Preparation of BN/SiO₂ ceramics by PIP method

Abstract

The precursor infiltration and pyrolysis (PIP) method for preparation of BN/SiO₂ composites was used to improve mechanical properties, dielectric properties and feasibility of high temperature dielectric parts with large dimensions and complex shapes. In the processing procedure, the porous BN ceramic matrix was first successfully prepared by compacting the mixed powders of B and BN and then sintering them at a certain temperature under normal pressure of N₂. The polycarbosilane (PCS) solution was vacuum infiltrated into porous BN ceramics at the room temperature and then at 800 °C in the air to depolimerize out amorphous SiO₂, and sintered further at 1 300 °C in N₂ to get BN/SiO₂ composites. The microstructure of materials was studied by means of X-ray diffraction and electron probe micro analysis. The thermo-decomposition mechanism of PCS was investigated by a TG-DTA and infrared (IR) spectrum analysis. The flexural strengths were measured by the three-point bending method. The dielectric constant and the loss tangent were measured by the wave-guide method. The results show BN/SiO₂ composites were fabricated. The obtained composites posses a flexural strength of 61.96–93.31 MPa, the dielectric constant in the range of 3.50–3.78 and the order of magnitude of the loss tangent at 10⁻³, which are good for the high temperature dielectric parts with large size and complex shapes.

Keywords

BN/SiO₂ ceramics / composites / properties

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