Transformation of waste crystalline silicon into submicro β-SiC by multimode microwave sintering with low carbon emissions

This paper presents a novel method for the transformation of waste crystalline silicon, including waste polysilicon (photovoltaic industry), single crystal silicon (waste chip), and activated carbon (AC) into submicro β-SiC in timescales of minutes using a multimode microwave rotary tube reactor under open-air conditions. This research addressed the difficult problem of microwave sintering temperature measurement by using light conducted by a quartz tube wall. The synthesis underwent a liquid-solid reaction at 1450 ± 50 °C for 6–8 min, which is a noticeable improvement when compared to industrial processes, where a heating time of 30 h and temperatures of 2200–2400 °C are commonly needed. Theoretical calculations show that the new synthesis method for β-SiC consumes 4.1–4.8 times less energy than modern production methods using quartz sand (SiO₂) as the raw material, and CO₂ emission using this method is reduced by 76–79%.