Microstructure and Dielectric Property of 3D BN_f/Si₃N₄ Fabricated by CVI Process

Abstract

As potential wave-transparent materials applied at high temperatures, 3D BN_f/Si₃N₄ ceramic matrix composites were prepared by low pressure chemical vapor infiltration or deposition (LPCVI/ CVD) process from SiCl₄-NH₃-H₂-Ar gas precursor at 800 °C. The densification process, microstructure and dielectric properties of 3D BN_f/Si₃N₄ composites were investigated. The results indicated that 3D BN_f/ Si₃N₄ was successfully fabricated by LPCVI/CVD, with final open porosity of 2.37% and density of 1.89 g/ cm³. Densification kinetics of 3D BN_f/Si₃N₄ is a typical exponential pattern. The Si₃N₄ matrix was uniformly infiltrated into porous BN_f preform. The deposited Si₃N₄ matrix was amorphous by XRD analysis. Introduction of BN fiber into Si₃N₄ ceramic lowered the permittivity of Si₃N₄. The fabricated BN_f/Si₃N₄ composites possess low permittivity of 3.68 and low dielectric loss of lower than 0.01, which are independent of temperature below 400 °C. Transmission coefficient of BN_f/Si₃N₄ composite is 0.57 and keeps stable below 400 °C. BN_f/Si₃N₄ can be fabricated at low temperature and may be candidates for the microwave transparent materials.

Keywords

BN_f/Si₃N₄ / LPCVI / dielectric property / high temperature stability

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