22P070-P
Effect of Anode Jet on Nanoparticle Production by Ar-H2 Arc
アルゴン-水素アークによる金属ナノ粒子生成におけるアノードジェットの影響
Tasuku Shimizu, Liang Feng, Manabu Tanaka, and Takayuki Watanabe
清水 佑, 梁 風，田中 学，渡辺隆行
Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology
4259 G1-22, Nagatsuta, Yokohama, Kanagawa 226-8502, Japan
東京工業大学大学院総合理工学研究科 〒226-8502 横浜市緑区長津田町4259番地G1-22
Anode jet is plasma flow, which occurs from raw material on anode under certain special conditions. The
anode jet is important phenomenon because it is one of factors which enhance metal evaporation for
preparing metal nanoparticle in hydrogen plasma metal reaction. The parameters involved with anode jet
are arc current, hydrogen concentration, shield gas flow rate and so on. The anode jet’s features wereobserved by high speed camera and emission spectroscopy to investigate this phenomenon effect onenhancement of metal evaporation.

1. Introduction
Thermal plasma can prepare nanoparticles withhigh productivity, because it has high temperature,
rapid quenching rate and high reactivity byradicals. Ohno and Uda developed hydrogenplasma metal reaction (HPMR) for the purpose ofnanoparticle synthesis by using DC arc [1]. Metalevaporation rate is increased by adding hydrogengas in argon gas. Dissociated hydrogen in arc
plasmas dissolves into molten metal and enhances
the vaporization of metal when the hydrogenatoms are emitted from the molten metals.
However, this explanation is not enough because
the particular metal’s evaporation is enhanced
selectively when metal mixture is used [2].
The anode jet is the plasma flow, which occurs
from raw material of anode, while the plasma
stream from cathode is the cathode jet. We foundthe anode jet by HPMR when nickel was used asraw material. The operating parameters involved
with anode jet are arc current, hydrogenconcentration, shield gas flow rate, anodematerial and so on [3].
The objective of this study is to investigate therelationship between hydride formation andselective metal evaporation, and the effect ofanode jet on the enhancement of metal
evaporation in nanoparticle synthesis.

Fig.1. Schematic of the experimental setup.

used for the evaporation of the raw material.
Typical operating conditions are as follows:
current: 50-200 A, voltage: 20-40 V, total pressure:
101 kPa, shield gas flow rate: 0-40 Nl/min, H2
concentration: 0, 30, 50vol%.

2. Experimental

2.2 Plasma analysis
The behavior of anode jet was observed by highspeed camera (Photron, SA WTI). The vaporized
species from the molten metal were identified byspectroscopic diagnostics with a spectrometer(Horiba Jobin Yvon, iHR-550) and a CCD detector(Horiba Jobin Yvon, Synergy). The weight
difference of the raw material was measured aftertreatment to estimate the evaporation rate of the rawmaterial.

2.1 Experimental setup
Figure 1 shows a schematic illustration ofexperimental setup for nanoparticle production. The
setup consists of a power supply, an arc chamber, aparticle collector, and a gas circulation pump. 50 gnickel ingot as raw material was placed on thewater-cooled copper anode. Ar and Ar-H2 arc was

3. Results and Discussion
The behavior of anode jet was observed inHPMR over 30% hydrogen with nickel substrate.
Fig.2 shows arc images for different plasma gas
conditions by high-speed camera.
In order to analysis the size of anode jet, 5,000
images which correspond to 500 ms are superposed.

2000

(b)

(a)

Ni

Ni

Ni

Ni

1800
H

radial5mm

Intensity

axial5mm

1200

It is enough to estimate time-averaged anode jet
area because the arc fluctuation frequency was 100
Hz (10ms).
The quantitative anode jet area was evaluatedfrom these superposed images. The size of anode jet
is changed according to shield gas flow rates in
30%-H2 arc. Effect of shield gas flow rate on anodejet area is shown in Fig.3. The anode jet area
decreases with increasing shield gas flow rate until
10 Nl/min. Because the cathode jet flow isenhanced with increasing the shield gas flow bythermal pinch effect. In contrast, the anode jet area
increases with increasing shield gas flow rate higher

10002Anode Jet area [mm ]

2.5
2.0
1.5
1.0
0.5
0.0010203040Sield Gas Flow Rate [L/min]Fig.3. Effect of shield gas flow rate on anodejet area.
0.12

Evaporation rate [g/min]

0.100.08

Ni

1400

Fig.2. High-speed camera images of(a) 100%-Ar arc (b) 30%-H2 arc.

3.0

Ni

1600

NiH

420

425430
Wavelength [nm]435

Fig.5. Emission spectrum of Ar-H2 arc.

than 10 Nl/min. This is because the anode spot shift
which leads to longer arc length. Consequently theanode jet flow became stronger due to smaller
momentum of cathode jet in axial direction.
The effect of shield gas flow rate on evaporation
rate of nickel is presented in Fig.4. The evaporation
rate has the same tendency with the anode jet area.
This result indicates that the evaporation rate issignificantly affected by the anode jet. The anodejet can improve metal nanoparticles generation.
The spectroscopic measurements of thevaporized species in anode jet region were carriedout to investigate the evaporation behavior. Fig.5
shows the atomic emission of nickel in 30%-H2 arc.
The nickel hydride peak was observed at 420.7 nm,
which is observed only in anode jet region. It isnecessary to understand the effect of the anode jeton the enhancements of hydride formation andmetal evaporation in future.
4. Conclusions
The effect of shield gas flow rate on the anode jet
phenomenon was investigated. The anode jet
behavior is influenced by momentum of cathode jetin axial direction. Moreover the nickel hydride peak
was observed in anode jet region by spectroscopy.
The reason for enhancement evaporation in HPMR
may be related to the formation of metal hydride.
At last, controlling anode jet phenomenon is thebest way to improve nanoparticle generation.

0.06

References

0.04
0.02
0.00
0102030
Shield Gas Flow Rate [L/min]Fig.4. Effect of shield gas flow rate on
evaporation rate.

40[1] S. Ohno and M. Uda: J. Jpn. Inst. Metals 48 (1984)
640.
[2] M. Tanaka and T. Watanabe: Thin Solid Films 516(2008) 6645.
[3] M. Tanaka, J. V. R. Heberlein and T. Watanabe: 19thInt. Symp. Plasma Chemistry (Bochum, Germany,26–31 July 2009) ed A von Keudell, et al., P1.1.19.