Characterization of inhibitor storage and release from commercial primers

Commercial primers are applied on aluminum alloys that are used in aerospace applications to prevent corrosion attack from aggressive environments. These primers contain inhibitors that help combat corrosion. During field operations, these primers store and release inhibitors to protect the underlying alloy. The goal of this study is to characterize storage and release behaviors of these commercial primers to better understand the rate and mechanism by which inhibitors are released. Three commercial primers were investigated in this study; 1) Akzo Nobel 10P20-13 High Solid Primer that contains strontium chromate (SrCrO₄), 2) Deft 02GN084 (Pr-based), and 3) Hentzen 16708TEP (BaSO₄-based). The primers were coated on a Teflon tape, then stripped off and broken to small pieces. Pieces of the primer coating were immersed into solutions of different Cl⁻ concentration, temperature, time, and pH. The solutions were then filtered and characterized by inductively coupled plasma mass spectroscopy (ICP-MS) to analyze the solution chemistry. Results showed that SrCrO₄ primer release behavior follows power law kinetics. Solubility limits played an important role in dictating the release kinetics of the chromate primer when accumulation of Cr ion occurs.The effect of pH and temperature can alter this solubility limit. Chloride seems to promote release of chromate because of greater ionic strength. The Pr-rich primer released a large amount of Ca²⁺ upon exposure and release kinetics were not time-dependent thereafter. The Ba-rich primer did not release soluble constituents to any significant extent.