and cooling rate of melt layers is calculated, which ensure the formation of X-ray amorphous structures typical for metallic glasses ( lC, vC ), and truly amorphous states without inclusions of «frozen-in crystallization centers» (lc*, vc* ). Correlation of the calculated values lC, vC with the known experimental estimates is C Cachieved. It is shown that both studied alloys demonstrate a predisposition to complete suppression of crystallization processes at physically correct values of the parameters lc* and vc* (10 μm; 1,3·107 K/s and 550 μm; 2,7·103 K/s for alloys based on Mg and Zr, respectively). It is concluded that the most significant factors controlling the tendency of materials to noncrystalline solidification are the decrease in the frequency of non-stationary nucleation with the increase in the rate of QLS, as well as relatively low <1018 m-3 s-1) maximum values of the rate of stationary crystallization centers formation.

Non-isothermal crystallization of LiNaGe4O9 glass

The glass of lithium-sodium tetragermanate LiNaGe4O9 is crystallized on heating under the control of differential scanning calorimetry and thermal gravimetric analysis. The measurements were prepared in the temperature range 300-870 K and showed the relatively weak endothermic DSC anomaly and 40-50 K above the single exothermic peak. The endothermic anomaly observed at Tg testified to softening the glass structure whereas the exothermic peak at TC manifested crystallization of the amorphous phase. Studying of TGA demonstrated smooth nearly linear dependences without any visible anomalies. Varying the heating rate from 1.2 up to 40 K/min resulted in noticeable increase of the characteristic temperatures Tg and TC. Lower limit of the glass transition temperature Tg0 was estimated with the help of the existing model. The mechanism of the LiNaGe4O9 glass crystallization is discussed.

Multi-component nitrated ion-plasma Ni-Cr coating

Method for ion-plasma deposition is applied for covering of heat-resistant Ni-Cr alloy XH78T. Coating deposition is performed under nitrogen gas atmosphere at the pressure from 3×10-5 to 1×10-2 Torr. The nitrogen content in the coating is reached up to 2,7 %. Nitrated coatings with a thickness of 184-222 μm is obtained without embrittlement and with a uniform distribution of microhardness. The effect of the nitrogen pressure in a vacuum chamber on the structure of the coatings, which changes from homogeneous to columnar with conical crystallites, is presented. Nitration increases microhardness of the coatings from 3669 to 7575 HV, the wear resistance of the coatings increases by 6-8 times. The received coatings can be used to increase the durability of metallurgical equipment parts.