Inorganic Materials最新文献

Known calculational implementations of the extremum principle of chemical thermodynamics, which are used to analyze equilibrium plasmas, are extended to description of nonequilibrium steady states of a low-temperature plasma (LTP) with the use of a physical model for the excess of energy in partially independent subsystems (electronic and vibrational) with temperatures T_e and T_v relative to T. At a statistical level, we introduce “multitemperature” functions of LTP components, which make it possible, in the framework of the Gibbs energy minimization method, to predict conditions of formation of condensed substances (materials) from the LTP. The simulation results on the composition of a nonisothermal microwave gyrotron plasma in a CO₂ + Ar mixture, with the use of an experimentally determined electron temperature, T_e = 0.7 eV = 8120 K, confirm the 30% CO₂ conversion reached in practice at T = 1900 K; that is, the CO₂ splitting temperature is approximately 700 K lower than that calculated for a thermal plasma. The calculated plasma composition agrees with experimental data, and Ar plasma gas is shown to influence characteristics of the plasma and CO₂ splitting conditions. In addition, the simulation results predict that the CO₂ splitting products contain no condensed carbon.

This paper describes different lead indium tantalate synthesis methods: Pb₂InTaO₆ synthesis from oxides without stabilizing additives, via firing for 2–8 h, followed by quenching; hot pressing; synthesis with the use of an InTaO₄ precursor presynthesized at different temperatures; and synthesis of boron oxide-stabilized Pb₂InTaO₆. We have assessed the effect of mechanical activation on the synthesis of lead indium tantalate and the formation of its perovskite and pyrochlore phases during both mechanochemical synthesis and subsequent firing. The results demonstrate that the key factor for the synthesis is to properly choose conditions of starting mixture preparation for sintering. We have compared different starting mixture preparation procedures differing in the mechanical activation sequence and the conditions under which the reagents were added, and identified optimal conditions that enable the preparation of piezoceramics containing the largest amount of the perovskite phase and having the highest density.

Glass-ceramic materials have been prepared by impregnating pressed erbium-doped yttrium aluminum garnet with molten 20Bi₂O₃–65B₂O₃–15BaO glass. A series of samples prepared at temperatures from 700 to 1500°C have been characterized by X-ray diffraction and differential scanning calorimetry, and their density has been measured as a function of impregnation temperature. We have found conditions for chemical and phase formation of yttrium and erbium borates and their subsequent conversion into the structure of Er:YAG.

We have studied the effect of Al₂O₃ nanofiber on the properties of fused silica ceramics such as are used to produce containers for molten semiconductor materials. The addition of 0.05 to 0.15 wt % alumina nanofiber has been shown to cause an increase in the mechanical strength of ceramics prepared via slip casting. The addition of 0.15 wt % nanofiber increased the compressive strength of the ceramic material obtained at a sintering temperature of 1200°C from 90 ± 4 to 143 ± 9 MPa and its bending strength from 28 ± 2 to 42 ± 3 MPa.

The effect of gamma irradiation on the electrical properties of extruded Bi_0.85Sb_0.15 solid solution samples doped with 0.001 to 0.05 at % Pb has been studied in the range ~77–300 K. The results suggest that irradiation of the undoped material to a gamma dose of ~1 Mrad produces donor defects and leads to an increase in carrier concentration n and electrical conductivity σ. The radiation-induced donor defects in the material containing 0.001 at % Pb compensate Pb acceptor centers, reducing σ. In the materials containing ≥0.005 at % Pb, conduction electrons are compensated by Pb acceptor centers, so electrons generated by gamma irradiation lead to an increase in σ. A good correlation is observed between the dependences of electrical conductivity σ, thermoelectric power α and Hall coefficient R_H on Pb content and gamma irradiation dose.

We examine possible interaction of molten aluminum oxide with a controlled (nitrogen) atmosphere in the pressure range 10⁴ to 10⁵ Pa at a temperature of 2400 K. Stochastic simulation is used to identify gas phase components and determine their concentration. We analyze the main chemical reactions that determine processes in the system. The results suggest that, even though neither molecular, nor atomic nitrogen directly interacts with molten aluminum oxide in the conditions under consideration, it is capable of entering into many chemical reactions in the form of its oxides or together with Al-containing dissociative melt vaporization products. We have calculated pressure ranges where the reactions under consideration and reverse reactions—aluminum oxide formation and precipitation in the melt—are possible on account of gas phase processes. Analysis of these processes makes it possible to optimize conditions for the use of nitrogen as a controlled atmosphere, the most important of which is to reduce the concentration of (atomic and molecular) oxygen and that of AlO₂ oxidizing oxide, which destroy the material of crystal growth system.

We report a new, convenient and simple low-temperature process for synthesis of γ-lanthanum(III) sulfide (γ-La₂S₃). In molten sodium thiocyanate with small KCN additions at a temperature of 350°C, lanthanum oxide converts into phase-pure γ-La₂S₃ with a cubic structure, as evidenced by X-ray powder diffraction data. The method is rather easy to implement and requires neither high temperatures nor vacuum apparatus.

The formation of compounds that include the impurities typical of the raw materials used in the Acheson process is studied using thermodynamic modeling. It is shown that the yield of silicon carbide in the Acheson process is significantly influenced by moisture and sulfur content in the coke. The sequence of gasification of elements from the reaction mixture during heating was determined. It is shown that sodium chloride significantly affects the state of metallic impurities facilitating gasification of aluminum, magnesium and calcium. The amount of volatile silicon chloride formed in the presence of sodium chloride was estimated.

We have studied the LiF–KCl–KBr–LiKCrO₄ stable tetrahedron of the quinary reciprocal system Li⁺,K⁺||F^–,Cl^–,Br^–,({text{CrO}}_{4}^{{2 - }}). According to experimental data obtained by differential thermal analysis, three solid phases crystallize in the stable tetrahedron: LiF, LiKCrO₄, and a continuous series of KCl_xBr_1–x solid solutions. The solid solutions are stable, and there are no invariant equilibrium points.

This paper reports on the use of titanium/hafnium diboride composite powders for producing metal–ceramic coatings. The composite powders were prepared by high-energy mechanochemical synthesis. The starting components used were PTOM-1 titanium powder (as a matrix powder) and hafnium diboride powder (as a reinforcing agent). The composite powders were characterized by microstructural analysis and their particle size composition was determined. Examination of their morphology showed that the number of hafnium diboride particles embedded in the surface layer of the titanium particles increased with increasing reinforcing agent content in the mixture for mechanochemical synthesis. Assessment of the particle size composition of the powders showed that the size range 10–60 μm accounted for the largest volume fraction of the particles: from 7 to 10%. The microhardness of the coatings produced by microplasma spraying was determined using their transverse polished microsections. Scanning electron microscopy images showed that increasing the percentage of hafnium diboride in the starting mixtures increased the amount of HfB₂ in the coatings. In all of the polished microsections examined, the coating was firmly adherent to the substrate material, without through pores. As the hafnium diboride content was raised from 10 to 60 wt %, the microhardness of the coatings increased in proportion to it. The composite powder containing 60 wt % hafnium diboride had the highest microhardness: 1076 HV.