Direct Nitridation Synthesis of Quasi-Spherical β-Si3N4 Powders with CaF2 Additive.

Lan Lan,Zhou Zhou,Wei Wei,Yin Yin,Li Li,Luo Luo

doi:10.3390/ma12182870

Abstract

In this work, the quasi-spherical β-Si3N4 powders were synthesized via an efficient direct nitridation strategy with CaF2 as the catalytic material under NH3 atmosphere. The effect of CaF2 on phase composition and crystalline morphology was studied. CaF2 additive can accelerate the nitridation of silicon powders, and the particles of nitridation products tend to have an equiaxed structure with the CaF2 additive increasing. When 4 wt% CaF2 additive or more was added, submicron β-Si3N4 particles with quasi-spherical morphology and eminent crystal integrity were obtained. In contrast, irregular α-Si3N4 particles appear as the main phase with less than 4 wt% CaF2 additive. The growth mechanism of Si3N4 particles was also discussed. CaxSiyOz liquid phase is crucial in the nitridation of silicon powders with CaF2 additive.

Highlights

Introduction βSi3 N4 has been extensively used in thermally conductive filler of high-performance, thermal interface materials due to its remarkable superiorities, such as high electrical resistivity, low dielectric loss, and high intrinsic thermal conductivity with the theoretical value of 200–300 Wm−1 K−1 [1,2,3].To improve the device performance, the compaction density of Si3 N4 powders must be as high as possible
Submicron β-Si3 N4 powders with quasi-spherical morphology were prepared through direct nitridation synthesis under NH3 atmosphere at 1300°C with appropriate content of
CaF2 additive can accelerate nitridation of silicon powders and its content has a great impact on the formation of Si3 N4 particles

Summary

Introduction

Si3 N4 has been extensively used in thermally conductive filler of high-performance, thermal interface materials due to its remarkable superiorities, such as high electrical resistivity, low dielectric loss, and high intrinsic thermal conductivity with the theoretical value of 200–300 Wm−1 K−1 [1,2,3]. To improve the device performance, the compaction density of Si3 N4 powders must be as high as possible. Equiaxed structure is beneficial to maximize the compaction density of Si3 N4 powder. Direct nitridation strategy is a simple and efficient method to acquire high purity Si3 N4 powders [7]. This process can be expressed by Equation (1) or (2): Si3 N4 particles are difficult to transform into spheres, but they tend to grow in specific directions, forming whiskers, fibers, and hexagonal crystals [4,5,6].

Methods

Results

Conclusion