Aluminate/cobalt composites developing for elevated-temperature and high-efficiency electromagnetic absorbing (EMA) materials

It is increasingly urgent to develop EMA materials that combine elevated-temperature and high-efficiency absorbing performances. Herein, aluminate/Co composites were prepared through mechanical mixing and hydration hardening. The microstructures of the specimens were controlled by adjusting the shape of Co particles, and cordierite particles were added to further regulate the distribution of Co particles. Flake-shaped Co particles exhibit superior electromagnetic parameters, while the excessively high conductivity of Co flakes filled specimens leads to a significant degradation in their impedance matching, resulting in a rapid attenuation of the electromagnetic performances. The temperature-dependent ionic conductivity plays an important role in controlling the elevated-temperature conductivity and can be suppressed by adding a second dielectric component. For a 2 mm specimen, the maximum reflection loss (RL_max) reaches −13.1 dB, and the effective absorption bandwidth (RL < −5 dB, ERL₅) covers the entire X band at 500°C, presenting great potential for developing into elevated-temperature and high-efficiency EMA materials.