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Simulação do crescimento de filmes sobre metais. O caso voltamétrico
(Universidade Federal de São Carlos, 2008-07-02) Boscheto, Emerson Paulinho; D'Alkaine, Carlos Ventura; https://lattes.cnpq.br/8699821828310072; https://lattes.cnpq.br/3833998257213933
In this work the anodic film growth on metals has been studied, under voltammetric conditions by simulation. It was supposed that: a) the films are ultrathin, i.e., the concentration gradient contributions for the ionic transport throughout the film are much lower than those of the electric field; b) the ionic transport throughout the film obeys an ohmic model where the film ionic resistivity varies during the transient in response to the injection and recombination of recombinant point defects. A new interpretation was given for the Flade potential as a function of the point defect concentration during a voltammetry. The simulations were able to reproduce some behaviors observed experimentally in current density curves versus potential during a voltammetry, such as the peak current density increment and dislocation for more anodic potentials while the sweep rate increases. The simulations have also shown that the point defect concentration passes by a maximum and the resistivity by a minimum in the course of a voltammetry. As regards to the hypotheses assumed during the application of the ohmic model for experimental results the simulations corroborate one of them, namely, that the curves of current density against the potential corrected by the potential drop in the film fall in a single curve for all sweep rates, and do not confirm another, namely, that the potential of minimum of resistivity coincides with the potential of peak current density.
Efeito de diferentes modelos experimentais sobre a expressão gênica e a atividade de metaloproteases no músculo esquelético
(Universidade Federal de São Carlos, 2008-07-02) Durigan, João Luiz Quagliotti; Salvini, Tânia de Fátima; https://lattes.cnpq.br/8295870661549352
Estudo do efeito da adição de Au, Pd e Pt em catalisadores Cu/CeO2 aplicados à reação de deslocamento gás-água a baixa temperatura
(Universidade Federal de São Carlos, 2008-07-02) Silva, André Leopoldo Macêdo da; Assaf, José Mansur; https://lattes.cnpq.br/9563312407691130; https://lattes.cnpq.br/3703720998942113
Cu/CeO2 catalysts doped with Au, Pd or Pt (WGSR) were prepared and applied in water gas shift reaction. The CeO2 support was prepared by four different way: urea co-precipitation-gelation (CeO2-UGC), hydrothermal method (CeO2-HT), precipitation with NH4OH (CeO2-P) and Pechini method (CeO2-Pe). The CeO2-ZrO2 oxide was prepared by Pechini (CeO2-ZrO2-Pe). The Cu deposition was performed by deposition-precipitation on CeO2- UGC, CeO2-HT and CeO2-P (3, 5 or 10wt% Cu/CeO2) and by impregnation on CeO2-Pe and CeO2-ZrO2-Pe. The Au, Pd and Pt (0,2, 0,5 or 0,8wt%) deposition was made by deposition-precipitation. The supports and supported catalysts were characterized by X ray diffraction (XRD), BET specific surface area, X ray energy dispersive spectroscopy (EDS), temperature programmed reduction (TPR), X ray photoelectron spectroscopy (XPS), electronic transmission microscopy (TEM), temperature programmed reduction with dispersive X-ray absorption spectroscopy (TPR-DXAS) and temperature programmed oxidation (TPO). The catalysts were tested in low-temperature water-gas shift reaction and the products were analyzed online by gas chromatography. The results showed that the addition of ZrO2 to CeO2 avoided the decrease of specific surface area of support. The CeO2-P support presented the higher specific surface area. The addition Au, Pd or Pt increased the activity of the catalysts with lower amount metal (< 3,0 wt%). In the catalysts with metal amount higher than 0,5 wt% only the Pd promoted catalysts showed the same or higher activity than copper catalysts. The bimetallic catalysts presented diverse behaviors. In the catalysts with Au the activity decreased with the increase of Au amount. On the other hand, the catalysts with Pd presented opposite performance, with the activity increasing when Pd amount increases. The Pt promoted catalysts do not showed activity changes with increase of Pt amount. The Pd showed the best performance among the materials tested as monometallic catalyst or as promoter in the copper catalysts.