Construction of Ni-loaded ceramic composites for efficient microwave absorption

Compared with fly ash, the magnetic NiFA composites obtained at different temperatures exhibit excellent microwave absorbing ability. [Display omitted] •The pure fly ash (FA) is directly used as matrix to design microwave absorbents.•The novel method realizes the recycling of FA and cut the cost of absorbents.•The NiFA composites are lightweight and possess excellent performance.•Impedance matching and interfacial polarization play a key role to performance. To realize the high-effective utilization of solid waste fly ash (FA) as microwave absorbent, the Ni-loaded FA composites (NiFA) used as microwave absorbents were synthesized by a two-step method using solid waste fly ash as the raw material. The experiments included the synthesis of FA-based ceramic matrix, loading Ni2+ and the heat-treatment process at different annealing temperatures. According to the XRD and SEM results, the pyrolysis products of nickel nitrate and/or the products from the carbothermal reduction were dispersed over interior and surface of ceramic matrix. For NiFA700 composite, the minimum reflection loss (RLmin) value reached −45.7 dB and the effective bandwidth (RL ≤ −10 dB) was 4.6 GHz when the coating thickness was 1.6 mm. The superior microwave absorption (MA) performance could be ascribed to the good impedance matching and polarization effect resulting from the interface between Ni particles and matrix. Therefore, this study not only provides a potential microwave absorber for application in the field of electromagnetic wave absorption and shielding, but also develops a novel utilization avenue for fly ash.