1,720,962 research outputs found
Raman and X-ray investigations of the incorporation of Ca2+ and Cd2+ in the ZrO2 structure
No full textThe formation of solid solution and ZrO2 phase stabilization were investigated by Raman spectroscopy and X-ray diffraction (XRD) in calcium-containing and cadmium-containing zirconium oxide samples heated at 1073 K in air. The adopted preparation procedure led to the incorporation of calcium and cadmium in solid solution into the zirconia structure. The solid solution favored the tetragonal and cubic zirconia phases at the expense of the thermodynamically stable monoclinic modification. Combined macro-and micro-Raman spectroscopy disclosed that instead of forming a homogeneous phase t '', intermediate between the tetragonal t' and the cubic phase, the tetragonal and cubic phases coexisted in the range 9.49-13.89 mol% for Ca and 11.88-17.23 mol% for Cd. At higher dopant contents the cubic form stabilized. The impurity content necessary to stabilize the high-symmetry phases was defined. Copyright (C) 2007 John Wiley & Sons, Ltd
Characterization of vanadium oxide on ZrO2-based catalyst precursors
No full textZirconia-supported vanadium oxide catalysts precursors were prepared by equilibrium adsorption in acid (pH 2.7) and basic (pH 10) conditions using hydrous zirconium oxide, ZrO2(383). After drying at 383 K the solids, containing vanadium up to 8.94%, were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, diffuse optical reflectance, surface area, differential thermal analysis measurements and chemical determinations. Samples of definite grain size ranges of ZrO 2(383) were also investigated. The results show that the pH affects the uptake and the nature of the V adsorbed species. The microporous nature of the support and the different anions size (small vanadium species at pH 10; large polyoxoanions at pH 2.7) affect the spreading degree of vanadium species. Under ambient conditions, the molecular state of the adsorbed species depends on the net surface pH at the point zero charge, that in its turn, is affected by the vanadium loading. During heating, the dispersed species interact with the zirconia surface. The DTA results indicate that the fraction of zirconia involved in the interaction depends on the pH of preparation
Characterization of VOx/ZrO2 Catalysts and their Activity in the Oxidation of Carbon Monoxide
No full text"Effect of Na+ ions on some properties of hydrous and thermally decomposed zirconium oxide"
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Morphological and textural characterization of vanadium oxide supported on zirconia by ionic exchange
No full textZirconia-supported vanadium oxide samples containing vanadium up to 6.8 wt.% were prepared by ionic exchange using aqueous solution of peroxovanadate complexes and hydrous zirconium oxide. The samples, heated at 823 K for 5 h in air, were studied by several techniques, including X-ray diffraction, surface area determinations, diffuse reflectance spectroscopy (UV-vis), Raman spectroscopy, pore size distribution measurements and atomic force microscopy. The results showed that the preparation procedure applied leads to good vanadium dispersion. The interaction between the anchored surface species and the support affects some ZrO(2) properties, including texture and phase transition. Depending on the vanadium loading, several species formed. In the most diluted sample small polyvanadate entities predominate, whereas at increasing vanadium loading (up to about 6 V atoms nm (2)) more condensed species formed yielding granular-type surface aggregates. At higher loading, granular-type particles and large. at structures, due to amorphous two- or three-dimensional polyvanadate species and ZrV(2)O(7)-like structures developed. Treatments with an ammonia solution specified that only a fraction of the vanadium species ( in a polymeric form) interacts with the zirconia surface. Atomic force microscopy directly imaged the formation of vanadium aggregates ( superimposed to the interacting species) at increasing vanadium content and their removal by the ammonia leaching. (C) 2008 Elsevier B. V. All rights reserved
Formation and stability of RuIII incorporated in TiO2 (rutile)
No full textTitanium dioxide containing a few percent of ruthenium has been investigated by electron spin resonance and X-ray diffraction. Prolonged treatment in hydrogen at temperatures < 350 °C or the addition of NbV to the rutile structure leads to the formation of the paramagnetic RuIII in solid solution. Upon increasing the temperature of the hydrogen treatment, the reduction is continued to RuII in solid solution and finally to Ru0 as a segregated phase
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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