Corrosion resistance of AISI 316L coated with an air-cured hydrogen silsesquioxane based spin-on-glass enamel in chloride environment

Abstract

The efficiency of thin hydrogen silsesquioxane (HSQ)-based corrosion barrier coatings on 316L substrates after oxidative thermal curing at 400-550 ºC in air was investigated. Infrared spectroscopy and electrochemical impedance spectroscopy showed that an increasing curing temperature leads to progressing coating densification, accompanied by decreasing barrier properties. Cyclic polarization measurements indicated that defects due to substrate oxidation are detrimental for the substrate passivity. Insufficiently polymerized coatings showed poor chemical stability in neutral salt spray testing and the chemical coating stability increased with curing temperature. Oxidative curing was found inadequate as polymerization treatment of HSQbased corrosion barrier coatings on 316L substrate.

Properties and performance of spin‐on‐glass coatings for the corrosion protection of stainless steels in chloride media

“…The coating microstructure with focus on the interface between coating and substrate has been investigated by TEM and a bright field micrograph of a coating cross‐section is shown in Figure . The coating/substrate transition is rendered sharp in the micrograph, indicating that the curing process has successfully suppressed the buildup of a unfavorable, thick interfacial oxide, like it was previously reported for air‐cured HSQ‐based enamels …”

“…Further, the coating chemistry was characterized by transmission FT‐IR and the FT‐IR absorbance spectra of all curing conditions, together with an absorbance plot of a thermally grown SiO 2 are shown in Figure (a). The spectral features were identified based on the data reviewed by Lampert et al In agreement with other groups, the thermal treatment leads to a distinct shift from HSQ‐cage‐ to ladder‐structure (i.e., polymerization of the oligomeric precursor), together with a distinct decrease in intensity of the Si‐H stretching vibration and the various bending vibrations below 950 cm −1 wavenumber. Similar to previous reports, the degree of polymerization is assessed based on the normalized integrated Si‐H stretching absorption, as shown in Figure (b).…”

“…The spectral features were identified based on the data reviewed by Lampert et al In agreement with other groups, the thermal treatment leads to a distinct shift from HSQ‐cage‐ to ladder‐structure (i.e., polymerization of the oligomeric precursor), together with a distinct decrease in intensity of the Si‐H stretching vibration and the various bending vibrations below 950 cm −1 wavenumber. Similar to previous reports, the degree of polymerization is assessed based on the normalized integrated Si‐H stretching absorption, as shown in Figure (b). The residual Si‐H absorption decreases to 72% for curing at 400 °C and to 0% for curing at 700 °C, indicating a significantly increased thermal budged of the process with respect to curing in ambient air and the formation of virtually hydrogenation‐free oxides for curing above 700 °C.…”

“…Our recent studies of SOG curing in air showed an extensive degradation of the substrate surface due to thermal oxidation at the coating/substrate interface. The buildup of a thick thermal oxide at the interface impaired the corrosion performance and coating adhesion of samples cured above 400 °C and restricted the curing temperature and achievable degree of coating polymerization.…”

“…Our recent investigations on air‐cured SOG systems emphasized that severe corrosive failure of inadequately coated stainless steels may be expected in chloride containing media. Since our previous investigation of non‐oxidatively cured coatings was solely focused on curing at 500 °C and electrochemical testing in chloride‐free, buffered neutral solution, the successful application of the technology as coating for marine heat exchanger plates necessitates a comprehensive investigation of the corrosion performance as well as the coating properties over a broad curing temperature range and in chloride containing media.…”