Effect of low-temperature pre-oxidation on the wave-absorbing properties of PIP-SiC/SiCN composites

SiC/SiCN composites, renowned for their exceptional high-temperature mechanical properties, wave-absorbing capabilities, and oxidation resistance, hold significant promise for applications in aerospace, national defense, and military industries. This study investigates the effect of low-temperature pre-oxidation treatment on the structure and electromagnetic properties of polysilazane (PSN) precursors, as well as their resulting SiC/SiCN composites. A variety of characterization techniques, including FTIR, TG, SEM-EDS, XRD, XPS, and Raman spectroscopy, are employed to elucidate the mechanisms by which pre-oxidation temperature influences the microstructure and chemical composition of the materials. The results demonstrate that pre-oxidation treatment substantially enhances the ceramic yield of PSN, which increases from 70.73 % to 82.09 % as the pre-oxidation temperature is raised from 150 °C to 350 °C. Furthermore, with the increase in pre-oxidation temperature, the content of the SiC_xO_y phase in the PSN pyrolysis products rises, while the concentrations of SiC microcrystals and free carbon decrease. This shift in microstructure leads to a notable reduction in the complex permittivity of the composites. Specifically, at a pre-oxidation temperature of 250 °C, the complex permittivity of the composites at 10 GHz decreases to 6.3-j4.3, demonstrating excellent wave-absorbing performance at room temperature. Additionally, pre-oxidation treatment significantly enhances the high-temperature electromagnetic performance of the composites. At a sample thickness of 3.5 mm, the material exhibits optimal wave-absorbing performance (−18.56 dB) at 700 °C. These findings provide a robust theoretical foundation for the development of high-performance wave-absorbing composites designed for high-temperature environments.