Strong contribution of in situ grown nanowires to enhance the thermostabilities and microwave absorption properties of porous graphene foams under different atmospheres

Free-standing and high-performance electromagnetic (EM) absorbing materials of three-dimensional (3D) hierarchical graphene foams (GFs) decorated with in situ grown Si3N4 nanowires (Si3N4nws) and SiC nanowires (SiCnws) were prepared using a one-step carbothermal reduction process under flowing N-2 and Ar, respectively. The as-obtained Si3N4nws consist of single crystalline Si3N4 cores similar to 200 nm in diameter and amorphous SiOx Layers similar to 2 nm in thickness, and the SiCnws are composed of single crystalline SiC cores about 200 nm in diameter and amorphous SiOx, sheaths with an average thickness of 25 nm. By incorporating Si3N4nws and SiCnws into GFs, the thermostabiLity and EM absorption of the composites were simultaneously improved effectively. The Si3N(4nws),-GFs and SiCnws-GFs were thermostabLe in an air atmosphere beyond similar to 640 degrees C with above 98% and 94% weight retention, respectively. Compared with those of pure GFs, the S3N(4nws)-GFs exhibit a stronger EM microwave absorption performance with a minimum reflection Loss (RL) value of -48.7 dB at 6.4 GHz with a thickness of 2.36 mm, and the minimum RL vaLue of the SiCnws-GFs could be as Low as -67.8 dB at 5.9 GHz with 2.6 mm thickness. The multiscale Si3N4nws-GFs and SiCnws-GFs in the present study are very promising as absorber materials with strong EM wave absorption performance in critical environments.