EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

In recent years, there has been a great effort to reduce CO2 emission in the metal production processes including the silicon production process. To reduce CO2 emission in the Si production, metallothermic, rather than carbothermic reduction of quartz is a possible alternative.
In the current work, the mechanism of reduction of natural quartz by Mg was studied. The reduction reaction has been performed on different quartz particle sizes, Mg to quartz mole ratios and various holding time. The temperature of reduction reaction was chosen relatively high, 1100 °C, to have reasonable reaction rate, especially for larger quartz particle sizes. Quantitative XRD analysis revealed that Mg2SiO4 and Mg2Si are the two main intermediate phases formed during the reduction reaction, and their amounts are decreased upon holding time at elevated temperatures. The formation of a MgO outer layer, however, confirmed that Mg diffusion through the product layers formed over an unreacted shrinking quartz core is the rate limiting step. Furthermore, the formed MgO has very porous structure, while Si nucleates randomly in the MgO matrix or forms outside the original SiO2 particles. The quartz particle size had a great influence on the progress of the reduction reaction, and Mg diffusion through the particles with size of around 57±25 µm after holding time of 20 minutes was observed causing complete quartz conversion. However, for larger particle size of 703±175 µm, there was some quartz left at the core of particles even after 2 h holding time.