Improved electromagnetic absorbing properties of Si3N4-SiC/SiO2 composite ceramics with multi-shell microstructure

Porous Si3N4-SiC composite ceramic was fabricated by infiltrating SiC coating with nano-scale crystals into porous beta-Si3N4 ceramic via chemical vapor infiltration (CVI). Silica (SiO2) film was formed on the surface of rod-like Si3N4-SiC grains during oxidation at 1100 degrees C in air. The as-received Si3N4-SiC/SiO2 composite ceramic attains a multi-shell microstructure, and exhibits reduced impedance mismatch, leading to excellent electromagnetic (EM) absorbing properties. The Si3N4-SiC/SiO2 fabricated by oxidation of Si3N4-SiC for 10 h in air can achieve a reflection loss of -30 dB (>99.9% absorption) at 8.7 GHz when the sample thickness is 3.8 mm. When the sample thickness is 3.5 mm, reflection loss of Si3N4-SiC/SiO2 is lower than -10 dB (>90% absorption) in the frequency range 8.3-12.4 GHz, the effective absorption bandwidth is 4.1 GHz. (c) 2013 Elsevier Ltd. All rights reserved.