Corrosion inhibiting and sensing ion exchange pigments for organic coatings

Cation-and anion-exchanging inorganic particulate additives for corrosion resistant organic coatings were synthesized and characterized. In this study, bentonite clay was synthesized with Ce³⁺ that exchanged with Na ⁺ ions in electrolytes. Additionally, a hydrotalcite particulate was synthesized with vanadate that exchanged with Cl ions. Zn²⁺ cations present in the compound were also released. Polarization curves were measured for 2024-T3 in electrolytes produced by equilibrating inhibitor-bearing particulate with chloride solutions. Results showed that the hydrotalcite additive modified the chloride solution in a way that made it less aggressive to the alloy. Similarly, a coating with the hydrotalcite additive provided more corrosion protection than a coating with the bentonite additive in both salt spray and electrochemical impedance testing. Predictable changes in the pigment crystal structure that occurred upon ion exchange enabled the kinetics of inhibitor release to be evaluated. Inhibitor release kinetics were diffusion-controlled and rapid for the bentonite pigment, but were very slow for the hydrotalcite.