ASIAN JOURNAL OF CHEMISTRY ASIAN JOURNAL OF CHEMISTRY https://doi.org/10.14233/ajchem.2017.20702 INTRODUCTION The use of mild steel in industries is due to its availability, good strength and comparatively low cost. The overall cost of metal is the total cost of itself plus its maintenance cost and it can be reduced by reducing the maintenance cost. The mainte- nance cost can be controlled and minimized. But presently in all countries, most of the industries are facing the problem of corrosion of mild steel in acidic medium [1]. It involves a significant cost expense for prevent or non-prevent of the metals. On the one hand if protection methods are not used, the maintenance and renovation cost will be increased due to many premature, unexpected and expensive failure in system. On the other hand, if protection methods are used, it involves the cost of corrosion prevention but protection of metal is a powerful tool to reduce the overall cost and liabilities of the system. The cost also increases due to high temperature and corrosive sulphur gases, surrounding chemical and petroleum industries in industrial areas. Cost of corrosion will escalate substantially during the next decade because of worldwide shortages of construction materials, higher energy costs, aggressive corrosion environment in coal conversion processes and other factors. In fact our economy would be drastically changed if there is no corrosion and appliances would not require coatings. However, corrosion rate can be controlled and minimized. Most of the methods reported in literature are not only expensive but also toxic in nature. Therefore, a great need to investigate a non-toxic replacement that is compatible with current industrial technologies with their availability and relatively low cost, naturally substances. The use of plant Tribulus terrestris Extracts: An Eco-Friendly Corrosion Inhibitor for Mild Steel in H 2 SO 4 Medium SUCHITRA CHAUDHARY * and RAKESH K. TAK Department of Chemistry, Samrat Prithviraj Chauhan Government College, Ajmer-305 001, India *Corresponding author: E-mail: suchitra_gca@yahoo.com Received: 1 May 2017; Accepted: 15 May 2017; Published online: 12 June 2017; AJC-18454 The easily available plant Tribulus terrestris can be used as low-cost, eco-friendly corrosion inhibitor for mild steel in aggressive industrial environment. The inhibition efficiencies of different extracts (fruit, leaf and stem) in relation to the concentration of inhibitor and temperature were determined by mass loss method. Further electrochemical measurements (EIS and potentiodynamic polarization) were also done. Surface analysis was examined by scanning electron microscope. The adsorption process obeys Langmuir adsorption isotherm. All these analysis confirm that plant Tribulus terrestris has good properties to prevent the corrosion of mild steel in acidic medium. Keywords: Corrosion inhibitors, Tribulus terrestris, Mass loss, Electrochemical measurement, Langmuir adsorption isotherm. Asian Journal of Chemistry; Vol. 29, No. 8 (2017), 1859-1865 extracts as corrosion inhibitors are economic, environmentally safe and readily available and it can be replaced the synthetic and toxic inhibitors. Extract of plants contain various organic compounds having hetero-atoms such as O [2], S [3] and N [3,4]. These hetero-atoms coordinate with the metal atom though their π electrons and form a protective film on metal surface, therefore corrosion is prevented. A lot of technological efforts have been studied to workout the natural corrosion inhibitors for iron or steel in acidic media, such as Amaranthus by Nigam and Srivastava [5], Prosopis juliflora by Chowdhary et al. [6], Azardirachta indica (Neem) by Oguzie [7], Emblica officinal (Indian Gooseberry) by Sartha and Vasudha [8], Facourita jangomas by Khalid Hasan and Sisodia [9], Andrographis paniculata (Kalmegh) by Singh et al. [10], Aloes by Cang et al. [11]. Tagetes erecta by Mourya et al. [12], Retema monosperma by Hamdani et al. [13] and Canna indica by Mathina and Rajlakshmi [14]. In the present work, an attempt has been made to study the influence of various concentrations of alcoholic extracts of fruit, leaf and stem constituents of plant Tribulus terrestris on mild steel in sulphuric acid as a powerful tool to reduce the cost of maintenance and increase the plant life. The Tribulus terrestris plant belongs to the Zygophyllaceae family. It is an annual creeping herb widespread in large area of India, China, eastern Asia and extends into western Asia and southern Europe. The preliminary phytochemical study of Tribulus terrestris revealed the presence of saponins, flavonoids, glycosides, alkaloids and tannins [15]. In India its usage in Ayurvedic medicine was for the purpose of impotency, poor appetite, jaundice, urogenital disorders and cardiovascular diseases [16].