Synthesis and Characterization of Si₃N₄ Powder Produced by Laser-Induced Chemical Reaction

In an attempt to prepare very fine, high-purity Si 3 N 4 powder from an NH 3 /SiH 4 system by CO 2 laser induced reaction, the reaction parameters relating to the laser operation and the reaction conditions were examined systematically. Both pulsed and continuous high-power CO 2 lasers were used, the Si 3 N 4 powders obtained exhibited various colors from brown to white. Their particle size was 10∼15 nm, and their nitrogen content was 37 wt%. The powders were composed of amorphous and partially-crystallized particles. The α-transformation in the heat treatment of two typical samples up to 1600°C was investigated by X-ray diffraction, and the surface area reduction produced by the heat treatment was also measured. The factors affecting the synthesis of the Si 3 N 4 powder were found to be the NH 3 /SiH 4 ratio, the reaction pressure, and the laser power density.