ARTICLE IN PRESS

0022-3697/$ - se

doi:10.1016/j.jp

�CorrespondiE-mail addre

Journal of Physics and Chemistry of Solids 69 (2008) 1391–1394

www.elsevier.com/locate/jpcs

Electrodeposition and mechanical properties of Ni–carbon nanotubenanocomposite coatings

Y.S. Jeona, J.Y. Byunb, T.S. Oha,�

aDepartment of Materials Science and Engineering, Hongik University, Seoul 121-791, Republic of KoreabCenter for Metals Processing, Korea Institute of Science and Technology, Seoul 158-791, Republic of Korea

Received 30 June 2007; received in revised form 3 October 2007; accepted 30 October 2007

Abstract

Electrodeposition behavior and mechanical properties of Ni–carbon nanotube (Ni–CNT) nanocomposites were examined with

variations of dispersion additive and the content of multiwalled carbon nanotubes (MWCNTs) in the nanocomposites. Incorporation of

MWCNTs into Ni matrix was greatly enhanced by using sodium dodecyl sulfate–hydroxypropylcellulose mixture as dispersion additive.

With increasing the MWCNT content of the Ni–CNT composite to 14.6 vol%, a fracture stress of the Ni–CNT/Cu bi-layer film was

improved from 607 to 780MPa, showing that strengthening can be achieved for the Ni–CNT nanocomposite by incorporating

MWCNTs into Ni matrix.

r 2007 Elsevier Ltd. All rights reserved.

Keywords: A. Nanostructures; B. Chemical synthesis; C. Electron microscopy; D. Microstructure

1. Introduction

Nanocomposite coatings, where nano-sized ceramicparticles are incorporated into metal matrix, have beenwidely investigated for various applications such as wear-resistant and tribological coatings [1–3]. Among variousprocess technologies for nanocomposites, electrodepositionhas advantages such as cost-effectiveness relative to sprayand sputtering processes [4]. Conventionally, nanopowderssuch as alumina, silicon carbide, and diamond were used asreinforcements for Ni-based nanocomposite coatings [1,3].Recently, carbon nanotube (CNT) has been applied as anew reinforcement material for nanocomposite coatingsdue to its excellent mechanical properties and high thermalconductivity [4–7]. As Ni exhibits high wear resistance,good ductility, and ferromagnetism, Ni–CNT compositecoatings have potential applications for wear-resistancecoatings and MEMS structures [4–7].

Property enhancement of a nanocomposite with embed-ding CNTs depends on the dispersion characteristics aswell as the volume fraction of CNTs in a nanocomposite

e front matter r 2007 Elsevier Ltd. All rights reserved.

cs.2007.10.049

ng author. Tel.: +822 320 1655; fax: +82 2 333 0127.

ss: ohts@hongik.ac.kr (T.S. Oh).

[6,7]. In this study, Ni–CNT nanocomposites were pro-cessed by electrodeposition and the intercalation behaviorof multiwalled carbon nanotubes (MWCNTs) into Nimatrix was investigated with different electrodepositionadditives such as sodium dodecyl sulfate (SDS) andhydroxypropylcellulose (HPC). Electrodeposition behaviorand fracture stress of the Ni–CNT nanocomposites werealso examined as a function of the MWCNT content in thenanocomposites.

2. Experimental procedure

Ni–CNT nanocomposite coatings were electrodepositedin a sulfate Watts bath of the following composition:260 g/L nickel sulfate (NiSO4 � 6H2O), 45 g/L nickel chloride(NiCl2 � 6H2O), 15 g/L boric acid (H3BO3), and 0.5 g/Lsaccharine. To improve MWCNT dispersion, SDS andHPC were added into the electrodeposition solutions byvarying the amounts of SDS and HPC from 0 to 10 g/L.The total amount of SDS and HPC was always kept as10 g/L. MWCNTs of 10–15 nm diameter, produced byCVD, were used to form the Ni–CNT electrodepositionsolutions. As the length of the as-received MWCNTs, about

ARTICLE IN PRESSY.S. Jeon et al. / Journal of Physics and Chemistry of Solids 69 (2008) 1391–13941392

20mm, was too long for coelectrodeposition, MWCNTswere cut to a length less than 5mm by ball-milling with ZrO2

balls for 24 h at 200 rpm. The weight ratio of MWCNT-to-ZrO2 was kept as 1:25 in an alumina jar.

After producing the Ni–CNT electrodeposition solutionswith MWCNT contents of 0, 1, 2, 5, 10 g/L, Ni–CNTnanocomposites of 50 mm thickness were electrodepositedon Cu substrates of 2 cm� 2 cm size at a current density of40mA/cm2. During electrodeposition of a Ni–CNT nano-composite, the bath was maintained at 40 1C withmechanical stirring at 500 rpm. To evaluate fracture stress,Ni–CNT nanocomposites of 50 mm thickness were electro-deposited on 20 mm-thick Cu films laminated onto 30 mm-thick polyimide (PI) films of 1 cm� 3 cm size. Afterelectrodepositing Ni–CNT nanocomposites, PI films werepeeled off and tensile tests were conducted for theNi–CNT/Cu bi-layer specimens.

1�m

1�m

Fig. 1. FESEM micrographs of the Ni–CNT nanocomposite electrodeposited

and 2.5 g/L HPC, (c) 5 g/L SDS and 5 g/L HPC, (d) 2.5 g/L SDS and 7.5 g/L

Morphologies of the Ni–CNT composites were observed byusing field emission scanning electron microscopy (FESEM).The content of MWCNTs in the Ni–CNT composites wascharacterized with a carbon/sulfur analyzer (ELTRA CS800).

3. Results and discussion

Fig. 1 illustrates surface morphologies of the Ni–CNTnanocomposites electrodeposited in solutions with differ-ent amounts of SDS and HPC as dispersion additives. TheMWCNT concentration of the electrodeposition solutionswas maintained as 10 g/L and the total amount of SDS andHPC was also kept as 10 g/L. Comparing Fig. 1(a) withFig. 1(e) indicates that SDS is more effective for MWCNTdispersion than HPC. As shown in Fig. 1(b) and (c),however, incorporation of MWCNTs into Ni matrix wasgreatly enhanced by using SDS–HPC mixture with the

1�m

1�m

1�m

in a bath containing dispersion additive of (a) 10 g/L SDS, (b) 7.5 g/L SDS

HPC, and (e) 10 g/L HPC.

ARTICLE IN PRESS

0 4 8 10

0

5

10

15

20

25

CN

T c

onte

nt (

vol%

)

CNT concentration (g/l)

2 6

Fig. 3. The MWCNT content (vol%) of the Ni–CNT nanocomposite as a

function of the MWCNT concentration (g/L) in the bath.

Y.S. Jeon et al. / Journal of Physics and Chemistry of Solids 69 (2008) 1391–1394 1393

SDS–HPC weight ratios of 3:1 and 1:1. Such SDS–HPCmixture might modify the surface chemistry of MWCNTsmore suitable for uniform dispersion in the electrolyticbath, resulting in great increase in the MWCNT content ofthe Ni–CNT nanocomposite. SDS–HPC mixture additiveaffected not only the MWCNT dispersion characteristicsbut also the properties of Ni matrix itself. While thehardness of a Ni coating electrodeposited withoutMWCNTs in a Watt bath containing SDS of 10 g/Lwas 430Hv, the value of one processed in a solutionwith the SDS–HPC mixture of the 3:1 weight ratioincreased to 527Hv.

Fig. 2 shows SEM micrographs of the Ni–CNTnanocomposites processed in the electrodeposition solu-tions with the MWCNT concentrations of 0–10 g/L andthe 10 g/L SDS–HPC mixture of the weight ratio of 3:1.The Ni–CNT nanocomposites were etched in nitric acidto remove the surface layer for observation of the internalmorphology. With increasing the MWCNT concentrationin the electrodeposition bath up to 5 g/L, more MWCNTswere incorporated into Ni matrix. However, microstruc-ture of the Ni–CNT composite became porous withincreasing the MWCNT concentration in the bathbeyond 2 g/L.

Using the weight fractions of the MWCNTs measuredfor the Ni–CNT composites electrodeposited with differentMWCNT concentrations, volume percentages ofMWCNTs in the nanocomposites were evaluated andplotted in Fig. 3, as a function of the MWCNTconcentration of the electrodeposition bath. To convertthe weight fraction of the MWCNTs in the composite to

1 �m

1 �m

Fig. 2. FESEM micrographs of the Ni–CNT nanocomposite electrodeposited

5 g/L, and (d) 10 g/L.

volume fraction, the following relation was used withvalues of 8.91 and 0.05 g/cm3 as the density of Ni and thebulk density of MWCNT, respectively [8]; volume frac-tion of MWCNTs ¼ dCNT�wCNT/[dNi�wCNT+dCNT�

1 �m

1 �m

in a bath containing an MWCNT concentration of (a) 1 g/L, (b) 2 g/L, (c)

ARTICLE IN PRESS

0 5 10 15 20 25

400

500

600

700

800

900

Frac

ture

str

ess

(MPa

)

CNT content (vol%)

Fig. 4. Fracture stress of the Ni–CNT/Cu bi-layer film as a function of the

MWCNT content in the Ni–CNT nanocomposite.

Y.S. Jeon et al. / Journal of Physics and Chemistry of Solids 69 (2008) 1391–13941394

(1�wCNT)], where dCNT and dNi are densities of MWCNTand Ni, respectively, and wCNT is weight fraction ofMWCNTs. The MWCNT content in the Ni–CNTnanocomposite became larger and reached a maximum of22.5 vol% with increasing the MWCNT concentration inthe bath up to 5 g/L. However, the MWCNT content in thecomposite decreased with further increasing the MWCNTconcentration in the bath beyond 5 g/L, which could be dueto the agglomeration of MWCNTs in the bath containingMWCNTs above the saturation concentration [4]. As theMWCNT content decreased and the microstructurebecame substantially porous for the nanocompositeprocessed in the bath containing MWCNTs of 10 g/L,mechanical characterization was not conducted for thisspecimen.

Fracture stress required to break the Ni–CNT/Cu bi-layerfilm, fabricated by peeling off a PI film after electrodeposit-ing the Ni–CNT onto a Cu/PI, is illustrated in Fig. 4.Thicknesses of the Ni–CNT composite and the Cu were 50and 20mm, respectively. With increasing the MWCNTcontent of the Ni–CNT composite to 14.6 vol%, the fracturestress was improved from 607 to 780MPa. However,the fracture stress dropped drastically to 534MPa forthe specimen with the MWCNT content of 22.5 vol% asfabricated in the bath of the MWCNT concentration of5 g/L. This might be due to the porous microstructure ofthe nanocomposite with MWCNT content of 22.5 vol%,as shown in Fig. 2(d). Microstructural analysis using

transmission electron microscopy is going on to understandwell the phenomenon of the drastic fracture–stress drop forthe specimen with the MWCNT content of 22.5 vol%.While various reports are available for hardness increase inNi–CNT nanocomposites [6,7,9], very few works can befound for strength increment of metal–matrix compositesreinforced by MWCNTs [10]. Although we measured thefracture stress of the Ni–CNT/Cu bi-layer specimen insteadof the Ni–CNT itself, our result shown in Fig. 4 would be auseful indication that strength improvement can be achievedfor the Ni–CNT composite by incorporating MWCNTs intoNi matrix.

4. Conclusions

For electrodeposition of the Ni–CNT nanocomposite,incorporation of MWCNTs into Ni matrix was greatlyenhanced by using SDS–HPC mixture instead of SDS asdispersion additive. The MWCNT content in the Ni–CNTnanocomposite increased, reached a maximum of22.5 vol% with increasing the MWCNT concentration inthe bath up to 5 g/L, and then decreased with furtherincreasing the MWCNT concentration in the bath due tothe agglomeration of MWCNTs in the bath. Withincreasing the MWCNT content of the Ni–CNT compositeto 14.6 vol%, fracture stress of the Ni–CNT/Cu bi-layerwas improved from 607 to 780MPa, showing thatstrengthening can be achieved for the Ni–CNT compositeby incorporating MWCNTs into Ni matrix.

Acknowledgment

This work was supported by the Center forElectronic Packaging Materials of Korea Science Engineer-ing Foundation.

References

[1] A.F. Zimmermann, G. Palumbo, K.T. Aust, U. Erb, Mater. Sci. Eng.

A 328 (2002) 137.

[2] Y.H. Choa, J.K. Yang, B.H. Kim, Y.K. Jeong, J.S. Lee,

T. Nakayama, T. Sekino, N. Kiihara, J. Magn. Mater. 266 (2003) 12.

[3] C.X. Changrong, X. Guo, F. Li, D. Peng, G. Peng, Colloids Surf.,

A: Physicochem. Eng. Aspects 179 (2001) 229.

[4] X.H. Chen, F.Q. Cheng, S.L. Li, L.P. Zhou, D.Y. Li, Surf. Coat.

Technol. 155 (2002) 274.

[5] G.R. Shen, Y.T. Cheng, L.N. Tsai, IEEE Trans. Nanotechnol. 4

(2005) 539.

[6] X. Chen, G. Zhang, C. Chen, L. Zhou, S. Li, X. Li, Adv. Eng. Mater.

5 (2003) 514.

[7] X.H. Chen, C.S. Chen, H.N. Xiao, H.B. Liu, L.P. Zhou, S.L. Li,

G. Zhang, Tribol. Int. 39 (2006) 22.

[8] L.N. Tsai, Y.T. Cheng, W. Hsu, W. Fang, J. Vac. Sci. Technol. B 24

(2006) 205.

[9] J. Tan, T. Yu, B. Xu, Q. Yao, Tribol. Lett. 21 (2006) 107.

[10] S.I. Cha, K.T. Kim, S.N. Arshad, C.B. Mo, S.H. Hong, Adv. Mater.

17 (2005) 1377.