Numerical Analysis on RF (Radio-frequency) Thermal Plasma Synthesis of Nano-sized Ni Metal

Numerical analysis on RF (Radio Frequency) thermal plasma treatment of micro-sized Ni metal was carried out to understand the synthesis mechanism of nano-sized Ni powder by HF thermal plasma. For this puipose, the behaviors of Ni metal particles injected into HF plasma torch were investigated according to their diameters (1 100 pin). RF input power (6~12 kW) and the flow rates of carrier gases (2 and 5 slpm). From the numerical results, it is predicted firstly that the velocities of carrier gases need to be minimized because the strong injection of carrier gas can cool down the central column of RF thermal plasma significantly, which is used as a main path for RF thermal plasma treatment of micro-sized Ni metal. In addition, the residence time of the injected particles in the high temperature region of RF thermal plasma is found to be also reduced in proportion to the flow rate of the carrier gas In spite of these effects of carrier gas velocities, however, calculation results show that a Ni metal particle even with the diameter of 100 pin can be completely evaporated at relatively low power level of 10 kW during its flight of HF thermal plasma torch (< 10 ms) due to the relatively low melting point and high thermal conductivity. Based on these observations, nano-sized Ni metal powders are expected to be produced efficiently by a simple treatment of micro-sized Ni metal using HF thermal plasmas.