The paper presents the results of experimental modeling of glass-like carbon synthesis from high pressure supercritical fluid in the C–O–H system at temperature 800 °C and pressure 500…1000 atm. A full characterization of the carbon material is described on the basis numerous methods, such as CHNS-O analysis, scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, X-ray and electron diffraction, infrared and multiwave Raman spectroscopy. According to the features complex and comparison with industrial glassy carbon, the produced carbon material is classified as a glass-like substance. The results of the experimental synthesis demonstrate possible different formation mechanisms and, as a result, the polygenesis of glass-like state of carbon. The resulting material, due to a radically different method of synthesis (by polycondensation), can potentially have special surface and bulk properties.
The results of the synthesis of complex paraniobate of the composition YErYbNbO7 using various methods are presented. The chemical composition of the final synthesis products is determined. The features of the thermal behavior of the precursors are revealed. The crystallographic parameters of single-phase samples are calculated and the sizes of crystallites are determined.
In this study, we investigated how the composition and ratio of sintering additives MgO and CaO influence the optical properties of ceramic materials YAG:Cr3+ and YAG:Cr4+. All samples exhibited high transparency at 1100 nm (greater
than 80 %). However, around ~340 nm, increased concentrations of Ca2+ or Mg2+ ions resulted in decreased light transmission coefficients for the samples. Following annealing in air, the most pronounced absorption in the 750…1100 nm range was observed in samples with higher amounts of sintering additives. As the fraction of Ca/Mg increased, so did the absorption of Cr4+ cations. Among the compositions studied, an optimal CaO content of 0.12 wt. % was identified; beyond this level, additional absorption due to microdefect formation was noted. Scanning electron microscopy data revealed a granular structure for the ceramic samples, with grain sizes ranging from 1 to 10 ?m, showing no significant variations in microstructure based on the type or quantity of sintering additives.
In article main types of defects in ceramic blanks and the causes of their occurrence are considered. Comparative analysis of the two materials used – duralumin alloy and caprolon – in the making of cores is presented. Influence of passive forming surface material of core on quality characteristics of quartz ceramic products is estimated. It is established that application of the caprolon, which has water-absorbing properties and does not require the use of lubricants for the formation of quartz ceramic products by slip casting method allowed to reduce appearance of technological defects of ceramic blanks to 25 %.
Chemical elements have been discovered that can contaminate high-purity crystalline, ceramic and glass materials during the production and research of photonic and electronic devices. The sources of pollution analyzed were street air in the spring and summer, air polluted with construction dust, various cosmetics, protective gloves and cleaning materials. Recommendations for reducing uncontrolled pollution are proposed.
The microstructure of solder compositions based on high-lead low-melting glass and lead titanate as a crystalline filler correcting the temperature coefficient of linear expansion (TCLE) of solder has been studied by optical microscopy in combination with birefringence testing with a locality of about 1 µm. The influence of the specific surface area and filler concentration on the TCLE of sintered composites was studied in order to obtain composites with abnormally low TCLR values for solder materials. In composites containing up to 55 % PbTiO3 powder with a specific surface area of less than 560 cm2/g, near-zero and even negative values have been achieved.
The PbO–Ga2O3 glass-forming system with a lead oxide content of more than 50 mol. % was studied. It was found that the introduction of lead oxide significantly affects the glass structure. Using vibrational spectroscopy methods, it was shown that PbO significantly reduces the number of Ga–O–Ga bridging bonds, which leads to a weakening of the glass network and the dominance of PbO4 pyramids in it. Structural changes lead to a significant change in the physicochemical properties of glasses. The article considers in detail the spectral and optical properties of the PbO–Ga2O3 system. The glasses have a wide transparency window (from 0.5 to 7.1 ?m), a high refractive index (?2.2) and a small Abbe number (about 12). The developed materials are promising for applications in optics and photonics for infrared devices.
Ceramic samples Bi2ZnxMn1–xTa2O9.5–? were synthesized for the first time using the solid-phase synthesis method. It was established that the samples contain the main phase of cubic pyrochlore (sp. gr. Fd-3m) and an admixture of BiTaO4 of the triclinic modification (sp. gr. P-1), the amount of which is proportional to the manganese content in the samples.
The formation of impurities is associated with the distribution of part of the transition element ions into the cationic sublattice of bismuth (III). The unit cell parameter of the pyrochlore phase increases with increasing content of zinc ions in the samples from 10.4895(5) (x = 0.3) to 10.5325(5) ? (x = 0.7), obeying the Vegard rule. It has been shown that the formation of impurities in samples can be prevented by creating a deficiency of bismuth ions in the bismuth sublattice by an amount proportional to the ?-BiTaO4 content. In this way, single-phase pyrochlores Bi2–yZnxMn1–xTa2O9.5–? were synthesized, the parameter of which increases with increasing content of zinc ions in the samples from 10.4764(5) (x = 0.3) to 10.5122(5) ? (x = 0.7). According to electron scanning microscopy, ceramic samples are characterized by a low-porosity microstructure with unclear outlines of grain boundaries. As the zinc content in the samples increases, the porosity of the preparations decreases. Samples with a deficient bismuth sublattice are characterized by a more porous microstructure due to a decrease in the content of the low-melting component of the reaction mixture – bismuth (III) oxide.
Ceramics in the Ca2P2O7–Ca3(PO4)2 system were obtained from powder mixtures containing calcium hydroxyapatite Са10(РО4)6(ОН)2 of natural origin and monocalcium phosphate monohydrate Ca(H2PO4)2·H2O. Fish scale powder was used as a source of calcium hydroxyapatite Са10(РО4)6(ОН)2 of natural origin. The molar ratios of Са10(РО4)6(ОН)2/Ca(H2PO4)2·H2O in the initial powder mixture equal to 1/4, 3/5 and 2/1 ensured the formation ceramics with phase composition, including calcium pyrophosphate Ca2P2O7 and/or tricalcium phosphate Ca3(PO4)2 after firing.
The homogenization of the components was carried out using repeated passing of the powder mixture through a sieve with a cell size of 200 microns. Plastic molding of the samples was carried out using ethyl alcohol as a binder. According to XRD data the phase composition of all samples after the addition of alcohol, molding and drying included monocalcium phosphate monohydrate Ca(H2PO4)2·H2O and calcium hydroxyapatite Са10(РО4)6(ОН)2. In the phase composition of the samples monetite CaHPO4 and brushite CaHPO4·2H2O were also present. The phase composition of prepared highly porous ceramic samples with relative density 27…55 % after firing in the range of 900…1100 ?C included ?-tricalcium phosphate ?-Ca3(PO4)2 and/or ?-calcium pyrophosphate ?-Ca2P2O7.
Porous ?-Al2O3–3YSZ ceramics were fabricated using slip casting, incorporating 15 wt. % submicron Al2O3 powders as sintering additives. These orders were synthesized via solution combustion synthesis using glycine or urea as fuels. After firing at 1550 ?C, the ceramics exhibited a closed porosity range of 14.1…24.0 %. The experimental results revealed a linear correlation between density and closed porosity in the corundum Al2O3–3YSZ ceramics. The ceramic samples, fired at 1550 ?C, attained a relative density of 75…85 % with an open porosity of 0.90…1.71 %. The morphology of the aluminum oxide additives, synthesized through combustion reactions, was found to exert a significant influence on the strength characteristics of the ceramic materials.
