Preparation and dielectric properties of porous mullite‐based wave transparent ceramics

Microwave sintering has been recognized as a new generation of sintering technology due to its advantages, such as efficient heating, energy conservation, safety, and environmental friendliness. To further enhance the exploration of liner materials that can maintain excellent wave transmission performance at high temperatures, porous mullite‐based ceramics were prepared by freeze‐drying combined with reactive sintering method; the effects of firing temperature, Al 2 O 3 content on microstructure, porosity, and compressive strength were investigated; and the variation of dielectric properties with temperature was analyzed. The results indicate that the porosity of porous mullite‐based ceramics ranges from 70.5% to 74.9%, and the optimal dielectric performance was achieved when Al 2 O 3 content is 70%. At 2.45 GHz, the dielectric constant and dielectric loss tangent of porous mullite‐based ceramics with a thickness of 7 mm were measured to be 1.73 and 2.0 × 10 3 . The tests on its high‐temperature dielectric properties show that the dielectric constant only increases from 1.73 to 2.17 at RT to 800°C, tanδ increases from 2.0 × 10 −3 to 5.0 × 10 −2 , and its wave transmittance is higher than 90% at 800°C, showing stable temperature dependence. In addition, the compressive strength of all the samples is higher than 3 MPa; all the above results suggest that the porous mullite‐based ceramics prepared in this paper are promising electromagnetic wave transparent materials.