Novel Technique for the Application of Azole Corrosion Inhibitors on Copper Surface

Transcription

1 Materials Transactions, Vol. 51, No. 9 (2010) pp to 1676 #2010 The Japan Institute of Metals EXPRESS REGULAR ARTICLE Novel Technique for the Application of Azole Corrosion Inhibitors on Copper Surface Faiza M. Al Kharafi, Nouria A. Al-Awadi, Ibrahim M. Ghayad*, Ragab M. Abdullah and Maher R. Ibrahim Chemistry Department, Faculty of Science, Kuwait University, Kuwait A new method was proposed for the application of azole corrosion inhibitors on the surface of copper. This method depends on the vacuum pyrolysis of the inhibitor in the presence of copper specimens. Three azole inhibitors namely; benzotriazole (Azole (1)), N-[Benzotriazol-1-yl- (phenyl)-methylene]-n-phenyl-hydrazine (Azole (2)) and N-[Benzotriazol-1-yl-(4-methoxy-phenyl)-methylene]-N-phenyl-hydrazine (Azole (3)) were tested. After pyrolysis copper samples were electrochemically tested in sulfide polluted salt water and compared to the behavior of copper tested in the sulfide polluted salt water containing dissolved benzotriazole. Results showed that copper specimens treated in the presence of Azoles (2) and (3) exhibit excellent corrosion resistance. Those samples could resist the poisoning effect of sulfide ions. Azole (1) shows good resistance at low sulfide concentration and failed at the high concentration. Surface investigation support the results of electrochemical tests. [doi: /matertrans.m ] (Received April 21, 2010; Accepted June 11, 2010; Published August 25, 2010) Keywords: copper, corrosion inhibitors, pyrolysis, azoles 1. Introduction Azoles and in particular Benzotriazole (C 6 H 5 N 3, BTAH) have long been known as inhibitors for the corrosion of copper and many of its alloys. 1 16) The remarkable inhibiting efficiency of BTAH is attributed to the formation of a protective film of Cu(I)BTA on the copper surface. 1 16) However, benzotriazole loses its inhibition efficiency in environments polluted with sulfide ions. An example of these environments is the formation waters in sour oil and gas wells. 17) These waters are heavily contaminated with dissolved sulfides which are mostly in the form of HS ions in nearly neutral media. 18) In sulfide polluted environments, sulfide ions compete for Cu(I) ions under a much stronger driving force than BTAH, consequently, sulfide ions can extract the Cu(I) ions from the Cu(I)BTA complex. This leads to the break down of the protective Cu(I)BTA film and occurrence of corrosion on the bare areas. 18) To the date of this work, there are not known inhibitors which can resist the poisonous effect of sulfide ions. This dilemma forced the authors to think of a new method of application of the azole corrosion inhibitors on the copper surface in particular and metals in general. This method depends on the vacuum pyrolysis of the inhibitor in the presence of copper specimens. Such method would cover the copper surface with a compact protective layer of the inhibitor. 2. Experimental Electrodes were prepared from Cu (99.9 mass%) obtained from Goodfellow Corporation. Copper disc specimens of 1 cm diameter and 2 mm thickness were polished using SiC papers successively up to 2400 grits to acquire a mirror-like finish. A conventional three-electrode cell was used with a Ag/AgCl reference electrode, E ¼ 0:197 V SHE, and a Pt *Corresponding author, ighayad@yahoo.com. Present address: P.O. Box: 5969 Sfat 13060, State of Kuwait sheet counter electrode. Solutions were prepared using double distilled water, BTAH (Azole (1) was purchased from Sigma-Aldrich, Azoles (2) and (3) were prepared as described previously 19) while Na 2 S and NaCl were purchased from Fluka Chemicals. Potentiodynamic polarization curves were measured on the Cu electrode in 3.5 mass% NaCl containing sodium sulfide and BTAH at a voltage scan rate of 5 mv s 1. The potential was controlled using a Gamry Instruments potentiostat which was also used in measuring potentiostatic polarization curves. Measurements were performed at 25 1 C while the electrolyte was stirred using a magnetic stirrer. The surfaces of the electrodes were examined using JEOL Ltd., JSM-6300 scanning electron microscope (SEM). The structure of the inhibitor deposited layer was determined using 1 H-NMR technique performed by Bruker AVANCE II 600 MHz NMR for solutions and solids. In the vacuum pyrolysis experiments, 3 polished specimens of copper were placed in a pyrex glass tube (15 mm diameter) together with about 0.3 g of the azole inhibitor. Three azole inhibitors namely; bnezotriazole (Azole (1)), N-[Benzotriazol-1-yl-(phenyl)-methylene]-N 0 -phenyl-hydrazine (Azole (2)) and N-[Benzotriazol-1-yl-(4-methoxy-phenyl)-methylene]-N 0 -phenyl-hydrazine (Azole (3)) were tested. The chemical structures of the tested azoles are illustrated in Fig. 1. The open part of the tube was narrowed to 3 mm diameter. The assembly was placed in liquid nitrogen to freeze the azole inhibitor inside and then connected to a vacuum pump which allows the pressure inside the tube to reach about 1.33 Pa. The tube was then sealed by heating its neck till melt and close. The tube is finally placed in the pyrolyser which adjusted to the desired temperature (200 C). After vacuum pyrolysis for the desired time (30 min); the glass tube was broken and the copper specimens were taken out and corrosion tested. In most instances, both sides of copper specimens are covered with the inhibitor. Under such condition, one side is repolished to make electrical connection through this side while the other side, covered with inhibitor, is exposed to the testing solution.

2 1672 F. M. Al Kharafi, N. A. Al-Awadi, I. M. Ghayad, R. M. Abdullah and M. R. Ibrahim (A) (B) (C) Fig. 1 Chemical structure of the tested azoles: (A) Benzotriazole (Azole (1)). (B) N-[Benzotriazol-1-yl-(phenyl)-methylene]-N 0 -phenylhydrazine (Azole (2)). (C) N-[Benzotriazol-1-yl-(4-methoxy-phenyl)-methylene]-N 0 -phenyl-hydrazine (Azole (3)). Potential, E / V (Ag/AgCl) Eb (1) 3.5 mass% NaCl (2) mol L -1 BTAH (3) mol L -1 HS - (4) mol L -1 HS - (4) (1) (2) (3) Potential, E / V (Ag/AgCl) Azole (2) Azole (3) Azole (1) Fig. 2 Effect of sulfide ions on the polarization curves of copper in 3.5 mass% NaCl with and without pretreatment in 10 2 mol L 1 BTAH at 25 C, see text Fig. 3 Potentiodynamic polarization curves of copper in 3.5 mass% NaCl containing mol L 1 HS. Prior to testing, copper was pyrolyzed in Azole (1), Azole (2) or Azole (3) at 200 C for 30 min. 3. Results and Discussion 3.1 Electrochemical tests of copper before pyrolysis Figure 2 illustrates the effects of BTAH and of sulfide ions on the polarization curves of copper, measured at 5 mv s 1. Curve (1) refers to the blank solution (3.5% NaCl), curve (2) was measured after the electrode was pretreated in the presence of 0.01 mol L 1 BTAH for 1 h while curve (3) was measured after injection of 10 3 mol L 1 HS following the above pretreatment. Curve (4) was obtained in the presence of 10 3 mol L 1 HS in the blank electrolyte. It is added for the sake of comparison with curve (3) which was measured after pretreatment with BTAH. The presence of BTAH decreases the rate of anodic dissolution of copper by about four orders of magnitudes (compare curves 1 and 2). 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. It extends about 500 mv and ends at the break down potential, E, 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 3 and 1). They also shift the polarization curve much closer to that of the unprotected copper. Furthermore, they lower both the breakdown potential E, and the free corrosion potential by hundreds of mv. 3.2 Electrochemical tests of copper after pyrolysis Figure 3 represents the polarization curves of copper tested in mol L 1 sulfide polluted salt water. Prior to testing, copper was pyrolyzed in Azole (1) (Benzotriazole), Azole (2) and Azole (3) at 200 C for 30 min. The application of Azoles (2) and (3) result in the increase of their inhibiting efficiency to a very large extent. A wide range passive region of about 2 V is observed for these inhibitors. A very low passive currents (<10 9 A) are observed. These extremely low currents indicate a 100% protection of copper. The polarization curve of copper treated with Azole (1) (benzotriazole) differs clearly from those obtained in the presence of Azole (2) and Azole (3). Although the treated copper could, to some extent, resist the 10 3 mol L 1 sulfide solution, the passive current obtained under this condition is 10 5 A which is fairly high compared to the one obtained in the presence of the other two inhibitors (>10 9 A). Figure 4 represents the polarization curves of copper tested in 0.01 mol L 1 sulfide polluted salt water. Prior to testing, copper was also pyrolyzed in Azole (1) (Benzotriazole), Azole (2) and Azole (3) at 200 C for 30 min. Copper treated in Azoles (2) and (3) still show good passivation but

3 Novel Technique for the Application of Azole Corrosion Inhibitors on Copper Surface 1673 Potential, E / V (Ag/AgCl) Azole (2) Azole (3) Azole (1) Fig. 4 Potentiodynamic polarization curves of copper in 3.5 mass% NaCl containing 0.01 mol L 1 HS. Prior to testing, copper was pyrolyzed in Azole (1), Azole (2) or Azole (3) at 200 C for 30 min Azole (1) mol L -1 HS - Azole (I) mol L -1 HS - Azole (3) mol L -1 HS - Azole (2) mol L -1 HS Time, t / s Fig. 5 Potentiostatic polarization curves of copper in sulfide polluted salt water. Prior to testing copper was pyrolyzed in Azole (1), Azole (2) or Azole (3) at 200 C for 30 min. Table 1 Variation of corrosion parameters (corrosion current, I corr, corrosion potential, E corr, and percentage Inhibition Efficiency, E) of copper subjected to vacuum pyrolysis in the presence of different azoles. Treated copper specimens were tested in 3.5 mass% NaCl containing either or 0.01 mol L 1 sulfide ions. Blank (Cu-only) Azole (1) Azole (2) Azole (3) C HS /mol L I corr /A 1: : : : : : : E (%) E corr /V 0:927 0:349 0: : :205 to a lower extent than that obtained in the mol L 1 sulfide solution. The corrosion potentials are shifted towards more negative values of 0:4 and 0:2 for Azole (2) and Azole (3), respectively compared to 0:00 and 0.12 V obtained in the mol L 1 sulfide solution. Passive current are also increased by about three orders of magnitude (10 7 A) compared to those obtained in the mol L 1 sulfide solution (10 10 A). On the other hand, copper treated in Azole (1) could not resist the 10 2 mol L 1 sulfide solution. Polarization curves are quite similar to those obtained in the sulfide solution containing dissolved benzotriazole (see Fig. 2). Potentiodynamic polarization curves were also used to deduce the corrosion parameters of copper namely; Corrosion potential (E corr ) corrosion and current (I corr ) which in turn used to calculate the inhibitor (azole) percentage inhibition efficiency (E) according to the following equation: 20) E ¼ I corr (Blank) I corr (Azole) 100 ð1þ I corr (Blank) Table 1 summarizes the results. Extremely low corrosion currents and very high inhibition efficiencies reach as high as 100% were obtained for copper pyrolyzed in the presence of Azoles (2) and (3). On the other hand considerable low inhibition efficiency (79%) was obtained for copper pyrolyzed in the presence of Azole (1) and tested at 0.01 mol L 1 HS. The shift of E corr towards more anodic values compared to the untreated copper is another evidence of the enhancement of corrosion resistance of copper subjected to vacuum pyrolysis in the presence of azole inhibitors. Figure 5 represents potentioststatic polarization curves of copper tested at 0.5 V (Ag/AgCl) in 0.01 mol L 1 sulfide polluted salt water. Prior to testing, copper was pyrolyzed in Azole (1), Azole (2) and Azole (3) at 200 C for 30 min. Steady state currents of 10 2, and 10 8 A were obtained for copper pyrolyzed in Azole (1), Azole (2) and Azole (3), respectively. The extremely low current shown by copper pyrolyzed in Azoles (2) and (3) again show a 100% inhibiting efficiency which supports the results of potentiodynamic tests. On the other hand, the high steady current shown by Azole (1) indicates its failure to resist sulfide attack. Copper pyrolyzed in Azole (1) was also tested in mol L 1 sulfide solution. Under this condition, it shows a steady current of 10 5 A. This low steady current indicates that Azole (1) could resist acceptably the low concentrations of sulfide ions. 3.3 Surface characterization Figure 6 and represents the surface of copper subjected to vacuum pyrolysis at 200 C in the presence of Azoles (2) and (3). Images show that copper surface is covered with a black layer of the inhibitor. However, Azole (2) shows some degree of roughness while Azole (3) show a smooth surface. Figure 7 and illustrates cross sections of copper samples subjected to vacuum pyrolysis in the presence of Azole (2) and Azole (3). Images differentiate two distinct layers; one represents the copper metal while the other represents a compact layer of the inhibitor deposited on the copper surface. The thickness of this layer (in its maximum) was shown to be 128 and 59 mm for the Azole (2)

4 1674 F. M. Al Kharafi, N. A. Al-Awadi, I. M. Ghayad, R. M. Abdullah and M. R. Ibrahim Fig. 6 SEM micrographs of copper pyrolyzed at 200 C for 30 min in Azole (2) and Azole (3). Fig. 7 SEM micrograph of the cross sectional area of copper pyrolyzed in either Azole (2) or Azole (3) for 30 min at 200 C. and Azole (3) respectively. These results show that the layer formed in the presence of Azole (2) to be thicker than that formed in the presence of Azole (3) which may account for the slightly lower current obtained for copper treated in the presence of Azole (2) (10 10 A) compared to the one obtained in the presence of Azole (3) (10 8 A). Figure 8 shows the surface of copper potentiostated in 0.01 mol L 1 sulfide polluted salt water after removal of the deposited layer of Azole (2) and Azole (1). The surface of copper treated in Azole (2) shows very good appearance with no corrosion attack. On the other hand the surface of copper treated in Azole (1) suffers from sever corrosion attack. These images are in full agreement with the electrochemical tests which show excellent corrosion resistance for Azole (2) and poor corrosion resistance for Azole (1). It was interesting to determine the chemical structure of the deposited inhibitor layer. Azole (3) was taken as example. After pyrolysis and corrosion testing of Azole (3), copper samples were taken and immersed in chloroform to dissolve the coat and then analyzed using 1 H-NMR. Figure 9 represents the 1 H-NMR chart of Azole (3) before pyrolysis while Fig. 9 shows the 1 H-NMR chart of the dissolved coating. It is clear that the structure of the coating is nearly the same as that of Azole (3) before pyrolysis. Surface investigations revealed that the deposited inhibitor layer is distinct and differentiated from the metal surface (see Fig. 7). 1 H-NMR charts shows that the structure of the coating resembles that of the mother material before pyrolysis. These observations suggest that there is no chemical interaction between the metal and the inhibitor and consequently look to the vacuum pyrolyisis of azoles as a kind of coating rather than chemisorption. The process looks like hot-melt dip coating. When azole reaches a temperature higher than its melting point it transfers into liquid which spreads and adheres to the surface of copper. The adhered layer behaves like a barrier hydrophobic coating that effectively prevent electrolyte from contacting the metal surface and excellently resist corrosion attack. The difference in efficiency between different azoles can be related to the properties of the formed barrier coating. Azole (1) (benzotriazole) is weakly soluble in water while Azoles (2) and (3)

5 Novel Technique for the Application of Azole Corrosion Inhibitors on Copper Surface 1675 Fig. 8 SEM micrographs of copper surface potentiostatic testing in 3.5 mass% NaCl containing 0.01 mol L 1 sulfide ions after removal of the deposited layer of Azole (2) and Azole (1). OCH3 Aromatic Hs Solvent NH Aromatic Hs OCH3 Solvent NH Fig. 9 1 H-NMR-Charts of Azole (3): Adhered layer of Azole Before pyrolysis (3) formed on the surface of copper after pyrolysis. Prior to NMR analysis, this layer was dissolved in chloroform. are not soluble at all. Depending on the afore mentioned facts, it is expected that the formed barrier coating by Azole (1) allows some penetration of the electrolyte to the copper surface and hence enables corrosion to occur. On the other hand, barrier coatings formed by Azoles (1) and (3) acts as perfect insulators preventing the penetration of the electrolyte. 4. Conclusions and Future Outlook The present work explores the application of azoles, some of which are new corrosion inhibitors for copper, using new methodology depends on the vacuum pyrolysis of azole inhibitor in the presence of copper specimens. The promising results obtained in this work encourages further application

6 1676 F. M. Al Kharafi, N. A. Al-Awadi, I. M. Ghayad, R. M. Abdullah and M. R. Ibrahim of this new methodology to other azoles and also to other metals. This also encourages investigation of this method to large scale application. Vacuum pyrolysis of Azole (2) and Azole (3) on copper leads to the deposition of a compact layer of the inhibitor on the copper surface. The thickness of this layer (in its maximum) was shown to be 128 and 59 mm for the Azole (2) and Azole (3) respectively. Surface investigations revealed that the deposited layer is distinct and differentiated from the metal surface. This layer could resist the poisoning effect of sulfide ions. On the other hand, layer deposited by Azole (1) failed to resist the poisoning effect of sulfide ions. Acknowledgements The authors acknowledge the support of this work by the Research Administration of Kuwait University, Grant Numbers SC06/07 and GS01/03. They also acknowledge the use of the scanning electron microscope (SEM). REFERENCES 1) F. El Taib Heakal and S. Haruyama: Corros. Sci. 20 (1980) ) R. Youda, H. Nishihara and K. Aramaki: Corros. Sci. 28 (1988) ) A. D. Modestov, G.-D. Zhou, Y. P. Wu, T. Notoya and D. P. Schweinsberg: Corros. Sci. 36 (1994) ) D. Tromans and G. Li: Electrochem. Solid-State Lett. 5 (2002) B5 B8. 5) Z. D. Schultz, M. E. Biggin, J. O. White and A. A. Gewirth: Anal. Chem. 76 (2004) ) 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 (1998) ) H. Y. H. Chan and M. J. Weaver: Langmuir 15 (1999) ) R. Youda, H. Nishihara and K. Aramaki: Electrochim. Acta 35 (1990) ) T. Kosec, D. K. Merl and I. Milošev: Corros. Sci. 50 (2008) ) S. M. Milić and M. M. Antonijević: Corros. Sci. 51 (2009) ) K. F. Khaled: Electrochim. Acta 54 (2009) ) D. Gopi, K. M. Govindaraju, V. Collins Arun Prakash, D. M. Angeline Sakila and L. Kavitha: Corros. Sci. 51 (2009) ) M. Finšgar, A. Lesar, A. Kokalj and I. Milošev: Electrochim. Acta 53 (2008) ) H. O. Curkovic, E. Stupnisek-Lisac and H. Takenouti: Corros. Sci. 52 (2010) ) M. M. Antonijević, S. M. Milić and M. B. Petrović: Corros. Sci. 51 (2009) ) G. Quartarone, M. Battilana, L. Bonaldo and T. Tortato: Corros. Sci. 50 (2008) ) L. Garverick (Ed.): Corrosion in the Petrochemical Industry, (ASM International, Metals Park, OH, 1994) p ) F. M. Al Khrafai, A. M. Abdullah, I. M. Ghayad and B. G. Ateya: Appl. Surf. Sci. 253 (2007) ) H. Al-Awady, M. R. Ibrahim, N. A. Al-Awady and Y. I. Ibrahim: J. Heterocyclic Chem. 45 (2008) ) B. M. Praveen and T. V. Venkatesha: Int. J. Electrochem. Sci. 4 (2009)