Effect of heat treatment on the structure of M-Type BaFe12O19 hollow ceramic microspheres prepared by self-reactive quenching technology and microwave absorption properties

Fe-Fe2O3-BaCO3-sucrose-epoxy resin and O-2 as reaction system and feeding gas, respectively, were used to prepare M-type BaFe12O19 hollow ceramic microspheres (BaM HCMs) absorbent by self-reactive quenching technology which combines flame thermal spraying, self-propagating high temperature synthesis (SHS), and rapidly solidification. The morphologies and phase composition before and after heat treatment of HCMs were studied by SEM, XRD, and EDS, and microwave absorption properties were also analyzed. The results showed that before heat treatment, the phase was composed of Fe3O4, Fe2O3, BaFe2O4, and BaCO3. And thick dendrite, eutectic of dendrite and amorphous and amorphous were formed on the surface of HCMs. After heat treatment, high purity single BaM HCMs was obtained, and the surface was transformed into nanolamella, micro-nano isometric grain, eutectic of nanolamella and isometric grain, and hexagonal crystal. Absorption test result showed that at 0.5-18 GHz, both epsilon' and epsilon aEuro(3) of HCMs reduced obviously, but the mu aEuro(3) increased by heat treatment. Therefore, the minimum reflectivity and bandwidth less than -10 dB were improved to -22.1 dB and 5.7 GHz (12.3-18 GHz), respectively. The improvement of electromagnetic match resulted by obvious reduction of permittivity, and the magnetocrystalline anisotropy, shape anisotropy, and various polarizations generated from special surface morphologies may be the main reasons to make microwave absorption properties better.