Smart and green hybrid coating offering long-term corrosion protection in corrosive media

摘要

With the approaching sunset date for the use of Cr(VI), there is an urgent need to find industrially viable alternatives to Cr(IV) surface treatments. Replacement treatments must match or exceed perfonnance expectations, while also addressing safety, environmental and economic concerns. To date, a great deal of research has been undertaken in search of such replacements; however, commercially available alternatives struggle to meet the necessary requirements. Sol-gel technology is fast becoming a recognized approach for producing anticorrosion coatings, notwithstanding potential liabilities such as cracks or compatibility with corrosion inhibition. Herein is described the development of a new smart and green hybrid sol-gel coating which offers long-term anti-corrosion protection. In addition, a novel method for the rapid screening of anticorrosive properties is presented. Neutral salt spray (NSS) is largely used to assess the anticorrosive properties of a coating system Based on pit density estimation, this method provides only qualitative information. Used in complement to NSS, electrochemical impedance spectroscopy (FJS) provides quantitative data, for instance the coating porosity, and the activity of corrosion inhibition agents. Nevertheless, these experiments are time-consuming. Combining appropriate electrochemical techniques, it is possible to drastically reduce the experimental time, while gathering data of equivalent value. To illustrate the power of this technique, EIS measurements have been performed on a new proprietary protective film after 24 h of accelerated tests. The results were compared with 1,000 h of NSS. Bode plots exhibit the same behaviour for each experiment with one charge transfer attributed to the coating properties, especially its barrier effect. Therefore, it has been demonstrated that this new investigation method is able to provide equivalent information in a shorter time. With such a powerful tool, it is now possible to rapidly tune coating formulations. The use of this accelerated method has allowed us to rapidly develop a protective film with outstanding anticorrosive properties, especially in terms of density, leading to a strong improvement of its barrier properties. The anticorrosive ability has been evaluated as well and it has been found that for both scratched and unscratched samples, the coating exhibits neither pit nor corrosion propagation in the vicinity of the damaged area after 3,000 h of NSS. Filiform corrosion resistance, which is the weak point of traditional polymer coatings, has been evaluated according to standards. The maximal length of filaments has been measured to 2 mm which is similar to state of the art for Cr(VI) coatings. Other properties such as mechanical and fluid resistance have been assessed. It emerges from this study that the hybrid sol-gel coating meets all evaluated specifications. Finding a viable alternative to chromate-based coatings in the next future is no longer a dream!