Chitosan as a corrosion inhibitor for gray cast iron and its role in mitigating the stiction phenomenon in automotive braking systems

• High-MW chitosan significantly reduces gray cast iron corrosion in 0.1 M HCl. • Polarization resistance of cast iron increase with chitosan concentration and immersion time. • SKPFM reveals early preferential adsorption on cathodic graphite flakes. • Corrosion inhibition is governed by surface blanketing and charge-transfer suppression. • FE-SEM and ATR-FTIR confirm a stable chitosan-containing surface layer. The corrosion inhibition effect of high molecular weight chitosan on gray cast iron discs for automotive applications was investigated using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) in a 0.1 M HCl solution containing 0.8, 1.5, and 3 gl⁻¹ of the inhibitor. The results suggest that, after 1 h of immersion in the chitosan-containing solutions, gray cast iron shows a modest reduction in cathodic current density, whereas no significant changes are observed in the anodic behavior. Scanning Kelvin probe force microscopy (SKPFM) confirmed the formation of an adsorbed inhibitor film over the cathodic sites at this early stage. To evaluate the stability of the polymer, PDP measurements were conducted after 48 hours of immersion, revealing a significant reduction in corrosion rate and notable inhibition efficiency across all tested concentrations. EIS analysis corroborated these findings, indicating the formation of an adsorbed layer of chitosan covering the entire surface of the gray cast iron samples. The protective effect of this layer was primarily attributed to the blanketing of active sites on the metal surface. Finally, the presence and integrity of the inhibitor films were confirmed through scanning electron microscopy (SEM) and attenuated total reflectance – Fourier transform infrared spectroscopy (ATR-FTIR).