Design and performance of lightweight high–temperature resistant microwave penetrating foamed ceramics

To develop lightweight microwave penetrating materials capable of operating at high temperatures, the technical potential of preparing foamed ceramics (FCs) from a simple material system using boron nitride (BN) as the foaming agent was studied. The preparation mechanism of the FCs is that the oxidation–derived nitrogen from BN blows up the molten ceramic body during sintering. The FCs sintered at 1000 °C from the material system containing 0.3 wt% ferric oxide have a uniform pore structure with a mean pore diameter of 1.0 mm, high total/closed porosities of 82 %/81 %, a low density of 0.45 g/cm3, and an adequate compressive strength of 6.9 MPa. The high porosity and simple composition allow the FCs to have a low permittivity of 2.09+j0.024 in the X–band and over 95 % penetration of incident microwaves in the 8.0–18.0 GHz frequency range. The FCs are potentially lightweight, moisture resistant and thermal insulating due to their low density, high closed porosity, and uniform pore structure, which are expected to be an excellent high–temperature microwave penetrating material based on their retention of pore structure and physical–mechanical properties at 800 °C.