Inorganic Materials最新文献

In this paper, we report boron carbide preparation of В₄С/ZrB₂ composite ceramics. The ceramics have been prepared via pressing of B₄C + ZrB₂ powder mixtures and by reaction pressing. The content of the ZrB₂ phase was varied from 10 to 30 mol %. Increasing the percentage of ZrB₂ has been shown to reduce the open porosity of the composite ceramics and increase their relative density. Visual inspection showed that simultaneous boron carbide synthesis and hot pressing made it possible to obtain a B₄C/10 mol % ZrB₂ material with ZrB₂ grains uniformly distributed over the bulk of the B₄C phase. The microhardness and fracture toughness of this material were 38.3 GPa and 3.9 MPa m^1/2, respectively, and its relative density was 99.9%. In the case of hot pressing of a presynthesized powder mixture, such results were obtained at a higher modifying additive content, corresponding to 30 mol % zirconium diboride. The composite ceramic containing 30 mol % ZrB₂ has been shown to have a larger thermal neutron absorption cross section in comparison with the unmodified ceramic.

Vanadium alloys (V₇₀Cr₃₀, V₇₀(Ni₈₀Cr₂₀)₃₀, and (V₉₅Cr₅)₇₀Cu₃₀) and metal–ceramic composites of these alloys and La_0.96Sr_0.04ScO₃ have been prepared by mechanochemical synthesis. The use of spark plasma sintering has made it possible to produce dense compacts with low porosity in a short sintering time. The phase composition of the synthesized materials was determined, morphological features were studied, and hardness measurements were carried out.

We have studied the electrical properties, strength, and structure of a ceramic material having the same composition as the commercially available VK94-1 ceramic. Ceramic samples have been prepared using a novel technological approach involving spray drying of a highly concentrated aqueous suspension of a mineral powder mixture with the VK94-1 composition, compaction of the resultant granulate by a combination of uniaxial semidry pressing and cold isostatic pressing, and subsequent sintering of the green compacts in air. The improved performance parameters of the materials studied are due to the good rheological properties of the granulate, which ensure an increased density of the green compacts and sintered material with a microcrystalline structure. The following properties of the material, superior to those of the commercially available VK94-1 ceramic, have been achieved: relative density, 98.7%; bending strength, 380–420 MPa, grain size in the structure of the sintered material, 1–5 μm; dielectric permittivity, 9.7; dielectric loss tangent, 3.4 × 10^–4; and volume resistivity, 5.3 × 10¹⁴ Ω cm. The ceramic produced in this study can be recommended as a material for special-purpose dielectric parts.

We report a systematic study of the self-propagating high-temperature synthesis of compositions in the Si₃N₄–Yb₂O₃ system. In our preparations, the ytterbium oxide content of the starting mixture was varied from 4 to 20 wt %. Ytterbium oxide has been shown to influence the combustion temperature, particle morphology, and the phase composition of synthesis products. Increasing the percentage of ytterbium oxide in the starting mixture has been found to increase the combustion temperature. We have optimized conditions for the synthesis of compositions with a high content of the alpha-phase of silicon nitride.

Regenerative medicine approaches require the creation of new types of resorbable inorganic materials for use in bone tissue engineering. This review considers magnesium-based materials, including magnesium phosphates, which are characterized by a high dissolution degree in the body environment, and their prospects for creating implants for the treatment of bone tissue defects, including cements, ceramics, and composite scaffolds.

The surface of oxygen-free copper has been modified by a focused beam of a nanosecond solid-state laser under a water layer at energy densities W_p in the range 20–32 J/cm², using uncoated copper and samples having absorbing coating. Laser treatment of the uncoated surface to an energy density of 32 J/cm² produced pits about 2.75 μm deep, whereas the pit depth on the coated surface was as large as 5 μm. The pit depth was determined as a function of laser pulse energy density. The effect of impact treatment of oxygen-free copper with a single high-power nanosecond laser pulse has been examined.

The surface of carbon electrodes has been modified by manganese oxide nanoparticles via anodic electrochemical deposition. The structural properties and elemental composition of the resultant MnO₂/C materials have been studied by energy dispersive X-ray microanalysis and transmission electron microscopy. Electrochemical characteristics of the electrodes have been investigated by cyclic voltammetry, galvanostatic charge–discharge measurements, and impedance spectroscopy. We have compared the specific capacitance of the MnO₂/C electrodes in 0.5 M Li₂SO₄, Na₂SO₄, and K₂SO₄ solutions. The materials studied have been shown to have the highest specific capacitance in the sodium sulfate solution.

This paper examines processes underlying the formation of layered materials, analogs of the natural mineral valleriite, CuFeS₂·1.53[(Mg,Al)(OH)₂], made up of alternating two-dimensional sulfide and hydroxide layers, under hydrothermal conditions. The synthesized materials have been characterized by X-ray diffraction, scanning and transmission electron microscopies, X-ray photoelectron spectroscopy, and laser diffraction. The results demonstrate that the formation of valleriite phase at 160°C in an autoclave proceeds through the formation and subsequent consumption of reaction intermediates: erdite (NaFeS₂·2H₂O), haycockite (Cu₄Fe₅S₈), and chalcopyrite (CuFeS₂). The formation of phase-pure valleriite has been shown to occur at a hydrothermal treatment time from 25 to 70 h, whereas shorter or longer treatment times lead to contamination of the reaction product with impurity phases. The nature of the anion in the starting materials (({text{SO}}_{4}^{{2 - }}) or ({text{NO}}_{3}^{ - })) has been shown to have little or no effect on characteristics of the synthesis product. The use of thiourea as a sulfur source instead of sodium sulfide makes it possible to obtain valleriite phase contaminated only slightly with spherical magnesium carbonate particles. Our results demonstrate that, under hydrothermal conditions, equilibrium in the formation of the material can be reached if chalcopyrite phase is used as a precursor of 2D valleriite layers.

A fine-particle Fe–Ni–Co–Cu polymetallic system has been prepared in an aqueous solution of metal chlorides using galvanic replacement by fine-particle aluminum. The elemental and phase compositions of the synthesized powders have been determined by X-ray fluorescence analysis and X-ray diffraction. The content of elemental metals (Fe, Ni, Co, and Cu) in the deposit has been shown to reach 98 wt %. X-ray diffraction data have been used to evaluate the crystallite size (~20 nm) and unit-cell parameters of the phases identified. The powder particles have the form of spherical micron-sized skeletal structures (~75 μm in size), with a large number of nuclei 50–60 nm in size.

Alkali halides have found wide application as thermal energy storage materials, electrolytes for electrochemical cells, and solvents of inorganic substances. Modeling with the use of data for bounding systems is important for constructing phase diagrams of ternary and multicomponent systems. Using three-dimensional vector graphics software, we have constructed a 3D model of equilibrium phase states in the pseudoternary system LiF–NaF–KBr, which is a stable composition triangle in the quaternary reciprocal system Li⁺,Na⁺,K⁺||F^–,Br^–. Based on the 3D model, we have constructed for the first time polythermal and crystallization polytherm. For two polythermal sections, we have demonstrated the presence of regions of limited sodium fluoride-based solid solutions and liquid miscibility gaps and identified the phase crystallization sequence. In the 620°C isothermal section, we have delineated liquid-phase and two- and three-phase fields. The polytherm comprises three crystallization fields: terminal solid solutions based on sodium fluoride, potassium bromide, and lithium fluoride, in which a liquid miscibility gap has been delineated. The stability of the LiF–NaF–KBr composition triangle has been confirmed by thermodynamic calculations for several temperatures of interaction in mixtures of substances in the unstable composition triangle LiBr–NaF–KF. The crystallization polytherm allows one to choose mixtures in the temperature ranges 625–650 and 625–700°C suitable for practical application as melting electrolytes of intermediate-temperature electrochemical cells and molten solvents of inorganic substances.