1,721,038 research outputs found
The point of zero charge of Co3O4 prepared by thermal decomposition of basic cobalt carbonate
No full textCo3O4 has been prepared by thermal decomposition of basic CoCO3 in the temperature range 200 to 800 °C. The pzc has been measured by potentiometric titration and has been found to coincide with the iep determined by microelectrophoresis. The pzc is constant at ca. 7.3 between 200 and 450 °C. The GCSG model of the electrical double layer has been applied to the experimental data to derive the real surface area of the oxide and the inner layer capacitance. The electrochemical surface area coincides with BET data. The results of this work have been compared with those obtained previously with Co3O4 prepared by thermal decomposition of the nitrate. © 1995
Surface characterization of Co3O4 electrodes prepared by the sol-gel method
No full textCo3O4 layers on an Ni support were prepared by the sol-gel method. Their properties were characterized by TGA, XRD and SEM. For comparison, Co3O4 was also prepared by thermal decomposition of Co nitrate. The surface electrochemical response was studied in alkaline solution by cyclic voltammetry at several potential scan rates. The electrochemical analysis included the open circuit potential, the voltammetric peak potentials, and the voltammetric charge. Extrapolation of the charge to scan rates v = 0 and v = ∞ allowed the 'electrochemical porosity' to be estimated. The results suggest that Co3O4 from the sol-gel method is less crystalline and more porous, although the highest difference in terms of surface charge with respect to the oxide from the nitrate is only a factor of 2. © Elsevier Science S.A
Analisi quantitativa EDXRF su gemme: valutazione degli elementi cromofori presenti in traccia
No full textLo studio e la caratterizzazione dei materiali costituenti gioielli di oreficeria antica sono di elevato interesse e dal punto di vista tecnologico e dal punto di vista storico. L’analisi EDXRF si rivela spesso utile per la sua non distruttività; in particolare anche per quanto riguarda la caratterizzazione delle gemme. Nell’ambito del nuovo modello interpretativo recentemente discusso (ref) sulle cause del colore nelle gemme, il presente lavoro si prefigge di valutare entro che limiti l'analisi XRF consenta, tramite la valutazione dei coefficienti di assorbimento dei campioni in esame e la valutazione degli effetti di eccitazione secondaria, di ottenere una analisi quantitativa accurata soprattutto per gli elementi in traccia
Resistivity and carrier mobility of the SmBa2Cu3O6+x superconductor with different doping levels
No full textRaman and infrared spectra of Mn and Fe halides tetrahydrated
No full textThe infrared absorption spectra of the powdered samples and the Raman spectra of single crystals of MnCl2. 4H(2)O, MnBr2. 4H(2)O and FeCl2. 4H(2)O were recorded at liquid nitrogen temperature. Comparing the predicted and observed vibrational bands the spectra have been interpreted paying attention to the site symmetry of the metal atom and assuming only one formula unit in the Bravais cell. (C) 1998 Elsevier Science Ltd. All rights reserved
EDXRF quantitative analysis of chromophore chemical elements in corundum samples
No full textCorundum is a crystalline form of aluminum
oxide (Al2O3) and is one of the rock-forming minerals.
When aluminum oxide is pure, the mineral is colorless, but
the presence of trace amounts of other elements such as
iron, titanium, and chromium in the crystal lattice gives the
typical colors (including blue, red, violet, pink, green,
yellow, orange, gray, white, colorless, and black) of
gemstone varieties. The starting point for our work is the
quantitative evaluation of the concentration of chromophore
chemical elements with a precision as good as possible to
match the data obtained by different techniques as such as
optical absorption photoluminescence. The aim is to give
an interpretation of the absorption bands present in the NIR
and visible ranges which do not involve intervalence charge
transfer transitions (Fe2+ → Fe3+ and Fe2+ → Ti4+),
commonly considered responsible of the important features
of the blue sapphire absorption spectra. So, we developed a
method to evaluate as accurately as possible the autoabsorption
effects and the secondary excitation effects which
frequently are sources of relevant errors in the quantitative
EDXRF analysis
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
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