Page 134 - Book Hosokawa Nanoparticle Technology Handbook

FUNDAMENTALS CH. 2 STRUCTURAL CONTROL OF NANOPARTICLES
Table 2.7.1
Main production methods of CNT.
Kind of CNT Production Use of
method catalyst
SWNT Arc Yes
Laser Yes
CVD Yes
DWNT Arc Yes
CVD Yes
MWNT Arc No
CVD Yes
Oxidation [15] of SiC No Figure 2.7.1
High resolution TEM image [24] of MWNT including 3Å
tube at the center. Insert is intensity profile of lattice fringes.
Two years after the discovery of CNT, Iijima et al. [7]
and IBM’s group [8] independently found single-wall
carbon nanotubes (SWNT), which is a single roll of of fullerenes. However, in the case of CNT production,
graphene sheet with honey-comb lattice. On the other such as CH gas [18, 19] including hydrogen atom is
4
hand, first-found CNT having a Russian dole structure better than inert gas to prepare high-crystalline
is called multi-walled carbon nanotubes (MWNT). MWNT. This is a big difference in the case of
Recently, double-wall carbon nanotubes [9] (DWNT) fullerene, which cannot be produced in a gas including
composed of two graphene sheets are noticed in the hydrogen atom. The best gas condition to prepare
field of their application, because DWNT has interme- high-crystalline and densely packed MWNT is found
diate characteristics of SWNT and MWNT. to be pure hydrogen gas [20, 21]at a pressure about 10
As described above, the first CNT was produced by kPa. Purification of these MWNTs is also easily done
0
arc discharge method. Later on, other evaporation by heat treatment at 500 C in air, because co-existing
sources were also used for CNT production, such as carbon nanoparticles are very little in hydrogen-arc
laser source [10] and chemical vapor deposition [11] produced MWNTs [22].
(CVD). In the case of MWNT production by arc dis- Usually, the smallest diameter [23] of the innermost
charge method, catalyst is not necessary, while for tube of MWNT produced by hydrogen-arc discharge
SWNT production by arc discharge method the use of is only 4Å. Exceptionally, thinner innermost tube of
catalyst is essential. However, in the case of CVD, diameter 3Å is also found [24], where the tube diam-
CNT cannot be produced without catalyst. In the case eter is smaller than the spacing of graphene layer in
of laser evaporation, SWNT can be produced by using graphite. Figure 2.7.1 shows a high-resolution trans-
appropriate catalyst metal, but no MWNT by any cat- mission electron microscope (HRTEM) image of such
alyst. Including the case of DWNT, production meth- thin innermost tube, 12 parallel symmetric lines of 3.4
ods of CNT are summarized in Table 2.7.1. Many Å spacing are seen. At the center, 3-Å diameter tube
books [12] and reviews [13, 14] are published on CNT. of weak contrast is seen between A and A ; the dis-
In this section, CNT production by arc discharge tance AA’ is about 120Å. The insert of Fig. 2.7.1 is a
method is mainly described. Especially, the case of densitometer curve along the line BB , in which a pair
MWNT and SWNT production is focused. of weak contrast peaks 00 are observed.

2.7.1 Production of MWNT by arc discharge method 2.7.2 Production of SWNT by arc discharge method
After a vacuum chamber is filled with an appropriate The first found SWNT was also produced by an arc
gas under a pressure of about 10kPa, arc voltage of dc discharge method [7, 8], but the quantity was limited.
20–30V is applied between the two graphite elec- After then, SWNT was produced by laser evaporation
trodes 1–2mm apart. Then, the anode is evaporated by [10] and CVD method [25] as well. In arc discharge
the heat of arc discharge and carbon soot generates in method, by using two kinds of catalyst metals such as
the chamber. In the soot, about 10% fullerenes are Ni and Y, a large amount of SWNT was produced by
included [16]. At the same time, some part of evapo- Journet et al. [26]. The present authors also improved
rated carbon deposits on the cathode and MWNT is the method by setting the two electrodes at a sharp
included within and at the surface of the cathode angle of 30 , and produced soot [27] including SWNT
deposit [2, 17]. at a rate 1g/min. However, the soot included a large
The atmospheric gas due to arc evaporation, usually quantity of impurities, not only catalyst metals but
inert gas such as He or Ar, is used for the production also amorphous carbon.

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