The Production of Si from SiO2 via the Ball-Milling Technique
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The ball-milling technique employs mechanical energy to reduce the particle size of reactants to a size small enough to cause defects in the reactants’ lattice structures and produce active sites. In exothermic reactions, solid-state diffusions within these active sites induce self-heat propagating synthesis (SHS), allowing a complete reaction via mechanical energy. However, extracting silicon from silicon oxide using aluminum is endothermic, and therefore milling alone does not complete the reaction. This study sought to supplement the solid-state diffusion via the lattice defects with energy supplied by moderate heat treatment as a method of producing pure silicon and to investigate the parameters of this method to maximize its efficiency. The parameters tested were annealing temperature, milling time, and annealing time. The relationship between annealing temperature and milling time was also investigated thoroughly. X-ray diffraction, as well as some comparison with Atomic Force Microscopy, was used to determine the presence of products in samples. The data confirmed that milling is necessary for the reaction to take place, and that even one minute of milling can change the products significantly. The use of milling, combined with a moderate heat treatment, can produce silicon in a way that is more environmentally friendly and cost-effective than current methods and can be used at tonnage proportions for industrial purposes.