Study On Composite Board Of Electromagnetic Shielding With Magnetic Expanded Graphite/Wood Fiber

In this study, two kinds of magnetic expanded graphite (EG) were made, and then the EG were respectively mixed with wood fiber to manufacture two different composites, which were used to make multilayer electromagnetic shielding composite board with lightweight, broadband-shielding and a certain degree of electromagnetic wave absorbing property by designing and optimizing the multilayer structure. The contents and results were shown as follow:1. NixZn(1-X)Fe2O4 powder was prepared by sol-gel auto-combustion method. As X=0.6, the powder had better magnetic property that the saturation flux density was 63.03emu/g. For the big difference of density, it is difficultly to mix ferrite and wood fiber with each other evenly, so the Ni0.6Zn0.4Fe2O4 was attached on the expanded graphite to reduce the density of the composite material. When the mass ratio of EG to Nio.6Zno.4Fe2O4 was 1:4, magnetic property of composite material was 45.50emu/g. Then Ni0.6Zn0.4Fe2O4/EG was used as a filling material to make a composite board with wood fiber. When the mass ratio of Ni0.6Zn0.4Fe2O4/EG to wood fiber was 3:2, thickness as 4mm, density as 1.0g/cm3, the minimum SE of the composite board was 55dB in the range of 100?1500MHz and the peak of reflectivity was -6.1dB in the range of 2?18GHz.2. C4H6O4Ni·4H2O and NaBH4 were used for the early treatment of EG, then NiSO4·6H2O, Na3C6H5O7·2H2O, CH3COONa·H2O and N2H4·H2O were used to chemical nickel-plating on EG. As a result, the biggest coating quality of EG per liter of plating solution was 3.57g. Expanded graphite nickel plating EG (Ni-EG) with different electromagnetic property can be prepared by changing the mass of the EG per liter of plating solution. The more of the ratio of EG was, the better electrical conductivity was; on the contrary, the better magnetic property was. And then Ni-EG was used as a filling material to make a composite fiberboard with wood fiber. When the EG amount was lOg per litter plating solution, the mass ratio of Ni-EG to wood fiber as 3:2, thickness as 2mm, density as 0.9g/cm3, the minimum SE of the composite board was 60dB in the range of 100?1500MHz and the peak of reflectivity was -1.8dB in the range of 2-18GHz. When the additive EG amount was 2g per litter plating solution, the minimum SE was 55dB and the peak of reflectivity was-3.6dB.3. After structure optimizing and designing, SiC layer as impedance matching layer, Ni0.6Zn0.4Fe2O4/EG/wood fiber composite board as absorbed layer, Ni-EG/wood fiber composite board as reflecting layer, a kind of multilayer structure composite board had been prepared. The minimum SE of the composite board was 66dB in the range of 100-1500MHz. The peak of the reflectivity was-11dB at 13GHz and the range of reflectivity less than -10dB was 12-14GHz.4. Mechanical and physical properties of composite boards met requirements of Chinese national standard GB/T11718-2009 "Medium Density Fiberboard".