Construction of Graphite Shells on Ferromanganese Oxide for Electromagnetic Wave Absorption

Ferromanganese oxide (FMO), a by-product of steelmaking industry, was coated with polyacrylonitrile (PAN) to construct an electromagnetic wave absorber (FMO@C) with a core-shell structure. The effect of heat treatment from 600 to 1000 °C on the phase transformation of FMO and carbonization of PAN was studied. Upon the heat treatment at 1000 °C, the reflection loss and effective bandwidth of the FMO@C reached -18.20 dB and 3.08 GHz at a thickness of 1.6 mm, presenting a significant improvement over FMO which only exhibited a reflection loss of -2.31 dB at 10 mm. Boric acid was infiltrated into the PAN shells to catalyze the carbonization process and adjust the impedance matching, which further improved the reflection loss to a minimum value of -28.25 dB. Via varying the concentration of boric acid, the reflection loss of -22.01 dB with an effective bandwidth of 3.36 GHz at a thickness of 1.3 mm was achieved. The enhanced EMW absorption performance was attributed to multiple reflections and polarization caused by the core-shell structure, magnetic loss from the phase transformation of FMO, dielectric loss from carbon shells, as well as the tunable impedance matching by boron-catalyzed carbonization. The construction of the core-shell structure could be a promising downstream processing of FMO and could extend the application of the solid wastes.