Abstract: Rapid development of high-speed aircraft technology poses an urgent demand for materials capable of integrating radar wave transmission and infrared transmission under extreme environments. Mullite ceramics have emerged as a promising candidate materials due to their excellent high-temperature mechanical properties, dielectric properties, and inherent infrared transparency. However, the traditional preparation methods of mullite ceramics typically require high sintering temperature and involve complex processes, which limit their practical applications. In this work, one-step rapid sintering of mullite ceramics at 1200 ℃ was successfully achieved by utilizing highly active, low-cost porous raw materials and spark plasma sintering (SPS) technology, significantly reducing the sintering temperature and shortening the preparation cycle. This process relies on the synergistic effect between the high-active surfaces released by mesoporous structure collapse and the SPS field effect, thereby developing a low-cost, short-cycle, and low-temperature preparation process. The effects of sintering process parameters on the microstructure, mechanical properties, dielectric properties, and infrared transmission properties of the ceramics were investigated in depth. Under the conditions of 1200 ℃, 70 MPa and a heating rate of 100 ℃·min^-1, the prepared ceramics exhibit a density of up to 3.06 g·cm^-3 and a porosity as low as 1.6%; the flexural strength reaches 152.9 MPa and the flexural modulus is 87.1 GPa. The high mechanical pressure promotes the transformation of mullite grains from acicular to short columnar, and the fracture mode transitions from intergranular to transgranular, endowing the ceramics with excellent mechanical properties. In the 8-16 GHz band, the average dielectric constant is 6.77 with good stability, the dielectric loss tangent (tanδ) is 4.7×10^-4, and the wave transmittance exceeds 70%, which is attributed to the significant reduction in dielectric polarization caused by the residual pores in the sintered ceramics. Meanwhile, the transmittance in the near-infrared (NIR) band reaches 45.11%, demonstrating promising application prospects in the field of radar/infrared dual-mode wave-transparent materials.

Key words: mullite ceramics, spark plasma sintering, low-temperature preparation, dielectric properties, infrared transmittance