www.tjprc.org editor@tjprc.org International Journal of Metallurgical & Materials Science and Engineering (IJMMSE) ISSN(P): 2278-2516; ISSN(E): 2278-2524 Vol. 4, Issue 2, Apr 2014, 9-18 © TJPRC Pvt. Ltd. SYNERGISTIC INHIBITION BETWEEN AMPICILLIN TRI-HYDRATE AND KI FOR CORROSION OF CARBON STEEL IN 1M HCl SOLUTION HAMEED HUSSEIN ALWAN Department of Electrochemical Engineering, College of Engineering, Babylon University, Iraq ABSTRACT The effect of Ampicillin tri-hydrate C 16 H 19 N 3 O 4 S on the corrosion of carbon steel in 1 M HCl solution was studied by weight loss and electrochemical polarization techniques at 30 ○ C (313 K), Ampicillin tri-hydrate concentrations used in the study were (0.001, 0.002, 0.003 and 0.004)M .The effect of KI addition on corrosion inhibition efficiency was also studied. The results show that inhibition efficiency increased with Ampicillin tri-hydrate concentration and synergistically increased in presence of KI. The adsorption of Ampicillin tri-hydrate and KI on carbon steel surface follows Freundlich isotherm and, adsorption on surface of carbon steel is spontaneously due to adsorption free energies calculation.The synergistic parameter values indicating that the enhancement of inhibition efficiency is due to synergism caused by adding halides ions. KEYWORDS: Corrosion, Corrosion Inhibitor, Adsorption Isotherm, Activation Energy, Synergistic Inhibition INTRODUCTION Carbon steel is widely used in various industrial operations and the study of corrosion of carbon steel and its protection is a subject of practical significance. In efforts to mitigate electrochemical corrosion, the primary strategy is to isolate the metal from corrosive agents. A useful method for achieving in this is addition of species to the solution in contact with the surface in order to inhibit the corrosion reaction and reduce the corrosion rate. [1-3] Study of organic corrosion inhibitors is an attractive field of research due to its usefulness in various industries. Most of the well-known acid inhibitors are organic compounds that containnitrogen, sulphur, oxygen and multiple bonds in the molecules through which are adsorbed on the metal surface. The protection of metals against the corroding action is accomplished by adding chemical substances of small concentration to environment; these chemicals are called “Inhibitors”. So inhibitors are chemical compounds that deposit on exposed metal surfaces from the corrosive environment. The inhibitor may form a uniform film, which like a coating, acts as a physical barrier. Organic compounds which containing sulfur, phosphorus; oxygen nitrogen and aromatic rings are most effective and efficient inhibitors for the metals in acidic medium due to their molecular structure. [4-6] The presence of halide ions in solution has been found to stabilize the adsorption of someorganic cations leading to improved inhibition efficiency. Synergism has become an increasing important phenomenon and serves as the basis for most modern corrosion inhibitor formulation. Trials to enhance the performance of naturally occurring substances by addition of small amount of halide ions have been reported by some authors. [3, 7-8]. In the present work it was examined the synergistic corrosion inhibition between Ampicillin tri-hydrate and potassium iodide for inhibit corrosion of carbon steel in 1M HCl solution in which Ampicillin tri-hydrate represented as cations while KI work as anions. Adsorption mechanism was studied and synergism parameter was evaluated also.