Surface & Coatings Technology 212 (2012) 207–213

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Surface & Coatings Technology

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Fabrication of metal coated carbon nanotubes by electroless deposition for improvedwettability with molten aluminum

Susumu Arai a,⁎, Yosuke Suzuki a, Junshi Nakagawa a, Tohru Yamamoto a, Morinobu Endo b

a Department of Chemistry and Material Engineering, Faculty of Engineering, Shinshu University, Nagano 380-8553, Japanb Department of Electrical and Electronic Engineering, Faculty of Engineering, Shinshu University, Nagano 380-8553, Japan

⁎ Corresponding author. Tel.: +81 26 269 5413; fax:E-mail address: araisun@shinshu-u.ac.jp (S. Arai).

0257-8972/$ – see front matter © 2012 Elsevier B.V. Allhttp://dx.doi.org/10.1016/j.surfcoat.2012.09.051

a b s t r a c t

a r t i c l e i n f o

Article history:Received 24 October 2011Accepted in revised form 27 September 2012Available online 5 October 2012

Keywords:Multiwalled carbon nanotubeElectroless depositionWettabilityNi–P alloyAu/Ni–P double-coatingAluminum

Ni–P alloy coated and Au/Ni–P alloy double-coated multiwalled carbon nanotubes (MWCNTs) were fabricat-ed using electroless plating. Three types of electroless Ni–P alloy plating baths were prepared to coat theMWCNTs with Ni–P alloy films of varying phosphorus content. Electroless gold coating of the Ni–P alloy coat-ed MWCNTs was also carried out using a non-cyanide bath. The microstructures of the coatings on theMWCNTs were examined by scanning electron microscopy and X-ray diffraction. The wettability of themetal-coated MWCNTs with molten aluminum was also evaluated. MWCNTs coated with Ni–P alloy filmscontaining 9–25 at.% phosphorus content were fabricated by electroless deposition. Electroless gold deposi-tion on the Ni–P alloy coated MWCNTs to form Au/Ni–P alloy double-coated MWCNTs was also possible. Thewettability of the metal-coated MWCNTs with molten aluminum was significantly improved compared tothat of non-coated MWCNTs. The coating metals of the MWCNTs dissolved into the molten aluminum,resulting in good wettability between the MWCNTs and molten aluminum and dispersion of the resultingbare MWCNTs in the aluminum matrix. The dissolved coating metals formed stable compounds with moltenaluminum.

© 2012 Elsevier B.V. All rights reserved.

Table 1Bath compositions for electroless Ni–P alloy plating.

Chemicals Low-phosphorus Moderate-phosphorus High-phosphorus

NiSO4·6H2O (M) 0.1 0.1 0.1NaH PO ·H O (M) 0.2 0.2 0.2

1. Introduction

Carbon nanotubes (CNTs) [1,2] exhibit excellent mechanicalcharacteristics (including high tensile strength and a high elasticmodulus) and have high thermal conductivity. Consequently, CNTcomposites such as metal-CNT composites are expected to havehigh strength and high thermal conductivity. However, CNTs havepoor wettability with molten metals such as aluminum. Applying ametal coating to CNTs is one of the most effective methods of improv-ing their wettability with molten metals. Metal coating or depositioncan impart various beneficial properties to CNTs, such as a high meandensity, magnetic properties, and catalytic properties. A high meandensity of metal coated CNTs can prevent the CNTs from becomingtoo easily airborne. CNTs coated with ferromagnetic metals can becontrollably moved by magnetic fields, which may lead to CNT com-posites with highly controlled micro-textures [3]. CNTs depositedwith catalytic metal particles may provide superior catalysts, withapplications such as improved fuel cell electrodes [4]. Electrolessdeposition is a very effective and practical method of uniformly coat-ing small powdery materials with metals [5–8]. Several investigationsof the metal coating of CNTs by electroless deposition have been

+81 26 269 5432.

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reported [9–14]. We have also reported that it is possible to coatCNTs with pure nickel [15], Ni–P alloy [16,17], Ni–B alloy [18], andcopper [19] by electroless deposition. These metal-coated CNTs pre-pared by electroless deposition should improve the wettability ofCNTs by molten metals. However, there have been very few reportson the effectiveness of the metal coating of CNTs in improving theirwettability with molten metals. An experimental evaluation of thewettability of metal-coated CNTs by molten metals was required.

In the present study, Ni–P alloy coated CNTs and Au/Ni–Palloy double-coated CNTs fabricated by electroless gold depositionon Ni–P alloy coated CNTs were prepared by electroless deposition,and their wettability with molten aluminum was evaluated.

2 2 2

C6H5Na3O7 (M) 0.2 0.5 0.35(NH4)2SO4 (M) 0.5 0.5 0.5Stearyl trimethylammoniumchloride (M)

1×10−5 1×10−5 1×10−5

Table 2Bath composition for electroless gold plating.

Chemicals Conc. (M)

NaAuCl4 0.01Na2SO3 0.32Na2S2O3·5H2O 0.01Na2HPO4 0.32

208 S. Arai et al. / Surface & Coatings Technology 212 (2012) 207–213

2. Experimental

2.1. Preparation of metal-coated CNTs

The CNTs used in the present study were commercially availablevapor-grown multiwalled carbon nanotubes (MWCNTs: Showa DenkoCo. Ltd.), formed via catalyst-assisted chemical vapor deposition andheat treated at 2800 °C in argon gas for 30 min. TheMWCNTswere typ-ically 150 nm in diameter and 10 μm in length. Before electroless Ni–Palloy deposition, pre-treatment of theMWCNTs was carried out using acommon two-step method (sensitization and activation). Because theMWCNTs were hydrophobic, 0.05 g of MWCNTs was initially dispersedin a 2×10−5 M polyacrylic acid (mean molecular weight of 5000:PA-5000) aqueous solution (0.05 dm3) with stirrer agitation and ultra-sonic irradiation. By this treatment, the PA-5000 dispersants adsorbedonto the MWCNTs, making them hydrophilic. After the dispersionprocess, the MWCNTs were filtrated and rinsed, then immersed in a4.4×10−2 M SnCl2·2H2O+0.12 M HCl solution (0.1 dm3) at 25 °Cwith agitation (ultrasonic irradiation: 1 min, stirrer agitation: 5 min)to adsorb Sn2+ ions on the MWCNTs (sensitization). After the filtra-tion and rinse, the MWCNTs were immersed in a 5.6×10−4 M

500 nm

(a)

500 nm

(c)

Fig. 1. SEM images of Ni–P alloy coatedMWCNTs formed from various electroless deposition babath, and (d) high-phosphorus bath.

PdCl2+0.12 M HCl solution (0.1 dm3) at 25 °C with agitation(ultrasonic irradiation: 1 min, stirrer agitation: 5 min) to formpalladium catalytic nuclei on the MWCNTs (activation). The elec-troless Ni–P alloy composite plating bath compositions used areshown in Table 1. Three different baths were prepared in order toform Ni–P alloy films with different phosphorus contents. Sodiumhypophosphite and sodium citrate were used as a reducing agentand a complexing agent, respectively. In order to homogeneouslydisperse the metal-coated MWCNTs in the plating baths, a stearyltrimethyl ammonium chloride dispersant was added to the platingbaths. The pH of the low-phosphorus and medium-phosphorusbaths was adjusted to 9. The pH of the high-phosphorus bathwas adjusted to 7. Electroless plating was carried out at 30 °Cfor the low- and medium-phosphorus baths and at 80 °C forthe high-phosphorus bath with stirrer agitation. The volume of allelectroless Ni–P alloy plating baths was 0.5 dm3. The resultingNi–P alloy coated MWCNTs were filtrated and rinsed. To fabricateAu/Ni–P alloy double-coated MWCNTs, the Ni–P alloy coated MWCNTswere placed in a non-cyanide electroless gold plating bath, which wascalled a substrate (Ni)-catalyzed electroless gold deposition bath [20].The bath composition used in this study is shown in Table 2. This bathcontained a sulfite and a thiosulfate as complexing agents for goldions, and the thiosulfate was considered to be the main complexingagent [20,21]. The sulfite acted as a reducing agent for gold ions onthe nickel (nickel alloy) substrate surface, but not on the gold surface[20,22]. The bath pH was adjusted to 9. The volume of the bath was0.5 dm3. Electroless gold depositionwas performed at 60 °Cwith stirreragitation. All chemicals usedwere regent grade, and purewater from anelectrodialysis water purifier (RFP343RA, Advantec MFS, Inc.) was usedin all experiments.

500 nm

(d)

500 nm

(b)

ths: (a) before electroless deposition, (b) low-phosphorus bath, (c)moderate-phosphorus

20 30 40 50 60

2θ / degree

Inte

nsity

/ ar

b. u

nit

Ni

MWCNTs

(a)

(b)

(c)

(d)

Fig. 2. XRD patterns of Ni–P alloy coated MWCNTs: (a) Ni–9 at.% P alloy coatedMWCNTs, (b) Ni–14 at.% P alloy coated MWCNTs, (c) Ni–25 at.% P alloy coatedMWCNTs, and (d) non-coated MWCNTs.

Au particles

(a)

500 nm

MWCNT

Ni−P alloy coating

Au coating

(b)

500 nm

Fig. 4. Cross-sectional SEM images of gold deposits on Ni–9 at.% P alloy coatedMWCNTs at different reaction times: (a) 10 min and (b) 20 min.

209S. Arai et al. / Surface & Coatings Technology 212 (2012) 207–213

2.2. Characterization of the metal-coated MWCNTs

The microstructures of the deposits were examined using field-emission scanning electron microscopy (FE-SEM, JEOL JSM-7000F)and by X-ray diffraction (XRD, Shimadzu Seisakusho XRD-6000).The phosphorus content of the Ni–P alloy coatings was measured

20 30 40 50 60 70 80

2θ / degree

Inte

nsity

/ ar

b. u

nit

Ni (a)

(b)

(c)

Au

MWCNTs

Fig. 3. XRD patterns of Ni–P alloy coated MWCNTs after electroless gold deposition atvarious reaction times: (a) before electroless gold deposition, (b) 10 min, and (c) 20 min.

using electron probe X-ray microanalysis (EPMA, Shimadzu Co.EPMA-1610). A specialized sample preparation system (Cross-sectionpolisher, JEOL SM-09010) was used to prepare cross-sectional sam-ples for FE-SEM observation.

2.3. Wettability of the metal-coated MWCNTs with molten aluminum

In the present study, pure aluminum (JIS H4160 A1N30) was used.The metal-coated MWCNTs were placed between a pure aluminumpan and a lid of the type generally used for thermal analysis, and thenthe pad/lid containing themetal-coatedMWCNTs was pressed by an ex-clusive presser (Shimadzu Co. Model MHP-1), to form a wettability testsample. The weight of the pan/lid was around 20 mg, and that of themetal-coated MWCNTs was around 2 mg. A wettability test was carriedout by analyzing cross sections of the test samples after heat treatment.The test samplewas placed in a carbon container, and the heat treatmentwas performed using an infrared heating furnace (ULVAC TechnologiesMila-3000) in vacuum at 700 °C for 7.5 min. Because the melting pointof the aluminum is 660 °C, the pressed aluminum pan/lid melted andcame into contact with the metal-coated MWCNTs as molten aluminumduring the heat treatment. After the heat treatment, cross sections of thetest samples were analyzed by SEM and EPMA.

3. Results and discussion

Fig. 1 shows SEM images of Ni–P alloy coated MWCNTs. The reac-tion time was 15 min. Fig. 1a shows the MWCNTs before the Ni–P

1 μm

(a)

(b)

MWCNTs

MWCNTs

Aluminum

Aluminum

1 μm

Fig. 5. Cross-sectional SEM images of wettability test samples after heat treatmentusing (a) non-coated MWCNTs and (b) Ni–9 at.% P alloy coated MWCNTs.

210 S. Arai et al. / Surface & Coatings Technology 212 (2012) 207–213

alloy coating was applied. Fig. 1b, c, and d is SEM images of Ni–P alloycoated MWCNTs using bath 1, bath 2, and bath 3, respectively. EPMAquantitative analysis indicated that the three coatings had phospho-rus contents of 9, 14, and 25 at.%, respectively. Therefore, threekinds of Ni–P alloy coatings containing different phosphorus contentswere formed on the MWCNTs by the electroless deposition technique.The thicknesses of the Ni–9 at.% P alloy, Ni–14 at.% P alloy, and Ni–25 at.% P alloy films were approximately 150–200 nm, 150 nm, and50 nm, respectively. The thicknesses of these coatings were controlla-ble by changing the reaction time. The low and moderate phosphoruscontents of Ni–P alloy coatings (Ni–9 at.% P and Ni–14 at.% P) wererelatively uniform, whereas the high phosphorus content coatingswere comparatively non-uniform.

Fig. 2 shows XRD patterns of the Ni–P alloy coated MWCNTsshown in Fig. 1. The bottom XRD pattern is that of the MWCNTsbefore Ni–P alloy coating (Fig. 2d). A strong peak assigned to theMWCNT (002) plane was observed at 26.4°. A broad peak assignedto the face-centered-cubic nickel (111) plane was visible for eachXRD pattern around 44° in addition to the MWCNT peak (Fig. 2a–c).The sharpness of the peak assigned to the face-centered-cubic nickel(111) plane decreased with increasing phosphorus content of the Ni–P alloy coating. Therefore, three Ni–P coatings with different phos-phorus contents and different crystallinities were fabricated on theMWCNTs.

The Ni–P alloy coated MWCNTs were then coated with gold byelectroless deposition using a thiosulfate–sulfite bath. Although golddeposition was possible on all three types of Ni–P alloy coated

MWCNTs, the uniformity of the coatings decreased with increasingphosphorus content of the Ni–P alloy films. Since the electrolessgold plating bath used in this study was a substrate (Ni)-catalyzedbath, the catalytic properties of the Ni–P alloy film might worsenwith increasing phosphorus content of the Ni–P alloy film, or inother words, with decreasing nickel content of the Ni–P alloy film.Therefore, the reduction of the nickel content might decrease the uni-formity of the gold coatings. Furthermore, in general, the phase struc-ture of electroless Ni–P alloy plating films changed with increasingphosphorus content from a crystalline structure of face-centered-cubic nickel containing a small amount of phosphorus in solid solu-tion to an amorphous structure. As shown in Fig. 2, the crystallinityof the electroless Ni–P alloy plating films on CNTs became lower;that is, the phase structure of the Ni–P alloy plating films becamemore amorphous-like, with increasing phosphorus content of thefilms. This phase structure change of the Ni–P alloy films could affectthe uniformity of the gold coating. Therefore, in the present study,low-phosphorus-content Ni–P alloy (Ni–9 at.% P alloy) coatedMWCNTs were used for the fabrication of Au/Ni–P alloy double-coated MWCNTs.

Fig. 3 shows XRD patterns of the resulting Au/Ni–P alloy double-coated MWCNTs at various reaction times. Compared to the XRDpattern of the Ni–P alloy coated MWCNTs (Fig. 3a: reaction time was0 min), sharp peaks assigned to face-centered-cubic gold were visibleat 38.1, 44.5, 64.6, and 77.6° in addition to the peaks assigned to theMWCNTs (26.4°) and the face-centered-cubic nickel of the Ni–9 at.% Palloy (around 44°) (Fig. 3b: reaction time was 10 min and Fig. 3c: reac-tion time was 20 min). Therefore, gold was successfully deposited onthe Ni–P alloy coated MWCNTs. The intensity of the peaks assigned togold increasedwith increasing reaction time (Fig. 3b and c), but saturat-ed after 20 min. Kato et al. reported that electroless gold deposition onan Ni–B alloy film substrate advanced primarily by a substrate(Ni)-catalyzed electroless gold deposition mechanism, with a minor contri-bution from a galvanic displacement reaction in the thiosulfate–sulfitebath [20]. Sato et al. reported that electroless gold films could also beproduced on electroless Ni–P alloy film substrates using a thiosulfate–sulfite bath [22]. In the present study, the electroless gold depositionon the Ni–P alloy coatings of the MWCNTs probably occurred via thesame mechanism.

Fig. 4 shows cross-sectional SEM images (composition mode) ofgold coatings on Ni–P alloy coated MWCNTs at different reactiontimes. White, gray, and black regions in the SEM images representareas of deposited gold, Ni–9 at.% P alloy coating, and MWCNTs, re-spectively. At 10 min, the gold deposited as particles, and the Ni–Palloy coatings were not uniformly coated with gold (Fig. 4a). At20 min, the Ni–P coating was uniformly coated with deposited gold,which was approximately 50 nm thick (Fig. 4b). There were no gapsbetween the gold coating and the Ni–P alloy coating, or betweenthe Ni–P alloy coating and the MWCNT. Furthermore, no voids werevisible in the cross section of the Au/Ni–P alloy coated MWCNT.Therefore, a defect-free Au/Ni–P alloy double-coating was formedon the MWCNTs. After 20 min, the thickness of the gold films didnot continue to increase. This is consistent with the XRD results(Fig. 3). As described above, the sulfite acts as a reducing agent forgold ions on nickel in the thiosulfate–sulfate bath [18]. Therefore,once the Ni–P coatings were completely covered with depositedgold, the gold coatings did not continue to grow. These results areconsistent with Sato's report describing electroless gold depositionbehavior on Ni–P alloy substrates using a thiosulfate–sulfite bath [22].

Ni–9 at.% P alloy coated MWCNTs and Au/Ni–9 at.% P alloydouble-coated MWCNTs were tested for wettability with molten alu-minum. Fig. 5a shows a cross-sectional SEM image of a wettabilitytest sample of non-coated MWCNTs after heat treatment. TheMWCNTs were not wet by the aluminum matrix at all, and theMWCNT layer remained in the aluminum matrix. Fig. 5b shows across-sectional SEM image (composition mode) of a wettability test

10 μm

SEM

Ni

CAl

10 μm 10 μm

10 μm

P

10 μm

O

10 μm

Fig. 6. EPMA elemental mapping of the cross section of a wettability test sample of Ni–9 at.% P alloy coated MWCNTs after heat treatment.

211S. Arai et al. / Surface & Coatings Technology 212 (2012) 207–213

sample of Ni–P alloy coated MWCNTs after heat treatment. The thick-ness of the coating was approximately 200 nm. The black areas indi-cate cross sections of the MWCNTs, and the gray matrix area isaluminum. The MWCNT layer observed in Fig. 5a disappeared, andthe MWCNTs dispersed individually throughout the aluminum ma-trix. There were no gaps between the MWCNTs and the aluminummatrix. Therefore, the Ni–P alloy coated MWCNTs were well-wettedby the molten aluminum. White and dark gray areas were also seenin Fig. 5b and the compositions of these areas were unknown. Inorder to clarify the microstructure of the wettability test samplesafter heat treatment, EPMA mapping analysis was performed.

Fig. 6 shows EPMA elemental mapping of the cross sections ofwettability test samples of Ni–P alloy coated MWCNTs after heattreatment. The gray matrix area in the SEM image (back-scatteringimage) was aluminum. The black areas correspond to carbon, indicat-ing that the MWCNTs were homogeneously distributed in the matrix.

Ni

Ni

P

P

Molten aluminum matrix (a)

Fig. 7. A schematic of thewetting process between Ni–P alloy coatedMWCNTs andmolten alummolten aluminum during heat treatment, (b) formation of stable compounds such as Ni–Al in

The white areas correspond to nickel. The dark gray areas correspondto phosphorus and oxygen. Since the distributions of carbon, nickel,and phosphorus were different, the MWCNTs were not coated withNi–P alloy films after heat treatment, but bare MWCNTs were distrib-uted throughout the matrix. The phosphorus in the Ni–P alloy coat-ings was believed to form phosphoric oxides such as P2O5 after heattreatment. The nickel in the Ni–P alloy coatings probably formed anAl–Ni intermetallic compound according to the Al–Ni binary alloyphase diagram [23].

Fig. 7 shows a schematic of the reaction between Ni–P alloy coatedMWCNTs and molten aluminum. During the heat treatment, the Ni–Palloy coating (that consists of nickel and phosphorus) completelydissolved into the molten aluminum, resulting in a good wettabilitybetween the molten aluminum, resulting in a good wettability be-tween the molten aluminum and the Ni–P alloy coated MWCNTs(Fig. 7a). Consequently, the MWCNTs dispersed individually into the

AlxNiy

Aluminum matrix

PxOy

AlxNiy

AlxNiy

PxOy

Px Oy

(b)

inum: (a) dissolution of the Ni–P alloy coating (consisting of nickel and phosphorus) intotermetallic compound (NixAly) and phosphorus oxide (PxOy) during coagulation.

10 μm

SEM

P O

NiCAl

10 μm 10 μm

Au

10 μm

10 μm10 μm10 μm

Fig. 8. EPMA elemental mapping of the cross-sectional sample after wettability testing between Au/Ni–9 at.% P alloy double-coated MWCNTs and molten aluminum.

212 S. Arai et al. / Surface & Coatings Technology 212 (2012) 207–213

molten aluminum matrix. During coagulation, the dissolved nickeland phosphorus formed a stable Al–Ni intermetallic compound anda phosphoric oxide in the aluminum matrix, respectively (Fig. 7b).

Fig. 8 shows the EPMA mapping analysis of a cross section of awettability test sample of Au/Ni–9 at.% P alloy double-coatedMWCNTs.The thicknesses of the Ni–P alloy coating and the gold coating wereapproximately 150 μm and 50 nm, respectively. The distributions ofaluminum, carbon, nickel, phosphorus, and oxygen were similar tothose of the Ni–P alloy coated MWCNTs shown in Fig. 6. Bare MWCNTswere distributed across thematrix. Gold was also distributed across thematrix. The gold and some parts of the nickel distributionswere similar.Gold and nickel form all proportional solid solution alloys [23]. Goldalso forms several stable intermetallic compounds with aluminum,depending on the alloy composition [23]. Although gold may formternary alloys such as Al–Au–Ni alloys, the exact composition andmicrostructure of the gold compound were unclear, as we are unawareof any information on the Al–Au–Ni ternary alloy phase diagram. Re-gardless, the Au/Ni–P alloy double-coated MWCNTs were well-wettedwith molten aluminum.

Ni

P

Molten alu

Au

Au

Au

Au

Molten aluminum matrix (a) (b)

Fig. 9. Schematic of the wetting process between Au/Ni–P alloy double-coated MWCNTs anheat treatment, (b) dissolution of the Ni–P alloy coating (consisting of nickel and phosphocompounds such as Au–Al intermetallic compound (AuxAly), Au–Ni solid solution (Aucoagulation.

Fig. 9 shows a schematic of the reaction between the Au/Ni–P alloydouble-coated MWCNTs and molten aluminum. During heat treat-ment, the gold coating first dissolved into the molten aluminum(Fig. 9a), and then the Ni–P alloy films (consisting of nickel and phos-phorus) also dissolved into the molten aluminum (Fig. 9b), resultingin a good wettability between the MWCNTs and the molten alumi-num. Consequently, the MWCNTs dispersed into the molten alumi-num matrix. During the coagulation process, the dissolved gold,nickel, and phosphorus formed stable compounds such as Al–Auintermetallic compound, Au–Ni solid solution, Al–Ni intermetalliccompound, and phosphoric oxide (Fig. 9c). In this study, since thewettability test was conducted in vacuum, it can be concludedthat the Ni–P alloy coated MWCNTs and the Au/Ni–P alloy double-coated MWCNTs both showed good wettability with molten alumi-num. However, the Au/Ni–P alloy double-coated MWCNTs shouldshow superior wettability to the Ni–P alloy coated MWCNTs in the at-mosphere, due to the prevention of oxidation. In the future, we willevaluate the wettability of metal-coated MWCNTs with moltenaluminum in the atmosphere. The metal coating of MWCNTs by

Ni

P

minum matrix

AlxNiy

Aluminum matrix

Px Oy

Au-Ni

Px Oy

PxOy

AlxAuy

(c)

Au-Ni

AlxAuyAlxNiy

d molten aluminum: (a) dissolution of gold coating into the molten aluminum duringrus) into the molten aluminum during heat treatment, and (c) the formation of stable–Ni), Ni–Al intermetallic compound (NixAly), and phosphorus oxide (PxOy) during

213S. Arai et al. / Surface & Coatings Technology 212 (2012) 207–213

electroless deposition is an effective technique to realize good wetta-bility between MWCNTs and not only molten aluminum, but alsoother metals such as magnesium.

4. Conclusions

Ni–P alloy coated MWCNTs with various phosphorus contentswere fabricated by electroless deposition. Gold coating of the Ni–Palloy coated MWCNTs was accomplished by electroless depositionusing a non-cyanide bath. The Ni–P alloy coating and the Au/Ni–Palloy double-coating of MWCNTs significantly improved the wetta-bility of MWCNTs with molten aluminum. This technique will beuseful not only for molten aluminum, but also for other moltenmetals such as magnesium.

In the future, the effects of the dissolved nickel, phosphorus, andgold on the mechanical properties of the composites will be evaluat-ed. Furthermore, the wettability of the metal-coated MWCNTs withmolten metals will be evaluated in an air atmosphere.

Acknowledgments

This researchwas supported by Regional Innovation Cluster Programof Nagano, granted by MEXT, Japan.

References

[1] A. Oberlin, M. Endo, T. Koyama, J. Cryst. Growth 32 (1976) 335.[2] S. Iijima, Nature 354 (1991) 56.[3] D. Shi, P. He, P. Zhao, F. Fang Guo, F. Wang, C. Huth, X. Chaud, S.L. Bud'ko, J. Lian,

Compos. Part B 42 (2011) 1532.[4] Z. Liu, X. Lin, J.Y. Lee, W. Zhang, M. Han, L.M. Gan, Langmuir 18 (2002) 4054.[5] W.S. Chung, S.Y. Chang, S.J. Lin, Plat. Surf. Finish. 83 (1996) 68.[6] Y.J. Lin, B.F. Jiang, J. Am. Ceram. Soc. 81 (1998) 2481.[7] G. Wen, Z.X. Guo, C.K.L. Davies, Scripta Mater. 43 (2000) 307.[8] C. Zhang, G.P. Ling, J.H. He, Mater. Lett. 58 (2004) 200.[9] Q. Li, S. Fan, W. Han, C. Sun, W. Liang, Jpn. J. Appl. Phys. 36 (1997) L501.

[10] J. Li, M. Moskovits, T.L. Haslett, Chem. Mater. 10 (1998) 1963.[11] X. Chen, J. Xia, J. Peng, W. Li, S. Xie, Compos. Sci. Technol. 60 (2000) 301.[12] M. Liebau, E. Unger, G.S. Duesberg, A.P. Graham, R. Seidel, F. Kreupl, W. Hoenlein,

Appl. Phys. A 77 (2003) 731.[13] W.X. Chen, J.P. Tu, L.Y. Wang, H.Y. Gan, D.Z. Xu, X.B. Zhang, Carbon 41 (2003) 215.[14] Y. Zhao, Y.J. Xue, H. Zheng, Y.X. Duan, New Carbon Mater. 25 (2010) 65.[15] S. Arai, M. Kobayashi, T. Yamamoto, M. Endo, Electrochem. Solid-State Lett. 13

(2010) D94.[16] S. Arai, M. Endo, S. Hashizume, Y. Shimojima, Electrochem. Commun. 6 (2004) 1029.[17] F. Wang, S. Arai, M. Endo, Carbon 43 (2005) 1716.[18] S. Arai, Y. Imoto, Y. Suzuki, M. Endo, Carbon 49 (2011) 1484.[19] F. Wang, S. Arai, M. Endo, Electrochem. Commun. 6 (2004) 1042.[20] M. Kato, J. Sato, H. Otani, T. Homma, Y. Okinaka, T. Osaka, O. Yoshioka, J. Electrochem.

Soc. 149 (2002) C164.[21] T. Osaka, M. Kato, J. Sato, K. Yoshizawa, T. Homma, Y. Okinaka, O. Yoshioka,

J. Electrochem. Soc. 148 (2001) C659.[22] J. Sato, M. Kato, H. Otani, T. Homma, Y. Okinaka, T. Osaka, O. Yoshioka, J. Electrochem.

Soc. 149 (2002) C168.[23] The Materials Information Society, Binary Alloy Phase Diagrams, 2nd ed., ASM

International, Materials Park, OH, 1996.