Interfacial Interaction of Oxidatively Cured Hydrogen Silsesquioxane Spin-On-Glass Enamel with Stainless Steel Substrate

Thin film silica coatings have proven to be efficient barrier coatings to protect stainless steels from corrosion in aggressive environments. The deposition of sub-μm silica films from liquid hydrogen silsesquioxane precursor has previously been demonstrated on metallic substrates, whereby the films were thermally cured in inert atmosphere, which required complicated processing equipment, such as gas or vacuum furnaces. In contrast, curing in air is a promising routine to simplify the curing process, reduce curing cost and increase the curing efficiency. In the present work, silica-like thin films were deposited on 316L grade austenitic stainless steel and oxidatively cured at 450°C in ambient air. Oxidative curing yielded well adherent films which solely showed microscopic delamination after standardized adherence testing. Further, the oxidative curing led to the formation of a pronounced interfacial duplex-oxide with an outer zone composed of Fe2O3 in a SiO2-x matrix and an inner zone composed of complex (Cr3+,Fe2+,Mn2+)-oxides. Moreover, a Cr depletion of the substrate in the immediate vicinity of the surface was observed. It was concluded that the interfacial formation is controlled by the kinetic limitation of Cr transport to the interface, which consequently led to the Cr-depletion of the sub-surface region.