Research Journal of Recent Sciences ______ ______________________________ ______ ___ __ _ ISSN 2277 - 2502 Vol. 1( ISC - 2011 ), 73 - 78 (201 2 ) Res.J. Recent .Sci. International Science Congress Association 73 Corrosion Inhibitive Effects of Withania Somnifera (A medicinal plant) on Aluminium in HCl Solution Dubey J., Jeengar N., Upadhyay R.K., Chaturvedi A. Department of Chemistry, Government College, Ajmer , Raj ., INDIA Available online at: www.isca.in (Received 30 th November 2011, revised 11 th January 2012 , accepted 9 th March 2012 ) Abstract Corrosion can be considered either chemical or electrochemical in nature. It decays the metallic properties of metals and lea d them unfit for their specific purpose in industry. Corrosion of metals may be prevented by either barrier protection or sacri fici al protection or by alloying or by anti rust solution of ligands containing N, S, O, Se and P as hetero atoms. The naturally occ urring plant products are eco - friendly, compatible, nonpolluting, less toxic, easily available, biodegradable and economic to be used as corrosion inhibitors. Extract of different parts of plant like seeds, leaves, stem can be used as inhibitor to reduce the cor rosion rate of metal like aluminium in acidic media.Corrosion inhibitive effects of naturally occurring Withania Somnifera (Ashwagandha ) have been studied in different concentrations of HCl for aluminium. Studies were carried out at two different temperatures o f extract of leaves and root of the said plant. Leaves extract has been found more effective corrosion inhibitor at lower temperature. The maximum corrosion inhibition efficiency was found 99.28% for leaves extract at 303K. Keywords: Corrosion inhibition efficiency, corrosion rate, reaction number, Withania S omnifera , alkaloid, surface coverage. Introduction Aluminium and its alloys are very important in many industrial as well as household applications due to their corrosion passivity in neutral media and atmospheric conditions due to formation of passive oxide layer on them. Although it is very reactive in emf series but becomes passive on exposure to water and atmosphere but it dissolves in hydrochloric acid liberating H 2 gas. 2Al + 6 HCl + 12 H 2 O 2 [Al (H 2 O) 6 ]Cl 3 + 3H 2 Compounds containing N, S and O have been found as good inhibitors due to high basicity and electron density and thus assist corrosion inhibition 1 . O, N and S are the active center for the process of adsorption on the metal surface. The size, orientation, shape and electric charges of the molecule also play a part in the effectiveness of inhibition. Corrosion not only causes enormous loss to the economy of country but also is a major threat to human safety. The government committee on corrosion in U.K. esti mated that the total loss to the national economy due to corrosion was 3.5% of GNP. Developed countries dump their scrap due to corroded alloys into sea and oceans and this material produces environmentally adverse effect on flora and fauna of oceans. Gase s evolved during corrosion like SO 2 , NO 2 causes acid rain which is very harmful for buildings, plants and animals. In addition to the heterogeneous organic compounds synthesized in laboratory some naturally occurring substances like Ficus virens 2 , Delonix regia 3 , Ocimum basilicum 4 , Caparis deciduas 5 , Sansevieria trifascinata 6 , Phylanthus amarus 7 , Prosopis julifforar 8 , Argemone maxicana 9 have been evaluated as effective corrosion inhibitors. The naturally occurring plant products are eco - friendly, compatibl e, nonpolluting, less toxic, easily available, biodegradable and economic to be used as corrosion inhibitors. These inhibitors have many N, O and S containing alkaloids which are get adsorbed on metal surface which essentially block the discharge of H + and dissolution of metal ions. Extract of different parts of plant like seeds, leaves, stem and bark can be used as inhibitor to reduce the corrosion rate of metal like aluminium in acidic media. In the present investigation the inhibition efficiencies of Wit hania Somnifera have been studied in different concentrations of HCl solution at two temperature i.e. 303 K (30 0 C) and 318K (45 0 C). Withania Somnifera is a very common plant in India and other regions having almost same climatic conditions. Alkaloids and steroidal lactones are the main constituents of Ashwagandha. Plant contains many alkaloids like anaferin, anahygrine, betasisterol, chlorogenic acid, cystein, cuscohygrine, pesudotropine, scopoletin, somniferiene tropanol, withanine, withananine etc. With aferin A and withanolides A - Y are the main steroidal lactones. The withanolides are a group of naturally occurring C - 28 steroidal lactones built on an intact or rearranged ergostane framework in which C - 22 and C - 26 are appropriately oxidized to form a six membered lactone ring. O O Research Journal of Recent Sciences ______ _ _ _______________________________ ______________ _ ______ ISSN 2277 - 2502 Vol. 1( ISC - 2011 ), 73 - 78 (201 2 ) Res.J.Recent.Sci International Science Congress Association 74 Material and Methods Commercially available aluminium was used for specimen preparation. The specimens were prepared by cutting the aluminium sheet into square shaped pieces having dimension 2.0  2.0  0.03cm containing a small hole of about 2mm diameter near the upper edge. Specimens were polished to mirror finish by using emery paper. Solutions of HCl were prepared by using double distilled water. All chemicals used were of AR grade. Extract of leaves and root of Withania Somnifera was obtained by refluxing the dried leaves and root in soxhlet in ethanol. Solutions of different concentrations of extract were prepared in ethanol. Each specimen was suspended by a V - shaped glass hook made of capillary an d plunge into a beaker containing 50mL of the test solution (HCl) at 303K and at 318K. After the sufficient exposure, test specimens were washed with running water and dried by hot air dryer. Duplicate experiments were performed in each case and mean value of weight loss was determined. The percentage inhibition efficiency was calculated as 10 . Where  W u and  W i are the weight loss of the specimen in uninhibited and in inhibited solution respectively. Degree of surface coverage (  ) was calculated as 11 . The corrosion rate in mm/yr can be obtained by the following equation 12 . Where,  W is weight loss in mg, A is area of specimen in cm 2 , T is time of exposure in hours, D is density of metal in gm/cm 3 . Results and Discussion Weight loss data and corresponding values of inhibition efficiency and corrosion rate for leaves and root extract as an inhibitor are g iven in table - 1 and t able - 2. It is obvious from the table - 1 that inh ibition efficiency increases with increasing acid strength and it also increases with increasing concentration of leaves extract. The maximum efficiency (i.e.99.28%) has been observed in 2N HCl at highest concentration of inhibitor (i.e.0.8%) for leaves ex tract at 303K. Observations of inhibition efficiency corresponding to same concentrations of acid and inhibitor at 318K show that efficiency of the inhibitor is less at 318K than that at 303K although the trends are same at 318K. Maximum efficiency at 318K is 98.53% for the same concentration of leaves extract (i.e. 0.8%) for 2N HCl. Variation of inhibition efficiency with concentration of leaves extract for 2N HCl at two different temperatures is shown in fig ure 1. Table - 1 Inhibition e fficiency (  %) for aluminium in HCl with leave extract of Withania Somnifera at 303K and 318K Area of specimen: 8.0cm 2 Conc. of inhibitor 0.5N HCl (173 hrs.) 1N HCl (2 . 25 hrs.) 2N HCl ( 25 min) -  W  % C.R.  W  % C.R.  W  % C.R. At 303K uninhibited 0.207 - 0.7148 0.117 - 31.06 0.279 - 400.680 0.1 0.163 21.27 0.5629 0.043 63.24 11.41 0.007 97.49 10.053 0.2 0.157 24.15 0.5421 0.015 87.17 3.98 0.005 98.2 7.185 0.4 0.154 25.6 0.5321 0.003 97.43 0.796 0.004 98.56 5.744 0.8 0.152 26.57 0.5249 0.002 98.29 0.531 0.002 99.28 2.872 At 318K uninhibited 0.324 - 1.118 0.364 - 96.65 0.273 - 652.51 0.1 0.271 16.35 0.9358 0.136 62.63 17.525 0.008 97.06 19.121 0.2 0.257 20.67 0.8875 0.085 76.64 11.68 0.006 97.8 14.341 0.4 0.254 21.6 0.8771 0.039 89.28 0.355 0.005 98.16 11.95 0.8 0.251 22.53 0.8668 0.037 89.83 9.824 0.004 98.53 9.56 Research Journal of Recent Sciences ______ _ _ _______________________________ ______________ _ ______ ISSN 2277 - 2502 Vol. 1( ISC - 2011 ), 73 - 78 (201 2 ) Res.J.Recent.Sci International Science Congress Association 75 Table - 2 Inhibition efficiency (  %) for aluminium in HCl with root extract of Withania Somnifera at 303K and 318K Area of specim en: 8.0cm 2 Table - 3 Surface coverage and log (  / 1 -  ) for aluminium in HCl with leave extract of Withania Somnifera at 303K and 313K Conc. Of inhibitor 0.5N HCl(173 hrs.) 1N HCl(2 . 25 hrs.) 2N HCl(25min..)  %  log (  / 1 -  )  %  log (  / 1 -  )  %  log (  / 1 -  ) At 303K uninhibited 0.1 21.27 0.2127 - 0.5684 63.24 0.6324 0.2356 97.49 0.9749 1.5893 0.2 24.15 0.2415 - 0.4970 87.17 0.8717 0.8321 98.20 0.9820 1.7368 0.4 25.60 0.2560 - 0.4633 97.43 0.9743 1.5788 98.56 0.9856 1.8353 0.8 26.57 0.2657 - 0.4415 98.29 0.9829 1.7595 99.28 0.9928 2.1395 At 318K uninhibited 0.1 16.35 0.1635 - 0.7089 62.63 0.6263 0.6544 97.06 0.9706 1.5187 0.2 20.67 0.2067 - 0.5841 76.64 0.7664 0.8567 97.80 0.9780 1.6479 0.4 21.60 0.2160 - 0.5599 89.28 0.8928 0.9206 98.16 0.9816 1.7271 0.8 22.53 0.2253 - 0.5364 89.83 0.8983 0.9461 98.53 0.9853 1.8263 Conc. of inhibitor 0.5N HCl (173 hrs.) 1N HCl (2 . 25 hrs.) 2N HCl ( 25 min)  W  % C.R.  W  % C.R.  W  % C.R. At 303K uninhibited 0.207 0.7184 0.117 31.06 0.279 400.680 0.1 0.180 13.04 0.6216 0.062 47.00 16.46 0.009 96.77 12.925 0.2 0.170 17.87 0.5870 0.017 85.47 4.51 0.007 97.49 10.053 0.4 0.155 25.12 0.5350 0.006 94.87 1.59 0.005 98.20 7.180 0.8 0.154 25.60 0.5318 0.004 96.58 1.06 0.004 98.56 5.744 At 318K uninhibited 0.324 1.118 0.364 96.65 0.273 652.51 0.1 0.273 15.74 0.9427 0.112 69.23 29.73 0.012 95.60 28.68 0.2 0.262 19.31 0.9047 0.108 70.32 28.67 0.009 96.70 21.51 0.4 0.261 19.44 0.9013 0.098 73.07 26.02 0.007 97.43 16.73 0.8 0.254 20.06 0.8944 0.057 84.34 15.13 0.006 97.80 14.34 Research Journal of Recent Sciences ______ _ _ _______________________________ ______________ _ ______ ISSN 2277 - 2502 Vol. 1( ISC - 2011 ), 73 - 78 (201 2 ) Res.J.Recent.Sci International Science Congress Association 76 Table - 4 Surface coverage and log (  / 1 -  ) for aluminium in HCl with root extract of Withania Somnifera at 303K and 313K Conc. Of inhibitor 0.5N HCl(173 hrs.) 1N HCl(2 . 25 hrs.) 2N HCl(25min..)  %  log (  / 1 -  )  %  log (  / 1 -  )  %  log (  / 1 -  ) At 303K uninhibited 0.1 13.04 0.1304 - 0.8240 47.00 0.4700 - 0.0522 96.77 0.9677 1.4765 0.2 17.87 0.1787 - 0.6624 85.47 0.8547 0.7695 97.49 0.9749 1.5893 0.4 25.12 0.2512 - 0.4743 94.87 0.9487 1.2670 98.20 0.9820 1.7368 0.8 25.60 0.2560 - 0.4633 96.58 0.9658 1.4509 98.56 0.9856 1.8353 At 318K uninhibited 0.1 15.74 0.1547 - 0.7286 69.23 0.6923 0.3522 95.60 0.9560 1.3370 0.2 19.31 0.1931 - 0.6210 70.32 0.7032 0.3746 96.70 0.9670 1.4669 0.4 19.44 0.1944 - 0.6174 73.07 0.7303 0.4335 97.43 0.9743 1.5788 0.8 20.06 0.2006 - 0.6004 84.34 0.8434 0.7312 97.80 0.9780 1.6479 95.5 96 96 . 5 97 97.5 98 98.5 99 99.5 0.1 0.2 0 . 4 0.8 Inhibition efficiency Concentration (%) Figure - 1 Variation of inhibition efficiency with concentration of leaves extract at 303 and 318 K 303 K 94 95 96 97 98 99 0 . 1 0 . 2 0.4 0 . 8 Inhibition efficiency Concentration (%) Fig - 2 Variation of inhibition efficiency with concentration of root extract at 303 and 318 K 303 K Research Journal of Recent Sciences ______ _ _ _______________________________ ______________ _ ______ ISSN 2277 - 2502 Vol. 1( ISC - 2011 ), 73 - 78 (201 2 ) Res.J.Recent.Sci International Science Congress Association 77 It is clear from the table - 2 that root extract also shows excellent inhibition efficiency for aluminium metal in HCl solution .it is obvious from the table that root extract shows same trends as leaves extract with increasing concentration of acid as well as with increasing concentration of inhibitor . R oot extract is also more efficient at 303K than 318K as an inhibitor . The maximum efficiency (i.e.98.56%) has been observed in 2N HCl at highest concentration of inhibitor (i.e.0.8%) for root extract at 303K. Variation of inhibition efficiency with concentration of root extract for 2N HCl at two different temperatures is s hown in fig ure 2 . The degree of surface coverage of metal (  ) covered by the adsorption of inhibitor to block the active sites on the surface at various concentrations of inhibitor for different HCl concentrations are shown in t able - 3 and t able - 4 for leaves and root extract. It is clear from the tables that degree of surface coverage increases with increasing concentration of inhibitor at both temperatures i.e.303K and 318K, however at 318K the coverage is less than that at 303K. Hoar and Holiday gave the Langmuir adsorption isotherm 13 l og  /(1 -  ) =log A + log C - Q /2.3 RT Where :  = Surface coverage , A = Temperature dependent constant , C = Bul k concentration of inhibitor (mol /L ) , Q = Heat liberated in reaction . According to which a straigh t line should be obtained if a graph is plotted between log  / ( 1 -  ) versus logC with gradient equal to one. In our investigation the graph is linear but gradient is not equal to unity. This deviation from unit behaviour can be explained on the basis of int eraction of the adsorbed molecules on the metal surface. According to L angmuir the adsorbed layer is unimolecular i.e. there is no interaction between adsorbed molecules themselves and between adsorbate and adsorbent molecules. Only then the gradient is unity but in actual practice there is an interaction between adsorbed molecules themselves and between adsorbate and adsorbent molecules that is why the gradient is not unity. Variation of log  / ( 1 -  ) wit h concentration of leaves and root extract for 2N HCl are shown in fig ure 3 and fig ure 4. 0 1 2 3 4 5 - 1 - 0 . 69 - 0.39 - 0 . 09 log (  / 1 -  ) Log C fig. 3 Langmuir adsorption isotherm in 2N HCl at 303 and 318K tempreture with the concentration of leaves extract 318 K 303 K 0 1 2 3 4 - 1 - 0 . 69 - 0.39 - 0.09 log (  / 1 -  ) Log C fig. 4 Langmuir adsorption isotherm in 2N HCl at 303 and 318K tempreture with the concentration of root extract 318 K 303 K Research Journal of Recent Sciences ______ _ _ _______________________________ ______________ _ ______ ISSN 2277 - 2502 Vol. 1( ISC - 2011 ), 73 - 78 (201 2 ) Res.J.Recent.Sci International Science Congress Association 78 Conclusion The studies on Withania Somnifera as corrosion inhibitor for aluminium in HCl have shown that this widely available plant is a very good corrosion inhibito r for aluminium. Studies have shown that both leaves and root extract show similar trends for different concentrations of acid as well as those of inhibitor. Further it can be concluded from the studies that Withania Somnifera is a better corrosion inhibit or at 303K than at 318K and leaves extract is more efficient than root extract. Acknowledgement One of the authors Dubey J. is thankful to the synthetic and surface science laboratory, Govt. College, Ajmer, India for providing facilities for the experime ntal work. References 1. Putilova I.N., Balizin S.A. and Baranik V.P., Metallic corrosion inhibitor Pergaman Press London ( 1960) 2. Jain T., Choudhary R. and Mathur S.P., Materials and Corrosion 57, 422 ( 2006 ) 3. Abiola O.K., Oforka N.C., Ebenso E.E. and Nwinuka N.M., Anticorrosion Methods and Material, 54, 219 ( 2007 ) 4. Oguzie E.E., Onuchukwu A.I., Okafor P.C. and Ebenso E.E., Pigment and Resin Technology , 35, 63 ( 2006 ) 5. Arora P., Kumar S., Sharma M.K. and Mathur S.P., E - Journal of Chemistry , 4, 450 ( 2007 ) 6. Oguzei E.E., Corrosion Science, 49, 1527 ( 2007) 7. Okafor P.C., Ikpi M.E., Uwah I.E., Ebenso E.E., Elcpe U.J. and Umoren S.A., Corrosion Science, 50, 2310 ( 2008 ) 8. Choudhary R., Jain T. Mathur S.P., Bulletin of Electrochem , 20 , 67 ( 2004 ) 9. Sharma P., Upadhyay R.K., Chaturvedi A. and Parashar R., J.T.R. Chem , 15(1) , 21 ( 2008 ) 10. Talati J.D. and Gandhi D.K., Ind. J. Tech., 29 , 277, ( 1991) 11. Dubey R.S. and Upadhyay S.N., J. Electrochem. Soc. India , 74 , 143, ( 1944 ) 12. Fontana M.G., Corrosion Engineering 3 rd Edition Mcgraw Hill Book Company, 173, ( 1987 ) 13. Hoar I.P. and Holiday R.D., J. App. chem. , 3 , 582, ( 1953 )