Vol 54, No 7 (2018)

We have studied the thermal behavior of synthetic lautite, a copper sulfoarsenide widespread in nature. The material was characterized by thermogravimetric analysis under nonisothermal and isothermal conditions. Using the data thus obtained, equations of nonisothermal formal kinetics, and the Kazeev–Erofeev–Kolmogorov equation with the Sakovich correction, we assessed kinetic parameters. Lautite decomposition to copper sulfides has been shown to be accompanied by the formation of tennantite as an intermediate phase. The sublimates consist of an alloy of arsenic sulfides. The E_a values obtained under nonisothermal conditions suggest that synthetic CuAsS dissociation is a kinetically controlled process. The E_a values obtained under isothermal conditions suggest that, at a temperature of 500°C, the lautite decomposition process switches from intermediate to diffusion control.

A magnetic sorbent based on exfoliated graphite modified with magnesium ferrite has been prepared by impregnating oxidized graphite in a mixed solution of FeCl₃ and Mg(NO₃)₂, followed by heat treatment of the impregnated oxidized graphite in air. X-ray diffraction and Mössbauer spectroscopy results demonstrate that the structure of the magnesium ferrite is an inverse spinel with a degree of inversion of 0.59. The saturation magnetization of the magnesium ferrite-containing exfoliated graphite is 16.1 emu/g, whereas its oil sorption capacity is as high as 54 g/g. Compaction of the exfoliated graphite to a density of 0.03 g/cm³ reduced its sorption capacity to 26 g/g. Further increasing the density of the material led to a considerable decrease in its sorption capacity.

Vanadium-based alloys with a BCC structure are considered to be an alternative to palladium alloys for hydrogen purification. Since the performance of membranes is influenced by not only their bulk characteristics but also their surface condition, we have investigated the effect of different surface preparation techniques (abrasive grinding and polishing, electrolytic polishing, and ion etching) on the surface microstructure of V₈₅Ni₁₅ membrane alloy using X-ray photoelectron spectroscopy. After electrolytic polishing and ion etching, we observed an increase in the percentages of vanadium and nickel metals in the surface layer of the alloy in comparison with its state after abrasive polishing. Such changes are expected to be favorable for an increase in the rate of hydrogen dissociation and recombination on the surface of the membrane material, eventually improving hydrogen transport efficiency.

The processes underlying the chemical and anodic oxidation of the surface of copper foil have been studied by X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. It has been shown that, in the case of anodic oxidation, at a given process duration (τ) the composition and density of initially forming Cu(OH)₂ films depend not only on the current density (j_a) but also on whether or not the electrolyte is stirred. A Cu₂O film with an optimal, coral-like structure has been produced by the anodic oxidation of copper foil for τ = 10 min at j_a = 5 mA/cm² without stirring, followed by the thermal reduction of the Cu(OH)₂ in a nitrogen atmosphere for 1 h at 500°C. In the case of the chemical oxidation of the copper foil surface, similar Cu₂O films with a coral-like structure can also be produced by the thermal reduction of initially forming Cu(OH)₂ at 500°C for 1 h.

In this paper, we report the solid-state synthesis, characterization, and physicochemical properties of Pb_4–xM_xNb₂O₉ (M = Cu, Ni; x = 0–1.0) solid solutions. We have identified the stability limits of the solid solutions. Using the tolerance factor and relative electronegativities of the A- and B-site atoms (A₄B₂O₉), we have identified the stability fields of the perovskite-related solid solutions. The materials have been characterized by X-ray diffraction, and the particle size composition of the synthesized powders has been determined. Their electrical conductivity has been measured as a function of temperature. We have studied the key electrochemical characteristics of solid-contact ion-selective electrodes fabricated using the synthesized materials: linear range and slope of the principal electrode function, working pH range, and response time.

Garnet ferrites with the overall composition (Y_1–xBi_x)3(Fe_1–yGa_y)₅O₁₂ (0 ≤ х ≤1, 0 ≤ y ≤1) have been synthesized and characterized by X-ray diffraction. A relationship has been demonstrated between an increase in the concentration of Ga³⁺ cations and an increase in Bi₂O₃ solubility in ss-Y₃(Fe,Ga)₅O₁₂.

We have measured photoluminescence spectra of an aqueous uranyl chloride solution under excitation by various light sources: semiconductor light-emitting diodes and cw laser. The excitation wavelength lay within a resonance absorption band of uranyl chloride, which ensured photoluminescence detection at exposure times of 10^–3 s using an extremely small volume of the substance (10^–9 cm³). The photoluminescence spectra were measured using a small minispectrometer, which allowed us to analyze the spectra in the range 200–1000 nm.

The temperature-dependent heat capacity of three high-purity (1–x)(0.75TeO₂–0.25WO₃) + xLa₂O₃ tellurite glass samples (x = 0.02, 0.04, and 0.06) has been determined by dynamic calorimetry in the range 320–1000 K. The experimental devitrification and heat capacity data have been used to evaluate standard thermodynamic functions: C_p^o(T), enthalpy, entropy, and Gibbs energy in glassy and supercooled liquid states. We have demonstrated model-parameter similarity of properties in a statistical approach and found correlation relationships for parameters as functions of composition, which make it possible to predict the thermodynamic functions of unexplored glasses of this series. We have identified crystallization-resistant compositions of (1–x)(0.75TeO₂–0.25WO₃) + xLa₂O₃ glasses as a basis for the development of optically active elements.

The morphology of inner interfaces in hydroxyapatite (HA) based calcium phosphate ceramics has been studied by transmission electron microscopy. Grain boundaries in the ceramics have been shown to have a vicinal character, which is related to the mechanism of secondary recrystallization in the material: layer growth of grains via sequential motion of elementary steps on planes corresponding to the \(\{ 1\bar 100\} \) HA prism faces, which grow through transitions of atoms from adjacent grains that are in contact through their planes with large Miller indices. The recrystallization process may be accompanied by a “collision” of vicinal growth surfaces of grains with relatively large misalignment angles and the formation of grain boundaries nanofaceted by prism planes of adjacent grains. The recrystallization process in such a case should be expected to continue in the grain with a smaller nonsingularity of the growth front. Grain boundaries may allow for a match between planes differing in Miller indices, nd_h1k1l1 ≈ md_h2k2l2, and the formation of grain-boundary Pumphrey dislocations, which compensate for the size mismatch between interplanar spacings and/or misalignment of the planes. The observed characteristic grain match configurations are typical of both ceramics produced by sintering HA powders and HA films produced by ion sputtering.

High-density ceramic samples of the Bi₃TiNbO₉ ferroelectric phase with a layered perovskite-like structure have been produced by tape casting slurry technology and hot pressing processes. The samples have been characterized by X-ray diffraction and dielectric, piezoelectric, and pyroelectric measurements. The results demonstrate that the samples have a well-defined texture due to the preferential orientation of the basal planes of their platelike grains across the pressing axis or along the film casting direction. The Curie temperature of the samples has been determined to be T_C = 1180 K. The samples have anisotropic electrical transport characteristics. Their piezoelectric constants d₃₃ in directions perpendicular and parallel to the texture plane is 22 and 5 pC/N, respectively. The conclusion has been drawn that the synthesized materials are potentially attractive for producing high-temperature piezoelectric elements.

This paper summarizes data on new approaches to the detection, identification, and quantitative determination of manifestations of spatial inhomogeneities in the chemical composition and structure of mixtures of inorganic solid phases by a standardless differential dissolution (DD) stoichiographic method. We present mathematical modeling results for DD processes in different models for mixtures of solid phases. Based on the modeling results, we formulate rules of stoichiographic calculations for DD results, which are confirmed in identifying manifestations of spatial inhomogeneities in the phase composition of real systems, including fanlike separation of phase mixtures, without their selective separation.