R. Khandelwal*, S. Sahu , S. K. Arora, S.P.Mathur,
Keywords: Cordia dicotoma, Aluminium, Mass loss method, Thermometric method, corrosion inhibitor, inhibition efficiency.
Abstract:
Abstract
The corrosion inhibition efficacy of alcoholic extracts of stem, leaves and fruits of Cordia Dicotoma towards hydrochloric acid for aluminium has been studied by using mass loss and thermometric methods. It has been observed that at constant acid concentration, the inhibition efficiency of all the extracts increases with the inhibitor concentration. At constant inhibitor concentration the inhibition efficiency decreases with the increase in acid concentration. It has been also observed from the values of Heat of adsorption (Qads) that the inhibition efficacy decreases with the increase in the temperature.
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Behavior of naturally occurring plant Cordia Dichotoma as corrosion inhibitor for aluminium in acidic mediaR. Khandelwal1, S. Sahu1, S.K. Arora1, S.P.Mathur1*,1 Material research laboratory, Department of Chemistry, Govt. College, Ajmer (Raj.) INDIA Abstract The corrosion inhibition efficacy of alcoholic extracts of stem, leaves and fruits of Cordia Dichotoma towards hydrochloric acid for aluminium has been studied by using mass loss and thermometric methods. It has been observed that at constant acid concentration, the inhibition efficiency of all the extracts increases with the inhibitor concentration. At constant inhibitor concentration the inhibition efficiency decreases with the increase in acid concentration. It has been also observed that the inhibition efficacy decreases with the increase in the temperature. Key words: Cordia dichotoma, Aluminium, Mass loss method, Thermometric method, corrosion inhibitor, inhibition efficiency. Introduction Aluminium is selected for variety of engineering applications because of lightness, strength, thermal and electrical conductivities, heat and light reflectivity and hygienic and non toxic qualities,1 but it suffers from a serious corrosion problem causing considerable revenue loss throughout the world.2 Aluminium is known to exhibit passive behaviour in aqueous solutions, but dissolves in aqueous acids with liberation of hydrogen gas.3 There are varieties of synthetic corrosion inhibitors available but our present focous on the naturally occurring inhibitors which are eco-friendly, eonomic and having no toxic effects without affecting the natural properties of metal. Numerous naturally occurring products such as Prosopis juliflora,4 Eugenia jambolans,5 Lawsonia extract,6 Opuntia extract,7 Swertia aungustifolia,8 Ficus religeosa,9 Heena,10 Datura stromonium,11 and Calotropis plants 12 have been evaluated as potential corrosion inhibitors. We present here our present study on the inhibitive action of alcoholic extracts of stem, leaves and fruits of Cordia Dichotoma on the corrosion of aluminium in presence of acidic media. Plant Introduction - Cordia dicotoma belongs to family Boraginaceae. Its common name is Indian cherry, lasura. Its chemical constitutions are mono and polysachharides, Beta- sitosterol, flavonol glycoside, taxifotin, 3-rhamnoside, 3-5-dirhamnoside, distylin, 3- xyloside, allantoin. It is Astringent, anthelmintic, diuretic, demulcent and expectorant (fruit) and useful in the cough, chest diseases hence it relieves from severe colic pain. Cordia dichotoma contains a large number of alkaloids containing oxygen and nitrogen, out of which Allantoin (Fig. 1) predominates which is effective for corrosion inhibition activity in acidic media for aluminium. (Fig. 1) Allantoin Experimental MASS LOSS MEASUREMENTS: Specimen preparation Rectangular specimens of iron of dimensions 2.54 x 1.52 x .02 cm with a small hole of about 2mm diameter near the upper edge were employed for the determination of mass loss measurements. Specimens were cleaned by buffing to produce mirror finish with the help of emery paper and were then degreased with acetone. Each specimen was suspended by a glass hook and immersed in a beaker containing 50 mL of test solution and left expose to air. Duplicate experiments were performed in each case and mean value of mass losses were calculated. Test solution preparation The hydrochloric acid solutions of 0.5N, 1.0 N and 2.0 N were prepared using doubly distilled water. The extracts of different parts of Cordia dichotoma were obtained by refluxing respective part in a soxhlet in ethanol. To observe the influence of various parameters like inhibitor concentration, acid concentration and time, the corrosion inhibition efficiency (η %) of the compounds have been calculated by mass loss method using following equation.13 η % = (∆ Mu - ∆ Mi ) / ∆ Mu × 100 Where ∆ Mu is mass loss without inhibitor and ∆ Mi is mass loss with inhibitor. The degree of surface coverage (θ) can be calculated as - (θ) = (∆ Mu - ∆ Mi) / ∆ Mu The corrosion rate in millimeter penetration per year (mmpy) can be obtained by following equation. 14 Corrosion rate (mmpy) = (∆ M × 87.6) / area × time × metal density Where ∆ M mass loss expressed in mg, area expressed in square cms of metal surface exposed, time expressed in hours of exposure and metal density expressed in g / cm 3. THERMOMETRIC MEASUREMENTS: Inhibition efficiencies were also determined by thermometric method. 15 In this method, the variation of temperature is followed as a function of time. The specimens of size 2.54 x 1.52 x .02 cm were immersed in 50mLof acid solution. The tests were carried out in different concentrations of HCl solutions. The inhibition studies were carried out in the concentrations 0.12%, 0.24%, 0.36% 0.48% and 0.60% of the extract of Cordia dichotoma, and observations were carried out in an insulated chamber. The results were used to calculate Reaction Number (R.N.) and inhibition efficiency (η %). Reaction Number can be calculated by the following equation- RN = (Tm - Ti) / t Where Tm and Ti are initial and maximum temperatures respectively and t is the time in minutes to attain Tm during the observations. The inhibition efficiency can be calculated as - η % = (RN free - RN i ) / RN free × 100 Where RNfree and RNi are Reaction Number in blank and inhibited system respectively. Ea has been calculated from the Arrhenius equation. Log P2/P1 = Ea / 2.303 R (1/T1 - 1/T2) Where P 1 and P 2 are the corrosion rate at temperature T1 and T2 respectively. The values of heat of adsorption (Qads) were calculated by the following equation.16 Qads = 2.303 R [log (θ 2 / 1 - θ 2) - log (θ 1 / 1 - θ 1)] × [ T1.T2 / (T2-T1) ] Where θ 1 and θ 2 [θ =(∆ Mu - ∆ Mi) / ∆ Mu] are the fraction of the metal surface covered by the inhibitors at temperature T1 and T2 respectively. The values of heat of adsorption (∆G0ads) were calculated from slope of the plot of the following equation. 17 log C = log (θ / 1 - θ ) - log B where log B = -1.74 - (∆G0ads / 2.303 RT), and C is the inhibitor concentration. The ∆H0ads and ∆S0ads were calculated using the following equations. ∆H0ads = Ea - R T T∆S0ads = ∆H0ads - ∆G0ads Table - 1 Effect of temperature on Mass loss and inhibition efficiency (η %) for Aluminium in 0.5 N HCl with given inhibitor addition. Area of exposure - 7.75 cm2 Time of exposure - 18hrs Inhibitorconcentration(%)300 K290 K ∆ M, (g)(θ)η %∆M, (g)(θ)η % Fruit extract Uninhibited0.1210.119 0.120.0240.80165380.165290.0140.88235388.23529 0.240.0210.82644682.644630.0120.8991689.91597 0.360.020.83471183.471070.0110.90756390.7563 0.480.0190.84297584.297520.0070.94117694.11765 0.600.010.91735591.735540.0040.96638796.63866 Leaves extract Uninhibited0.1210.119 0.120.0250.79338879.338840.0160.86554686.55462 0.240.0220.81818281.818180.0130.89075689.07563 0.360.0210.82644682.644630.0120.8991689.91597 0.480.0190.84297584.297520.0090.9243792.43697 0.600.0130.89256289.25620.0060.9495894.95798 Stem extract Uninhibited0.1210.119 0.120.0270.7768677.685950.0170.85714385.71429 0.240.0240.80165380.165290.0140.88235388.23529 0.360.0230.80991780.991740.0120.8991689.91597 0.480.0220.81818281.818180.010.91596691.59664 0.600.0140.88429888.429750.0070.94117694.11765 ISSN 1466-8858 Volume 13, Preprint 12 submitted 18 February 2010 © 2010 University of Manchester and the authors. 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.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. Table - 2 Effect of acid concentration on Mass loss and inhibition efficiency (η %) for Aluminium at 300 ± 0.1 K with given inhibitor addition. Area of exposure - 7.75 cm2 Time of exposure - 18hrs Inhibitor concentrati on (%)0.5N HCl1.0 N HCl2.0N HCl ∆M (g)η %∆M (g)η %∆ M, (g)η % Fruit extract Uninhibited0.1210.1320.185 0.120.02480.165290.03275.757580.05968.10811 0.240.02182.644630.0377.272730.05271.89189 0.360.0283.471070.02878.787880.04774.59459 0.480.01984.297520.02481.818180.03978.91892 0.600.0191.735540.01787.121210.03680.54054 Leaves extract Uninhibited0.121 0.1320.185 0.120.02579.338840.03573.484850.06266.48649 0.240.02281.818180.03176.515150.05371.35135 0.360.02182.644630.0377.272730.04973.51351 0.480.01984.297520.02779.545450.04376.75676 0.600.01389.25620.01985.606060.03780 Stem extract Uninhibited0.121 0.1320.185 0.120.02777.685950.03672.727270.06664.32432 0.240.02480.165290.03275.757580.05769.18919 0.360.02380.991740.03176.515150.05271.89189 0.480.02281.818180.0377.272730.04973.51351 0.600.01488.429750.02184.090910.03978.91892 Table - 3 Corrosion rate, Activation energy (Ea), Heat of adsorption (Qads), and free energy of adsorption (∆G0ads) for Aluminium in 0.5 N HCl with given inhibitor addition at 300 ± 0.1 K. Area of exposure - 7.75 cm2 Time of exposure - 18 hrs S.N o.Inhibitor concentration (%)Corrosion rate (Ea) (KJ /mol) (Qads) (KJ /mol)(∆G0ads) (KJ/mo l)∆H0ads (KJ/mol)∆S0ads (J/ mol / K) Fruit extract 1BLANK0.030.0159-2492.98 20.120.00558 60.514936 237-1434.85-18.75926-2492.49-2492.42 30.240.00488 80.534635 1-1714.90-17.43983-2492.47-2492.41 40.360.00465 50.571150 156-1897.23-16.5753-2492.43-2492.37 50.480.00442 20.953955 503-3178.40-16.01044-2492.05-2491.99 60. 600.00232 70.875388 431-5766.71-17.2653-2492.12-2492.07 Leave extract 1BLANK0.02816 30.0159-2492.98 20.120.00581 90.426365 293-1218.31-18.63163-2492.57-2492.51 30.240.00512 00.502608 827-1561.23-17.29879-2492.5-2492.44 40.360.00488 80.534635 1-1714.90-16.42883-2492.47-2492.41 50.480.00442 20.713859 499-2392.11-16.01044-2492.29-2492.23 60. 600.00302 60.738675 466-3728.72-16.5428-2492.26-2492.21 Stem extract 1BLANK0.02816 30.0159-2492.98 20.120.00628 40.441972 471-1136.11-18.38725-2492.56-2492.50 30.240.00558 60.514936 237-1434.85-17.03094-2492.49-2492.43 40.360.00535 30.621545 989-1724.95-16.15162-2492.38-2492.32 50.480.00512 00.753261 413-2132.82-15.57046-2492.25-2492.20 60. 600.00325 80.662205 784-3146.47-16.33483-2492.34-2492.28 Table - 4 Reaction Number (RN) and Inhibition efficiency (η %) for Aluminium in 0.5 N and 1.0 N HCl solution with given inhibitor addition at 299 ± 0.2 K Area of exposure - 7.75 cm2 Time of exposure - 18 hrs Inhibitor concentration (%)0.5 N HCl1.0 N HCl RNη %RNη % Uninhibited0.075-0.078- Fruit extract 0.120.01777876.29630.02055673.9437 0.240.015800.01722278.16904 0.360.01111185.185190.01333383.09862 0.480.01055685.925930.01166785.21129 0.600.0186.666670.01111185.91551 Leave extract 0.120.01888974.814810.02222271.83103 0.240.01611178.518520.01888976.05637 0.360.01222283.70370.01580.98594 0.480.01055685.925930.01277883.80284 0.600.0186.666670.01166785.21129 Stem extract 0.120.01944474.074070.02444469.01413 0.240.01666777.777780.02277871.1268 0.360.01277882.962960.02055673.9437 0.480.01222283.70370.01722278.16904 0.600.01166784.444440.01388982.39439 Variation of Reaction Number (RN) with inhibitor concentration of Cordia dicotoma extracts for Al in 0.5 N HCl 0 0.005 0.01 0.015 0.02 0.025 0.120.240.360.480.6 Inhibitor concentration (%) RN (K/ Min.)furit extract leaves extract Stem extract Variation of Reaction Number (RN) with inhibitor concentration of Cordia dicotoma extracts for Al in 1.0 N HCl 0 0.005 0.01 0.015 0.02 0.025 0.03 0.120.240.360.480.6 Inhibitor concentration (%) RN (K/Min.)furit extract leaves extract Stem extract adsResult and discussion The results are presented in Table 1-4, and Fig. 1-2. The effect of temperature on the corrosion of aluminium is shown in Table -1. It shows that corrosion rate is increased with the temperature and the inhibition efficiency decreases with the increase in temperature. The corrosion rate may be increased with temperature due to thermal activated kinetics. 18 The effect of acid concentration on the corrosion of aluminium is shown in Table -2. It shows that the I.E. decreases with increase in the acid concentration. At constant acid concentration the I.E. increases with increase in the inhibitor concentration, e.g. in 0.5N HCl the I.E. was found to be 80.16, 82.64, 83.47, 84.29 and 91.73 % with respect to 0.12, 0.24, 0.36, 0.48 and 0.60 inhibitor concentration (fruit extract) (Table - 2). For all acid concentrations the inhibition efficiency of alcoholic extracts of fruit, leaves and stem of Cordia dichotoma was calculated by massloss and thermometric methods, and it was observed that the fruit extract shows the maximum inhibition efficiency at both the temperatures. (Table 1, 2and 4). From Table -3 it is evident that in all cases the values of Qads are negative (- 1434.85 to -3146.47 ) . The negative values shows that the adsorption, and hence the inhibition efficiency, decreases with a rise in temperature. 19 The negative values of DGo ensure the spontaneity of the adsorption process and stability of the adsorbed layer on the metal surface. Generally, values of ∆G0ads lower than - 40 KJ/mol is consistant with the electrostatic interaction between the charged molecules and the charged metal (physisorption) ; those around -50 KJ/mol or higher involve charge shairing or charge transfer from organic molecule to the metal surface to form a coordinate bond (chemisorption) 20,21. In the present work, the calculated values of DGo ads are lower than -40 kJ mol-1, indicating, therefore that the adsorption mechanism of extracts of Cordia dicotoma on metal surface in 0.5 N HCl solution was typical of physisorption ( Table 3). The enthalpy changes are negative (Table 3) means that heat is released from the adsorption process. Generally, an exothermic adsorption process signifies either physi- or chemi-sorption, while endothermic process is attributable unequivocally to chemi-sorption 22. The absolute value of the adsorption enthalpy∆H0ads, increases with the increase in surface coverage and the inhibitor concentration due to the attractive interaction between the adsorbed molecules indicating the validity of the Temkin model 23. Large and negative values of the entropy (Table 3) imply that the activated complex in the rate determining step represents an association rather than a dissociation step, meaning that a decrease in disordering takes place on going from reactants to the activated complex 24,25The increase in E a o (Table 3) is proportional to the inhibitor concentration, indicating that the energy barrier for the corrosion interaction is also increased 26,27. This means that the corrosion reaction will be further pushed to the surface sights that are characterised by progressively higher values of E a o as the concentration of the inhibitor in the solution becomes larger. In other words, the adsorption of the inhibitor on the metal surface leads to the formation of a physical barrier that reduces the metal reactivity in the electrochemical reactions of corrosion 28. From (Table 4) it is concluded that the Reaction Number (RN) decreases with the increase in the inhibitor concentration while the inhibition efficiency increases with the inhibitor concentration. Conclusions In the present work, mass loss and thermometric methods were used to study the effect of temperature on the ability of extracts of Cordia dichotoma to inhibit the corrosion of aluminium in acidic conditions. The principle conclusions are: ·The rate of corrosion decreases with increase in the inhibitor concentration. ·The corrosion rate increases and the inhibition efficiency decreases with the increase in temperature. ·The fruit extract of Cordia dichotoma shows the maximum inhibition efficiency as compered to the leaves and stem extracts. ·The thermodynamic parameters revealed that the inhibition of corrosion by extracts of Cordia dichotoma is due to the formation of a physisorbed film of the inhibitor on the metal surface. ·The inhibition efficiency (IE%) of extract of Cordia dichotoma was temperature-dependent and its addition led to an increase of the activation corrosion energy. References 1.T. Sethi, A. Chaturvedi, R.K.Upadhayay and S.P.Mathur : Polish J Chem. 82,591,(2008). 2.R. Chowdhary , T.Jain, M.Rathoria and S.P.Mathur : Bull.Electrochem., 20, 67, (2004). 3.T. Sethi, A. Chaturvedi, R.K.Upadhayay and S.P.Mathur : J. chil.Chem. Soc., 52, 1206, (2007). 4.R. Chowdharyand S.P. 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