Heat-Resistance and Phase Composition of Ti-Si Coatings on Niobium

A diffusion silicide coatings on refraotory under thermal shook. A prospective method of improving their durability in the formation of multi-component coatings. Ti is one of the widespread components of such coatings. In this work, process of simultaneous diffusion saturation of niobium by Ti and Si in powder mixtures has been investigated. The coatings can be divided into two basic types : Nb-Ti solid solutions and Nb and Ti silicides. The coatings of the first type obtained in Ti-Ti5Si3 powder mixtures. The complex silicide layers were observed in the packs with higher silicon activity (Ti5Si3 - TiSi and TiSi2-TiSi mixtures). The activities of Ti and Si have been shown to be principal controlling factores in coating phase in composition. The coatings allows to increase heat-resistance of the niobium and niobium alloys up to 2000°C (1,5 hour)

General statement of the challenge of selection of decisions to improve the protection of objects of life support from the population from the impact of air shock wave

The formulation of the problem of choosing solutions to improve the security of life support facilities for the population to the effect of an air shock wave from conventional weapons is set forth in the article in a formalized form. An algorithm for solving the problem is presented. A multi-factor model for assessing the security of an object against the impact of a shock wave is the basis of the algorithm. Feature of the considered algorithm is the account of scenarios of application of various means of defeat, constructive features of object of life-support. The developed multifactor model allows to choose the measures for increasing the security of economic objects taking into account the contribution of independent controllable parameters. The example of calculation for the block complete transformer substation of the full factory readiness in the reinforced concrete shell is given

About the approach to determining the indicator and constructing the scale of evaluating the protection of a dangerous production object

The article presents an approach to determining the values ​​of the protection index of hazardous industrial facilities exposed to shock-wave action. The approach is based on energy methods. A geometric interpretation of the definition of the values ​​of the protection index is given, for the main cases of destruction. The algorithm for grading the conditional security scale for a specific hazardous production facility is presented using a numerical experiment in the SolidWorks Simulation program. The obtained values ​​of the indicator are applicable to the development of engineering and technical measures of civil defense, with a quantitative evaluation of measures that increase the stability of the functioning of economic objects

Theoretical Analysis of Oxidative Carbonylation of Methanol: Saegusa’s Scheme of Dimethylcarbonate Synthesis over Binuclear Cationic Oxo-Clusters in CuNaX Zeolite

Possible mechanism of oxidative carbonylation of methanol via >Cu­(OCH₃)₂Cu< binuclear cationic oxo-clusters in the CuNaX zeolite with Cu²⁺ cations is analyzed theoretically within the scope of periodic boundary conditions with VASP. Such scheme was first derived by Saegusa et al. (<i>J. Org. Chem.</i><b>1970</b>, <i>35</i>, 2976) and was never tested by theoretical modeling to our best knowledge. For the CO attack we have computed the activation energy value that is close to experimental values obtained in Cu-zeolites. We suppose that this scheme can correctly describe the oxidative carbonylation at medium and high Cu loading when the copper oxo-clusters can be formed

Annealing-Induced Structural Behavior of Mn Dopant Ions in Calcium Orthovanadate Ca3(VO4)2Single Crystals

The crystal and local structures of Czochralski-grown calcium orthovanadate (Ca3(VO4)2) single crystals doped with over-stoichiometric 0.05 wt % Mn2O3 (CVO:0.05Mn) and annealed under different conditions are studied by single-crystal conventional and synchrotron X-ray diffraction, X-ray absorption spectroscopy, and electron paramagnetic resonance for the first time. Bottom (annealing in air) and top (annealing in air and in vacuum) parts of the CVO:0.05Mn crystal differ in the manganese content (higher in the bottom part), formal charge (Mn4+ and Mn(3+)+, respectively), and color (orange bottom part; light orange and yellow top parts annealed in air and vacuum, respectively). Manganese ions are located in one (Ca3, distorted two-capped trigonal prism) of five crystallographic Ca sites and have octahedral coordination, which is consistent with crystal-chemical properties of transition-metal ions. The presence of vacancies in one of three V sites is revealed. Formal charge 5+ for vanadium ions is confirmed by X-ray photoelectron spectroscopy. Different colors of CVO:Mn crystals and different formal charges of manganese are explained depending on the growth and post-growth treatment conditions. © 2022 American Chemical Society