Study On Mn_xZn_1-xFe₂O₄/Expanded Graphite Electromagnetic Shielding Plywood

To develop lightweight wood-based electromagnetic shielding composite with broadband application,low reflection and high absorption property,based on the multiple reflection absorption mechanism,a kind of SiO₂-TiO₂ modified veneer and Mn_0.5Zn_0.5Fe₂O₄/expanded graphite?EG?/carbon fiber composite was made respectively,and then both the veneer and the composite as the main body was used to manufacture electromagnetic shielding composite plywood with trilaminar structure,good electromagnetic shielding effectiveness?SE?and a certain electromagnetic wave absorbing ability was prepared.The reseach contents and results were shown as follow:1.Mn_xZn_1-xFe₂O₄ powder was prepared by sol-gel calcinations method.When X=_0.5,the powder had the best magnetic properties and its saturation flux density was 67.46emu/g.The saturation flux density was 43.22emu/g and the electrical resistivity was 984.81m?·cm at the mass ratio of 3:7 between EG and Mn_0.5Zn_0.5Fe₂O₄.The SEM and EDS analysis results show that Mn_0.5Zn_0.5Fe₂O₄ was evenly inset in the gap among layers of EG.A depletion layer was prepared using above Mn_0.5Zn_0.5Fe₂O₄/EG and carbon fiber with"#" glyph laying at the areal density of 100g/m².Having single-layer thickness of 1mm,3 layers and density of 1g/cm,the composite plywood possessed SE of not lower than 55dB in the range of 200?1500MHz and reflectivity peak of-6.19dB in the range of 2?18GHz,but less than-5dB in the range of 9?13GHz.2.Sapele veneers modified with SiO₂-TiO₂ was prepared by both sol-gel method and half-limit pressure impregnation method in the condition that former pressure was 1MPa,former holding time was 60min,vacuum pressure was 0.09MPa and latter holding time 20min in the impregnation process.The SEM and EDS analysis results found that a uniform SiO₂-TiO₂ dual sol coating formed on the veneer and a portion of the dual sol permeated into the veneer.Resistivity decreased with gradual increase of TiO2 in dual sol.When the molar ratio of TiO₂ and SiO₂ was 3:7,resistivity was 812.27m?·cm,and reflectivity within the thr range of 7.2-18GHz is better than-6dB,and had peak value of-7.14dB at 9.2GHz.3.Different laminar structure of electromagnetic shielding composite plywood was prepared by SiO₂-TiO₂ modified veneer?A?,Mn_0.5Zn_0.5Fe₂O₄/EG/carbon fiber composite materials?B?,conductive aluminum foil?C?and unmodified wood veneer?D?according to different combinations.The thickness of A,B and D was 1mm,thickness of C was 0.06mm.Result showed that layers of modified veneers affected the reflectivity.Preparation according to combination way of A+B+D+B+D+B+D+C,the composite plywood had the peak reflectivity of 8.8dB that was-2.61dB less than the unmodified panels.As preparation according to combination way of A+B+A+B+D+B+D+C,the composite plywood had the minimum SE of 75dB in the range of 200?1500MHz and the reflectivity peak of-11.15dB.Reflectivity was less than 8.9 dB in the range of 2?18GHz,and the range of reflectivity less than-10dB was 13.8?18GHz.4.Using the migration method for interface processing with coupling agent KH-560 and adhesive consumption as 10%of the composites,bonding strength of the composite plywood was up to the second class of GB/T 9846-2015"Ordinary Plywood Board".The composite plywood can be used for the secret room resistance to electromagnetic interference and information leakage,important electronics crate and national defense requirements of stealth technology,etc.