Available online at www.derpharmachemica.com ISSN 0975-413X CODEN (USA): PCHHAX Der Pharma Chemica, 2016, 8(20):20-30 (http://derpharmachemica.com/archive.html) 20 Corrosion Inhibition Effect of Allium Cepa Extracts on Mild Steel in HCl Cleophas Akintoye Loto *1,2 , Roland Tolulope Loto 1 , Ohwofasa Osugbunu 1 and Abimbola Patricia Popoola 2 1 Department of Mechanical Engineering, Covenant University, Canaan land, Ota, Nigeria 2 Department of Chemical, Metallurgical and Materials Engineering, Tshwane University of Technology, Pretoria, South Africa _____________________________________________________________________________________________ ABSTRACT A study of the effect of allium cepa extract as an inhibitor on mild steel corrosion in 0.5M HCl was made at ambient temperature. The experiments were performed with the weight loss/corrosion rate and potentiostatic polarization measurement techniques. Polarization measurement was performed using a potentiostat (Autolab PGSTAT 30 ECO CHIMIE) interfaced with a computer for data acquisition and analysis. Effective corrosion inhibition of the extract on the steel test specimens in the different concentrations of HCl used was achieved as indicated with the results obtained. There was increasing inhibition performance with increasing concentration of the extract inhibitor. The best inhibition performances were achieved at the lower exposure times for all the extract concentrations used in the 0.5 M HCl . A good correlation of results was obtained for the gravimetric and polarization experiments. A mixed type inhibitor is indicated with the results of ba and bc. Key words: Corrosion, onion, mild steel, inhibition, hydrochloric acid. _____________________________________________________________________________________________ INTRODUCTION The very wide application of mild steel and its usefulness in domestic, services, construction, marine, industrial and engineering purposes makes it unique among other metallic materials. The challenge, however, is that it is subject to environmental/corrosive degradation in service. Among the means to mitigate this destructive phenomenon is the use of chemical inhibitors – the chemical compounds that are adsorbed on the metal surfaces to control, prevent and/or minimise destructive corrosion reactions processes. Various researchers have recently shown interest in the use of plant extracts which are also referred to as green inhibitors, for corrosion inhibition of metals/ alloys in different test environments [1-12]. In many cases, the corrosion inhibitive effect of some plants’ extracts has been attributed to the various complex chemical constituents of the extracts which include tannin among others [7-9]. Extracts of plants used as inhibitors are environment friendly. This present work investigates extract of onion, Allium cepa. Allium cepa (onion) are known [13] to contain on analysis, vitamin C, vitamin B 6 , folic acid and other nutrients though in small quantities. Onions have also been found [14] to contain other chemical compounds such as phenolics and flavonoids. These have been described [15] to include quercetin and its glycosides quercetin 3, 4'-diglucoside and quercetin-4'-glucoside.