Low-cost preparation of Ni/C/CG composites for microwave absorption by recycling coal gangue

With coal gangue (CG) as the carbon-containing carrier, starch as supplementary C source and nickel nitrate as Ni source, Ni/C/CG composite microwave absorbing materials were prepared by a solution impregnation and then a carbothermal reduction process. The influence of the carbothermal reduction temperature on the composition, microstructure and performance of materials was carefully studied. It was found that, the carbothermal reduction temperature had a great effect on the crystalline state of carbon and Ni, as well as the size of Ni particles, further greatly affected the electromagnetic properties, especially the dielectric properties of the materials. Due to the combination of good impedance match and strong microwave attenuation ability, the Ni/C/CG composites prepared under a wide temperature range of 600−800 ℃ all displayed excellent microwave absorption performance. For the sample heat-treated at 800 ℃, the minimum reflection loss could reach −20.9 dB at 12.9 GHz and the corresponding effective absorption band was 3.7 GHz with a coating thickness of only 2 mm. In addition, the dielectric loss was the dominant microwave absorption mechanism, which mainly originated from the conductive loss caused by the graphite carbon and Ni particles, and the interfacial polarization loss due to the existence of interface between Ni, C and CG.