Glass and Ceramics最新文献

Self-propagating high-temperature synthesis (SHS) was used to prepare SHS compositions based on the system Si₃N₄–Yb₂O₃ system. Synthesis was conducted in a nitrogen atmosphere at 4 MPa in a 30 L reactor. The weight of the loaded charge was 3 kg. It was ascertained that the amount of ytterbium oxide in the charge affects the combustion temperature and the phase composition of the synthesis products. As the proportion of ytterbium oxide in the charge increases, the α-Si₃N₄ content decreases, and the secondary phases are represented by quaternary silicon ytterbium oxynitride and ytterbium disilicate.

Perlite, an inexpensive mineral raw material, served as a base to synthesize an opaque glass-crystalline material containing in the bulk nanosized wollastonite and gehlenite crystals of average size 100 nm. The phase composition, microstructure, and strength properties of the material were investigated. Changes effected in the composition and size of the crystal grains by varying the amount of catalyst and silica content in the initial mixtures make it possible to control the physical and mechanical properties of the resulting material. High strength and high hardness make it possible to use this material for protection against high-velocity impacts, including bullets from firearms.

The phase composition and spectral-luminescent properties of samples of a luminescent ceramic, based on oxide compositions with makeup described by the general formula Y_2.98–xCe_xAl_5.02O₁₂, where x = 0.05, 0.10, 0.20, 0.30, 0.45, and 0.60 formula units (f.un), were investigated. It is demonstrated that the phase composition of ceramic powders depends substantially on the cerium concentration and the calcination atmosphere. It was ascertained that the maximum concentration of cerium cations in the garnet lattice on calcination in air is equal to about 0.1 f.un, and in an argon and hydrogen atmosphere approximately 0.16 f.un The photoluminescence of ceramic samples excited by a 445 nm laser was investigated. It is shown that ceramic samples obtained by sintering in argon and hydrogen have a higher luminescence intensity compared to samples synthesized in vacuum. The possibility of shifting the wavelength of the maximum luminescence intensity from 546 to 570 nm by changing the cation composition and the sintering conditions of the ceramics was demonstrated. It is shown that oxidative annealing of ceramic samples adversely affects the intensity and position of luminescence maxima in highly cerium-doped oxide compositions Y_2.98–xC_exAl_5.02O₁₂.

The effect of sintering additives based on magnesium oxide MgO and silicon oxide (TEOS) at concentrations0.02 – 0.10 wt.% and 0.2 – 0.5 wt.%, respectively, on the microstructure and optical properties of ceramics with the composition Y_2.82Yb_0.15Er_0.03Al₅O₁₂, made from powders synthesized by chemical coprecipitation. The results demonstrated that the introduction of an MgO-based sintering additive into ceramic powder does not affect its phase composition, structural, or morphological characteristics. It was shown that for ceramics with the composition Y_2.82Yb_0.15Er_0.03Al₅O₁₂ the best optical transmittance value was achieved at vacuum sintering temperature 1800°C and sintering additive concentrations 0.06 wt.% MgO and 0.3 wt.% TEOS. The sintering mechanism of the ceramic Y_2.82Yb_0.15Er_0.03Al₅O₁₂ depends on the ratio of the sintering additives MgO and TEOS.

The effect of immersion in a coffee drink solution on the color stability of two CAD/CAM ceramic restorations was investigated in this in vitro study. To this end, zirconia-reinforced lithium silicate (ZLS) and lithium disilicate (LDS) glass-ceramic blocks were surface-treated using mechanical polishing and glazing techniques. In addition, their color was examined before and after immersion in a coffee solution using a spectrophotometer, and the color changes were evaluated. A two-way analysis of variance (ANOVA) was used to examine the color changes. The material type significantly influenced color changes (P < 0.001). After glazing and mechanical polishing, LDS exhibited considerably less color change in both groups than ZLS. In both types of ceramics, the glazed group experienced less color variation than the mechanically polished group. Color changes were clinically acceptable across all groups. The glazing surface treatment produced superior color stability than the mechanical polishing technique. LDS exhibited more color stability than ZLS in both surface treatments.

Matted glass compositions have been developed for the top layer and bottom structural layer of composite glass-crystal cladding material based on waste from the phosphoric industry: phosphoric slag, phosphorite fines, boiler dust, and cullet.

The preparation process for the composites CuO/ZnO/γ-Al₂O₃, which can be used as the main component of catalysts for large-tonnage methanol production and carbon monoxide conversion, was investigated by means of x-ray phase, x-ray crystalline, and synchronous thermal analysis as well as scanning electron microscopy, and low-temperature adsorption-desorption of nitrogen. The influence of the production method and the nature and intensity of processing on the phase composition of the resulting precursors and the physicochemical properties of the resulting composites was determined. The processes occurring at the stage of mechanochemical activation of a mixture of anhydrous oxides CuO/ZnO/γ-Al₂O₃ and a mixture of oxides with ammonium carbonate and ethanedioic [oxalic] acid were studied. The optimal parameters for obtaining CuO/ZnO/γ-Al₂O₃ composites with a developed specific surface and porous structure were determined.

The results of the preparation of strengthened syntactic carbon materials that can be used for industrial-grade heat insulation in conditions of heightened pressures and temperatures are presented. Strengthened syntactic carbon material is obtained by mixing hollow carbon microspheres, pre-treated with vanadium (III) chloride catalyst, with a phenol-formaldehyde binder with the addition of fine polydimethylsilane, molding the composition at low pressure, soaking the mold at 150°C for 2 h, followed by heat treatment in an inert environment at 375°C and final carbonization in combination with carbidization when the temperature rises at a rate of 100 K/h to 900°C. The physicomechanical and thermophysical characteristics were studied. Syntactic material can be used for the manufacture of heat-insulation products operating at high temperatures.

The application of an integrated research approach to the reconstruction of ceramic production technology on the territory of the Kyrgyz Republic is considered based on the results obtained by modern methods. For the first time, the results of studying physicomechanical and physicochemical properties are summarized and an attempt is made to open up methods of technical analysis of ceramic artifacts. A unified scientific approach has been developed to the ceramics of various periods ranging from the 2nd millennium BC to our era up to the 10th – 12th centuries, and excavated in Kyrgyzstan, so as to determine the relationship between their microstructure and physical and mechanical properties. Ceramic technology, like no other industry, requires this kind of research because of the specificity of technical information associated with both natural and social factors. The lack of solid knowledge in the field of ceramics technology prevents the acquisition of important information about the history, culture, and economy of Kyrgyzstan as a nation-building entity. However, a comprehensive study of production techniques, types, compositions, and quality of ceramics would open up completely new prospects for confirming the antiquity of Kyrgyzstan.

The conditions for the synthesis of mullite-corundum ceramic prepared on the basis of Al₂O₃ and SiO₂ powders were investigated. The composition of mullite-corundum ceramic with Al₂O₃ < 80 wt.%, which affords the best thermomechanical compatibility with molybdenum, was determined. 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 Mo–Si-containing ceramic interface, was confirmed. It was ascertained that the use of a barrier layer substantially reduces the likelihood of thermal stresses arising at the interface between two phases. It is demonstrated that the technological parameters of the process of preparing Al₂O₃–SiO₂ powder mixtures require elaboration in order to increase the thermochemical compatibility of molybdenum with mullite-corundum ceramic.