Vol 54, No 9 (2018)

Manganese monoarsenide samples have been prepared by the sealed-ampule technique and characterized by X-ray diffraction, differential thermal analysis, and scanning electron microscopy. The hexagonal- to-orthorhombic phase transition of MnAs has been studied using differential scanning calorimetry (DSC) and magnetic measurements. The enthalpy and temperature range of the transition have been determined to be ΔH =–5.6 J/g and 312.5–319 K, respectively. The enthalpy and temperature range of the transition are influenced by the quality of the samples. The samples containing inclusions of the metastable, orthorhombic phase have a lower enthalpy and broader temperature range of the magnetostructural transformation of manganese monoarsenide. It has been demonstrated that DSC is an effective tool for assessing the quality of MnAs samples. Temperature dependences of specific magnetization and magnetic permeability for MnAs lend support to the DSC results. From these data, the Curie temperature of MnAs has been determined to be 40°C, in good agreement with previously reported data.

This paper presents results of microwave processing of materials consisting of montmorillonite–hydromica clays and diatomite with combined additions based on an aluminum oxide modifier. We have determined the phase composition of fired materials prepared from mixtures before and after microwave processing. After microwave processing, an exothermic phase formation process has been identified in the temperature range 900–980°C. The samples based on bentonite clay and diatomite with a combined aluminum sodium chloride modifier have been found to contain particles less than 10 nm in size between aluminosilicate grains. After firing, the samples activated by microwave processing contain nanoscale inclusions and have enhanced strength.

Thin indium oxide films and In–Y–O films containing 0.7 to 3.6 at % Y have been grown by ionbeam sputtering of an indium target and a composite (indium + weighed amounts of yttrium) target in a mixture of argon and oxygen. The thin indium oxide films have a cubic crystal structure (sp. gr. Ia\(\bar 3\)). The incorporation of yttrium atoms into indium oxide leads to the formation of an amorphous structure in the as-grown films and an increase in their room-temperature electrical resistance by several orders of magnitude. Lowtemperature electrical resistance data indicate a change in conduction mechanism. High-temperature heat treatment of the thin In–Y–O films leads to the crystallization of their amorphous structure and an increase in their electrical resistance.

A hydroxyapatite/TiO_y nanocomposite material has been studied by X-ray diffraction, infrared spectroscopy, and Raman spectroscopy. The results demonstrate that annealing at 400°C changes the valence state of the titanium and leads to the formation of [Ti(OH)₂]²⁺ and [TiHPO₄]²⁺ surface groups and terminal carbonyls and partial heterovalent cation substitutions of Ti³⁺ and Ti⁴⁺ for Ca²⁺. As the annealing temperature is raised to 600°C, surface groups disappear. The amount of inflowing oxygen is insufficient for the complete oxidation of TiO_0.92 to TiO₂ in hydroxyapatite/TiO_0.92. The result is the formation of an intermediate nanophase with the composition Ti_4.5O₅.

We have studied the magnesium reduction of the Mg₄Ta₂O₉ tantalate in the combustion regime and assessed the influence of starting mixture parameters on the combustion speed and temperature, the degree of reduction, and characteristics of the resultant tantalum powders. The use of Mg₄Ta₂O₉ as a precursor for the reduction process has made it possible to increase the degree of reduction and the specific surface area of tantalum powders. We have obtained powders with a specific surface area of up to 21 m²/g, which is a factor of 4–5 larger than in the case of the reduction of Ta₂O₅ under the same conditions.

Polycrystalline HoBiGeO₅ and ErBiGeO₅ samples have been prepared by solid-state reactions, by firing stoichiometric mixtures of Ho₂O₃ (Er₂O₃), Bi₂O₃, and GeO₂. The effect of temperature on the heat capacity of the synthesized compounds has been investigated by differential scanning calorimetry in the range 350–1000 K. The experimental C_p(T) data have been used to evaluate the thermodynamic functions of bismuth holmium and bismuth erbium germanates: enthalpy increment, entropy change, and reduced Gibbs energy.

This paper presents a method of calculating and estimating the composition of starting mixtures for metasilicate glass-ceramics of a new class: Sikams. The method relies on crystal-chemical principles and takes into account isovalent and heterovalent isomorphism under directional solidification conditions. It ensures a high crystallization rate, a desired degree of structural and chemical homogeneity, and optimal physicochemical properties of the material, in which the crystalline component consists of pyroxene solid solutions. Moreover, it simplifies the fabrication process and reduces energy consumption.

Technologically viable principles have been developed for the preparation of the MAX phase Ti₂AlC by self-propagating high-temperature synthesis (SHS) with a reduction step, using titanium dioxide. We have studied the influence of synthesis conditions (starting-mixture composition and ratio of reactants) on the composition, structure, and particle size of Ti₂AlC powders. The results demonstrate that an excess of magnesium in the starting mixture leads to a decrease in the percentage of MgAl₂O₄ (spinel), and carbon deficiency in the starting mixture reduces the percentage of titanium carbide in the final product. The Ti₂AlC powders prepared by SHS consist of agglomerates of layered particles differing in size: from coarse (several microns) to ultrafine and nanometer-sized particles. The composition of the powders was confirmed by chemical analysis, microstructural examination, and X-ray diffraction.

This paper reports a study of the physicochemical properties of composites and scaffolds (synthesized for the first time) based on dicalcium phosphate dihydrate (DCPD, brushite), hydroxyapatite (HA), and chitosan. The crystallite size of the composites has been shown to increase with increasing chitosan concentration in the starting solution. The first technique has been proposed for the fabrication of scaffolds based on brushite, HA, and chitosan gel. The pore size in the scaffolds has been shown to increase with increasing brushite content. Raising the calcination temperature improves the stability of the scaffolds, whereas the composites persist in the form of powder independent of heat treatment. Analysis of the dissolution behavior of the synthesized composites and scaffolds in an isotonic solution indicates that, in the DCPD–chitosan system, the dissolution rate decreases with increasing chitosan concentration, whereas the HA–chitosan system exhibits opposite behavior.