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Abstract: We report the results of our studies on oxygen permeability, phase stability, and chemical compatibility of a dual-phase membrane consisting of A-site deficient mixed-conducting perovskite, Sr0.95Fe0.5Co0.5O3−δ (SFC), and an ionically conducting fluorite, Ce0.9Gd0.1O2−δ (CGO), with 1:1 volume ratio. The permeation rate of the SFC–CGO membrane with activated surface was found to be appreciably high (~0.3mlcm−2min−1 at 850°C). More importantly, the perovskite phase of SFC in the dual-phase membrane remained stable even under the conditions where the single-phase SFC membrane undergoes phase transformation. Furthermore the results of spatially resolved electron energy-loss spectroscopy (EELS) analysis indicated no sign of chemical reaction or intermixing between the two oxide phases during the membrane operation, which is often reported to occur in the similar types of dual-phase membranes. Therefore this SFC–CGO dual-phase membrane may meet the requirements for the oxygen transport membrane (OTM) used in the oxy-fuel reactors. [Copyright &y& Elsevier]

Abstract: The presence of agglomerates during nanopowder sintering can be problematic and can limit achievable final densities. Typically, the practical solution is to use high pressures to overcome agglomerate breakdown strengths to reach higher packing fractions. The strength of agglomerates is often difficult to determine and makes processing parameters challenging to optimize. In this work, we used in situ transmission electron microscopy nanoindentation experiments to assess the mechanical properties of individual MgAl2O4 agglomerates under constant indenter head displacement rates. Electron microscopy revealed highly porous agglomerates with pores on both the micron and nanometric length scales. Individual agglomerate strength, at fracture, was calculated from compression tests with deformation behavior correlating well with previously reported modeling results. Macroscopic powder properties were also investigated using green-pressed pellets consolidated at pressures up to 910MPa. The unexpectedly high strength is indicative of the role agglomerates play in MgAl2O4 nanopowder densification. [Copyright &y& Elsevier]

Abstract: Here, we investigated the properties of Au nanoparticles prepared via three different techniques and supported on three different MgAl2O4 spinels. After careful characterization of bare and gold-loaded supports (XPS, BET, XRD, STEM) and catalytic test for the selective oxidation of glycerol, we concluded that the surface composition and area of the spinel play an important role in determining the selectivity of the catalyst as well as gold particle size. When supported on surface characterized by a similar Al/Mg ratio, gold clusters selectivity is not mediated by particle dimension. For example, large gold particles on MgAl2O4, which typically produce high selectivity to glycerate when supported on aluminum-rich surfaces instead, enhance the C–C bond cleavage reaction. Accordingly, the selectivity of similarly sized AuNPs on MgAl2O4 spinels with the same surface Al/Mg ratio is similar but we demonstrate that the activity depends on gold surface exposure (at.% Au by XPS) and on support surface area. [ABSTRACT FROM AUTHOR]

Electric field-assisted sintering techniques demonstrate accelerated densification at lower temperatures than the conventional sintering methods. However, it is still debated whether the applied field and/or resulting currents are responsible for the densification enhancement. To distinguish the effects of an applied field from current flow, in situ scanning transmission electron microscopy experiments with soft agglomerates of partially stabilized yttria-doped zirconia particles are carried out. A new microelectromechanical system-based sample support is used to heat particle agglomerates while simultaneously exposing them to an externally applied noncontacting electric field. Under isothermal condition at 900 °C, an electric field strength of 500 V/cm shows a sudden threefold enhancement in the shrinkage of the agglomerates. The applied electrostatic potential lowers the activation energy for point defect formation within the space charge zone and therefore promotes consolidation. Obtaining similar magnitudes of shrinkage in the absence of any electric field requires a higher temperature and longer time.