Synthesis And Electromagnetic Wave Absorption Properties Of Several Kinds Of Electromagnetic Absorbing Materials Containing Cobalt

The technology of electromagnetic shielding and electromagnetic absorption could protect the normal work of electronic equipment and optimize people's living environment,Especially in the military field,it is of great significance to improve our military equipment battlefield viability.In this paper,nano-hollow Co particles,Co tubes,Fe@air@Co particles,Fe@Co particles,hollow Co@Fe double shell particles,hollow Co@SiO₂ double shell particles and FeCoNiCrAl_x high entropy alloy powder are prepared.The electromagnetic wave performance in the frequency range of 2¹8GHz is studied and the following research contents are completed.?1?Using the prepared Fe particles and Fe chains as templates,the Co layer is coated on the Fe surface.Electrode potentials of Fe and Co are different in acid,which is used to dissolve the Fe core.The average diameter of hollow Co particle is about 280 nm,and a thickness is 32 nm.The average diameter of Co tube is about 113 nm and a wall thickness is 28 nm.The preparation method is simple and easy,and a large quantities of nanometer hollow Co particles and Co tubes can be prepared quickly.?2?The electromagnetic?EM?wave performance of hollow Co particles and Co tubes are studied.When the hollow Co and Co tubes are filled with 40 wt.%,the Co tube has a large specific surface area and strong interfacial polarization,and the dielectric loss is larger.The reflection loss?-42.5dB?is higher than that of the hollow Co particles?-30.4dB?,but the effective absorption bandwidth is narrow.When the filling ratio of the hollow Co particles and the Co tube is 60wt.%,the longer Co tube is easy to form a continuous conductive network in the absorbing coating,weaken the interface polarization,and the dielectric loss is lower than that of the hollow Co particles.Therefore the EM wave absorption performance is poor.When the coating thickness is 1.5mm,the maximum reflection loss of Co tube is only-14.0dB,corresponding to the effective absorption bandwidth of 2.9GHz,maximum reflection loss value of hollow Co particle is as high as-41.7dB,corresponding to the effective absorption bandwidth is 3.2GHz.?3?Fe@Co particles and Fe@air@Co particles with more interfacial polarization types are prepared to extend the effective absorption bandwidth.The electromagnetic wave absorption properties of Fe@Co particles,Fe@air@Co particles and hollow Co particles are investigated.When Fe@Co particles,Fe@air@Co particles and hollow Co particles are filled in the absorbing coating samples.When the content is 70wt.%,the volume fraction of the hollow Co particles is the largest and the interface is the strongest,and the maximum reflection loss is also the largest,which is-45.06dB?coating thickness of 1.7mm?.The volume fraction of Fe@air@Co particles in the absorbing coating is second and the maximum reflection loss value of Fe@air@Co particles is-42.75dB?coating thickness of1.6mm?.The maximum reflection loss of Fe@Co particles is the smallest with a value of-22.02dB?coating thickness of 1.4mm?.The effective absorption bandwidth of Fe@air@Co particles is 4.1GHz,which is higher than that of Fe@Co particles of 3.2GHz.?4?Hollow Co@Fe particles have much more interfacial polarization type and interfacial area than those of hollow Co particles.Due to the introduction of the interface between Fe shell and Co shell and its polarization,when the particle filling ratio of the absorbing coating is 60wt.%,the maximum reflection loss of hollow Co@Fe particles is-47.30dB,corresponding to the effective absorption bandwidth of 5.0GHz and coating thickness of1.5mm,which are better than those of hollow Co particles?-41.7dB,3.2GHz,1.5mm?.Hollow FeCo alloy particles are obtained by diffusion heat treatment of hollow Co@Fe particles with Fe/Co atomic ratio of 1:1.Due to the diffusion of Fe and Co atoms,the interfacial polarization between Fe shell and Co shell is eliminated,which reduces the absorption of electromagnetic wave.When the filling ratio of hollow FeCo alloy particles is60wt.%,the maximum reflection loss is-23.68dB,the effective absorption bandwidth is2.8GHz,and the corresponding coating thickness is 1.3mm.The EM wave absorption performance is obvious lower than that of hollow Co@Fe particles.This indicates that the interface polarization has a significant effect on the EM wave absorption properties.?5?The hollow Co@SiO₂ particles are prepared by coating non-conductive material SiO₂on the hollow Co particles.Because of the weak reflection effect for electromagnetic wave of SiO₂ layer,the impedance of the hollow Co@SiO₂ particle is obviously lower than that of the hollow Co@Fe?Fe/Co=1:1?particles,and more electromagnetic waves can be attenuated.The maximum reflection loss of hollow Co@SiO₂ particles?Si/Co=1:9?is-58.94 dB when the filling ratio of the hollow Co@SiO₂ particles in the absorbing coating sample is 60 wt.%?corresponding to the coating thickness of 1.4mm?,better than that of hollow Co@Fe particles with a maximum reflection loss value of-47.30dB?corresponding coating thickness of 1.4mm?.The effective absorption bandwidth of the hollow Co@SiO₂particles is 4.7GHz.?6?The electromagnetic wave performance of high entropy alloy powder was studied for the first time.The FeCoNiCrAl_x?x=0,0.5,1.0,1.5,2.0?high entropy alloy powders with FCC and BCC biphasic structure are prepared by ball milling.When the high entropy alloy powders filling ratio is 50wt.%,FeCoNiCrAl_0.5 high entropy alloy powder has the smallest impedance and the maximum electromagnetic attenuation constant,therefore,it has the best EM wave absorption properties with maximum reflection loss of-37.32dB,effective absorption bandwidth of 3.0GHz and the corresponding coating thickness of 2.3mm.The EM wave absorption properties of FeCoNiCrAl_0.5 high entropy alloy powder are investigated with the filler content of 40wt.%,50wt.%,60wt.%and 70wt.%.When the filling ratio is 60 wt.%,the maximum reflection loss is-44.60dB with an effective absorption bandwidth of 3.4GHz and corresponding coating thickness of 1.2mm.This suggests that high-entropy alloy powders can be further studied as electromagnetic absorbers.?7?The effect of vacuum magnetic field annealing on the electromagnetic absorption performance of magnetic absorbing material is investigated for the first time.The FeCoNiCr high entropy alloy powder was annealed at 700?without and with a magnetic field of 10T.It is found that when the high entropy alloy powders are filled with 40wt%The maximum reflection loss value of the high entropy alloy powder was increased from-32.58dB?thickness of 6.0mm?without magnetic field to-60.96dB?5.8mm?with magnetic field.When the filling ratio is 60wt.%,the maximum reflection loss value is calculated from-47.33 dB?thickness of 2.3mm?increased to-55.12 dB?thickness of 2.5mm?.?8?FeCoNiCrAl_0.8 high entropy alloy powder and the corresponding components of amorphous alloy powders are prepared.When the fillers in the absorbing coating samples are 70wt.%,the high entropy alloy powder obtains the maximum reflection loss value of-41.8dB,the effective absorbing bandwidth is 4.7GHz,and the coating thickness is 2.3mm,which are higher than those of amorphous powder?-25.5dB,3.6GHz,1.7mm?.