Numerical Analysis of Metallic Nanoparticle Synthesis Using RF Inductively Coupled Plasma Flows

Abstract

A thermal plasma flow is regarded as a multifunctional fluid with high energy density, high chemical reactivity, variable properties, and controllability by electromagnetic fields. Especially a radio frequency inductively coupled plasma (RF-ICP) flow has a large plasma volume, long chemical reaction time, and a high quenching rate. Besides, it is inherently clean because it is produced without internal electrodes. An RF-ICP flow is, therefore, considered to be very useful for nanoparticle synthesis. However, nanoparticle synthesis using an RF-ICP flow includes complicated phenomena with field interactions. In the present study, numerical analysis was conducted to investigate the synthesis of metallic nanoparticles using an advanced RF-ICP reactor. An advanced RF-ICP flow is generated by adding direct current (DC) discharge to a conventional RF-ICP flow in order to overcome the disadvantages of a conventional one. The objectives of the present work are to clarify the formation mechanism of metallic nanoparticles in advanced RF-ICP flow systems and to detect effective factors on required synthesis. A two-dimensional model as well as a one-dimensional model was introduced for nanoparticle growth to investigate effects of spatial distributions of thermofluid fields in RF-ICP flows on synthesized nanoparticles. In an advanced RF-ICP flow, a characteristic recirculation zone disappears due to a DC plasma jet. Larger numbers of nanoparticles with smaller size are produced by using an advanced RF-ICP flow. Thermofluid fields in RF-ICP flows can be controlled by applied coil frequency by means of skin effect. Larger numbers of nanoparticles with smaller size are produced near the central axis. Dispersion of particle size distributions can be suppressed by higher applied coil frequency through control of RF-ICP flows. Applied coil frequency can be a remarkably effective factor to control nanoparticle size distribution.