In situ surface film evolution during Mg aqueous corrosion in presence of selected carboxylates

Mechanisms of inhibition of Mg aqueous corrosion in presence of chloride by sodium salicylate (Sal), 2,5-pyridinedicarboxylate (PDC) and fumarate (Fum) were studied by in situ Raman spectroscopy, ATR-FTIR, GD-OES and hydrogen collection. In situ detected surface films were composed by Mg(OH)2 nano-crystals and included inhibitors. All carboxylates significantly modified Mg(OH)2 growth kinetics as well as pevented chloride incorporation in the film. Vibrational spectra of the surface films demonstrated specific interactions between the carboxylates and the surface: adsorption of Sal and Fum on the oxide/hydroxide, precipitation of coordination polymer by PDC, dissolution of iron inclusions via formation of iron-Sal soluble complexes.publishe

Active corrosion protection of AA2024 by sol-gel coatings with cerium molybdate nanowires

Amorphous cerium molybdate nanowires (CMN) have been used to impart active corrosion protective properties to hybrid sol-gel coatings on AA2024. Inhibitive ability of the novel sal-gel coatings against corrosion has been studied in detail by electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET). Localized electrochemical measurements demonstrate significant suppression of corrosion activity in micro-scale defects made in sal-gel coatings loaded with CMN when compared to blank systems. The mechanism of active protection involves release of cerium and molybdate ions from the sal-gel coating during immersion in NaCl electrolyte and their inhibiting action in corroding defects. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved

Influence of stripping and cooling atmospheres on surface properties and corrosion of zinc galvanizing coatings

In this work the influence of stripping/cooling atmospheres used after withdrawal of steel sheet from Zn or Zn-alloy melt on surface properties of Zn (Z) and Zn-Al-Mg (ZM) hot-dip galvanizing coatings has been studied. The aim was to understand how the atmosphere (composed by nitrogen (N-2) or air) affects adhesion strength to model adhesive and corrosive behaviour of the galvanized substrates. It was shown that the surface chemical composition and Volta potential of the galvanizing coatings prepared under the air or nitrogen atmosphere are strongly influenced by the atmosphere. The surface chemistry Z and ZM surfaces prepared under N-2 contained a higher content of metal atoms and a richer hydroxide density than the specimens prepared under air atmosphere as assessed by X-ray photoelectron spectroscopy (XPS). The induced differences on the microstructure of the galvanized coatings played a key role on the local corrosion induced defects as observed by means of in situ Atomic force microscopy (AFM). Peel force tests performed on the substrates coated by model adhesive films indicate a higher adhesive strength to the surfaces prepared under nitrogen atmosphere. The obtained results have been discussed in terms of the microstructure and surface chemical composition of the galvanizing coatings. (C) 2016 Elsevier B.V. All rights reserved

Initial stages of localized corrosion at cut-edges of adhesively bonded Zn and Zn-Al-Mg galvanized steel

The mechanisms of the initial stages of localized corrosion at cut edges were investigated for adhesively bonded Zn (Z) and Zn-Al-Mg (ZM) galvanized steel. The results provided strong evidence for the localized nature of corrosion of galvanized coatings at the cut edges and at the adhesive/zinc interface. In both cases a defined localized corrosion attack on zinc in Z sample was observed. On the contrary, in the case of the ZM specimen both zinc solid solution and eutectics exhibited local corrosion. The local attack at the adhesive/Z(ZM) interface was correlated with an anodic undermining process. It develops near the cut-edge surface and at the buried deep adhesive-zinc interface and results in adhesive disbonding in the buried interface. The electrochemical studies revealed that the corrosion kinetics at the metal cut-edges decreases during immersion, which could be due to formation of corrosion products on both steel and zinc surfaces. (C) 2016 Elsevier Ltd. All rights reserved