Fabrication and properties of borazine derived boron nitride bonded porous silicon aluminum oxynitride wave-transparent composite

摘要

Boron nitride bonded porous silicon aluminum oxynitride composite was fabricated by gel-casting, precursor infiltration and pyrolysis process, and the composition, microstructure, mechanical and dialectical properties of the composite were characterized. The results show lhat the composite is comprised of β-SiAlON (z = 3) synthesized from mixed ceramic powders, and continuous h-BN pyrolyzed from borazine, with a relatively high porosity of 24.21%. The flexural strength, elastic modulus and fracture toughness of the composite are 178.58 MPa, 75.51 GPa and 4.54 MPa m"2, respectively. The sintering shrinkage of SiAlON ceramics can be greatly decreased by the borazine infiltration and pyrolysis process. The exi stence of h-BN phase and the high porosity reduce the values of dielectric constant and loss tangent of the composite, which are 3.51 -3.69 and 0.9-3.1 x 10 ' a( the frequency from 7 to 18 GHz with the elevating temperature from 25 to 1200 °C.