International Journal of Scientific Engineering and Research (IJSER) ISSN (Online): 2347-3878 Impact Factor (2018): 5.426 Volume 7 Issue 2, February 2019 www.ijser.in Licensed Under Creative Commons Attribution CC BY Thermodynamics Study of Inhibitory Action of Lignin Extract from Gmelina arborea on the Corrosion of Mild Steel in Dilute Hydrochloric Acid Ezeibe A.U. 1 , Nleonu E.C. 2 , Ahumonye A.M. 3 Chemistry/Biochemistry Department, Federal Polytechnic Nekede, Owerri – Imo State, Nigeria Abstract: Inhibitive effect of Lignin extract from Gmelina arborea bark on the corrosion of mild steel in 1M Hydrochloric Acid solution was studied by weight loss method with various periods of contact and temperature. The study revealed that the percentage inhibition efficiency increased with increase in inhibitor concentration. The temperature studies reflect that the adsorption of inhibitor on metal surface takes place via physisorption and through a spontaneous process. The inhibition at the metal surface was confirmed by X- ray diffraction examination. Keywords: Lignin extract, mild steel, corrosion inhibitor, thermodynamic studies, Gmelina arborea 1. Introduction Metallic materials are still the most widely used group of materials particularly in both mechanical engineering and transportation industry. However, the usefulness of metals and its alloys are constrained by corrosion (Buchweishaija, 2009). Corrosion is an undesirable phenomenon that ought to be prevented using corrosion inhibitors. Corrosion inhibitors have continued to play a crucial role in the industry where metals are exposed to acid environment. Plant extracts have been receiving increasing attention as green corrosion inhibitors because of their richness in natural biodegradable chemicals that are environmentally friendly (Olusegun et al., 2011). This paper reports the inhibition of corrosion of mild steel in dilute HCl solution using lignin extracted from Gmelina Arborea. 2. Experiments 2.1 Extraction of Lignin Gmelina arborea tree readily available in Federal Polytechnic Nekede, Owerri, Imo State Nigeria was utilized as the source of lignin. The Gmelina arborea bark were collected from the tree, cut into small pieces and were sun dried for one week. The dried samples were then pulverized into fine powder using an electric grinding machine. The wood sample was subjected to extraction with 15% (w/v) NaOH at 80 o C for 2 hours with continuous agitation. The ratio of wood sample to liquid in the extraction was 1:10. After 2 hours, the mixture was removed, allowed to cool for 12 hours after which it was filtered and the filtrate was acidified by drop-wise addition of 40% H 2 SO 4 to a pH of 2.0. The lignin was isolated by precipitation and was filtered, washed with 70% ethanol and dried in an oven at 60 o C to obtain pure lignin extract of Gmelina arborea bark. 2.2 Solution Preparation Solution of HCl was prepared by dilution of concentrated HCL 37% (w/v) from BDH using deionized water. All chemicals and solvents used were of analytical reagent grade. All solutions were prepared using deionized water. 2.3 Coupons Preparation The metal coupon used in this study was mild steel. Rectangular coupons of mild steel were cut into 3.0mm x 3.0mm x 0.7mm dimensions. Pre-treatment of the surface of coupons was carried out by cleaning with emery paper, rinsed with deionized water, degreased with acetone, dried and stored in a dessicator prior to use. 2.4 Weight Loss Measurements The polished and pre-weighed mild steel coupons were immersed in 100ml of 1M HCl solutions of the respective inhibitor/blank solutions maintained at 303, 313, 323, 333 and 343K in a thermostated bath for 2 hours with 1.0 % lignin extract. After which the coupons were removed washed, cleaned and weighed. Another set of experiment was carried out at room temperature for various concentrations of 0.5, 1.0, 1.5, 2.0 and 2.5% of lignin respectively in 1M HCl for 12 days. The coupons immersed in these solutions were weighed at two days intervals. Mass loss and corrosion rate measurements were deployed to evaluate the corrosion behavior of the test samples. The corrosion rate (g/cm 2 /hr) and Inhibition efficiency (%) were calculated from the relationship: Corrosion Rate (CR) =W/At (g/cm 2 /hr) (1) Where, W = Weight loss of the mild steel after time t (grams), A = the area of the mild steel coupon (cm 2 ), t = the time of immersion (hours) Inhibition Efficiency IE (%) = 1 – W 1 /W 2 x 100 (2) 2.5 FT – IR Analysis The FT-IR analysis of the pure Lignin extract and Lignin extract after corrosion were studied using Fourier Transform Infrared Spectrophotometer (Happ-Genzel Model) to determine the functional groups present in the lignin and responsible for its inhibitive properties. Paper ID: IJSER18649 133 of 136