Graphene-polymer nanocomposites Coatings for Corrosion Inhibition of Mg

摘要

Mg is a very promising material for lightweight construction and biomedical applications. However,the applicability of Mg and its alloys is hindered by its high corrosion susceptibility. [1] Moreover,due to the toxicity of most inorganic conversion coating systems, the development of novel pretreatmentstrategies for technical alloys are of vital importance. Recently, the application ofintrinsically conducting polymers (ICPs) have been introduced as an alternative approach forcorrosion protection of Mg alloys. [2] ICPs with electronic conductivity are known to be able topassivate small defects, however they fail in the presence of large defects due to fast coatingreduction and increased cation transport if macroscopically extended percolation networks exist.[3]The aim of this study is to develop graphene-polymer nanocomposite thin films for corrosionprotection of Mg-alloys. As polymer matrix, poly(4-vinyl pyridine) (P4VP) was selected due to itssemiconducting properties and protonic conductivity. In contrast to ICPs with electronicconductivity, the pH-dependant, reversible protonation/de-protonation capability of the P4VP hasbeen utilized to synthesize environment-responsive coatings. Graphene sheets, synthesized viaexfoliation of graphite in the presence of perylene tetracarboxylic acid (PTCA) were incorporated asnanofillers to create more tortuous path for the diffusion of corrosive ions and water, to minimizepercolation effects, as well as to improve the mechanical properties of the nanocompositecoatings.The macroscopic corrosion properties of the nanocomposite coatings were investigated by meansof electrochemical methods such as linear sweep voltammetry (LSV) and electrochemicalimpedance spectroscopy (EIS) in different corrosive media simulating technical and biomedicalapplications. For both environments significant reduction in anodic corrosion activities have beenobserved, which indicates a suppression of both Mg-dissolution and anodic hydrogen evolutionreactions. Electrochemical studies were complemented by in situ Atomic Force Microscopy (AFM)investigations to analyse localized corrosion processes and coating degradation in the presence ofartificial defects as well as under simultaneous corrosive and mechanical load.The presentation will summarize our recent results on the synthesis and characterization of thisnovel coating system with a special focus on their interfacial stability and corrosion protectionproperties.