International Journal of Materials and Chemistry 2017, 7(3): 47-54 DOI: 10.5923/j.ijmc.20170703.01 Evaluation of the Inhibitive Effect of Annona Muricata .L Leaves Extract on Low-Carbon Steel Corrosion in Acidic Media N. B. Iroha 1,* , M. A. Chidiebere 2 1 Department of Chemistry, Federal University Otuoke, Yenagoa, Nigeria 2 Electrochemistry and Materials Science Research Laboratory, Department of Chemistry, Federal University of Technology, Owerri, Nigeria Abstract The inhibition of low-carbon steel corrosion in 1 M HCl by extracts of Annona Muricata .L leaves was investigated using gravimetric and electrochemical techniques. The results show that the leaves extract functioned as effective corrosion inhibitor for low-carbon steel and its inhibition efficiency was concentration dependent. Weight loss method showed that the inhibition efficiency of the extracts increases with increase in its concentration and exposure time but decreases with increase in temperature. Potentiodynamic polarization results showed Annona Muricata .L leaves to be a mixed type inhibitor in 1 M HCl environment, whereas the electrochemical impedance spectroscopy results revealed adsorption of the extracts species on the steel surface. Fitting of the experimental data to the Arrhenius equation revealed that the constituents of the leaves extract were physically adsorbed on the corroding carbon steel surface. The experimental data complied with the Langmuir adsorption isotherm and the negative values of the Gibb’s free energy of adsorption obtained suggested that inhibitor molecules have been spontaneously adsorbed onto the carbon steel. Keywords Steel, Annona Muricata .L, Corrosion inhibitor, Weight loss, Potentiodynamic polarization, Electrochemical impedance spectroscopy 1. Introduction Iron and its alloys are very useful in diverse industrial and structural applications. Acid solutions like hydrochloric acid are widely used in the chemical industry for removal of undesired scales and rust, processes which usually leads to metal corrosion. Since aggressive acid solutions are widely used for industrial purposes, the addition of inhibitors effectively secures the metal against an acid attack. Most synthetic corrosion inhibitors are highly toxic to both human beings and the environment. This has motivated the use of some natural products as corrosion inhibitors. Most of the natural products are non-toxic, biodegradable and readily available [1-3]. Most researchers recently started studying the application of extracts of some common plant as corrosion inhibitors [4-9]. These extracts contain different hydroxy organic compounds, e.g. tannins, pectin, flavoniods, anthraquinones, steroids, saponins and coumarins in addition to other nitrogen containing compounds. * Corresponding author: nkemib@yahoo.com (N. B. Iroha) Published online at http://journal.sapub.org/ijmc Copyright © 2017 Scientific & Academic Publishing. All Rights Reserved The leaves of Annona muricata .L are dark green, glossy, oblong and smooth, with no hairs. The phytochemical screening of Annona muricata L leaves revealed the presence of flavonoids, saponins, terpenes, tannins and alkaloids [10]. The major constituent in the leaves of Annona muricata L is an alkaloid named 6-hydroxyundulatine among other alkaloids. The presence of these heterocyclic compounds is believed to be responsible for its inhibitory action. 2. Materials and Methods 2.1. Material Preparation Carbon steel coupons of dimension 2 x 4 x 0.15cm with weight percentage composition as follows: C, 0.05; Mn, 0.6; P, 0.36; Si, 0.3; and the balance Fe were used in this study. The coupons were prepared and cleaned as described elsewhere [9]. The blank corrodent was a solution of 1.0 M HCl. Stock solutions of Annona muricata .L leaves extract were prepared by boiling weighed amounts of the dried and ground plant material for 4 h in 1 M HCl. The solutions were cooled and then filtered and stored. From the respective stock solutions, inhibitor test solutions were