221 resultados para SOLID AMALGAMS


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Endo-polygalacturonase (endo-PG), exo-polygalacturonase (exo-PG) and pectin liase (PL) were produced by solid-state fermentation of a mixture of orange bagasse and wheat bran (1:1) with the filamentous fungus Penicillium viridicatum RFC3. This substrate was prepared with two moisture contents, 70% and 80%, and each was fermented in two types of container, Erlenmeyer flask and polypropylene pack. When Erlenmeyer flasks were used, the medium containing 80% of initial moisture afforded higher PL production while neither exo- nor endo-PG production was influenced by substrate moisture. The highest enzyme activities obtained were 0.70 U mL(-1) for endo-PG, 8.90 U mL(-1) for exo-PG, and 41.30 U mL(-1) for PL. However, when the fermentation was done in polypropylene packs, higher production of all three enzymes was obtained at 70% moisture (0.7 and 8.33 U mL(-1) for endo- and exo-PG and 100 U mL(-1) for PL). An increase in the pH and decrease in the reducing sugar content of the medium was observed. The fungus was able to produce pectin esterase and other depolymerizing enzymes such as xylanase, CMCase, protease and amylase. (c) 2005 Elsevier Ltd. All rights reserved.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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The corrosion resistance of three of the constituent phases in high copper dental amalgams has been investigated by electrochemical methods in 0.9% NaCl solution. Polarization curves show corrosion potentials most positive for gamma(1)-Ag2Hg3, followed by Ag-Cu, and gamma-Ag3Sn in agreement with the order of corrosion resistance deduced from the corrosion currents. Complex plane impedance plots at the open circuit potential showed distorted semicircles with diffusional components at low frequency for Ag-Hg and Ag-Cu, while for gamma-Ag3Sn a layer of corrosion products is formed, partially or completely covering the surface of the electrode. Impedance and noise spectra have been compared in the frequency domain, and show good agreement. (C) 2004 Elsevier Ltd. All rights reserved.

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Dental amalgams, formed by reaction of mercury with a powder alloy containing mainly Ag, Sn, Cu and Zn, have a complex metallurgical structure which can contain up to six phases. Their observed corrosion is thus a complex process, which involves contributions from each of the phases present as well as intergranular corrosion. It is thus of interest to investigate the corrosion of individual phases present in dental amalgams. In this work the corrosion behaviour in 0.9% NaCl solution of Ag-Hg, Ag-Sn and Sn-Hg phase components of dental amalgams was investigated by electrochemical methods. The corrosion resistance was found to decrease in the order gamma (1)-Ag2\Hg3, gamma -Ag3Sn and gamma (2)-Sn7Hg. (C) 2001 Elsevier B.V. Ltd. All rights reserved.