23P010-O
Effect of Intermittent Supply of the Raw Material and Quenching Gas during
Nanopowder Synthesis using Pulse Modulated Induction Thermal Plasmas
PMITPを用いたナノ粒子生成における原料・クエンチングガスの間歇投入効果
Weixuan Guo, Tatsuya Tsuke, Yasunori Tanaka, Yoshihiko Uesugi (Kanazawa University)
Shu Watanabe and Keitarou Nakamura (Nisshin Seifun Group Inc.)郭 韋萱, 附 達也，田中 康規，上杉 喜彦（金沢大学）
渡邉 周 中村 圭太郎（日清製粉グループ本社）
Faculty of Electrical and Computer Eng., Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan
金沢大学電子情報学系〒920-1192 金沢市角間町
Research Center for Production and Technol., Nisshin Seifun Group Inc., Tsurugaoka, Fujimino-shi 356-8511, Japan
日清製粉グループ本社生産技術研究所〒356-8511埼玉県ふじみ野市鶴ヶ岡5-3-1
This paper describes the effect of intermittent feeding of the raw material and quenching gas using the pulse
modulated induction thermal plasma (PMITP), during TiO 2 nanopowder synthesis. The fast solenoid valves wereadopted to control quenching gas flow and raw material feeding intermittently being synchronized with the pulse
modulation. Synthesized nanopowder was analyzed by SEM and XRD. The mean particle diameter of synthesized
nanoparticles were compared with/without the pulse modulation, intermittent feeding of raw materials andintermittent supply of quenching gas.

1. Introduction
Titanium oxide (TiO 2) nanoparticles in anatase
phase are continuously receiving attention for use
as photocatalysts, photonic crystals, photovoltaiccells, gas sensors, and a strong deoxidationmaterial. It is also used for producing hydrogengas from water for fuel cells. The authors haveinvestigated a pulse modulated induction thermal
plasmas (PMITP) system to be used for TiO 2nanoparticles [1,2]. The PMITP are establishedby the modulated coil current, which perturbs thethermal plasma temperature. From those results
we found that adoption of the pulse modulation
providedsmaller
nanoparticles
becauseevaporated material was rapidly cooled [1,2].
In the present work, the fast solenoid valves
were used to control intermittent feeding of both
quenching gas flow and raw material. Theintermittent feeding was synchronized with thepulse modulation. Using this system, nanoparticle
synthesis was made to study intermittent feeding
effects.
2. Experimental setup
Fig.1 shows a schematic diagram of experimentalsetup for nanopowder synthesis. This setup has fourparts: a plasma torch, an upstream chamber, adownstream chamber, and a collection filter. Inside
the plasma torch, an inductively coupled thermal
plasma is formed. The coil current sustaining thethermal plasma can be modulated into a rectangular
waveform. Ar-O2 gas was supplied as a sheath gas
along the inside wall of the torch. Ar/Ti powder
was injected through a water-cooled tube with Ar

carrier gas from the top of the torch. The Arquenching gas was also supplied in radial direction
from 8 holes located downstream of the torch.
These Ar/Ti powder and Ar quenching gas can beintermittently supplied by switching fast responsesolenoid valves installed, which was synchronized
to the coil current modulation for sustaining thermal
plasmas. The experiment condition is shown in
Table 1. Note that the total Ar quenching gas flowrate was 40 slpm for intermittent supply ofquenching gas, while it was lower than 50 slpm forcontinuous supply of quenching gas. Synthesizedparticles were collected from the filter.
3. Experimental results
Fig.2 presents examples of FE-SEM
micrographs of particles five conditions: (a)non-modulation, continuous feeding of raw materialand continuous feeding of quenching gas (NM/CWFM/CWFQ), (b) non-modulation, intermittent
feeding of raw material, and continuous feeding ofWater-cooled probe
Ar+Ti powder
QuenchinggasElectromagneticvalve

M
Ar+O2
TorchArgas

M
Upstream chamber

Observation
window

Downstream chamber

Filter
Vaccumpump

Cooling Water

Fig.1. Experimental setup for nanopowder synthesis.

3.1 Effect of pulse modulation
Fig.3 shows the estimated mean diameter ofnanoparticles synthesized under different fiveconditions. The condition NM/CWFM/CWFQ
corresponds to the conventional one with
continuous feeding of gas and raw material. We
have had results that use of the pulse modulation
with no quenching gas decreased the mean particle
diameter around 50-65 nm [1,2]. In that case, rapid
cooling of evaporated material might occur mainly
in off-time of the pulse modulation. On the other
hand, use of quenching gas in the present work
provides much smaller particles around 30-40 nm
as shown in Fig.3. In this case, the pulsemodulation offers a larger mean particle diameterby comparing results NW/CWFM/CWFQ andPM/CWFM/CWFQ. This may be because the pulse
modulation causes a large disturbance in the plasma,
which may decrease the temperature gradientstrongly formed by quenching gas.
3.2 Effect of intermittent supply of raw material
Effect of intermittent supply of raw material canbe seen by comparison between the results ofNM/CWFM/CWFQ and NW/IMFM/CWFQ in
Fig.3. The mean diameter of nanoparticles
produced with intermittent feeding of raw material
is a little smaller than that with its continuous
feeding. This may be because the raw material was
evaporated or cooled efficiently in the intermittent
feeding. It will be possible to produce smaller
nanoparticles and to improve the production
efficiency by adjusting timing of the intermittent
feeding of raw materials [2].
3.3 Effect of intermittent supply of quenching gas
We compared results between NM/CWFM/CWFQ and NM/CWFM/IMFQ or between

PM/CWFM/CWFQ and PM/CWFM/IMFQ. Noteagain that total gas amount for intermittent supplyof quenching gas is lower than that for continuous
supply. In spite of that, nanoparticles with similar
mean diameter could be obtained. This means thatuse of intermittent supply of quenching gas
efficiently produces area with a high temperature
gradient where evaporated material is cooled down.
Table 1.Experimental condition.
Input powerPressure
Gas composition
Carrier gas flow rate
Quenching gas flow rate
Quenching gas supply direction
Immersion length ofwater-cooled probe
Modulation cycle
Shimmer current level SCL
Duty factor
Ti powder feed rate

20 kW
300 torr
90%Ar+10%O2
Ar:4 slpm
Ar:50 slpm
(40 slpm forintermit. supply)
Radial134 mm
15 ms
80%
80%
3～4 g/min(a)NM/CWFM/CWFQ (b) NM/IMFM/CWFQ (c) NM/CWFM/IMFQ(d)PM/CWFM/CWFQ(e) PM/CWFM/IMFQ

Fig.2. SEM images of synthesized TiO2 nanoparticles.
PM means the pulse modulation of the coil current,
whereas NM means non-modulation. CWFM means thecontinuous feeding of raw material, CWFQ means thecontinuous feeding of quenching gas, IMFM meansintermittent feeding of raw materials, and IMFQ meansintermittent feeding of quenching materials.
60

Mean particle diameter [nm]quenchinggas(NM/IMFM/CWFQ),(c)non-modulation, continuous feeding of raw material,and intermittent feeding of quenching gas(NM/CWFM/IMFQ), (d) pulse modulation,
continuous feeding of raw material, and continuous
feeding of quenching gas (PM/CWFM/CWFQ), (e)pulse modulation, continuous feeding of raw
material, and intermittent feeding of quenchinggas(PM/CWFM/IMFQ). For any condition,
nanoparticles were confirmed to be synthesized.
Using the micrographs, the particle size distribution
and then the mean particle diameter were obtained
from observation of 200 randomly sampled
particles. The XRD analysis was also made for thesynthesized particles, indicating they contained
85%-90% anatase TiO2 for any condition.

PM/CWFM/CWFQ

5040

NM/IMFM/CWFQ

3020100
NM/CWFM/CWFQ

NM/CWFM/IMFQ

PM/CWFM/IMFQ

Fig.3. Mean particle diameter of produced particles.
References[1] Y. Tanaka: Proc.20th Int. Symp. Plasma chem.
ISPC-20, (4pp)[2] Y. Tanaka: J.Phys.D:Appl.Phys.43 (2010) 265201(12pp)