Phosphate-Based Organic Molecules Interleaved with Layered Double Hydroxide: Unraveling the Roles of Host Cations and the Guest-Inhibiting Effect in Aluminum Corrosion Protection

• Published in: European journal of inorganic chemistry 2012-11, Vol.2012 (32), p.5396-5404
• Main Authors: Stimpfling, Thomas, Leroux, Fabrice, Hintze-Bruening, Horst
• Format: Article
• Language: English
• Subjects: Alumnium; Corrosion; Layered compounds; Organic-inorganic hybrid composites; Polymer coatings
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201200504

The incorporation of 2‐hydroxyethyl phosphate (2‐HEP) into layered double hydroxide (LDH) galleries results in the formation of new organic–inorganic hybrid assemblies, subsequently studied as a functionalized filler with regards to their corrosion inhibition as an epoxy‐based polymer primer coating of aluminum AA 2024. Hybrid layered assemblies as well as the concomitant conveivable processes that consist of the release of interleaved 2‐HEP and the uptake of corrosive Cl– anions were studied by X‐ray diffraction. From DC polarization experiments, it is demonstrated that the anodic corrosion inhibition of 2‐HEP is not impeded when the molecule is intercalated in the LDH container despite the absence of its release through anion exchange. Owing to the relatively low anticorrosive activity of 2‐HEP, the importance of the dissolution of the platelets over the course of the anodic corrosion process is uncovered in addition to the impact of the particles on barrier effects. In accordance with discussed anticorrosive mechanisms, the results reveal that the Mg2+‐based LDH host accelerates cathodic oxygen reduction, whereas the Zn2+‐based counterpart reduces anodic metal (or copper) dissolution. Additionally, through electrochemical impedance spectroscopy that probes the coating resistance after long immersion times, Zn2Al/2‐HEP hybrid LDH phase was found to perform as well as a chromate‐bearing LDH. The synergistic effect of an organic corrosion‐inhibitor agent combined with an appropriate chemical composition of an inorganic layered double hydroxide (LDH) host structure prevents the corrosion of aluminum alloy 2024. The dissolution of the LDH framework during the anodic corrosion process provokes the release of both cation and anion corrosion‐inhibitor species.