Silica-Zirconia Coatings Produced by Dipping and EPD from Colloidal Sol–Gel Suspensions

SiO2-ZrO2 sols have been prepared via acid catalysis using a commercial colloidal suspension of zirconia and two silica alkoxides; tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES). Suspensions with 10, 15 and 25-mol% of ZrO2 were prepared. The stability of the suspensions was followed by rheological measurements showing that the amount of water incorporated with the colloidal suspension is the factor that limits the maximum ZrO2 content. Coatings have been prepared by dipping using the suspensions up to 25-mol% ZrO2 onto glass-slides at different withdrawal rates. EPD process has been used to prepare coatings onto stainless steel AISI 304 using the suspension with 25-mol% ZrO2 at different pHs. The parameters associated with the EPD process (current density, electric field, potential and deposition time) have been evaluated. The critical thickness for a ZrO2 addition of 25-mol% was 0.8 μm and it increased for diminishing ZrO2 content. 8