F. M. Al Kharafi, I. M. Ghayad and B. G. Ateya
Keywords: Intergranular corrosion, copper, salt water, sulfide, SEM, XPS, benzotriazole
Abstract:
Copper undergoes extensive general and intergrannular corrosion (IGC) in sulfide polluted salt water. On the other hand, when copper was pretreated for one hour in the presence of 10 mM benzotriazole (BTAH) under a mild oxidizing potential, only localized corrosion occurred at the grain boundaries while the grain surfaces remained well protected. Under this condition, sulfur was detected using energy dispersive spectroscopy (EDS) at the grain boundaries, but not on the grain surfaces. X-ray photoelectron spectroscopy revealed the presence of sulfide ions and BTAH on the corroded surface. This pretreatment resulted in a protection efficiency of about 92%.
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ISSN 1466-8858 Volume 12, Preprint 12 submitted 29 March 2009 © 2009 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. Effect of Pretreatment with Benzotriazole on the Corrosion of Copper in Sulfide Polluted Salt Water F. M. Al Kharafi, I. M. Ghayad and B. G. Ateya* Chemistry Department, Faculty of Science, Kuwait University P.O.Box: 5969 Sfat 13060, State of Kuwait, e mail: bgateya@yahoo.com Abstract Copper undergoes extensive general and intergrannular corrosion (IGC) in sulfide polluted salt water. On the other hand, when copper was pretreated for one hour in the presence of 10 mM benzotriazole (BTAH) under a mild oxidizing potential, only localized corrosion occurred at the grain boundaries while the grain surfaces remained well protected. Under this condition, sulfur was detected using energy dispersive spectroscopy (EDS) at the grain boundaries, but not on the grain surfaces. X-ray photoelectron spectroscopy revealed the presence of sulfide ions and BTAH on the corroded surface. This pretreatment resulted in a protection efficiency of about 92%. Key words: Intergranular corrosion, copper, salt water, sulfide, SEM, XPS, benzotriazole 1 ISSN 1466-8858 Volume 12, Preprint 12 submitted 29 March 2009 © 2009 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. Introduction Copper and many of its alloys are manufactured in various forms and utilized in many industries, particularly in marine environments. The corrosion of copper and many of its alloys in such environments has been extensively studied. 1-4 Sulfide ions are known to promote the corrosion of copper. 5-10 This is believed to occur via an initial adsorption step, i.e. HS - + Cu = Cu : HS - (ads) [1] Cu : HS - (ads) = CuS (s) + H + + 2e - [2] where Cu : HS - (ads) refers to an adsorbed HS - ion on the copper surface. Sulfide attack on copper and its alloys is particularly relevant to the proposed use of copper canisters for the disposal of Swedish, Finnish and Canadian high level nuclear waste deep in granite environment, 8,9 the rapid failure of copper nickel condenser tubes in wet hydrogen sulfide atmosphere 11 and the extensive use of copper and its alloys in sulfide polluted environments. Benzotriazole (C 6 H 5 N 3 , BTAH) has long been known as an inhibitor for the corrosion of copper and many of its alloys. The remarkable inhibiting efficiency of BTAH is attributed 2 ISSN 1466-8858 Volume 12, Preprint 12 submitted 29 March 2009 © 2009 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. to the formation of a protective film of Cu(I)BTA on the surface, which inhibits the anodic corrosion reaction. 12-19 . The mechanism of inhibition involves adsorption of BTAH, which can be represented by: Cu (s) + BTAH (aq) = Cu:BTAH (ads) [3] where Cu:BTAH (ads) refers to BTAH adsorbed on the copper surface. Under anodic potentials, this adsorbed species can be oxidized to give the complex Cu(I) BTA, 19 i.e. Cu : BTAH = Cu (I) BTA + H + + e - [4] The above mechanisms of inhibition are well accepted in unpolluted media. It is now widely recognized that many natural water bodies and industrial waste water streams are polluted. For example, formation waters in sour oil and gas wells are heavily contaminated with hydrogen sulfide which promotes metallic corrosion. 20 In such environments, copper and its alloys serve in media that are inhibited by BTAH and polluted with sulfide ions. The objective of this work is to assess the efficiency of pretreatment of copper with BTAH on its resistance to sulfide attack. 3 ISSN 1466-8858 Volume 12, Preprint 12 submitted 29 March 2009 © 2009 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. 2. Experimental Electrodes were prepared from electrolytic copper (99.9 % ) in the form of rods having 0.96 cm diameter. The working electrode was the cross sectional area of the rod while the immersed length of the rod was coated with a protective adhesive so that only the cross sectional area is exposed to the solution. Electrical contact to the external circuit was made through the rod. The working electrodes were polished using SiC papers successively down to 2400 grits, followed by 0.3 micron alumina to acquire a mirror-like finish. Measurements were performed using a Gamary potentiostat and software. A conventional three-electrode cell was used with a Ag/AgCl reference electrode, E = 0.197 V SHE, and a Pt sheet counter electrode. Solutions were prepared using deionized water, AnalaR Na 2 S and NaCl from Fluka, BTAH from Aldrich. Measurements were performed at 25 ± 1 o C in 3.5 wt. % NaCl solution which was open to air and stirred using a magnetic stirrer. The surfaces of the electrodes were examined using JSM- 6300 JEOL scanning electron microscope (SEM) and XPS, VG SCIENTIFIC 200 Spectrometer (UK), using MgK radiation (1253.6 eV) operating at 300W, 13 kV and 23 mA. 4 ISSN 1466-8858 Volume 12, Preprint 12 submitted 29 March 2009 © 2009 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. Results and Discussion Polarization tests Fig.1 illustrates the effects of BTAH and of sulfide ions on the polarization curves of copper, measured at 5 mV s -1 . Curve (a) refers to the blank solution (3.5% NaCl), curve (b) was measured after the electrode was pretreated in the presence of 0.01 M BTAH for 1 h while curve (c) was measured after injection of 10 -3 M HS - following the above pretreatment. Curve (d) was obtained in the presence of 10 -3 M HS - in the blank electrolyte. It is added for the sake of comparison with curve c which was measured after pretreatment with BTAH. Current / A 10 -9 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 Potential / V (Ag/AgCl) -1.0-0.50.00.51.0 (a) 3.5% NaCl (b) ---+ 10 -2 M BTAH (1 h) (c) ---+ ---+ 10 -3 M HS - (d) ---+10 -3 M HS - ab c d Eb Fig. 1: Effect of sulfide ions on the polarization curves of copper in 3.5%NaCl with and without pretreatment in 10 -2 M BTAH at 25 o C, see text. 5 ISSN 1466-8858 Volume 12, Preprint 12 submitted 29 March 2009 © 2009 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. The presence of BTAH decreases the rate of anodic dissolution of copper by about four orders of magnitudes (compare curves a and b). A passive region appears in the anodic branch of the curve, which is attributed to the formation of a protective film of the Cu(I)BTA complex, Eq.4. It extends for about 500 mV and ends at the break down potential, E b , beyond which the current increases rapidly with potential. The sulfide ions diminish the passivity caused by BTAH by increasing the current in the passive region by about three orders of magnitude (compare c and b). They also shift the polarization curve much closer to that of the unprotected copper. Furthermore, they lower both the breakdown potential E b , and the free corrosion potential by hundreds of mV. Potentiostatic current transients were measured in the BTAH inhibited electrolyte at a potential of 0.0 V (Ag/AgCl), before and after injection of sulfide ions. This potential was chosen to be in the passive region. Fig.2 illustrates some of the results. The remarkable 6 ISSN 1466-8858 Volume 12, Preprint 12 submitted 29 March 2009 © 2009 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. Time / s 0 2000 4000 6000 8000 Current/ A 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 1) 3.5% NaCl + 10 -2 M BTAH 2) after injection of 10 -3 M HS - 3) 3.5% NaCl + 10 -3 M HS - Injection of 10 -3 M HS- 12 3 Fig. 2: Potentiostatic current transients of copper at 0.0 V under different conditions: 1) In the presence of 10 -2 M BTAH. 2) After injection of 10 -3 M HS - . 3) In the sulfide polluted salt solution. inhibiting efficiency of BTAH is reflected in a passive current of less than 0.1 µA cm -2 in the presence of 10 -2 M BTAH after one hour (curve 1). Upon injection of 10 -3 M HS - , a rapid increase in current to about 200 ˤA was obtained (curve 2). The magnitude of this sudden increase in current upon injection of sulfide ions is taken as a measure of the intensity of sulfide attack. Curve (3) was measured in the presence of 10 -3 M HS - , without pretreatment in BTAH, for the sake of comparison. The current obtained upon injection of the sulfide 7 ISSN 1466-8858 Volume 12, Preprint 12 submitted 29 March 2009 © 2009 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. ions (2) is much less than the current obtained under the same conditions without pretreatment without BTAH (3). This indicates clearly that the pretreatment of copper in the presence of BTAH improves its resistance to sulfide attack. The efficiency of an inhibitor (%P) can be calculated from the following equation: %P = 1- i 2 / i 1 [5] where i 2 and i 1 are the currents with and without inhibitor treatment, respectively. These results indicate that the above pretreatment with BTAH achieves a protection efficiency of about 92% against sulfide attack. It is shown below that the high currents obtained without pretreatment in BTAH (curve 3 in Fig. 2) result from general corrosion of the metal at the grain surfaces and from localized intergranular attack. On the other hand, the exceedingly low currents (~ 0.1 ˤA) before injection of sulfide ions (curve 1) point to a well protected surface, while the current jump seen after injection of sulfide (2) is due to localized intergranular corrosion only at the grain boundaries. 8 ISSN 1466-8858 Volume 12, Preprint 12 submitted 29 March 2009 © 2009 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. Scanning electron microscopy (SEM) Figs. 3a-c show the morphology of copper surfaces that were potentiostated for 1 h in the salt solution at 0.0 V (Ag/AgCl). While the surface treated with BTAH is well protected (3a), extensive corrosion appears with more visible grain boundary attack on the surfaces that were not pretreated in 10 -2 M BTAH (3b). On the other hand, only localized intergranular corrosion occurred at the grain boundaries of the surfaces that were pretreated with BTAH (3c). A closer look at the topography of the corroded surfaces is given in Figs.4a and b at a greater magnification. Fig.4a was obtained on samples corroded in the sulfide polluted medium without pretreatment in the presence of BTAH. It reveals extensive corrosion on the grain surfaces in addition to the grain boundary attack. This explains the higher currents seen in Fig.2 for the electrodes that were not pretreated in 10 -2 M BTAH (curve 3). On the other hand, the topography of the surface that was pretreated in the presence of 10 - 2 M BTAH shows much less general corrosion at the grain surfaces. However, there is still a moderate degree of intergranular attack due to the sulfide ions, which explains the increase in current upon injection of HS - ions (curve 2). 9 ISSN 1466-8858 Volume 12, Preprint 12 submitted 29 March 2009 © 2009 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. 10 a b c Figs. 3 SEM micrographs of copper potentiostated for 1 h at 0.0 V (Ag/AgCl) in 3.5% NaCl under the following conditions: a) In the presence of 10 -2 M BTAH. b) In the presence of 10 -3 M HS - . c) In the presence of 10 -2 M BTAH followed by injection of 10 -3 M HS - and further potentiostating for another hour. ISSN 1466-8858 Volume 12, Preprint 12 submitted 29 March 2009 © 2009 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. 11 ba Fig. 4: SEM micrographs of copper potentiost ated for 1 h at 0.0 V (Ag/AgCl) under the following conditions: Fig. 4: SEM micrographs of copper potentiostated for 1 h at 0.0 V (Ag/AgCl) under the following conditions: a) In the presence of 3.5% NaCl+10 -3 M HS - . a) In the presence of 3.5% NaCl+10 -3 M HS - . b) In the presence of 3.5% NaCl+10 -2 M BTAH followed by injection of 10 -3 M HS - and further potentiostating for another hour. b) In the presence of 3.5% NaCl+10 -2 M BTAH followed by injection of 10 -3 M HS - and further potentiostating for another hour. Characterization of the corrosion products Characterization of the corrosion products The corrosion products were characterized using energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). While EDS can analyze selected regions, it requires a fairly thick layer and provides no indication of oxidation states. On the other hand, XPS can analyze several atom layers and reveal oxidation states. However, the XPS technique samples the entire surface. Both techniques complemented each other towards the objectives of this work. The corrosion products were characterized using energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). While EDS can analyze selected regions, it requires a fairly thick layer and provides no indication of oxidation states. On the other hand, XPS can analyze several atom layers and reveal oxidation states. However, the XPS technique samples the entire surface. Both techniques complemented each other towards the objectives of this work. ISSN 1466-8858 Volume 12, Preprint 12 submitted 29 March 2009 © 2009 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. EDS results were obtained from regions inside and outside the grain boundaries in Fig.4b. Fig.5 shows EDS spectra of spots shown in Fig.4b on the grain surface (a) and inside the grain boundary (b). A weak sulfur signal appears in the EDS spectrum record ed off the grain boundary while no sulfur signals were detected on the gra in surface. Fig. 5: EDS spectra of regions in Fig.4b. (a) on the grain surface and (b) at the grain boundary. 12 ISSN 1466-8858 Volume 12, Preprint 12 submitted 29 March 2009 © 2009 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. Fig.6 illustrates parts of the XPS spectra obtained from the copper surface that was imaged in Fig.4b. The spectra show a strong S 2p peak at a binding energy of 162.8 eV (referred to C1s at 284.6 eV). This is characteristic for copper sulfide. 4,21 . Fig. 6 shows also an XPS signal of nitrogen at a binding energy of 400.5 eV. It reveals the presence of BTAH on the corroded surface, even after injection of sulfide ions. Binding energy / eV 160162164166168170 Counts / s 050100150200250 S2p a Binding energy / eV 396398400402 Counts / s 0200400600800100012001400 b N1s Fig. 6: XPS spectra of copper potentiostated for 2 h at 0.0 V (Ag/AgCl) in 3.5% NaCl+10 -2 BTAH before the injection of 10 -3 M HS - and further potentiostating for an hour. 13 ISSN 1466-8858 Volume 12, Preprint 12 submitted 29 March 2009 © 2009 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. Conclusions The present work provides three well documented conclusions: 1- The intensity of sulfide attack on copper is considerably diminished upon pretreatment of copper in the presence of 10 -2 M BTAH. 2- Pretreatment of copper in the presence of BTAH provided a much higher protection efficiency on the grain surface and relatively lower efficiency at the g rain boundary. 3- After sulfide attack on the pretreated copper; copper sulfide was detected only at the corroded grain boundaries while some BTAH remain on the surface. Pretreatment in the presence of BTAH leads to the development of a Cu(I)BTA film on the copper surface, according to Eq.4. The grain boundary region is often less homogeneous and more rich in impurities than the grain surfaces. This is often attributed to segregation of impurities to the grain boundaries. 22-24 The results indicate that the Cu(I)BTA film on the grain surface is much stronger than that which forms at the grain boundaries. The breakdown of the protective film at the grain boundary is attributed to the strong tendency of copper to form copper sulfide, i.e. Cu(I)BTA + HS - = CuS + BTAH + e [6] 14 ISSN 1466-8858 Volume 12, Preprint 12 submitted 29 March 2009 © 2009 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. Acknowledgements The authors acknowledge the support of this work by the Research Administration of Kuwait University, Grant Numbers SC06/07 and GS01/01. They also acknowledge the use of the scanning electron microscope (SEM). References 1. G. Kear, B.D. Barker, and F.C. Walsh, Corr. Sci., 46, 1, pp109-135, 2004 . 2. Chmielova M., Siedlerova J., and Weiss Z., Corros. Sci., 45, 5, pp883-88 9, 2003. 3. X. Zhu and T. Lei, Corros. Sci., 44, 1, pp 67-79, 2002. 4. S. J. Yuan, and S. O. Phenkonen, Corros. Sci., 49, 3, pp1276-1304, 2007. 5. M. Vazquez and S. R. De Sanchez, J. Appl. Electrochem., 28, 11, pp1383- 1388, 1998. 6. J. N. Alhajji and M. R. Reda, J. Electrochem. Soc., 141, pp1432-1439, 19 94. 7. K. Rahmouni, M. Keddam, A. Srhiri, H. Takenouti, Corros. Sci., 47, 8, pp3249-3266, 2005. 8. I. Escobar, C. Silva, E. Silva and L Werme1, Nuclear Waste Containment Materials, Technical Report TR-01-25, p. 25, Swedish Nuclear Fuel and Waste Management Co, Sweden, August 2001. 15 ISSN 1466-8858 Volume 12, Preprint 12 submitted 29 March 2009 © 2009 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. 9. J. Smith, Z. Qin, F. King, L. Werme, and D. W. Shoesmith, Corrosion (Houston), 63, 2, pp135-144, 2007. 10. F. M. Al Kharafi, I. M. Ghayad, and B. G. Ateya, Electrochemical and Solid-State Letters, 11, 4, ppG15-G18, 2008 . 11. A. Veld, Materials Performance, 45, 4, pp52-54, 2006. 12. F. El Taib Heakal and S. Haruyama, Corros. Sci., 20, 7, pp887-898, 1980 . 13. R. Youda, H. Nishihara, and K. Aramaki, Corros. Sci., 28, 1, pp87-96, 19 88. 14. A. D. Modestov, G.-D. Zhou, Y.P. Wu, T. Notoya, and D. P. Schweinsberg, Corros. Sci., 36, 11, pp1931-1946, 1994. 15. D. Tromans and G. Li, Electrochem. Solid-State Lett., 5, ppB5-B8, 2002. 16. Z. D. Schultz, M. E. Biggin, J. 0 . White, and A. A. Gewirth, Anal. Chem ., 76, 3, pp604-609, 2004. 17. J. E Walsh, H. S. Dhariwal, A. Gutierrez-Sosa, P. Finetti, C. A. Muryn. N. B. Brookes, R. J, Oldman, and G. Thornton, Surf. Sci., 415, 3, pp423-432, 1998. 18. H. Y. H. Chan and M. J. Weaver, Langmuir, 15, pp3348-3355, 1999. 19. R. Youda, H. Nishihara, and K. Aramaki, Electrochim. Acta, 35 (6), pp1011-1017, 1990. 16 ISSN 1466-8858 Volume 12, Preprint 12 submitted 29 March 2009 © 2009 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. 17 20. L. Garverick, Editor, Corrosion in the Petrochemical Industry, p. 259, ASM International, Metals Park, OH (1994), p. 259. 21. C. D. Wagner, in Practical Surface Analysis, Vol. 1, Auger and X-Ray Photoelectron Spectroscopy, 2nd ed., D. Briggs and M. P. Seath, Editors, p. 595, John Wiley & Sons, New York (1990). 22. S. Divinski, J. Ribbe, G. Schmitz, and C. Herzig, Acta Materialia, 55, pp3337-3346, 2007. 23. G. Erdelyi, G. Langer , J. Nyeki , L . Kover , C. Tomastik , W.S.M Werner, A. Csik, H. Stoeri, and D. L. Beke, Thin Solid Films, 459, 1-2, pp303-307, 2004. 24. Y. Zhu, K. Mimura, and M. Isshiki, Oxid. Met., 59, 5-6, pp575-590, 2003.