Inorganic Materials最新文献

In this paper, we discuss general trends in the IR luminescence of colloidal PbS quantum dots 3 nm in average size, capped with thioglycolic acid molecules (PbS/TGA QDs). Treatment of the PbS/TGA QDs with a KI solution has been shown to cause a shift of a composite luminescence band peaking at 1120 nm to shorter wavelengths, to 1060 nm; an increase in the quantum yield of its shorter wavelength component, related to excitonic emission, from 1 to 10%; and quenching of its longer wavelength component, due to radiative recombination at defect levels. In this process, the cubic structure of PbS undergoes no changes. The average size of the PbS/TGA QDs has been shown to decrease slightly, by 0.2–0.3 nm. The conclusion has been drawn that the increase in the quantum yield of excitonic emission from the PbS/TGA QDs as a result of KI treatment is due to the more efficient passivation of interfacial defects, which act as both recombination luminescence and nonradiative carrier recombination channels. Using thermoluminescence in the temperature range from 80 to 350 K, we have demonstrated the presence of two types of shallow localized states, at 0.17- and 0.25-eV depths, whose density is only slightly sensitive to treatment of the PbS/TGA QDs with a KI solution. We assume that some of the traps identified are due to native defects in the nanocrystals—interstitial lead and sulfur ions—rather than to dangling bonds of surface lead and sulfur atoms.

Ti–6Al–5V titanium alloy was subjected to surface saturation with carbon, nitrogen, and oxygen in order to study the effect of surface modification on its wear resistance and biocompatibility. The alloy was saturated with carbon and nitrogen in low-pressure atmospheres. Oxygenation was carried out by heating the alloy in a solid carburizing agent. The structure and phase state of the grown layers were studied by optical microscopy and X-ray diffraction. General trends in the saturation of the titanium alloy with nonmetals are the formation of a diffusion layer and an increase in the amount of phases based on the α-Ti solid solution, followed by the formation of intermediate phases, such as carbides, nitrides, and oxides differing in stoichiometry, on the surface of the continuous layer. After saturation, the alloy was covered with thin carbide, nitride, and oxide surface layers and had diffusion layers under them. The hardness of the nitrogenated and oxygenated surfaces was 950–1000 HV, and that of the surfaces saturated with carbon was 570 HV. The wear resistance of the alloy was lowest in the as-prepared state and highest after oxygenation. Biocompatibility was assessed from the proliferation of osteoblast-like cells of the MG-63 line. The best biocompatibility was demonstrated by the oxygenated samples, and the biocompatibility of the nitrogenated samples was better than that of the carburized samples. The untreated alloy showed the lowest biocompatibility.

In this paper, we report the synthesis of crystalline ruthenium ditelluride (RuTe₂) and its thermodynamic properties in the range from 10 to 965 K, evaluated from its isobaric heat capacity C_p determined using calorimetry. At low temperatures, between 6.86 and 335.11 K, the heat capacity of the synthesized material—pure, free of impurities and foreign phases—was determined by adiabatic calorimetry. In the range 315.3–965.3 K, C_p was determined by differential scanning calorimetry. The data obtained above 298 K have been used to determine empirical coefficients of the Maier–Kelley and Khodakovsky equations. In the range 10–965 K, we have evaluated the standard thermodynamic functions: heat capacity, entropy, enthalpy increment, and reduced Gibbs energy. At 298.15 K, we have obtained (C_{p}^{ circ }) = 72.43 ± 0.14 J/(K mol), S° = 94.94 ± 0.19 J/(K mol), Н°(298.15 K) − Н°(0) = 14.60 ± 0.03 kJ/mol, and Ф° = 45.97 ± 0.09 J/(K mol). Using the absolute entropy determined by us and data in the literature and handbooks, we have estimated the standard Gibbs energy of formation of RuTe₂: Δ_fG°(RuTe₂, cr, 298.15) = −130.5 ± 2.9 kJ/mol.

Organomineral sorbents have been prepared by “mild” mechanical activation of air-dry clinoptilolite rocks with synthetic polymer (polyacrylamide) additions in an IVCh-3 laboratory-scale vibratory attritor (shear impact treatment for 3 min; specific mechanical energy delivered to the material, 2.16 kJ/g). The materials were characterized by scanning electron microscopy, infrared spectroscopy, differential scanning calorimetry, thermogravimetry, X-ray powder diffraction, and low-temperature nitrogen adsorption–desorption measurements. We have determined their specific surface area, specific pore volume, pore diameter, loose bulk and true densities, hygroscopic humidity, and oil sorption capacity. Modification of clinoptilolite rocks with 5 and 10 wt % polyacrylamide has been found to reduce the oil sorption capacity of the zeolites by 6–18%. The oil sorption capacity of the material modified with 20 wt % polyacrylamide was essentially the same as that of mechanically activated polymer-free clinoptilolite rocks.

We have studied the behavior of Y_{1 – y}Ca_yBaCo_{4 – x}M_xO_{7 + δ} solid solutions in cyclic oxygen absorption/release processes in air at temperatures in the range 350–580°C. Y_0.8Ca_0.2BaCoO_{7 + δ} has been found to absorb the largest amount of oxygen: 0.52 wt % (325 μmol O/g). The incorporation of calcium and iron into the structure of the YBaCo₄O_{7 + δ} cobaltite has been shown to shift the oxygen exchange process to higher temperatures and increase the oxygen storage capacity of the material.

We have studied the effect of sodium fluoride as a sintering aid for β-sialons on the phase composition and physicomechanical properties of Si₅AlON₇ and Si₄Al₂O₂N₆. Two-step high-temperature firing of the β-sialons in the presence of NaF under a nitrogen atmosphere has been shown to cause no significant changes in the phase composition of the materials. The density and microhardness of the materials prepared using 0.5 and 5.0 wt % NaF are lower than those of the materials prepared without sintering aids, but the bending strength is higher by up to 14.3% in the case of Si₅AlON₇ prepared using 0.5 wt % NaF and by 4.9% in the case of Si₄Al₂O₂N₆ prepared using 5.0 wt % NaF.

We report the preparation of molybdenum–tungsten alloy powders via magnesium and calcium vapor reduction of the Mo_0.3W_0.7O₃, MgМо_0.7W_0.3O₄, and CaМо_0.7W_0.3O₄ compounds in the temperature range 750–880°C at residual pressures in the reactor from 5 to 15 kPa. The specific surface area of the Mo–W alloy powders prepared by reducing Mo_0.3W_0.7O₃ slightly exceeds that of the mixture of metal powders obtained by reducing a mixture of WO₃ and MoO₃ under similar conditions. The specific surface area of the Mo–W alloy powders prepared via magnesium vapor reduction of the CaМо_0.7W_0.3O₄ and MgМо_0.7W_0.3O₄ compounds exceeds that in the case of calcium vapor reduction. We have obtained molybdenum–tungsten alloy powders having lattice parameters of 0.3153 ± 0.0001 and 0.3160 ± 0.0001 nm and ranging in specific surface area from 9 to 22 m²/g. The average crystallite size of the alloys, evaluated using the Scherrer formula, lies in the range 12–35 nm. The powders have a mesoporous structure.

Using LaBWO₆ as a host, we have prepared a series of erbium-doped lanthanum borotungstates (LBTs), La_{1 – x}Er_xBWO₆, and Yb/Er-codoped La_{1 – x – y}Yb_xEr_yBWO₆, which crystallize in monoclinic crystal system (sp. gr. P2₁). The materials have been synthesized by ceramic route and a sol–gel (Pechini) process, followed by annealing. We have studied the spectral properties of the synthesized LBTs exhibiting the luminescence in the green spectral region upon the excitation in the near-infrared region. The highest efficiency, with B_en = 0.55%, has been obtained for La_0.97Yb_0.02Er_0.01BWO₆ composition. Sol–gel synthesis (Pechini process) has been shown to be the optimal approach for the preparation of such phosphors. Due to a combination of high upconversion efficiency and thermal stability, the synthesized upconversion phosphors can be used for the design of white light sources pumped in the near-IR spectral region.

Experimental temperature-dependent density data for boron have been used to evaluate its linear thermal expansion coefficient. Applying the mixing rule to components of amorphous alloy, we have estimated the thermophysical properties of amorphous Fe₈₀B₂₀ alloy in the locally equilibrium two-phase region model. The dominant role of iron atoms in the formation of a disordered medium has been demonstrated. The theoretical results obtained in this study are prognostic and require experimental verification.

In search of novel waste form materials for vitrifying high-level radioactive waste with various compositions and improving the way in which they are used, we have prepared and investigated waste form materials in the Na₂O–Rb₂O–SrO(Ba,Ca)–B₂O₃–SiO₂–Al₂O₃–ZrO₂ system. Using electron microscopy, X-ray diffraction, and infrared spectroscopy characterization of samples prepared by rapid cooling of melts containing 3.6–4.5 mol % rubidium, we have demonstrated the formation of a homogeneous glassy material, determined the solubility limit of zirconium in the glass, and identified uniformly distributed baddeleyite crystals, which indicate that the starting melt contained excess zirconium. In samples containing 6.7–8.5 mol % rubidium, we observed the formation of a less homogeneous material with considerable amounts of crystalline zirconium- and rubidium-containing phases. Analysis of the data obtained has made it possible to optimize the percentages of zirconium and rubidium in the composition of radioactive waste in the case of its immobilization via vitrification with the use of waste form materials of the system studied here.