Characterization and Microstructural Evolution of Continuous BN Ceramic Fibers Containing Amorphous Silicon Nitride.

Yang Li,Shouquan Yu,Huifeng Zhang,Weigang Zhang,Zhiguang Wang,Min Ge,Chuanbing Huang,Weijia Kong

doi:10.3390/ma14206194

Abstract

Boron nitride (BN) ceramic fibers containing amounts of silicon nitride (Si3N4) were prepared using hybrid precursors of poly(tri(methylamino)borazine) (PBN) and polycarbosilane (PCS) via melt-spinning, curing, decarburization under NH3 to 1000 °C and pyrolysis up to 1600 °C under N2. The effect of Si3N4 contents on the microstructure of the BN/Si3N4 composite ceramics was investigated. Series of the BN/Si3N4 composite fibers containing various amounts of Si3N4 from 5 wt% to 25 wt% were fabricated. It was found that the crystallization of Si3N4 could be totally restrained when its content was below 25 wt% in the BN/Si3N4 composite ceramics at 1600 °C, and the amorphous BN/Si3N4 composite ceramic could be obtained with a certain ratio. The mean tensile strength and Young’s modulus of the composite fibers correlated positively with the Si3N4 mass content, while an obvious BN (shell)/Si3N4 (core) was formed only when the Si3N4 content reached 25 wt%.

Highlights

IntroductionBecause of the occurrence of re-crystallization and particle coarsening, quartz fibers undergo serious degradation of mechanical strength at temperatures above 900 ◦ C [6]
The microstructural developments of pure Boron nitride (BN) and Si3 N4 pyrolyzed at different temperatures from PBN and PCS were investigated by X-ray diffraction (XRD) (Figure 1)
For Si3 N4 (Figure 1b), it can be seen that the as-pyrolyzed ceramics were amorphous below 1400 ◦ C, and the crystallization process started at 1500 ◦ C, which would affect the high temperature stability of ceramics or ceramic fibers

Summary

Introduction

Because of the occurrence of re-crystallization and particle coarsening, quartz fibers undergo serious degradation of mechanical strength at temperatures above 900 ◦ C [6]. BN fibers show excellent high-temperature stability, with a melting point above 2900 ◦ C [7,8,9], their low mechanical strength impedes any further development [10,11]. It is urgent to develop new types of ceramic fibers containing B, N, and Si to combine the merits of both BN and Si3 N4 fibers in order to ensure excellent dielectric properties, high mechanical properties and good thermal resistance [13,14,15,16]

Methods

Results

Conclusion