Synthesis of Highly Porous Yttria-Stabilized Zirconia by Tape-Casting Methods

Porous ceramics of Y₂O₃-stabilized ZrO₂ (YSZ) were prepared by tape-casting methods using both pyrolyzable pore formers and NiO followed by acid leaching. The porosity of YSZ wafers increased in a regular manner with the mass of graphite or polymethyl methacrylate (PMMA) to between 60% and 75% porosity. SEM indicated that the shape of the pores in the final ceramic was related to the shape of the pore formers, so that the pore size and microstructure of YSZ wafers could be controlled by the choice of pore former. Dilatometry measurements showed that measurable shrinkage started at 1300 K, and a total shrinkage of 26% was observed, independent of the amount or type of pore former used. Temperature-programmed oxidation (TPO) measurements on the green tapes demonstrated that the binders and dispersants were combusted between 550 and 750 K, that PMMA decomposed to methyl methacrylate between 500 and 700 K, and that graphite combusted above 900 K. The porosity of YSZ ceramics prepared by acid leaching of nickel from NiO–YSZ, with 50 wt% NiO, was studied as a function of NiO and YSZ particle size. Significant changes in pore dimension were found when NiO particle size was changed.     

Anodes for Direct Oxidation of Dry Hydrocarbons in a Solid‐Oxide Fuel Cell

The manufacture of fuel cells that can operate directly on various hydrocarbon fuels, without the need for reforming, has the potential of greatly speeding the application of fuel cells for transportation and distributed‐power applications. This paper will briefly review the literature in this area and describe recent developments in solid‐oxide fuel cells (SOFCs) that demonstrate that direct‐oxidation fuel cells are possible with Cu‐based anodes. A new method for synthesizing thin‐electrolyte, anode‐supported cells is described that is based on tape casting with graphite pore formers (see Figure), followed by impregnation with aqueous solutions of Cu(NO₃)₂ and Ce(NO₃)₃. The performance of model SOFCs for direct conversion of n‐butane and methane is shown. Finally, future developments that are needed for this technology to be commercialized are discussed.     

TPD study of the reaction of CH3CH2SH and (CH3CH2)2S2 on ZnO(0001) and ZnO

Superior activation of on 1 wt% Pt/TiO₂ catalysts for the oxidation of CO was attained by loading a large amount of Fe-oxide (100 wt%) and TiO₂. In situ IR spectra of CO proved that the structural transformation is brought about on the Pt-sites by loading of Fe-oxide, where predominant Pt-sites giving linear CO change to highly reactive bridge CO Pt-sites. In contrast, no transformation of the linear CO sites to the bridge CO sites takes place by loading of TiO₂ but the environment of Pt-sites for linear CO is changed.     

Perfectionism, perceived weight status, and self-esteem interact to predict bulimic symptoms: A model of bulimic symptom development.

An interactive model of perfectionism, perceived weight status, and self-esteem was tested on 342 female undergraduates to predict bulimic symptoms. Using a longitudinal design, the authors tested the model on data collected at 2 points: the spring of participants' senior year of high school and during participants' first year of college. The authors hypothesized and found that self-esteem moderates the interaction between perfectionism and perceived weight status in predicting bulimic symptoms. Women who are high in perfectionism and who consider themselves overweight exhibit bulimic symptoms only if they have low self-esteem (i.e., if they doubt they can attain their high body standards). High self-esteem women with the same diathesis-stress conditions are less likely to exhibit bulimic symptoms. These findings clarify the role of perfectionism in bulimic symptomatology. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An examination of praseodymia as an oxygen‐storage component in three‐way catalysts

The redox properties of praseodymia have been compared to those of ceria using temperature‐programmed desorption (TPD) of O₂ from films prepared by vapor deposition onto an α‐Al₂O₃(0001) support, in order to assess the potential for praseodymia as an oxygen‐storage component in three‐way catalysts. Desorption of O₂ was observed between 700 and 1000 K, and diffraction measurements confirmed that the films change from Pr₆O₁₁ to Pr₂O₃ in this temperature range. However, once reduced, the films could not be reoxidized by exposures to O₂ in the vacuum system. Evidence was found for oxygen transfer from Pr₆O₁₁ to supported Rh particles. Following CO adsorption on Rh particles deposited onto Pr₆O₁₁ film, significant amounts of CO₂ were observed in TPD until the film was completely reduced to Pr₂O₃. Following deposition of Rh particles onto Pr₆O₁₁, the oxygen desorption curves became identical to those normally observed for Rh. These results are compared with similar measurements performed on ceria films and the implications for automotive, emission‐control catalysis are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization of ceria films on α-Al2O3(0001) and polycrystalline zirconia using O2 TPD with labeled 18O2

The nature of weakly bound oxygen on ceria films was studied using temperature-programmed desorption with labeled ¹⁸O₂. For α- Al₂O₃(0001)-supported ceria, a desorption feature between 800 and 1300 K is shown to result from partial reduction of ceria. However, this oxygen accounts for only a small fraction of the total oxygen in the ceria film and isotopic labeling studies suggest that this oxygen does not exchange freely with the remaining oxygen in the film. In contrast, results for zirconia-supported ceria demonstrate that much more oxygen desorbs in the low temperature regime below 1300 K, and that there is significant isotope exchange throughout the ceria film and with the zirconia substrate. Finally, exposure of reduced, zirconia-supported ceria to water at 670 K resulted in reoxidation of the ceria film. Oxygen from ceria was then shown to react with CO adsorbed on supported Rh particles, completing the catalytic cycle for the water-gas-shift reaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Support effects in the dissociation of CO on Rh/CeO2(111)

The adsorption and reaction of CO on Rh particles supported on stoichiometric and partially reduced CeO₂(111) surfaces was studied using a combination of HREELS and TPD. A fraction of the CO adsorbed on the supported Rh particles was found to undergo dissociation to produce adsorbed C and O atoms. TPD results for isotopically labeled CO demonstrated that O atoms produced by CO dissociation rapidly exchange with the oxygen in the ceria lattice. The fraction of adsorbed CO which dissociated was found to increase significantly with the extent of reduction of the CeO₂(111) surface, suggesting that oxygen vacancies on the surface of the support play a direct role in the CO dissociation reaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Direct in situ determination of the polarization dependence of physisorption on ferroelectric surfaces

The ability to manipulate dipole orientation in ferroelectric oxides holds promise as a method to tailor surface reactivity for specific applications. As ferroelectric domains can be patterned at the nanoscale, domain-specific surface chemistries may provide a method for fabrication of nanoscale devices. Although studies over the past 50 yr have suggested that ferroelectric domain orientation may affect the energetics of adsorption, definitive evidence is still lacking. Domain-dependent sticking coefficients are observed using temperature-programmed desorption and scanning surface potential microscopy, supported by first-principles calculations of the reaction coordinate. The first unambiguous observations of differences in the energetics of physisorption on ferroelectric domains are presented here for CH(3)OH and CO(2) on BaTiO(3) and Pb(Ti(0.52)Zr(0.48))O(3) surfaces.