Numerical study of nanoparticle formation in two-coil tandem-type modulated induction thermal plasmas with simultaneous modulation of upper- and lower-coil currents

Abstract

A numerical study was conducted of nanoparticle (NP) formation and growth in two-coil tandem-type modulated induction thermal plasma (tandem MITP) with method of moment. Two-coil tandem MITP, which has two induction coils in one plasma torch, has been developed for the synthesis of large amounts of NPs. The two-coil tandem MITP is operated by modulated or non-modulated two coil currents for induction thermal plasma under a transient state. Furthermore, time-controlled feedstock feeding (TCFF) is involved with tandem MITP. For this tandem MITP + TCFF method, we developed a numerical model with three components: calculation of time-varying tandem-MITP fields, calculation of intermittent feeding of feedstock particles including dynamic motion, heating and evaporation of feedstock particles, and the calculation of NP formation and growth from feedstock vapour in time-varying tandem MITP fields. Two-way interactions among these three parts were also considered. Calculation was made Si NP formation in Ar tandem MITP with intermittent feeding of feedstock Si microparticles. Calculation results demonstrated that two-coil tandem-type MITP with simultaneous modulation of upper-coil and lower-coil currents can produce more rapid decay in the temperature field in the reaction chamber during the off-time, and that this rapid temperature decay promotes nucleation of NPs and suppresses particle growth. This finding indicates that tandem MITP can offer a temperature field with greater variation, which is preferred for NP synthesis.