Probing the Chemistry of Adhesion between a 316L Substrate and Spin-on-Glass Coating

Hydrogen silsesquioxane ([HSiO_3/2] _n)-based "spin-on-glass" has been deposited on a 316L substrate and cured in Ar/H₂ gas atmosphere at 600 °C to form a continuous surface coating with submicrometer thickness. The coating functionality depends primarily on the adhesion to the substrate, which is largely affected by the chemical interaction at the interface between the coating and the substrate. We have investigated this interface by transmission electron microscopy and electron energy loss spectroscopy. The analysis identified a 5-10 nm thick interaction zone containing signals from O, Si, Cr, and Fe. Analysis of the energy loss near edge structure of the present elements identified predominantly signal from [SiO₄]^4- units together with Fe²⁺, Cr²⁺, and traces of Cr³⁺. High-resolution transmission electron microscopy images of the interface region confirm a crystalline Fe₂SiO₄ interfacial region. In agreement with computational thermodynamics, it is proposed that the spin-on-glass forms a chemically bonded silicate-rich interaction zone with the substrate. It was further suggested that this zone is composed of a corundum-type oxide at the substrate surface, followed by an olivine-structure intermediate phase and a spinel-type oxide in the outer regions of the interfacial zone.