Vol 52, No 2 (2016)

Nanocrystalline SnO₂ has been synthesized and its surface has been modified with Au⁰ and Co(II, III). The distribution of the modifiers over the nanocomposites has been studied by X-ray diffraction, inductively coupled plasma mass spectrometry, and transmission electron microscopy. The effect of the modifiers on the hydrogen reduction of nanocrystalline SnO₂ has been assessed. The CO sensing properties of the synthesized materials (10 ppm CO in air) have been studied in situ by electrical conductance measurements. The addition of both Au⁰ and Co(II, III) allows the working temperature of the SnO₂-based semiconductor sensor to be lowered to 215°C.

We have studied the dynamic chemical polishing of single crystals of PbTe and Pb_1–xSn_xTe solid solutions in H₂O₂–HBr–citric acid bromine-releasing etchants under reproducible hydrodynamic conditions and constructed projections of constant etch rate surfaces using simplex design of experiments. The dissolution of the crystals in the polishing mixtures has been shown to be diffusion-limited. The polished surfaces have been characterized by microstructural analysis, scanning electron microscopy, and atomic force microscopy. We have determined the compositions of H₂O₂–HBr–citric acid polishing etchants that can be used for high-quality polishing of the surface of the PbTe and Pb_1–xSn_xTe semiconductor materials at dissolution rates in the range 3.0–18.0 μm/min.

Quasicrystalline Al–Cu–Fe–Cr alloys have been prepared by mechanical activation. The morphology of powder particles has been investigated after thermomechanical processing under various conditions. We have identified the sequence of phase transformations in the quaternary alloys in the stability region of quasicrystalline phases and optimized conditions for obtaining a maximum fraction of a decagonal state in powder materials.

This paper describes the reduction of titanium dioxide with a mixture of silicon carbide and silicon powders at a temperature of 1550°C under vacuum. It has been shown that the use of the combined reductant enables the preparation of the ternary phase Ti₃SiC₂ through concurrent carboand silicothermic processes. The optimal compositions for Ti₃SiC₂ formation are TiO₂ + (1.5–x)SiC + 2xSi with x = 0.4–0.5. The Ti₃SiC₂ yield then reaches 96 wt %.

In LiNbO₃:Zn crystals with near-threshold doping levels ( 4.5–4.7 mol % Zn), high-temperature measurements and high-temperature annealing under short-circuit conditions lead to considerable changes in spontaneous unipolarity. The considerable changes in spontaneous unipolarity are accompanied by well-defined low-frequency dielectric dispersion and sharp anomalies in temperature dependences of electrical conductivity and dielectric permittivity. As a result, the piezoelectric modulus d₃₃₃ increases to a level approaching the highest values reported in the literature for single-domain nominally pure LiNbO₃ crystals.

SiO₂–TiO₂ binary aerogels have been synthesized for the first time using methyl tert-butyl ether as supercritical fluid. It has been shown that the aerogels prepared in methyl tert-butyl ether and isopropanol contain nanocrystalline anatase and that amorphous SiO₂–TiO₂ aerogels with a homogeneous distribution of their components can be obtained in CO₂. A considerable contribution to the large specific surface area of the aerogels is made by micropores, especially when supercritical drying is carried out in CO₂ and isopropanol.

Structural changes in Sr₉In(PO₄)₇ during the antiferroelectric (AFE) phase transition are studied by X-ray powder diffraction, electron microscopy, second-harmonic-generation, and dielectric measurements. Sr₉In(PO₄)₇ complements a group of Ca₃(VO₄)₂-type ferroelectric (FE) phosphates and vanadates and is the first example of an AFE material in this family. Antiparallel shifts of Sr atoms from their average positions and ordering of the P1O₄ tetrahedra form two contributions in the structural mechanism of the AFE phase transition: a displacive contribution and an order-disorder constituent, respectively. The displacive and order-disorder type of structural changes may account for the obtained value of the Curie–Weiss constant (C ~ 10⁴ K) which is in between the value usually observed for pure displacive (C ~ 10⁵ K) and that for orderdisorder phase transitions (C ~ 10³ K). The structural mechanism of the AFE phase transition in Sr₉In(PO₄)₇ is very similar to that of the FE phase transition in Ca₉R(PO₄)₇ and Ca₉R(VO₄)₇. Both displacive and orderdisorder contributions are responsible for the physical properties of the Ca₃(VO₄)₂-type materials.

This paper presents simulation results obtained for an unsteady-state flow of a multicomponent gas mixture in a flow-type vertical reactor using a three-dimensional mathematical model that takes into account the convective mass and heat transport, compressibility, viscosity, and thermal conductivity of the components and gas flow turbulization. We identify the gas dynamic mechanism behind eddy formation in the reactor and examine the influence of the viscosity, density, and speed of the flow components on eddy formation and the homogeneity of the gas mixture over the substrate.

We have demonstrated the feasibility of synthesizing sol–gel composite coatings consisting of SiO₂ and multiwalled carbon nanotubes (MWCNTs) on float glass, and investigated the effect of the nature of surfactants, which ensure stability of MWCNT suspensions in water and SiO₂ sol and wetting of the glass by the suspensions. We have found conditions that enable uniform MWCNT dispersion and stabilization during the growth of composite coatings. Different, technologically viable approaches to producing composite coatings have been examined. Using laser Raman spectroscopy, we have assessed the MWCNT distribution over the composite coatings. The electrical conductivity, microhardness, and optical transmission of the coatings have been measured. It has been shown that the MWCNT-containing composite coatings possess enhanced microhardness and high electrical conductivity compared to the uncoated glass.

Single-phase ceramic samples of La_1–xNd_xInO₃ (0.007 ≤ x ≤ 0.05), LaIn_0.99M_0.01O₃, and La_0.95Nd_0.05In_0.995M_0.005O₃ (M = Cr³⁺ and Mn³⁺) solid solutions have been prepared by solid-state reactions, and their crystal structure, magnetic field dependences of their specific magnetization at 5 and 300 K, and temperature dependences of their molar magnetic susceptibility have been studied. It has been shown that the 300-K specific magnetization of the La_1–xNd_xInO₃ (x = 0.02, 0.05), La_0.95Nd_0.05In_0.995M_0.005O₃ (M = Cr³⁺ and Mn³⁺), and LaIn_0.99Mn_0.01O₃ solid solutions increases linearly with increasing magnetic field strength up to 14 T and that the magnitude of the 300-K specific magnetization of the La_0.993Nd_0.007InO₃ and LaIn_0.99Cr_0.01O₃ solid solutions increases linearly, but they have diamagnetic magnetization. At a temperature of 5 K, the magnetization of all the indates studied here increases nonlinearly with increasing magnetic field strength, gradually approaching magnetic saturation, without, however, reaching it in a magnetic field of 14 T. In the temperature range where the Curie–Weiss law is obeyed (5–30 K), the effective magnetic moments obtained for the Nd³⁺ ion (\({\mu _{effN{d^{3 + }}}}\)) in the La_1–xNd_xInO₃ solid solutions with x = 0.007, 0.02, and 0.05 are 2.95μ_B, 3.09μ_B, and 2.75μ_B, respectively, which is well below the theoretical value \({\mu _{effN{d^{3 + }}}}\)= 3.62μ_B. The effective magnetic moments of the Cr³⁺ and Mn³⁺ ions in the LaIn_0.99Cr_0.01O₃ and LaIn_0.99Mn_0.01O₃ solid solutions are 3.87μ^B and 5.11μ^B, respectively, and differ only slightly from the theoretical values \({\mu _{effC{r^{3 + }}}}\)= 3.87μ^B and \({\mu _{effM{n^{3 + }}}}\)= 4.9μ^B.

We present a study of the extraction separation of a rare-earth group concentrate (GC) recovered from phosphogypsum waste from OAO Voskresensk Mineral Fertilizers using different extractants, followed by the preparation of neodymium oxide suitable for the fabrication of magnets. The proposed process has been tested using a pilot GC separation apparatus which includes three sequential automatic cascades of EC-10FA centrifugal extractors (Skaigrad Group).