Modelling of SI nanoparticle synthesis by inductively coupled thermal plasma: Optimization of curtain gas injection in a conical reaction chamber

Summary form only given. Increasing attention has been devoted to nanoparticle production technology in the last decades as a consequence of the increasing interest for nanoparticle properties, such as modified physical properties with respect to bulk materials and high area to volume ratio, that allow their successful use in biomedical, optical, energy and electronic applications. Inductively coupled thermal plasma technology, whose distinctive features are high energy density, high process purity, large plasma volume and long residence time, has proven to be a viable means for nanoparticle synthesis. Productivity, product quality control and affordability are the main challenges still to be solved for this technology. Over the last few years, many studies have been directed towards the optimization of the synthesis of nanoparticles by inductively coupled thermal plasma, intended for the production of nanoparticles of specific size and with a narrow PSD. Also, the use of conical reaction chamber geometry and of a curtain gas to protect the reaction chamber walls from nanoparticle deposition has been suggested to increase the yield of the process, defined as the ratio of nanoparticles mass flow rate at the outlet of the reaction chamber and precursor feed rate.In this paper, we report on design oriented modeling for the optimization of the number of curtain gas injection points in a conical reaction chamber, their position along reaction chamber walls, the gas flow rate and the direction of injection, with the final aim of controlling particle size while maintaining high process yield. A computational approach is adopted to describe plasma thermo-fluid dynamics, electromagnetic field, precursor trajectories and thermal histories, and nanoparticle nucleation and growth, being the latter modeled using the moment method. Results showed that higher number of injection points results in higher process yield (>60%), at the cost of a higher total curtain gas flow rate (>200 slpm), which suggest the use of gas recirculation unit in industrial scale setups. Finally, the control of nanoparticle size can be achieved by changing the flow rate and position of the curtain gas injection points.