Silica-based coating for corrosion protection of electrogalvanized steel

This paper presents a new silica-based coating procedure for the protection of electrogalvanized steel against corrosion. Besides corrosion resistance properties, one of the main objectives of the study was to evaluate the viability of a simple and industrially easy-to-implement substitute to the widely employed chromate coatings that must be abandoned in the next years in the European Union. The silica-based layer was prepared from simple immersion of electrogalvanized sheets in a deposition bath composed of a nanometric silica particles/sodium metasilicate mixture at room temperature. After optimization of several parameters as deposition bath composition, immersion time, drying temperature and so on, the corrosion resistance was evaluated mainly by means of salt spray tests (SST) but also by electrochemical impedance spectroscopy (EIS) measurements. Results have shown to be very promising since the silica-based protective layer behaved almost as well as chromate coatings.