« The study of mechanisms of galvanic corrosion between aeronautical structural parts and its control applying local electrochemical techniques » par M. Léonardo BERTOLUCCI COELHO

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Le 18 septembre 2018 À 10:00
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Campus Polytech - Salle académique

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Résumé :

Electrochemical corrosion is one major cause of economic losses in developed nations, because metals are known to undergo corrosion when exposed to water. The existing anti-corrosion approaches, developed for protecting single-material structures, generally fail when applied to control multi-material structures. In order to meet the actual energy saving policies, the aeronautical sector has employed higher contents of composite materials in combination with aluminium alloys. However, the situation in which dissimilar materials are electrically connected creates a high risk condition for the rise of galvanic corrosion. For that reason, huge efforts under progress aim at developing new strategies for active and passive corrosion protections of aeronautical materials, which specially refer to aluminium alloys and fibre-reinforced composites. In particular, the aerospace industry has an urgent interest on corrosion inhibitors because of the environmental regulations concerning the hexavalent chromium, by virtue of its attested toxic and carcinogenic properties. In parallel, the relatively recent local electrochemical techniques have been able to successfully extract useful information on the corrosion and corrosion inhibition processes at the micro-scale level. For instance, the Scanning Vibrating Electrode Technique (SVET) stands out as an important monitoring tool suitable for galvanic coupling inhibition analyses, being widely reported in the literature. In this work, two of the most recurrent galvanic couplings encountered in aeronautics were investigated: aluminium/copper and AA2024/carbon fibre-reinforced polymer (CFRP). First, an Al/Cu galvanic coupling model suitable for SVET analysis was elaborated in view of simulating a galvanic couple characteristic of AA2024 and the inhibitive effects provided by benzotriazole and cerium chloride were evaluated, separately and combined, in neutral aerated NaCl solutions. Next, their inhibitive effects on actual AA2024 samples were assessed by means of Electrochemical Impedance Spectroscopy. Concerning the AA2024/CFRP galvanic coupling investigation, two distinct local electrochemistry approaches were considered by employing models with different alloy/graphite area ratios. In the first one, several organic and inorganic compounds were evaluated as potential inhibitors for the AA2024-T3/graphite galvanic corrosion in NaCl solution. SVET and Zero Resistance Ammeter were applied in order to directly measure the current densities related to the galvanic corrosion processes. The second approach consisted of applying SVET and SIET for quasi-simultaneous measurements of, respectively, the current density and pH distributions associated with the corrosion of the galvanic couples exposed to inhibitor-containing (cerium salt or triethanolamine) NaCl solutions.

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