Reinforcement of an alkyd resin coating incorporating a swelling clay encapsulated with L-cysteine molecules: Characterization and corrosion inhibition of Cu-36Zn alloy

Abstract

Corrosion is a real industrial scourge; it is defined as the degradation of a material in corrosive environments such as seawater and acids, causing a huge economic loss, especially in the automotive, building and marine industries. To cope with this issue, a swelling clay was used as corrosion inhibiting reservoir of an amino acid (L-cysteine). For this purpose, the before-hand developed composite was characterized and incorporated into an organic coating. The clay fractions of this swelling clay were modified by the cysteine inhibitor. The modification was confirmed by X-ray diffraction (XRD), where the d002 reflection of the I-S clay fraction was increased from 4.66 Å (Na-clay) to 5.57 Å (Cys-clay). FTIR and UV–vis–NIR techniques were also used for characterization purposes. The sudied clay is a mixture of clay minerals (illite-smectite as the main component, kaolinite and chlorite) and associated minerals (quartz and calcite). The progressive release of cysteine molecules leads to a durable corrosion protection of brass in a 3 % NaCl solution, resulting in the lowest corrosion current density (10.36 μA/cm2) and reaching a maximum inhibition efficiency of about 86 %. The resulting composite was used as a charge to cover the brass surface by being mixed with an alkyd resin (5 % of the mass of the resin). The impedance modulus |Z|0.05 Hz reached a maximum value (1419 kΩ.cm2) at the end of the immersion period. The corresponding charge transfer resistance value (1.82 MΩ.cm2) was twice that of the coating containing a commercial inhibitor (0.92 MΩ.cm2), reflecting the composite efficiency and the novelty of this work. Electrochemical techniques such as open circuit potential (OCP), polarization curves and electrochemical impedance spectroscopy (Nyquist, Bode Magnitude and Bode Phase) were performed. Corrosion products and protective layers are analyzed using optical microscopy and scanning electron microscopy techniques coupled to an energy dispersive X-ray spectrometer (SEM-EDX). The development of this new smart coating will expand the range of applications for electrochemically active materials.