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Browsing by Author "Fonseca, I. T. E."

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  • Galvanic corrosion of two non noble dental alloys
    Publication . Capelo, S.; Proença, L.; Fernandes, J. C. S.; Fonseca, I. T. E.
    "This study aims to evaluate the corrosion resistance of two nonnoble dental alloys, namely, the Wiron®88 (Ni–Cr–Mo) and the Remanium 2000+ (Co–Cr–Mo–W). A noble alloy, the V-Gnathos® Plus (AuPt) previously studied was also considered for the purpose of comparison. The study was conducted in artificial saliva, pH 7.1, at 37 °C, by cyclic and linear sweep voltammetry, electrochemical impedance spectroscopy and chronoamperometry. The Rp value of the alloy of high contents of Ni, the Wiron®88, was 26.2±0.2 kΩ cm2 and of the one with high contents of Co, the Remanium 2000+, was 22.5±0.6 kΩ cm2. Data from linear polarization resistance and electrochemical impedance spectroscopy lead to the same order for the resistance against corrosion. The order from the less to the more reactive alloy is: Wiron®88 → Remanium 2000+. The galvanic cell obtained by coupling the two nonnoble alloys presents very low cell potential (a few mV, -18 mV), while the galvanic cell between one noble alloy (the V-Gnathos® Plus) and the Wiron®88 showed a higher cell potential (-104 mV). Both galvanic couples, under short circuit, have lead to the release of cations, namely, Co2+, in the case of the Wiron®88|Remanium 2000+ and Ni2+ for the Wiron®88|V-Gnathos® Plus, galvanic couples, respectively, with the ionic concentrations reaching values of 12.15 and 7.30 μg L-1 (7.30 ppb), respectively. SEM micrographs obtained after 25 days immersion in artificial saliva, at 37 °C, showed the formation of well-defined pits on the surface of the two non-noble alloys."
    2014Journal article Open access Show more
  • The corrosion resistance of Wiron88 in the presence of S. mutans and S. sobrinus bacteria
    Publication . Proença, L.; Barroso, H.; Figueiredo, N.; Lino, A. R.; Capelo, S.; Fonseca, I. T. E.
    "The corrosion resistance of Wiron®88, a Ni–Cr–Mo alloy, was evaluated in liquid growth media in the absence and presence of the Streptococcussobrinus and Streptococcus mutans strains. Open circuit potential measurements, cyclic voltammetry, linear sweep voltammetry, as well as electronic microscopy coupled to electron diffraction spectroscopy (SEM/EDS), were the main techniques used in this study. It was concluded that the presence of S. sobrinus and S. mutans have only a slight effect on the corrosion resistance of the Wiron®88 alloy, with the S. mutans being slightly more aggressive. For both strains the corrosion resistance Rp is of the same order (kΩ cm2). After 24 h immersion the S. sobrinus lead to and Rp of 11.02, while the S. mutans lead to of 5.59 kΩ cm2. SEM/EDS studies on the Wiron®88 samples, with 24 days of immersion, at 37 °C, have confirmed bio-corrosion of the alloy occurring through the dissolution of Ni as Ni2+ and formation of chromium and molybdenum oxides. The bacterial adhesion to the surface is not uniform."
    2015-01Journal article Restricted access Show more