O.K. Abiola, N.C. Oforka, and E.E. Ebenso
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If you wish to view the human-readable version of the preprint, then please Register (if you have not already done so) and Login. Registration is completely free.ISSN 1466-8858 Volume 5 Preprint 10 THE INHIBITION OF MILD STEEL CORROSION IN AN ACIDIC MEDIUM BY FRUIT JUICE OF CITRUS PARADISI Olusegun K. Abiolaa*, N. C. Oforkaa, E.E. EBENSOb a Department of Pure and Industrial Chemistry, University of Port Harcourt, P.M.B. 5323, Port Harcourt, Rivers State – Nigeria. b Department of Pure and Applied Chemistry University of Calabar P.M.B. 1115 Calabar, Nigeria *Corresponding author Name: Olusegun K. Abiola E-mail: abiolaolusegun @yahoo.com Tell N0. +2348033360504 This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.umist.ac.uk/corrosion/jcse in due course. Until such time as it has been fully published it should not normally be referenced in published work. © UMIST 2004. ABSTRACT The corrosion inhibition of mild steel in HCl solution in the presence of fruit juice of citrus paradisi at temperature range of 3050oC was studied using weight loss technique. The fruit juice of citrus paradisi acts as an inhibitor in the acid environment. The inhibition efficiency increases with increase in inhibitor concentration but decreases with an increase in temperature. The inhibition is attributed to the adsorption of the inhibitor on the surface of the mild steel. Keywords: Citrus paradisi; mild steel; corrosion inhibition; adsorption. INTRODUCTION Metals and its alloy are exposed to the action of acids in industry . Processes in which acids play a very important part are acid pickling, industrial acid cleaning, cleaning of oil refinery equipment, oil well acidizing and acid descaling [1,2]. The exposures can be most severe but in many cases, corrosion inhibitors are widely used in industry to prevent or to reduce the corrosion rates of metallic materials in these acid media [2,3]. Because of the toxic nature and high cost of some chemicals currently in use it is necessary to develop environmentally acceptable and less expensive inhibitors. Natural products can be considered as a good source for this purpose . The possible replacement of some expensive chemicals as corrosion inhibitors for metal in acid cleaning process by naturally occurring substances of plant origin has been studied by Hosary and Saleh . Natural products of plant origin contain different organic compounds (e.g. alkaloids, tannins, pigments, organic and amino acids, and most are known to have inhibitive action [4,5]. In our earlier communication  it was found that cocosnucifera juice inhibits the corrosion of mild steel in hydrochloric acid solution (HCl). Ekpe et al.  and Saleh et al.  used the aqueous extracts of some natural products (fruits, fruit shells, leaves, seeds) as corrosion inhibitors of some metals. The fruit juice of citrus paradisi can be use in the production of non-toxic inhibitors to replace toxic corrosion inhibitors. Accordingly, this work deals with the study of the corrosion inhibition properties of fruit juice of citrus paradisi. The aim of this study was to determine the inhibition efficiency of the fruit juice of citrus paradisi as an inhibitor for the corrosion of mild steel in 0.5MHCl. Weight loss technique was employed to carry out the measurements. Citrus species are utilized in many industries for the production of the various brands of citrus juices . The juice is also rich in vitamin C, folic acid and significant quantities of other vitamins, pectins, flavonoids among others [8,9]. Nootkatone contributes to the flavour of the grape fruit. At high concentration, nootkatone exerts a bitter flavour . Nitrogenous compounds are present to the extent of 0.05 – 1.0% and most are free amino acids – asparagines, alanine, arginine, aspartic acids, glutamine, glutathione, histidine, betaine, cysteine, proline, serine and stachydrine [6,8,9]. The principal acid in citrus fruits is citric acid (80 – 90% of the total acids). Others are malic, tartaric, benzoic, succinic, quinic, oxalic and formic acid . The compounds in citrus paradisi fruit juice especially the nitrogen containing organic compounds can adsorb on the metal surface and block the active sites on the surface and thereby reduce the corrosion rate in acid environment. EXPERIMENTAL PROCEDURES Material Preparation The composition and preparation of mild steel coupons are described in detail as reported previously . All test solutions were prepared from analytical grade reagents and double-distilled water. The citrus paradisi fruit juice was used as an additive for this investigation. The additive concentration of 0.5, 1.0, 1.5, 2.0 and 2.5% volume/volume percent (v/v) were prepared in 0.5M HCl (corrodent) solutions at 30, 40 and 50oC. Weight loss measurement Previously weighed mild steel coupons were immersed in 250ml open beakers containing 0.5M HCl solution (blank) without additive, and additive concentration of 0.5, 1.0, 1.5 2.0 and 2.5% in 0.5M HCl solution at 30, 40 and 50oC. The variation of weight loss was follow at 3hr. interval progressively for 15hr. at 30, 40 and 50oC. The procedure for weight loss determination was similar to that reported previously [10,11]. The inhibition efficiency (1%) was determined from : I% = Wb − Wi x 100 Wb (1) Where Wb and Wi are the weight loss of mild steel per unit area (mg/cm2) of coupons in the corrodent (blank) and corrodentinhibitor systems. 1 RESULTS AND DISCUSSION Effect of citrus paradisi fruit juice on the corrosion of mild steel in HCl solution Figure 1 shows the variation of the weight loss with time (hours) for mild steel corrosion in 0.5MHCl and 0.5M HCl with various concentrations of additive (citrus paradisi juice) at 30oC. Similar trends were observed at 40 and 50°C. From the variation of weight loss with time of immersion in HCl solution without additive compared with mild steel in HCl solution containing the additive at 30°C (Fig. 1), there is a general decrease in weight loss, signifying the inhibition of the acid corrosion of mild steel by citrus paradisi juice. The extent of the decrease in weight loss was found to depend on the concentration of additive. Figure 2 also confirms that the additive is a corrosion inhibitor; since there was a general decrease in corrosion rate (mgcm-2h-1). The corrosion rate as a function of additive concentration and at different temperatures (30 - 50°C) is shown in figure 2. The corrosion rate decreases with increasing concentration of citrus paradisi juice at each of the temperature. This confirms that the presence of the additive in 0.5M HCl solution inhibits the corrosion of mild steel by HCl and that the degree of corrosion inhibition depends on the amount of the citrus paradisi juice present. Figure 3 illustrates the variation of the inhibition efficiency, I%, versus the concentration of the additive at 30, 40 and 50°C. The inhibition efficiency increases with increasing the concentration of the inhibitor. As shown in figure 3 inhibition efficiency increases with increase in concentration of the inhibitor up to 2.5%v/v at a maximum efficiency of 45.6%, 37.3% and 24.1% at 30%, 40 and 50°C respectively. Figure 3 shows the effect of increasing temperature from 30°C to 50°C on the inhibition efficiency. From the plot of the inhibition efficiency with concentration of the inhibitor and from the result given in Table 1, it was observed that with increase in temperature there was a decrease in the inhibition efficiency of the inhibitor. This indicates that inhibition decreases as temperature of the system increases, and on this basis we suggest the mechanism of physisorption of the inhibitor on the metal surface. This is in agreement with the results of several investigators [2,11,12]. Adsorption considerations The surface coverage, θ at each concentration of inhibitor was evaluated using the equation . θ =1 − Wi Wb (2) Where Wb and Wi are the weight loss in corrodent and corrodent-inhibitor systems respectively at constant temperature. The surface coverage data and corrosion rate are recorded in Table 2. The experimental observed linear decrease in corrosion rate as seen in Table 2 with surface coverage, θ therefore supports the observation that the inhibitor inhibits corrosion by being adsorbed at the reaction sites on the mild steel surface . A curtailment of these reaction sites would therefore lead to a reduction in the corrosion rate and this may be precisely how the inhibitor achieves inhibition by being adsorbed on the mild steel surface at the reaction sites Figure 4 shows the plot of logarithm inhibition efficiency (I%) versus logarithm inhibitor concentration for the additive at 30, 40, and 50°C – a linear plot is obtained which obeys the Freundlish isotherm. CONCLUSION From the present investigation, the following conclusions can be drawn. The rate of corrosion of the mild steel in HCl is a function of the concentration of citrus paradisi juice. The inhibition by this additive increased with increased additive concentration and decreased temperature. Citrus paradisi fruit juice is a corrosion inhibitor for mild steel in HCl solution and can be used to replace toxic chemicals. References 1. 2. 3. 4. 5. 6. G.I Gardner. Corrosion inhibitors, C. C. Nathan Ed., NACE, 156. S.S. Abd El Rehim, M.A.M. Ibrahim and K.F. Khalid. The Inhibition of 4 – (2`- amino-5’ – Methylphenylazo) antipyrine on corrosion of mild steel in HCl solution. Material Chemistry and Physics, 70 (2001) 268 L.I. Antropov, Theoretical Electrochemistry, Moscow. R. Hosary and H. Salem. The Inhibitive action of Molasses on the corrosion of mild steel in acidic media. Corrosion Eng. Vol. 1 (1984) 63-74. U.J. Ekpe, E.E. Ebenso and U.J. Ibok. Inhibitory action of Azadirachta indica leaves extract on corrosion of mild steel in Tetraoxosulphate (VI) acid. J.W. Afr. Sci. Assoc. 37, (1994) 13 – 30. O.K. Abiola and N.C. Oforka. The corrosion inhibition Effect of Cocosnucifera Water on Mild Steel in Hydrocholoric Acid solutions. Proceeding s of the Chemical society of Nigeria, 25th International Conference (2002). 2 7. 8. 9. 10. 11. 12. 13. R.M. Saleh, A.A. Ismail and A.A. ElHosary. Corrosion Inhibition by Naturally occurring substances. Br. Corros. J. 17 (3) 17(13) (1980) 131. U.O. Anthony and U.E. Offiong. Nutritional quality of plant foods. Post Harvest Research Unit Dept. of Biochemistry University of Benin, Benin (1998). 96. A.I. Ihekoronye and P.O. Ngoddy. Integrated Food Science and Technology for the Tropics. Macmillian (1984) 305 O.K. Abiola and N.C. Oforka. Inhibition of the Corrosion of Mild Steel in Hydrochloric Acid by (4-Amino – 2 – Methyl-5-Pyrimidinyl Methylthio) Acetic Acid and its Precursor. The Journal of Corrosion Science and Engineering 3 (2002) 21 http:/www2. umist. ac.uk/corrosion/JCSE/Volume 3/paper 21/v34p21.htm U.J. Ekpe, U.J. Ibok, B.I. Ita, O.E. Offiong and E.E. Ebenso. Inhibitory action of Methyl and Phenylthiosemicarbazone derivatives as the Corrosion of Mild Steel in hydrochloric acid. Material Chemistry and Physics, 48 (1995) 87. U.J. Ekpe, P.C. Okafor, E.E. Ebenso, O.E. Offiong and B.I. Ita Mutual Effects of Ihiosemicarbazone derivatives on the Acidic Corrosion of Aluminum. Bulletin Electrochemistry 3 (2001) 131. B.B. Damaskin. Adsorption of Organic Compound on Electrodes New York, 1977. TABLE 1: The effect of fruit juice of citrus paradisi on mild steel corrosion in 0.5M HCl Inhibitor efficiency (I%) Inhibitor Conc. v/v 30°C 40°C 50°C 0.0% 0.5% 30.6 18.2 9 1.0% 33.3 21.4 10.3 1.5% 41.4 29.0 15.6 2.0% 43.1 34.1 20.3 2.5% 45.6 37.3 24.4 TABLE 2: Surface coverage, θ and corrosion rate during corrosion of mild steel in concentrations of the fruit juice of citrus paradisi at 30°C Concentration of inhibitor v/v% 0.5% 1.0% 1.5% 2.0% 2.5% Surface Coverage, θ 0.31 0.33 0.41 0.43 0.46 0.5M HCl containing various Corrosion rate (mgcm-2h-l) 0.1736 0.1669 0.1466 0.1424 0.1361 3 4 5 6 7