7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Numerical Study of Nanoparticle Synthesis in Tandem-PMITP+TCFF Methodwith Variation of Modulation PeriodRio Okano1 , Peng Jingqian1 , Kouya Ishinokoshi1, Reo Tanaka1
Y. Tanaka1 , Y. Nakano1 , T. Ishijima1 ,S. Sueyasu2 , S. Watanabe2 , K. Nakamura21
Faculty of Electrical & Computer Eng., Kanazawa Univ., Kanazawa, Japan2
Research Center for Production & Technol., Nisshin Seifun Group Inc., Fujimino
E-mail: kmajpt-186@stu.kanazawa-u.ac.jp

We have constructed a numerical simulation model forsilicon nanoparticle synthesis using “Tandem-type Pulse
Modulated Induction Thermal Plasma (Tandem-PMITP)”
and “Time-Controlled Feeding of Feedstock (TCFF)
method” [1][2]. The model can calculate theelectromagnetic thermal-fluid fields in Tandem-PMITP,
as well as the behavior of feedstock materials and thenucleation and growth of nanoparticles. In this study, weinvestigated the effect of modulation period on thenumber and size of synthesized nanoparticles using thismodel.
In this numerical simulation model, the thermal plasma
was treated as electromagnetic thermofluid. The
governing equations includes the conservation equations
for mass, momentum, and energy, as well as the Poisson
equation for the two vector potentials generated by thetwo coil currents. The SIMPLE method was adopted tosolve the temperature and gas flow velocity fields. The
feedstock particles were considered as Lagrangianparticles, and their conservation equations for mass,momentum, and energy were solved using the 4th order
Runge-Kutta method. For nanoparticle formation andtransport, the aerosol general dynamic equation wassolved using the method of moment (MOM). Calculation
conditions were as follows. Ar gas was injected from thetop of the torch as a sheath gas with a 90 L/min flow rate.
Si feedstock was intermittently supplied at a rate of 1.0
g/min/rad, synchronized with the modulation cycle of thecoil current, with Ar carrier gas with a 4 L/min flow ratefrom the water-cooled tube at the center of the torch.
Fig.1 shows the relationship between the modulated coilcurrent and the feedstock feeding phase for two
conditions as examples. The lower coil current amplitude
was modulated into a rectangular waveform with a 50%
duty factor (DF). The modulation cycles of the lower coilcurrent were set as Tperiod = 20 ms, 40 ms, 60 ms, 80 ms
and 100 ms.
Fig. 2 shows the calculated particle size distribution in
the computational domain of the reaction chamber for
Tperiod = 20 ms and 80 ms. In addition, Fig. 3 indicatesthe relationship between the number of synthesized
nanoparticles and the averaged particle diameter 𝑑̅ foreach conditions. The particle size distribution wasobtained by calculating the time-averaged values of thethree moments for each computational mesh and thenadding the local particle size distribution for each meshbased on the geometric mean diameter and geometricmean volume. The nanoparticles with diameters less than
5 nm were ignored. As seen in these figures, an increasein modulation period from 20 ms to 80 ms elevates theFig. 1 : Coil current and feed rate at Tperiod = 20 ms, 80ms.

Fig. 2 : Calculated particle size distribution at Tperiod = 20ms, 80 ms.

Fig. 3: Calculated nanoparticle count and mean diameter foreach conditions.

nanoparticle synthesis rate by approximately 8 times.
This is because the increase in low-temperature durationof the plasma due to elongating the modulation period
can keep the temperature field around 2000 K, where Si
nucleation becomes dominant. On the other hand, theincrease in the modulation period also increases theaverage particle size, because the increase in thehigh-temperature duration of the plasma has led to easiercoagulation of the generated nanoparticle nuclei.
References[1] K. Onda, et al., J. Phys. D: Appl. Phys., 53, 325201,(2020)[2] R. Furukawa，et al，Plasma Chem．& Plasma Process，
42，435 (2022)