Resource utilization of coal hydrogasification residue to Ni/carbon-based composites for efficient microwave absorption

In this study, semi-coke (a type of coal hydrogasification residue, SC for short) was utilized to fabricate Ni/C-based composite microwave absorbents. The synthesis mainly involved an ethanol solution loading of nickel nitrate onto SC and then an in situ carbothermal reduction. The results showed that, for a fixed Ni load of 20 wt%, heat treating at 700 °C and above could bring out the characteristics of carbon-based materials of SC by removal of most coal tar and could also give rise to the complete reduction of nickel species to Ni. Hence, composite NiSC700 exhibited the best performance. Its minimum reflection loss reached − 42.6 dB at a coating thickness of 2.5 mm, with an effective absorption bandwidth of 4.1 GHz; while an bandwidth of 5.6 GHz was realized at a coating thickness of 2 mm. This was attributed to the impedance matching and strong intrinsic dissipation capacity, which primarily benefited from the effective regulation on the input impedance of carbothermal temperature and magnetic component Ni, strong conduction loss from graphite carbon, and polarization losses due to interfaces and defects in the multicomponent composite.