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The interaction of iron oxide nanoparticles with an aqueous medium has been studied. The composition of the nanoparticles corresponds to magnetite–maghemite solid solutions with different Fe2+/Fe3+ ratios. Nanoparticles that most closely correspond to the composition of maghemite (γ-Fe2O3) have largest hydrodynamic diameters and cause a drastic decrease in the pH of the dispersion medium during the dispersion of the powders in water. Nanoparticles that have a phase composition of a solid solution corresponding to the middle of the magnetite–maghemite series are characterized by a gradual and less pronounced decrease in pH. It has been shown that dilution of aqueous suspensions obtained from preliminarily dried powders within a concentration range of 100–0.001 mg/L followed by sonication leads to a significant increase in the hydrodynamic diameter of iron oxide particles. A possible mechanism of the studied interaction of nanoparticles with the aqueous medium has been considered. This mechanism comprises the hydration of Lewis acid sites formed by iron ions and changes in the character of the dissociation of hydroxyl groups depending on the pH of a suspension. The effect of surface passivation of the studied nanopowders with oleic acid on the processes under consideration has been investigated. The results obtained make it possible to predict the aggregative stability and a number of other characteristics of the studied suspensions being diluted with water. [ABSTRACT FROM AUTHOR]

Finely dispersed mesoporous powders of the following composition are synthesized by the method of cocrystallization of nitrate salts with ultrasonic treatment: La1–xSrxNiO3–δ, La1–xSrxCoO3–δ, and La1–xSrxFe0.7Ni0.3O3–δ (x = 0.30; 0.40). Based on them, ceramic nanomaterials of the given composition with a coherent scattering region (CSR) of ~65–69 nm (1300°С) are obtained. Ceramics fired at 1300°C are single-phase and have a tetragonal and orthorhombic perovskite-type structure in the La2O3‒SrO‒Ni(Co,Fe)2O3–δ system. Solid solutions have mixed electron–ion conductivity with transfer numbers te = 0.98–0.90 and ti = 0.02–0.10. Ceramics with a tetragonal perovskite-type crystal structure exhibit higher electrical conductivity than materials having an orthorhombic perovskite-type crystal structure. According to their electrophysical properties related to the structural features of solid solutions, ceramic materials obtained based on them are promising as solid oxide cathodes for average-temperature fuel cells. [ABSTRACT FROM AUTHOR]

(In2O3)0.95(SnO2)0.05, (TbOх)0.50(Y2O3)0.50, and (CeO2)0.80(Y2O3)0.20 single-phase cubic solid solution xerogels and nanocrystalline powders have been synthesized via coprecipitation of hydroxides. Using these powders as precursors, nanoscale film electroconductive materials on a corundum substrate have been produced by screen printing. The highest speed of sensor response to ozone is attributed to In0.95Sn0.05O1.5 films, reaching 8–10 s at a temperature of 473 K. (TbOх)0.50(Y2O3)0.50 thin film is found to be sensitive to changes in the concentrations of (CO + CO2) (the sensitivity coefficient S = 25.11) and ozone (S = 3.16–7.94). (CeO2)0.80(Y2O3)0.20 film exhibits a sensor response to (CO + CO2) (S = 3.10). This study opens up the prospects of using the obtained nanopowders and relevant thin films as materials for resistive gas sensors operating at oxygen pressures of 103–104 Pa. [ABSTRACT FROM AUTHOR]

Using the liquid-phase methods of synthesis—the coprecipitation of hydroxides and the hydrothermal method—mesoporous xerogels are obtained based on the ZrО2-Y2О3-CeО2 system with 5-8-nm particles and powders (after the heat treatment of xerogels at 600°C) with a coherent scattering region (CSR) size of 9 to 10 nm and Ssp = 96-156 m2/g. After calcination at 1400°C, the powders are transformed into tetragonal solid solutions with a CSR size of 65 nm in the synthesis by the coprecipitation method, and they are transformed into solid solutions with a CSR size of 84 nm with a high degree of tetragonality of c/a = 1.438-1.431 in the synthesis by the hydrothermal method. [ABSTRACT FROM AUTHOR]

Precursor powders in the ZrO2–HfO2–Y2O3–CeO2, In2O3–ZrO2, and NiO–Nd2O3 systems for components of solid oxide fuel cells have been prepared by liquid-phase synthesis. We have determined formation conditions and the particle size of ZrO2- and In2O3-based solid solutions and neodymium nickelate (Nd2NiO4), demonstrated the feasibility of producing nanocrystalline powders (10–30 nm) of tailored chemical composition in the temperature range 500–900°C, and optimized powder consolidation conditions. Nanoceramics with a crystallite size from 60 to 90 nm have been obtained and their microstructure and phase composition have been investigated. We have studied the electrical properties of the ZrO2- and In2O3-based solid solutions and the Nd2NiO4 compound and established the range of their electrical conductivity at temperatures from 300 to 1000°C: 2.27 × 10–3 to 2.51 S/cm for the ZrO2-based solid solution, 8.91 × 101 to 6.59 × 103 S/cm for the In2O3-based solid solution, and 3.98 × 102 to 5.02 × 102 S/cm for Nd2NiO4. [ABSTRACT FROM AUTHOR]

The results of the studies of the conditions of the liquid-phase synthesis of highly dispersed xerogels with a low degree of agglomeration and precursor nanopowders (~10-12 nm) based on zirconium dioxide in the ZrO-HfO-YO(CeO) system are presented. The thermal decomposition of xerogels and formation of crystalline solid solutions with the structure of fluorite are investigated. The optimal conditions for the solidification of nanodispersed powders for fabricating compact ceramics based on solid solutions of ZrO and the physical-chemical properties of these ceramics are studied. [ABSTRACT FROM AUTHOR]

A synthesis technology for ceramics based on a tetragonal solid solution of zirconia in ZrO-YO-CeO and ZrO-YO-AlO systems with a high degree of tetragonality (∼1.436) and an average crystal size of 45-70 nm has been developed; it can be recommended for producing bioceramics in restorative dentistry. [ABSTRACT FROM AUTHOR]

Methods of the synthesis of nanostructured oxide films have been suggested for gas sensors based on zirconium and cerium dioxides with a cubic structure and crystallite size of 10-12 nm. The compositions in the CeO-ZrO system having the highest sensitivity have been predicted, based on quantum-chemical calculations via the density functional method (DFT). These calculated data are correlated to the experimental results of the measurement of electroconductivity on air and in a reducing medium (CO + CO). The obtained nanosized oxide films have a high response time (5-6 s) and sensitivity; they are promising as resistive sensors for the detection of media with reduced oxygen content. The method of computer simulation allows the reduction of the search period of new materials for gas sensors. [ABSTRACT FROM AUTHOR]