Corrosion,Mechanical and Catalytic Properties of Coatings Based on FeNiCrWMoCoCB Metallic Glasses

Protection of Metals and Physical Chemistry of Surfaces - This work is devoted to the deposition of coatings based on FeNiCrWMoCoCB metallic glasses on a surface made of 35 steel; the deposition is...     

Numerical analysis of a model of metal solidification, 2D case

The work discusses numerical simulation of metal solidification. The difficulties of calculatibg such processes are that simulation is conducted at several scale levels simultaneously. At present experimental studies cover numerous aspects of metal solidification; however, there is no generalized concept of this process. The model applied in this study is based on the concept of solidified alloy in the form of a porous medium, where propagation of perturbations is described by the Biot equations. In order to describe nucleation, the modified Cahn-Hillard equation is applied. Previously a one-dimensional (1D) numerical model has been developed, its convergence has been demonstrated and a possibility of obtaining of various modes of solidification has been shown at modification of parameters. This work presents the 2D numerical model and examples of calculations. Since a multiscale approach requires high CPU resources, the 2D calculations are based on explicit and explicit-iterative algorithms which are efficiently implemented using a multiprocessor computer.     

Anisotropy of the thermopower in higher silicide of transitions metals

A new technique for measuring the thermopower anisotropy using polycrystals on the basis of repeated measurements of an array of randomly oriented microcrystals and statistical analysis of the data obtained is proposed. The thermopower anisotropy of a series of higher silicides of transition metals (β-FeSi₂, doped MnSi_1.75, ReSi_1.75, and CrSi₂) is measured using polycrystals. It is found that, in β-FeSi₂ crystals, a very high thermopower anisotropy can be observed; in ReSi_1.75 crystals, the thermopower can have different signs; and, in CrSi₂, the absolute value of the thermopower depends heavily on the heat-treatment mode. The temperature dependences of the electrical conductivity and thermopower of CrSi₂ needles are measured. The thermopower anisotropy in CrSi₂ needles, as in bulk single crystals, is retained in a wide temperature range.     

The possibility of using acid-alkali solutions to precipitate rubidium in the form of its hexachlorotelluride

The possibility of isolating rubidium from acid-alcohol solutions in the form of its complex halogenide with tellurium is considered. The solubility of potassium, sodium, and rubidium in solutions of the mixture of hydrochloric acid and ethanol with their various volume ratios at t = 25°C is investigated. The possibility of increasing the degree of isolation of Rb in the form of its hexachlorotellurite (Rb₂TeCl₆) upon going from acidic to acid-alcohol solutions is shown.     

Calculation of Thermobimetallic Releases of Circuit Breakers with Indirect Heating for Currents from 63 to 250 A

Thermal releases based on thermobimetallic elements (TBEs) form the current-dependent part of the protective characteristic of a circuit breaker. The design of a mechanism of free releasing and the characteristics of a thermobimetallic element are analyzed. The operating condition for the thermal release is formulated, which is based on comparison of the mechanical characteristics of an actuator and thermomechanical characteristic of TBEs. Experimental studies of thermobimetallic releases, which are analogues of the breakers to be developed, were carried out. Taking into account the results of these experiments, a design procedure of thermobimetallic release was developed, which is applicable for all types of TBE heating (direct, indirect, combined). The procedure makes it possible to determine the geometrical dimensions of a TBE and the methods of its heating, as well as the operating temperature of release depending on the rated current of the breaker. It has been noted that, to provide the possibility of operating current adjusting, as well as for reliable operation of circuit breakers under vibration and shock conditions, it is necessary to provide for the free running of TBE during design. Comparison of design and experimental data showed the accuracy of procedure, which is acceptable for practical calculations.     

The technology and electrical characteristics of ceramics based on hydroxylapatite

In this paper, we have examined the synthesis and structure of hydroxylapatite and methods for obtaining a dense and porous hydroxylapatite, as well as methods for producing a dense and porous HA-based ceramics. The temperature dependence of conductivity and dielectric loss tangent of hydroxylapatite were investigated.     

Interaction between Copper(II) Oxide and Aqueous Ammonia in the Presence of Ethylenediaminetetraacetic Acid

The interaction of copper(II) oxide with aqueous ammonia containing ethylenediaminetetraacetic acid (H₄L) is analyzed in terms of formal heterogeneous kinetics and the fractal dimension of the dissolving space. It is shown experimentally that, in the presence of H₄L, the dissolution rate of CuO grows with increasing ammonia concentration. At a fixed ammonia concentration, the dissolution rate of CuO passes through a maximum at an H₄L concentration of 8 × 10^–3mol/l. Two mechanisms of dissolution are suggested, namely, an adsorption and a redox mechanism. The adsorption mechanism involves four intermediate species and implies that the dissolution rate is a fractional rational function of the EDTA concentration. The redox mechanism takes into account the oxide/electrolyte interfacial potential. The role of the CuOHL^3–ion is elucidated, and the kinetic parameters of dissolution are derived.