Papers by Keyword: Barium Cerate

Abstract: Crystalline barium cerate was synthesized by oxalate coprecipitation from nitrates of barium and cerium [1]. The oxalate precursor prepared by chemical methods was calcined at different temperatures up to 950°C. The barium cerate was studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). X-ray diffraction investigation enables the determination of the phases that originate at different stages of synthesis and the crystal structure of final barium cerate, as well. From XRD patterns the average size of coherent regions was estimated by using Halder-Wagner method [2]. Both size and shape of crystallites were also studied by scanning electron microscopy. It was found that crystallites of barium cerate arise within the initial particles of the oxalate precursor.

Abstract: Ceramics based on Y-doped BaCeO₃ were prepared by citrate process. The X-ray fluorescence shows that barium stoichiometry deviation is established during calcination step. Through the SEM analysis of fracture surface of sintered samples it was possible to infer that powder highly deficient of barium shows higher diffusion coefficient during sintering than stoichiometric powder promoting grain growth and, consequently, trapping pores into the grains.

Abstract: Protonic conductors of BaZr_0.5Ce_0.3Ln_0.2O_3-δ (BZCLn532, Ln=Y, Sm, Gd, Dy) were successfully synthesized by using a cost-effective solid state reactive sintering (SSRS) method with 1 wt.% NiO was added as a sintering aid. The pellets of the BZCLn532 were obtained at sintering temperatures between 1300 - 1600 °C. The results show that the morphologies and the final relative densities of the obtained BZCLn532 pellets are influenced significantly when different sintering temperatures were applied. Densified pellets of the BZCLn532 can be prepared at sintering temperatures of 1600 °C (BaZr_0.5Ce_0.3Y_0.2O_3-δ) and 1400 °C (BaZr_0.5Ce_0.3Sm_0.2O_3-δ, BaZr_0.5Ce_0.3Gd_0.2O_3-δ and BaZr_0.5Ce_0.3Dy_0.2O_3-δ,). The conductivity results show that the BaZr_0.5Ce_0.3Y_0.2O_3-δ (BZCY532) and BaZr_0.5Ce_0.3Dy_0.2O_3-δ (BZCD532) ceramics are demonstrated to be good candidates of oxygen ion conductor and proton conductor materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) applications.

Abstract: Doping perovskite structure ceramics constitute an important type of solid oxides fuel cell (SOFC) cathode materials. In this study, BaCe1-xTaxO3+δ powders were prepared by solid state reaction at 1500oC for 4h. BaCe1-xTaxO3+δ ceramics were pressureless sintered at 1600oC for 5h. The results indicated that the relative density of BaCe1-xTaxO3+δ ceramics reached the range of 84.15 - 90.88%. At the frequency of 1Hz, the conductivity of BaCe0.65Ta0.35O3+δ ceramic samples varied greatly, when the testing temperature rose from room temperature to 900oC in increments of 100oC. The highest conductivity was obtained at 600oC with the value of 6.74×10-5 S/cm.

Abstract: The perovskite-type Ba(Zr_0.63Ce_0.27)Y_0.1O_3-δ (BZCY) was synthesized by solid-state reaction. Sintering behavior and electrical conductivity of the electrolyte materials were improved through optimizing the content of ZnO as sintering aid. The obvious enhancement of density of sintered body was observed due to ZnO reacting with BZCY powder. Relative densities of the samples increased with ZnO content added. A conductivity of 9.27×10^-3 S/cm tested in humid hydrogen at 800°C was obtained when the ZnO content was 2 mol%. A peak power density of 12.4 mW/cm² was delivered based on a single fuel cell with electrolyte-supported configuration.

Abstract: Polycrystalline ytterbium-doped barium cerate with composition BaCe0.95Yb0.05O3- has been fabricated by solid state reaction. The compound has an orthorhombic perovskite structure and a fine and homogeneous grain size distribution, with a mean value of 0.4 m. The creep behavior was studied by means of constant crosshead-speed compression tests in air at temperatures of up to 1300 °C. At the lower strain rates and higher temperatures, the material deformed by grain boundary sliding; the corresponding true stress-true strain curves displayed an initial strength drop followed by an extended steady state stage. A continuous transition towards a brittle regime was observed with increasing initial strain rate and/or decreasing temperature.

Abstract: BaCe0.9Y0.1O3-a and SrCe0.9Y0.1O3-a powders were synthesized by both the solid-state reaction method and the liquid citrate method. The shrinkage, porosity and relative density of membranes prepared from these powders were determined, after sintering at 1550°C (BaCe0.9Y0.1O3-a membrane) or 1450°C (SrCe0.9Y0.1O3-a membranes) for 3 hours. The XRD patterns show that the crystal structures of the prepared powders and the sintered membranes are orthorhombic perovskite structures. The membranes prepared from the powders synthesized by the solid-state reaction method are denser than those from the powders synthesized by the citrate method with the same composition under the identical sintering conditions.