BIOSCIENCES BIOTECHNOLOGY RESEARCH ASIA, June 2012. Vol. 9(1), proof * To whom all correspondence should be addressed. Dr. Amal Hamdy, Researcher at Analysis and Evaluation Department, EPRI. E-mail: amalhamdy66@hotmail.com Adsorption Properties and Inhibitive Effect of Antibacterial Drug on Carbon Steel Corrosion in HCl Medium M. Abbass, Khaled Z. Mohammed and A. Hamdy* Egyptian Petroleum Research Institute (EPRI), Nasr City, Cairo, Egypt. (Received: 15 August 2011; accepted: 10 October 2011) The corrosion inhibition of carbon steel in 1.0 M HCl by antibacterial drug named Cephradine (CPD), has been investigated by weight loss and potentiodynamic polarization techniqes. The results showed that CPD is an effective inhibitor for the carbon steel corrosion in acidic solution. The inhibition efficiency increases with increasing inhibitor concentration, while it decreases with the increase in solution temperature. Thermodynamic parameters were calculated and discussed. Adsorption characteristics of the inhibitor has been studied and it is found that cephradine inhibits the corrosion of carbon steel by being adsorbed on the surface of carbon steel by a physical adsorption mechanism. The adsorption of the inhibitor was also found to be spontaneous and consistent with the assumptions of Langmuir adsorption isotherm. Surface analysis using energy dispersive X-ray ( EDX) and scanning electron microscope (SEM) was applied to confirm the inhibition efficiency of cephradine. Key Words: Corrosion inhibition, Cephradine, carbon steel, polarization, adsorption. The study of carbon steel corrosion phenomena has become an important industrial and academic topic, especially in acid media, this is due to the increased industrial applications of acid solutions. The most important fields of application being acid pickling, industrial cleaning, acid descaling, oil-well acid in oil recovery and the petrochemical processes¹. However, the rate of corrosion at which metals are destroyed in acidic media is very high, especially when soluble corrosion products are formed. Therefore, investigating and exploring corrosion inhibitors for steel corrosion in acid solutions is important not only for its academic meaning but also for its practical application 2,3 . Corrosion inhibitors are used to prevent metal dissolution as well as acid consumption 4,5 . Most organic inhibitors are substances with at least one functional group, which considered as the reaction center for the adsorption process. The adsorption of inhibitors is related to the presence of heteroatom as nitrogen 6-9 , phosphorus and sulfur 10–12 . Sulphur and nitrogen containing compounds are more effective as corrosion inhibitor in hydrochloric acid 13,14 . Unfortunately most of the organic inhibitors are toxic, very expensive and environmentally unfriendly. Due to increasing environmental awareness and adverse effect of some chemicals, research activities in recent times are geared towards developing cheap, non-toxic and environmentally acceptable corrosion inhibitors 15 . Recently, studies on the use of drug derivatives as corrosion inhibitors have been