The synthesis of polyindole-based binder-free coating and its effect on the corrosion behavior of mild steel in 3.5% NaCl solution

The influence of three polyindole samples on the corrosion rate of mild steel in the absence and presence of different amounts of acetonitrile was investigated in 1-M HClO4. All samples were characterized by Scanning Electron Microscopy, Energy-Dispersive X-ray Spectroscopy, Fourier transform infrared spectroscopy, UV–vis spectroscopy, X-ray Powder Diffraction, and contact angle measurements. Through measurements, it was determined that the polymers differ from each other on the basis of morphology, conjugation, molecular mass, and crystallinity. Also, it was found that all samples include FeCl3 used as an oxidant. The corrosion tests were performed using Electrochemical impedance spectroscopy and polarization curve technique. Among the samples, PIn1 has the highest anti-corrosive property as it includes the highest amount of Fe and the highest density of hydrophobic group, such as ClO4−. According to the characterization measurement recorded after corrosion tests, corrosion species (based on Fe compound) are formed and they increased the passive film protection. From the electrochemical measurement results, it was found that PIn1 inhibited the cathodic corrosion reaction of MS in 3.5% NaCl and showed 98% protection efficiency. Long-term stability analysis shows that Rct increases with time indicating passive film protects the mild steel. So it was found that all polyindole-based inhibitors have a synergistic inhibition effect in the solution. Also, the temperature effect was investigated in the corrosion protection ability of polyindol-based inhibitor.