The poor wet-oxidation resistance limits the long-life service of SiC f /SiC composites as the hot end components of aero-engines. The stability of SiC f /SiC composites under high-temperature wet oxygen environment can be promoted by more robust SiC matrix. In this work, the effect of Y 2 O 3 on the corrosion behaviors of SiC ceramics in flowing O 2 /H 2 O atmosphere at 1400 ℃ was studied. Duo to the continuous Y 2 Si 2 O 7 layer formed on the surface, SiC-Y 2 O 3 ceramics exhibit much better wet-oxidation resistance than original SiC ceramics. During the oxidation process , Y 2 O 3 dispersed in the ceramics migrates to the surface and reacts with SiO 2 to form β-Y 2 Si 2 O 7 . Subsequently, the β-Y 2 Si 2 O 7 aggregates and grows to form a continuous Y 2 Si 2 O 7 layer, inhibiting the corrosion from oxidizing medium to the inner SiC matrix. This study is expected to provide important ideas for the design and structure regulation of wet-oxidation resistant SiC f /SiC composites.
Polymer derived SiCN ceramics (PDC SiCN) are the key high-temperature matrix materials for structural and stealth integrated ceramic matrix composites (CMC). However, low crystallization degree and homogeneous microstructure of PDC SiCN ceramics results in the lack of effective microwave attenuation mechanism. Hence, a new kind of nonmagnetic metal oxide (Y 2 O 3 ) was in-situ formed in SiCN ceramics to enhance the conductivity loss as well as the polarization loss. Y 2 O 3 modified PDC SiCN ceramics (SiCN-Y 2 O 3 ceramics) were fabricated by pyrolysis polysilazane with different Y(NO 3 ) 3 content at 900 ºC. For the SiCN-Y 2 O 3 ceramic, Y 2 O 3 nanoparticles were dispersed in SiCN ceramic uniformly forming a large number of Y 2 O 3 -SiCN heterogeneous amorphous interface, defects and dipole polarization to enhance its microwave absorbing properties. Due to the multiple polarization loss mechanism, SiCN-Y 2 O 3 ceramic with 10 wt% Y(NO 3 ) 3 content achieved excellent microwave absorption performance at a wide thickness range with the microwave absorbing efficiency more than 90% in the whole X band, and the RC min could reach − 50.2 dB at the thickness of 3.5 mm.
危险品化学品经营许可证（带存储）