Assessment of Azolla Microphylla Plant Extract as an Environmentally Benign Corrosion Inhibitor for Low-Carbon Steel in Acidic Media

In this study, Azolla Microphylla Extract (AME) appears as a potent corrosion inhibitor, effectively reducing the corrosion rate of low-carbon steel (CS) in a 1.0 M HCl solution. Comprehensive investigation methods, including weight loss (WL), potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM), were employed. The inhibition efficiency (IE) was evaluated across a range of extract concentrations (50-300 ppm) and temperatures (298-313 K). There is a good agreement between the results of the electrochemical and WL methods. A remarkable IE of 98.1% was achieved at 313 K with 300 ppm of AME, displaying its effectiveness. At 298 K, the IE was 81.3%. Adsorption of AME on CS followed Langmuir isotherm and at temperatures of 308 K or lower, the 0G o ads magnitudes were below-20 kJ mol-1, indicative of physical adsorption. However, at 313 K, 0G o ads exceeded -20 kJ mol-1, signalling a change to chemical adsorption. AME belongs to the anodic inhibitors. The activation energy for the blank solution is 98.13 kJ mol-1, which decreased to 62.98 kJ mol-1 in the presence of 300 ppm of AME. Nyquist plots showed that AME inhibited CS dissolution in HCl without altering the dissolution reaction mechanism. Attenuated total reflection infrared (ATR-IR) and scanning electron microscopy (SEM) inspections confirmed the adsorption of AME on CS. AME satisfies the general structural requirement of the corrosion inhibitor as it has O atoms in functional groups (O-H, C=C, and C=O) and an aromatic ring. The findings align well with other environmentally friendly inhibitors previously reported for CS corrosion.