Microstructure and Dielectric Properties of LPCVD/CVI-SiBCN Ceramics Annealed at Different Temperatures.

Jianping Li,Fang Ye,Nan Chai,Hailong Qin,Litong Zhang,Laifei Cheng,Mingxi Zhao,Yongsheng Liu

doi:10.3390/ma10060655

Abstract

SiBCN ceramics were introduced into porous Si3N4 ceramics via a low-pressure chemical vapor deposition and infiltration (LPCVD/CVI) technique, and then the composite ceramics were heat-treated from 1400 °C to 1700 °C in a N2 atmosphere. The effects of annealing temperatures on microstructure, phase evolution, dielectric properties of SiBCN ceramics were investigated. The results revealed that α-Si3N4 and free carbon were separated below 1700 °C, and then SiC grains formed in the SiBCN ceramic matrix after annealing at 1700 °C through a phase-reaction between free carbon and α-Si3N4. The average dielectric loss of composites increased from 0 to 0.03 due to the formation of dispersive SiC grains and the increase of grain boundaries.

Highlights

Siliconboron carbonitride ceramics (SiBCN) are considered as promising materials for high-temperature structural ceramics, continuous fiber reinforced ceramic matrix composites (CFCC) [1,2,3,4,5], and agents for electromagnetic wave (EMW) absorber [6], etc., because of their low density, supreme ultra-high temperature stability up to 2000 ◦ C [7], good resistance to oxidation and creep [8], and high strength and modulus [7,8,9]
The Si3 N4 ceramics fabricated using the previous method [26] were machined into specimens with dimensions of 2.16 mm × 10.16 mm × 22.86 mm for dielectric properties measurement
These samples were put into a CVD/CVI furnace to infiltrate SiBCN ceramics using methyltrichlorosilane (CH3 SiCl3, MTS ≥ 99.99%), boron trichloride (BCl3 ≥ 99.99%), and ammonia (NH3 ≥ 99.99%) as gas resources at 800 ◦ C

Summary

Introduction

Siliconboron carbonitride ceramics (SiBCN) are considered as promising materials for high-temperature structural ceramics, continuous fiber reinforced ceramic matrix composites (CFCC) [1,2,3,4,5], and agents for electromagnetic wave (EMW) absorber [6], etc., because of their low density, supreme ultra-high temperature stability up to 2000 ◦ C [7], good resistance to oxidation and creep [8], and high strength and modulus [7,8,9]. For non-magnetic ceramic materials, ideal EMW absorption materials must satisfy two requirements: (1) the impedance matching between free space and the material surface to prevent the wave being reflected, which requires the complex permittivity to be close to 1; and (2) materials can absorb as many incident waves as possible inside of absorbers, which requires materials exhibit strong dielectric loss [13]. In the quaternary SiBCN ceramics, SiC is a wide band gap semiconductor material and carbon is a good conductor, both of which have excellent EMW absorption and shielding properties and can be good dielectric loss phases [12,14,15]. SiBCN ceramics have aroused much enthusiasm for high-temperature functional materials because of the excellent EMW absorption property

Methods

Discussion

Conclusion