Ammonium molybdate added in hybrid films applied on tinplate: Effect of the concentration in the corrosion inhibition action

• Hybrid films are stable and transparent, and protecting the tinplate from corrosive attack.
• Hybrid films are constituted by a silica network linked to poly(methylmethacrylate).
• Protection mechanism from corrosion is based the release of molybdate ions.

One of the ways to improve the anticorrosive properties of the hybrid films is with the addition of corrosion inhibitors based on inorganic salts. The protection mechanism involves the release of molybdate ions inserted in coatings by sol–gel during the immersion in the electrolyte, thereby minimizing the corrosion process. Siloxane–PMMA hybrid films are constituted by a silica network, to which the chains of poly (methyl methacrylate) (PMMA) are connected by covalent bonds (Class II) or by physical interactions (Class I). The stability and transparency enable the application of these materials in the coating of tinplate packagings in order to enhance corrosion resistance and reduce the brittleness of these products. In this context, the objective of this study is to coat the tinplate with a hybrid siloxane–PMMA (Class II) film obtained from a sol constituted of the alkoxide precursors: 3-(trimethoxysilylpropyl) methacrylate (TMSM), poly(methyl methacrylate) PMMA and tetraethoxysilane (TEOS), by varying the added corrosion inhibitor concentration from 0.01 to 0.02 M. The films were obtained by a dip-coating process and characterized according to their morphological and electrochemical behavior. The results showed that hybrid films doped with corrosion inhibitors showed an increase in the layer thickness in comparison to the inhibitor-free film. Furthermore, the addition of a higher concentration of ammonium molybdate resulted in an increase of the corrosion performance of the hybrid films.