| Electromagnetic(EM)wave absorption technique is an important subject not merely in the military field,but also plays an important role in the commercial field.Therefore,EM absorption materials have gradually attracted the worldwide attention.Although electromagnetic waves techniques have been well developed in wireless communication and military fields,there are still many issues that cannot be ignored,such as electromagnetic interference and information leakage.Hence,there is an urgent demand to develop a promising EM absorption material with excellent performance that meets the requirements of light weight,thin thickness,strong absorption,and wide frequency range.Due to Fe3O4’s unique low saturation magnetic moment,high magnetic susceptibility,superparamagnetism,high coercive force,low toxicity,low cost,etc.it has become one of the most promising EM wave absorption materials.Pitifully,Fe3O4 also has some intrinsic disadvantages that cannot be ignored,such as high density,low absorption intensity,and narrow absorption frequency range.In light of these problems,this thesis is to develop a simple and feasible method to obtain structure-controllable nanosized Fe3O4 composite materials,to explore in depth the absorption mechanism of composite materials,and to control the microstructure of composite materials by electrochemical methods,and to explore the effects of microstructure changes on absorption Impact of performance.The main research results obtained so far are as follows:A preliminary exploration of the EM wave absorption properties of nano Fe3O4 spheres and MWCNT was conducted and the results showed that the optimal reflection loss of nano Fe3O4 spheres is-10 dB,and the optimal reflection loss of MWCNT is-5 dB,which is far from the actual application requirements.Therefore,two different structures of Fe3O4 composite materials were synthesized by solvothermal method and in-situ polymerization and high temperature carbonization method:Fe3O4/MWCNT "necklace-structure" composites and Fe3O4@C "core-shell" composites.Among them,the optimal reflection loss of Fe3O4/MWCNT composites is up to-25 dB,and the optimal reflection loss of Fe3O4@C composites is up to-17 dB.The absorption range under-10 dB is about 3 GHz with the 3 mm thickness layer.The different microstructure of nano Fe3O4/MWCNT composites was constructed by adjusting the amount of Fe3+,the time of solvothermal reaction,the amount of precipitating agent and the electrochemical redox reaction.The adjustments of the experimental parameters were used to obtain the controllable preparation of the size,density and microstructure composition of the composite material,and to explore their influence on the EM absorption performance.Fe3O4/MWCNT microstructure regulations are achieved through the redox reaction and ion intercalation in the electrochemical reaction process.After being charged,the Fe3O4/MWCNT composites showed excellent absorption performance in the range of 2 to 18 GHz.The maximum reflection loss reached-50 dB and the absorption range under-10 dB is about 2 GHz with 3.5 mm thickness layer.The different microstructure of nano Fe3O4@C composites was constructed by adjusting the heat treatment process parameters and electrochemical redox reactions.XRD,SEM,In-Situ TEM and other methods were used to characterize the microstructure changes of nano Fe3O4 composites,and to explore the influence of the changes in the morphology and microstructure of Fe3O4@C on the absorption properties.By adjusting the holding time,preparation of Fe@Fe3C@C composite structure by carbothermal reduction method,,and its microwave absorption performance is greatly improved.The maximum reflection loss reached-49 dB and the absorption range under-10 dB is about 7 GHz with 1.5 mm thickness layer. |
PDF Full Text Request