Evaluation of self-healing ability in protective coatings modified with combinations of layered double hydroxides and cerium molibdate nanocontainers filled with corrosion inhibitors

abstract

Nowadays, there is a strong demand on the search of thinner, but more effective organic coatings for corrosion protection of metallic substrates, like galvanised steel, used in the automotive industry. In order to guarantee effective corrosion protection of these coatings, and because chromate-based pigments cannot be used, one of the most attractive strategies consists on the modification of the organic matrix with nano-additives filled with corrosion inhibitors, which can be released to the active sites. In this work, two different nano-additives are explored as potential self-healing materials for the development of active protective coatings. These additives are layered double hydroxides and cerium molybdate hollow nanospheres loaded with mercaptobenzothiazole, as a corrosion inhibitor. These additives were added to epoxy primers, individually, or combining the two nanoadditives in the same layer. The electrochemical behaviour and the potential of self-healing ability were studied by electrochemical impedance spectroscopy, scanning vibrating electrode technique and scanning ion-selective electrode technique. The results reveal that both types of nanocontainers can provide effective corrosion inhibition on artificial induced defects, at different stages of the degradation process. Moreover, the results also show that there is a synergistic effect concerning corrosion inhibition and self-healing potential when a mixture of the two nanocontainers is used. The mechanism of self healing is presented and discussed in terms of effect of organic inhibitor and role of the nanocontainers, including effect of cerium ions released from cerium molibdate nanoparticles. (C) 2011 Elsevier Ltd. All rights reserved.

keywords

SOL-GEL COATINGS; GALVANIZED STEEL; THIAZOLE DERIVATIVES; ZINC; PRETREATMENTS; SVET; RESERVOIRS; ALUMINUM; SURFACE

subject category

Electrochemistry

authors

Montemor, MF; Snihirova, DV; Taryba, MG; Lamaka, SV; Kartsonakis, IA; Balaskas, AC; Kordas, G; Tedim, J; Kuznetsova, A; Zheludkevich, ML; Ferreira, MGS

Groups

G3 - Electrochemical Materials, Interfaces and Coatings

Projects

MUST - Multi-level protection of materials for vehicles by "Smart" nanocontainers (MUST )

Corrosion adn corrosion protection in multi-material systems (PTDC/CTM/108446/2008)

acknowledgements

The authors acknowledge the MUST (NMP3-LA-2008-214261) project, funded by the FP7 programme and all the partners that provided contributions to this work: Production of model coatings: Mr Thomas-Schmidt-Hansberg and Valerie Gandubert from Chemetall and their team; discussions with prof. Grundmeier and his group. A. Salak is acknowledged for XRD measurements on LDHs. Support by Portuguese Foundation for Science and Technology (FCT) through the project PTDC/CTM/108446/2008 is also acknowledged. D.V.S. and M.G.T. thank their personal FCT grants SFRH/BD/72497/2010 and SFRH/BD/72602/2010. J. Tedim thanks FCT for Post-Doctoral grant (Ref. SFRH/BPD/64335/2009).