Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X Vol. 2(9), 37-41, Sept. (2012) Res.J.Chem.Sci. International Science Congress Association 37 The Effects of Inula viscosa Extract on Corrosion of Copper in NaOH SolutionNawafleh E.*, Irshedat M., Bataineh T., Muhaidat R., Al-Qudah M. and Alomary A. Department of Chemistry, Faculty of Science, Yarmouk University, Irbid, JORDAN Department of Biology , Faculty of Science, Yarmouk University, Irbid, JORDAN Available online at: www.isca.in Received 1st June 2012, revised 7th June 2012, accepted 10th June 2012Abstract The effect of Inula viscosa extracts on the corrosion of copper in 1M NaOH solution was studied using weight loss method at various temperatures varying from 298 to 328 K. Experimental data revealed that Inula viscosa extract acted as an inhibitor in the alkaline environment. It was found that the inhibition efficiency increased with an increase in Inula viscosa extract concentration. Adsorption enthalpies were determined and discussed. Effect of temperature was also investigated and activation parameters were evaluated. Keywords: Inula viscosa, weight loss, inhibition efficiency, copper. Introduction Copper has been one of preferred metals in industry owing to its excellent electrical and thermal conductivities, good mechanical workability, and its relatively noble properties. In spite of the fact that copper is a relatively noble metal, it reacts easily in oxygen containing electrolytes. However, wide industrial application of copper has been based on its corrosion stability, which is the result of formation of an oxide/hydroxide layer on the metal surface. The oxide layer has, in general, a duplex structure made up of an inner CuO layer followed by CuO and then a Cu(OH) layer depending on the electrode potential 1 . Thin passivity layer formed on copper in neutral and alkaline solution has attracted considerable interest particularly in the corrosion catalysis and double layer structure research 2 . Some of these corrosion inhibitors are however, toxic to the environment. This has prompted the search for green corrosion inhibitors that are non-toxic and eco-friendly for metals and alloys in acidic and alkaline solutions. These green corrosion inhibitors have been found to have centre for -electrons and functional groups (such as –C = C-, -OR, -OH, -NR, -NH and –SR) which provide electrons that facilitate the adsorption of the inhibitor on the metal surface. Research on the use of plant extracts as corrosion inhibitors for metals/alloys in acid or alkaline media has therefore been intensified3-10. This is because plants are rich sources of naturally occurring chemical compounds that are environmentally acceptable, cheap and readily available. Inula viscosa is a perennial herbaceous plant that profusely colonizes sub nitrophile and sub-saline soils in abandoned and plowed fields in the Mediterranean region. It exhibits simple alternate leaves, covered with glands secreting a sticky substance, and bright yellow flowers that bloom between August and November. This species is used topically in folk medicine as an anti-scabies and anti-inflammatory agent, and to promote wound healing11-12. Various compounds have been described that exhibit antioxidant such as Resveratrol, 1,3-dicaffeoylquinic acid13. The aim of the present work is to study the inhibition of copper surface by addition of Inula viscosa extract as inhibitor in NaOH solution by using weight loss technique. Material and Methods The weight loss measurements were carried out in a test tube placed in a thermostat water bath. The solution volume was 10 mL. The used copper coupons had a rectangular form (length = 1 cm, width = 1 cm, thickness = 0.03 cm). Prior to all measurements, the coupons were first polished successively with metallographic emery paper of increasing fineness up to1200 grits. The coupons was then washed with doubly distilled water, degreased with acetone, washed using doubly distilled water again and finally, dried with paper tissue at room temperature. Inhibitor material: A Stock solution of the inhibitor material was prepared by refluxing 12.5 g of dry Inula viscosa powder with 250 mL of 1M NaOH for 3 hours. The refluxed solution was allowed to stand overnight and filtered through ordinary filter paper. From this solution, different concentrations of inhibitor solutions ranging from 0.1 to 0.7% were diluted. Weight loss method: Pre-weighed copper specimens (in triplicate) were suspended for 1 hour in 1M NaOH with and without the inhibitor in different volume ranging from 1 to 7 mL of extract. After the specified time the coupons were removed Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 2(9), 37-41, Sept. (2012) Res.J.Chem.SciInternational Science Congress Association 38 from test solution, thoroughly washed with acetone solution and de-ionised water, dried well and then reweighed. Results and DiscussionThe plot of weight loss (mg) of copper coupon versus inhibitor volume for 60 min immersion period at different temperatures is shown in figure-1. Weight loss as a function of inhibitor volumes decreased gradually. This indicates that Inula viscosaextract inhibits the corrosion of copper in 1M NaOH solution. The values of percentage inhibitor efficiency (%I) for various concentrations of the inhibitor was determined for 1hr immersion periods by using the following equation: %I = [Wu –Wb/Wu]×100 Where u and b are the uninhibited and inhibited weight losses, respectively. Assuming a direct relationship between inhibition efficiency (%I) and surface coverage () for different inhibitor concentrations, the degree of surface coverage () was calculated by using the following relationship: = %I/100 Table-1 collects the percentage inhibition efficiency for 60 min immersion periods at 25, 35, 45 and 55C. The percentage inhibition efficiency values, as presented in table-1 for triplicate copper specimens. As seen in table-1, the percentage inhibition efficiency values increase with increasing extract concentration, but decrease with increasing temperature. The highest inhibition efficiency of 86.49% was obtained at 7mL of extract at 25C. This result suggests that increase in extract concentration increases the number of inhibitor molecules adsorbed onto copper surface and reduces the surface area that is available for the direct base attack on the metal surface. The inhibitive effect of Inula viscosa is ascribed to the presence of organic compounds in the extract. Inula viscosa is rich in several organic compounds of high molecular weight with heteroatom and centers in their molecular structures. These include 3-O-methylquercetin, 3,3-di-O-methylquercetin, viscic acid, ilicic acid, resveratrol, cynaric acid 1,3-dicaffeoylquinic acid, 2,5-dihydroxyisocostic acid, 2,3-dihydroxycostic acid, isocostic acid, carabrone, tomentosin and hispidulin14-15. Table -1 Inhibition efficiency of Inula viscosa extract on copper in 1M NaOH for 60 min immersion period at different temperatures Extra ct %I at 25 ºC %I at 35 ºC %I at 45 ºC %I at 55 ºC 1 55.00 46.30 33.00 18.90 2 64.00 58.00 46.72 28.67 3 74.00 71.24 56.96 41.95 5 83.17 79.06 74.02 60.84 7 86.49 82.59 78.74 72.73 2,5-dihydroxy-isocostic acid 2,3-dihydroxycostic acid 1,3-dicaffeoylquinic acid Research Journal of Chemical Sciences ______ Vol. 2(9), 37-41, Sept. (2012) International Science Congress Association The inhibition effect of Inula viscosa may be due to the presence of these organic compounds in the extract. Since viscosa contains several compounds, synergistic and antagonist ic effects may play an important role on the inhibition efficiency of Inula viscosa as an inhibitor. Organic compounds having centers for electrons and functional groups of O have been reported as corrosion inhibitors for copper in basic solutions16. The adsorption of these compounds on copper surface reduces the surface area that is available for the attack of the aggressive ion from the basic solution. As seen in figure the weight loses decrease with increase in extract concentration due to higher de gree of surface coverage, enhanced inhibitor adsorption. Similar view has been reported previously5-8. Also, figure- 2 confirms that the inhibition is due to the adsorption of the active organic compounds onto metal surface. This is because a straight line is obtained when C/ plotted against C and the linear correlation coefficient of the fitted data is close to 1, indicating that the adsorption of the inhibitor molecules obey the Langmuir’s adsorption isotherm expressed asC/ = C + 1/K Where C is the inhibitor concentration and K the equilibrium constant for the adsorption/desorption process of the inhibitor molecules on the metal surface. The effect of increase in solution temperature from 25 to 55 ºC on the inhibitor efficiency is summarized in table increased in temperature with produce a decrease in the inhibitor efficiency and this suggest that the process of adsorption of the inhibitor molecules is physical in nature. The apparent activation energy, Ea of the corrosion reaction was calculated by using the Arrhenius equation. Log(RCorr1/RCorr2) = E/2.303R(1/T-1/TWhere RCorr1 and RCorr2 are corrosion rates at temperature T , respectively. The corrosion rate (RCorr , mg cm exposure time were calculated as follows 17-19 . W = (W-W)/A Corr = W/ t The plot of weight loss of copper coupon versus volume of ______ _________________________________ ______________ International Science Congress Association may be due to the presence of these organic compounds in the extract. Since Inula contains several compounds, synergistic and ic effects may play an important role on the inhibition as an inhibitor. Organic compounds electrons and functional groups of O have been reported as corrosion inhibitors for copper in basic adsorption of these compounds on copper surface reduces the surface area that is available for the attack of the aggressive ion from the basic solution. As seen in figure -1, the weight loses decrease with increase in extract concentration gree of surface coverage, as a result of enhanced inhibitor adsorption. Similar view has been reported 2 confirms that the inhibition is due to the adsorption of the active organic compounds onto metal a straight line is obtained when C/ is plotted against C and the linear correlation coefficient of the fitted data is close to 1, indicating that the adsorption of the inhibitor molecules obey the Langmuir’s adsorption isotherm Where C is the inhibitor concentration and K the equilibrium constant for the adsorption/desorption process of the inhibitor The effect of increase in solution temperature from 25 to 55 ºC efficiency is summarized in table -1. An increased in temperature with produce a decrease in the inhibitor efficiency and this suggest that the process of adsorption of the inhibitor molecules is physical in nature. The corrosion reaction was are corrosion rates at temperature T and , mg cm -2 -1) over the . Where, W is the original weight (mg) of the copper specimen, W2 the weight after immersion in the test electrolyte, A is the area in cm , and t is the time of exposure in h. The heat of adsorption, Qads was calculated by using the following equation19. Q ads =2.303 R [log (/1- ) - log ( Where and are the values of surface coverage at temperatures T and T. Arrhenius plot of logarithmic of corro reciprocal of absolute temperature (1/T) is shown graphically in figure- 4 at different concentration of inhibitor. The values of activation energy (E ) and heat of adsorption (Q presented in table- 2. The observed increase in in the presence of inhibitor from 53.06 to 71.97kJ mol attendant decrease in inhibition efficiency of the inhibitor as temperature increases, suggests physical adsorption of the inhibitor molecules on the copper surface. This is i with the findings of other workers the Qads of adsorption and the high values of the adsorption constant indicate a spontaneous adsorption of these inhibitors on copper. This means that the inhibitive action of the results from the physical adsorption of these molecules on the surface of copper. Table- 2 The activation energy (Ea) kJ/mol and Q copper with and without inhibitions (%v/v) Ea (kJ/mol) 0 53.06 1 58.30 2 61.19 3 63.10 5 63.47 7 71.97 Figure-1 The plot of weight loss of copper coupon versus volume of Inula viscosa extract in 1M NaOH for 60 min. immersion period at different temperatures ______________ _____ ISSN 2231-606X Res.J.Chem.Sci 39 is the original weight (mg) of the copper specimen, the weight after immersion in the test electrolyte, A is the , and t is the time of exposure in h. was calculated by using the log ( /1- )] x (T/T-T) are the values of surface coverage at Arrhenius plot of logarithmic of corro sion rate against the reciprocal of absolute temperature (1/T) is shown graphically in 4 at different concentration of inhibitor. The values of ) and heat of adsorption (Q ads) are 2. The observed increase in activation energy in the presence of inhibitor from 53.06 to 71.97kJ mol -1, with attendant decrease in inhibition efficiency of the inhibitor as temperature increases, suggests physical adsorption of the inhibitor molecules on the copper surface. This is i n accordance with the findings of other workers 11,19. The negative values of of adsorption and the high values of the adsorption constant indicate a spontaneous adsorption of these inhibitors on copper. This means that the inhibitive action of the se substances results from the physical adsorption of these molecules on the 2 The activation energy (Ea) kJ/mol and Q ads(kJ/mol) of the copper with and without inhibitions Q ads (kJ/mol) - -37.98 -29.57 -32.35 -9.13 -22.54 extract in 1M NaOH for 60 min. immersion period Research Journal of Chemical Sciences ______ Vol. 2(9), 37-41, Sept. (2012) International Science Congress Association Inhibition efficiency of Inula viscosa extract on copper in 1M NaOH for 60 min immersion period at different temperatures Langmuir isotherm for the adsorption on the copper surface of Arrhenius plot for copper dissolution in 1M NaOH in the absence and presence inhibitor ______ _________________________________ ______________ International Science Congress Association Figure-2 extract on copper in 1M NaOH for 60 min immersion period at different temperatures Figure-3 Langmuir isotherm for the adsorption on the copper surface of Inula viscosa extract at different temperature Figure-4 Arrhenius plot for copper dissolution in 1M NaOH in the absence and presence inhibitor ______________ _____ ISSN 2231-606X Res.J.Chem.Sci 40 extract on copper in 1M NaOH for 60 min immersion period at different temperatures extract at different temperature Arrhenius plot for copper dissolution in 1M NaOH in the absence and presence inhibitor Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 2(9), 37-41, Sept. (2012) Res.J.Chem.SciInternational Science Congress Association 41 ConclusionThe extract of Inula viscosa inhibits the corrosion of copper in 1M NaOH solutions, with inhibition efficiency of 86.49% at 7mL of extract and the % inhibition efficiency decreased with increase in temperature. The adsorption of the inhibitor molecules was consistent with Langmuir adsorption isotherm. Acknowledgment The authors would like to thank the Yarmouk University for providing financial support. Special thanks are due to Prof. Dr. Mohammad Al-qudah. 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