Preparation of High Purity Si Powder from SiO_2 by Self- Propagating High-Temperature Synthesis Process

摘要

The high purity Si powder was prepared by Self-propagatingHigh-temperature Synthesis(SHS) process from a mixture of SiO_2 and Mg asraw materials. The effect of the processing parameters on the characteristics ofthe product such as molar ratio, particle size, compaction pressure andleaching conditions were studied. In the case of 20-60 mesh of Mg particlesize, the complete reduction of 5i02 required excess magnesium, 2.6 mole,whereas unreacted SiO_2 was completely eliminated with stoichiometricmolar ratio, 2.0 mole of 140-200 mesh Mg powder. As the Mg particle sizewas decreased, the combustion temperature increased and the particle size ofthe product decreased. The concurrently formed MgO in the product wasleached with an diluted HC1 solution at 70deg C for 3 hours. The productsilicon had a purity of 99.88 percent which was higher than that of the reactantSiO_2. This is because the impurities were either volatilized at the hightemperature generated during the rapid exothermic reaction or dissolved intothe HCl solution during leaching.