Electromagnetic Performance of CVD Si 3 N 4 –SiCN Ceramics Oxidized from 500 to 1000 °C

In this paper, SiCN ceramics are introduced into Si 3 N 4 substrate by chemical vapor deposition (CVD) using SiCl 4 –C 3 H 6 –NH 3 –H 2 –Ar mixture gases, and then the as‐prepared Si 3 N 4 –SiCN ceramics are oxidized at 500, 800, 1000   °C for 5   h. At 500   °C, the weight and electromagnetic (EM) wave absorbing performance of Si 3 N 4 –SiCN ceramics change slightly with the increasing oxidation time, indicating that there is no obvious oxidation occurring for Si 3 N 4 – 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 Si 3 N 4 –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 Si 3 N 4 –SiCN ceramics disappear completely after 5   h, showing EM wave transparent properties. The EM wave absorbing properties of Si 3 N 4 –SiCN ceramics are mainly dominated by SiC. In addition, the content of absorbing agents can be calculated by analyzing the weight change of Si 3 N 4 –SiCN ceramics at 1000   °C.