Kálmán, Erika

Shaban, Abdul

Szőcs, Edit

Vastag, Gy.

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Pure Appl. Chem., Vol. 73, No. 12, pp. 1861–1869, 2001.© 2001 IUPAC1861New inhibitors for copper corrosion*Gy. Vastag1, E. Szöcs2, A. Shaban2, and E. Kálmán2,‡1University of Novi Sad, Faculty of Natural Sciences and Mathematics, Yugoslavia;2Chemical Research Center, HAS, Bp., H-1525, P.O. Box 17, Hungary Abstract: The study of the effectiveness of several potential copper corrosion inhibitors inacidic media was studied. The investigated thiazole derivative functional groups containheterocyclic atoms such as nitrogen, sulfur, and oxygen. Thiazole derivatives, 5-benzyli-dene-2,4-dioxotetrahydro-1,3-thiazole (BDT) 5-(4′-isopropylbenzylidene)-2,4-dioxote-trahydro-1,3-thiazole (IPBDT), 5-(3′-thenylidene)-2,4-dioxotetrahydro-1,3-thiazole (TDT),and 5-(3′,4′-dimetoxybenzylidene)-2,4-dioxotetrahydro-1,3-thiazole (MBDT) were testedfor copper corrosion inhibition properties. The electrolyte solution was 0.1 M Na2SO4.In situ information on corrosion and inhibition processes can be obtained using differ-ent techniques. Electrochemical measurements (EIS), in situ scanning probe microscopy(SPM), in addition to quartz crystal microbalance (QCM) measurements were applied. Thosemethods are very useful owing to their high sensitivity and resolution. Dynamic STM andAFM measurements on Cu(111) single-crystal electrode with and without the addition ofsome inhibitors were performed.The presence of the isopropyl group in the case of IPBDT produced far better protec-tion against copper corrosion in acidic sulfate-containing media than the rest of the deriva-tives.INTRODUCTIONCopper is one of the most essential metals owing to its large industrial applications, such as electron-ics, etc. It is generally a relatively noble metal, however, it is susceptible to corrosion by acids andstrong alkaline solutions, especially in the presence of oxygen or oxidants. In the pH range between 2and 5, the dissolution of Cu is very rapid, and the formation of a stable surface oxide layer, which canpassivate metal surfaces, is hindered. An oxide surface layer can only be formed in weak acid or alka-line solutions. The behavior of Cu in acidic media is extensively investigated, and several schemes havebeen presented for the dissolution process [1–5].One of the most important methods in the corrosion protection of metals is the use of organicinhibitors to protect the metal surface from the corrosion environment. The role of adsorption-type inhibitors can be explained by the Lewis acid-base interaction onmetal surfaces. The molecular structure is one of the major factors that influence this interaction [2].The molecular structure of thiazoles, tetrazoles contain atoms like N and S, which are easily able tobridge with other molecules [1,2,6–15]. For a metal such as copper, which can form multi-bonds,inhibitor molecules containing those atoms are strongly recommended.Thiazole derivatives molecules adsorb probably through the sulfur atom or through coordinationwith the surface, forming a protective layer [16].*An issue of reviews and research papers based on presentations made at the IUPAC/ICSU Workshop on Electrochemistry andInterfacial Chemistry in Environmental Clean-up and Green Chemical Processes, Coimbra, Portugal, 6–7 April, 2001.‡Corresponding authorOwing to stricter environmental regulations, low inhibitor toxicity is an important requirement forthe applied inhibitors. The latest trend in industry is to replace toxic inhibitors, such as triazoles, withnontoxic organic chemicals that can cause no harm to the environment. In closed systems, thiazolederivatives can act as an excellent replacement for the toxic triazoles.Previous studies have produced some promising results, showing that some thiazoles derivativeshave excellent inhibition properties against copper corrosion [16]. The studied thiazole derivatives inthis study are: 5-benzylidene-2,4-dioxotetrahydro-1,3-thiazole (BDT), 5-(4′-isopropylbenzylidene)-2,4-dioxotetrahydro-1,3-thiazole (IPBDT), 5-(3′-thenylidene)-2,4-dioxotetrahydro-1,3-thiazole (TDT),and 5-(3′,4′-dimetoxybenzylidene)-2,4-dioxotetrahydro-1,3-thiazole (MBDT). These molecules havebeen studied on copper and cuprous oxide surfaces in an electrochemical environment.Several investigations utilized quartz crystal microbalance (QCM) to investigate copper electrodebehavior in acidic environment [11–17]. QCM is capable of detecting mass changes in the nanoscalerange. It consists of piezoelectric quartz, with electrodes on both faces, inserted into a properly designedoscillator circuit. When a voltage is applied between the two faces, the crystal oscillates. The oscilla-tion frequency of a quartz crystal is highly sensitive to the mass supported by the two faces of thedevice. When one face of the crystal is modified to function as the working electrode, changes of theelectrode mass can be continuously monitored [18–19]. In situ STM and AFM were used to study processes at the solid/liquid interface at nanoscale.Local investigations of copper single-crystal electrode surfaces and the adsorption of those thiazolederivatives molecules on copper and cuprous oxide surfaces have been studied in an electrochemicalenvironment.The aim of this work was to investigate the adsorption and inhibition effect of different thiazolederivatives, on copper surface in acidic solution, and to analyze the dependence of polarization resist-ance and mass change in function of the type of the inhibitor molecule. The electrochemical behaviorof copper and the inhibitor effectiveness were studied using electrochemical, electro-gravimetrical, andsurface analytical sensitive measurements.EXPERIMENTALElectrodesA polycrystalline Cu (99.99%) electrode was used for the electrochemical measurements.Electrochemically deposited copper layers were used for QCM studies. A single-crystal electrode,Cu(111), was used for EC-STM experiments.Reagent grade chemicals and double-distilled water were used to prepare the following elec-trolytes:0.1 M Na2SO4 at pH = 2.94, pH was adjusted using diluted sulfuric acid.Investigated inhibitorsThiazole derivatives:5-benzylidene-2,4-dioxotetrahydro-1,3-thiazole (BDT) 5-(4′-isopropylbenzylidene)-2,4-dioxotetrahydro-1,3-thiazole (IPBDT)5-(3′-thenylidene)-2,4-dioxotetrahydro-1,3-thiazole (TDT)5-(3′,4′-dimetoxybenzylidene)-2,4-dioxotetrahydro-1,3-thiazole (MBDT)All experiments were done at open atmosphere and room temperature. Due to the low solubilityof the tested thiazole derivatives, inhibitors were first dissolved into 20 ml of ethanol.Gy. VASTAG et al.© 2001 IUPAC, Pure and Applied Chemistry 73, 1861–18691862Electrochemical measurementsA three-electrode cell was used for the electrochemical impedance measurements (EIS), copper-work-ing electrode, SCE- reference electrode, and Pt- counter electrode. The working electrode was con-structed from high-purity copper rods (99.99% Cu). The electrode was wet-polished with SiC papers(grit sizes of 800 and 1200), rinsed with acetone and double distilled water, then immersed in the elec-trolyte solution. Measurements were performed at room temperature according to the proceduredescribed in ASTM G-5-93 standard. A computer-controlled potentiostat (Model Solartron ECI-1286)and a frequency response analyzer (Solartron FRA-1250) were applied for the electrochemical meas-urements.QCM measurementsThe quartz crystal applied for this investigation had gold layers deposited at both sides (thickness 150nm) over a thin layer of Cr (thickness 15 nm, for adhesion purpose). Copper layers were galvanostati-cally electrodeposited on one face of the crystal, facing the solution, at room temperature. The deposi-tion bath contained 0.5 M CuSO4, 0.5 M H2SO4, and 1 M C2H5OH in double-distilled water. The cellreference and counter electrodes were SCE and a Pt wire, respectively.The freshly deposited copper layer was investigated in three time intervals. In the first interval,the deposited Cu surface was exposed to the corrosive solution (0.1 M Na2SO4). Then, in the secondinterval, the solution was changed to an inhibitor-containing electrolyte for a longer exposure period.Finally, the solution was changed back to the corrosive electrolyte and the measurement was conducteduntil most of the deposited Cu was removed or there was no significant change of the electrode fre-quency. During all three intervals, frequency (mass) change was monitored. Data collected were ana-lyzed and stored using specially developed software.SPM measurementsIn situ EC-STM measurements were performed using molecular imaging picostat. The tunneling tipswere made of Pt and covered with an epoxy layer up to the operational tip, to decrease the Faradic cur-rent [20]. A three-electrode electrochemical cell was used, Cu(111)- working electrode and Pt wires-reference and counter electrodes. The electrochemical potentials of the electrode and tip were independently controlled by meansof a potentiostat. The working electrode was Cu(111) single-crystal. The sample was electrochemicallypolished in 66% ortho-phosphoric acid at an anodic potential 1.8 V vs. Cu counter electrode.Subsequently, it was rinsed with ultra-pure water and the clean sample was mounted in the STM cell,covered with the desired electrolyte. RESULTS AND DISCUSSIONElectrochemical measurementsThe electrochemical behavior of copper in acidic solution with the addition of thiazole derivatives waspublished in previous publication [16,17]. Figure 1 shows a typical electrochemical impedance spec-troscopy (Nyquist and Bode) plots of copper electrode in 0.1 M Na2SO4 electrolytes without and withthe addition of tested inhibitors. Polarization resistance values of the thiazole derivatives, in compari-son to the blank aggressive solution, are depicted in Fig. 1a. Rp values were obtained by calculatingthe semicircle intersection with the real part of the impedance amplitude. It is clear that IPBDT pro-© 2001 IUPAC, Pure and Applied Chemistry 73, 1861–1869New inhibitors for copper corrosion 1863duced the highest Rp value, which is an indication of the formation of an effective protective film thathindered corrosion. The inhibition efficiency (η%) was determined using the following formula:η (%) = (1 – Rpinh / Rpo) ⋅ 100 (1)where Rpo and Rpinh represent the electrode polarization resistance in the absence and presence of theinhibitor in the electrolyte, respectively. Polarization resistances and inhibition efficiency results are presented in Table 1. The inhibitor5-IPBDT produced the highest polarization resistance, thus the highest inhibition efficiency against Cucorrosion (η = 93%). The order of protection produced by the EIS method is as follows: IPBDT > BDT> TDT > MBDT. This can be explained by the presence of N and S in the molecule structure, and thelonger chain serves as a protecting shield on the copper electrode surface. Figure 1b shows the Bode plot for the tested thiazole derivatives. Phase shift vs. the log of the fre-quency gives an indication of the behavior of the protective film formed on the electrode surface due tothe inhibitor adsorption. It can be seen from this figure that the process taking place at the electrode sur-face has one relaxation time constant. The location of the relaxation time constant did not change muchfrom one inhibitor, but the phase shift value increased with IPBDT having the highest value at the peaklocation. This is an indication that the adsorption of all inhibitors on the electrode surface follows thesame pattern but with different intensities [16]. In a further study, a model will be used to simulate thephysical processes taking place at the electrode surface.Gy. VASTAG et al.© 2001 IUPAC, Pure and Applied Chemistry 73, 1861–18691864Table 1 EIS (Rp and η) results for the tested thiazole derivatives.Inhibitor IPBDT BDT TDT MBDTRp (k ohm) 115 15 9.3 7.3InhibitorEfficiency % 93 86 80 71Fig. 1a Nyquist plot of EIS for the tested thiazole derivatives.QCM resultsQCM measurements were carried out in 0.1 M Na2SO4 solution without and with the addition ofinhibitors. The adsorption properties of thiazole derivatives were studied, and the electrode mass changewas monitored.During the first interval, all experiments showed almost the same behavior. The electrode massdecreased, which means that the copper dissolution proceeds (Fig. 2). The similar behavior can beexplained by the fact that conditions for this interval are the same for all experiments performed.Negligible deviations can be related to difference in surface roughness during Cu deposition. The addi-tion of IPDBT and BDT show significant decreases in the electrode mass change during the secondinterval. These two thiazole derivatives slowed the Cu dissolution, and the electrode mass changealmost stabilized in the case of IPBDT. TDT and MBDT did not produce as much protection as in thecase of IPBDT and BDT. Absence of the inhibitor increased the corrosion rate, but not as high as in the© 2001 IUPAC, Pure and Applied Chemistry 73, 1861–1869New inhibitors for copper corrosion 1865Fig. 1b Bode plot of EIS for the tested thiazole derivatives.Fig. 2 Mass changes of Cu in acidic 0.1 M Na2SO4 solution without and with the addition of the tested thiazolederivatives in time.first interval. This is due to the remaining adsorbed inhibitor molecules or complexes on the electrodesurface. By using Faraday’s law, the Cu thickness reduction rate was calculated as:δ = (∆m ⋅ 3600 ⋅ 24 ⋅ 365 ⋅ 10 000) / A ⋅ D ⋅ t (2)where δ, thickness reduction rate [µm/yr]; ∆m, mass loss; A, electrode surface area (cm2); t, time (s);D, Cu density (g cm–3).The Cu electrode thickness reduction rate results, calculated using eq. 2, and the inhibition effi-ciencies of the tested thiazoles are tabulated in Table 2. The protection order result from QCM resultswas in good agreement with the electrochemical measurements.The QCM results showed that the adsorbed layers of the tested inhibitors are of a 2D type wherea mono or even a sub-monolayer is adsorbed on the Cu surface. This result was also confirmed by othermethods [16]. The EIS (Rp values) and the QCM analyses showed that the highest inhibitor efficiencyis provided by IPBDT (more than 90%). These results are expected by molecular structure analysis,which predicted the effectiveness of those molecules due to their favorable structure. SPM resultsThe surface morphology was followed in presence of different thiazole derivatives using AFM. ACu(111) single crystal was pretreated and electrochemically polished before each measurements. At aninhibitor concentration of 10–5 M, surface morphology without any structure changes could be observedat OCP, as seen in Fig. 3. Copper surface was covered with an inhibitor layer, which gets thicker in time,in the case of IPBDT. The surface roughness, which is represented by RMS values, varied with the addi-tion of the inhibitors comparing to the electropolished surface. IPBDT produced the smoothest surfaceand thus was the most effective among the tested thiazole derivatives. Figure 4 shows Cu(111) surface morphology developed shortly after changing the electrolyte toinhibitor-containing solution (10–5 M 5-IPBDT). The STM images give a clear indication of the refor-mation of the surface by the addition of the IPBDT. Presence of 5-IPBDT masked the atomic terracesand smoothed the surface, while the local imperfections are still visible. The atomic terraces (2.56 Å)were still visible on some sites, which shows that the surface was partially covered with 5-IPBDT. Thesurface morphology did not change significantly during the measurement; only the stepped structurebecame less visible (Fig. 4). This result can be explained by the 5-IPBDT molecule reordering on thecopper surface.Gy. VASTAG et al.© 2001 IUPAC, Pure and Applied Chemistry 73, 1861–18691866Table 2 Thickness reduction rate of copper in 0.1 M Na2SO4 with and with-out the addition of thiazole derivativesSolutions Thickness reduction rate (µm/yr) η (%)Blank 126 -IPBDT 15 89BDT 18 86TDT 44 65MBDT 47 73© 2001 IUPAC, Pure and Applied Chemistry 73, 1861–1869New inhibitors for copper corrosion 1867Fig. 3 AFM images of Cu electrode surface without and with the addition of the tested thiazole derivatives.CONCLUSIONSThe inhibition effectiveness of thiazole derivatives (IPBDT, BDT, TDT, and MBDT) against copper sur-faces was studied using EIS, QCM, and in situ SPM techniques. The results are summarized below:• The presence of thiazole derivatives (especially IPBDT and BDT) hindered copper corrosion. Theapplied techniques showed that IPBDT, among the tested thiazole derivatives, produced the bestprotection against copper corrosion in acidic 0.1 M Na2SO4 solution.• STM images in presence of IPBDT showed that the surface is partially covered with an inhibitorlayer.• The formed thiazole layers are very thin and might be in the monolayer order as shown by QCMand STM.• The application of QCM technique provided real-time corrosion rate measurements as well as themonitoring of the inhibitor effectiveness. This thin layer hinders copper corrosion even in theabsence of the inhibitor in the solution.• The excellent protection provided by IPBDT is credited to its molecular structure. The longerchain improved the effectiveness and played an umbrella-type role. • STM images in presence of IPBDT showed that the surface is covered with an inhibitor layerwhich thickness increased in time.• The investigated thiazole derivatives (especially IPBDT) showed a great potential to replace toxicinhibitors (such as triazoles) that are applied in closed systems. REFERENCES1. F. Mansfeld (Ed.). Corrosion Mechanisms, p. 119, Marcel Dekker, New York (1987).2. G. Trabanelli. Corrosion 47 (6), 410 (1991).3. L. Kiss. Kinetics of Electrochemical Metal Dissolution, Elsevir, Amsterdam (1988).4. A. Shaban, E. Kálmán, J. Telegdi. Electrochim. Acta 43, 159–163 (1998).5. A. Jardy, A. Legal Lasalle-Molin, M. Keddam, H. Takenouti. Electrochim. Acta 37, 2195 (1993).6. J. Uehara, H. Nishihara, K. Aramaki. J. Electrochem. Soc. 137, 2677 (1990).Gy. VASTAG et al.© 2001 IUPAC, Pure and Applied Chemistry 73, 1861–18691868Fig. 4 STM images of Cu(111) surface in solution without and with the addition of IPBDT.7. J. Uehara and K. Aramaki. J. Electrochem. Soc. 138, 3245 (1991).8. M. Itoh, H. Nishihara, K. Aramaki. J. Electrochem. Soc. 141, 2018 (1994).9. M. Itoh, H. Nishihara, K. Aramaki. J. Electrochem. Soc. 142, 1839 (1995).11. Y. Yamamoto, H. Nishihara, K. Aramaki. J. Electrochem. Soc. 140, 436 (1993).12. A. Shaban, E. Kálmán, J. Telegdi, Gy. Dóra. J. Appl. Phys. A66, 545–549 (1998).13. N. Ohno, J. Uehara, K. Aramaki. J. Electrochem. Soc. 140, 2512 (1993).14. E. Szöcs, Gy. Vastag, A. Shaban, G. Konczos, E. Kálmán. J. Appl. Electrochem. 29, 1339–1345(1999).15. A. Shaban, E. Kálmán, J. Bácskai. Proceedings of the 8th European Symposium on CorrosionInhibition, p. 951, Ferrara, Italy (1995). 16. D. Jope, J. Sell, H. W. Pickering, K. G. Weil. J. Electrochem. Soc. 142, 2170 (1995). 17. Gy. Vastag, E. Szöcs, A. Shaban, I. Bertóti, K. Popov-Pergal, E. Kálmán. Solid State Ionics141–142, 87–91 (2001).18. J. Telegdi, A. Shaban, E. Kálmán. Electrochim. Acta 45, (22–23) 3639 (2000).19. G. Sauerbrey. Z. Phys. 155 206 (1959).20. S. Bruckenstein and M. Shay. Electrochim. Acta 30, 1295 (1985).21. R. Kazinczi, E. Szöcs, E. Kálmán, P. Nagy. J. Appl. Phys. A66, 535–538 (1998). © 2001 IUPAC, Pure and Applied Chemistry 73, 1861–1869New inhibitors for copper corrosion 1869

New inhibitors for copper corrosion

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