Nanoparticles and 3D sponge-like porous networks of manganese oxides and their microwave absorption properties

Hydrohausmannite nanoparticles (similar to 10 nm) were prepared by the hydrothermal method at 100 degrees C for 72 h. Subsequent annealing was done in air at 400 degrees C and 800 degrees C for 10 h, Mn3O4 nanoparticles (similar to 25 nm) and 3D Mn2O3 porous networks were obtained, respectively. The products were characterized by XRD, TEM, SAED and FESEM. Time-dependent experiments were carried out to exhibit the formation process of the Mn2O3 networks. Their microwave absorption properties were investigated by mixing the product and paraffin wax with 50 vol%. The Mn3O4 nanoparticles possess excellent microwave absorbing properties with the minimum reflection loss of -27.1 dB at 3.1 GHz. In contrast, the Mn2O3 networks show the weakest absorption of all samples. The absorption becomes weaker with the annealing time increasing at 800 degrees C. The attenuation of microwave can be attributed to dielectric loss and their absorption mechanism was discussed in detail.