Corrosion-resistant organic-inorganic hybrid pretreatments obtained by UV-initiated process suitable for primer-less coating systems

摘要

A photo-initiated sol-gel process has been developed to deposit organic-inorganic hybrid (OIH) thin films on metal substrates for corrosion protection. Wet films of non-aqueous compositions containing specially designed organo-silane precursors and photo-latent catalysts -photo-acid generator (PAG) or photo-base generators (PBG)-, were exposed to ultraviolet (UV) radiation under ambient moisture environment leading to OIH films by sol-gel reactions. Synthesis and curing of organo-silanes were characterized using instrumental and gravimetrical techniques. Moreover, the corrosion resistance performance of OIH films based on two families of organo-silane precursors cured by PAG and PBG were compared with those obtained by the conventional aqueous sol-gel process. The effects of precursor and photocatalyst type, UV light intensity, cure conditions, and film thickness on anti-corrosion performance of OIH coatings were studied using various qualitative and quantitative techniques such as DC polarization, electrochemical impedance spectroscopy (EIS), and accelerated salt spray test. Results revealed that selected OIH pretreated samples showed corrosion current density as low as 1.2 nA/cm(2), which is superior compared to conventional hexavalent chromium-based Cr (VI) pretreatments. The study demonstrates the feasibility of this sustainable photo-initiated sol-gel process for many applications, such as primer-less coating systems.