IOSR Journal of Applied Chemistry (IOSRJAC) ISSN: 2278-5736 Volume 1, Issue 6 (Sep-Oct 2012), PP 17-23 www.iosrjournals.org www.iosrjournals.org 17 | Page Electrochemical and Gravimetric Corrosion Inhibition Investigations of A Heterocyclic Schiff Base Derived From 3- Formylindole. 1 Aby Paul, 2 Joby Thomas K, 3 Vinod P Raphael, 4 Shaju K S Research Division, Department of Chemistry, St.Thomas’ College (University of Calicut) Thrissur, Kerala, India Abstract: The corrosion inhibition efficiency of Schiff base, 3-formylindole-3-aminobenzoic acid (3FI3ABA) on mild steel (MS) in 1.0 M HCl solution have been investigated using weight loss measurements, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies. 3FI3ABA exhibited good inhibition on mild steel in HCl medium even at low concentrations and the inhibition efficiencies increases with increase in concentration of the inhibitor. The adsorption of inhibitor on the surfaces of the corroding metal obeys Langmiur isotherm. Polarization studies revealed that 3FI3ABA act as a mixed type inhibitor. Thermodynamic parameters (K ads , ∆G 0 ads ) were calculated using Langmiur adsorption isotherm. Keywords: Corrosion inhibitors, Impedance. Isotherm, Mild Steel, Schiff base, I. Introduction Schiff bases, are organic molecules possessing azomethine linkage (C=N), have innumerable advantages, right from pharmaceutical applications to the corrosion inhibitions, in the various fields of science. The hetero atoms present in these molecules are of key importance and are responsible for the corrosion inhibition in acidic media on the metal surface [1-3]. Some recently reported Schiff bases showed effective inhibition for mild steel (MS), Aluminum, Copper and Zinc in acidic media [4-11]. Enormous use of hydrochloric acid for acid pickling, de-scaling and cleaning process of mild steel surface are the major reasons for the corrosion problems in the world. Increasing efforts have been made to study the corrosion behavior of metals and mechanism of inhibition during the past decade mainly through electrochemical investigations [8,9]. Limited work has been reported for the corrosion inhibition of compounds derived from 3-formylindole in acid media. The present investigation was undertaken to examine the corrosion inhibition capacity and mechanism of inhibition of a novel heterocyclic Schiff base (3FI3ABA) molecules derived from 3-formylindole and 3- aminobenzoic acid in 1M HCl solution on MS. The study was performed using weight loss measurements, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization analysis. II. Experimental Inhibitor Heterocyclic Schiff base was obtained by the condensation of equimolar mixture of 3-formylindole and 3-amino benzoic acid in ethanol. The reaction mixture was refluxed for 2 hours, evaporated and cooled in ice bath to obtain yellow coloured compound. Figure 1 shows the molecular structure of heterocyclic Schiff base 3FI3ABA. Anal.calcd for C 16 H 12 N 2 O 2 : C, 72.72; H, 4.55; N, 10.61 ; O, 12.12%. Found. C, 70.96; H, 5.10; N, 9.98 ; O, 12.17% ; m.p. = 180 0 C; IR (KBr) : ν C=N = 1600 cm -1 . 1 Hnmr: δ COOH 11.99, δ CH=N 9.79, δ NH 6.83. 13 Cnmr: δ COOH 187.56, δ CH=N 130.32. Mass:M + peak m/z:264 (Base peak). NH N HOOC Figure 1: Molecular Structure of 3FI3ABA Solutions The aggressive solutions of 1M HCl were prepared by dilution of A.R grade 37% of HCl (Merck) with de-ionized water. Inhibitor solutions were prepared in the range, 0.1mM-1mM concentrations. Weight loss measurements Mild steel specimens of dimension 1.5x 2x 0.1 cm were cut abraded with various grades of silicon carbide papers (200, 400, 600, 800, 1000, 1200and 2000). The exact area and thickness of each coupon were measured and washed with distilled water containing detergent. Specimens were then degreased again with acetone and finally dried. After weighing with sensitive electronic balance, specimens were immersed in 50ml