Coatings produced by electrophoretic deposition from nano-particulate silica sol–gel suspensions

Abstract

Sol–gel technology allows the production of hybrid coatings on metals using low temperatures for densification, but has an important limitation related with the maximum coating thickness attainable, typically lower than 2 mm. The incorporation of nano-particles to the sol can make it possible to increase the coating thickness, without increasing the sintering temperature. This work deals with the preparation of thick sol–gel coating by electrophoretic deposition (EPD). Commercial SiO2 nanoparticles are suspended in an acid-catalysed SiO2 sol, whose stability is largely increased by adding tetramethylammonium hydroxide (TMAH) up to pH 6. Coatings are formed by dipping and by EPD on AISI 304 stainless steel substrates. The protective behaviour against corrosion in aggressive media (i.e. marine water) of the produced films is studied. EPD leads to coatings as thick as 5 mm with good corrosion resistance, while the suspension stability is increased by 15 times compared with that of the starting acid suspension.