Int. J. Corros. Scale Inhib., 2018, 7, no. 1, 25 – 37 25 Expired Podocip drug as potential corrosion inhibitor for carbon steel in acid chloride solution 1 P. Dohare, a * D.S. Chauhan a,b and M.A. Quraishi c a Department of Chemistry, Indian Institute of Technology, Banaras Hindu University, Varanasi 221005, India b Present Address: C-8, Ashokpuram, Dafi, Varanasi-221011, India c Center of Research Excellence in Corrosion, Research Institute, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia *E-mail: paruldohare.17@gmail.com Abstract The application of expired drugs as corrosion inhibitors provides a cost effective and environmentally benign alternative to otherwise tedious and costly disposal/degradation process. In this context, we have investigated the use of expired Podocip (PCIP) drug as corrosion inhibitor for carbon steel in 1 M HCl by weight loss and electrochemical methods. Polarization curves revealed that the inhibiting action of the PCIP is mixed-type. The adsorption of PCIP on carbon steel surface obeys the Langmuir isotherm. Impedance analysis showed that the presence of inhibitor considerably affects the charge transfer resistance and the double layer capacitance of carbon steel surface. SEM and AFM studies evidenced the formation of a protective film over metal surface. Keywords: Podocip; carbon steel; electrochemical analysis; adsorption. Received: November 30, 2017. Published: December 25, 2017 doi: 10.17675/2305-6894-2018-7-1-3 1. Introduction Carbon steel is extensively used in a number of industries owing to its cost effectiveness and excellent mechanical strength. Industrial processes use mineral acids such as hydrochloric and sulphuric acids for acid pickling and acid descaling etc. to improve oil recovery and removal of scales and salt deposits [1 – 3]. These acids cause severe corrosion of the oil well/pipe or such structures made up of carbon steel [4 – 7]. To prevent this corrosive attack, the use of organic inhibitors is one of the most prominent methods [8, 9]. These organic inhibitors have hetero atoms like oxygen, nitrogen, sulphur, phosphorus. Universally it is reported that N-containing organic inhibitors behave as valuable corrosion inhibitors for carbon steel in acidic solution. The adsorption of inhibitors on carbon steel surface, takes place via formation of co-ordinate covalent bonds (chemical adsorption), or 1 Note from the Editors: The authors’s opinion that the degree of surface coverage by an inhibitor can be calculated from mass loss data for compounds that affect the activation energy of corrosion is deemed not quite valid by the Editors, as explained in detail in Int. J. Corros. Scale Inhib., 2015, 4, no. 2, 108 .