Investigation on the enhanced ion impermeability of bipolar corrosion resistant coating prepared with Mg/Al-HT

Hydrotalcite (HT), which contains a large amount of easily exchanged hydroxyl groups, and has attracted great attention in the field of corrosion protection. Taking this aspect into consideration, this study has prepared bipolar corrosion resistant coating with modified magnesium-aluminum synthetic hydrotalcite (Mg/Al-HT), which restrains both the anion and cation migration in the coating. It is achieved by applying sodium dodecylbenzene sulfonate (SDBS) and cetyltrimethylammonium bromide (CTAB) to modify Mg/Al-HT and blending with phenolic epoxy resin. The chemical composition and morphology of the modified Mg/Al-HT are analyzed using SEM, FT-IR, and Raman spectroscopy. The ion selectivity of the prepared coating is evaluated with membrane potential test. Observation of the macroscopic pictures revealed that no corrosion products were observed on the surface of the bipolar coating after 60 days of immersion in 3.5 wt% NaCl solution. The corresponding interfacial impedance behavior is investigated. The typical impedance modulus @0.01 Hz remains constant at about 10⁹ Ω cm² after 60 days of exposure in 3.5 wt% NaCl solution, which is 10²-10³ times higher than that of the conventional coating. The mechanism of the enhanced ion impermeability is discussed in the paper.