Papers by Keyword: Zirconium Tungstate

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: Negative thermal expansion material ZrW₂O₈ was synthesized by hydrothermal method. The prepared ZrW₂O₈ and the precursor were characterized by x-ray diffractometer, thermo-gravimetric/differential thermal analyzer, FT-IR spectrometer and scanning electron microscope. The results show that a single-phase ZrW₂O₈ can be synthesized when HCl concentration is as low as 4mol/L. ZrW₂O₈ was obtained through the precursor dehydration and debonding O-H bond. The dehydration reaction includes two stages. There is a sharp endothermic peak in the first stage of the dehydration reaction and the second stage is a slow endothermic process. A new phase appeared when the sintering temperature is above 600 °C. ZrW₂O₈ and the precursor have the same rod-like shape and grow up along a specific direction. The synthesized ZrW₂O₈ particles obtained from 4mol/L HCl appeared large size. It became much finer and the rod with multiple crystal face was easy to form when the concentration of HCl increased to 6~8 mol/L.

Abstract: The Cu/ZrW₂O₈ gradient films have been deposited on silicon substrates by RF magnetron sputtering with copper and compound targets followed by annealing in argon atmosphere at 750 °C for 3 min. The three different compound targets were B1 (nZrO₂:nWO₃=1:2.2), B2 (nZrO₂:nWO₃=1:2.5) and B3 (ZrW₂O₈), respectively. The as-deposited gradient films were amorphous, while a post-deposition annealing at elevated temperature was required for the development of the cubic ZrW₂O₈. The structure and surface morphology of the gradient films were then studied using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometer (EDS). The globular and slender rod crystals can be found in annealed films, which are copper and ZrW₂O₈, respectively. The fine gradient film should be obtained using the target B1.

Abstract: Availability of advanced materials has opened up opportunities in meeting several functional requirements through hybridization. Hybrids consisting of ceramics, metals and high performance polymers could benefit many aircraft and space satellite applications. They could meet requirements of low weight, high environmental stability, and high thermal or dimensional stability. In this study, hybrid materials consisting of high performance polymer, porous ceramics (glass microballoons) and other constituents such as Zircornium Tungstate (with negative coefficient of thermal expansion (CTE)) and nanoclay were studied. Specimens were successfully produced with a range of density from 0.4 to 1.1 g/cm3 depending on the degree of fill in the syntactic foams. CTE tailoring was achieved to greatly reduce the residual stress arising from processing and CTE mismatch of dissimilar materials. The evaluations of dimensional stability were examined from thermomechanical analysis. The synergistic effects of resin, ceramic constituents and pores on the hybrid properties will be presented.

Abstract: The mismatch of the coefficient of the thermal expansion (CTE) is one of the main causes of crack initiation and delamination for carbon fiber-reinforced polymer hybrids and metal/polymer hybrid materials. In this research, a negative CTE ceramic material (zirconium tungstate) was incorporated with a thermoset polymer (bismaleimide) resulting in a ~40% reduction in CTE and a significant improvement in thermal stability. The morphology showed good dispersion of the zirconium tungstate particles within the bismaleimide. Comparisons of the experimental CTE values with the rule-of-mixture and the analytical micromechanical models will be discussed.

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.