The paper studies the conditions for synthesis of mullite-corundum ceramics obtained on the basis of Al2O3 and SiO2. The composition of mullite-corundum ceramics with an Al2O3 content < 80 wt.% has been determined, which ensures the best thermomechanical compatibility with molybdenum. The possibility of obtaining a composite material based on a mullite-corundum matrix and molybdenum, as well as its use as a barrier layer at the interface of Мo–Si-containing ceramics, has been confirmed. It is established that use of barrier layer significantly reduces the likelihood of thermal stresses in the interface of the two phases. It is shown that there is a need to refine the technological parameters of the preparation of the powder Al2O3–SiO2 mixture to increase the thermochemical compatibility of molybdenum with mullite-corundum ceramics.
In this study, LuAG:Ce ceramic powders with compositions of Lu2.98Ce0.02Al5O12 and Lu2.93Ce0.07Al5O12 were synthesized using chemical precipitation. Luminescent ceramic samples were then produced from these powders by vacuum sintering green bodies in the temperature range of 1600 – 1800 ?C. The study aimed to investigate the effect of cerium concentration and vacuum sintering temperature on the optical properties of LuAG:Ce ceramics. The spectral luminescence properties of the LuAG:Ce ceramic samples were analyzed. Results showed that the luminescence intensity was dependent on the activator concentration and vacuum sintering temperature. Additionally, a shift in the maxima of the luminescence spectral bands of the LuAG:Ce ceramics was observed when varying the vacuum sintering temperature within the 1600 – 1800 ?C range.
In this work, using the methods of X-ray phase, X-ray diffraction, synchronous thermal analysis, scanning electron microscopy, low-temperature adsorption-desorption of nitrogen, the process of obtaining CuO/ZnO/?-Al2O3 composites, which can be used as the main component of catalysts for large-tonnage processes for methanol production and monoxide conversion, was studied. carbon. The influence of the method of preparation, the nature and intensity of processing on the phase composition of the resulting precursors and the physicochemical properties of the resulting composites was established. The processes occurring at the stage of mechanochemical activation of a mixture of anhydrous CuO/ZnO/?-Al2O3 oxides, a mixture of oxides with ammonium carbonate and ethanedienic acid have been studied. The optimal parameters for obtaining CuO/ZnO/?-Al2O3 composites with a developed specific surface area and porous structure have been determined.
The phase composition and spectral-luminescent properties of ceramic samples obtained from oxide compositions with the general formula Y2.98-хCeхAl5.02О12 (x = 0.05, 0.10, 0.20, 0.30, 0.45, 0.60 formula units (f.u.)) were investigated. It was found that the phase composition of the ceramic powders depended significantly on the concentration of cerium and the calcination atmosphere. The maximum concentration of cerium cations in the garnet lattice was determined to be approximately 0.1 f.u. when calcined in air, and approximately 0.16 f.u. when calcined in the argon – hydrogen atmosphere. The photoluminescence of the ceramic samples was studied when excited by a laser with a wavelength of 445 nm. It was observed that ceramic samples sintered in argon and hydrogen had a higher luminescence intensity compared to samples synthesized in a vacuum. The possibility of shifting the wavelength of the maximum luminescence intensity from 546 nm to 570 nm by changing the cationic composition and sintering conditions of the ceramics was demonstrated. Additionally, the negative effect of oxidative annealing of ceramic samples on the intensity and position of luminescence maxima in Y2.98-хCeхAl5.02О12 oxide compositions heavily doped with cerium was shown.
The paper presents the results of obtaining hardened synthetic carbon materials that can be used for technical thermal insulation under conditions of elevated pressures and temperatures. The hardened syntactic carbon material is obtained by mixing hollow carbon microspheres pretreated with a catalyst with vanadium (III) chloride with a phenol-formaldehyde binder with the addition of fine polydimethylsilane forming the composition at low pressure, holding the mold at 150 ?C for 2 hours, followed by heat treatment in an inert medium at 375 ?C and final carbonation in combination with carbidization when the temperature rises at a rate of 100 ?C/h to 900 ?C. The physicomechanical and thermophysical characteristics are studied. Synthetic material can be used for the manufacture of thermal insulation products operating under high temperature conditions.
The purpose of this work was to prepare and identify the features of the microstructure and the degree of texturing of the thermoelectric material Bi2Te2.7Se0.3 doped with dysprosium. Textured Bi2-xDyxTe2.7Se0.3 compounds with x = 0.0000; 0.0010; 0.0025; 0.0050; 0.0100 and 0.0200 were prepared by using solvothermal synthesis and spark plasma sintering of starting powders. Dy-doping results in several interconnected effects. First of them is reducing in size of particles in starting powders with increasing x. This effect is attributed to increasing in ionic bonding fraction in polar covalent Bi(Dy)–Te bonds with increasing Dy content due to difference in electronegativity of Bi and Dy. With increasing x, grain size in bulk samples is also reducing, which is governed by relevant changing in the size of particles in the starting powders with different dopant content. This effect also results in enhancing in texturing degree in samples.
The paper presents the results of the research on the production of electrical porcelain on the basis of available traditional raw materials of Uzbekistan. It is shown that in conditions of a shortage of high-grade mineral raw materials for the production of electrical porcelain, it is advisable to add about half of the kaolin in the pre-fired state to the batch. At the same time, the products of firing at 1350 ?С of primary and secondary Angren kaolins allow us to consider them as a mullite-containing component, which further provides high physical, mechanical and dielectric properties of the porcelain material. The phase composition of the obtained porcelain is mainly represented by new crystalline components such as mullite and cristobalite, which gives the right to relate it to the mullite type of electro porcelain.
The results of studies of the chemical and mineralogical compositions and the main characteristics for determining the suitability of trachybasaltic porphyrite from the Gavasay deposit of Uzbekistan for obtaining heat-insulating material, in particular mineral fiber, are presented. It has been established that this new deposit of igneous rock can be used as the main raw material component for the production of basalt fiber products, a widely demanded and modern material in the construction industry.
In the present study, we built predictive models of the mechanical properties (Young's modulus, fracture strength and toughness) of ?-Al2O3. Experiments carried out on samples produced by spark plasma sintering (SPS). The experimental results were the basis for the evaluation of mathematical models and predictions by both the radial basis function neural network (RBFNN) and multiple linear regression (MLR) models. The results of the comparison of MLR and RBFNN models showed good agreement between the experimental data and the RBFNN model predictions whereas the MLR model reveals modest agreement with the studied mechanical properties.
The crystallization properties of multicomponent glass based on the Li2O–Al2O3–SiO2 system are investigated. By the Marotta et al method, temperature of 670 ?C at a holding time of 2 hours provides the maximum rate of nucleation the crystalline phase of ?-eucryptite-like solid solutions was found. The activation energy of nucleation and the Avrami parameter were measured by the DSC method, allowing to estimate the crystallization characteristics. The gradient crystallization method has established the temperature range of heat treatment, within which it is possible to obtain a transparent glass-ceramic. The refinement of regime the nucleation stage made it possible to reduce the time of the second stage crystallization required for the complete formation of the transparent glass-ceramic structure. Varying the holding time at a temperature of 710 ?C makes it possible to smoothly change the CTE in the range of ?(3…+41)?10–7 K?1 in the temperature range from ?120 to +500 ?C.
