Том 55, № 3 (2019)

We have studied the magnetic properties of Cd_{1 –x}Fe_xCr₂S₄ solid solutions in the FeCr₂S₄–CdCr₂S₄ system in the range 0.6 ≤ x < 1. Measurements were made in the temperature range 5–300 K in static (≤7960 A/m) and ac (10, 100, and 1000 Hz) magnetic fields of 79.60 A/m peak. All of the materials have been shown to exhibit low-temperature magnetic anomalies due to the effect of orbital ordering in FeCr₂S₄, a basic component, at 10 K.

By reacting tantalum or hafnium carbide with iridium in the presence of a small amount of silicon, we have prepared refractory hafnium- and tantalum-containing materials consisting of a mixture of phases: the intermetallic compound MIr₃, recrystallized tantalum or hafnium carbide, and iridium silicide. We have studied the behavior of the materials during an exposure to a high-speed plasma flow at a sample surface temperature of 2000°C and demonstrated that, owing to their special microstructure, the absence of pores, and the low oxidation rate of the iridium-containing components, they exhibit a good ablation resistance and that the hafnium system withstands a longer exposure.

We have examined the feasibility of preparing high-purity aluminum oxide by oxidizing granulated aluminum in a 0.1 M potassium hydroxide solution, followed by heat and acid treatments of the oxidation products. The aluminum oxidation product, consisting of two phases of Al(OH)₃ (bayerite and gibbsite), was first heat-treated at temperatures of 300, 600, 900, and 1200°C; then treated with hydrochloric acid; and calcined at a temperature of 1450°C. It has been shown that raising the preheat treatment temperature increases the total concentration of impurities, including Fe impurities, but reduces the concentration of alkali metals (K, Na, and Li). Using 99.7%-pure aluminum, we have prepared aluminum oxide with a purity at a level of 99.886%. Using 99.98%-pure aluminum, we have obtained aluminum oxide with a purity at a level of 99.993%.

Nanostructured materials based on cobalt-doped SnO₂ have been prepared through alkaline hydrothermal treatment of aqueous solutions of inorganic Sn(II) and Co(II) salts. It has been shown that raising the cobalt concentration to 10 wt % leads to significant changes in the morphology and ferromagnetic properties of the synthesis products. The phase composition of the materials corresponds to tetragonal SnO₂ with the rutile structure. Calcination above 450°C leads to Co₂SnO₄ formation. The saturation magnetization and magnetic susceptibility of the materials vary nonlinearly with the amount of cobalt added to the reaction mixture. The nanostructured material obtained in the presence of ~6 wt % Co has an anomalously high room-temperature saturation magnetization, ~3.5 emu/g, which is almost two orders of magnitude higher than that of highly dispersed powders with a similar composition prepared via chemical precipitation.

This paper presents a method for the fabrication of a foam glass ceramic, an inorganic heat-insulating material, by extruding a mixture of opal–cristobalite rock and a sodium hydroxide solution through calibrated holes. The method ensures excellent mixture homogenization and allows mixing of components and granulation of the mixture to be combined in a single step. As a result of active reactions of amorphous phases in the opal–cristobalite rock with sodium hydroxide in the SiO₂–Na₂O–H₂O system, the average density of the material decreases by a factor of 1.5. This ensures an economic benefit: a proportional reduction in the percentage of sodium hydroxide, an expensive component. Using electron microscopy, we have assessed the effect of temperature on structure formation in the material. The pore formation process begins at 200°C and is accompanied, up to 500°C, by the formation of a loose structure in the form of an inhomogeneous network. In the range 400–500°C, the material undergoes a transition. Above 600°C, a cellular structure begins to form. As a result, the materials synthesized at 850°C have an average density from 0.38 to 0.57 g/cm³ and compressive strength from 3.1 to 5.9 MPa.

Powders of the double borate PbCd₂B₆O₁₂ and PbCd_{2 –x}Mn_xB₆O₁₂ solid solutions have been prepared by solid-state reactions and the crystallographic characteristics of the synthesized phases have been determined (sp. gr. P2₁/n). Using differential scanning calorimetry and X-ray diffraction, the PbCd₂B₆O₁₂ compound has been shown to melt incongruently at 734°C. The effect of activator ion concentration on the thermoluminescence intensity in phases of variable composition at temperatures in the range 25–400°C has been studied for the first time. The sample containing 5 mol % Mn²⁺ ions has been shown to offer the highest luminescence brightness in the visible spectral region.

This paper presents numerical modeling results and experimental data on thermal conditions in Ti–Al–C MAX phase-based materials during self-propagating high-temperature synthesis (SHS) and extrusion. Based on a mathematical model for the thermal conditions of SHS extrusion, which makes it possible to analyze longitudinal and radial temperature profiles in an extruded sample with a model composition (64.2 wt % Ti + 27.1 wt % Al + 8.7 wt % C), we make recommendations as to favorable conditions for MAX phase formation in relation to strain, predict such conditions, and qualitatively compare the theoretical results and experimental data. We examine the effect of the delay time before compaction on the surface defect density of the samples and the effect of strain on the structure and surface quality of the extruded materials. Samples 10 mm in diameter are shown to be free of titanium carbide, whereas samples 5 and 8 mm in diameter contain 6–8 wt % titanium carbide.