Inorganic Materials最新文献

Phosphates isostructural with the mineral monazite—NdPO₄, GdPO₄, and a La_0.3Nd_0.5Sm_0.1Eu_0.1PO₄ solid solution modeling the composition of the lanthanide components of radioactive waste—and YbPO₄, crystallizing in the xenotime structure, have been prepared via direct precipitation from acid solutions. Under hydrothermal conditions, we have prepared the crystalline hydrate NdPO₄·0.67Н₂О isostructural with the mineral rhabdophane and the YbPO₄ phosphate with the xenotime structure. The powders range in crystallite size from 13 to 65 nm. The particle morphology and size have been shown to depend on the synthesis process. During heating to 1170 K, the phase composition of the powders remained unchanged. Their average 900-K thermal expansion coefficients lie in the range (5.6–9.6) × 10^–6 K^–1, so these phosphates can be regarded as having medium thermal expansion.

The quinary reciprocal system Li⁺,K⁺||F^–,Cl^–,Br^–,({text{CrO}}_{4}^{{2 - }}) has been divided into simplexes using graph theory: by making up an adjacency matrix and solving a logical expression. The results have been used to construct the phase tree of the system, which has a linear structure and consists of four stable secant tetrahedra, four stable pentatopes, and one stable hexatope. The number and composition of phases crystallizing in the system have been predicted. The LiF–KCl–KBr–Li₂CrO₄ stable tetrahedron has been studied using differential thermal analysis and X-ray diffraction. The tetrahedron has no invariant equilibrium points. The continuous series of solid solutions between potassium chloride and potassium bromide has been shown to be stable, without decomposition. Three solid phases have been shown to crystallize in the tetrahedron: LiF, Li₂CrO₄, and KCl_xBr_1–x.

In this paper, we report an experimental study concerned with the synthesis of MgAl₂O₄ spinel via plasma-assisted melting of powder components at an Al₂O₃/MgO weight ratio varied from 1 to 4. The presence of excess Al₂O₃ in the starting mixture has been shown to cause the characteristic Bragg peak 111 (~65°) of crystalline MgAl₂O₄ to shift to larger 2θ angles and broaden. According to scanning electron microscopy results, the surface microstructure of the synthesized materials is formed by densely packed octahedral stoichiometric MgAl₂O₄ crystals ranging in size from 10 to 500 μm. The materials have been found to contain local regions that allow the dynamics of crystal growth during melt solidification to be examined. The proposed spinel synthesis method can find application in the fabrication of small thermally stable parts by casting.

α-Si₃N₄-based powder composites containing 3 wt % Y₂O₃–Al₂O₃ sintering aids with 2 : 1, 1 : 1, and 3 : 5 stoichiometries have been prepared by the Pechini process and spray drying. We have studied four ceramic samples produced by spark plasma sintering of the powder composites. The sintering process was run under a load of 70 MPa at a heating rate of 50°C/min as long as shrinkage of the powder composites continued. We have analyzed the shrinkage behavior of the powder composites during the sintering process; evaluated the activation energy for sintering; and measured the density, microhardness, and fracture toughness (cracking resistance) of the ceramic samples. The highest hardness, H_V = 16.5 GPa, in combination with a fracture toughness K_Ic = 3.8 MPa m^1/2, was offered by the material with an Y₂O₃ : Al₂O₃ molar ratio of 3 : 5 sintered at 1860°C. The corresponding densification factor was 99.0%. The starting mixture for this material was synthesized using spray drying.

Oxide Y_2.5Nd_0.5Al₅O₁₂ with the structure of the garnet mineral has been obtained by coprecipitation after annealing at 1000°C. Fine-grained ceramics has been produced by spark plasma sintering based on synthesized powder. The relative density of the ceramics was 99.1%. The chemical stability of the ceramics has been studied in static mode at 90°C in distilled and mineral water, acidic solution, and alkaline solution. The minimum rates of Y and Nd leaching were 10^–10 to ~10^–6 g/(m² day). The effect of the contact environment on the rate and mechanism of Y and Nd leaching from the Y_2.5Nd_0.5Al₅O₁₂ ceramics was studied during 42 days.

We have synthesized a hydride phase based on a TiZrHfMoTa high-entropy alloy with a body-centered cubic lattice. Hydride formation has been shown by X-ray and neutron diffraction to be accompanied by a cubic-to-tetragonal lattice transformation. Structure analysis of a deuteride based on the same alloy has made it possible to locate the deuterium atoms and determine their position parameters.

In this paper, we report a process for lithium extraction from spodumene raw materials. We demonstrate that a promising approach for processing spodumene is sintering with sodium acetate. In the reaction between these components, the crystal structure of spodumene remains intact. Ion exchange reaction between CH₃СOONa⋅3Н₂О and LiAlSi₂O₆ yields water-soluble sodium acetate and water-insoluble sodium aluminosilicate (NaAlSi₂O₆). The sodium acetate dissolved in water is converted to lithium carbonate by adding a Na₂CO₃ solution. The lithium carbonate precipitate is essentially free of foreign impurities. We analyze the effect of process parameters on the degree of Li⁺ extraction from spodumene.

Oxyfluoride glasses in the SrF₂–SiO₂–B₂O₃–Bi₂O₃–ZnO–Y₂O₃ system have been designed and prepared at various ratios of batch components, and we have studied absorption spectra and luminescence properties of Er₂O₃- and Yb₂O₃-doped glasses. According to X-ray diffraction data, all of the glasses are X-ray amorphous. We have determined their glass transition temperature (t_g). Their local structure has been studied by IR spectroscopy and it has been shown that, independent of composition, the glasses contain complex polyborate anions formed by [BO₃] and [BO₄] groups. Bismuth is incorporated into the glass network to form Bi–O–Si bonds and network-formers in the form of [BiO₆] groups.

This paper reports on the preparation of precursors of mixed oxide systems by an electrochemical process based on anodic dissolution of titanium in an electrolyte containing Cl^–, NO^3–, Al³⁺, Zr⁴⁺, and Y³⁺ ions in the presence of OH^– ions electrogenerated on a cathode, interaction of electrode reaction products, their hydrolysis, and coprecipitation of hydrolyzed species. Synthesis was carried out in a coaxial diaphragmless electrochemical reactor having electrodes differing considerably in area and resulted in the formation of primary particles of precursors to oxide phases through hydrolysis, polycondensation, and crystallization. The proposed approach allows complex titania-based systems to be prepared in the form of anatase and brookite phases stable in the temperature range 80–550°C, and the addition of Al³⁺ ions leads to the formation of the boehmite phase, which undergoes no changes up to 550°C. Heat treatment of the precipitates at 1100°C raised the degree of crystallinity of the samples, and all of the synthesized oxide systems were found to contain the rutile phase (TiO₂) and the mixed oxide TiZrO₂. The formation of Ti₂Y₂O₇ makes it possible to stabilize the cubic zirconia phase formed during the electrolysis process, which ensures high mechanical strength, corrosion resistance, and sinterability of ceramic particles based on alumina- and yttria-modified titania and zirconia.

We have studied the effect of discharge pulse duration in the electrospark deposition process on the structure and properties of FeCrWMoCB metallic glass coatings. The coating thickness has been shown to rise from 19.1 to 39 μm with increasing pulse duration. The heat resistance of the coated samples over 100 h of testing at 700°C was 27 to 176 times that of the steel and it increased with increasing pulse duration. The hardness of the coatings ranged from 11.3 to 11.9 GPa. The coatings have been shown to reduce the friction coefficient and wear of the steel by a factor of up to 3.7 and improve its corrosion resistance.