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Benzoic acid, salicylic acid, Anthranilic acid, 2- Nitro benzoic acid, 2- Chlorobenzoic acid compounds containing acidic group as a corrosion inhibitor for carbon steel was investigated. The study revealed that the various group such as (- COOH, OH, Cl and –NO2) containing in organic compounds has an inhibitory action on the corrosion of carbon steel in the investigated medium. Corrosion rate of mild steel was studied using chemical weight loss method at room temperature. This research paper presents use of carboxylic group organic compounds as corrosion inhibitors for metals in 0.1N, 0.01N and 0.001N (HCl, HNO3 and H2SO4) acidic medium. A common mechanism for inhibiting corrosion involves formation of a coating, often a passivation layer, which prevents access of the corrosive substance to the metal. Organic corrosion inhibitors adsorb on the surface to form protective film, which displace water and protect it against deteriorating. Effective organic corrosion inhibitors contain nitrogen, oxygen, sulphur and phosphorus with lone electron pairs as well can contain structural moieties with π-electrons that interact with metal favouring the adsorption process. This review presents mechanisms and monitoring of corrosion, laboratory methods for corrosion study, relationship between structure and efficacy of corrosion inhibitions, theoretical approach to design new inhibitors and some aspects of corrosion. Keywords: Corrosion, Inhibition, carbon steel, Weight loss and acidic group (-COOH, OH, -Cl and –NO2) group containing organic compounds.

Inhibition of corrosion of mild steel in hydrochloric acid by natural plant leaves extract of of Bahunia Varigata (Aapta), Azadirachta Indica (Neem), Pongamia Pinnata (Karanj), Santalum Album (Sandal Wood) and Astonia Scholaris (Saptparni) has studied using weight loss measurement. It was, found that the leaves extract act as a good corrosion inhibitor for mild steel in all concentrations of the extract. The inhibition action depends on the concentration of the leaves extract in the acid solution. Results for weight loss measurements indicate that inhibition efficiency increase with increasing inhibitor concentration. Extract of natural plants is one of the most important metallic corrosion inhibitors. They are readily available, nontoxic, environmentally friendly, biodegradable, highly efficient, and renewable. Several organic compounds with heteroatom such as N, O, S and P present in the plant extracts are, adsorbed directly onto the metals surface through polar atoms and thereby forming the protective layer. Plants represent a class of interesting source of compounds currently being, explored for use in metal corrosion protection in most systems, as possible replacement of toxic synthetic inhibitors. This paper discusses the different types of natural green plant leaves extract inhibitors for corrosion control of mild steel in acid medium. Keywords: Corrosion, Inhibition, carbon steel, Weight loss and natural plant leaves extract.

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