Plant extracts as corrosion and scale inhibitors: A review

The definition, classification, properties, chemical composition and uses of plant extracts were reported in this review article. Corrosion of metals and alloys influences infrastructures, buildings, industrial economy, modern and old ancient works. Protection of metals and alloys against corrosion can be achieved by using different methods such as cathodic protection, environmental control, anticorrosion coatings and adding inhibitors. Plant extracts were studied as low cost eco-friendly corrosion inhibitors. They not contain heavy metals or other toxic compounds. In addition they are biodegradable and renewable source of materials. Plant extracts were classified into inhibitors for corrosion of the following metals and alloys in different aggressive corrosion media: carbon steel, aluminium and its alloys, copper and its alloys, zinc and its alloys and nickel and its alloys. Mineral scale deposits in industrial water represent a major problem leading to unexpected shutdowns and costly chemical or cleaning actions. Control of scale formation including acidification, ion exchange softening and scale inhibitors addition. The environment concerns lead the research to develop new environmentally friendly chemicals, currently named "Green" scale inhibitors. Plant extracts are recently used as green antiscalents and classified into inhibition of crystallization of each of carbonates and sulphates.