Preparation of single-helix carbon microcoils (SH-CMCs)
using Fe-Ni alloy catalyst
I. Ozeki, S. Yang, X. Chen, and S. Motojima
Department of Applied Chemistry, Faculty of Engineering, Gifu University, Gifu 501-1193, Japane-mail: motojima@apchem.gifu-u.ac.jp
Abstract
Carbon microcoils (CMCs) are a kind of vapor growth carbon fibers, which have an interesting 3D-helical/spiral structure with a coil diameter of micrometer orders andhave a very high elasticity. Conventional double helix carbon microcoils(DH-CMCs) were prepared were prepared by a CVD process using Ni as a catalyst, acetylene as acarbon source gas under the atmosphere of nitrogen, hydrogen, and hydrogen sulfide. While the single helix carbon microcoils (SH-CMCs) were prepared by using an Fealloy as a catalyst. The composition of the Fe-Ni alloy affect the morphology of the SH-CMCs dramatically. In this study, we synthesized SH-CMCs using an alloy FeNi(50:50) as a catalyst, the SH-CMCs with a different morphology comparing to those SH-CMCs grown over an Fe-Ni(90:10) alloy catalyst; the preparation conditions, themorphologies, structure of SH-CMC and the growth mechanism were examined using SEM, TEM and Raman . The obtained SH-CMCs have a high purity. The coildiameter, coil’s gap and fiber diameter were 1~2 μm, ~1 μm, 0.2~0.5 μm, respectively. Fig. 2c SH-CMCs are grown by a single growth direction mode, while fig.2b SHCMCs are by double-growth direction mode. The structures of as-grown SH-CMCs and heat-treated SH-CMCs were compared. As-grown SH-CMCs were composed ofamorphous carbon, while heat-treated SH-CMCs were graphitized in some degree.

Comparison of SH-CMC with CMC.

Synthesis approach.

(a)Source Gas Inlet

(b)

(c)

(C2H2+H2+H2S+N2)

Reaction Tube

Alumel-chromel
thermocouple(Quartz,30mmΦ)3㎛
800-830℃

5㎛

Catalyst

1.8㎛

1㎛

2㎛

0.8㎛

Substrate

Fig. 2. SEM images of CMC and SH-CMC.
Table 1. Difference in synthesis condition.
Gas Outlet

Reaction temperature(℃)
750~800
700~730800~830

Catalyst

Fig. 1. Reaction tube for the preparation of single-helix carbon(a) CMC(b) SHCMC(c) SHCMCmicrocoils (SH-CMCs).

Ni
Fe+Ni (90:10)
Fe+Ni (50:50)

Morphology
Double helix
Single helix
Single helix

Structure of SH-CMC.

Growth observation.

0.352

0.6(a)

(a)

(b)

0.35

(b)

0.55

Int.

Int.

0.348
0.5

0.346
0.344

0.45

0.342

0.4
900

1100

1300

1500

1700

1900

0.34
1000

1200

(d)

(c)

1600

1800

2000

Raman shift [cm ]

(d)

(c)

1400

-1

Raman shift/cm-1

Fig. 4. Raman spectra of SH-CMC.
(a) as-grown SH-CMC,(b) heat-treated SH-CMC.

Fig. 5. TEM images and electron
diffraction patterns of SH-CMC.
(c) as-grown SH-CMC,(d) heat-treated SH-CMC.

Fig. 3. SEM images of growth tip.
(a) CMC (b) SH-CMC (Fe:Ni=90:10), (c) SH-CMC (Fe:Ni=50:50),(d) Heat-treated SH-CMC (Fe:Ni=50:50)

Conclusion
Influence of C2H2 flow rate.

Efficiency of Fe/Ni ratio.

332 .5

2.5①. We obtained SH-CMCs using an Fe-Ni
alloy catalyst at 820℃.
Single helix

Fe/Ni=80:20

Coil gap [㎛]Co il diame t e r [ ㎛]

Fe/Ni=70:30

21 .5

2Fe/Ni=90:10

Double helix

1.51Fe/Ni=20:80

Fe/Ni=50:50②. SH-CMCs are grown by a double growth
direction mode.
③. As-grown SH-CMCs were composed ofamorphous carbon, while heat-treated SHCMCs were graphitized in some degree.

Fe/Ni=40:60

10.50 .550100150200250

C 2 H 2 flo w r at e [ ml/ min ]300350④. We could control the coil diameter when
C2H2 flow rate was changed.

Fe/Ni=60:40
Fe/Ni=30:70 Fe/Ni=10:90

00123Coil diameter [㎛]45Fig. 6. Relationship between coil diameter and C2H2 flow rate. Fig. 7. Relationship between Fe/Ni ratio and coil’s morphology.