Inorganic Materials最新文献

The thermal conductivity of a series of single crystals of Ca_1–x–ySr_xNd_yF_2+y ternary solid solutions containing 0–30 mol % SrF₂ and 10–30 mol % NdF₃ has been measured in the temperature range 50–300 K by an absolute steady-state axial heat flow technique. An increase in the percentage of strontium and, especially, neodymium in the solid solutions is accompanied by a decrease in their thermal conductivity. The temperature dependence of thermal conductivity for all of the solid solutions studied is characteristic of disordered materials.

We have synthesized hydride phases based on a series of TiZrNbTa(Mo_1–xV_x) (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) high-entropy alloys with a body-centered cubic lattice. X-ray diffraction characterization results show that, as a result of hydride formation reaction, the cubic lattice of the alloys transforms first into a tetragonal lattice and then into a face-centered cubic one. As the vanadium content of the alloys increases, the fraction of the cubic phase and hydrogen content rise.

In this paper, we examine the purity level and impurity composition of the vanadium, niobium, and tantalum samples in the Exhibition–Collection of Extrapure Substances and present estimates of the average and total concentrations of elemental impurities in the purest samples. We examine the impurity composition of the array of the group 6 elements and contributions of particular groups of impurities and discuss the purity level of the group 6 elements and their compounds manufactured in Russia and abroad.

The effect of the solution acidity on the phase composition and morphology of alumina powers precipitated from solution using Al(NO₃)₃·9H₂O and NH₄HCO₃ was studied. In the рН range of 5–7, an amorphous precursor powder was typically formed; at рН 8–9, NH₄AlCO₃(OH)₂ crystals were formed. When annealed, the powders precipitated from acidic solutions were 100% α-Al₂O₃, which was represented by agglomerated equiaxed particles sized ca. 100–200 nm. The powders prepared in neutral or alkaline solutions, when annealed, formed additional minor θ-Al₂O₃ and γ-Al₂O₃ phases in equiaxed particles sized ca. 20–25 nm.

This paper reports our results on utilization of industrial waste having a multicomponent mineralogical composition and resulting from apatite–nepheline ore beneficiation. Using a high-energy planetary ball mill, the mineral mixture was ground into fine powder. We have studied the process of dispersing the mineral components of the mixture in relation to the main process parameters: vial rotation speed, ball-to-powder weight ratio, and milling time. The results demonstrate that, under “severe” grinding conditions, disintegration of brittle particles of the minerals sphene and aegirine slows down owing to the plasticity of the particles of the minerals apatite and nepheline, which reduces the efficiency of the high-energy grinding process, aimed at reducing the particle size and increasing the specific surface area of the material. The grinding process has been shown to cause not only a reduction in the size of mineral particles, but also changes in their optical properties through amorphization of their surface. This allows mechanically activated powder to be used as a precursor for the preparation of weather-resistant color filler pigments for building and paint materials instead of expensive synthetic analogs.

The specific heat of lanthanum-containing AlMg5.5Li2.1Zr0.15 duralumin-type aluminum alloy has been measured during cooling in the range 300–800 K. We have derived polynomials representing the cooling rates of the lanthanum-containing alloys and a reference. Based on the experimentally determined cooling rates of the alloys and reference and their weights, we have obtained cubic polynomials for the temperature dependence of the specific heat. Using integrals of the specific heat, we derived polynomials for the temperature dependences of enthalpy, entropy, and Gibbs energy changes. The results demonstrate that, with increasing temperature, the specific heat, enthalpy, and entropy of the alloys decrease, whereas their Gibbs energy decreases. The lanthanum content of the alloys has the opposite effect.

We consider the effect of mechanical activation on the particle size and strain of natural sphalerite particles and demonstrate that mechanical activation of the mineral for 20 min in a high-energy planetary mill reduces the crystallite size to 20 nm and that in this process the lattice strain in sphalerite reaches 0.73–0.85%. Thermogravimetry, calorimetry, and mass spectrometry have been used to study sphalerite oxidation processes during nonisothermal heating to a temperature of 1000°C in flowing air before and after mechanical activation. Mechanical activation of sphalerite has been shown to lead to a slight increase in the rate of sulfate formation, a decrease in the temperature and enthalpy of the thermal effects involved, and release of sulfur dioxide as a product of interaction with oxygen starting at a temperature of 150°C.

A process has been developed for the preparation of ultrafine amorphous precursors (starting mixtures) differing in the ratio of Er:YAG to 20Bi₂O₃–60B₂O₃–20BaO. Using selective laser sintering, we have demonstrated the feasibility of producing functional glass-ceramics—with a crystalline phase consisting of yttrium erbium aluminum garnet and an yttrium erbium borate—from the synthesized precursor. The chemical and phase transformations during heat treatment of the precursor were analyzed using differential scanning calorimetry and X-ray diffraction, and changes in the macrocomposition of the glass-ceramics at characteristic synthesis temperatures were assessed by inductively coupled plasma atomic emission spectroscopy. The results demonstrate that the ultrafine precursor we used is potentially attractive for the fabrication of optical integrated circuits by selective laser sintering.

Information on the exciton sizes in bulk copper, silver, zinc, cadmium, mercury, tin, and lead sulfides has been summarized using data on the effective masses of charge carriers and permittivity. The possible impact of exciton size effects on the electronic (optical) properties of these sulfides in the nanosized (nanocrystalline) state has been considered.

Nanosized NiFe₂O₄ and ZnFe₂O₄ were synthesized by the citrate combustion method. The nanopowders were characterized by elemental analysis and powder X-ray diffraction; size, dispersion, and morphological features were determined. It was established that the nanopowders of the synthesized ferrite spinels (average particle size 38 ± 3 nm for NiFe₂O₄ and 49 ± 3 nm for ZnFe₂O₄) are effective catalysts for the oxidation reaction of methylene blue dye (degradation efficiency 92% for nickel ferrite and 95% for zinc ferrite). The observed dependence of the catalytic activity of nanosized ferrites on the type of illumination is more pronounced for nickel ferrite (a 2.5-fold increase in the reaction rate constant and a 31% increase in the degradation efficiency).