The dielectric adjustment in SiCf/mullite composites limited carbon content by in situ growth SiO2 layer

Abstract

Recently, SiC-continued fiber-reinforced ceramic matrix composites were widely used in high-temperature absorbing materials. However, the excessive carbon content indicated the deteriorative absorbing property. To solve the impedance mismatching of the SiC matrix and increase the charge accumulation at the multi-phase interface, SiC_f/mullite composites were prepared in this paper by using the sol–gel method. The introduction of mullite matrix without free carbon improved impedance matching characteristics. The strong bonding between the in situ grown SiO₂ layer and the mullite matrix caused by high temperature induced the Maxwell–Wagner effect, which effectively optimized the absorbing performance. The complex dielectric constant of the composite increased with higher sintering temperatures. The highest reflection loss reached − 23.1 dB at the sintering temperature of 1100 °C. With the two-step drying process, the porosity was reduced to 16.1% and the density increased. The crystallinity and density of the mullite matrix increased in the rising sintering temperatures, with the highest bending strength reaching 157.89 MPa for composites sintered at 1100 °C.