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

Abstract

In an attempt to prepare very fine, high-purity Si₃N₄ powder from an NH₃/SiH₄ system by CO₂ laser induced reaction, the reaction parameters relating to the laser operation and the reaction conditions were examined systematically. Both pulsed and continuous high-power CO₂ lasers were used, the Si₃N₄ 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 Si₃N₄ powder were found to be the NH₃/SiH₄ ratio, the reaction pressure, and the laser power density.