Rust morphology characterization of silicone-based marine antifouling paints after salt spray test on scribed specimens

A newly developed, silicone-based, marine antifouling coating, containing 0.56% immobilized Econea, was examined in terms of its anticorrosion performance. The novelty of the experimental formulation arises from the immobilization of the biocide which minimizes leaching and was accomplished via a newly developed functionalization method, based on reaction of the biocide with highly reactive isocyanate functionality. The painting system was applied on steel specimens, then scribed with a sharp cutter and examined for 12 weeks in cyclic salt spray exposure. Identification of the rust morphologies was done with XRD, Raman spectroscopy, SEM and EDS methods. The observed paint swelling during the experiment caused the formation of large, coarse rust agglomerates without adherence, which detached frequently causing reinitiation of the corrosion process. This procedure was revealed by the oxyhydroxide nature of the corrosion products. The basic corrosion morphology observed was a mixture of akaganeite and goethite. A commercial, silicone-based, foul-release coating served as a reference. The experimental formulation exhibited superior anticorrosion performance overall, since the reference system presented higher enlargement of the scribed areas, increased substrate material loss, a highly inhomogeneous corrosion layer with voids and smaller (stable) goethite amounts in the rust areas containing mainly akaganeite/goethite mixture.