Synergistic Effect of Potassium Iodide on Corrosion Inhibition of Mild Steel in HCl Medium by Extracts of Nypa Fruticans’ Wurmb

Abstract

The effect of Nypa fruticans' wurmb extract and the mixture of various concentration of KI and Nypa fruticans' wurmb extract on corrosion of mild steel in 0.1M and 0.5M HCl have been investigated using weight loss methods. The study revealed that mild steel is more efficiently inhibited by Nypa fruticans' wurmb in the presence of KI than pure extract of Nypa fruticans' wurmb. The inhibition efficiencies increased with increased concentration of the additives. The highest inhibition efficiency of 77.31% was observed with single Nypa fruticans' wurmb extract. An improved inhibition efficiency of 95.36% was observed with the mixture of Nypa fruticans' wurmb extract and KI at 30 o C in 0.5M HCl. Inhibition efficiency decreased with increase in temperature from 30-40 O C but increased at relatively high temperature of 50 O C an effect attributed to synergism between Nypa fruticans' wurmb extract and KI. The adsorption of inhibitor molecules on metal surface followed langmuir isotherm. Thermodynamic parameters such as heat of adsorption, ∆H, free energy of adsorption ∆G and enthropy of adsorption are obtained from experimental temperatures ranging from 30-50 O C.@JASEM Corrosion of metals has continued to receive attention in the technological world. Corrosion scientists are relentless in seeking better and more efficient ways of combating the corrosion of metals. Among other methods, adding inhibitors to the corrosion environment has been employed.The efficiency of these inhibitors is sometimes improved by the addition of some other compounds which act in synergism. Many studies have been carried out using synergistic corrosion inhibitors (Beloglazow, 1989 and Ebenso et al,1999) to mention but a few. In the search for more environmentally friendly and readily available inhibitors, researchers have reported the use of local plants such as Vernonia Amygdalina (Loto, 1998), Lawsonia (El-ttre, et al 2005); among others. In line with these Nypa fruticans' wurmb a local plant has also been reported as inhibitor for mild steel in HCl medium (Orubite and Oforka 2004); which has similar inhibition properties with 1, 5, Di-phenyl carbazone (Orubite and Oforka 2004);. The inhibition efficiency of Nypa fruticans' wurmb on mild steel in HCl medium as reported in previous work could be improved. Reports (Guan Nan Mu, Xueming Li 2004); have shown that inhibition efficiency of an inhibitor can be improved by the addition of halide ions to the inhibitor, a process referred to as synergism. Synergistic inhibition effectively improves the inhibition efficiency of an inhibitor. It also results in decrease in amount of inhibitor used and diversification of application in corrosive media. Many investigations on synergistic inhibition are available in literature. Not much has been reported on the synergistic effects on naturally occurring inhibitors. Synergism between Nypa fruticans' wurmb and halide ions is not available in literature. This paper investigates the synergistic inhibition between Nypa fruticans' wurmb extract and KI in HCl medium using weight loss method. MATERIALS AND METHODS Mild steel sheets of composition. They were cut in 5 x 4cm components of 0.07-cm thickness. The coupons were prepared as explained elsewhere (Loto, 1998). A total of 125 pieces of coupons were used. Solutions: The corrosive medium was HCl. Standard solutions of different concentrations were prepared using distilled water (0.1, 0.5, 1.0, 1.5, 2.0, 3.0M). Nypa fruticans' wurmb extract: Nypa fruticans' wurmb extract was obtained as explained in previous work (Mohammedi et al 2004). A stock was prepared by dissolving 0.6g of the extract in 1dm 3 of HCl. Thereafter concentrations of 0.06, 0.09, 0.15, 0.24 and 0.36gdm-3 were obtained by dilution. Concentrations of KI prepared were 0.01, 0.03 and 0.05M. Weight loss measurement: A set of six 250ml beakers containing 0.1, 0.5, 1.0, 1.5, 2.0, 3.0M HCl solution for 30 O C and another set of six of same concentrations for elevated temperatures of 40 and 50 O C were used. A thermostated water bath was used to maintain the temperatures. The coupons were washed several times with distilled water, rinsed in ethanol, dipped in acetone and dried using a stream of air and left in a desicator before weighing. After weighing accurately the coupons were immersed in 250ml beakers each containing 200ml of hydrochloric acid with and without additives. The coupons were retrieved every 24hrs for 7 days (168 hrs.).