Assessment of The Green Corrosion Inhibition Performances of Thymus Algeriensis Microwave-Assisted Extracts on Mild Steel in Acid Solution

The diversity of extractable compounds provides a potentially rich source of high-value products. The corrosion inhibition performances of seven Thymus algeriensis extracts on mild steel in 0.5 M HCl were investigated using the gravimetric method, electrochemical measurements, and surface analysis. The results indicate that the addition of all the extracts significantly decreases the corrosion rate of mild steel with efficiency proportional to the extract concentration. A maximum percentage of inhibition was obtained for the microwave-assisted aqueous extract (T = 100 °C, extraction time = 15 minutes) at a concentration of 500 ppm, which is the most phenolics-enriched extract. Potentiodynamic polarization curves show that the extracts acted as mixed-type corrosion inhibitors and slowed down the anodic and cathodic reaction kinetics. Scanning electron microscopy confirms the presence of a protective film. The inhibition properties were attributed to the synergism of the active components of the extracts, mainly flavonoids, carotenoids, chlorophylls, and phenolic compounds with functional groups such as conjugated double bonds, aromatic rings, and heteroatoms, which adsorb on the metal surface of the mild steel to form a protective layer preventing the contact of the aggressive medium.