Addition of Schiff Bases to Hybrid Silane Sol–Gel Coatings: An Efficient Strategy to Develop an Active System for Corrosion Protection of Copper

The main objective of this work was to improve the corrosion resistance of silane coatings, which have recently attracted much attention for their barrier properties. An organic–inorganic hybrid silane coating prepared by the sol–gel process was developed for the corrosion protection of copper in 1 M HCl solution. The hybrid sol was fabricated by mixing tetraethylorthosilicate (TEOS) and triethoxyvinylsilane (TEVS) in an acidic medium. Two Schiff bases, namely [3-(4-methoxyphenyl)isoxazole-5-yl]-methanol (MOPI) and [3-(4-methylphenyl)isoxazole-5-yl]-methanol (MPI), were synthesized and then incorporated into the silane coatings in various concentrations. The structural characterizations of the prepared coatings were performed using scanning electron microscopy, Fourier transform infrared spectroscopy, x-ray diffraction, and atomic force microscopy. The corrosion behavior of the coatings was evaluated by electrochemical impedance spectroscopy and potentiodynamic polarization. The results indicated that the addition of 1 mM of the MPI and MOPI Schiff bases to the silane coating increased the corrosion resistance from 1.92 to 14.65 and 18.95 kΩ cm², respectively. The effect of immersion time on the performance of the proposed coatings was also investigated, and increasing immersion time from 1 to 12 and 24 h reduced the protection ability of the coatings. Nevertheless, the corrosion inhibition provided by the Schiff base-containing coatings was satisfying after 24 h of exposure to the corrosive medium.