Inorganic Materials最新文献

Data on the thermochemical synthesis of molybdenum carbide on the basis of the (NH₄)₆Mo₇O₂₄–NH₄NO₃–C₆H₁₂N₄ system at different component ratios have been reported. Thermodynamic computations have been performed to establish composition regions for probable exothermic reactions to produce molybdenum carbide: 10–20 moles of ammonium nitrate per 1 mole of ammonium molybdate and the ratio of reducing agent to oxidizing agent (φ) equal to 1.5–4.0. It has been found that the reaction in ammonium molybdate–ammonium nitrate–urotropin system includes several stages, the main exothermic reaction is observed after temperature of 120–180°C is reached. Molybdenum carbide forms at φ ≥ 6.5 after thermal treatment at 1000°C under inert atmosphere. The reaction leads to fine crystalline structure of particles with size of 100–200 nm. The obtained materials based on molybdenum carbide show catalytic activity in the conversion of products of incomplete combustion of biofuel (pyrolysis resins). Addition of the obtained materials to pyrolysis resin in 1/10 ratio enhances its conversion (rate parameter increases by 2–10 times), reduces average process temperature by 50–100°C, and decreases activation energy from 82 to 52–65 kJ/mol.

The vapor–liquid separation factors for the system Ni(PF₃)₄–impurities, in which the impurities include pentane (3.8 ± 0.8), hexane (1.3 ± 0.3), heptane (0.6 ± 0.2), dichloromethane (3.5 ± 0.8), trichloromethane (1.5 ± 0.3), tetrachloromethane (3.0 ± 0.7), phosphorus(III) fluoride (27.7.3 ± 7.8), and branched alkanes (2-methylpentane, 3-methylpentane, 2-methylhexane, 3-methylhexane, and 3-ethylhexane) were determined at 298 K by the static phase balancing method. The experimental data were in good agreement with the estimates of the vapor–liquid separation factors based on the conformal solution theory using Lennard-Jones potential parameters.

Composites based on poly(methylmethacrylate) (PMMA) and lead and europium salts, with the compositions PMMA/Pb(CF₃COO)₂ and PMMA/Pb(CF₃COO)₂,Eu(CF₃COO)₃, have been prepared by curing methylmethacrylate (MMA) based solutions via thermal radical block polymerization of MMA. The refractive index of MMA + Pb(CF₃COO)₂ solutions and the density of the PMMA/Pb(CF₃COO)₂ polymer composites have been shown to increase linearly as the Pb salt concentration increases to 83 wt % (40 wt % elemental Pb). The optical transmission of the composites at wavelengths above 450 nm and the highest lead and europium concentrations reaches 90% at sample thicknesses of up to 5 mm. The lead equivalent at a Pb(II) concentration of 40 wt % is 0.010. Photoluminescence in the PMMA/Pb(CF₃COO)₂,Eu(CF₃COO)₃ composites is due to Eu³⁺ electronic transitions from the ⁵D₀ metastable electron energy level to the ⁷F_j sublevels of the ground level. We have demonstrated the influence of lead(II) and europium(III) on the properties of the matrix and the influence of the matrix and Pb(II) on absorption and luminescence spectra of europium(III).

Abstract―Compound Cu₃NaS₂ has been prepared by solid-phase reactions from copper and sodium sulfides Cu₂S and Na₂S. It has been shown that compound Cu₃NaS₂ has hexagonal structure with lattice parameters a = 13.9398 ± 23 Å and c = 21.4637 ± 74 Å. After 6 months after synthesis, compound Cu₃NaS₂ spontaneously transforms at ambient temperature from hexagonal structure into phase with face-centered cubic (FCC) lattice. The dimension of coherent-scattering regions (CSR) for the FCC phase determined from the broadening of diffraction lines varies from ~25 nm at ambient temperature to ~110 nm at 500°C. DSC curves show anomalies at temperatures of 108 and 436°C corresponding to endothermal reversible transitions without change in the type of crystal lattice. The authors consider these anomalies to be due to redistribution of copper and sodium cations over possible crystallographic positions.

One-dimensional layered α-МоО₃ structures have been synthesized via hydrothermal treatment of peroxo molybdenum complexes. Treatment of the structures in aqueous sucrose solutions under hydrothermal conditions after drying at 80°C has been shown to cause partial reduction of their surface. The reduction process is accompanied by a change in Mo–O bond length as a consequence of distortion of the MoO₆ octahedra. Local supersaturation with reduction products in aqueous solution under hydrothermal conditions leads to the formation of new crystallization centers and growth of dumbbell-shaped particles. The forming nanostructured α-МоО₃/MoO₂ two-phase material, with two morphological species of particles, contains no carbon. Such a strategy for designing one-dimensional α-МоО₃ structures can be aimed at monitoring electrochemical degradation of high-capacity electrodes and controlling the associated deformation dynamics.

Titanium nickelide alloys have been prepared by self-propagating high-temperature synthesis compaction using equiatomic mixtures of nickel and titanium powders. The alloys were synthesized in a “sand” press die with the use of a “chemical furnace” and in a rigid press die. In the latter process, reaction mixtures were first subjected to mechanical activation (MA), which made it possible to carry out exothermic synthesis and consolidation of the synthesis products without preheating. No inert atmosphere was used in the syntheses. We obtained titanium nickelide samples 70 mm in diameter and 8 mm in thickness. The percentage of the NiTi phase has been shown to depend on the combustion temperature of the Ni + Ti powder mixture and the percentages of oxygen and hydrogen in the starting titanium powder. The largest percentage of the NiTi phase (85 vol %) was reached at a combustion temperature of 1400°C with the use of titanium containing 0.55 wt % oxygen and 0.14 wt % hydrogen. An increase in the oxygen content of the Ni + Ti powder mixture to 2.3 wt % as a result of MA leads to an increase in the content of the Ti₂Ni phase in the alloy to 53 vol %. As the hydrogen content of titanium increases to 0.6 wt %, the combustion temperature and speed decrease and free Ni remains in the alloy. The alloys with the highest content of the NiTi phase have the lowest microhardness: HV = 6.2 GPa. As the percentage of the Ti₂Ni, Ni₃Ti, and Ni₄Ti₃ phases in the alloys increases, their hardness rises to HV = 11.1 GPa.

We have studied three-dimensional homogeneous and heterogeneous crystal nucleation in and optical properties of stoichiometric lithium disilicate glasses containing silver and/or cerium dioxide additions. The plasmon resonance has been demonstrated on Ag nanoparticles formed under X-ray irradiation.

We have studied the effect of the grain size of aluminum oxide and calcium tungstate on the transport properties of (1 – x)СaWO₄–xAl₂O₃ composites with a mole fraction of aluminum oxide x ≤ 0.35. The phase composition and thermodynamic stability of the composites were ascertained by X-ray diffraction, thermogravimetry, and differential scanning calorimetry. Their surface morphology was examined by electron microscopy and their elemental composition was determined by X-ray microanalysis. The electrical conductivity of the composites was determined by electrochemical impedance measurements and analyzed as a function of temperature, oxygen pressure in the gas phase, dispersoid (aluminum oxide) concentration, and the grain size of their components. The conductivity of the (1 – x)СaWO₄–xAl₂O₃ composites containing 5–10 mol % aluminum oxide was found to exceed that of CaWO₄ by more than one order of magnitude. Varying the average grain size of the Al₂O₃ nanopowder from 21 to 82 nm caused no appreciable changes in the conductivity of the composites, which was due to the polydispersity of the aluminum oxide, whereas reducing the average grain size of CaWO₄ from 6.4 to 1.6 μm led to a twofold increase in the conductivity of the composites.

Eu_1–xSr_xMnO₃ (x = 0.0, 0.25) manganites have been characterized by X-ray diffraction, thermal analysis, and magnetometry. At room temperature, they have a perovskite-like structure, with space group Pbnm. Partial heterovalent substitution of Sr²⁺ for Eu³⁺ cations reduces the Jahn–Teller (JT) distortion of the crystal structure of the manganites because of the decrease in the number of Mn³⁺ ions involved in the distortion mechanism. As the temperature is raised, the europium manganites undergo a transition from an ordered to a disordered state (JT transition), and substitution of strontium for 25% of europium cations lowers the structural JT transition temperature by more than a factor of 4. The manganites undergo a paramagnetic–antiferromagnetic phase transition with a characteristic Néel temperature (T_N). Substitution of Sr for 25% of Eu cations raises T_N from 49 K at x = 0.0 to 65 K.

A ternary molybdate with the composition KSrGd(MoO₄)₃ and a monoclinic scheelite-like structure has been synthesized. Codoping KSrGd(MoO₄)₃ with Er³⁺/Yb³⁺ ions, we have obtained an upconversion phosphor exhibiting anti-Stokes luminescence in the range 400–700 nm under IR excitation. The synthesized phosphor has been characterized by X-ray diffraction, differential thermal analysis, and vibrational spectroscopy, and its luminescence spectra have been measured.