Corrosion Inhibition by an Aqueous Extract of Rhizome Powder

An aqueous extract of the plant material rhizome (Curcuma longa L.) powder has been used as a corrosion inhibitor in controlling corrosion of carbon steel immersed in an aqueous solution containing 60 ppm of Cl^–, by the mass-loss method, in the absence and presence of Zn²⁺. The main constituent of this plant extract is curcumin. It has good inhibition efficiency (IE) and shows good IE at extreme pH values. In the presence of Zn²⁺, there exists a synergistic effect. Synergism parameters have been calculated. The protective film has been analyzed using Fourier transform infrared (FTIR) spectroscopy. The film consists of a Fe²⁺-curcumin complex and zinc hydroxide (Zn[OH]₂). It is found to be UV-fluorescent. Electrochemical studies such as potentiodynamic polarization and alternating current (AC) impedance have been used to find the mechanistic aspects of corrosion inhibition.