The main objective of this dissertation is to demonstrate two strategies for incorporating highly efficient organic corrosion inhibitors into aerospace coatings and to establish fundamental guidelines for designing such coatings. Each chapter tackles important scientific and industrial challenges related to corrosion, organic inhibitors, and coating systems, using newly developed inhibitor-loading strategies, lab-scale operando optics, electrochemistry, spectroscopic and surface techniques, and industrial techniques.

Recent works have shown the potential of diatomaceous earth (DE) as an efficient and environmentally friendly storage system for active chemicals such as corrosion inhibitors in coatings. The storage of organic inhibitors is nevertheless challenging. To address this challenge, in this work, we study the effect of surface modification of DE particles on the loading and release of organic corrosion inhibitors in solution and from coatings. To this aim, three trichlorosilanes with varying alkyl chain lengths (C4, C8, C18) were used to modify the surface of sp. Aulacoseira-type diatomite (DE). 2,5-Dimercapto-1,3,4-thiadiazolate di-potassium salts (KDMTD) were selected as a model corrosion inhibitor for its high solubility and effectiveness in protecting Cu-rich aerospace alloys, such as AA2024-T3. UV-Vis spectroscopy revealed a relationship between chain length and inhibitor loading and release, with mid-length silane (C8) adsorbing 3.5 times more inhibitor with no negative effect on release kinetics. When incorporated into epoxy-amine coatings, C8 surface modification significantly improved DE particle dispersion and protection of the inhibitor from the polymer matrix, preventing unwanted side reactions. This increased the availability of active organic inhibitors for protection at damaged sites. In-situ reflected microscopy during immersion and postmortem analysis of damaged coatings demonstrated high levels of corrosion protection and the formation of stable protective layers at damaged sites. The research opens the path to more efficient use of functional DE particles in coatings.

The most common way to protect metallic structures from corrosion is through the use of passive and active corrosion protection with coatings containing dispersed corrosion inhibitor particles. Current approaches use inorganic microparticles containing mostly toxic and/or critical elements (e.g. CrVI, Li-salts). Organic inhibitors have been identified as a potential replacement technology due to their high inhibiting efficiency in solution, high versatility and lower toxicity. Nevertheless, when brought into organic coatings these inhibitors lose their efficiency due to unwanted side reactions with the surrounding organic matrix (coating). In this work we propose a novel strategy to isolate the organic corrosion inhibitor microparticles from the surrounding matrix. The new approach is based on the gas-deposition of an oxide nanolayer on the microparticles using gas deposition in a fluidized bed reactor. As a result, the organic particles are better dispersed in the coating and do not react with the surrounding matrix. Upon coating damage the particles are exposed to water and release sufficiently high amounts of the organic corrosion inhibitor at the damaged location. The work introduces a technique that can be used in other applications with similar challenges and a new technology that enables for the first time to store large amounts of active organic corrosion inhibitors in reactive organic coatings for efficient protection of metallic infrastructure. This opens the path to the practical use of highly efficient organic inhibitors in coatings for corrosion protection.

The interaction of 2,5-dimercapto-1,3,4-thiadiazole (DMTD) with the AA2024-T3 local microstructure (S-phase, secondary phases and matrix) as function of the NaCl concentration is studied. The inhibiting power and the local interaction of DMTD with the metal were studied by in–situ opto-electrochemistry, XPS and Raman spectroscopy. The stability of the inhibiting layers was evaluated by re-exposing the samples to NaCl solutions without inhibitor. The amount of DMTD and its interaction state (chemisorption/physisorption) vary with the local microstructural composition and NaCl concentration. Higher stability of the inhibiting layers is obtained when these are formed in presence of small amounts of NaCl (0.025–0.25 M).