Abstract
The corrosion protection of coatings can be reinforced by the addition of entrapped corrosion inhibitors. β-cyclodextrin (β-CD) can form inclusion complexes with small inhibiting organic molecules that, when entrapped in coatings, allow the inhibitor release and adsorption at corrosion initiation sites. In this paper, several Nuclear Magnetic Resonance (NMR)-based experiments (e.g., Complexation-Induced Shifts (CIS), NMR titration, Diffusion-Ordered Spectroscopy (DOSY)) were performed to study the stability and geometry of a complex formed by β-cyclodextrin with 5-mercapto-1-phenyl-tetrazole (MPT). The complex was also detected by Electrospray Ionization (ESI) mass spectrometry and characterized by Fourier Transform Infrared (FTIR) spectra. Its influence on the protectiveness of a silane coating against bronze corrosion was evaluated in plain (AR) and concentrated (ARX10) synthetic acid rain, under different exposure conditions. In particular, the time evolution of the polarization resistance values during 20 days in ARX10 and the polarization curves recorded at the end of the immersions evidenced a higher protectiveness of the coating with the β-CD–MPT complex in comparison to that containing only MPT or only β-CD. The cyclic AR spray test carried out on coated bronze coupons with cross-cut scratches evidenced the absence of underfilm corrosion starting from the scratches only in the complex-containing coating.
Highlights
The corrosion protection of an organic coating depends largely on the intrinsic barrier properties of the polymeric film towards oxygen, water, and aggressive species, but can be reinforced by entrapped corrosion inhibitors [1,2,3]
In the case of bronze artworks exposed outdoors, commercial coatings such as Incralac® and Soter® contain benzotriazole (BTA) that operates in the dual functions of an inhibitor of bronze corrosion and an anti-UV additive [4]
It was equipped by a deuterated triglycine sulfate (DTGS) detector, which allowed for the investigation of the 4000–400 cm−1 wavenumber region with a resolution of 4 cm−1
Summary
The corrosion protection of an organic coating depends largely on the intrinsic barrier properties of the polymeric film towards oxygen, water, and aggressive species, but can be reinforced by entrapped corrosion inhibitors [1,2,3]. In the case of bronze artworks exposed outdoors, commercial coatings such as Incralac® and Soter® contain benzotriazole (BTA) that operates in the dual functions of an inhibitor of bronze corrosion and an anti-UV additive [4] In these coatings, the inhibitor dissolves in the electrolyte (in the rain) and penetrates through the coating, so producing an inhibited solution that exerts a protective action at the coating/metal interface. The former polyelectrolyte-coated carriers can release inhibitor molecules due to local variations of solution pH linked to the onset of corrosion phenomena, while the latter carriers with intercalated inhibiting anionic species limit the access of aggressive anions, such as chlorides, to the metal substrate and release corrosion inhibiting species by ion-exchange phenomena Beside these carriers, cyclodextrins (CD) were used to host corrosion inhibitors due to their complexing capability towards small organic molecules with corrosion inhibition properties.
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