Microwave Absorbing Mortar Using Magnetic Hollow Fly Ash Microspheres/Fe3O4 Composite as Absorbent

A new type of microwave absorption cement-based material was prepared by using a magnetic hollow fly ash microspheres $(\mathrm{HFAM})/{\mathrm{Fe}}_3{\mathrm{O}}_4$ composite as the absorbent. Through the chemical precipitation method, a nano-${\mathrm{Fe}}_3{\mathrm{O}}_4$ layer was coated on the surface of HFAM to obtain the $\mathrm{HFAM}/{\mathrm{Fe}}_3{\mathrm{O}}_4$ composite. Then the composite was added into mortar to prepare microwave absorption cement-based material. The mineral components, micromorphology, and electromagnetic parameters of the $\mathrm{HFAM}/{\mathrm{Fe}}_3{\mathrm{O}}_4$ composite and the reflection loss of the cement-based material were investigated. It was found that the $\mathrm{HFAM}/{\mathrm{Fe}}_3{\mathrm{O}}_4$ composite had superparamagnetism, and its saturation magnetization and the residual magnetization were $32.67\mathrm{emu}/\mathrm{g}$ and almost zero, respectively. The best microwave absorption of the cement-based material was obtained at 3% $\mathrm{HFAM}/{\mathrm{Fe}}_3{\mathrm{O}}_4$ composite to cement, of which the bandwidth of the reflection loss lower than $-10\mathrm{dB}$ (responding to 90% microwave absorption) was nearing 8 GHz, showing excellent microwave absorption performance.