Journal of the Korean Chemical Society 2014, Vol. 58, No. 1 Printed in the Republic of Korea http://dx.doi.org/10.5012/jkcs.2014.58.1.25 -25- Aqueous Extract of Coriander Seeds as Green Corrosion Inhibitor for 304 Stainless Steel in Hydrochloric Acid Solutions Abd El-Aziz. S. Fouda * , Salah M. Rashwan † , and Hytham A. Abo-Mosallam ‡ Department of Chemistry, Faculty of Science, El-Mansoura University, El-Mansoura-35516, Egypt. * E-mail: asfouda@mans.edu.eg † Department of Chemistry, Faculty of Science, Suez Canal University, Egypt ‡ Water and Wastewater Company, Dakahlia, Egypt (Received September 3, 2013; Accepted January 16, 2014) ABSTRACT. Corrosion inhibition of 304 stainless steel (SS) in 1 M HCl by aqueous extract of coriander seeds was studied using weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and electrochemical frequency modu- lation (EFM) techniques. Values of inhibition efficiency obtained are dependent upon the concentration of extract and temperature. Gen- erally, inhibition was found to increase with inhibitor concentration, but decrease with temperature. Physical adsorption mechanism has been proposed for the inhibition with Langmuir adsorption isotherm obeyed. Values of activation energy of the inhibited cor- rosion reaction of 304 SS are greater than the value obtained for the blank. Thermodynamic consideration reveals that adsorp- tion of aqueous extract of coriander seeds 304 SS surface is spontaneous. Key words: Corrosion, Coriander seed extract, 304 SS, Langmuir adsorption isotherm INTRODUCTION Pure metals and alloys react chemically/electrochemi- cally with corrosive medium to form a stable compound, in which the loss of metal occurs. The compound so formed is called corrosion product and metal surface becomes corroded. Corrosion involves the movement of metal ions into the solution at active areas (anode), passage of electrons from the metal to an acceptor at less active areas (cath- ode), an ionic current in the solution and an electronic cur- rent in the metal. The cathodic process requires the presence of an electron acceptor such as oxygen or oxidizing agents or hydrogen ions. 1 Corrosion of metals is a major problem that must be confronted for safety, environment, and eco- nomic reasons. It can be minimized by suitable strategies which in turn stifle, retard or completely stop the anodic or cathodic reactions or both. Among the several methods of corrosion control and prevention, the use of corrosion inhib- itors, is very popular. Most of the efficient inhibitors are organic compounds that contain in their structures mostly nitrogen, sulfur or oxygen atoms. Unfortunately, the use of some chemical inhibitors has been limited because of some reasons namely their synthesis is very often expen- sive and they can be toxic and hazardous for human beings environment as well. This has prompted the search for eco- friendly corrosion inhibitors as an alternative to replace inorganic and organic inhibitors to foster sustainable green- ness to the environment. These nontoxic, benign, inexpensive, renewable and readily available alternative corrosion inhibi- tors have been found in different parts of plant extracts. 2 The use of plant products as corrosion inhibitors are justied by the phytochemical compounds present therein, with molecular and electronic structures bearing close similar- ity to those of conventional organic inhibitor molecules. Some research groups have reported the successful use of naturally occurring substances to inhibit the corrosion of metals in acidic and alkaline environment. Delonix regia extracts inhibited the corrosion of aluminum in hydrochloric acid solutions, 3 rosemary leaves were studied as corrosion inhibitor for the Al + 2.5 Mg alloy in a 3% NaCl solution at 25 o C, 4 El-Etre investigated opuntia extract as corrosion inhib- itor for aluminum. 5 The inhibitive effect of the extract of ginger on the corrosion of steel in polluted sodium chloride solution was investigated. 6 Also, Fouda et al. 7 investigated camellia sinensis as corrosion inhibitor for mild steel in chloride and aluminum sulfate solution. The present study is aimed to investigate the inhibitive and adsorption properties of aqueous extract of coriander seeds for the corrosion of 304 SS in HCl. EXPERIMENTAL Materials The experiments were performed with stainless steel type