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

Abstract

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.