Study of the corrosion behavior of a Cu-Sn-Ni alloy by ...The electrodeposition process is an interesting option for the production of Cu-Sn-Ni alloy since, commonly, they are produced

Study of the corrosion behavior of a Cu-Sn-Ni alloy by anodic stripping voltammetry coupled with spectroscopic techniques

W. Rubin1, I.A. Carlos1

1 Department of Chemistry - UFSCar, São Carlos - SP - Brazil

ABSTRACT

The electrodeposition process is an interesting option for the production of Cu-Sn-Ni alloy since, commonly,

they are produced by casting. The literature shows that the anodic stripping voltammetry (ASV) is very sensitive

to study the type of alloy electroplated. Thus, the ASV of the Cu-Sn-Ni deposits was performed in order to

investigate its dissolution process in HCl solution, i.e., a very corrosive environment. For this study, the anodic

voltammetric curves of the electrodeposits were performed in different HCl concentrations and also at various

potential sweep rates in order to assess if the corrosion products of the alloy are influenced by the electrolyte

concentration and / or the sweep rate, which simulate the time action. The remaining deposits after each

dissolution peak were investigated by SEM, EDX and XRD.

Keywords: Cu-Sn-Ni, electrodeposition, anodic stripping voltammetry, aspartic acid, XRD.

1- INTRODUCTION

The Cu-Sn-Ni alloy is an alternative to the Cu-Sn-Pb alloy, which is widely used in high-load bearings in

many applications due to its high resistance and therefore used as an alternative to bronze to protect parts steel

[1]. The electroplating process is an interesting way for the formation of these alloys, since generally its

production is done by casting.

The electrodeposition of metal alloys can produce different structures in the also the electrodeposit, not

always corresponding to the equilibrium phase diagrams. Anodic stripping voltammetry (ASV) is very sensitive

to the type of alloy electrodeposited, so, the study of the dissolution process of the Cu-Sn-Ni alloy by ASV

becomes important due to its applications.

The aim of this study was to use the ASV technique for the investigation of the dissolution process of Cu-

Sn-Ni electrodeposits produced without or with aspartic acid as an additive in the plating bath in order to stydy

the effect of this additive on the properties of the electrodeposits. For this study, the anodic voltammetric curves

of the deposits were performed in different HCl concentrations, i.e. a very corrosive environment, and also at

various sweep rates in order to assess whether the corrosion products of the alloy are influenced by the

electrolyte concentration and also the sweep rate (simulating the action of time). Thus, the ASV with X-ray

diffraction spectroscopy (XRD) was used to investigation of the dissolution process of Cu-Sn-Ni electrodeposits.

2- EXPERIMENTAL

Encontro e Exposição Brasileira de tratamento de superficieIII INTERFINISH Latino Americano

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All chemicals were analytical grade. Distilled deionized water was used throughout. The electrodeposits

were obtained potentiostatically at -1.0 V and deposition charge density (qd) of 10.20 C cm-2 from acid baths (pH

~ 1.20) containing CuSO4, SnCl2, NiSO4, and C4H7NO4 (Aspartic acid) as an additive. Each electrochemical

experiment was performed in a freshly prepared HCl bath. A Pt disk (0.196 cm2), a Pt plate and an Hg/Hg2Cl2 |

KCl 0.1 mol L-1 system were employed as working, auxiliary and reference electrodes, respectively. Immediately

prior to the electrochemical measurements, the Pt working electrode was polished with 0.3 µm alumina powder,

dipped in a concentrated sulphuric-nitric acid mixture and then rinsed with double-distilled water.

Potentiodynamic curves were recorded with an AutoLab-800 mA potentiostat/galvanostat. All experiments were

carried out at room temperature (25°C). The deposition current efficiency (CE) was calculated from the

stripping/deposition charge ratio (qdiss / qd). Scanning electron microscope (SEM) with field emission gun (SEM-

FEG) photographs were taken with a Philips XL 30 microscope. Energy dispersive spectroscopy (EDS)

measurements were made with an eLX Oxford microscope, equipped with EDS Si/Li with an ultra-thin Be

window. X-ray diffraction (XRD) patterns were produced with Cu Kα radiation (1.5406 Å), using a Rigaku

Rotaflex RU200B X-ray goniometer, in 2θ scanning mode (fixed ω = 2◦).

3- RESULTS AND DISCUSSION

Firstly, the influence of HCl concentration to be used in the dissolution studies of the electrodeposits

(produced with or without aspartic acid, as an additive) was investigated. The micrographs of the deposits

showed that they were without cracks or dendrites and also recovered totally the Pt substrate. EDS analysis of

the electr od eposi ts showed that t he deposit was compos ed of 4.1 wt % O, 3. 5 wt% Ni , 24.3 wt % Cu, 68.1 wt %

Sn. Also, DRX analysis showed that both deposits were formed of a mixture of Sn, Cu6Sn5, Ni3Sn2 and CuNi2Sn.

The ASV curves of Cu-Sn-Ni-asp electrodeposits in various HCl concentrations, at v = 10 mV s-1, are

shown in Figure 1. It can be seen that they were similar for HCl concentration 0.8 mol L-1 or 1.0 mol L-1, being

that for the latter the area of anodic peak was the highest among the HCl concentrations investigated. On

contrary, for HCl concentration 2.0 mol L-1, small areas of anodic peaks were obtained during voltammetric

dissolution. Moreover, when the eletrodeposits were submitted to voltammetric dissolution in HCl 0.5 mol L-1,

they did not dissolve by complete (see by visual inspection at naked eye), even decreasing v at 5.0 mV s-1. Also,

it can be seen that the initial dissolution potential is more negative for low HCl concentration. Also, by

comparing the current efficiency (CE) of voltammetric dissolution of Cu-Sn-Ni and Cu-Sn-Ni-asp (inset in Fig.

1), it can be seen that the highest CE was obtained when the electrodeposits was dissolved in HCl 0.8 mol L-1.

Also, the smaller CE was for HCl 2.0 mol L-1, indicating, in this case, significant chemical dissolution of the

electrodeposit. In addition, it can be seen that the CE was always lower than 100%, due to the hydrogen

evolution reaction (HER) in parallel to deposition process. These results showed that the voltammetric

dissolution of the electrodeposits depends on the HCl concentration.

Figure 1 – Anodic stripping voltammetric curves of Cu-Sn-Ni-asp electrodeposits dissolution in various HCl concentrations, i.e., 0.5 mol L-

1 (__), 0.8 mol L-1 (---), 1.0 mol L-1 (…) and 2.0 mol L-1 (-.-) at v = 10 mV s-1. The insert shows the current efficiency of each HCl concentration.


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Figure 2 shows ASV curves of Cu-asp (---), Sn-asp (…), and Ni-asp (-.-) and Cu-Sn-Ni-asp (__) deposits

in HCl 0.8 mol L-1. Cu-asp and Sn-asp electrodeposits were obtained potentiostatically at Ed = -0.8 V with qd of

1.02 C cm-2 and 2.55 C cm-2, respectively, while the Ni-asp electrodeposit was obtained voltammetrically from

0.0 V until final potential of -1.7 V (to activate more Pt sites to deposition so that deposition of Ni occurs),

returning until current zero, qd = 21.0 C cm-2.

Figure 2 – ASV curves of Cu-Sn-Ni-asp (___), Cu-asp (---), Sn-

asp (...) and Ni-asp (-.-) electrodeposits in HCl 0.8 mol L-1 at v=10 mV s-1. Pt substrate.

ASV curves of Sn-asp and Ni-asp show an anodic peak at Ep= -0.56 V and at Ep= -0.09 V, respectively,

while for Cu-asp two anodic peaks were formed, i.e., Ep= -0.15 V and at Ep= +0.24 V, due to oxidation of Cu to

Cu+, forming CuCl, and after the oxidation to Cu2+.

Comparing Cu-Sn-Ni-asp dissolution voltammetric curve (__) and those of pure metals, it can be seen

that the Sn and compounds containing Sn (Cu6Sn5, Ni3Sn2 and CuNi2Sn) initiated to dissolve in the region of

anodic peak a. However, as can be seen latter, compounds containing Cu and Ni also initiated to dissolve,

already, in the region of peak a. In ord er to evaluate t he di ss ol ut ion process of Cu -Sn-Ni-as p electrod eposi ts, volt ammetric di ssol ut ions

of they in HC l 0.8 mol L-1 at 10.0 mV s-1 wer e perf or med. Th en, anal ysis of t he remaining deposits after each

voltammetric dissolution peak, i.e., anodic peaks a and b were analyzed by SEM (Fig. 2), EDS and XRD.

Fig. 2 shows micrographs of the remaining deposits after dissolution of peaks a and b. Figures 2(a) and

2(b) refers to Cu-Sn-Ni (produced without the additive) after voltammetric dissolution of deposits up to

formation of peaks a and b, respectively. Similarly, Fig. 2(c) and 2(d) refers to Cu-Sn-Ni-asp deposits after

voltammetric dissolution of deposits up to formation of peaks a and b, respectively. Comparing the micrographs

of deposits after dissolution peak a, it can be seen that they proved to be porous, dendritic and also, Pt substrate

was exposed. In turn, comparing the deposits remaining after dissolution of the peak b it can be inferred that the

morphologies of these electrodeposits are quite different, ie, Cu-Sn-Ni showed only a few isolated crystallites

distributed over the Pt surface (b), while Cu-Sn-Ni-asp (d) showed deposit with many cracks but still covering

the Pt substrate. So, the presence of aspartic acid seems to produce a deposit that possbly better protect the

substrate against corrosion.

Figure 2 – Micrographs of the remaining electrodeposits after dissolution of peak a (a, c) and b (b, d) in HCl 0.8 mol L-1. The deposits were obtained with (a and b) or without the additive (c and d). v = 10 mV s-1.

a

b

c


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The XRD analysis of Cu-Sn-Ni or Cu-Sn-Ni-asp electrodeposits, after the dissolution peaks a and b,

shows that the Sn and Cu6Sn5 phases would be dissolving in the region of peak a, as can be seen by the

suppression of the diffractogram peaks for these phases (Fig. not shown here). So, the remaining electrodeposit

was composed of SnO, result of Sn dissolution/passivation, Ni3Sn2 and CuNi2Sn. In turn, after the dissolution of

peak b, the difractogram shows that the deposit was composed only of SnO.

In addition, EDS analysis were performed on Cu-Sn-Ni and Cu-Sn-Ni-asp electrodeposits, as produced

and after the dissolution peaks a and b and it can be verified that even after dissolution process a and b, there

was still Cu, Sn and Ni in the eletrodeposit. This can be explained by the fact of the different phases formed have

different energies so different dissolution potentials too.

4- CONCLUSIONS

Comparing the results obtained from voltammetric curves and those from XRD and EDX it can be

inferred that in the region of the dissolution peak a, the dissolution/passivation of Sn together with Cu6Sn5

dissolution occurred. According to the XRD analysis, the remaining deposit was composed of SnO, Ni3Sn2,

CuNi2Sn which would be oxidizing in the region of peak b, where Ni oxidized to Ni2+ and Cu to Cu+, forming a

CuCl film. Finally, the remaining deposit after dissolution of peak b, was composed only of SnO according to

XRD but, EDX analysis showed that Cu, Sn and Ni still remains in the electrodeposit, so, in the region of peak c,

these species would be oxidizing since after that, no electrodeposit was seen at Pt substrate. Also, from XRD

analysis after each dissolution process it can be concluded that the protective character of this alloy is shown by

the formation of CuCl and SnO (peak a) and SnO2 (peak b) during the dissolution of the same in this aggressive

envi ron ment. SE M, EDX and XRD analysis aft er the dissolution of the peak b showed that as partic aci d was

advantageous in the deposition process (allowing the codeposition of metals and the formation of the ternary

alloy), since after deposit dissolution these films were more compact and homogeneous. Furthermore, EDS

results of remaining deposit after peak b, led to suggest that this film still contain CuNi2Sn alloy, indicating that

this alloy has excellent resistance to corrosive environments.

5- ACKNOWLEDGMENTS: FAPESP, CAPES e CNPq.

6- REFERENCES

1- www.mahle.com – accessed September 15th 2011

2- G. A. Finazzi, Tese de doutorado (Orientadora: I. A. Carlos), UFSCar, 2004.

3- I. A. Carlos, C. A. C. Souza, E. M. J. A. Pallone, R. H. P. Francisco, V. Cardoso, B. S. Lima-Neto. J.

Appl. Electrochem. 30: 987-994, 2000.

4- L.L. Barbosa, M.R.H. de Almeida, R.M. Carlos, M. Yonashiro, G.M. Oliveira, I.A. Carlos. Surf. Coat.

Technol., 192, 2-3, 2005, 145-153.

5- P. C. Túlio, S. E.B. Rodrigues, I. A. Carlos, Surf. Coat. Technol 202 (2007) 91-99.


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6- A. C. M. Moraes, J. L.P.Siqueira, L.L.Barbosa, I.A.Carlos, J. Appl. Electrochem. DOI.10.1007/s10800-

008-9680-6. (2008).

7- J. L. P. Siqueira, I. A .Carlos, J. P. Sources, 166 (2007) 519-525.

8- I. A. Carlos, E.D. Bidóia, C. A. C. Souza, E. M. J. A. Pallone, M. R. H. Almeida. Surf. Coat. Technol.

157 (2002) 14-18.

9- I.A.Carlos, E.M.Oliveira, G.A.Finazzi, Surf. Coat. Technol. 187(2004) 377-387.

10- G. M. de Oliveira, M.R. da Silva, I. A. Carlos, J. Mat. Science, 42 (2007) 10164-10172.

11- G. M.de Oliveira; L.L.Barbosa, R.L Broggi, I.A.Carlos, J. Electroanal. Chem. 578 (2005) 151–158

12- M. S. Pereira, L.L. Barbosa, C.A.C. Souza, A.C.M. Moraes, I.A. Carlos. J. Appl. Electrochem. 36

(2006) 727.

13- E. M. Oliveira, I. A. Carlos, J. Appl. Electrochem., 38 (2008)1203-1210.

14- E. M. Oliveira, G.A. Finazzi, I. A. Carlos. Surf. Coat. Technol. 200 (2006) 5978- 5985.

15- R. L. Broggi; G. M. Oliveira; L. L. Barbosa; E. M. J. A. Pallone, I. A. Carlos. J. Appl. Electrochem., 36

(2006) 403-409.

16- L. L. Barbosa; I. A. Carlos, G.A.O. Brito, M. C. Lopez, R.L. Broggi, Electrochim. Acta. 50, 24 (2005)

4710-4714.

17- L. L. Barbosa, G. A. Finazzi, P. C. Tulio, I. A. Carlos, J. Appl. Electrochem. 1, 38 (2008) 115-125.

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19- J.L. P. Siqueira, I.A. Carlos J. P. Sources 169, 2 (2007) 361-368.

20- A. Brenner, Electrodeposition of alloys. Principles and Practice, v.1, Acad. Press, N.Y, 1963.


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7- AUTHOR DETAILS

Wesley Rubin possui graduação em Química pela

Universidade de Franca (2006), mestrado em Química

Analítica pela Universidade Federal de São Carlos (2009)

e atualmente é doutorando em Química Analítica,

também pela Universidade Federal de São Carlos –

Departamento de Química, bolsista FAPESP

(2009/50483-2), sendo integrante do Grupo de

Eletrodeposição e Eletrodissolução de Metais e Ligas –

LEEMEL, chefiado pela Profa. Dra. Ivani Aparecida

Carlos. Atua como co-orientador em projetos de Iniciação

Científica no mesmo grupo de pesquisa.

Ivani Aparecida Carlos possui graduação em Química

pela Universidade Federal de São Carlos (1975),

Mestrado em Físico-Química (1979) e Doutorado em

Físico-Química (1990) pela Universidade de São Paulo.

Atualmente é professora associada nível I junto à

Universidade Federal de São Carlos. Tem experiência na

área de Química, com ênfase em

Eletroanalítica/Eletroquímica atuando nos seguintes

temas: filmes eletrodepositados de metais puros e ligas,

pós-metálicos, cinética e mecanismo do processo de

eletrodeposição, eletroanalítica, desenvolvimento de

banhos não cianetados, caracterização de filmes por

espectroscopia de difração de raio-X; microscopia

eletrônica de varredura, espectroscopia de dispersão de

raio-X e espectrofotometria de absorção atômica.


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Documents

Study of the corrosion behavior of a Cu-Sn-Ni alloy by ...The electrodeposition process is an interesting option for the production of Cu-Sn-Ni alloy since, commonly, they are produced