High Purity Porous Silicon Powder Synthesis by Magnesiothermic Reduction of Tunisian Silica Sand

Abstract

Crystalline metallurgical silicon nanopowder was successfully produced from Tunisian silica sand by magnesiothermic reduction. Silica sand was first transformed into silica powder via a specific chemical process. The produced silica powder was reduced by magnesium granules at a temperature range of 500–800 °C. Thermal analysis shows that a low-temperature ramp rate (5 °C min⁻¹) allows the initiation of a solid-state reaction at around 528 °C. X-ray diffraction shows that the produced mixture is the result of a rather complex reaction leading to the formation of Si, and other by-products such as MgO, Mg₂Si, and Mg₂SiO₄. In order to remove the by-products, a two-steps leaching approach was used. After leaching, Si with a rate exceeding 99% was obtained. SEM images show that the produced silicon powder is composed of macro and microporous silicon crystallites having an average size dimension of about 47 nm. The porosities of the produced metallurgical silicon particles are resulting from the nature of the magnesio-reduction process. Raman investigations confirm that the resulted metallurgical silicon powder is essentially composed of silicon nanoparticles–based porous matrix. A comparison of the Fourier Infrared Spectroscopy spectrum of the produced metallurgical silicon powder with slightly doped solar grade silicon shows that both products exhibit a bulk Si-Si stretching vibrational mode at around 619 cm⁻¹. These results show that pure porous and crystalline silicon powder can be easily produced at low energy cost from an abundant local and low-cost raw material.