Simulation Studies of Electronic Properties and Atomic Ordering in the b-Si3N4 – Mg – O SYSTEM

Simulation studies of the electronic structure, interatomic bonds, chemical composition, and atomic ordering in solid solutions Si_6–x Mg_xO_2x N_8–2x of the β-Si₃N₄ – Mg – O system and solid solutions Si_6–x Mg_xO_xN_8–2x X_x (X = S, Se) and Si_6–x Mg _x/2M _x/2O_xN_8–x (M = C, Si, Ti, Ge, Zr, Sn, and Pb) are carried out using the strong-coupling energy-band method. Stabilization of solid solutions Si_6–x Mg_xO_2x N_8–2x is accomplished in the presence of S, Se or Zr. In these solutions, Mg and O atoms are capable of forming quasi-unidimensional structures (dopant, or impurity, channels) similar to those predicted for β-sialons.     

Luminescence of a Transparent Alumina Ceramic Doped with Chromium and Titanium

Specimens of transparent alumina ceramic (TAC) are prepared by slip casting. An alumina spinel, formed during sintering under vacuum or under reducing conditions, as well as individual phases, produced by thermochemical doping with chromium and titanium, are identified. The spectra of steady-state x-ray luminescence (SXL) and pulsed cathodoluminescence (PCL) and the PCL decay kinetics are studied. The highest STL and PCL intensity were observed in specimens that were prepared by thermal diffusion using a carbon + TiO₂ pack. Ti-doped TAC, characterized by a rapid decay of luminescence in the UV region, can be recommended as a promising material for the detector of a scintillation dosimeter. The luminescent chromium ions (isomorphic substituents of aluminum ions in the crystal lattice) are unsuitable for that purpose because of their long luminescence de-excitation time.     

First-principle quantum-chemical calculations of several thermomechanical parameters of beryllium ceramics

The first-principle quantum-chemical calculations of elastic constants for beryllium oxide and their approximation (the Voigt-Reuss-Hill model) for a polycrystalline material are used to derive quantitative estimates of several thermomechanical parameters of BeO ceramics: isothermal compression coefficient, sound velocity, the Debye temperature, and coefficients of linear and volume temperature expansion, as well as the temperature dependence of molar heat capacity and thermal conductivity. The results are discussed in correlation to available experimental data. __________ Translated from Novye Ogneupory, No. 10, pp. 38–42, October, 2006.     

Effects of atomic relaxation and the electronic structure of niobium (100) and (110) surfaces

A comparative analysis of the atomic relaxation and electronic structure of niobium (100) and (110) surfaces has been carried out using the VASP-PAW method. The relaxation-induced changes in interlayer spacings of surface layers demonstrate an oscillating behavior but they substantially differ for the two analyzed surfaces; namely for the (110) surface with the closest atomic packing two outermost surface layers are contracted by 4.3% and the relaxation becomes noticeable for three outer layers, while for the more “open” (100) surface these quantities equal 13.1 and six layers, respectively. An analysis of the layer-by-layer distribution of the densities of states, spatial distribution of the charge density, and densities of states at the Fermi level indicates that the most considerable changes near Fermi level take place for (100) surface.     

Electronic structure and properties of beryllium oxide

This review focuses on computer simulation studies of the nature of chemical bonding in BeO and its electronic structure and physicochemical properties. The capabilities of modern quantum-chemical methods are analyzed with application to various structural defects in BeO, phase equilibria in the Be-O system, pressure-induced polymorphic transformations of BeO, and its mechanical, thermal, and spectroscopic properties.     

Improvement of the designs of steam turbines produced by the ZAO ural turbine works

We present fundamentally new design solutions aimed at making the steam turbines produced by the ZAO Ural Turbine Works more reliable, economically efficient, maneuverable, and suitable for massscale production.     

The T-53/67-8.0 cogeneration steam turbine for the PGU-230 combined-cycle plant at the Minsk TETs-3 cogeneration station

The design features of the turbine unit and the basic solutions found for its thermal scheme and layout are considered. The fundamental principles for controlling the turbine are described, and its economic indicators are given.     

Prospects for constructing cogeneration stations equipped with back-pressure steam turbines

The possibilities of using back-pressure cogeneration turbines developed on the basis of serially produced ones are considered together with the thermal process circuits in which such turbines are applied. Design versions and advantages of cogeneration stations in which the proposed process circuits are implemented are described.