Session 12: Advances in Surface Finishing
This talk summarizes novel completely non-chromate organic coatings development for use on plated steels. The organic coating chemistry and formulation using polymeric Schiff base inhibitors will be discussed.
Advances in Research
Hexavalent chromium (Cr6+) containing sealers are primarily used to enhance corrosion protection of metal plating, Al anodizing and other sacrificial layers when exposed to corrosive atmospheric environments. The need to reduce or eliminate the use of Cr6+ containing anodizing and passivating sealing solutions remains a top priority for the DoD to reduce risks associated with environmental, human health, and compliance issues. Many Cr6+ free corrosion inhibitors and coating systems have been researched and implemented to various extents over the last several decades. Most corrosion inhibitors can be classified as inorganic or organic based on their molecular formula. The focus of this study is organic inhibitors, specifically those containing a Schiff base (SB) or an azomethine functional group (--RC=N--). Boeing Research and Technology (BR&T) has discovered a unique functionality of these SB inhibitors that enables high polarization resistance of Al when exposed to chloride-containing corrosive media. Twenty- three different corrosion inhibitors with the Schiff base functionality were synthesized and characterized using fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). Corrosion inhibition of the organic inhibitors were evaluated using polarization resistance and potentiodynamic scans of the metal surface. Electrochemical corrosion resistance performance of the inhibitors were ranked using inhibitor efficiency and the corrosion rate of the metal was calculated using Faraday’s law and the corrosion current from potentiodynamic scans. BR&T is partnering with the Missouri University of Science and Technology (Missouri S&T) and the Naval Air Systems Command (NAVAIR) to develop and mature organic Schiff base (SB) containing passivating solutions for zinc (Zn), zinc-nickel (ZnNi), cadmium (Cd) plating.