Microstructure and properties of nickel prepared by electrolyte vacuum boiling electrodeposition

Microstructure and properties of nickel prepared by electrolyte vacuum boiling electrodeposition

Surface & Coatings Technology 213 (2012) 299–306 Contents lists available at SciVerse ScienceDirect Surface & Coatings Technology journal homepage: ...

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Surface & Coatings Technology 213 (2012) 299–306

Contents lists available at SciVerse ScienceDirect

Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat

Microstructure and properties of nickel prepared by electrolyte vacuum boiling electrodeposition Pingmei Ming a,⁎, Yingjie Li b, Shuqing Wang a, Songzhao Li a, Xinhua Li a a b

School of Mechanical and Power Engineering, Henan Polytechnic University, Jiaozuo 454000, Henan, China Qingdao Haixi Electric Machine Limited Company, Huangdao 266555, Shandong, China

a r t i c l e

i n f o

Article history: Received 2 May 2012 Accepted in revised form 27 September 2012 Available online 6 November 2012 Keywords: Electrodeposition Vacuum boiling Microstructure Microhardness Corrosion resistance

a b s t r a c t A nontraditional electrodeposition technique carried out in an electrolyte vacuum boiling environment was introduced, and nickel deposits with a favorably good surface quality were prepared at a considerably high growth rate of up to 0.307 μm/s. The studies of influences of cathode current density on the microstructure, microhardness and corrosion resistance of deposits showed that, in comparison to the deposit obtained at 9 A/dm 2, the one electrodeposited at 63 A/dm 2 exhibited finer grains (about 100 nm) and a denser structure in the absence of additives, and the preferred orientation degree of (400) decreased while (220) increased correspondingly; with the current density increasing from 3 A/dm2 to 81 A/dm 2, the microhardness, as a whole, increased up to 605.5 HV, and the corrosion rate also increased, from 5.2% to 19.2% in 10 wt.% HCl solution and from 3.5% to 14.6% in 10 wt.% H2SO4 solution. In addition, the preferred orientation crystal plane was not affected by the additives, while the corrosion resistance of the deposits prepared with a sodium dodecyl sulfate additives was enhanced. These variations are mainly due to multiple effects of vacuum environment including boiling-motion effect of the electrolyte immediately close to the cathode surface or deposited films, vacuum degassing effect and purification effect. Compared with the nickel deposits from an atmosphere electrodeposition bath, the ones prepared by electrolyte vacuum boiling electrodeposition presented different texture, higher microhardness as well as better corrosion resistance. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Electrodeposition is a frequently-used technique to make metal and alloy coatings. Recently, requirements for considerably excellent surface quality and favorable properties (such as giant magnetoresistance and higher corrosion resistance) of the electrodeposited coatings have been expected in some industrial application fields. Since surface quality and properties of electrodeposits depend largely on bath constitutes and operating conditions, it is a popular research task to optimize systematically process conditions, such as cathode–anode configurations, electrolyte compositions, cathode current density, temperature, stirring and additives, to achieve a desired coating. Furthermore, some non-conventional electrodeposition methods carried out in an ambient air environment, such as ultrasonic electrodeposition [1], mechanical attrition electrodeposition [2], jet electrodeposition [3] and magneto-convection electrodeposition [4], have been also employed. To obtain some unique properties of electrodeposited materials, such as ultrastability and ultra high sensitivity, or to realize the electrodeposition of some active metals, a few electrodeposition

⁎ Corresponding author. E-mail address: [email protected] (P. Ming). 0257-8972/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.surfcoat.2012.09.067

techniques performed in a special environment have been developed, and evaluations of the electrodeposits have also been done. Tsai et al. [5] prepared the nickel deposit featuring almost no pinhole defects and fine grains under a high pressure (318.8 kPa) condition, and the microhardness of electrodeposits is bigger by about 20% than those deposited in a normal environment. Nam et al. [6,7] implemented electrodeposition in a vacuum environment (53–80 kPa), and a kind of pinhole-free and ultrastable Pd–Ni alloy composite membrane for catalysis applications was prepared. Chung et al. [8] obtained a nanocrystalline Ni–C film with a big microhardness and a good corrosion resistance from the bath containing 15 MPa supercritical CO2 fluid. Studies of the effect of high gravity on the microstructure and properties of electrodeposited Ni films were done by Liu et al. [9], and showed that surface of electrodeposits was fairly smoother, and hardness as well as tensile stress were both significantly higher than those plated under a normal gravity condition. Generally, several favorable effects including degassing, eliminating gas bubble, reducing oxidation and contamination can be acquired in a subatmospheric pressure or vacuum environment, and have been widely used in the industrial production to obtain some particular process capacities. Another common application for this kind of environment is to promote mass and heat transfer by using the boiling effect occurred at a low temperature under the normal boiling-point. Rationally, subatmospheric pressure or vacuum

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environment may probably provide greatly helpful bath conditions for electrodeposition process to reduce the generation of pinholes and nodules, hydrogen embrittlement, and oxides in the deposits produced with a high rate, and also to enhance mass transfer within high-aspect-ratio microtrenches during microelectroforming. Therefore, a notable improvement in surface quality and properties of electrodeposits may be obtained for some metals whose reduction potential is close to hydrogen overpotential, or for the electroformed microarticles with high-aspect-ratio structures. This paper aims at introducing the fundamentals of electrolyte vacuum boiling electrodeposition technique, and analyzing and evaluating microstructure characteristic and properties of the nickel deposits prepared using this technique. 2. Experimental Fig. 1 illustrates a schematic view of electrolyte vacuum boiling electrodeposition process. The electrodeposition bath was placed in a closed cell and the electrolyte was in the bath. A nickel plate was used as the anode and a stainless steel (SUS 304) sheet (47 mm in diameter, 1 mm in thickness) was used as the cathode. Before each experiment the stainless steel sheet was carefully pre-treated by a series of steps, such as polishing, degreasing, rinsing with distilled water, HCl solution and NaOH solution, and drying. The anode was positioned horizontally 25 mm or so far from the cathode facing each other in order to speed up the eliminating of gas bubbles formed on the deposits. Two heating pipes were, respectively, installed in the cathode interiorly and the bath to heat the cathode surface and the bulk electrolyte. Since boiling point of electrolyte changes with atmospheric pressure, the motion state of electrolyte can be controlled by adjusting the temperature at a given atmospheric pressure. During the electrodeposition, the electrolyte immediately close to cathode surface or deposited films was always kept boiling resulting from a higher temperature from a heated cathode surface at a temperature of 65 ± 1 °C, on the other hand, to reduce loss of electrolyte vaporization, the electrolyte elsewhere in the bath was made naturally flow due to a lower temperature of 35 ± 1 °C which is less than the boiling point at a vacuum degree of 5 ± 0.2 kPa. The pressure in the bath can be regulated by a vacuum-adjusting valve. Bulk electrolyte was naturally stirred by the boiling effect. To make the buffer H3BO3 work well, the pH of bath was adjusted to the value of 3.8–4.2 with hydrochloric acid and sodium hydroxide. The size of electrodeposited samples was 45 mm in diameter and the thickness was about 80 μm by controlling the electrodeposition time. Electrolyte compositions and operating conditions were listed in Table 1. The electrodeposition rate was calculated by the formula v = L / t, where L is the average thickness of deposits measured in five different places with a micrometer (minimum graduate 0.01 mm), and t is the

Table 1 Electrolyte composition and operating conditions. Category

Amount or conditions

Ni(NH2SO3)2·4H2O (concentrated solution ) NiCl2·6H2O H3BO3 CH3(CH2)11OSO3Na (additive) Cathode current density (DC) Vacuum degree Temperature

450 mL/L 10 g/L 40 g/L 0.05 g/L 3–81 A/dm2 5 ± 0.2 kPa Bulk electrolyte 35 ± 1 °C, cathode surface 65 ± 1 °C 3.8–4.2

pH

deposition time. The cathode polarization curve was recorded by an electrochemical workstation (PAR 2273, USA) with a sweep rate of 20 mV/s. Surface morphologies of the deposit were, respectively, examined by a white light interferometer (Talysurf CCI6000, UK) and a scanning electron microscope (JSM-6300, Japan). A transmission electron microscope (Tecnai G2F30S-TWIN, USA) and an X-ray diffractometer (D/max 2500VL/PC, Japan) were used to measure the grain size and to characterize the microstructure. The preferred orientation degree of nickel deposits was calculated as follows [10]:

TC ðhklÞ ¼

IðhklÞ =IoðhklÞ  100% n X IðhklÞ =IoðhklÞ i¼1

where I(hkl) is the relative peak intensity from the experimental data and Io(hkl) is the relative peak intensity in the PDF (Power Diffraction File) cards. Here, n = 4 is the number of diffraction peaks. The larger the TC(hkl) is, the higher the preferred orientation degree is. Microhardness tests were performed using an intelligent digital microhardness tester (HXS-1000A, China) with a load of 980 mN exerted for 10 s. The microhardness of deposit is the average of seven measurements in different places. Corrosion resistance is reflected by a corrosion rate, which is expressed by the ratio of corrosion mass loss to total mass of the deposit before corrosion. The corrosion rate was measured using a mass-loss method, and the corrosion process was carried out in a 10 wt.% HCl solution and a 10 wt.% H2SO4 solution for 14 days. Before and after corrosion, deposits were washed with distilled water and acetone for several times, dried in vacuum, and then subjected to related test and analysis. A precision electronic balance (Mettler Toledo, Switzerland) with a precision of 0.1 mg was used to weigh the quality before and after corrosion.

Bulk electrolyte Bulk electrolyte temperature sensor heating pipe Vacuum fine-tuning valve Cathode substrate

Dryer Vacuum meter Gland nut Vacuum pump

Copper support

Gasket Lock nut Electrodeposition bath

Anode Cathode unit

Baseplate

Heating pipe

Fig. 1. System of the electrolyte vacuum boiling electrodeposition process.

sensor

P. Ming et al. / Surface & Coatings Technology 213 (2012) 299–306

Cathode current density, A/dm2

100

301

45–81 A/dm 2. And at 81 A/dm 2, which is a limit value in our experiments, the electrodeposition layer showed a curly shape with an outer-ring burnt-deposit. The conventional deposition experiments under an atmosphere environment were carried out to a maximum current density of 9 A/dm 2, at which a lot of defects appeared without additives. The microstructures including preferred orientation, XRD pattern characteristic and grain size of the electrodeposited layer prepared at the above corresponding current density were analyzed. The predominant crystal orientation of deposits changed as the current density was increased from 3 A/dm 2 to 81 A/dm 2, and had an almost similar changing characteristic as those plated under the atmospheric environment when the current densities were less than 9 A/dm 2.

90 80 70 60 50 40 30 20 10 0 0.0

-0.5

-1.0

-1.5

-2.0

-2.5

-3.0

Cathode potential ,V 2500

Fig. 2. Cathodic polarization curve of electrolyte vacuum boiling electrodeposition.

(220)

(c)

2000

Cathodic polarization curve of electrolyte vacuum boiling electrodeposition was illustrated in Fig. 2. The cathode limiting current density was significantly increased, up to 90 A/dm 2 in an electrolyte vacuum boiling environment. This is mainly due to the fact that the electrolyte in the immediate vicinity of cathode surface or deposits was kept in a state of surface boiling, which leads to an extremely thin diffusion layer at the cathode and therefore a remarkable improvement in mass transfer efficiency. Electrodeposition rate tests indicated that the deposition rate increased almost linearly with the increase of the current density, from 3 A/dm 2 to 81 A/dm 2, and at 81A/dm 2, the feasible maximum deposition rate of 0.307 μm/s was achieved, which was about 70 times as big as that obtained under a conventional electrodeposition condition at 3 A/dm 2, as illustrated in Fig. 3.

3.2. Microstructure

1500

1000

(200) (111) (311)

500

0 125000

100000

Intensity,counts

3.1. Cathodic polarization curve and electrodeposition rate

Intensity,counts

3. Results and discussion

With a vacuum degree of 5 ± 0.2 kPa, electrodeposition samples were made at different current density from 3 A/dm 2 to 81 A/dm 2, increasing every 2 A/dm 2 in the range of 3 − 25 A/dm 2, every 4 A/dm 2 in the range of 25–45 A/dm 2, and 6 A/dm 2 in the range of

(200)

(b)

75000

50000

25000

(400)

(111)

(311)

0

32000

(a)

(200)

0.307

Intensity,counts

Deposition rate,µm/s

0.30 0.25 0.20 0.15

24000

16000

8000

(111) 0.10

(400)

(311) 0

0.05 30 0.00

0

8

16

24

32

40

48

56

64

72

80

Cathode current density, A/dm2 Fig. 3. Electrodeposition rate in the electrolyte vacuum boiling environment.

40

50

60

70

80

90

100

110

120

130

2θ/(o) Fig. 4. XRD patterns of nickel deposits obtained without additive: (a) conventional environment 9 A/dm2; (b) electrolyte vacuum boiling, 9 A/dm2; and (c) electrolyte vacuum boiling, 63 A/dm2.

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Table 2 Preferred orientation degree (TC(hkl)) of nickel deposits obtained without additive. (hkl)

Fig. 4(a)

Fig. 4(b)

Fig. 4(c)

(111) (200) (220) (311) (400)

24.6% 24.3% 0 25.5% 25.6%

24.8% 24.6% 0 25.7% 24.9%

25.2% 24.6% 24.1% 26.1% 0

Fig. 4 showed the XRD patterns of nickel deposits obtained without additives and at a lower current density of 9 A/dm 2 and a higher current density of 63 A/dm 2, respectively. As shown in Fig. 4, in comparison with the nickel deposit achieved under the conventional conditions at 9 A/dm 2, the one prepared using electrolyte vacuum boiling electrodeposition with the same current density showed few changes in diffraction spectrum characteristics and predominant crystal orientation. However, when at a high current density of 63 A/dm 2, the diffraction intensity of (111), (200), and (311) and (400) crystal plane dropped, but that of (220) plane notably increased. The highest diffraction intensity peak crystal face transformed from (200) at 9 A/dm 2 to (220) at 63 A/dm 2. The preferred orientation degree also altered at the different current densities, see Table 2. The preferred orientation degree of (400) reduced from 24.9% to 0, transforming from preferred orientation face to non-preferred orientation face, while the preferred orientation

3500

(b)

degree of (220) increased from 0 to 24.1%, transforming from non-preferred orientation face to preferred orientation face. According to the metal electrocrystallization theories [11], in the course of electrodeposition, the preferred orientation degree of crystal plane is essentially dependent on cathode overpotential. Electrodeposited nickel is most likely to form (111)-like texture at lower overpotentials, while as the overpotential increases, the preferred orientation may change from (200) to (220) texture. Our experimental tests indicated that, under the electrolyte vacuum boiling condition, the cathode overpotential increased from 0.12 V at 3 A/dm2 to 0.48 V at 9 A/dm2, then to 2.32 V at 63 A/dm2, thus probably resulting in the formation of (400) texture (the parallel plane of (200)) at 9 A/dm2 and (220) texture at 63 A/dm2. This kind of change tendency was similar to that reported in Ref. [12]. In addition, Fig. 5 and Table 3 presented the diffraction pattern and crystal face texture coefficient of vacuum boiling electrodeposition nickel layers prepared with 0.05 g/L of CH3(CH2)11OSO3Na additive and at the same current densities mentioned the above. Basing on these results, conclusion that, under the electrolyte vacuum boiling condition, CH3(CH2)11OSO3Na additive had few effects on XRD pattern and preferred orientation degree can be made. A further analysis using TEM showed that, average grain size of the deposit prepared at a low current density of 9 A/dm 2 was larger than 500 nm, while the one electrodeposited at a high current density of 63 A/dm 2 is approximately 100 nm, see Fig. 6. According to the diffraction patterns of two deposits, the former exhibited some intermittent diffraction spots distributing relatively uniform on the diffraction rings, however, the latter exhibited more spots that tended to form better continuous diffraction rings, presenting a corrugate structure, which reflected that the microstructure was more compact and homogeneous in the selected region [13].

(220) 3.3. Microhardness

Intensity,counts

3000

As illustrated in Fig. 7, the microhardness of Ni electrodeposits both from additives-containing and additives-free baths altered with the increase of current density, reducing from about 300 HV at 3 A/dm 2 to 260 HV at 9 A/dm 2, then rising to about 600 HV at 81 A/dm 2. This may be due to the fact that, at lower current densities of 3–9 A/dm 2, the electrodeposits featured coarse grains, poor compactness and a rough surface (shown in Fig. 8(a)–(b)), resulting from a relatively weak cathode polarization effect. This variation tendency in Ni-layer's microhardness is similar to that reported by Banovic et al. [14] and Kendrick et al. [15]. However, at higher current densities of 9–81 A/dm2,on the one hand, the cathode overpotentials gradually augmented with increasing current densities, which accordingly accelerated nucleation rate and nucleation probability [16,17], resulting in a finer and finer grains, and a compacter and compacter structure (see Fig. 8(c)–(f)). Moreover, Ni(OH)2 and H may, to a certain extent, form because of mass transportation limitation in a specially higher current density range, and then were incorporated into the deposits, which generally leads to a higher internal stress and hydrogen embrittlement stress. All these factors comprehensively gave rise to an approximate-linear increase in microhardness of Ni-layer

2500 2000 1500 1000

(111) (200)

500

(311)

0

50000

(a)

(200)

Intensity,counts

40000

30000

20000

10000

(111)

(400)

(311)

0 30

40

50

60

70

80

90

100

110

120

130

2θ/(o) Fig. 5. XRD patterns of two nickel deposits prepared with additive: (a) electrolyte vacuum boiling 9 A/dm2; and (b) electrolyte vacuum boiling 63 A/dm2.

Table 3 Preferred orientation degree (TC(hkl)) of nickel deposits prepared with additive. (hkl)

Fig. 5(a)

Fig. 5(b)

(111) (200) (220) (311) (400)

24.6% 24.6% 0 25.6% 25.2%

24.6% 25.5% 23.9% 26% 0

P. Ming et al. / Surface & Coatings Technology 213 (2012) 299–306

(a)

(a-1) (a-1)

500nm

(a-1) (a-1)

500nm 500nm (b-1) (b-1)

(b) (b)

303

100nm 100nm

(b-1) (b-1)

100nm 100nm

Fig. 6. TEM micrographs (bright field, dark field and diffraction pattern) of nickel deposits electrodeposited at different cathode current density. (a) 9 A/dm2; (b) 63 A/dm2.

plated by this technique with the current density. Though the change tendency in the microhardness of electrodeposits from additivescontaining and additives-free bath was almost identical, the specific microhardness values vs. current density were slightly different. In general, the former was bigger than the latter when current densities were less than 33 A/dm 2, but then the situation was just opposite at higher current densities. This may result from the different effect of additives on the microstructure of the deposits at different current densities to this technique.

600

without additive with additive

Microhardness, HV

550 500 450 400 350 300 250 0

6

12 18 24 30 36 42 48 54 60 66 72 78 84

Cathode current density, A/dm2 Fig. 7. Relation curve of microhardness and cathode current density.

3.4. Corrosion resistance Fig. 9 shows the relationship curve of current density and corrosion rate of nickel deposits without additives in 10 wt.% HCl solution and 10 wt.% H2SO4 solution. The corrosion rate rose from 5.2% to 19.2% in HCl solution and from 3.5% to 14.6% in H2SO4 solution with the increase of current density from 3 A/dm 2 to 81 A/dm 2, especially, increasing more sharply when the current densities were less than 15 A/dm 2. The variation trend of corrosion rate may mainly be correlated with the increase of internal stress and hydrogen content in the electrodeposits with increasing current density. Although in the electrolyte vacuum boiling environment mass transportation can be fairly improved and hydrogen is easy to be eliminated, more and more hydrogen may be embedded in the films and a gradual increase in internal stress of electrodeposited layer may occur with the sharp enhancement of the current density, which accordingly resulted in a continuous augmentation in hydrogen brittleness corrosion and stress corrosion. As shown in Fig. 10, the electrodeposited films began to curl and burnt appearance appeared at the current densities of more than 75 A/dm 2. In addition, the reason why there was a quicker increase in corrosion rate at current densities of 3–15 A/dm 2 may be found in the facts that surface roughness of electrodeposited layers prepared at these current densities increased rapidly (see Fig. 11), and bigger surface roughness means larger contact area with corrosive medium, leading to severer penetration corrosion. Although the corrosion rate of nickel film prepared by this vacuum electrodeposition technique at 81 A/dm 2 was up to 19.2% in HCl solution and 14.6%in H2SO4 solution, respectively, its corrosion resistance was still better than that of the nickel films plated at

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(a)

(b)

1μm

(d)

(c)

1μm

(e)

1μm

1μm

(f)

1μm

1μm

Fig. 8. Microstructure of nickel deposits electrodeposited at different cathode current density. (a) 3 A/dm2; (b) 9 A/dm2; (c) 21 A/dm2; (d) 45 A/dm2; (e) 63 A/dm2; (f) 81 A/dm2.

9 A/dm 2 in a normal environment whose corrosion rate was 20.1% and 15.6%. Fig. 9 also showed that, the corrosion rate in HCl solution was notably higher than that in H2SO4 solution. It was majorly due to the different effect of Cl − and SO42− in the corrosive solution on nickel electrodeposits: Cl − has an activation effect on anodic dissolution and can damage the surface passivation film of the deposit [18], causing a higher corrosion rate, but SO42− sometimes plays a certain role of protecting passivation film due to its oxidizability [19,20]. Fig. 12 presents the corrosion rate in 10 wt.% HCl solution and 10 wt.% H2SO4 solution of two nickel deposits prepared at 63 A/dm 2 with and without additives. Morphologies of two kinds of deposit after corrosion were shown in Figs. 13 and 14, respectively. Without any additives, the corrosion rate was 12.9% in HCl solution and 16.4% in H2SO4 solution. With additives, the corrosion rate in HCl

Fig. 9. Relation curve of corrosion rate and cathode current density.

solution and H2SO4 solution decreased to 10.5% and 14.3%, respectively. Since almost no additive elements were detected in the deposits, the reasons for it may be mostly owing to the fact that the additives increased the cathode polarization to a certain extent, therefore resulting in finer grains and a compacter deposit.

Fig. 10. Photos of nickel deposit prepared at high cathode current density. (a) 75 A/dm2; (b) 81 A/dm2.

P. Ming et al. / Surface & Coatings Technology 213 (2012) 299–306

(a)

0.72

Surface roughness,µm

305

0.68

0.64

0.60

1µm

0.56

(b)

0.52 0

8

16

24

32

40

48

56

64

72

80

Cathode current density, A/dm2 Fig. 11. Relation curve of surface roughness and cathode current density.

4. Conclusions

1µm 1) A nickel electrodepositon film with a considerably good surface quality and few electrodeposition defects can be obtained at a high electrodeposition rate of up to 0.307 μm/s under an electrolyte vacuum boiling condition and without additives. 2) The nickel deposits obtained in an electrolyte vacuum boiling environment present different texture, higher microhardness and better corrosion resistance in comparison with those prepared in a normal environment. 3) Cathode current density has a remarkable effect on grain size, preferred orientation, microhardness and corrosion resistance of the deposit prepared without additives, but different range of

(a)

16.4%

Corrosion Rate,r/%

16 12.9%

Fig. 13. Morphology of two nickel deposits after corrosion in 10 wt.% HCl solution: (a) with additive; and (b) without additive.

current density, such from 3 A/dm2 to 9 A/dm2 and from 11 A/dm2 to 81 A/dm2, gives rise to different influencing characteristic. 4) For the electrolyte vacuum boiling electrodeposition technique, sodium dodecyl sulfate additives have no obvious influence on the preferred orientation, microhardness and surface quality, but it helps to improve the corrosion resistance. A further evaluation of some other properties of the electrodeposition layer, for example, hydrogen and oxygen content, and a feasibility study of electroforming high-aspect-ratio microstructures using the new technique are being carried out.

12

(a) 8

4

0

Corrosion Rate,r/%

16

12

with additives

(b)

without additives

1µm

14.3%

(b) 10.5%

8

4

0

with additives

without additives

Fig. 12. Corrosion rate of two nickel deposits in different corrosion mediums. (a) 10 wt.% HCl solution; and (b) 10 wt.% H2SO4 solution.

1µm Fig. 14. Morphology of two nickel deposits after corrosion in 10 wt.% H2SO4 solution: (a) with additive; and (b) without additive.

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Acknowledgment Financial supports from the National Science Foundation of China (no. 51175152) and the Program for Science and Technology Innovation Talents in Universities of Henan Province (no. 2012HASTIT012) are highly appreciated. References [1] M.E. Hyde, R.G. Compton, J. Electroanal. Chem. 531 (2002) 19. [2] C.H. Ning, Y.D. He, Acta Metall. Sin. 44 (2008) 75l (in Chinese). [3] G.Y. Qiao, T.F. Jing, M. Gao, Y. Wang, Y.W. Gao, D.S. Han, Trans. Mater. Heat Treat. 25 (2004) 61 (in Chinese). [4] O. Devos, A. Olivier, J.P. Chopart, J. Electrochem. Soc. 145 (1998) 401. [5] T.H. Tsai, H. Yang, R. Chein, Microsyst. Technol. 10 (2004) 351. [6] S.E. Nam, S.H. Lee, K.H. Lee, J. Membr. Sci. 153 (1999) 163.

[7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20]

S.E. Nam, Y.K. Seong, J.W. Lee, K.H. Lee, Desalination 236 (2009) 51. S.T. Chung, W.T. Tsai, Thin Solid Films 518 (2010) 7236. T. Liu, Z.C. Guo, Z. Wang, M.Y. Wang, Chin. J. Nonferrous Met. 18 (2008) 1858. X.P. Ye, M. De Bonte, J.P. Celis, J.R. Roos, J. Electrochem. Soc. 139 (1992) 592. N.A. Pangaros, J. Electroanal. Chem. 9 (1965) 70. Z.J. Tian, D.S. Wang, G.F. Wang, L.D. Shen, Z.D. Liu, Y.H. Huang, Trans. Nonferrous Met. Soc. 20 (2010) 1037. Z.W. Zhu, D. Zhu, N.S. Qu, Sci. China Ser. E 51 (2008) 911. S.W. Banovic, K. Barmak, A.R. Marder, J. Mater. Sci. 33 (1998) 639. R.J. Kendrick, Trans. Inst. Met. Finish. 42 (1966) 235. A.M. Sherik, U. Erb, J. Mater. Sci. 30 (1995) 5743. N.S. Qu, D. Zhu, K.C. Chan, W.N. Lei, Surf. Coat. Technol. 168 (2003) 123. F.L. Sun, G.Z. Meng, T. Zhang, Y.W. Shao, F.H. Wang, C.F. Dong, X.G. Li, Electrochim. Acta 54 (2009) 1578. W.F. Zhang, D. Zhu, Corros. Sci. Prot. Technol. 18 (2006) 325 (in Chinese). A. Emad, A.E. Meguid, T. Oki, Mater. Trans. 36 (1995) 659.