Preparation of Silicon Nanopowder by Recycling Silicon Wafer Waste in Radio-Frequency Thermal Plasma Process

Abstract

Silicon nanopowders were prepared from silicon waste by using radio-frequency thermal plasma. Silicon waste, generated from the manufacturing process of silicon wafers, was pulverized to form micrometer-sized silicon starting powder. In order to obtain as much silicon nanopowder as possible from thermal plasma processing, the enhancement of vaporization and the quenching rate of the silicon starting powder were considered as major factors. A counter-flow injection apparatus (CFIA) was introduced for improved vaporization and homogeneous nanoparticles. It was designed to inject argon as a quenching gas in the direction opposite the thermal plasma flame flow. The controlled location of the CFIA injection nozzle and the flow rate of the quenching gas affect the residence time of the injected staring powder by recirculating flow and the vapor density by gas mixing. The variation of the flow pattern inside the reactor and the characteristics of the products were investigated to determine the optimal processing environment to prepare uniform and small silicon nanopowder particles. The environment was defined by two parameters: the flow rate of the counter quenching gas and the distance between the torch and CFIA nozzles. The flow rate of the quenching gas was controlled from 30 to 70 L/min. The distance between the torch and CFIA nozzles was adjusted from 150 to 350 mm. When the quenching gas flow rate of 70 L/min and the distance of 350 mm were applied, the uniform and smallest silicon nanopowders were obtained.