Papers by Keyword: Tungstic Acid

Abstract: In this paper, zirconium tungstate ceramic with negative thermal expansion coefficients was prepared from zirconium oxide and tungstic acid by solid phase synthesis and high temperature quenching technique with a sintering temperature of 1200 °C. The phase structure of the material was determined by X ray and the thermal expansion coefficient was measured by dilatometer, while the TG-DTA analysis of the prepared material was also carried out. The results showed that zirconium tungstate with high purity could be obtained by rapid chilled while fired at 1200 °C. The coefficient of thermal expansion at 300 °C was minus 8.5413 × 10^-6K^-1, which is identical with the theoretical value. The thermal expansion coefficient of the material was negative fired lower than 750 °C, while it was positive fired higher than 750 °C, and this indicates that the decomposition temperature of zirconium tungstate is about 750 °C.

Abstract: A zirconium tungstate (ZrW2O8) precursor was synthesized by a novel sol-gel method with zirconium oxychloride and tungstic acid as the zirconium and tungsten sources, respectively. Heat treatment at 600oC for 10 hours was adequate to crystallize the precursor. Use of excess zirconium source and the concentration of hydrochloric acid were found to affect the phase purity and crystallization temperature of ZrW2O8. Sizes of particles obtained were in submicron range in the absence of a microemulsion system. On the other hand, using water/oleylamine/hexane reverse micelle microemulsion technique monodispersed particles with sizes between 10 to 100nm were obtained. Nanoparticles were then successfully dispersed in a solvent with a carrier polymer to produce ZrW2O8 nanofibers with electrospinning technique.

Abstract: Tungstate-based inorganic−organic hybrid nanobelts/nanotubes were synthesized in a system of H2W2O7·xH2O/n-octylamine/heptane (n-octylamine:H2W2O7·xH2O molar ratio: 30), and the effects of the volume ratios of heptane to n-octylamine and the amounts of interlayer water in H2W2O7·xH2O on the formation behavior of the hybrids were investigated. The belt/tubelike hybrids obtained were 10–20 +m in length and 200–500 nm in apparent diameter. Large volume ratios of heptane to n-octylamine not only enhanced the degree of the long-range order of the lamellar structures in the hybrids, but they also improved the morphologic uniformity of the hybrids. The existence of interlayer water in H2W2O7·xH2O was indispensable to the formation of tungstate-based inorganic−organic hybrid nanobelts/nanotubes. The amounts of interlayer water in H2W2O7·xH2O varied over a wide range (x, from 0.85 to 4.1), had a neglectable effect on the morphology of the tungstate-based nanophase hybrids, but exerted a remarkable influence on the rate of the reaction of H2W2O7·xH2O with n-octylamine in the heptane solvent. The larger the amount of interlayer water, the more rapid the reaction rate.