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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 %.
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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.
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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.
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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.
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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.
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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.
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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.
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The temperature regimes of the thermal extraction method for obtaining silicon dioxide from rice husk and various conditions of subsequent milling were investigated. Elemental, X-ray phase, petrographic analyses, electron and atomic force microscopy, differential scanning calorimetry, and laser granulometry were employed. The appearance of silicon dioxide was observed at a temperature of around 650 ?C, and its structure remained stable during pyrolysis and subsequent heat treatment in the presence of air. After heat treatment at 1000…1100 ?C, cristobalite was the predominant phase.
The milling of the heat-treated products was associated with a significant loss of process efficiency due to the hereditary cellular structure of aggregates and their plastic character of destruction.
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This article demonstrates the possibility of synthesizing a sulfur chemisorbent based on ZnO deposited on a granular ?-Al2O3 substrate by impregnation with an aqueous solution of zinc salt followed by thermal decomposition. The strength and textural characteristics of the resulting sorbent were studied using low-temperature nitrogen adsorption, X-ray diffraction, and scanning electron microscopy. The synthesized absorber has high strength and surface utilization compared to traditional ZnO-based sorbents used in natural gas processing. The proposed sorbent showed relatively high values of static sulfur capacity when absorbing H2S compared to industrial analogues of the zinc absorber.
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Polyoxotungssilicates with the general formulas Cat4[SiW12O40] ? mH2O and Cat6[SiW11O39Ni(H2O)] ? nH2O, where Cat = Rb+, Cs+, (CH3)4N+, were synthesized. Using IR spectroscopy and X-ray phase analysis, it was shown that the compounds have the Keggin anion structure. When thermolysis of the resulting compounds in the temperature range 600…800 ?C, previously unknown phases are formed with the pyrochlore structure of the compositions Rb12/13Si2/13W22/13Ni2/13O6 and Cs12/13Si2/13W22/13Ni2/13O6 with unit cell parameters a = 10,284 and 10,309 ? and tungsten bronze Rb12/20Si3/20W36/20O6 and Si3/38W36/38O3. The synthesis of tungstosilicates with a pyrochlore and tungsten bronze structure by thermolysis of polyoxotungssilicates reduces their production temperature to 600…650 ?C and heating time to 1 hour, expands the range of chemical compositions and their morphological diversity.
