Preparation of Spherical Alumina Powder by RF Thermal Plasma: Numerical Simulation and Experimentation

doi:10.15541/jim20170266

Abstract

Abstract:

Behavior of alumina powder particles in inductively coupled thermal plasma (ICTP) can provide theoretical reference and guidelines for improving preparation process of plasma spheroidization. In this study, the motion trajectories and heating process of alumina powder particles in ICTP were investigated by means of numerical simulation with FLUENT software. Then the plasma spheroidization experiment was carried out on the basis of simulation results, and the effect of input power, powder feeder rate and particle size distribution on alumina powder spheroidization were studied by combination of experimental and the theoretical analyses. The results show that the small particles absorb enough heat from thermal plasma and therefore be heated to completely melt. Furthermore, the particle can get more energy from plasma while the input power of system is increased or the powder feeder rate is decreased, which improve the spheroidization effect of alumina powder particles.

Key words: ICTP, alumina particles, trajectory of particles, heating history, numerical simulation

CLC Number:

TB43

CHEN Wen-Bo, CHEN Lun-Jiang, LIU Chuan-Dong, CHENG Chang-Ming, TONG Hong-Hui, ZHU Hai-Long. Preparation of Spherical Alumina Powder by RF Thermal Plasma: Numerical Simulation and Experimentation[J]. Journal of Inorganic Materials, 2018, 33(5): 550-556.

Figures/Tables 12

Fig. 1 Schematic diagram of inductively coupled plasma spheroidization system (a) and plasma torch structure (b)

Table 1 Physical properties for alumina powders

Density /(kg·m^-3)	Specific heat /(J·kg^-1· K^-1)	Melting point /K	Fusion enthalpy /(J·kg^-1)	Boiling point /K	Vaporization enthalpy /(J·kg^-1)
3900	1020	2326	1.07×10⁶	3800	2.466×10⁷

Fig. 2 Trajectory of alumina particles with different particle sizes(a) Dp=20-30 μm; (b) Dp=40-50 μm

Fig. 3 Particle mean temperature of alumina particles with different particle size distribution

Fig. 4 Particle mean temperature of alumina particles with different input powers

Fig. 5 Trajectory of alumina particles with different input powers(a) P=56 kW; (b) P=63 kW; (c) P=70 kW

Fig. 6 Spatial distribution of temperature fields with different input powers(a) P=56 kW; (b) P=63 kW; (c) P=70 kW

Fig. 7 Distribution of temperature fields with different powder feed rates(a) 6.0 g/min; (b) 66.0 g/min; (c) 96.0 g/min

Fig. 8 Particle mean temperature of alumina particles with different powder feed rates

Table 2 Dimensions of RF inductively coupled plasma torch

Parameter	1# Particle	2# Particle
Particle mean diameter/μm	45	25
Plasma power/kW	63.75	56.00
Carry gas flow rate/(L·min^-1)	5	5
Sheath gas flow rate/(L·min^-1)	70	70
Center gas flow rate/(L·min^-1)	34.5	34.5
Powder feed rate/(g·min^-1)	35.0	35.0~65.7
Chamber pressure/kPa	40	40

Fig. 9 SEM images of 1# alumina particles(a) Precursor; (b) After being spheroidization

Fig. 10 SEM images of 2# alumina particles(a) Precursor; (b) Powder feed rate at 35 g/min; (c) Powder feed rate at 65.7 g/min

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