Hybrid corrosion-resistant coatings analyzed using electrochemical noise

Purpose - The purpose of this paper is to study the corrosion of carbon steel without coating and when protected using three different hybrid coatings, i.e. a bi-component polyurethane with nano-particles of SiO2 with and without sacrificial anode particles, and a mono-component polyurethane with SiO2 particles. Design/methodology/approach - In this investigation three different nano-structured coatings are developed and applied to steel substrates and then tested for their corrosion resistance (defined as R-n), under a very aggressive medium (pH = 1.5) in a dynamic system (loop reactor). Their performance is evaluated using an electrochemical noise (EN) resistance technique. The electrodes are connected to a potentiostat and measurements are recorded as per the EN technique over a 2,048 s duration at 0, 24, and 48 h intervals. Scanning electron microscopy (SEM) are obtained before and after the corrosion trials to characterize the control and the different coating systems. Findings - The results show that a bicomponent coating, made up of alkyd resin and silica nanoparticles demonstrated the best performance, whereas the coating formed by SiO2 nanoparticles and polyurethane resin showed relatively low corrosion resistance. The inclusion of zinc nanoparticles in a third coating as sacrificial nano-anodes led to segregation and resulted in moderate corrosion resistance. These results are confirmed by SEM observations. Originality/value - The results obtained in this paper provide an insight to the understanding of the anticorrosion properties of three different hybrid coatings in a dynamic system (loop reactor).