N. O. Eddy
Keywords: Zinc corrosion, inhibition
Abstract:
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ISSN 1466-8858 INHIBITION 10, Preprint 1 November 2007 OF CORROSION Volume OF ZINC IN 410.01M H2SO4 submitted BY 5-AMINO-1CYCLOPROPYL-7-[(3R,5S)3,5-DIMETHYLPIPERAZIN-1-YL]-6,8-DIFLUORO-4-OXOQUINOLINE-3-CARBOXYLIC ACID (A) *N. O. Eddy and B. O. Abasiekong Department of Chemistry University of Calabar, Calabar. E-mail: nabukeddy@yahoo.com Abstract Effect of A on the corrosion of zinc has been studied by using weight loss and gasometric methods. The study revealed that A inhibits the corrosion of zinc with corrosion efficiency ranging from 34.64 – 73.50%. The kinetics of uninhibited and inhibited corrosion reactions of zinc is found to be first order. Values of rate constant and half-life ranged from 0.1076 – 1.10893 and from 24 – 154days respectively. An average value of activation energy (Ea) of the inhibited corrosion reaction (5.1751J/mol) was higher than average values of activation energy obtained for the uninhibited corrosion reaction (-13.0760J/mol). Also average values of enthalpy change (∆Hads =15.1751J/mol) and entropy change (∆Sads = -279.8631J/mol) indicated that the adsorption of A on zinc surface is exothermic and is accompanied by increase in degree of orderliness. Between 303 and 323K, values of free energy of adsorption (∆Gads) ranged from -84.7852 - -90.3805KJ/mol indicating that the adsorption of A is spontaneous and follows the mechanism of chemical adsorption. Lagmuir adsorption isotherm has been found to be applicable to the adsorption of A on mild steel surface. Key Word: Zinc corrosion, inhibition, A 1 © 2007 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. ISSN 1. 1466-8858 Introduction Volume 10, Preprint 41 submitted 1 November 2007 A corrosion inhibitor is a chemical substance that when applied in small quantities to corrosive medium reduces the rate of corrosion of a metal or its alloy [16.]. A search for a suitable inhibitor for the corrosion of zinc (in acidic medium) involves a choice between those synthesized from cheap raw materials and those containing hetero-atoms (N, O, S or P) in aromatic or long chain carbon compound [4-6]. In addition to other uses, zinc is often used for electro- protection of iron against corrosion implying that a search for an inhibitor that can retard zinc corrosion requires adequate attention. 5-amino-1-cyclopropyl-7-[(3R,5S)3,5-dimethylpiperazin-1-yl]-6,8- difluoro-4-oxo-quinoline-3-carboxylic acid (A) contained heteroatoms in their aromatic ring. It has a high molecular mass and can easily be synthesized by chemical method [7]. Due to its unique properties, A may be a good inhibitor for the inhibition of zinc corrosion. The present studies seek to investigate inhibitive properties of 5-amino-1cyclopropyl-7-[(3R,5S)3,5-dimethylpiperazin-1-yl]-6,8-difluoro-4-oxo-quinoline-3carboxylic acid (A) for the corrosion of zinc in 0.01M H2SO4. 2. Materials and methods 2.1 Materials The sample (A) was by Livemore pharmacy, Ikot Ekpene, Nigeria. Zinc specimens used for the study were of dimension 5 x 4 x 0.11cm. The acid solutions (H2SO4) were prepared from analar grade manufactured by BDH chemicals. Concentration of acid used for weight loss experiment was 0.01M while 2.5M was used for gasometric experiment. Double distilled water was used for the preparation of all 2 © 2007 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. ISSN 1466-8858The reagents. 10, Preprint 41 for weight loss submitted 1 November 2007 concentration range Volume of inhibitor prepared and gasometric studies was 0.0001 –0.0005M. 2.2 Weight loss measurement. Weight loss measurements were carried out as described in literature [1-6]. The volume of solution used was 150ml. A maximum immersion time was 168hours. Solutions were not stirred but specimens were removed from their respective solutions after every 24hours, washed in 5% chromic acid solution containing 1% silver nitrate (in 10% aluminum chloride), rinsed in boiling water, dried in acetone and weighed. Weight loss experiments were carried out at different temperatures (303, 313, 323 and 333K) and different concentrations (0.0001 –0.0005M) of inhibitor were used. From weight loss measurement, inhibition efficiency and degree of surface coverage were calculated using equations 1 and 2 respectively [2-5]. %I = (1 – W 1/W 2) x 100 (1) θ = = 1 - W 1/W 2 (2) where W 1 and W 2 are the weight losses (g/dm3) for zinc in the presence and absence of inhibitor respectively. 2.3 Gasometric method Gasometric methods were carried out as described in literature [11-13] Mild steel coupons of dimension similar to those used for weight loss method were also used for hydrogen evolution studied. From the volume of hydrogen evolved after every minutes, inhibition efficiency of different concentration of A was calculated using equation 3 I(%) = {1 - V’Ht } x 100 V0Ht (3) 3 © 2007 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. ISSN 1466-8858 Volume 10, Preprint 41 submitted 1 November 2007 Where V’Ht is the volume of hydrogen evolved at time t for inhibited solution and V0Ht is the volume of hydrogen evolved at time t for unhibited solution 3.0 Results and discussion 3.1 Effect of concentration and temperature. Fig. 1 shows weight loss of zinc (in 0.01M H2SO4) in the presence of 0.0001 – 0.0005M of A while Fig. 1b (inserted) shows weight loss of zinc (in 0.01M H2SO4) in the absence of the inhibitor. Comparing Fig. 1 with Fig. 1b, it can be seen that values obtained for weight losses of zinc in the presence of different concentration of A were generally lower than values obtained for the blank (Fig.1b) indicating that A retard the corrosion of zinc. Weight losses were observed to increase with temperature indicating that corrosion rate of zinc is lowered at higher temperatures and that the mechanism of adsorption of A on zinc electrode is chemical adsorption [14-15]. 3.2 Kinetics and thermodynamics considerations In order to study the kinetic of the inhibited corrosion reaction, attempts were made to fit data obtained from weight loss measurement into different kinetic plots including zero order, first and second order and by far the inhibited corrosion reaction was found to proceeds via first order. For a first order reaction, the concentration of zinc [Zno] at time t = 0 and the concentration after time t is related to each other according to equation 4 [16]: -log[Zno] – [Zn] = K1t/2.303 (4) 4 © 2007 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. ISSN 1466-8858 where K is 1 Volume 10, Preprint 41 By plotting values submitted 1 November 2007 the rate constant for a first order reaction. of –log[weight loss] versus time for the corrosion reactions of zinc in the presence and absence of A (Fig. 2 and 2a), straight lines were obtained implying that the corrosion reactions of zinc in the absence and presence of A proceeds according to first order kinetics. Values of half life for the corrosion reaction of zinc in the absence and presence of A were calculated using equation 5[16]: t1/2 = 0.693/K1 (5) Calculated values of t1/2 for inhibited corrosion reaction of zinc are recorded in Table 1. These values are found to be higher than values obtained for the blank indicating that A extends the half life of zinc corrosion. In order to calculate the activation energy of the corrosion reaction of zinc in the absence and presence of A, the Arrhenius equation was used (equation 6) [16-17]: K = exp(-Ea/RT) (6) where K is rate constant obtained from the slope of kinetic plots (Fig. 2), Ea is the activation energy of corrosion reaction of zinc, R is the gas constant and T the is temperature. Transforming equation 6 to logarithm form, equation 7 is obtained: logK = -Ea/2.303RT (7) From equation 7, a plot of logK versus 1/T should produce a straight line with slope equals to –Ea/2.303R from where the value of Ea can be computed. Fig. 4 shows Arrhenius plot for the corrosion of zinc in the presence of A. From the plot, calculated values of Ea ranged from 21.2552 – 70.2336J/mol(mean = 5.1751J/mol)(Table 2) implying that the Ea for inhibited corrosion reaction of zinc is higher than that of 5 © 2007 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. ISSN 1466-8858 uninhibited Volume 10, Preprint submitted November 2007 corrosion reaction of zinc(average Ea 41 = - 13.0760J/mol). The1 observed differences confirm that A retards the corrosion of zinc in H2SO4. In order to calculate thermodynamic parameters for the corrosion reaction of zinc, the transition state equation (equation 8) was used[16-17]: K = RT/Nhexp(∆S/R)exp(-∆H/RT) (8) Rearranging equation 8, equation 9 is obtained. log(K/T) = logR/Nh + ∆S/2.303R - ∆H/2.303RT (9) where N is the Avogadro’s number and h is the plank constant. From equation 9, a plot of logK/T versus 1/T should produce a straight line with slope equals to -∆H/2.303R and intercept equals to logR/Nh + ∆S/2.303R Values of ∆Hads (Table 2) calculated through slopes of lines on the transition state plot (Fig. 3) ranged from –72.8913 – 39.4852J/mol(mean = -15.2737J/mol) indicating that the inhibited corrosion reaction of zinc is exothermic. Also, values of ∆Sads calculated from intercepts of lines on the plot (Fig.3) ranged from –130.9684 - 484.4800J/mol (mean = -279.8631J/mol indicating that adsorption of A on zinc surface is controlled by activation complex and that there is association instead of dissociation. Values of free energy of adsorption (∆Gads) were calculated by substituting values of ∆Hads and ∆Sads into the Gibb-Helmoltz equation (equation10) [16]: ∆Gads = ∆Hads - T∆Sads (10) Calculated values of ∆Gads are recorded in Table 2. the values ranged from – 84.7832 - -90.3805J/mol indicating that adsorption of A on zinc surface is spontaneous and proceeds via chemical adsorption mechanism. [10-15]. 6 © 2007 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. ISSN 1466-8858 3.3 Volume 10, Preprint 41 submitted 1 November 2007 Adsorption consideration Adsorption isotherm provides a clue to the mode and mechanism of adsorption. Attempts were made to fit data obtained from weight loss measurement into different adsorption isotherm including those of Lagmuir, Frumkin, Freundlich, Temkin, Florry Huggins, and El awardy isotherms. By far the data fitted Lagmuir adsorption isotherm best. Assumptions of Lagmuir adsorption isotherm relates concentration of inhibitor in the bulk electrolyte to the degree of surface coverage according to equation 11 [18-20]: C/θ = 1/K + C (11) where C is inhibitor’s concentration, θ is the degree of surface coverage and K is the binding constant. From equation 11, if the assumptions of Lagmuir are obeyed, a plot of C/θ versus C should give a straight line with intercept equals to 1/K [12] Lagmuir plot for the corrosion reaction of zinc in the presence of A is shown by Fig 4. The fact that lines on the Figures are linear and very close to each other confirms that Lagmuir adsorption isotherm is applicable to the adsorption of different concentration of A within the temperature range of 303 –323K. It also indicates that A causes a high increase in the free energy with respect to uninhibited system. These results show strong adsorption of inhibitors on the mild steel surface and suggest the existence of monolayers of adsorption [18-20]. From the intercept of Lagmuir plot (Fig. 4) calculated values of the binding constant, K at 303, 313 and 323K were 5000, 50000 and 111111.10 respectively. These values are large confirming the mechanism of chemical adsorption. 7 © 2007 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. ISSN 1466-8858 3.4 Volume 10, Preprint 41 submitted 1 November 2007 Inhibition efficiency of A Values of inhibition efficiency of A calculated from weight loss measurement are recorded in Table 3. The result shows that Inhibition efficiency of A increase with temperature indicating that A is chemically adsorbed on zinc electrode. Fig. 6 shows a plot of variation of inhibition efficiency of A with concentration Inserted (Fig.6a) is the plot showing the variation of inhibition efficiency of different concentration of A with temperature. From the Figure, it is obvious that inhibition efficiency of A vary slightly with concentration but largely with temperature. The results obtained for inhibition efficiency of A from gasometric method compares favourably with results obtained from weight loss method at 303K (r= 0.8288) confirming that A inhibits the corrosion of zinc. . 3.5 Mechanism of inhibition The used inhibitor has a high molecular weight of 392.41g/mol and molecular formula, C19H22F2N4O3. It contains heteroatoms (N, O) bonded to three aromatic rings (Structure I) Its high molecular mass and electron rich bonds/functional groups are factors that enhanced the inhibition action of A.. Based on its structure Structure I), the following inhibition mechanism is proposed for the used inhibitor (A): Structure I 8 © 2007 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. ISSN 1466-8858 i. Volume 10, Preprint 41 submitted 1 November 2007 In acidic medium, A undergoes dehydration to yield anhydrosparfloxacin which suffers further cleavages and lactorization ii. Dilute acid promotes epimerization of C-bonds, therefore, it is proposed that the adsorption of A on zinc surface (hence its inhibition efficiency )is stabilized by each molecule of A donating electron to a vacant orbital of iron. iii. The proposed mechanism is supported by moderate values of activation energy (mean = 5.1751J/mol) and other thermodynamic parameters. The fairy high negative values of entropy (mean = -279.8631J/mol) of adsorption suggest the formation of a compact activated complex with fewer degrees of freedom. 4. Conclusion From the results of the study, the following conclusions are drawn, i. A is a good inhibitor for zinc corrosion in H2SO4. Inhibition efficiency of A is enhanced mainly by its structural properties. ii. Inhibited corrosion reaction of Zn is controlled by activation complex iii. Adsorption of A on zinc surface is spontaneous and proceeds via chemical adsorption mechanism. iv. Lagmuir adsorption isotherm is best applicable to the adsorption of A on zinc electrode. 5. Acknowledgment. We are most grateful to staff of Chemistry laboratory, University of Calabar for providing equipments used for the study and to Edikan Nnabuk Eddy for typing the work. 9 © 2007 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. ISSN 1466-8858 Volume 10, Preprint 41 submitted 1 November 2007 6. References 1. A. O. James, N. C. Oforka and K. Abiola, Intern. J. Electrochem. Sc. 2(2007) 284 E. E. Ebenso, P. C. Okafor, U. J. Ekpe, U. J. Ibok and A. I. Onuchukwu, J. Chem. Soc. Nigeria 29(2004) 25 E. E. Ebenso, Nigerian J. of Chem. Res. 6(2001) 12 U. J. Ekpe, P. C. Okafor, E. E. Ebenso, O. E. Offiong, B. I. Ita, Bullentin of Electrochem. 17(2001) 135. S. Muralidharan, R. Chandrasek and S. K. Iyer, Proc. Indian Acad. Sci. 112(2000) 136 G. Tranbonella and V. Carassiti, Advances in corrosion sciences and Technology. Phenium press,New York B. A. Mandell, T. A. Meredith, E. Aguilar, A. el-Massry, A. Sawant, and S. Richard, P., L. Gutmann, J. Antimicrob. Chemother. 30(1992):739–744 K. S. Rayappa and T. V. Venkatesha, Turk. J. Chem. 27(2002) 196 W. A. Monika and A. D. Siddique, Portugaliae Electrochimica acta, 23(2005) 455Sekine, Arzneimittelforschung 41(1991) 746 Emregul, R. Kurtaran and O. Atakol, Corrosion Sc. 45(2003) 2817 O. K. Abiola, J. Childean Chem Soc. 4(2005) 690 E. E. Oguzie, Pigment & resin Technology 6(2006) 340 E. E. Oguzie, E. E. Ebenso, Pigment & Resin Tech. 35(2006) 35 P. Tavassoli-Salardini, Inhibition of corrosion of mild steel in aqueous solution. Ph.D Thesis, University of Sydney M. Ehteshamzade, T. Shahrabi and M. G. Hosseini, Appl. Surf. Sc. 252(2006) 2959 M. Abdallah, Corrosion Sc. 46(2004) 1996 M. Abdallah, Corrosion Sc. 44(20020 728 K. Orubite-Okorosoye, N. C. Oforka, J. Appl. Sc and Environm. Mgt. 8(2004) 61 S. D. Shetty, P Shetty and H. V. S. Nayak, J. Chilean Chem. Soc. 2(2006) 853 P. W. Atkin, A textbook of physical chemistry. Oxford University press, (1991) 938 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 10 © 2007 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. ISSN 1466-8858 Volume 10, Preprint 41 submitted 1 November 2007 Table 1: Values of rate constant and half-life (days) for corrosion of Zn in 0.01M H2SO4 in the presence of 0.0001 – 0.0005M A Con. K1(303) K1(313) K1(323) t1/2(303) t1/2(313) t1/2(323) mol/dm3 0.0001 0.1076 0.3376 0.2906 154 48 58 0.0002 0.1253 0.3109 0.3452 132 53 48 0.0003 1.4117 0.3300 0.2607 24 56 72 0.0004 1.0893 0.2665 0.2549 24 63 72 0.0005 0.2326 0.3669 0.3878 72 48 48 Table 2: Thermodynamic parameters for the corrosion of zinc in 0.01 –0.01M H2SO4 in the presence of 0.0001 –0.0005M A Con. Ea ∆Ho ∆ So ∆Go(303) ∆Go(313) ∆Go(323) mol/dm3 (J/mol) (J/mol) (J/mol) (KJ/mol) (KJ/mol) (KJ/mol) 0.0001 -41.3329 38.6753 -134.2310 -40.7107 -42.0530 -43.3953 0.0002 -42.1429 39.4852 -130.9684 -39.7229 -41.0326 -42.3423 0.0003 70.2336 -72.8913 -484.4801 -146.7246 -151.5694 -156.4142 0.0004 60.3729 -63.0401 -454.3234 -137.5970 -142.1402 -146.6834 0.0005 -21.2552 -18.5976 -195.3123 -59.1610 -61.1142 -63.0673 5.1751 -15.2737 -279.8631 -84.7832 -87.5819 -90.3805 Mean 11 © 2007 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. ISSN 1466-8858 Table 3: Inhibition Preprint 41 of Zn in 0.01Msubmitted efficiency of AVolume for the10,corrosion H2SO4 1 November 2007 Con Gasometric methods 0.01M tetraoxosulphate(VI) (mol/dm3) (2.5M H2SO4) acid(weight loss) 303K 313K 323K 0.0001 48.45 57.07 62.22 72.89 0.0002 48.40 57.66 64.97 69.8 0.0003 50.21 56.8 56.57 70.17 0.0004 52.32 59.27 66.42 70.09 0.0005 45.21 34.64 65.71 73.50 12 © 2007 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. ISSN 1466-8858 Volume 10, Preprint 41 submitted 1 November 2007 Fig. 1b: Weight loss of zinc(blank) 0.7000 2.0000 Weight loss(g) 0.8000 313K 303K 323K 1.5000 1.0000 0.5000 0.0000 1 2 3 4 5 6 7 Immersion period(days) 0.6000 0.0001M(303) 0.0002M(303) 0.0003M(303) 0.0004M(303) 0.0005M(303) 0.0001M(313) 0.0002M(313) 0.0003M(313) 0.0004M(313) 0.0005M(313) 0.0001M(323) 0.0002M(323) 0.0003M(323) 0.0004M(323) 0.0005M(323) Weight loss(g) 0.5000 0.4000 0.3000 0.2000 0.1000 0.0000 1 2 3 4 5 6 7 Immersion period (days) Fig. 1: Weight loss of zinc in 0.1M tetraoxosulphate (VI) acid in the presence of A 13 © 2007 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. ISSN 1466-8858 Volume 10, Preprint 41 submitted 1 November 2007 Fig. 2a: Kinetic plot for corrosion of Zn in the blank 1 1.8000 -Log[weight loss] 0.8 1.6000 0.01M(303) 0.01M(313) 0.01M(323) 0.6 0.4 0.2 0 -0.2 1.4000 -0.4 1 2 4 5 6 7 immersion period(days) 1.2000 -Log[weight loss] 3 0.0001M(303) 0.0002M(303) 1.0000 0.0003M(303) 0.0004M(303) 0.8000 0.0005M(303) 0.0001M(313) 0.0002M(313) 0.6000 0.0003M(313) 0.0004M(313) 0.4000 0.0005M(313) 0.0001M(323) 0.0002M(323) 0.2000 0.0003M(323) 0.0004M(323) 0.0000 0.0005M(323) 1 2 3 4 5 6 7 Time(days) Fig. 2: Kinetic plot for the corrosion of Zn in 0.01M acid in the presence of A(insert, plot for the blank) 14 © 2007 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. ISSN 1466-8858 Volume 10, Preprint 41 submitted 1 November 2007 0.4000 0.0001M 0.2000 0.0002M 0.0003M 0.0000 -0.2000 0.0004M 0.0005M y = -2.1587x + 6.249 R2 = 0.6391 y = -2.201x + 6.4194 R2 = 0.8266 y = 3.6681x - 12.043 R2 = 0.8524 y = 3.1536x - 10.468 R2 = 0.7728 y = -1.1101x + 3.0589 R2 = 0.8304 LogK 0.0001M -0.4000 0.0002M 0.0003M 0.0004M -0.6000 0.0005M -0.8000 -1.0000 -1.2000 3.05 3.1 3.15 3.2 3.25 3.3 3.35 1/T x 0.001(/K) Fig. 3: Arrhenius plot for corrosion of zinc in 0.01M acid corrosion in the presence of A 15 © 2007 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. ISSN 1466-8858 Volume 10, Preprint 41 submitted 1 November 2007 -2.0000 -2.2000 0.0001M y = -2.0199x + 3.3095 2 R = 0.6083 0.0002M y = -2.0622x + 3.4799 2 R = 0.8075 0.0003M -2.4000 0.0004M 0.0005M Log(K/T) -2.6000 y = 3.8069x - 14.983 2 R = 0.8613 y = 3.2924x - 13.408 2 R = 0.7873 y = -0.9713x + 0.1194 2 R = 0.7903 0.0001M 0.0002M 0.0003M 0.0004M 0.0005M -2.8000 -3.0000 -3.2000 -3.4000 -3.6000 3.05 3.1 3.15 3.2 3.25 3.3 3.35 1/T x 0.001(/K) Fig. 4: Transition state plot for the corrosion of zinc in 0.01M acid in the presence of A 16 © 2007 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. ISSN 1466-8858 Volume 10, Preprint 41 submitted 1 November 2007 0.0016 0.0014 303K 313K 323k 0.0012 303K 0.001 313K C/0 323k y = 2.8644x - 0.0002 2 R = 0.8538 y = 1.4948x + 2E-05 2 R = 0.9814 y = 1.3703x + 9E-06 2 R = 0.9972 0.0008 0.0006 0.0004 0.0002 0 0 0.0001 0.0002 0.0003 0.0004 0.0005 0.0006 Concentration (mol/dm3) Fig. 5: Curve fitting for adsorption of sparfloxacin on mild Zn according to Lagmuir 17 © 2007 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. ISSN 1466-8858 Volume 10, Preprint 41 submitted 1 November 2007 80.00 70.00 303K 313K 323K 50.00 Fig. 6b: variation of inhibition efficiency with temperature 75.00 40.00 Inhibition efficiency(%) Inhibition efficiency (%) 60.00 30.00 20.00 70.00 65.00 0.0001M 0.0002M 0.0003M 60.00 0.0004M 0.0005M 55.00 50.00 300 10.00 305 310 315 320 325 Temperature (K) 0.00 0 0.0001 0.0002 0.0003 0.0004 0.0005 0.0006 Concentration of A (mol/dm3) Fig. 6: Variation of inhibition efficiency of A with concentration of A 18 © 2007 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.