Design Synthesis And Performance Study Of New Ferrite Absorbing Materials

The ferrite electromagnetic wave absorbing materials have been one of the main research points of absorbing materials because of the double loss characteristics of dielectric loss and magnetic loss.However,traditional ferrites still have disadvantages such as low absorption of electromagnetic wave,narrow absorption band and large density,which make it unable to meet the requirements of high quality absorbing materials.The absorbing properties of ferrites can be effectively improved by combining ferrites and metal particles,changing ferrite shape,adding rare earth ions to ferrite,and combining ferrite with graphene.Therefore,taking these above into account,in this thesis in order to improve the traditional ferrite absorbing performance,the composite of ferrite dispersed metal Fe particles was prepared,mesoporous ferrite and mesoporous ferrite doped rare earth La were prepared,and the composite of a three-dimensional porous graphene loaded ferrite was prepared.Some important results and conclusions are summarized as follows:?1?The alloys Nd_xYFe_92.5-xB_6.5?x=3,4,5,6,7?were prepared by alloy melting method,then the alloys were milled under vacuum and naturally oxidized in the air.The composite of metal Fe particles dispersed in Fe₂O₃ferrite and a small amount of rare earth oxide and metal boride was obtained.The absorption performance of the samples was tested,and the results showed that:In the X-band,the microwave absorption A increased first and then decreased with the increase of x,and the microwave absorption A reaches the maximum when x=4.In addition,the effect of different ball milling time M-t on the microwave absorption A of the samples was studied.The results showed that the microwave absorption A increased with the increase of milling time.However,when the ball milling time increased from 30 h to 40 h,the amount of A increased was no longer obvious.Finally,the heat treatment of the samples after the ball milling and natural oxidation was carried out in vacuum,and the effect of heat treatment time on the absorption properties of the samples was studied.The results show that the microwave absorption A of the sample increases first and then decreases with the increase of heat treatment time.When the heat treatment time was H-t=15 min,the sample Nd₄YFe_88.5B_6.5 with ball milling 40 h shows good wave absorption characteristics.The average microwave absorption A was higher than 115dB,and the microwave absorption A of the sample was up to 132.415 dB at the incident electromagnetic wave frequency of 12.45 GHz.?2?The ordered mesoporous CoFe₂O₄?O-CFO?nanoparticles with spinel structure were synthesized by hydrothermal method using the mesoporous silica SBA-15 prepared as a template.It is found that O-CFO has a specific surface area of 105.3 m²/g and a smaller M_S value.The reflection loss R_L reaches the minimum value of-27.36 d B at the frequency of 13.4 GHz with the thickness is3.0 mm.Good absorbing properties can be attributed to the mesoporous structure,which increased the dielectric loss,improved the impedance matching,improved the absorption coefficient,and caused multiple reflection of electromagnetic wave in channel.In order to improve the absorption properties of the samples,the ordered mesoporous CoLa_0.12Fe_1.88O₄?O-CFO?was first prepared by replacing Fe with the rare earth element La.It is found that the specific surface area of the sample O-CLFO is 117.6 m²/g,the M_S value is further reduced and the coercivity increases.The doping of the rare earth element La causes the rearrangement of CO²⁺and Fe³⁺ions and the enrichment of the surface and grain boundary of the La elements.O-CLFO shows excellent absorbing performance.The minimum R_L loss is-46.47 d B at the frequency of13.4 GHz with the thickness is 3.0 mm,and the effective bandwidth is 4.9 GHz,which is 2.2 times the effective bandwidth of O-CFO.?3?Three dimensional multilayered graphene material 3D-HPG was prepared by the convenient,effective,cheap,stable and large-scale application ion exchange method with metal ion exchange resin as carbon precursor,and the characteristics of 3D-HPG wave absorption are measured for the first time.The testing results indicate that 3D-HPG possesses hierarchical pore structure including of micro-,meso-,and macropores,and the macropores wall forms graphene like structure,and the specific surface area of 3D-HPG reached 1135.3m²/g.The minimum R_L loss is-34.75 dB at the frequency of 11.7 GHz with the thickness is 3.0 mm.In order to obtain high performance absorbing materials,the Fe₃O₄ ferrite was loaded to 3D-HPG by hydrothermal method to produce3D-HPG/Fe₃O₄ composite.It is found that the specific surface area of the composite is reduced to 857.6 m²/g,and the absorption performance of3D-HPG/Fe₃O₄ is excellent.The minimum R_L loss is-46.8 dB at the frequency of 11.8 GHz with the thickness of 3.0 mm.The excellent absorbing properties of3D-HPG/Fe₃O₄ can be attributed to the good impedance matching characteristics,and the high dielectric loss and magnetic loss of the composite,In addition,the multiple reflection and destructive interference of the electromagnetic wave in the material channel and the cavity,and the high interfacial polarization loss caused by the Fe₃O₄ doping are also the important reasons.