Super-impermeable polyurethane coating constructing inspired by passive film structure

The deficiency in ion barrier capability, leading to coating failure, is a tough issue for corrosion-resistant coating. Inspired by the corrosion resistance of stainless steel, our team propose a modified p/n polyaniline heterojunction coating for carbon steel. This structure produces the built-in electric field at the p/n junction, causing cations and anions to accumulate only on either side of the depletion region, creating an effective barrier against charge transfer. The structure and morphology of the fillers are analyzed using SEM, TEM, FT-IR, and Raman spectroscopy, while their electronic structure is investigated through Mott-Schottky tests and their ion selectivity is verified through membrane potential testing. The protective performance of coating is evaluated via electrochemical impedance spectroscopy (EIS) and salt spray tests. Results show that after 200 days of immersion, the impedance modulus |Z|@ 0.01 Hz of the p/n-PANI Coating remains at 10 10  Ω cm 2 , four orders of magnitude higher than Pure PUA. The pull-off test indicates the p/n-PANI Coating achieves the highest adhesion strength at 11.55 MPa after immersion in 3.5 wt% NaCl solution for 200 days. Further analysis of the ion impermeability of coatings using SEM and EDS reveals its exceptional protective mechanism. Overall, these findings highlight the potential of p/n-PANI Coating for marine oil and gas equipment, offering promising long-term anti-penetration and corrosion resistance.