Production of solar-grade silicon from metallurgical silicon by precipitation from aluminum melt
Author: Bochang Chen
Year: 2023
Supervisors: Guðrún A. Sævarsdóttir, Halldór G. Svavarsson
Abstract:
Solar-grade silicon (SoG-Si) is conventionally produced from metallurgical silicon (MG-Si) via the so-called Siemens process. The Siemens process involves the use and production of highly hazardous silane gases and hydrochloric acid. This makes the process environmentally unfriendly and costly. This work aims to use a metallurgical method to produce SoG-Si from MG-Si precursor with lower environmental impact and less cost than with the Siemens process. This is achieved by melting aluminum and silicon together and then cooling the resulting alloy. Upon cooling, silicon starts to precipitate out of the melt. The working principle of this experiment is that impurities are better accommodated in the melt rather than in the solid. The ratio in which the equilibrium concentration of an impurity in a liquid is to the concentration of an impurity in a solid is defined with so-called segregation coefficient, which is quite high for many impurities in the Si(s)-SiAl(l) system. The resulting silicon crystals were inspected by four different characterization methods, inductively coupled plasma, scanning electron microscope, energy dispersive X-ray, and X-ray diffraction, to evaluate the morphology of the samples and analyze the remaining impurities.
We believe this approach could be feasible for SoG-Si production with less environmental impact and lower energy consumption compared to the conventional production methods. Adding to that, this method is simple and requires less hazardous chemicals in comparison to the Siemens process.