Key Engineering Materials Vols. 368-372

Abstract: The series of powders with the general formula of Ce0.8-xZrxLa0.2O1.9 (x=0, 0.05, 0.10, 0.15) and Ce0.8-xZrxY0.2O1.9 (x=0, 0.05, 0.10, 0.15) were synthesized by the sol-gel method. The samples sintered at 1500°C all possess the single phase with cubic fluorite structure. The lattice parameter and the ionic conductivity decrease with increasing the content of Zr. However, the ionic conductivity of ceria co-doped with Zr and La reduces with decreasing the lattice strain.

Abstract: Pr2O3-doped ceria nanopowders were synthesized by a nitrate-citrate combustion process. This route is based on the gelling of nitrate solutions by the addition of citric acid and ammonium hydroxide, followed by an intense combustion process due to an exothermic redox reaction between nitrate and citrate ions. XRD analysis showed that no impurity were observed up to x=0.3 in Ce1-xPrxO2-δ systems. The influence of ignition temperature on the characteristics of the powders was studied. The change of the crystal structure with the content of doped Pr was investigated. The highest ionic conductivity, σ600°C=2.45×10-3S/cm, was found for the composition of x=0.15.

Abstract: Ni-BaCe0.9Y0.1O3-δ mixed protonic-electronic conductor can be used to separate hydrogen from syngas. Considering that water exists in syngas, it is necessary to evaluate the effect of moisture on chemical stability and hydrogen permeability of the cermet. In this paper, hydrogen permeation rates of Ni- BaCe0.9Y0.1O3-δ (40:60 in volume ratio) in different water partial pressures were measured at intermediate temperatures (600-750°C). It is found that hydrogen permeation rate of the cermet is highest at an appropriate water partial pressure. Samples after experiment were analyzed by XRD, ICP and pH value measurement, in which Ba(OH)2 and doped CeO2 were found. The reaction of water with samples resulting in insulating Ba(OH)2 and doped CeO2 is contributed to the decrease of hydrogen permeation in excessive water partial pressure.

Abstract: SrFe0.6Cu0.3Ti0.1O3-δ (SFCTO) composite-oxide powder was synthesized by citric acid complex method and studied as mixed oxygen-ionic and electronic conducting membrane material. The formation process of the perovskite-type compound was detected by XRD, infra-red spectrum and thermo gravimetric analysis; the effects of ethylene glycol added in the sol formation process on the size distribution of the powder and the oxygen permeation flux of the membrane were examined. A stable sol was formed when the molar ratio of total metal ions to citric acid and ethylene glycol was 1:2:3 and the pH value was 5.5; the characteristic absorption peaks of citric acid in the dried gel, O-H and -COO-, moved toward low frequency direction for 200 cm-1 and 135 cm-1 respectively due to the complexing action of the metal ions and citric acid. As the dried gel was heated in air up to 400°C, SrCO3 phase appeared by the combustion of citric acid and ethylene glycol. The perovskite phase started to form at 700 °C, SrCO3 phase reduced gradually and the single phase of SFCTO was obtained at 900 °C. The SFCTO dense membrane prepared under the optimum conditions exhibited an oxygen permeation flux of 0.7 ml·min-1·cm-2 at 900°C.

Abstract: A thick film type of limiting current oxygen sensor which uses yttria (8% mol) stabilized zirconia (YSZ) as oxygen ion conducting solid electrolytes and dense La0.8Sr0.2MnO3 (LSM) as diffusion barrier was developed successfully. The oxygen sensor showed excellent performance at oxygen concentrations ranging from 0 to 10 ppm. The advantages of the sensor are simple construction, low cost and potential long term stability.

Abstract: Mg ion conductors, MgAl2O4 and MgZr4(PO4)6, were prepared by solid state reaction. Their electrical properties were measured and their application in electrochemical sensors for on-line determination of Mg in molten Al in the refining process and alloying process was examined. The activation energies for Mg ion conduction in MgAl2O4 and MgZr4(PO4)6 are 2.08 eV and 1.7 eV, respectively. The sensors have been found to respond rapidly to the change of Mg content in molten aluminium around 1000 K.

Abstract: GdSrCoO3-δ and Gd1-XSrXCoO3-δ (x=0.1~0.5) were synthesized using glycine-nitrate process (GNP). The formation process of perovskite phase and microstructure of powders were characterized using TG-DTA and XRD. All the powders with different doping amounts of Sr2+ on A-site were single-phase solid solutions, and the stable perovskite phase was formed completely after calcination at 1100°C. The crystal structures of the solid solutions transfer to a higher symmetrical perovskite.

Abstract: The monoclinic LiMn0.9Cr0.1O2 irreversibly transforms to spinel-like structure m-LiMnO2 during the electrochemical cycling. Experimental results indicated that the (440) interplanar distance of LixMn2O4 at the charged state increases as the cycle number increases, while the (440) interplanar distance of LixMn2O4 at the discharged state decreases as the cycle number increases.A model for the transformation of monoclinic LiMn0.9Cr0.1O2 to the spinel LiMn2O4 is suggested. According to the suggested model, there may exist two types of s-LixMn2O4 when m-LiMnO2 transforms into s-LixMn2O4. The two types of spinel LixMn2O4 develop the nanodomain.

Abstract: A series of Mn-doped LiNi0.85−xCo0.15MnxO2 compounds (x= 0, 0.1, 0.2 and 0.4) were prepared by the co-precipitation method. The effect and mechanism of Mn–doping on the microstructures and crystallite sizes of LiNi0.85−xCo0.15MnxO2 cathode materials were studied. The non-equivalent substitution of Mn ions for Ni ions induces a decrease in the average valence of nickel ions. The Mn-doping promotes the formation of the single phase compounds with more ordered structure.

Abstract: This paper studied structures of ceria-carbonate two-phase composites, with an emphasis on the interfacial structures and interactions between the two constituent phases of ceria and carbonate. The phase structure was analyzed by DSC, XRD and SEM. The IR measurements were carried out to identify the bonding situations and interfaces. Some new absorptions and wavenumber shifts of the bands appeared in IR spectra. There are strong indications of the interfacial phenomena exist in the two-phase composites through comparison between the two-phase composite with each individual constituent phases. The results opened a new interesting subject on the two-phase composite structures with significant importance for applications in advanced low temperature (300-600°C) SOFC.