Electromagnetic Performance of CVD Si₃N₄–SiCN Ceramics Oxidized from 500 to 1000 °C

In this paper, SiCN ceramics are introduced into Si₃N₄ substrate by chemical vapor deposition (CVD) using SiCl₄–C₃H₆–NH₃–H₂–Ar mixture gases, and then the as-prepared Si₃N₄–SiCN ceramics are oxidized at 500, 800, 1000 °C for 5 h. At 500 °C, the weight and electromagnetic (EM) wave absorbing performance of Si₃N₄–SiCN ceramics change slightly with the increasing oxidation time, indicating that there is no obvious oxidation occurring for Si₃N₄–SiCN ceramics. At 800 and 1000 °C, the initial oxidation of SiCN ceramics is controlled by oxidation of carbon, which is transformed into oxidation of SiC with the increasing oxidation time. At 800 °C, the dielectric properties and EM wave absorbing performance of Si₃N₄–SiCN ceramics decrease finally. The minimal reflection coefficient (RC) is only –3.8 dB at the thickness of 2.65 mm. At 1000 °C, the absorbing agents in Si₃N₄–SiCN ceramics disappear completely after 5 h, showing EM wave transparent properties. The EM wave absorbing properties of Si₃N₄–SiCN ceramics are mainly dominated by SiC. In addition, the content of absorbing agents can be calculated by analyzing the weight change of Si₃N₄–SiCN ceramics at 1000 °C.