Electrochemical impedance spectroscopy (EIS) is a versatile tool for electrochemistry, particularly when applied locally to reveal the properties and dynamics of heterogeneous interfaces. A new met...

Electrochemical Impedance Measurements in Scanning Ion Conductance Microscopy

Earlier studies on cerium-loaded naturally occurring silica microparticles (i.e., diatomaceous earth) demonstrated the potential to efficiently protect small scratches in epoxy-coated AA2024-T3 panels during relatively short immersion times. The current work investigates the potential of such inhibitor-loaded microparticles to protect wide and deep scribes (up to 1 mm wide) in long-time immersion testing and during cyclic (wet/dry) conditions. For this, cerium nitrate and 2,5-dimercaptothiadiazole (DMTD) were used as inorganic and organic corrosion inhibitors. The corrosion protection was evaluated using a hyphenated real-time optics/electrochemistry method and two individual local techniques measuring oxygen concentration and electrochemical impedance (LEIM) inside the scribe. SEM/EDS was used to analyze the samples after exposure. The results show significant levels of corrosion protection at damaged locations at low cerium concentrations (3.7 wt % Ce3+ relative to the total coating mass) during 30 days of immersion in salt solution. However, for a given scribe geometry, the protection was found to be dependent on the electrolyte volume with larger electrolyte/exposed metal ratios leading to short protection time. A partial replacement of the Ce3+ by DMTD in the microcarriers resulted in a higher degree of passivation than when DMTD was used alone. Wet/dry cyclic exposure tests showed that cyclic conditions can increase the buildup of stable inhibitor-containing layers in the case of cerium-loaded silica microparticles. This underlines the need for more research using wet/dry exposure conditions.

https://pubs.acs.org/doi/pdf/10.1021/acsami.0c03368

Corrosion Inhibition at Scribed Locations in Coated AA2024-T3 by Cerium- and DMTD-Loaded Natural Silica Microparticles under Continuous Immersion and Wet/Dry Cyclic Exposure

Detection and quantification of defect evolution at buried metal-oxide-polymer interface on rough substrate by local electrochemical impedance mapping

Abstract Anticorrosive coatings are extensively used to protect metals and alloys, especially in the marine environment. This study reports the enhancement of coating performance of epoxy primer coating on zinc in 3.5% NaCl at 303 K by impregnating the epoxy primer with micro and nano particulates of biopolymers. Initially, conditions were standardized to achieve optimum efficiency of Maltodextrin (MLD) and Glycogen (GLY) for corrosion of zinc in 3.5% NaCl. The optimum concentration of inhibitors was then added to the epoxy primer coating a applied on zinc. Anti-corrosion performance of epoxy primer with biopolymer was compared with that of standard coating, which was devoid of biopolymers. The coating characteristics were further enhanced by incorporating nanoparticles of MLD and GLY into the epoxy primer matrix. Potentiodynamic polarization measurement (PDP) and Electrochemical impedance spectroscopy (EIS) were employed to study corrosion rate measurement. Detailed surface morphology was studied using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) techniques. Electrochemical and surface studies clearly demonstrated the capability of micro and nanosized biopolymers in improving the anti-corrosion performance of the coating. The average efficiency of epoxy primer coating improved to a considerable extent by studying biopolymers. The overall efficiency of the coating formulation was found to be 99.5%. Surface morphology studies showed that coating thickness increased to 32.1 µm from 27.2 µm after incorporating biopolymers. In addition to this, there was a remarkable change in the surface roughness of epoxy primer coating in contact with 3.5% NaCl after the addition of biopolymers into it. The coating formulation developed turned out to be eco-friendly with significant environmental benefits.

Enhanced anticorrosion performance of epoxy primer coating on zinc in 3.5% NaCl by micro and nano particulates of biopolymers

The main objective of the work described in this dissertation is to explore the route towards new anticorrosion coatings for the protection of aerospace aluminium alloys using alternative strategies that can replace the currently used toxic chromate corrosion inhibitors. As such, each chapter of this dissertation is devoted to relevant scientific and industrial challenges whereby the research on corrosion, inhibition and coating systems is combined with a newly developed in-situ optical-electrochemical technique.

A. Krasnova

Papers

Development of anodic and cathodic blisters at a model Zn/epoxy interface studied using local electrochemical impedance