Preparation and performance of foamed-ceramic-based microwave absorbing composites using dendritic nickel as absorbent

To improve the microwave absorbing (MA) performance and thermal stability, the technical potential of preparing foamed-ceramic-based MA composites using dendritic nickel (DN) as absorbent was investigated. The DN, which are in dendritic morphology and assembled from the micro-spherical particles, were synthesized via a simple electrodeposition method. The synthesized DN exhibited good oxidation resistance due to the formation of a protective passivation layer at elevated temperatures. Subsequently, the foamed-ceramic-based MA composites were prepared through a foaming-sintering process using a mixture powders containing BN blowing agent and DN absorbent. The resulting composites possessed a uniformly porous structure, with average pore diameters ranging from 0.95 to 1.38 mm and porosities between 76% and 82%. Notably, DN was well preserved in composites, attributed to its inherent oxidation resistance and the nitrogen-rich protective atmosphere generated by BN oxidation. At 15 wt% DN content, the composites achieved outstanding microwave absorption, with an average reflection loss (RL) of −14.1 dB, a RL_min of −42.2 dB@13.7 GHz, and an effective absorption bandwidth (EAB) of 6.8 GHz. Furthermore, the composites well maintained their physical properties, mechanical strength, and MA performance after 100-h heat treatment at 800 °C in air, demonstrating excellent thermal stability.