Corrosion Inhibition of Metals and Alloys in the Presence of Extracts of Plant Materials: An Overview
Extracts of plant materials are low cost and environmentally friendly. They contain many active ingredients. The molecules of these ingredients may contain hetero-or polar atoms such as sulfur, nitrogen, oxygen, and phosphorous. Corrosion is a spontaneous and thermodynamically favorable process. Because of corrosion, every year 5% gross national product of any country is lost. Plant extracts are environmentally friendly, nontoxic, cheap, and biodegradable. The inhibition efficiency of an aqueous extract of Adhatoda vasica leaves in controlling corrosion of mild steel in well water has been evaluated by the weight loss method. To evaluate the corrosion inhibition efficiency of various plant extracts, several methods such as weight loss method and electrochemical studies have been employed. AC impedance spectra are useful in confirming the formation of a protective film on the metal surface. If a protective film is formed on the metal surface, the charge transfer resistance increases, double-layer capacitance decreases, and impedance increases.