Search

Using the methods of the cocrystallization and coprecipitation of hydroxides, xerogels and powders based on zirconium dioxide are synthesized and ceramics based on them are obtained. The influence of the synthesis conditions on the physicochemical properties of the obtained materials is assessed. [ABSTRACT FROM AUTHOR]

Xerogels and powders of solid solutions based on zirconium dioxide are synthesized by the method of the coprecipitation of hydroxides from aqueous solutions of nitrate salts of zirconium, yttrium, aluminum, and cerium with an aqueous solution of ammonia. The characteristics of the resulting materials are studied. The influence of stabilizers and additives on their synthesis, sintering, and properties is assessed. [ABSTRACT FROM AUTHOR]

By using the method of coprecipitation of hydroxides in the ZrO2–CaO–MgO system, xerogels, powders, and ceramics based on them are obtained. The effect of low temperatures during the preparation of precursors on the phase composition and physicochemical properties of the materials is studied. It is shown that the use of precipitate's cryotreatment makes it possible to reduce the open porosity and water absorption of the ceramics. [ABSTRACT FROM AUTHOR]

Xerogels and powders of a solid solution based on zirconium dioxide are synthesized by the method of coprecipitation of hydroxides from aqueous solutions of salts of zirconium nitrate ZrO(NO3)2⋅2H2O, aluminum Al(NO3)3⋅9H2O, and cerium Ce(NO3)3⋅9H2O with an aqueous 1 M solution of ammonia NH4OH. A dense ceramic with low porosity and water absorption is obtained. The effect of the ultrasonic treatment of the precipitate and mechanical treatment of the xerogel on the physicochemical properties of the obtained materials is evaluated. [ABSTRACT FROM AUTHOR]

This article describes the production of nanodisperse xerogel and powders (average CSR size of 9 nm) in the ZrO2–Y2O3–Al2O3 system by coprecipitation of hydroxides. A strong highly porous ceramic has been produced from the initial powder with the composition of [(ZrO2)0.97(Y2O3)0.03]0.8(Al2O3)0.2 with pore forming additives using patented solid phase sintering. Using Doppler sonography, the volume of blood flow in arteriolas and capillaries has been estimated 150 and 250 days after implantation of plates. Therefore, the microcirculatory Doppler sonography seems to be a promising intravital method of estimating blood flow in the zone of plates from biocompatible nonresorbable material and, probably, inside the plates. It has been found that the ceramic plates based on zirconium dioxide in the body of experimental animals do not result in a negative reaction of animal's body. The in vivo experimental results make it possible to state that the obtained bioceramic based on zirconium dioxide is a promising material for endoprosthetics. [ABSTRACT FROM AUTHOR]

Mesoporous nanosized aerogels, xerogels, and powders in the ZrO2–Y2O3–CeO2 and ZrO2‒Y2O3–Al2O3 systems have been obtained by liquid-phase synthesis methods. The thermolysis, phase composition, and textural features of the synthesized materials have been studied. It has been found that the predominance of Lewis acid sites (LASs) on the surface of their particles indicates its lower hydroxylation and, as a consequence, a lower degree of agglomeration of the obtained materials. [ABSTRACT FROM AUTHOR]

Nanopowders of the composition of (СeO2)1 –x(Sm2O3)x (x = 0.02, 0.05, 0.10, and 0.20) were synthesized by two methods of chemical liquid-phase synthesis: coprecipitation of hydroxides with freezing and co-crystallization of salts with an average CSR size of ~8–11 nm and Ssp = 40–83 m2/g. On their basis, ceramic nanomaterials with a cubic crystal structure of the fluorite type, with a CSR of ~65–81 nm (1300°C), were obtained. The dependence of the phase composition, microstructure, and electric transport properties of the obtained samples on the content of Sm2O3 in a solid solution based on CeO2 and the synthesis method is revealed. It is shown that, in the series (СeO2)1 –x(Sm2O3)x (x = 0.02, 0.05, 0.10, and 0.20), a solid solution of the composition (CeO2)0.80(Sm2O3)0.20 has the highest ionic conductivity σ700°C = 2.7 × 10–2 S/cm. The resulting ceramic can be used as a solid electrolyte for intermediate-temperature fuel cells owing to its physical and chemical characteristics. [ABSTRACT FROM AUTHOR]

Methods of coprecipitation of hydroxides in the bulk and in a microreactor with counterswirling flows are used to obtain mesoporous nanodispersed xerogels based on zirconium dioxide. The features of the morphology and state of the surface of the obtained xerogels are studied. It is shown that the investigated method of obtaining nanosized xerogels based on zirconium dioxide in counterswirling flows makes it possible to reduce the degree of particle agglomeration. [ABSTRACT FROM AUTHOR]

Nanopowders of the compositions BaHf1 –xYbxO3 – δ (x = 0.04, 0.08, 0.10) and BaCe0.9 –xZrxY0.1O3 – δ (x = 0, 0.5, 0.6, 0.7, 0.8) were synthesized by the combined crystallization of nitric acid salts and the citrate-nitrate method. Those nanopowders were used to produce ceramic materials with a cubic crystal structure of the perovskite type, with a grain size of ~20–70 nm. The study of electrophysical properties revealed that they have a proton type of conductivity in the temperature range of 500–700°C; σ = 10–2–10–5 S/cm. The type and mechanism of electrical conductivity of ceramics of the composition BaHf1 –xYbxO3 – δ (x = 0.04, 0.08, 0.10) were studied both experimentally and using theoretical calculations by computer modeling using the electron density functional method; the results are in good agreement. The research shows the prospects of using the obtained ceramic materials as proton-conducting electrolytes for solid oxide fuel cells. [ABSTRACT FROM AUTHOR]

Nanocrystalline ceramic samples of the ZrO2–3 mol % Y2O3 composition with varying degrees of tetragonality c/a (1.4337 and 1.0425) are obtained. The process of the low-temperature degradation of ceramics is studied by the methods of X-ray phase analysis and electron microscopy. It is found that samples with a high degree of tetragonality are more resistant to the action of a humid environment, while the phase composition in the bulk of the samples remains practically unchanged and the transformation t-ZrO2 → m-ZrO2 occurs mainly in the surface layers without significantly affecting the mechanical properties of the ceramics. [ABSTRACT FROM AUTHOR]

Nanopowders of BaHfO3 and BaZrO3, are synthesized by the cocrystallization of nitric acid salts. Ceramic materials based on them with a crystalline cubic structure of the perovskite type, grain size 70–75 nm, and open porosity 8–10% are obtained. The mechanisms of proton electrical conductivity and the pathways of hydrogen migration in ceramic materials of the BaHfO3 and BaZrO3 composition are studied using the theoretical calculations: computer modeling by the method of the electron density functional and the sum of the valence forces. The energy parameters characterizing the behavior of hydrogen in these materials are determined. It is revealed that proton conduction occurs in two stages: rotation around the oxygen ion and intraoctahedral proton transfer between neighboring oxygen ions. The studies carried out show that the use of the obtained ceramic materials is promising as proton-conducting solid electrolytes in hydrogen power engineering. [ABSTRACT FROM AUTHOR]

It is shown that the high-temperature (1100°C) microwave treatment of the ZrO2–Y2O3–Eu2O3 luminophores obtained by wet mixing using zirconium oxochloride and yttrium acetate leads to a significant growth in the luminescence brightness that exceeds that of an industrial luminophore based on Y2O3 : Eu3+ by a factor of 1.75. For a luminophore with the identical composition obtained by the coprecipitation of hydroxides from a solution of the corresponding nitrates, a similar microwave thermal treatment leads to a sharp decrease in the brightness. The observed differences in the characteristics of the synthesized luminophores are compared to the changes in the functional composition of their surface and dispersity as a result of the microwave treatment. [ABSTRACT FROM AUTHOR]

Xerogels in the ZrO2–Y2O3–CeO2 system are obtained by coprecipitation. The influence of the synthesis method on the acid-base xerogel surface properties are studied. The sinuous dependence of the Lewis and Brønsted site content on the particle surface on the conditioning time of precipitates in the mother liquor and the presence of subsequent low-temperature processing is established. The relationship is established between the resulting ceramics properties, precipitate processing conditions, and the functional xerogel structure. [ABSTRACT FROM AUTHOR]

By using the method of coprecipitation of hydroxides in the ZrO2–CaO–MgO system, xerogels, powders, and ceramics based on them are obtained. The effect of low temperatures during the preparation of precursors on the phase composition and physicochemical properties of the materials is studied. It is shown that the use of precipitate's cryotreatment makes it possible to reduce the open porosity and water absorption of the ceramics. [ABSTRACT FROM AUTHOR]