Effect of heat-treatment on the microstructure of precipitates in metallurgical grade silicon

The microstructure and content of precipitates in metallurgical grade silicon (MG-Si) play a crucial role in the synthesis of silicone monomers. However, only few studies were focused on the regulation of precipitates due to the complexity. Herein, the evolution of the macro and microscopic structural transformation of the precipitates was explored by investigating the responses to heat-treatment at different temperatures. The results demonstrate that as the heat-treatment temperature increases, macroscopically, the inclusions first split and then gradually turn to roundness. Furthermore, the Si8Al6Fe4Ca phase was significantly increased after the heat-treatment at 900 °C, enhancing the selectivity of the silicone monomer synthesis. The chemical reaction is assumed according to the conservation of elements mass, 3Si2Al2Ca + 4FeSi2 = Si8Al6Fe4Ca + 2CaSi2 +2Si. This work provides the potential of heat-treatment in regulating the precipitates of MG-Si, which could provide a higher-quality raw material for the synthesis of silicone monomers