A Study on the Nitridation Mechanism of Silicon Particles

Abstract

Si₃N₄ ceramics can be obtained by nitridation of Si powder compact accompanying a little volume change. Elucidating the nitridation mechanism of Si particle is important to control the form of Si₃N₄ particle. In this work, TEM analysis of the initial stage of nitridation of Si particle was conducted, and following are concluded; (a) at the initial stage of nitridation of Si particle, at temperature between 1100 to 1250°C, 10nm to 50nm thickness of Si₃N₄ layer is formed between the Si body and the surface oxide layer, which indicates the nitriding velocity is low. (b) the Si₃N₄ layer becomes thinner with decreasing the radius of Si particle. (c) The nitridation mechanism of Si particle can not be explained by linear-parabolic model, and it suggests that not only the diffusion velocity of N₂ and the reaction velocity of Si and N₂. (d) The volume expansion of Si₃N₄ shell leads a radius compressive stress and circumferential tensile stress, which are proportional to the third power of a particle radius. The radius compressive stress increases with decreasing the radius of Si particle, and it controls a nitriding velocity.