RESEARCH ARTICLE EXPERIMENTAL AND THEORETICAL STUDIES ON THE CORROSION INHIBITIVE PROPERTIES OF MILD STEEL IN 2M H2SO4 ACID SOLUTION BY ETHANOLIC EXTRACT OF BRACHYSTEGIA EURYCOMA SEED Chimezie P. Ozoemena 1 *, Milam Charles 2 , and Mary C. Ugwuoke 3 1 Department of Chemistry, University of Uyo, Akwa Ibom State, Nigeria 2 Department of Chemistry, Moddibo Adama University of Technology, Adamawa State, Nigeria 3 Department of Biochemistry, Michael Okpara Univsrsity of Agriculrure,Umudike, Abia State, Nigeria ARTICLE INFO ABSTRACT The experimental aspect of the corrosion inhibition potentials of Brachystegia eurycoma seed extract was carried out using Phytochemical Screening and gravimetric techniques as well as scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR), whereas the theoretical aspect was studied using the density functional theory calculations to be performed and modeling the electronic structures of some extract constituents, including physiosorptive interactions with the mild steel surface. The analysis of the weight loss results showed that the Inhibition efficiency of the Brachystegia eurycoma seed extract is directly proportional to its concentration and inversely proportional to solution temperature and mild steel contact time in the test solution. The inhibition efficiency increases gradually reaching a maximum value of 96% within the first 24 hours at a concentration of 0.5g/l. The kinetic study shows that the inhibitory action is a first order kinetics with the concentration of the seed extract of Brachystegia eurycoma which is best fitted with the Langmuir adsorption isotherm. This was further supported by the thermodynamic parameters which indicate that the adsorption of Brachystegia eurycoma seed extract onto the metal surface was spontaneous, exothermic and has contributed to physical adsorption process. FTIR results showed that the inhibition mechanism was an absorption process through the functional groups present in the seed extract. Surface morphology also revealed that corrosion product confirmed the protection offered by the extract on the surface of the metal immersed in the acid media. Quantum chemical studies indicated that inhibition was due to adsorption of active molecules leading to formation of a protective layer on surface of mild steel. Quantum chemical parameters such as highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy levels, HOMO–LUMO energy gap and electronic density were virtually identified. Quantum analysis demonstrated reactive centres of electrophilic and nucleophilic attack and strong inhibition properties of bioactive molecules of BES extract. Copyright © 2019, Chimezie P. Ozoemena et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. INTRODUCTION The use of mild steel and any other metals in chemical industries cannot be overstressed due to its mechanical properties and wide range of application as structural material for vessels reactor, pipelines, tank, construction works and other industrial equipment which are known to corrode invariably in contact with various solvents (S. Junaedi et al., 2012). Acid solutions especially sulfuric acid used for industrial processes such as acid pickling, industrial cleaning, acid descaling, etching of metal and acidic operations may cause damage to metal surface (Akalezi et al., 2012; Okorokwo et al., 2015; Peter et al., 2016; Akalezi and Oguzie, 2015). *Corresponding author: Chimezie P. Ozoemena, Department of Chemistry, University of Uyo, Akwa Ibom State, Nigeria. However, contact between the metal and acidic media exposed most industrial equipment to corrosion. Corrosion degrades the useful properties of materials and structures including strength, appearance and permeability to liquids and gases thereby affecting the tensile strength and utility efficiency of the material (Samuel et al., 2015). In view of the nation’s economy and financial implications of corrosion menace, researchers are compelled to do copious scientific studies in an attempt to improve the resistance of metals. Corrosion inhibitors have proven to be the most convenient means of protecting metals due to their unique properties which enhances their capability to resist the corrosion process as compared to other methods (i.e. electroplating, coatings, alloying elements, and plastic deformation) (U. Leon-Silva et al., 2010; Gutierrez et al., 2016; EL-Basiony et al., 2019). ISSN: 0976-3376 Asian Journal of Science and Technology Vol. 10, Issue, 12, pp.10532-10544, December, 2019 Available Online at http://www.journalajst.com ASIAN JOURNAL OF SCIENCE AND TECHNOLOGY Article History: Received 15 th September, 2019 Received in revised form 29 th October, 2019 Accepted 17 th November, 2019 Published online 30 th December, 2019 Key words: Corrosion, Corrosion Inhibitors, Mild Steel, Weight Loss, scanning electron microscopy, Quantum Analysis, Kinetic, Thermodynamics. Citation: Chimezie P. Ozoemena, Milam Charles and Mary C. Ugwuoke. 2019. “Experimental and Theoretical Studies on the Corrosion Inhibitive Properties of mild Steel in 2M H2SO4 Acid Solution by Ethanolic Extract of Brachystegia Eurycoma Seed”, Asian Journal of Science and Technology, 10, (12), 10532-10544.