Assessment of Berlinia grandiflora and cashew natural exudate gums as sustainable corrosion inhibitors for mild steel in an acidic environment

The study examined the effectiveness of Berlinia grandiflora (BEG) and cashew (CEG) exudate gums in protecting mild steel from corrosion in 1 M HCl solution using weight loss, electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), and potentiodynamic polarization (PDP). The corrosion products were analyzed using scanning electron microscopy with energy dispersive spectroscopy (SEM/EDX), atomic force microscopy (AFM), Fourier Transformed Infrared spectroscopy (FTIR), and optical profilometry. Results indicate that the exudate gums are effective against the corrosion of mild steel in an HCl solution. The EIS results reveal that the charge transfer resistance of the metal in the acid solution increased from 82.2 Ω cm² to 1074.0 Ω cm² and 325.1 Ω cm² in the presence of 1000 ppm BEG and CEG, respectively corresponding to inhibition efficiency (η) of 92% and 75% at 25 °C. The Gum's performance depends on immersion time and temperature. It improves with an increase in immersion time up to 48 h but thereafter slightly diminishes. The η of 1000 ppm of BEG and CEG after 48 h of immersion is 76% and 67%, respectively at 30 °C. With a temperature rise, η of BEG appreciates to 80% while that of CEG depreciates to 57% at 60 °C after 24 h of immersion. Both BEG and CEG retard the metal corrosion through an adsorptive mechanism whereby it blocks the active corrosion reaction sites on the surface. The adsorption was confirmed by SEM/EDX, AFM, UV–vis, and FTIR. BEG and CEG are promising and sustainable sources for metal corrosion inhibitor formulations.