Anticorrosive Effect of Halogenated Aniline Enaminoesters on Carbon Steel in HCl

Four enaminoesters derived from halogenated aniline, with potential anticorrosion activity, were synthesized and tested against carbon steel AISI 1020 in acid medium using 1.0 mol L-1 HCl. The synthesis was demonstrated through the reaction of ethyl acetoacetate with four different amines, in the presence of glacial acetic acid and molecular sieve, using ethanol as solvent for 24 h. The evaluation of the anticorrosive activity was performed using the gravimetric technique and electrochemical methods, such as electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), and potentiodynamic polarization (PP). Results indicated that the F-EN (Ethyl (2Z)-3-[(4-fluoro-phenyl)-amino]-but-2-enoate) inhibitor had higher corrosion inhibition efficiency, of 98% by mass loss, and 85% by electrochemical techniques. Adsorption obeyed the Langmuir isotherm, thus suggesting that the inhibitors form a monolayer film in metal surface. These results also contributed to the calculations of the physicochemical parameters of $E_{\text{a}}$ , $△{H^{\ne }}_{\text{ads}}$ , and $△{S^{\ne }}_{\text{ads}}$ , which confirmed the corrosion inhibition when compared to the absence of the inhibitors.

Molecular Assembly between Weak Crosslinking Cyclodextrin Polymer and trans-Cinnamaldehyde for Corrosion Inhibition towards Mild Steel in 3.5% NaCl Solution: Experimental and Theoretical Studies

Constructing molecular assembly between a soluble cyclodextrin polymer (SCDP) and an anticorrosive component is conducive to increasing the availability of a corrosion inhibitor with low molecular polarity in aqueous solution. The SCDP was prepared via the weak crosslinking effect of glutaraldehyde using β-cyclodextrin as the subunit, whose structure was confirmed by proton nuclear magnetic resonance spectra (¹H NMR), X-ray diffraction and morphology. An assembly between SCDP (host) and trans-cinnamaldehyde (guest, CA) was constructed, and the intermolecular interactions were disclosed by Fourier transform infrared spectra (FTIR). The corrosion inhibition of SCDP/CA assembly for mild steel in 3.5% NaCl solution was assessed through electrochemical and surface analyses. ¹H NMR results showed that exterior hydroxyls of β-cyclodextrin were the active sites for crosslinking. Hydrogen bonds might be the binding force between SCDP and CA according to FTIR analyses. Electrochemical measurements revealed that SCDP/CA assembly could suppress both cathodic and anodic reactions and enhance the polarization impedance for mild steel in the corrosive medium with a maximum efficiency of 92.2% at 30 °C. Surface analyses showed that CA molecules could be released from the assembly followed by the energy competition mechanism, and solely adsorb on the steel surface in parallel form, which was further evidenced by theoretical modeling.