Studies of the conversion coatings formed by combined use of lanthanum salt and benzotriazole on commercial brass Hongqiang Fan, Shuying Li and Zhicong Shi School of Chemical Engineering, Dalian University of Technology, Dalian, China
Xuefei LV Electromechanics Engineering College, Jilin Institute of Chemical Technology, Jilin, People’s Republic of China, and
Zongchang Zhao School of Chemical Engineering, Dalian University of Technology, Dalian, China Abstract Purpose – The aim of this paper is to investigate the synergism effect between lanthanum salt (La(NO3)3) and benzotriazole (BTAH) on the corrosion inhibition of commercial brass and to further study the inhibition mechanism. Design/methodology/approach – Potentiodynamic polarization curves were carried out on bare brass and brass treated with additions of optimum concentration of BTAH, La salt and La salt þ BTAH to the basal deposition solutions in 3.5 wt. percent sodium chloride solution. The inhibition mechanism of the composite conversion coatings on brass obtained in optimal deposition techniques were investigated by electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), X-ray diffraction (XRD), and FT-IR reflection spectra. Findings – A “Critical La(NO3)3 content” and “Critical BTAH content” were both observed, at which the coatings prepared performs the highest protectiveness, and La(NO3)3 and BTAH had an excellent synergism effect on the corrosion inhibition of brass. The corrosion mechanisms for uncoated and coated brass are different. A remarkable enhancement of the brass’s corrosion protection was obtained by the formation of composite conversion coatings consisted of Cu(I)BTA and La coordinate thing except for Cu2O and La2O3, which acted as a barrier avoiding the release of metal ions and inhibited the diffusion of the oxygen. Originality/value – The results from this paper showed that La(NO3)3 and BTAH could be used together to prepare the novel composited conversion coatings on commercial brass for the good corrosion inhibition. Keywords Corrosion inhibitors, Coatings technology, Brass, Lanthanum salt, Benzotriazole, Conversion coatings Paper type Research paper
As non-toxic corrosion inhibitors, the rare earth compounds have been successfully introduced to provide corrosion protection of different metallic materials such as magnesium alloys (Ardelean et al., 2008; Rudd et al., 2000), aluminium alloys (Yasakau et al., 2008; Conde et al., 2008), and stainless steels (Arenas and de Damborenea, 2003). In these applications, rare earth compounds are used as environmental-friendly alternatives to classical procedures, e.g. chromate-based corrosion inhibitors, showing promising results via direct immersion in rare earth salt solutions and rare earth conversion coatings. In general, rare earth cations, especially lanthanum (La), are classified as cathodic inhibitors on an copper alloys surface, although, it is not clarified the species which contribute to the formation, in the cathodic areas, of the oxide/hydroxide of the lanthanide ion (Shim et al., 2002). Moreover, benzotriazole (C 6H 5N3 , BTAH) and its derivatives as the excellent corrosion inhibitors for copper and its alloys have been researched by many researchers. Shih and Tzou (1993) have investigated the brass resistance to corrosion in fluoride solutions, in the presence of BTAH. Otieno-Alego et al. (1996) and Jinturkar et al. (1998) have described the BTAH influence on the corrosion and dezincification of brass in H2SO4 solutions and suggested that the protective film containing multilayers of (Cu(I)BTA)n complex. Wu et al. (1993) first noticed the existence of a synergistic inhibiting effect between BTAH and iodide ions
1. Introduction Owing to the attractive combination of properties, e.g. good machinability, high thermal and electrical conductivity, the brass has been widely used in almost all industries for functional or aesthetic purposes (Brandl et al., 2009). In spite of the relatively high-standard electrode potential, brass susceptibly undergoes dealloying in some media, a phenomenon named dezincification (Maciel et al., 2008). Chromate conversion coatings, which involves altering only the surface layers of a material, has been proved to be an effective method to improve the corrosion resistance of brass in some erosive media (Liu et al., 2005). However, chromate conversion involves the use of hexavalent chromium, a substance which is now recognized as both highly toxic and carcinogenic (Osborne, 2001). As a result, a significant research effort has been directed towards the development of alternative corrosion inhibitors for brass. The current issue and full text archive of this journal is available at www.emeraldinsight.com/0003-5599.htm
Anti-Corrosion Methods and Materials 59/1 (2012) 32– 38 q Emerald Group Publishing Limited [ISSN 0003-5599] [DOI 10.1108/00035591211190526]
32
Conversion coatings formed by use of La(NO3)3 and BTAH on brass
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Volume 59 · Number 1 · 2012 · 32 –38
on the corrosion of brass in sulfuric acid electrolyte. This effect is attributed to formation of cuprous iodide (CuI2) complex that is relatively stable and cuprous ions can react with protonated 2-mercaptobenzoimidazole (MBI) and form (Cu þ MBI) film that is the best protection against corrosion (Antonijevic and Petrovic, 2008). Villamil et al. (2003) also have showed that the synergistic effect exists between BTAH and sodium dodecylsulfate on the inhibition of copper corrosion in sulfuric acid solution. Synergism has become one of the most important effects in the inhibition processes and it serves as the basis for all modern corrosion inhibitor formulations (Allam et al., 2009). However, the effect of BTAH associated with rare earth compounds on the corrosion inhibition of brass has not been extensively studied yet. The purpose of this work was to investigate the synergism effect between La salt and BTAH on the corrosion inhibition of commercial brass, and to further study the inhibition mechanism of the conversion coatings by electrochemical measurements, scanning electron microscopy (SEM), X-ray diffraction (XRD), and FT-IR reflection spectra.
of the specimens in the frequency range of 100 kHz to 0.02 Hz with perturbation amplitude of 10 mV at OCP. Each experiment was repeated at least three times to check the reproducibility and the impedance data were analyzed using the ZSimpWin 3.00 software (EG&G, USA). 2.4 Coatings characterization The morphology and compositions of as-deposited product were characterized by SEM with a field emission gun (JSM5600LV model) and XRD (Philips, PW-1830 X-ray diffractometer) operated at V ¼ 30 kV, I ¼ 30 mA. The interaction between the molecules and the metal substrate was studied by means of FT-IR reflection spectra using a Perkin-Elmer FT-IR spectrophotometer and Nexus-670.
3. Results 3.1 Potentiodynamic polarization measurement Figures 1 and 2 show polarization curves for bare brass and brass treated by the basal deposition solutions containing various concentrations of La salt and BTAH, respectively, in the 3.5 wt% sodium chloride solution. From Figure 1 and Table I, all the samples treated with La salt, the corrosion rate was lower compared to the one for the bare alloy. The most protective effect was observed for the conversion coatings when the La salt added was about 4.5 g l2 1: a significant decrease of the corrosion current density from 20.26 to 2.4 mA cm2 2 and of the anodic dissolution current density (more than one order of magnitude) in comparison with the bare alloy. As can be seen from Figure 2, the addition of BTAH significantly decreased the anodic current density overall and the corrosion potential shifted noble. The results revealed that BTAH was anodic brass corrosion inhibitor. It was shown from Figure 3 that as the BTAH content increases, h values for conversion coating first increase and then reach a quasisteady value. A critical BTAH content, namely 8 g l2 1, was observed, under which the composite conversion coating performed the highest protectiveness. Figure 4 shows polarization curves corresponding to brass treated with the presence of optimum concentration of BTAH,
2. Experimental 2.1 Brass substrates The experiments were performed by using 40 £ 20 £ 1.5 mm sheets of commercial brass with the following chemical composition (wt%): Cu 63.5-68.0; Fe 0.10; Pb 0.03; Sb 0.005; Bi 0.002; P 0.01; Zn balance. Prior to coating, the specimens were polished with 800 and 1,200-grit emery papers, degreased by ethyl alcohol in an ultrasonic cleaner, rinsed with distilled water and finally dried in air. 2.2 Coating deposition Coating deposition experiments were conducted using a basal deposition solutions containing sulfosalicylic acid (10 g l2 1), citric acid (15 g l2 1), and sodium dodecyl sulfonate (0.5 g l2 1) by dip-coated technique. To study the effects of lanthanum salt (La salt) and BTAH, appropriate amount of La(NO3)3 and BTAH were added to the basal deposition solutions, respectively, and the mixed solutions were further stirred for about 0.5 h to disperse the additions. The dip-coated experiments were conducted at 608C for 3 min, after which samples were taken out and blow-dried with nitrogen to remove any excess liquid.
Figure 1 Polarization curves of bare brass (1) and brass treated with different additions of La(NO3)3: 3.5 g l2 1 (2), 4.0 g l2 1 (3), 4.5 g l2 1 (4), 5.0 g l2 1 (5) and 5.5 g l2 1 (6) to the basal deposition solutions
2.3 Electrochemical tests Potentiodynamic (Tafel) polarization curves were carried out using a computer-controlled CHI 660B electrochemical workstation using a sweep rate of 0.16 mV s2 1. Before the tests, individual specimens were immersed in 3.5 wt% sodium chloride solution for 30 min to achieve a relatively steady open-circuit potential (OCP). For quantitative analysis, the corrosion current densities (Icorr) were determined from the Tafel polarization curves by the Tafel extrapolation method, and the inhibiting efficiency (h) was then calculated by equation (1): I corr £ 100 ð1Þ h¼ 12 I8corr
0.10
Potential/V (vs SCE)
0.05 0.00 –0.05 –0.10 –0.15
4 –0.20 3 –0.25
1 2
–0.30
where Icorr and I8corr refer to the current densities for the coated and uncoated electrodes, respectively. Electrochemical impedance spectroscopy (EIS) was employed to evaluate the corrosion performance
5
–0.35 10–7
10–6
10–5
6 10–4
j/A.cm–2
33
10–3
10–2
Conversion coatings formed by use of La(NO3)3 and BTAH on brass
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Volume 59 · Number 1 · 2012 · 32 –38
Figure 2 Polarization curves of bare brass (1) and brass treated with different addition of BTAH: 0.0 g l2 1 (2), 4.0 g l2 1 (3), 8.0 g l2 1 (4), 12.0 g l2 1 (5), and 16.0 g l2 1 (6) to the basal deposition solutions
Figure 4 Polarization curves for bare brass (1) and brass treated with additions of optimum concentration of BTAH (2), La salt (3) and La salt þ BTAH (4) to the basal deposition solutions 0.5
6
0.05
0.4
0.00
0.3
–0.05
Potential/V (vs SCE)
Potential/V (vs SCE)
0.10
3
–0.10 –0.15
5
4 –0.20 –0.25
1
2
14 2
3
65
0.2 0.1 0.0 –0.1 –0.2
–0.4
–0.35 10–7
10–6
10–5
10–4 j/A.cm–2
10–3
10–2
10–8
20.26 12.22 10.74 2.4 8.43 11.05
0.239 0.144 0.111 0.028 0.099 0.129
100 80 60 40 20 0 4
8 12 BTA concentration (g/l)
10–6
10–5 10–4 j/A.cm–2
10–3
10–2
10–1
3.2 Electrochemical impedance testing In Figure 5, electrochemical impedance data, recorded under open-circuit conditions in the 3.5 wt% sodium chloride solution following an 120-min immersion period, are presented for the uncoated and coated brass electrodes together with their equivalent circuit for each EIS spectrum. In the EIS spectra for the uncoated brass (Figure 5 (a)), there is only one part of the semicircle, which means that the reaction is a one-step process. Therefore, the simulated equivalent circuit for uncoated brass is R(CR). However, an interesting feature of the impedance for coated brass (Figure 5(b)) is that the first semicircle is a negative Faradic impedance in the real component, which suggests the presence of an inductive component because the inductance current is 1808 off the capacitive current phase (Chen et al., 2006). The simulated equivalent circuit for coated brass is LR(C(R(CR))). All the parameters (L, Rs, Cd, Rp, Cc, and Rcp) obtained for the uncoated and coated brass, based on the fitting procedure, are tabulated in Table III. It was observed that double-layer
Figure 3 Variation of percentage of inhibitor efficiency as function of BTAH concentrations
0
10–7
From Table II, we can see that the polarization resistance of La/BTAH-coated brass in optimum concentration was increased by a factor of nearly 5, and the corrosion current density was reduced by about one order of magnitude. The inhibition efficiency followed the order La/ BTAH . BTAH . La and reached the maximum value of 93.8 percent in the presence of La/BTAH at the optimum concentration.
La salt (g l2 1) Ecorr (V) Icorr (mA cm2 2) Corrosion rate (mm year2 1) 2 0.249 2 0.164 2 0.203 2 0.176 2 0.193 2 0.191
4 2 31
–0.5
Table I Electrochemical parameters for brass treated with various concentrations of La(NO3)3 in basal deposition solutions
Inhibitor efficiency (%)
1 32
–0.3
–0.30
Bare brass 3.5 4.0 4.5 5.0 5.5
4
Table II Potentiodynamic scan data fitting procedure for different specimens of brass
16
La salt and La salt þ BTAH in basal deposition solution after 30 min of immersion in 3.5 wt% sodium chloride solution. As a reference, the curve corresponding to a bare brass is included in this figure. The main difference we can note between curve (1) and curves (2-4) was the decrease of anodic dissolution current density after coating deposition which was sufficient to reduce the corrosion rate in principle. 34
Specimens
Ecorr Icorr Rp Inhibition efficiency (mV) (mA cm2 2) (V cm2) (%)
Uncoated BTAH coated La coated (La/BTAH) coated
2197 2187 2203 2184
1.96 0.46 1.08 0.13
2,345 4,958 3,866 12,624
– 76.5 44.9 93.8
Conversion coatings formed by use of La(NO3)3 and BTAH on brass
Anti-Corrosion Methods and Materials
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Volume 59 · Number 1 · 2012 · 32 –38
Figure 5 Impedance spectra for the brass electrodes
140
100 80 60 40
1.0×105 8.0×104 6.0×104
20
4.0×104
0
2.0×104 0
experimental calculate
1.2×105 –Z'/Ω m2
–Z''/Ω cm2
1.4×105
experimental calculate
120
40 80 120 160 200 240 280 320 360
0.0
cm2
Z'/Ω (a)
8.0×1041.6×1052.4×1053.2×1054.0×105 Z'/Ω cm2 (b) Cc
Cd
L
Rs
Rs
Cd
L Rp
Rcp
(c)
(d)
Rp
Notes: (a) Uncoated brass; (b) coated brass; (c) equivalent circuit for uncoated brass; (d) equivalent circuit for coated brass; Rs is solution resistance; Cd is double-layer capacitance; Rp is polarization resistance; L is inductance of the electrode; Cc is capacitance of the coating; Rcp is resistance of coating with pores Table III EIS simulation data for uncoated and coated brass Specimens Uncoated brass Coated brass
L (H)
Rs (V cm2)
Cd (F)
Rp (V cm2)
Cc (F)
Rcp (V cm2)
– 0.00408
3.582 3.469
2.5 £ 102 4 2.1 £ 102 4
245.4 3.425 £ 104
– 2.793 £ 102 7
– 4.2 £ 103
capacitance (Cd) decreased after coating, but not significantly, possibly because conversion coatings did not completely cover the surface. The value of Rp is related to polarization resistance of electrical double layer, i.e. the cathodic sites which are in direct contact with the solution, which significantly increases after coating from 245.4 to 3.425 £ 104 V cm2. On the other hand, the inductance L, in parallel with the resistance Rcp of coating, has been attributed to the active dissolution sites in the oxide layer, taking into account the damaged areas of the film, correlated with the low frequency processes. The EIS results and their equivalent circuits also revealed that the corrosion mechanisms for uncoated and coated brass are different.
Figure 6 SEM micrograph of brass prior to (a) and after (b) the formation of conversion coatings
(a)
3.3 Conversion coatings characterization Figure 6 shows the SEM image of samples before and after treating with optimal deposition techniques. From Figure 6(b), a typical crazing-like islands could be seen on the surface of brass after coating, similar to the one detected on 6061-SiC by Mishra (Mishra et al., 2007), while no crack was found in Figure 6(a). The crevices in Figure 6(b) seemed to be filled with a substance in different composition or different density.
(b)
The XRD spectrum of uncoated and coated brass is shown in Figure 7. The detected peak at 2u ¼ 42.58, 79.58 and 888could be attributed to La2O3. Similarly, the several weak diffraction peaks of Cu2O were also found at 2u ¼ 62.58. However, the peak at 2u ¼ 42.58, 498, and 718 could be indexed as CuZZn. In our case, the conversion coatings was thin and the peaks of CuZZn were due to the contribution from the substrate of brass 35
Conversion coatings formed by use of La(NO3)3 and BTAH on brass
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Volume 59 · Number 1 · 2012 · 32 –38
4. Discussion
Figure 7 XRD patterns of uncoated and coated with optimal deposition techniques on brass (200)
La2O3 Cu2O Cu-Zn
4.1 Effect of La salt and BTAH on conversion coatings The modifications caused by the addition of La salt to basal deposition solutions behaves as a anodic barrier which restrains the anodic reactions, and therefore inhibits the entire corrosion process in the system. Moreover, an extra large amount of La salt in deposition solutions degrades the corrosion performance of the conversion coating, because the premature coating deterioration is most likely the result of water intrusion due to the increase in the coating porosity. The relatively high inhibiting efficiency compared to the reported values (Cao et al., 2002) may be due to the excellent synergism effect between the BTAH and the other compositions of the basal deposition solution which is beneficial for the formation of a protective layer at the surface. The phenomenon of synergism between La salt and BTAH was supported by the synergism parameter (S), which was calculated by using the relationship:
(222)
(110)
(220) (422)
(400) (a) (200)
(220)
Cu0.64 Zn0.36 (111)
20
30
40
50
60
70
80
2 θ (degree)
S¼
i1 £ i2 i 12 £ i 0
ð2Þ
(b)
where i1, i2, and i12 are the corrosion current density in the presence of optimum concentration of La salt, BTAH and La salt/BTAH, respectively; i0 the corrosion current density for the blank. The synergism parameter (S) values was 1.95, suggesting the excellent synergism effect of La salt and BTAH on the corrosion inhibition of brass.
Notes: (a) Coated brass; (b) uncoated brass (CuZZn). Therefore, the conversion coatings could make a bonding with the old bone by the formation of the surface oxide layer consisted of La2O3 and small amounts of Cu2O. The structural characteristics of conversion coatings prepared with optimal techniques on brass was investigated by FT-IR spectroscopy in the range of 3,500-800 cm2 1 (Figure 8). Three peaks at about 1,162, 2,925, and 3,347 cm2 1 were assigned to the NZH stretching vibration showing the characteristic vibration peak of benzenoid units. The peak recorded at 3,241 cm2 1 was associated with the presence of vCZH groups in the polymer structure. The bands at 1,450 and 1,656 cm2 1 could be attributed to CvC stretching vibration on benzene ring which was from BTAH breathing. The above results demonstrated that BTAH adsorption on brass was carried out through nitrogen from the azole ring, thereby baffling the release of metal ions in anodic sites.
4.2 Proposed inhibition mechanism Figure 9 schematically shows the effect of conversion coating on corrosion inhibition of brass. First, the dissolution of substrate takes place in anodic sites: 2Cu ! 2Cu2þ þ 4e
When the basal deposition solutions was loaded with moderate amounts of BTAH, the reaction towards formation of complex Cu(I)BTA was described by the following reactions (Allam et al., 2009): ½BTAHaq þ CuðsÞ ¼ ½BTAHads : Cu
ð4Þ
where [BTAH]aq refers to BTAH dissolved in aqueous electrolyte and [BTAH]ads:Cu refers to BTAH molecules
Figure 8 FT-IR spectra (3,500-800 cm2 1 region) of conversion coatings on brass
Figure 9 Proposed scheme for the effect of conversion coating on corrosion inhibition of brass
1,162
2,925
50
1,450
1,656
3,347 3,241
2,335
100
Transmittance (%))
ð3Þ
0 3,500
3,000
2,500 2,000 Wavenumber (cm–1)
1,500
1,000
36
Conversion coatings formed by use of La(NO3)3 and BTAH on brass
Anti-Corrosion Methods and Materials
Hongqiang Fan et al.
Volume 59 · Number 1 · 2012 · 32 –38
adsorbed on the brass surface. Under oxidizing conditions, this adsorbed species could be oxidized to give the protective complex, i.e.:
on the corrosion inhibition of brass was also observed with the synergism parameter (S) values 1.95. The EIS results and their equivalent circuits also revealed that the corrosion mechanisms for uncoated and coated brass are different. The improved corrosion inhibition of commercial brass can be attributed to the formation of the composited conversion coatings consisted of La2O3 and small amounts of Cu2O except for the Cu(I)BTA and La coordinate thing, which acted as a barrier inhibiting the diffusion of the oxygen and blocking the release of metal ions.
2 ½BTAHads : Cu ¼ CuðIÞBTAðsÞ þ Hþ ðaqÞ þ e
ð5Þ
The as-formed protective complex Cu(I)BTA gets adsorbed onto the brass substrate through nitrogen from the azole ring (Figure 8), baffling the dissolution of substrate in anodic sites. Such anodic inhibition is confirmed in the potentiodynamic polarization test with a shift in Ecorr to higher values (Figure 2). In addition, oxygen reduction reaction occurs on the cathodic sites resulting in generation of OH2 groups over the cathodic intermetallic precipitates. This leads to local increase in pH at the cathodic sites. La(III) ion in the deposition solution gets adsorbed onto the brass substrate due to attraction between ions in the solution and surface of the substrate, and reacts with the OH2 group formed over the cathodic sites. This reaction gives rise to the formation of lanthanum oxide (La2O3) islands (Figures 6(b) and 7). The blockage of the cathodic sites by these islands on the surface can inhibit the diffusion of the oxygen which represents the cathodic reduction reaction (6), decrease the cathodic current, thereby reduce the overall corrosion rate: O2 þ 2H 2 O þ 4e2 ! 4OH 2
References Allam, N.K., Nazeer, A.A. and Ashour, E.A. (2009), “A review of the effects of benzotriazole on the corrosion of copper and copper alloys in clean and polluted environments”, Journal of Applied Electrochemistry, Vol. 39 No. 7, pp. 961-9. Antonijevic, M.M. and Petrovic, M.B. (2008), “Copper corrosion inhibitors: a review”, International Journal of Electrochemical Science, Vol. 3 No. 1, pp. 1-28. Ardelean, H., Frateur, I. and Marcus, P. (2008), “Corrosion protection of magnesium alloys by cerium, zirconium and niobium-based conversion coatings”, Corrosion Science, Vol. 50 No. 7, pp. 1907-18. Arenas, M.A. and de Damborenea, J.J. (2003), “Growth mechanisms of cerium layers on galvanised steel”, Electrochimica Acta, Vol. 48 No. 24, pp. 3693-8. Brandl, E., Malke, R., Beck, T., Wanner, A. and Hack, T. (2009), “Stress corrosion cracking and selective corrosion of copper-zinc alloys for the drinking water installation”, Materials and Corrosion – Werkstoffe Und Korrosion, Vol. 60 No. 4, pp. 251-8. Cao, P.G., Yao, J.L., Zheng, J.W., Gu, R.A. and Tian, Z.Q. (2002), “Comparative study of inhibition effects of benzotriazole for metals in neutral solutions as observed with surface-enhanced Raman spectroscopy”, Langmuir, Vol. 18 No. 1, pp. 100-4. Chen, W., Kim, J., Sun, S.H. and Chen, S.W. (2006), “Electro-oxidation of formic acid catalyzed by FePt nanoparticles”, Physical Chemistry Chemical Physics, Vol. 8 No. 23, pp. 2779-86. Conde, A., Arenas, M.A., de Frutos, A. and de Damborenea, J. (2008), “Effective corrosion protection of 8090 alloy by cerium conversion coatings”, Electrochimica Acta, Vol. 53 No. 26, pp. 7760-8. Jinturkar, P., Guan, Y.C. and Han, K.N. (1998), “Dissolution and corrosion inhibition of copper, zinc, and their alloys”, Corrosion, Vol. 54 No. 2, pp. 106-14. Liu, Y., Skeldon, P., Thompson, G.E., Habazaki, H. and Shimizu, K. (2005), “Chromate conversion coatings on aluminium-copper alloys”, Corrosion Science, Vol. 47 No. 2, pp. 341-54. Maciel, J.M., Jaimes, R.F.V.V., Corio, P., Rubim, J.C., Volpe, P.L., Agostinho, A. and Agostinho, S.M.L. (2008), “The characterisation of the protective film formed by benzotriazole on the 90/10 copper-nickel alloy surface in H2SO4 media”, Corrosion Science, Vol. 50 No. 3, pp. 879-86. Mishra, A.K., Balasubramaniam, R. and Tiwari, S. (2007), “Corrosion inhibition of 6061-SiC by rare earth chlorides”, Anti-Corrosion Methods and Materials, Vol. 54 No. 1, pp. 37-46.
ð6Þ
Furthermore, the excellent synergism effect of La salt and BTAH on the corrosion inhibition of brass was related to the formation of Cu(I)BTA and La coordinate thing (Figure 10). The fact that the presence of Cu(I)BTA and La coordinate thing strongly modified the morphological features of the brass substrates, changed the energy of electrode/electrolyte interface and baffled the anodic reaction (3). Such further anodic inhibition was confirmed in the potentiodynamic polarization test with the decrease of anodic dissolution current density in curve (4) after coating (Figure 4). Further investigation in the inhibition mechanism is under progress.
5. Conclusion Potentiodynamic polarization curves showed that the lanthanum salt and benzotriazole both had inhibitory effects on the corrosion process of brass at moderate condition, and “Critical La salt content” (4.5 g l2 1) and “Critical BTAH content” (8 g l2 1) were both observed, at which the coatings prepared performs the highest protectiveness. Inhibition efficiencies of BTAH were higher than that of La salt, and the excellent synergism effect of Lanthanum salt and BTAH Figure 10 Cu(I)BTA and La coordinate thing structural formula
La Cu
N Cu
N N
N
La
N N La
Cu
Cu
N N
N
37
Conversion coatings formed by use of La(NO3)3 and BTAH on brass
Anti-Corrosion Methods and Materials
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Volume 59 · Number 1 · 2012 · 32 –38
Osborne, J.H. (2001), “Observations on chromate conversion coatings from a sol-gel perspective”, Progress in Organic Coatings, Vol. 41 No. 4, pp. 280-6. Otieno-Alego, V., Hope, G.A., Notoya, T. and Schweinsberg, D.P. (1996), “An electrochemical and sers study of the effect of 1(N,N-bis-(hydroxyethyl)aminomethyl)-benzotriazole on the acid corrosion and dezincification of 60/40 brass”, Corrosion Science, Vol. 38 No. 2, pp. 213-23. Rudd, A.L., Breslin, C.B. and Mansfeld, F. (2000), “The corrosion protection afforded by rare earth conversion coatings applied to magnesium”, Corrosion Science, Vol. 42 No. 2, pp. 275-88. Shih, H.C. and Tzou, R.J. (1993), “Studies of the inhibiting effect of 1,2,3-benzotriazole on the stress-corrosion cracking of 70 30 brass in fluoride environments”, Corrosion Science, Vol. 35 Nos 1-4, pp. 479-88. Shim, S.I., Park, Y.S., Kim, S.T. and Song, C.B. (2002), “Effects of rare earth metal addition on the cavitation erosion-corrosion resistance of super duplex stainless steels”, Metals and Materials International, Vol. 8 No. 3, pp. 301-7.
Villamil, R.F.V., Cordeiro, G.G.O., Matos, J., D’Elia, E. and Agostinho, S.M.L. (2003), “Effect of sodium dodecylsulfate and benzotriazole on the interfacial behavior of Cu/Cu(II), H2SO4”, Materials Chemistry and Physics, Vol. 78 No. 2, pp. 448-52. Wu, Y.C., Zhang, P., Pickering, H.W. and Allara, D.L. (1993), “Effect of KI on improving copper corrosion inhibition efficiency of benzotriazole in sulfuric-acid electrolytes”, Journal of the Electrochemical Society, Vol. 140 No. 10, pp. 2791-800. Yasakau, K.A., Zheludkevich, M.L. and Ferreira, M.G.S. (2008), “Lanthanide salts as corrosion inhibitors for AA5083: mechanism and efficiency of corrosion inhibition”, Journal of the Electrochemical Society, Vol. 155 No. 5, pp. C169-77.
Corresponding author Shuying Li can be contacted at:
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