Extracts of leaves as corrosion inhibitors - An overview and corrosion inhibition by an aqueous extract of henna leaves (Lawsonia inermis)

To update hazardous poisonous inhibitors, extracts of plant leaves are used as corrosion inhibitors. They are less toxic and nonpoisonous. They are inexpensive and easily, readily available in plenty. The active ingredients of these extracts contain many organic compounds along with terpenes, alkaloids etc. They in particular contain polar atoms which include oxygen, nitrogen and sulphur etc. These extracts are used to manipulate corrosion of several metals and alloys in various media along with acidic, basic and neutral. They are also used to manipulate corrosion of metals and alloys in well water and sea water. The active principle of these extracts coordinates through their polar atoms with metal ions to form metal-inhibitor complexes. They feature as protecting film. Various methods of controlling of corrosion are discussed. A case has a look at of corrosion resistance of mild steel in sea water in the presence of an aqueous extract of henna leaves is discussed. An aqueous extract of henna leaves (Lawsonia inermis) has been used as corrosion inhibitor in controlling corrosion of mild steel in well water. The inhibition efficiency has been evaluated by weight loss method. The mechanistic aspects of corrosion inhibition have been studied by electrochemical studies such as polarization study and AC impedance spectra. The protective film formed on the metal surface has been analyzed by luminescence spectra, FTIR, SEM and AFM. The protective film consists of iron-lawsone complex. The adsorption of inhibitor molecules on the metal surface obeys Langmuir adsorption isotherm.