Localized dealloying corrosion mediated by self-assembled monolayers used as an inhibitor system

Abstract

The structure and chemistry of thiol or selenol self-assembled organic monolayers have been frequently addressed due to the unique opportunities in functionalization of materials. Such organic films can also act as effective inhibition layers to mitigate oxidation or corrosion. Cu-Au alloy substrates covered by self-assembled monolayers show a different dealloying mechanism compared to bare surfaces. The organic surface layer inhibits dealloying of noble metal alloys by a suppression of surface diffusion at lower potentials but at higher applied potentials dealloying proceeds in localized regions due to passivity breakdown. We present an in situ atomic force microscopy study of a patterned thiol layer applied on Cu-Au alloy surfaces and further explore approaches to change the local composition of the surface layers by exchange of molecules. The pattern for the in situ experiment has been applied by micro-contact printing. This allows the study of corrosion protection with its dependence on different molecule densities at different sites. Low-density thiol areas surrounding the high-density patterns are completely protected and initiation of dealloying proceeds only along the areas with the lowest inhibitor concentration. Dealloying patterns are highly influenced and controlled by molecular thiol to selenol exchange and are also affected by introducing structural defects such as scratches or polishing defects.

Planar Arrays of Nanoporous Gold Nanowires: When Electrochemical Dealloying Meets Nanopatterning

“…Free corrosion, which consists in the direct exposure of a metal alloy to a highly corrosive electrolyte such as nitric acid, is the simplest way to apply the dealloying approach. , Dealloying can be also performed using an electrochemical process in a less corrosive electrolyte . In comparison to free corrosion, electrochemical dealloying provides better results, since it allows an accurate real-time control of the dealloying process via a direct monitoring of the electrochemical parameters. , …”

In Operando Atomic Force Microscopy Imaging of Electrochemical Interfaces: A Short Perspective

“…[51] Localized dealloying occurs with a variation in pit density at higher electrochemical (critical) potentials on the different inhibitorprotected surfaces. [52,53] It is noted that this SEM image illustrates the clear necessity of complementary characterization in parallel with the AFM study and a wise choice of samples and location to avoid picking up nonrepresentative reactions (a typical AFM fieldof-view is shown in Figure 2). This is important to consider, in particular for AFM devices with a smaller field-of-view (typical scan areas are between 30 and 100 μm 2 ), when studying course-grained polycrystalline surfaces, or for processes which occur at a small number of locations only, such as local breakdown or pitting.…”

“…a-d) Reproduced with permission. [53] Copyright 2015, Royal Society of Chemistry. e) Reproduced with permission.…”

“…The height appears larger and the stiffness of the boundary region is higher as visible from the lower phase shift. a-d) Reproduced with permission [53]. Copyright 2015, Royal Society of Chemistry.…”

Corrosion chemistry closing comments: opportunities in corrosion science facilitated by operando experimental characterization combined with multi-scale computational modelling

“…Some topics of focus included replacement pigments for chromate, novel graphene and electro-reactive coatings, water uptake in intact organic coatings and lm forming or molecular adsorbing inhibitors. [16][17][18]25,[42][43][44][45] The benets of atomistic scale observation were evident from the study of adsorbing inhibitors in the case of dealloying. Here, adsorbing inhibitors which formed a lm and limited surface diffusion were effective towards limiting dealloying from solid solution alloys where one element was displaced far from its equilibrium oxidation potential.…”