ASIAN JOURNAL OF CHEMISTRY ASIAN JOURNAL OF CHEMISTRY https://doi.org/10.14233/ajchem.2017.20449 INTRODUCTION Corrosion stand as one of the most serious problems in our modern societies and the resulting losses each year are in hundreds of billions of dollars [1,2]. Several ways to control the corrosion of the metallic materials are constantly reviewed and discussed by corrosion scientists and engineers. Never- theless, the corrosion damage is not totally prevented but it can be minimized using different corrosion control methods [3,4]. The use of corrosion inhibitors (CIs) is one of the best known methods to control the corrosion and mostly used in the industries due to its low cost and easy practice method [5,6]. An efficient inhibitor is compatible with the environment and is economical for application [7]. Nowadays, the corrosion control method of metallic materials using various types of eco-friendly green corrosion inhibitors is becoming a funda- mental research concern of corrosion scientists and engineers, because a corrosion inhibitor is a chemical substance that when added in small amounts to a corrosive environment, effectively decreases the corrosion rate of the materials exposed to corro- sive environments [3-5]. A practical criterion for the selection of corrosion inhi- bitors is not only their inhibition efficiency but also safety of use, economic constraints and compatibility with other chemi- cals in the system. In the past, many inorganic salts and organic compounds employed as corrosion inhibitors were found to Extract of Different Plants of Nepalese Origin as Green Corrosion Inhibitor for Mild Steel in 0.5 M NaCl Solution MANOJ RANA, SUSAN JOSHI * and JAGADEESH BHATTARAI * Central Department of Chemistry, Tribhuvan University, GPO Box 2040, Kathmandu, Nepal *Corresponding authors: Fax: +977 9841609766; Tel: +977 01 4333748; E-mail: susanjoshi68@gmail.com; bhattarai_05@yahoo.com Received: 16 December 2016; Accepted: 18 February 2017; Published online: 10 March 2017; AJC-18313 Corrosion inhibition effect of Areca catechu, Laurus nobilis and Catharanthus roseus plant extracts on mild steel was investigated in 0.5 M NaCl solution in open air at 28 ± 1 °C using immersion tests, inhibition mechanism and corrosion potential measurements. The corrosion rate of the steel was decreased with increasing the concentration of the extracts up to 2000 ppm. Catharanthus roseus plant extract was found to be most efficient inhibitor among the three extracts used in this study. Adsorption of all three plant extracts on the surface of the mild steel obeyed both Langmuir and Temkin adsorption isotherms. Areca catechu and Catharanthus roseus plant extracts acted as an anodic type corrosion inhibitor, while Laurus nobilis extract acted as mixed type inhibitor based on the potential measurement. Consequently, all the three plant extracts can be used as an environmentally friendly inhibitor to control the corrosion of mild steel in aggressive environments. Keywords: Green inhibitor, Plant extract, Corrosion, Mild steel, 0.5 M NaCl. Asian Journal of Chemistry; Vol. 29, No. 5 (2017), 1130-1134 be quite toxic and do not fulfill completely the requirements imposed by the environmental protection standards, although they showed high corrosion inhibition efficiency even in aggre- ssive solutions. The concern regarding toxicity and pollution free environment is recently increased, because of its direct impact on human health. Many inorganic salts and organic compounds employed as corrosion inhibitors are found to be quite toxic and do not fulfill all the requirements imposed by the environmental protection standards. Therefore, better alternatives for such toxic corrosion inhibitors are the green corrosion inhibitors. In recent years, the reason for the search of less toxic corrosion inhibitors alternatives is becoming very interesting topics of research [8]. There is a trend of replacing harmful corrosion inhibitor by effective non-hazardous green corrosion inhibitors mostly of plant extracts, because the green inhibitors are generally biodegradable, do not contain heavy metals and impose zero or negligible toxicity to the environment and human beings. The green corrosion inhibitors extracted from plants presumably possess biocompatibility due to their biological origin. In addition, these plant extracts are easily available, because abundant of plant resources in nature. On the other hand, in order to ensure the more durability of the new steel-structures exposed to aggressive environments, we need to understand what can be done to reduce the corrosion risk of the structural materials in different corrosive environ- ments. In general, iron or steel passivated at a pH higher than