Effect of flame partition and flight behaviors on intrinsic characteristics and absorption properties of hollow ceramic microspheres

• High-speed photography used for flame field partition and flight combustion behaviors.
• Relationship between intrinsic characteristics of HMCMs and flame characters was investigated.
• Relationship between intrinsic characteristics and absorbing properties was established.

Fe–MnO2–Fe2O3–sucrose–epoxy resin and self-reactive quenching technology were used to prepare two kinds of hollow multiphase ceramic microspheres (HMCMs). The results obtained by high-speed photography, SEM, XRD and laser particle size analysis showed that the flame field partition (“edge region”, “junction region” and “center region”) and different flight combustion behaviors of particles (“self-burst”, “collision effect” and “self-diminution”) are the main reasons to generate different intrinsic characteristics (particle size, microstructure and chemical composition) between coarse and fine HMCMs. On the one hand, these differences resulted in different electromagnetic parameters. Coarse HMCMs, owing to low resistivity, Fe–Fe3+ dipoles formed and more defects or vacancy, possessed higher dielectric loss. And due to the same main phase (MnFe2O4), the two kinds of HMCMs have close magnetic properties, however, the magnetic loss of fine HMCMs will move to low-frequency which resulted from infinite solid solution formed. On the other hand, different optimal match thickness (dcoarse = 2.5 mm and dfine = 2 mm), minimum reflectivity (Rcoarse = −24dB and Rfine = −25dB) and effective absorption bandwidth (fcoarse = 4 GHz and ffine = 4.2 GHz) were caused by these differences. This also illustrate that the match thickness will reduce along with the decrease of particle size. In addition, the two kinds of HMCMs belong to dielectric loss dominated material. And in the same thickness (2 mm), because of low permittivity of fine HMCMs, the electromagnetic match property was improved to broaden effective absorption bandwidth (4 GHz).