Abstract
In this study, a two-dimensional numerical model was developed to simulate operation conditions in the non-transferred plasma torch, used to synthesis nanosilica powder. The turbulent magnetohydrodynamic model was presented to predict the nitrogen plasma flow and heat transfer characteristics inside and outside the plasma torch. The continuity, momentum, energy, current continuity equations, and the turbulence model were expressed in cylindrical coordinates and numerically solved by COMSOL Multiphysics software with a finite element method. The operation conditions of the mass flow rate of ionized gas ranging from 78 sccm to 240 sccm and the current varying between 50 A to 200 A were systematically analyzed. The variation in the electrothermal efficiency with the gas flow rate, the plasma current, and the enthalpy was also reported. The results revealed that the increase in working current lead to a raise in the effective electric power and then an increase in the distribution of plasma velocity and temperature. The efficiency of the torch was found to be between 36% and 75%. The plasma jet exited the nozzle torch with a larger fast and hot core diameter with increasing current. The numerical results showed good correlation and good trends with the experimental measurement. This study allowed us to obtain more efficient control of the process conditions and a better optimization of this process in terms of the production rate and primary particle size. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the primary nanosilica powder that was experimentally collected. The arc plasma method enabled us to produce a spherical silicon ultra-fine powder of about 20 nm in diameter.
Highlights
Plasma technology has in the last years evolved to be a promising technique for the efficient manufacture of nano-sized materials, which are in increasing demand by recent technological advancement for diverse applications such as industrial, biomedical, and environmental purification processes [1,2,3,4,5,6,7]
Nano-metal powders have been broadly generated by transferred DC plasma torches [11,12]
In this kind of plasma torch the manufacturing process often becomes non-continuous because target metals, used as electrodes, should be replaced after each batch of metal nano-powder by reason of their non-resistance to the elevated temperature generated in the plasma torch
Summary
Plasma technology has in the last years evolved to be a promising technique for the efficient manufacture of nano-sized materials, which are in increasing demand by recent technological advancement for diverse applications such as industrial, biomedical, and environmental purification processes [1,2,3,4,5,6,7]. Post et al [9] describe that the plasma-manufactured nanoparticles are the best technique to obtain homogenized coating on metal nanoparticles and to control their outer surface properties Another important aspect of plasma-based nanomaterials is the possibility to adjust the thermal efficiency of the solar cells and the use of atmospheric pressure plasma in order to generate silver and gold nanoparticles on tin oxide solar cells [10]. Alternative technologies, non-transferred DC, or RF plasma torches have been used to offer a continuous production system of nano-sized powders. Guo [23] and Modirkhazeni [24] employed new models with the large eddy simulation technique to simulate the turbulent plasma flow inside a DC non-transferred arc plasma torch and the effect of particle injection. The gravity effects are negligible due to a high Froude number (≈ 3 × 106). The arc is assumed to be steady and rotationally symmetric. Thermodynamic and transport properties of gas plasma expressed as a function of the local temperature and pressure are obtained from the literature provided by Boulos et al study [27]
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