24G14
TiO2 and Ni Nanoparticle Synthesis
using Pulse-Modulated Induction Thermal Plasmas
パルス変調誘導熱プラズマを用いた TiO2 および Ni ナノ粒子生成
Tatsuya Tsuke1 , Weixuan Guo1 , Yasunori Tanaka1 , Yoshihiko Uesugi1
Syu Watanabe2 , Keitaro Nakamura2
附 達也 1 , 郭 韋萱 1 , 田中康規 1 ，上杉喜彦 1
渡邉 周 2 , 中村圭太郎 2
1Kanazawa University, Kakuma-machi, Kanazawa, Ishikawa, 920-1192, Japan2
Nisshin Seifun Group Inc., 5-3-1 Tsurugaoka, Fujimino 356-8511, Japan1
金沢大学 〒 920-1192 石川県金沢市角間町
2
日清製粉グループ本社 〒 356-8511 ふじみ野市鶴ケ岡 5-3-1

Nanoparticles of titanium dioxide(TiO2 ) and nickel(Ni) were synthesized by direct evaporation of titanium
and nickel powders using Ar-O2 or Ar-H2 pulse-modulated induction thermal plasma(PMITP). The PMITP
has been developed to control temperature and gas flow fields of the thermal plasma in time domain. Eﬀectof the pulse modulation was investigated on synthesized particles in terms of the mean particle diameter,
the standard deviation, the morphology and the phase constituent. Fabricated particles were analyzed byFE-SEM, BET (Brunauer, Emmet and Teller’s equation) and XRD.

1.

Intorduction
Nowadays, various types of eﬀective vapor-phaseprocessing techniques are well known for nanoparticle syntheses [1]. The inductively coupled thermal
plasma (ICTP) method is one of them to synthesize
nanoparticles [2]. The ICTP method have great advantages for nanoparticle syntheses from their featuresof high enthalpy and radical density, and high temperature gradient. It is also characterized by little contamination because of no electrodes. These advantages allow highly-functional nanoparticles to be synthesized by direct evaporation of raw material powders. On the other hand, our group have developed
a pulse modulated induction thermal plasma (PMITP)
system, which is established by periodically modulated coil-current in a rectangular waveform [3]. Sucha pulse modulation of the coil-current leads thermal
plasmas to be under periodical transient states in milliseconds time scale. The rapid temperature variationin the PMITP can be expected to be utilized for eﬀective nanoparticle synthesis.
In this study, the authors experimentally investigated
the application of the PMITP to nanoparticle synthesis. The TiO2 nanoparticles were selected as a target
in this work because these materials are widely used
as a photocatalyst for cleaning, water processing, etc.
Additionally, we began to research Ni nanoparticles
synthesis with the PMITP to study its usefulness forsynthesis of diﬀerent materials nanoparticles.

2. Experimental setup
2.1. Experimental arrangements
Fig.1 portrays the experimental arrangement usedfor this study. The plasma torch is configured identically to that used in our previous work [4]. Its details were described in our earlier papers. The plasma
torch has two coaxial quartz tubes. The interior quartz
tube has an inner diameter of 70 mm; its length is 370
mm. An argon-oxygen gas mixture was supplied as asheath gas along the inside wall of the interior quartz
tube from the top of the plasma torch. Titanium raw
material was fed using a powder feeder with Ar carrier gas through a water-cooled tube probe. The watercooled tube probe was inserted from the top of theplasma torch head, as depicted in Fig.1. Downstreamof the plasma torch, the water-cooled chambers were
installed vertically and then horizontally, as depicted
in Fig.1. The total length of the vertical chamber is
600 mm; its inner diameter is130 mm. Similarly, thetotal length of the horizontal chamber is 600 mm; its
inner diameter is 130 mm. Further downstream of thehorizontal chamber, a powder-collecting filter and thecollecting chamber are set up. A vacuum pump is set
up further downstream.
2.2. Experimental conditions
In TiO2 nanoparticle synthesis, the total flow rate of
Ar-O2 sheath gas was fixed at 100.0 standard litres perminute (slpm). The O2 gas admixture ratio to Ar wasWater-cooled probe
Ar+Ni powder
Ar+H2

Mean particle diameter [nm]70TorchUpstream chamber

Observation
window

Downstream chamber

Without modulation

65
60
55

72%DF
60%DF
80%DF
100

9080

7060

SCL [%]
Cooling WaterFig. 1: Experimental setup for nanoparticle synthesis.
10% in the sheath gas in the gas flow rate. The gas
flow rate of Ar carrier gas was 4 slpm. On the otherhand, for Ni nanoparticle synthesis, the flow rate of Ar
sheath gas was fixed at 90 slpm. The flow rate of H2
sheath gas set up with 1, 2, 3, and 4 slpm. The gas
flow rate of Ar carrier gas was 7 slpm. Ti or Ni powder with a mean diameter of 30 µm was used as rawmaterial. The powder feed rate of these raw material
was fixed around 3.0 to 4.0 g/min for both cases. The
pressure inside the chamber was controlled to be fixedat 300 Torr (=40 kPa) with an automatic feedback controller. The time-averaged input power to the rf power
supply was fixed at 20 kW. The PMITP was adopted
for a reactive plasma field periodically disturbed by themodulated coil current. The on-time and the oﬀ-time
for the modulated current were fixed respectively at 12ms and 3 ms for the PMITP. The shimmer current level(SCL), which was defined as the ratio of the lower current level to the higher current level, was taken as amodulation parameter.

Fig. 2: SEM imageof synthesized TiO2
nanoparticles

Fig. 3: Dependence ofmean diameter of synthesized TiO2 nanoparticles
on SCL
10070% SCL
No-modulation

80dBET [nm]Vaccumpump

67%DF5045

Filter

90%DF604060% SCL
201Fig. 4: SEM image of synthesized Ninanoparticles

23H2 [slpm]

4Fig. 5: Ni nanoparticles diameter estimeted by specific surface areaaround 100 nm were synthesized in this case. The
synthesized Ni nanoparticles were analyzed by BET
method to measure specified surface area S BET , andthen mean particle diameter dBET . Fig. 5 shows the dependence of dBET on the H2 gas flow rate, and also on
the modulation condition with DF=80%. It was foundfrom this figure that dBET is decreased from 82 nm to2.3. TiO2 nanoparticle synthesis with PMITP
Fig. 2 presents the example of FE-SEM micrograph 38 nm with H2 gas flow rate from 1 to 3 slpm. Furtherof synthesised TiO2 nanoparticles. From the micro- more, the use of the PMITP decreases dBET comparedgraph, the mean diameter d̄ was subsequently estimated to the non-modulated plasmas. This means that thefrom observation of 200 randomly sampled particles. PMITP may provide a more rapid cooling eﬀects also
Such estimation was done for diﬀerent modulation con- for Ni evaporated materials.
ditions. Fig. 3 shows the dependence of d̄ on SCL
and duty factor DF. As seen, d̄ decreases with reducing 3. Conclusion
SCL except for DF=60%, i.e. too small DF. In particWe have investigated the eﬀects of use of the PMITPular, around DF from 67% to 80%, d̄ is declined by re- on nanoparticle synthesis. The TiO2 and Ni nanopartiducing SCL. The condition 80%DF-65%SCL provides cles were synthesized using the PMITP. Results showed
the smaller nanoparticle synthesized in the present work. that use of the pulse modulation provides smaller nanoparThis result implies that the PMITP oﬀers the eﬀective ticles synthesized for both cases.
rapid-cooling of evaporated material, which prevents aparticle growing up.
References
2.4. Ni nanoparticle synthesis with PMITPThe Ar-H2 PMITP was in trial used for Ni nanoparticle synthesis in this work. Fig. 4 presents the example of FE-SEM micrograph of synthesised Ni nanoparticles. These particles were collected in the upstream
chamber wall. We can confirm that Ni nanoparticles[1] J. Haidar et al.:J. Phys. D: Appl. Phys，31，1223，(1998)[2] M. Shigeta and T. Watanabe, J. Appl. Phys，108,043306 (2010)[3] Y.tanaka et al.,Thin Solid Films, 519, pp.7100-7105,(2010)[4] Y. Tanaka et al., J. Phys. D: Appl. Phys，43，265201，(2010)