The effects of annealing treatment on the morphology and microwave absorption properties of α-MnO2

Chemically synthesized alpha-MnO2 powder was annealed at different temperatures with (NH4)(2)S2O8 as the oxidant and MnSO4 as the manganese source. The obtained samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and vector network analysis. Results indicated that the structures and morphologies of the products did not change remarkably, mainly consisting of alpha-MnO2 with a sea urchin-like shape, when the annealing temperature was below 500 degrees C. However, it was observed that the powder changed from alpha-MnO2 to Mn2O3 at 500 degrees C and 600 degrees C. The scanning electron microscopy images showed that the morphologies of the resulted Mn2O3 powder were microspheres in various sizes. Microwave absorption properties of the as-synthesized samples were also discussed, which showed that the dielectric loss tangent, magnetic loss tangent and reflection loss could be improved significantly by increasing the annealing temperature appropriately (<500 degrees C).