Validation of the silicon nanoparticle production on the pilot plant scale via long-term gas-phase synthesis using a microwave plasma reactor

The formation of crystalline silicon nanoparticles by homogeneous gas-phase reactions as a direct way to produce high-purity raw material is applied. For this purpose, a microwave-assisted plasma reactor is used. Goal of this paper is to show the scalability of our process technology from laboratory scale to pilot plant scale while maintaining the particle characteristics. This is demonstrated by producing and analyzing silicon nanoparticles during long-term synthesis in a pilot-scale microwave plasma reactor over a period of six hours. The focus is on a high production rate in conjunction with consistent particle characteristics. A continuous production of the mostly spherical crystalline silicon particles with a count median diameter (CMD) of 23.4 nm and a geometric standard deviation of 1.5 is shown using TEM analysis. The stability of the synthesis process is monitored by means of regular sampling and analyzing batch samples extracted from the process every 30 min. Here it is shown that the CMD varies statistically between 21 and 26 nm. Moreover, the decomposition rate of the precursor was determined to be 99%, while the energy supply remained constant. A constant production rate of about 200 g∙h−1 is shown

A hydrogen-based burner concept for pilot-scale spray-flame synthesis of nanoparticles: Investigation of flames and iron oxide product materials

Nanoparticle synthesis in spray flames is a flexible method to produce materials with a wide range of compositions, morphologies, and properties. On the road to industrial application, the transfer from laboratory to pilot scale is an important intermediate step. In the present paper, nanoparticle synthesis based on spray combustion combined with a novel burner concept based on a fuel/air pilot flame ignited by an electrical heat ring is presented. When operating with H2, the burner concept allows nanoparticle production with a sustainable fuel. The temperature profile in the flame is one of the key factors determining the kinetics of precursor decomposition, particle formation, and growth. In this work, we have studied the gas-phase temperature in the reactive zone using non-intrusive multi-line NO-LIF temperature imaging. A solution of iron nitrate nonahydrate dissolved in ethanol was used as nanoparticle precursor mixture, atomized by a commercial two-fluid nozzle, and ignited by the premixed flame to synthesize iron-oxide nanoparticles. The burner can be operated at different conditions to direct the properties of the nanoparticles produced. To this goal, process conditions were varied in a targeted manner. In addition to variations in fuel gas and flow rates, the use of compressed air instead of pure O2 as a dispersion gas has also been investigated. The effects of these variations on temperature distribution and materials properties have been investigated. It has been determined that the dispersion gas mass flow has relatively small influence on the materials properties, while higher flame temperatures are advantageous to suppress the often-undesired liquid-to-particle synthesis pathway