Effects of pyrolysis time on properties of hollow silica fibre reinforced BN–Si₃N₄ matrix composites

Abstract

Hollow silica fibre reinforced BN–Si₃N₄ matrix composites (SiO_2f/BN–Si₃N₄ composites) were fabricated by repeated infiltration and pyrolysis from a hybrid precursor. The effects of pyrolysis time on densification behaviour, mechanical properties, dielectric properties and microstructures of the composites were investigated. With increasing pyrolysis time, the density of SiO_2f/BN–Si₃N₄ composites increases, the elastic modulus increases accordingly; however, the flexural strength and the dielectric properties decrease. The composites prepared at 400°C with the pyrolysis time of 1 h exhibit a maximum flexural strength of 132·4 MPa, a low dielectric constant of 2·78 and a low loss angle tangent value of 1·4 × 10^–3. The high performance of the composites results from the good state of the silica fibres, controlled fibre/matrix interfacial microstructures, high purity hollow silica fibres with excellent dielectric properties and low density non-carbon nitride matrix. The calculation results of dielectric performance show that the composites prepared with the pyrolysis time of 1 h have broadband transmission properties.

Keywords:

• PYROLYSIS TIME
• COMPOSITES
• PRECURSOR INFILTRATION AND PYROLYSIS
• MECHANICAL PROPERTIES
• DIELECTRIC PROPERTIES