Sol-gel coatings obtained from electrophoretic depositions (EPD) on metals

Sol-gel process is a suitable method for the production of glass-like coatings onto metals, acting as barrier against oxidation and providing an increased resistance to corrosion. Hybrid and inorganic coatings of different compositions have been used for coating several metals by using techniques like dipping, spin-coating and spraying. Although these methods lead to good properties the final coatings are restricted by the thin thickness (up to 2 mum), thus limiting the application range. Electrophoretic deposition (EPD) is considered a highly versatile technique for producing homogeneous thicker coatings. The aim of this work deals with the preparation of coatings onto metals by EPD from hybrid silica sols (TEOS, MTES) and from colloidal silica suspensions where the hybrid sols constitute the suspending medium. Both the solutions and the suspensions have been studied in terms of viscosity, density and conductivity. Furthermore, the physical parameters associated to EPD, such as deposition time and current density, have been also studied, taking into account the additional contribution to the laver formed by EPD occurring by dipping during withdrawal. The coatings obtained by dipping and by EPD have been characterised by perfilometry and optical microscopy.