02Ba01
ナノ粒子生成用変調熱プラズマにおける原料粒子挙動のレーザストロボ観測
Laser Strobe Observation of Feedstock Particle Dynamics
in Modulated Thermal Plasma for Nanoparticle Synthesis
古川颯大*1，明石恵太1，長瀬有理奈1，田中康規1，中野裕介1，石島達夫1，末安志織2，渡邉周2，中村圭太郎2
Ryudai Furukawa*1, Keita Akashi1, Yurina Nagase 1, Yasunori Tanaka1, Yusuke Nakano1,Tatsuo Ishijima1 Shiori Sueyasu2, Shu Watanabe2, Keitaro Nakamura2
1
金沢大学，2日清製粉グループ本社
Kanazawa University, 2 Nisshin Seifun Group Inc.
frequency of YAG laser was 4000 Hz with a pulse
width of 1-10 ns, which was synchronized with ahigh-speed video camera, whose frame rate was4000 fps. Detailed plasma condition was the sameas described in [1].
3. Observation results
Fig.2 shows observation results for PMITP+
TCFF condition at the timing of (a) plasma on-time
at t=6 ms and (b) final state in on-time at t=12 ms,
where on-time is realized from t=0 ms to 12 ms.
Reflected light from feedstock was clearly detected
near the central axis of the plasma torch. FromFig.2(b), feedstock particles with a smaller particle
size by evaporation were seen to be diffused inradial direction because of gas flow originatingfrom rapid temperature change in thermal plasma.

Fig.1 Observation system for feedstock particle
behavior in induction thermal plasma.
Coil Position

Plasma Torch Edge

Water Cooled Wall

Water Cooled Wall

Coil Position

Water Cooled Wall

1. Introduction
Nanoparticles are expected as breakthroughelements in various fields of environment, energy,electronics, and so on. The authors have developed
pulse modulated induction thermal plasma (PMITP)
and time-controlled feedstock feeding (TCFF)
method for synthesizing large amounts ofnanoparticles. In the PMITP+TCFF method,
completesynchronization
betweenplasmamodulation and feedstock feeding, and suppressionof adhesion of the molten feedstock to torch wall
are issues to be solved for further production rate. It
is therefore necessary to understand the behavior offeedstock particles in the PMITP. In this report, alaser stroboscopic imaging system was adopted toobserve dynamics of feedstock particles with mean
size of about 20 μm in PMITP+TCFF method.
2. Observation system and experimental condition
It is required to suppress the strong emission
from the thermal plasma for observation offeedstock particle behavior. Fig.1 shows aschematic diagram of a high-speed laser strobe
imaging system adopted. A pulsed YAG laser beamwith a wavelength of λ = 532 nm and power of
0.266 mJ was used as a light source forvisualization of feedstock particles. This laser beam
was converted to a vertical sheet-like collimatedlight beam by an optical system using a
combination of concave and convex cylindricallenses. This sheet laser beam incident to the plasma
torch is partially reflected by feedstock particles.
The reflected light and thermal plasma light are
guided to a band pass filter with a wavelength widthof λ = 532 ± 1 nm. As a result, almost only thestrong reflected light of the laser beam istransmitted to a high-speed video camera, while
attenuating the strong irradiation from the thermal
plasma. Furthermore, synchronizing the repetition
frequency of the YAG laser and the frame rate of
the high-speed video camera enables us to measure
the reflected light from the particles. The repetition

Water Cooled Wall1Plasma Torch Edge(a) t = 6 ms(b) t = 12 ms
Fig.2 Observation results for PMITP + TCFF condition
4. Reference[1] Y. Ishisaka, et al., Applied Physics Express,
vol.10, 096201, 2017