Many industries face corrosion caused by the alkaline medium. There are various techniques to minimize the corrosion such as anodic protection, cathodic protection, coatings and green corrosion inhibitor. To minimize the effect of corrosion in an alkaline medium, green technology i.e. green corrosion inhibitor has been widely used. Natural plant-based extract is used as green corrosion inhibitor to mitigate the problem of corrosion. It is naturally occurring, non-expensive, safe and ecologically acceptable. The plant origin extract contains tannins, alkaloids, organic, amino acids which are main functional groups in mitigating the corrosion. The present review paper summarizes the various plant-based green corrosion inhibitor used for minimizing the corrosion of mild steel in an alkaline medium. Also, the plausible mechanism for the inhibition of corrosion in alkaline medium is explained comprehensively.

Acidic solutions is widely adapted in industries for various operations whereas green corrosion inhibitors is used for the elimination of corrosion / deposition of scales. By using inhibitors, control of metal corrosion occurs in aggressive environment. Various types of natural composites were designed for finding out corrosion inhibition efficiency. Organic compounds possessing nitrogen, sulphur and oxygen exposed excellent inhibition effectiveness. Nevertheless, large number of natural compounds have toxic effect on environment as well as on living organism. Hence, it is necessary to point out cheap, easily available, biodegradable and eco-friendly inhibitor to corrosion with high inhibition efficiency. This article deliberates the properties of inhibitor, adsorption mechanism of inhibitor, inhibition mechanism and inhibitor efficiencies of plant extract in aggressive acidic environment.