Electrosynthesis of molybdate-doped P(ANI-co-PY) copolymer coating in ionic liquid for corrosion protection of 304 stainless steel

TiO2 Nanocontainers Coconstructed Using Polymers and Corrosion Inhibitors for Anticorrosion Reinforcement of Waterborne Epoxy Coatings

Stimulus-responsive coatings can provide active corrosion protection in response to environmental changes, but they have not reached their anticipated application prospects because of the intricate preparation processes of hollow materials and methods for loading corrosion inhibitors. Herein, polyaniline molybdate corrosion inhibitor and polydopamine-wrapped titanium dioxide nanocontainers (named TiO2/PANI-MoO42-/PDA) are synthesized via a simple three-step electrostatic assembly technique. Introducing TiO2/PANI-MoO42-/PDA nanocontainers in smart waterborne epoxy (WEP) coatings affords the latter with high barriers and long-term corrosion protection. The successful deposition of each layer on the TiO2 nanocontainer surface was validated via Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. Release test results show that the molybdate corrosion inhibitor exhibits notable pH-responsive activity under acidic conditions and slow release in neutral environments, which improves the corrosion resistance of coatings. The addition of synthetic nanocontainers greatly improves the impermeability of WEP coatings. The charge transfer resistance of WEP/TiO2/PANI-MoO42-/PDA coatings is 1.79 × 1011 Ω cm2 after 30 day immersion in a 3.5 wt % NaCl solution, which is 3.32 × 105 times higher than that of WEP coatings. WEP/TiO2/PANI-MoO42-/PDA coatings remain uniform and reliable, even after 50 days of salt spray exposure. The excellent corrosion protection of WEP/TiO2/PANI-MoO42-/PDA coatings is attributed to (1) the enhanced dispersion and compatibility of PDA in the coating for nanocontainers, (2) the combination of phenolic hydroxyl groups of PDA and Fe, which inhibit corrosion activity on the exposed metal surface, and (3) the on-demand release of the MoO42- inhibitor, which provides sustained passivation protection. This work proposes a strategy to simplify the preparation of responsive long-term anticorrosion coatings and extend their service lives.

Optimized Anticorrosion of Polypyrrole Coating by Inverted-Electrode Strategy: Experimental and Molecular Dynamics Investigations

To improve the poor adhesion and the ensuing insufficient anticorrosion efficacy of electropolymerized polypyrrole (PPy) on copper surface, an inverted-electrode strategy was applied after the passivation procedure, for which the compact coating (PPy-I) was deposited on the substrate in a cathodic window. Morphological and physical characterizations revealed that PPy-I exerted satisfactory adhesion strength and suitable thickness and conductivity compared with the analogue prepared via the traditional protocol (PPy-T). Potentiodynamic polarization, electrochemical impedance spectroscopy and frequency modulation were employed to ascertain the propitious protection of PPy-I for copper in artificial seawater (ASW). Due to the dominant electroactivity, the PPy-I-coated sample possessed higher apparent current density and lower charge transfer resistance than its PPy-T-protected counterpart, which maintained the passivation of the substrate. Surface analysis also supported the viability of PPy-I for copper in ASW for a well-protected surface with inferior water wettability. Molecular dynamics simulations evidenced that PPy-I with the higher density retained efficient anticorrosion capacity on copper at elevated temperatures. Therein, the derived time-dependent spatial diffusion trajectories of ions were locally confined with low diffusion coefficients. Highly twisted pore passages and anodic protection behavior arising respectively from the tight coating architecture and electroactivity contributed to the adequate corrosion resistance of PPy-I-coated copper.