Synthesis of Silicon Nitride Nanoparticles by Upcycling Silicon Wafer Waste Using Thermal Plasma Jets

Silicon (Si) waste generation is a critical issue in the development of semiconductor industries, and significant amounts of Si waste are disposed via landfilling. Herein, we propose an effective and high value-added recycling method for generating nitride nanoparticles from Si waste, such as poor-grade Si wafers, broken wafers, and Si scrap with impurities. Si waste was crushed and used as precursors, and an Ar-N2 thermal plasma jet was applied at 13 kW (300 A) under atmospheric pressure conditions. A cone-type reactor was employed to optimize heat transfer, and Si waste was injected into the high-temperature region between the cathode and anode to react with free/split nitrogen species. Spherical Si3N4 nanoparticles were successfully synthesized using isolated nitrogen plasma in the absence of ammonia gas. The crystalline structure comprised mixed α- and β-Si3N4 phases with the particle size <30 nm. Furthermore, the influence of ammonia gas on nitridation was investigated. Our findings indicated that Si3N4 nanoparticles were successfully synthesized in the absence of ammonia gas, and their crystallinity could be altered based on the reactor geometry. Therefore, the as-proposed thermal plasma technique can be used to successfully synthesize high value-added nanopowder from industrial waste.