INHIBITION AND ADSO-KINETIC STUDIES OF Gmelina arborea FRUIT EXTRACT ON CORROSION OF ARMOUR STEEL PLATE IN HYDROCHLORIC ACID

The evaluation of inhibitive action of crude Gmelina arborea fruit extract (GAFE) on armor steel plate ASP) in 0.1M HCl solutions has been investigated using different methods viz; weight loss method at temperature 303K-313K, Electrochemical technique (Linear Polarization Resistance) and Surface morphologic examination, using Phenom Prox Scanning Electron Microscope. The inhibitive action is observed to increase with increase in concentration of the extract, but decreases with increase in temperature. The Extract gave highest inhibition efficiency (IE) of 87.50% at 303K and 78.87% at 313K at maximum extract concentration of 0.5g/L. Inhibition efficiency (IE) of extract decreased with increasing temperature for both acids. Thermodynamic parameters evaluated gave heat of adsorption (Qads) range between -24.4904 kJ/mol -16.4337 kJ/mol with an average of 6.1547kJ/mol. The Activation energy parameter (Ea) is between 4.11 to 14.76 kJ/mol, which indicates physisorption. Free energy of adsorption process (∆G°ads) showed negatives values, which explained the spontaneous adsorption activity. Adsorption process of GAFE on armor steel plate best fitted and obeyed the El-Awady isotherm. The El-Awady 1/y parameter is <1 at all test conditions. Electrochemical investigations (LPRcurve), reveals that GAFE acts as a mixed inhibitor by retarding the cathodic and anodic reaction. Micrographs from SEM, shows evidence of plant material adsorption on ASP under similar test conditions with near smooth surface. In contrast, Micrographs of ASP after immersion in acids without GAFE shows evidence of general and localized corrosion (pitting). Keyword: Gmelina arborea, Armour steel Plate, ductility, Corrosion, Inhibition and toughness 1.0 INTRODUCTION Armor steels are versatile materials alloys of iron used in Military and defense related field in manufacture of combat air craft, Tanks, ships and submarines. They are largely low-carbon, mediumalloy steels of special compositions used for protection from projectiles and ballistics dues to it toughness, weldability, and ductility (Laible, 1980; Prifti et al., 1997). Armour Steels like every other material corrodes and poses a major challenge to defence industries fleets against optimum performance and combat readiness. The effect of corrosion can best be appreciated by the annual cost of its prevention, the direct and indirect value of which, survey on the costs of corrosion showed that the direct cost of corrosion was estimated at $276 billion in the United States for 2002, which is approximately 4% of their Gross National Product (Koch et al., 2002). The Wall Street Journal (1981) estimates it to be over hundreds of millions of US dollars all over the world. In view of the foregoing, corrosion no doubt has proven to be an undesirable phenomenon that must be arrested or controlled (Buchweishaija , 2010). In order to reduce the metal loss as a result of corrosion, tests and use of suitable inhibiting agents as corrosion inhibitors in different environment is necessary. (NACE, 1984; 2002) defines inhibitor as a chemical substance that, when added in a small concentration to an environment, effectively decreases the corrosion rate of the material. Most of these inhibiting compounds are not only expensive; they are toxic and not environmental friendly. Due to the toxicity of some corrosion inhibitors, there has been increasing search for green or organic corrosion inhibitors (Muthukrishnan et al, 2013). These natural organic inhibitors has been tested and found to be effective in various media and and at same time environmentally friendly, non-toxic, biodegradable, inexpensive, and readily available in nature (El-Etre, 2007; Okafor et al., 2008). These anti corrosion effect has been suggested to be due to the presence of hetero atoms (N, O, and S) as well as IJSER International Journal of Scientific & Engineering Research, Volume 6, Issue 9, September-2015 702 ISSN 2229-5518