Forsyth and co-workers reported studies on combination of rare earth metallic element with a multifunctional organic component to achieve synergistic corrosion protection of AA2024. 24,25 Recently, Kallip and co-workers reported the synergistic inhibition of galvanically coupled Ze + Fe metals, when 1,2,3-benzotriazole and Ce(NO 3 ) 3 were combined.
26One topic that has not yet been covered in detail is the co-intercalation of different corrosion inhibitors within the same carrier. The incorporation of MBT in cerium molybdate hollow nanospheres were found to render corrosion protection to galvanized steel substrates when combined in coatings with LDH-MBT. 12 In this case, authors suggested that the inhibiting effect could be associated with MBT, as well as to dissolution of cerium and molybdate ions from the nanospheres under acidic conditions. Very recently, Ferrer and co-workers reported the preparation of NaY zeolites with cerium and diethyldithiocarbamate corrosion inhibitors, investigating the effect of this double-doped zeolite for corrosion protection of AA2024 alloy.27 Positive results were obtained with the zeolites in solution and when added to sol-gel coatings. Apart from these works, not much has been done in the co-intercalation of corrosion inhibitors.In this paper we go beyond mono-, towards multiintercalation and release of corrosion inhibitors in a controlled manner (Scheme 1). The strategy followed consists of using a system well known for its intrinsic controlled release mechanism (LDHs), modifying its surface with polyelectrolytes by the Layer-by-Layer (LbL) technique. The use of polyelectrolytes allows the intercalation of additional corrosion inhibitors between layers, which can be released due to pHdependent permeability of polyelectrolytes.
28,29The objective of this work is to investigate Zn-Al LDHs as containers for two corrosion inhibitors simultaneously. 2-mercaptobenthiazole (MBT), a well-known corrosion inhibitor for AA2024, 30 was intercalated in interlayer of the LDH structure by anion-exchange according to a procedure described in the literature, 31 while Ce 3+ , also known as an effective corrosion inhibitor for AA2024, 32 was adsorbed between polyelectrolyte layers on the surface of LDH-MBT platelets. The modied LDH particles (LDH-Mod) were characterized by X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). Furthermore, the inuence of LDH surface modication in the release of MBT was investigated by UV-visible spectrophotometry and correlated with electrochemical studies by DC polarization and electrochemical impedance spectroscopy (EIS), in solution and as additives to a hybrid sol-gel coating.
Experimental
MaterialsAll the chemicals were obtained from Aldrich, Fluka, and Riedel-de Haen, with $98% of ground substance, and used as received. AA2024-T3 with the following composition was used: Cu 3.8-4.9%, Mg 1.2-1.8%, Mn 0.3-0.9%, Fe 0.5%, Si 0.5%, Zn 0.25%, Ti 0.15%, Cr 0.1%, other 0.15%, balance Al. All the alloy pane...
