Efficient carbothermal reduction of diatomaceous earth to silicon using microwave heating

The microwave-assisted carbothermal reduction of silica (SiO2) to Si was studied using diatomaceous earth (DE) as SiO2 source instead of quartz to economically produce high-purity Si for solar cell use. Under microwave irradiation, polycrystalline Si was produced at 1580-1680 degrees C within 10-20 min, The temperature and reaction time were much lower and shorter, respectively than those required over 2000 degrees C and some decades of minutes for the conventional arc-furnace process. When the C/SiO2 mole ratios were 2.0 and 1.0-1.5, the main products were silicon carbide and Si, respectively. When the C/SiO2 mole ratio was lower than 0.8, the temperature was not high enough for the formation of Si. These temperature reductions and reaction rate acceleration effects were attributed to the reaction enhancement by the amorphous nature of DE, the catalytic action of impurities of DE such as iron, and the selective fast heating effect of microwaves.