Study on preparation of silica nanospheres by oxidation of micron silicon powder

The oxidation of molten silicon powder in a high-temperature suspension phase represents a promising technique for the continuous production of spherical silica. However, the agglomeration of silicon powder at high temperatures increases particle size and reduces reactant surface area, ultimately slowing the oxidation rate and disrupting the suspension state, leading to failed silica preparation. To address these issues, a pre-oxidation step was implemented, whereby an oxide layer was created on the silicon powder. This was done to prevent molten silicon from agglomerating. This paper investigates the effect of pre-oxidation time and melting temperature on the generation of spherical silica using a static suspension method. The 5 µm average-sized silicon powder underwent pre-oxidation at 1300°C for 30 min, followed by oxidation at the silicon's melting point. This resulted in amorphous spherical silica, ranging from 200 to 400 nm. Pre-oxidation results in a Si@SiO₂ core–shell structure, which effectively prevents molten silicon agglomeration and significantly enhances particle oxidation rates. These findings lay the foundation for scaled-up production of spherical silica using the airflow suspension method.