The effects of annealing treatment on the morphology and microwave absorption properties of α-MnO 2

Chemically synthesized α-MnO₂ powder was annealed at different temperatures with (NH₄)₂S₂O₈ 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 α-MnO₂ with a sea urchin-like shape, when the annealing temperature was below 500 °C. However, it was observed that the powder changed from α-MnO₂ to Mn₂O₃ at 500 °C and 600 °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 °C).