Abstract: The silicon mixture mechanically activated for 20h could combust in air. It was found that the burning of silicon powder occurred via two-stage self-propagating regime. The surface and center of the synthesized products are demonstrated to be with different features. On the surface of the product, α-Si₃N₄ is the major phase coexisting with minor Si₂N₂O and amorphous SiO₂, while in the center of the lump, loose grey powders are Si₃N₄ powders whose phase composition depends on the reaction conditions. The whole combustion process of silicon powders in air after mechanical activation approves the feasibility of silicon combustion in air. The qualitative discussion given shows the formation of Si3N4 instead of SiO₂ in air. Furthermore, the phase composition of product can be controlled by adjusting the composition of the reactant mixtures.

Key words: mechanical activation, combustion synthesis in air, Si3N4