Preparation And Properties Of Soft/Hard Ferrite-based Electromagnetic Wave Absorption Materials

Electromagnetic interference and electromagnetic pollution not only affect the normal operation of precision electronic equipment,but also seriously threaten human health.Electromagnetic wave absorption materials are one of the most effective measures to effectively absorb electromagnetic waves and eliminate electromagnetic pollution.Ferrite is a typical magnetic loss absorbing material with high magnetic permeability and electrical resistivity,and has been widely used in the field of microwave absorption.However,the disadvantages of traditional ferrite materials such as high density,low absorption intensity,and narrow absorption band limit their further applications.Polyaniline?PANI?is an electric loss absorbing material with light weight,strong absorption and electrical loss characteristics.The paper uses soft and hard ferrite as the matrix,self-propagating method,co-precipitation method combined with in-situ polymerization method and high-temperature carbonization technology to prepare soft and hard ferrite/polyaniline and soft and hard ferrite/carbon composite materials.The DSC,XRD,FTIR,SEM,Raman and TEM were used to analyze the composition,structure and morphology of the composites.The magnetic properties and absorbing properties of the composites were characterized by VSM and VNA.The research results show that the prepared composite material has the advantages of strong absorption,frequency bandwidth and light weight,and has broad application prospects in military and civilian fields.The results of this paper are as follows:The Ni_0.5Zn_0.5Fe₂O₄/SrFe₁₂O₁₉ composite ferrite was successfully prepared by sol-gel self-propagation method.With the increase of hard magnetic phase,the average grain size of soft magnetic phase Ni_0.5Zn_0.5Fe₂O₄ was reduced from 32 nm to 18 nm,the average grain size of the SrFe₁₂O₁₉ increased from 28 nm to 42 nm.With the increase of the hard magnetic phase,the hysteresis loop gradually changes from"bee waist type"to single-phase hysteresis loop,the Ms value decreases monotonously from 67.2 emu/g to50.0 emu/g,and the Hc value gradually rises from 750.0 Oe to 4056.25 Oe.When the mass ratio of Ni_0.5Zn_0.5Fe₂O₄ and SrFe₁₂O₁₉ reaches 1:3,the exchange coupling effect is best.As the hard magnetic phase increases,the reflection loss of the sample at the same thickness increases first and then decreases.When the mass ratio of soft to hard magnetic reaches 1:3,the maximum reflection loss(RL_max)value and effective absorption bandwidth?RL<-10 dB?reach the maximum?-38.4 dB and 6.4 GHz?at a thickness of 4 mm.Ni_0.5Zn_0.5Fe₂O₄/BaFe₁₂O₁₉ composite ferrite was prepared by co-precipitation method.Polyaniline?PANI?and different soft/hard magnetic mass ratios of Ni_0.5Zn_0.5Fe₂O₄/BaFe₁₂O₁₉@PANI composite were prepared by in-situ polymerization.The Ni_0.5Zn_0.5Fe₂O₄/BaFe₁₂O₁₉@PANI composite exhibits a short rod shape.When the content of hard magnetic material is 75 wt.%,the exchange coupling effect of the composite material is best.With the increase of hard magnetic content,the saturation magnetization gradually decreased from 65.9 emu/g to 35.1 emu/g,and the coercivity increased from 307.94 Oe to 4882.5 Oe.In addition,when the hard magnetic content is increased,the reflection loss at the same thickness increased first and then decreased.As the hard magnetic content of 75 wt.%,the RL_maxax of the composite reached-25.6 dB,and the effective absorption bandwidth reached 7.24 GHz at 3.5 mm thickness,and the impedance matching of the composite is best at this time.Ni_0.5Zn_0.5Fe₂O₄/BaFe₁₂O₁₉@PANI composites with different ferrite contents were preparedby coprecipitation combined with in-situ polymerization method.Ni_0.5Zn_0.5Fe₂O₄/BaFe₁₂O₁₉@C composites with different ferrite contents were successfully prepared after carbonization at 550? for 2.5 h.The surface of the carbonized composite material has a slight shrinkage and crosslinked carbon spheres appear.As the ferrite content decreases,the saturation magnetization of the composite decreases and the coercivity decreases.As the ferrite content increases,the maximum reflection loss increased first and then decreased.When the mass ratio of ferrite is 20wt.%,the reflection loss is maximized.At 2.5 mm thickness,the composite has a RL_maxax of-61.91 dB and an effective absorption bandwidth of 9.83 GHz.At this time,the Ni_0.5Zn_0.5Fe₂O₄/BaFe₁₂O₁₉@C composite has good impedance matching.