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The formation of an effective anti-corrosion film on copper surfaces from 2-mercaptobenzimidazole solution
139
J. Electrounal. Chem., 310 (1991) 139-148 Elsevier Sequoia S.A., Lausanne
The formation of an effective anti-corrosion film on copper surfaces from 2-mercaptobenzimidazole solution Gi Xue *, Xue-Ying Department
of Chemistry,
Huang, Jian Dong and Junfeng Zhang Nanjing University, Nanjing .21&W8 (China)
(Received 19 July 1990; in revised form 9 January 1991)
Abstract
The formation of an effective anti-corrosion film on copper surfaces has been achieved by immersion of a chemically cleaned copper plate into a solution of 2-mercaptobenzimidazole in ethanol. This film is extremely stable as compared with the anti-corrosion layer formed on an oxidized surface.. The formation mechanism and the structure of the inert film have been investigated by the use of infrared and X-ray photoelectron spectroscopy. Its anti-corrosion characteristics in several media were investigated by the use of cyclic voltammetry.
INTRODUCTION
Imidazole and its derivatives are becoming very important both as corrosion inhibitors for metals and as ligands in many biological systems [l]. Benzotriazole (BTAH) and 2-mercaptobenzimidazole (MBI) have been generally recognized as effective organic reagents for controlling surface oxidation on copper and copper alloys since 1947 [2]. Subsequently, several researchers have examined the mechanism by which BTAH and MB1 inhibit surface reactions on copper [3-71, with the usual conclusion that BTAH or MB1 are chemisorbed onto copper oxide surfaces to form an inert co-ordination film. The presence of metal oxides was widely accepted as a key factor in the mechanism of corrosion protection [S-12]. In our previous study, however, we found that imidazole or benzimidazole can also react with copper metal directly to form a complex film [13-161. In this paper, we report the formation of an effective anti-corrosion film on copper by the reaction of MB1 on chemically cleaned surfaces.
* To whom correspondence should be addressed. 0022-0728/91/$03.50
Q 1991 - Elsevier Sequoia S.A.
140 EXPERIMENTAL
Copper plates were etched in 3% HNO, solution for one minute to remove the surface oxides, and then washed repeatedly with ethanol. The chemically cleaned copper plates were immersed in 2% MB1 + ethanol solution before direct exposure to air. A known thickness of the complex film was formed on the copper surface by agitating the mixture of MBI-ethanol solution with copper mercaptobenzimidazolate at 60” C for the required length of time. After being withdrawn from the MB1 + ethanol solution, the plates were rinsed with ethanol thoroughly to remove the physisorbed material, and were then heated under vacuum at 80 o C for an hour. The pre-treated MB1 plates were used as electrodes for the cyclic voltammetry experiments. For comparison studies, copper plates covered with oxide were treated with MBI. In addition, BTAH was used to treat chemically cleaned copper electrodes in a similar procedure. When copper powder etched with HNO, was mixed with MB1 + ethanol solution and stirred vigorously for two days, a yellow material formed. After separation, the composition of this reaction product was studied by infrared (IR) and X-ray induced Auger (X-AES) spectroscopy, and by elemental analysis. The spectrum of the reaction product of metallic copper was compared with those from cuprous and cupric oxides. The IR spectra were recorded with a Nicolet 170 SX spectrometer. The X-ray spectra were recorded with an ESCA LAB MK-II spectrometer, using Mg-K,,, as the exciting source. The cyclic voltammograms were recorded using a Model 79-l Voltammeter. A one compartment cell was used. A saturated calomel electrode (SCE) served as the reference electrode for all experiments and a platinum wire was used as the counter electrode. RESULTS
AND DISCUSSION
Figure 1 shows IR spectra of MB1 and its reaction products with copper powder, cuprous oxide, and cupric oxide. There are obvious differences between these spectra. MB1 shows strong N-H.. . S intermolecular hydrogen bonding in the solid state, which is indicated by a strong and broad absorption in the 3600-2300 cm-’ region of the IR spectrum. The spectrum of the reaction product of copper metal and MB1 shows a much weaker and narrower band in this region, indicating that partial deprotonation occurred during the reaction. Conversely, the spectra of the reaction products of copper oxides with MB1 show strong N-H absorption bands indicating that little deprotonation took place during the reaction. Another distinguishing feature is that the spectra of MB1 and its reaction products with copper oxides show strong absorptions near 1170 and 600 cm-’ which are due to vibrations of the C=S bond [17,18] whereas these bands are absent from the spectrum of the product of copper metal and MBI. The spectral differences thus indicate that MB1 reacts with the metallic copper, cleaving the C=S bond and losing most of the
141
(A) 1162
604 740
(B)
740 1162
740 I
4000
I
2400
1400
6008/~m-~
Fig. 1. IR spectra: (a) reaction product of MB1 with cupric oxide; (B) reaction product of MB1 with cuprous oxide; (C) reaction product of MB1 with metallic copper; (D) MB1 in solid state.
pyrrole hydrogen atoms, although benzene and heterocyclic rings still exist in the product as indicated by the strong bands near 1400 and 740 cm-‘. Figure 2 shows the X-AES spectra recorded for Ar+ etched, sputter-copper metal, cuprous oxide grown sufficiently thick by an electrochemical method so as to be much thicker than the expected electron escape depth, and MBI-treated copper metal. The spectra are in agreement with previously published results for metallic Cu and Cu,O [19]. Treatment of chemically cleaned copper with ethanol + MB1 solution for 2 min resulted in the development of a new feature at a kinetic energy of 915.8 eV, which is interpreted to indicate formation of a complex involving Cu+ and MB1 anions.
(A)
(B)
(Cl
910
930
Kinetic
Energy
/ eV
Fig. 2. X-AS spectra of copper: (A) copper metal treated with MBI; (B) Cu,O model compound; (C) Argon-etched copper metal.
MB1 contains two nitrogen atoms, the so-called pyrrole nitrogens. An XPS spectrum of neat MB1 is expected to show one binding energy value for the N,, level. Deprotonation at the imino group results in the formation of anionic MBIand MBI*-, which are also aromatic
MBI-
MB1
2-
Chgies in the N,, binding energy and peak shape take place for the complex of MB1 with copper. The binding energy of the N1, level for neat MB1 is 400.3 .eV, whereas for the complex the peak appeared to be significantly broader, from 399.6 to 394.2 eV, indicating that both MBI- and MBI*- exist. Although MB1 is a weak acid, copper has not been considered to be active enough to substitute for the pyrrole proton in MB1 ethanol solution. The formation
143
of the 2-mercaptobenzimidazolate complex seems to follow a new reaction scheme. In solution, at near neutrality, MB1 usually functions as a ligand through sulfur. Therefore it seems reasonable to propose the formation of a complex composed of MB1 and Cu(0) as the first step of the reaction. In this surface complex both MB1 and Cu are activated due to a coordination-induced activating effect. In air, MB1 is
20 ~.~A/crn~ (Cl 1, 2, 3, 4
-0.8
-0.4
0.0
Potential
+0.4 / V(vs.
+0.8 SCE)
Fig. 3. Cyclic voltammetry of copper electrodes: (A) chemically cleaned copper metal; (B) copper covered with oxides, and then treated with MBI; (C) copper metal treated with MBI.
144
deprotonated and copper is oxidized, to form CutMB12or Cu+MBII. Elemental analysis for the reaction product of copper powder and MB1 gives C, 35.5; N, 11.92; H, 2.02; Cu, 36.9%, indicating that the reaction yielded a mixture of the complexes Cu;MBI’and Cu+MBI-. Deprotonation at the imino groups resulted in the formation of the MB1 anion, which is also aromatic, with the negative charges distributed over several atoms. The sulfur and nitrogen atoms could bind to the cuprous cations. Each cuprous cation could co-ordinate with two ligands. These properties make it possible to form a polymeric structure on the copper surface. Since each Cu~MB12- linkage contains three ligation sites, the polymeric film is compact and bound strongly to the copper matrix. Voltammogram A in Fig. 3 was obtained from a pure copper electrode. It shows clearly two anodic oxidation and two cathodic reduction peaks. Voltammogram B was obtained from MBI-treated copper on which a layer of oxides, 5 nm thick, had been previously developed by heating [ll], while voltammogram C is from MB1 treated copper metal. Treatment with MB1 of oxidized surfaces shows some prevention of oxidation in the initial two cycles, as illustrated in voltammogram B.
2
L
20 pA/m2
50
I
’
-0.8
-0.4 Potential
0.0
+0.8
+0.4
/ V (vs.
SCE)
Fig.4.Fifty sweepsin the cyclic voltammetry of copper electrode treated with MBI.
145
However, as the scan number was increased, the oxidation and reduction current peaks increased rapidly. The electrode of metallic copper pretreated with MB1 shows a strong anti-corrosion effect, whose scan current is almost zero in the initial four scans. The voltammograms shown in Fig. 3 indicate that the modification of metallic surfaces with MB1 resulted in a much higher anti-corrosion property than the treatment for the oxidized surface. The difference in anti-corrosion effect could be deduced from their structures. The IR spectra depicted in Fig. 1 indicate that the reaction of metallic copper with MB1 opens the C=S bonds and deprotonates MB1 to form a compact polymeric structure; this reaction does not occur with the copper oxides. Figure 4 illustrates the voltammograms obtained from MBI-treated metallic copper at 50 o C for 30 min, which shows good anti-corrosion behavior. In the initial 10 scans, the current is almost zero. This indicates that the compact film on the
20 pA/cm2 (B)
1, 2, 3, 4, 5
-0.8
-0.4 Potential
+0.4
0.0
/V
+0.8
(vs. SCE)
Fig. 5. (A) Cyclic voltammetry of BTA-modified copper electrode after immersion in 10% HCl for 1 h; (B) Cyclic voltammetry of MBI-modified copper electrode after immersion in 10% HCl for 24 h.
z
20
pa/cm2
20 pU/cm2
5
(B)
-0.8
-0.4 Potential
O.fl
+0.8
+0.4
/ V (VS.
SCE)
Fig. 6. Cyclic voltammetry: (A) BTA-modified copper electrode after immersion in 15% NaOH for 1 h; (B) MBI-modified copper electrode after immersion in 15% NaOH for 24 h.
surface is very stable, and that a higher positive potential or a longer time is required to destroy the film. The anti-corrosion properties in strong acid or strong alkali solution were also studied. Figures 5 and 6 shows voltammograms for copper electrodes that were pre-treated with MB1 or BTAH, and then immersed in 10% HCl or 15% NaOH, respectively. After 1 h etching, the surface protection film of BTAH-copper complex disappeared completely. Conversely, the compact film from MB1 did still protect the metal effectively even after 24 h etching. Copper “etching agents”, which contain ammonia and alkali, are usually used in print circuit manufacture to etch the metal. A piece of copper foil 0.06 mm thick could be corroded and dissolved completely upon immersion in these “etching
147
-0.8
-0.4
+0.4
0.0
Potential
/V
+0.8
(vs.SCE)
Fig. 7. Multiple-sweep cyclic voltammetry of copper electrode pretreated “etching agents” (a mixture of ammonia and alkali) at 60 o C for 6 min.
with MBI, and immersed
in
agents” at 60°C for 5 min. However, we have found that the complexes formed from the copper metal and MB1 could protect the metal effectively under the severe conditions. Figure 7 illustrates voltammograms obtained using an electrode of copper treated with MB1 after it was immersed in the “etching agents” at 60 o C for 6 min. It is astonishing to find that the current for the initial three sweeps still remains zero, which indicates that the surface complex film shows strong anti-corrosion behavior even under severe conditions. CONCLUSION
Metallic copper reacts directly with 2-mercaptobenzimidazole under mild conditions to form Cu-MB1 complexes, which are different from the reaction product from MB1 and copper oxides. The complex forms a film that covers the surface and shows strong anti-corrosion behavior under acid, alkaline, and some severe conditions. ACKNOWLEDGEMENTS
We are grateful for the support from the National Science Foundation of China and from the Solid Structural Study Laboratory of Nanjing University, China.
148 REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
R.J. Sunderberg and R.B. Martin, Chem. Rev., 74 (1974) 471. G.W. Poling, Corros. Sci., 10 (1970) 359. N. Morito and W. Suetaka, Nippon Kinzoku Gakkaishi, 35 (1971) 1165. J.B. Cotton and I.R. Scholes, Brit. Corros. J., 2 (1967) 1. R.F. Roberts, J. Electron. Spectrosc. Relat. Phenom., 4 (1974) 273. I. DugdaIe and J.B. Cotton, Corros. Sci., 3 (1963) 69. N.D. Hobbins and R.F. Roberts, Surf. Technol., 9 (1979) 235. H.G. Tompkins and S.P. Sharma, Surf. Interface Anal., 4 (1982) 261. S. Yoshida and H. Ishida, J. Mat. Sci., 19 (1982) 2323. D. Chadwick and T. Hashemei, Surf. Sci., 89 (1979) 649. S. Yoshida and H. Ishida, Appl. Surf. Sci., 20 (1985) 497. C. McCrory-Joy and J.M. Rosamilia, J. EIectroanal. Chem., 136 (1982) 105. G. Xue, Q. Dai and S. Jiang, J. Am. Chem. Sot., 110 (1988) 2393. G. Xue, J. Zhang, G. Shi and Y. Wu, J. Chem. Sot., Perkin Trans. II, (1989) 33. G. Xue, J. Ding, P. Wu and G. Ji, Electroanal Chem., 270 (1989) 163. G. Xue, P. Wu and R. Chen, J. Chem. Sot., Chem. Commun. (1990) 495. C.N.R. Rao and R. Cenkatarakhavan, Spectrochim. Acta, 20 (1964) 541. M.L. Shankaranarayana and C.C. Patel, Spectrochim. Acta, 21 (1965) 95. T. Hashemi and C.A. Hogarth, Ehctrochim. Acta, 33(8) (1988) 1123.
J. Electrounal. Chem., 310 (1991) 139-148 Elsevier Sequoia S.A., Lausanne
The formation of an effective anti-corrosion film on copper surfaces from 2-mercaptobenzimidazole solution Gi Xue *, Xue-Ying Department
of Chemistry,
Huang, Jian Dong and Junfeng Zhang Nanjing University, Nanjing .21&W8 (China)
(Received 19 July 1990; in revised form 9 January 1991)
Abstract
The formation of an effective anti-corrosion film on copper surfaces has been achieved by immersion of a chemically cleaned copper plate into a solution of 2-mercaptobenzimidazole in ethanol. This film is extremely stable as compared with the anti-corrosion layer formed on an oxidized surface.. The formation mechanism and the structure of the inert film have been investigated by the use of infrared and X-ray photoelectron spectroscopy. Its anti-corrosion characteristics in several media were investigated by the use of cyclic voltammetry.
INTRODUCTION
Imidazole and its derivatives are becoming very important both as corrosion inhibitors for metals and as ligands in many biological systems [l]. Benzotriazole (BTAH) and 2-mercaptobenzimidazole (MBI) have been generally recognized as effective organic reagents for controlling surface oxidation on copper and copper alloys since 1947 [2]. Subsequently, several researchers have examined the mechanism by which BTAH and MB1 inhibit surface reactions on copper [3-71, with the usual conclusion that BTAH or MB1 are chemisorbed onto copper oxide surfaces to form an inert co-ordination film. The presence of metal oxides was widely accepted as a key factor in the mechanism of corrosion protection [S-12]. In our previous study, however, we found that imidazole or benzimidazole can also react with copper metal directly to form a complex film [13-161. In this paper, we report the formation of an effective anti-corrosion film on copper by the reaction of MB1 on chemically cleaned surfaces.
* To whom correspondence should be addressed. 0022-0728/91/$03.50
Q 1991 - Elsevier Sequoia S.A.
140 EXPERIMENTAL
Copper plates were etched in 3% HNO, solution for one minute to remove the surface oxides, and then washed repeatedly with ethanol. The chemically cleaned copper plates were immersed in 2% MB1 + ethanol solution before direct exposure to air. A known thickness of the complex film was formed on the copper surface by agitating the mixture of MBI-ethanol solution with copper mercaptobenzimidazolate at 60” C for the required length of time. After being withdrawn from the MB1 + ethanol solution, the plates were rinsed with ethanol thoroughly to remove the physisorbed material, and were then heated under vacuum at 80 o C for an hour. The pre-treated MB1 plates were used as electrodes for the cyclic voltammetry experiments. For comparison studies, copper plates covered with oxide were treated with MBI. In addition, BTAH was used to treat chemically cleaned copper electrodes in a similar procedure. When copper powder etched with HNO, was mixed with MB1 + ethanol solution and stirred vigorously for two days, a yellow material formed. After separation, the composition of this reaction product was studied by infrared (IR) and X-ray induced Auger (X-AES) spectroscopy, and by elemental analysis. The spectrum of the reaction product of metallic copper was compared with those from cuprous and cupric oxides. The IR spectra were recorded with a Nicolet 170 SX spectrometer. The X-ray spectra were recorded with an ESCA LAB MK-II spectrometer, using Mg-K,,, as the exciting source. The cyclic voltammograms were recorded using a Model 79-l Voltammeter. A one compartment cell was used. A saturated calomel electrode (SCE) served as the reference electrode for all experiments and a platinum wire was used as the counter electrode. RESULTS
AND DISCUSSION
Figure 1 shows IR spectra of MB1 and its reaction products with copper powder, cuprous oxide, and cupric oxide. There are obvious differences between these spectra. MB1 shows strong N-H.. . S intermolecular hydrogen bonding in the solid state, which is indicated by a strong and broad absorption in the 3600-2300 cm-’ region of the IR spectrum. The spectrum of the reaction product of copper metal and MB1 shows a much weaker and narrower band in this region, indicating that partial deprotonation occurred during the reaction. Conversely, the spectra of the reaction products of copper oxides with MB1 show strong N-H absorption bands indicating that little deprotonation took place during the reaction. Another distinguishing feature is that the spectra of MB1 and its reaction products with copper oxides show strong absorptions near 1170 and 600 cm-’ which are due to vibrations of the C=S bond [17,18] whereas these bands are absent from the spectrum of the product of copper metal and MBI. The spectral differences thus indicate that MB1 reacts with the metallic copper, cleaving the C=S bond and losing most of the
141
(A) 1162
604 740
(B)
740 1162
740 I
4000
I
2400
1400
6008/~m-~
Fig. 1. IR spectra: (a) reaction product of MB1 with cupric oxide; (B) reaction product of MB1 with cuprous oxide; (C) reaction product of MB1 with metallic copper; (D) MB1 in solid state.
pyrrole hydrogen atoms, although benzene and heterocyclic rings still exist in the product as indicated by the strong bands near 1400 and 740 cm-‘. Figure 2 shows the X-AES spectra recorded for Ar+ etched, sputter-copper metal, cuprous oxide grown sufficiently thick by an electrochemical method so as to be much thicker than the expected electron escape depth, and MBI-treated copper metal. The spectra are in agreement with previously published results for metallic Cu and Cu,O [19]. Treatment of chemically cleaned copper with ethanol + MB1 solution for 2 min resulted in the development of a new feature at a kinetic energy of 915.8 eV, which is interpreted to indicate formation of a complex involving Cu+ and MB1 anions.
(A)
(B)
(Cl
910
930
Kinetic
Energy
/ eV
Fig. 2. X-AS spectra of copper: (A) copper metal treated with MBI; (B) Cu,O model compound; (C) Argon-etched copper metal.
MB1 contains two nitrogen atoms, the so-called pyrrole nitrogens. An XPS spectrum of neat MB1 is expected to show one binding energy value for the N,, level. Deprotonation at the imino group results in the formation of anionic MBIand MBI*-, which are also aromatic
MBI-
MB1
2-
Chgies in the N,, binding energy and peak shape take place for the complex of MB1 with copper. The binding energy of the N1, level for neat MB1 is 400.3 .eV, whereas for the complex the peak appeared to be significantly broader, from 399.6 to 394.2 eV, indicating that both MBI- and MBI*- exist. Although MB1 is a weak acid, copper has not been considered to be active enough to substitute for the pyrrole proton in MB1 ethanol solution. The formation
143
of the 2-mercaptobenzimidazolate complex seems to follow a new reaction scheme. In solution, at near neutrality, MB1 usually functions as a ligand through sulfur. Therefore it seems reasonable to propose the formation of a complex composed of MB1 and Cu(0) as the first step of the reaction. In this surface complex both MB1 and Cu are activated due to a coordination-induced activating effect. In air, MB1 is
20 ~.~A/crn~ (Cl 1, 2, 3, 4
-0.8
-0.4
0.0
Potential
+0.4 / V(vs.
+0.8 SCE)
Fig. 3. Cyclic voltammetry of copper electrodes: (A) chemically cleaned copper metal; (B) copper covered with oxides, and then treated with MBI; (C) copper metal treated with MBI.
144
deprotonated and copper is oxidized, to form CutMB12or Cu+MBII. Elemental analysis for the reaction product of copper powder and MB1 gives C, 35.5; N, 11.92; H, 2.02; Cu, 36.9%, indicating that the reaction yielded a mixture of the complexes Cu;MBI’and Cu+MBI-. Deprotonation at the imino groups resulted in the formation of the MB1 anion, which is also aromatic, with the negative charges distributed over several atoms. The sulfur and nitrogen atoms could bind to the cuprous cations. Each cuprous cation could co-ordinate with two ligands. These properties make it possible to form a polymeric structure on the copper surface. Since each Cu~MB12- linkage contains three ligation sites, the polymeric film is compact and bound strongly to the copper matrix. Voltammogram A in Fig. 3 was obtained from a pure copper electrode. It shows clearly two anodic oxidation and two cathodic reduction peaks. Voltammogram B was obtained from MBI-treated copper on which a layer of oxides, 5 nm thick, had been previously developed by heating [ll], while voltammogram C is from MB1 treated copper metal. Treatment with MB1 of oxidized surfaces shows some prevention of oxidation in the initial two cycles, as illustrated in voltammogram B.
2
L
20 pA/m2
50
I
’
-0.8
-0.4 Potential
0.0
+0.8
+0.4
/ V (vs.
SCE)
Fig.4.Fifty sweepsin the cyclic voltammetry of copper electrode treated with MBI.
145
However, as the scan number was increased, the oxidation and reduction current peaks increased rapidly. The electrode of metallic copper pretreated with MB1 shows a strong anti-corrosion effect, whose scan current is almost zero in the initial four scans. The voltammograms shown in Fig. 3 indicate that the modification of metallic surfaces with MB1 resulted in a much higher anti-corrosion property than the treatment for the oxidized surface. The difference in anti-corrosion effect could be deduced from their structures. The IR spectra depicted in Fig. 1 indicate that the reaction of metallic copper with MB1 opens the C=S bonds and deprotonates MB1 to form a compact polymeric structure; this reaction does not occur with the copper oxides. Figure 4 illustrates the voltammograms obtained from MBI-treated metallic copper at 50 o C for 30 min, which shows good anti-corrosion behavior. In the initial 10 scans, the current is almost zero. This indicates that the compact film on the
20 pA/cm2 (B)
1, 2, 3, 4, 5
-0.8
-0.4 Potential
+0.4
0.0
/V
+0.8
(vs. SCE)
Fig. 5. (A) Cyclic voltammetry of BTA-modified copper electrode after immersion in 10% HCl for 1 h; (B) Cyclic voltammetry of MBI-modified copper electrode after immersion in 10% HCl for 24 h.
z
20
pa/cm2
20 pU/cm2
5
(B)
-0.8
-0.4 Potential
O.fl
+0.8
+0.4
/ V (VS.
SCE)
Fig. 6. Cyclic voltammetry: (A) BTA-modified copper electrode after immersion in 15% NaOH for 1 h; (B) MBI-modified copper electrode after immersion in 15% NaOH for 24 h.
surface is very stable, and that a higher positive potential or a longer time is required to destroy the film. The anti-corrosion properties in strong acid or strong alkali solution were also studied. Figures 5 and 6 shows voltammograms for copper electrodes that were pre-treated with MB1 or BTAH, and then immersed in 10% HCl or 15% NaOH, respectively. After 1 h etching, the surface protection film of BTAH-copper complex disappeared completely. Conversely, the compact film from MB1 did still protect the metal effectively even after 24 h etching. Copper “etching agents”, which contain ammonia and alkali, are usually used in print circuit manufacture to etch the metal. A piece of copper foil 0.06 mm thick could be corroded and dissolved completely upon immersion in these “etching
147
-0.8
-0.4
+0.4
0.0
Potential
/V
+0.8
(vs.SCE)
Fig. 7. Multiple-sweep cyclic voltammetry of copper electrode pretreated “etching agents” (a mixture of ammonia and alkali) at 60 o C for 6 min.
with MBI, and immersed
in
agents” at 60°C for 5 min. However, we have found that the complexes formed from the copper metal and MB1 could protect the metal effectively under the severe conditions. Figure 7 illustrates voltammograms obtained using an electrode of copper treated with MB1 after it was immersed in the “etching agents” at 60 o C for 6 min. It is astonishing to find that the current for the initial three sweeps still remains zero, which indicates that the surface complex film shows strong anti-corrosion behavior even under severe conditions. CONCLUSION
Metallic copper reacts directly with 2-mercaptobenzimidazole under mild conditions to form Cu-MB1 complexes, which are different from the reaction product from MB1 and copper oxides. The complex forms a film that covers the surface and shows strong anti-corrosion behavior under acid, alkaline, and some severe conditions. ACKNOWLEDGEMENTS
We are grateful for the support from the National Science Foundation of China and from the Solid Structural Study Laboratory of Nanjing University, China.
148 REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
R.J. Sunderberg and R.B. Martin, Chem. Rev., 74 (1974) 471. G.W. Poling, Corros. Sci., 10 (1970) 359. N. Morito and W. Suetaka, Nippon Kinzoku Gakkaishi, 35 (1971) 1165. J.B. Cotton and I.R. Scholes, Brit. Corros. J., 2 (1967) 1. R.F. Roberts, J. Electron. Spectrosc. Relat. Phenom., 4 (1974) 273. I. DugdaIe and J.B. Cotton, Corros. Sci., 3 (1963) 69. N.D. Hobbins and R.F. Roberts, Surf. Technol., 9 (1979) 235. H.G. Tompkins and S.P. Sharma, Surf. Interface Anal., 4 (1982) 261. S. Yoshida and H. Ishida, J. Mat. Sci., 19 (1982) 2323. D. Chadwick and T. Hashemei, Surf. Sci., 89 (1979) 649. S. Yoshida and H. Ishida, Appl. Surf. Sci., 20 (1985) 497. C. McCrory-Joy and J.M. Rosamilia, J. EIectroanal. Chem., 136 (1982) 105. G. Xue, Q. Dai and S. Jiang, J. Am. Chem. Sot., 110 (1988) 2393. G. Xue, J. Zhang, G. Shi and Y. Wu, J. Chem. Sot., Perkin Trans. II, (1989) 33. G. Xue, J. Ding, P. Wu and G. Ji, Electroanal Chem., 270 (1989) 163. G. Xue, P. Wu and R. Chen, J. Chem. Sot., Chem. Commun. (1990) 495. C.N.R. Rao and R. Cenkatarakhavan, Spectrochim. Acta, 20 (1964) 541. M.L. Shankaranarayana and C.C. Patel, Spectrochim. Acta, 21 (1965) 95. T. Hashemi and C.A. Hogarth, Ehctrochim. Acta, 33(8) (1988) 1123.