Surface modification of natural porous silica microparticles to control the loading and release of organic corrosion inhibitors in coatings

Abstract

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.