Preparation And Electromagnetic Properties Of Micro-nano Manganese Dioxide

MnO₂ with different morphology and crystal structure were synthesized via a low-temperature hydrothermal method, using potassium chlorate and ammonium persulfate two reaction systems. And the properties of the products were discussed. The as-synthesized samples were characterized by instrumental analyses including XRD, SEM, TEM, VSM, TG/DTA system. Theγ-MnO₂ powders with a self-grown core-shell structure andβ-MnO₂ nanorods were obtained in the potassium chlorate system. And in the ammonium persulfate systemα-MnO₂ nano-wires andβ-MnO₂ nanorods were prepared.The measurements of complex relative permittivity and permeability versus frequency were carried out in the frequency range of 2-18 GHz by using a coaxial waveguide technique. The EM absorption properties of MnO₂/CB/EPS/EP composite flat slab with different volume fractions and thicknesses were tested in the X and Ku bands by reflection/transmission technique. The selected volume fractions were13 %, 26 %, 39 %, 52 % and 65 %. And 3, 4 and 6mm thicknesses were selected for the test. Both in the ammonium persulfate and potassium chlorate systems, with increasing frequency, the real parts of permittivity for the obtained samples decreased from 18 to 4 and 30 to 8, respectively. But the imaginary parts of permittivity increased slowly from 1 to 8 and 2 to 8 with increasing frequency, respectively. Moreover, in the two reaction systems, the real parts of permeability were approach 1.2 and 1.0, respectively. However, the imaginary parts of permeability for the samples obtained in the two systems almost kept zero with less variation throughout the whole frequency range. Based on these results, the obtained MnO₂ did not have the capacity of diamagnetism and magnetic loss. For the EM absorption properties of MnO₂/CB/EPS/EP composite flat slab, when the volume fraction of carbon black 15 % (CB / (CB+EP)) and the filling ratio of MnO₂ and CB 65:15 (in volume) with coated EPS were adopted, it showed the minimum reflection loss of about -31.5dB at 15 GHz, and the effective absorption band below -4 dB reaches 8.7GHz (4.6-6.9 GHz,11.6-18 GHz). And EPS filling in the samples performed better absorbing properties in the high-frequency, comparing to in the low-frequency performance.