Influence of Embedded Nanocontainers on the Efficiency of Active Anticorrosive Coatings for Aluminum Alloys Part II: Influence of Nanocontainer Position

Abstract

The present work contributes to the coating design of active anticorrosive coatings for the aluminum alloy, AA2024-T3. Part II is a continuation of Part I: Influence of Nanocontainer Concentration and describes further surprising aspects of the design of nanocontainer based active anticorrosive coatings, which influence their performance. The studied coating system consists of a passive sol-gel (SiO(x)/ZrO(x)) matrix and inhibitor (2-mercaptobenzothiazole) loaded mesoporous silica nanocontainers (MBT@NCs), which are dispersed only in half of the coating volume. Varying position and concentration of MBT@NCs the synergetic effect of inhibitor amount and path length on the metal surface were analyzed, considering the balance between optimum barrier properties, active protection and adhesion. The impact of MBT@NC position on passive and active corrosion resistance was investigated by electrochemical impedance spectroscopy and scanning vibrating electrode technique. Increasing the distance between MBT@NCs and metal surface led to better barrier properties but worse active corrosion inhibition. These findings improve the understanding of the factors influencing the overall performance of active anticorrosive coatings and enable the development of a coating system with optimum anticorrosion efficiency.

Self-healing coatings in anti-corrosion applications

“…The encapsulation of corrosion inhibitors and the introduction of the capsules into the matrix of the coating are considered to be a viable way of avoiding the above disadvantages [27]. There are literature reports corroborating the more beneficial effect of inhibitor encapsulation on the quality of coatings in comparison with the cases in which an inhibitor is added directly to the coating [28].…”

“…Figure 6 schematically shows how a capsule is created using the particular methods [29]. As the building material, the following are used: poly(urea-formaldehyde) (PUF) [32][33][34][35], melamine-urea-formaldehyde (MUF) [35,36], phenol-formaldehyde [37], epoxy resin [38,39], methylene diphenyl diisocyanate (MDI) [40], poly(methyl methacrylate) (PMMA) [41,42], polystyrene [32,41], poly(allylamine) [43], polyvinyl alcohol (PVA) [43,44], polyurethane [40], polyphenol, amphiphilic block copolymers (polypyrrolidones, poly(ethylene oxide) [31], poly(caprolactone)) [31,32], cerium molybdate [45], zinc and aluminium nitrate [46,47], silica [27,32,[48][49][50], silver [42], gold [51], copper(II) sulphide [51], c-AlO(OH) [51], tin(IV) oxide [51] and titania oxides [42,52,53] and CaCO 3 microbeads [54]. The capsule material and the way of preparing capsules affect their shape and size.…”

“…The capsules are filled in different ways, e.g. by agitating the suspension of capsules and fillers, also under reduced pressure, the soaking of capsules in inhibitor solution and by applying the LBL deposition procedure [27,54,56,70]. In the case of soaking encapsulation, different inhibitor retention mechanisms can be distinguished.…”

“…In the considered example, CaCO 3 microbeads were used as containers [54]. Micro/nanocontainers can be incorporated into a polymeric coating [35,54,68,71], less often into a sol-gel coating [27,72], and sporadically into a metallic coating, e.g. one based on electrochemical nickel [73].…”

“…The amount of the inhibitor should be sufficient to assure a satisfactory degree of protection and small enough to preserve the barrier properties of the coating. Studies into the effect of the location of capsules in the coating have shown that coatings with containers located close to the metal surface provide better active protection against corrosion than coatings in which the coating layer with capsules is separated from the protected surface by an additional layer devoid of capsules [27]. The effect of the distribution of the encapsulated corrosion inhibitor in the coating matrix on the release of the inhibitor was determined through a theoretical analysis [74].…”