Microstructure and Thermo‐Kinetics Analysis in Combustion Synthesis of Si₃N₄ with High α‐Phase Content

Abstract

In this work, Si 3 N 4 powders containing~88% by weight of aphase were prepared by adopting a facile yet efficient combustion synthesis strategy under a nitrogen pressure of 6 MPa. A unique radial-spheroidal cluster morphology was strikingly observed in the as-fabricated Si 3 N 4 products. More significantly, a three-step growth mechanism was rationally proposed herein based on quenching experiments and thermo-kinetic calculations. As concluded, both the combustion temperature achieved and the sustaining time in high-temperature period played significant roles in obtaining silicon nitride powders with controlled high contents of a-phase Si 3 N 4 .

Crystal Growth in the Combustion Synthesis of α‐Si3N4 Using Si with Different Particle Sizes

“…(a), a large amount of special radial‐spheroidal‐cluster grains ranging from 10 to 50 μm in size are observed for the sample A. Lots of elongated needlelike whiskers grow in a radial form from the center of several columnar β‐Si 3 N 4 , similar to the previous work conducted by our research group . The sample B in Fig.…”

“…As proposed in our previous work, the formation of spheroidal‐cluster structures mainly in the sample A can be elucidated as follows. With a sudden rise of the temperature in the combustion wave zone, Si vapors generate and react with nitrogen via the vapor–crystal (VC) mechanism to form α‐Si 3 N 4 nuclei.…”

“…This result strongly indicates that the coarse equiaxial grain in the center is the unreacted Si particle, and shows good agreement with the crystal growth process proposed above. In the formation and growth process of Si 3 N 4 , the α‐Si 3 N 4 nuclei may also grow parallelly to the surface of liquid Si droplets and wrap along the Si droplet, leading to the sealing off of the unreacted Si and the suspending of the nitridation . Owing to the mismatch of stress between the crustaceous α‐Si 3 N 4 and the inner Si, the double‐deck sphere cracks when the temperature changes and the inner Si is exposed in the nitrogen atmosphere once again, as illustrated in Fig.…”

“…As the vaporization process of Si particles is significant to understand the whole growth process, a calculation model was developed by Mukas'yan to delve the vaporization process of single spherical Si particle in the CS system of Si–N 2 –Si 3 N 4 . Based on the model, an integral operation for the evaporation rate versus time is further carried out in our previous work . In this study, the reactant powder beds are loosely packed with a high porosity of up to ~70% under a high nitrogen pressure of 6 MPa to guarantee the excellent permeation and the sufficient nitrogen supply.…”

Catalytic Effects of Cr on Nitridation of Silicon and Formation of One-dimensional Silicon Nitride Nanostructure

“…Several methodologies and techniques have been developed to produce Si 3 N 4 powders from siliceous raw materials, including carbothermal reduction nitridation of silica56, chemical vapor deposition789, direct nitridation of silicon (Si)10, sol-gel processing1112, and combustion synthesis1314. Among these, the direct nitridation of Si powder is regarded as a low-cost and straightforward route for the large scale production of Si 3 N 4 powder and bulk Si 3 N 4 based materials.…”