Electromagnetic Wave Absorption And Corrosion Resistance Of Iron-Based Magnetic Nanocapsules

Dielectric-soft magnetic nanocapsules are a new type of electromagnetic wave absorption composite material.Its dielectric shell has a relatively adjustable dielectric constant.Its soft magnetic core has a high saturation magnetization and a low magnetic crystal anisotropy,which makes a high permeability.Combining the advantages of them,such nanocapsules will show a strong electromagnetic wave absorption ability,thereby knowns as become a hotspot of electromagnetic wave absorption materials in recent years.On this basis,using the chemical inertia of the dielectric shell can further expand the development of the corrosion resistance of the nanocapsule,thus realizing the dual functions of electromagnetic wave absorption and corrosion protection,and laying a theoretical and experimental foundation for the development of electromagnetic wave absorption materials in complex environments.In this paper,nitrogen doped FeNi3@C nanocapsules,multiple carbon shells coated FeNi nanocapsules and porous carbon coated Cu nanoparticles loaded with Fe3O4 were prepared by plasma arc technology and sol gel method,taking Fe based dielectric soft magnetic nanocapsules as the research objectives.It is found that the regulation of the dielectric constant and permeability of the above nanostructures can be realized by doped elements into the nanocapsules,constructing multiple shells and changing the morphology to control the microstructure of the nanostructures,and then the electromagnetic wave absorption performance can be controlled.At the same time,good inorganic and organic corrosion resistance can also be achieved.In this paper,we designed and synthesized a kind of nanocapsule of FeNi3(JCPDS 38-0419)soft-magnetic alloy coated with amorphous carbon shell.During the reaction process,acetonitrile(C2H3N),as a nitrogen source,in situ introduced N atoms to the carbon shell,and produced a lot of defects on the surface of the carbon shell,which making the density and crystallinity of the carbon layer inconsistent.By modulating the crystalline state of the shell,the polarization site of the electric dipole is increased,and the dielectric loss of the outer carbon shell is enhanced significantly.It makes the amorphous carbon shell and the soft-magnetic FeNi3 core have better impedance matching,thus nitrogen doped FeNi3@C nanocapsules have good electromagnetic wave absorption properties.When the absorber thickness is 3 mm,the minimum reflection loss(RL)of-47.26 dB can be obtained at 13 GHz and the absorption bandwidth can reach 7.04 GHz(RL<-10 dB).In addition,SQUID and DSC-TG results show that FeNi3@C nanocapsules have extremely stable magnetic behavior in the range of 5 K to 300 K and thermal stability at 719 K.On the basis of FeNi3@C nanocapsules,it was found that their similar FeNi@C nanocapsules have similar magnetic properties and better magnetic temperature stability.Moreover,due to the special structure of their high Curie temperature core and graphite shell,they have natural inorganic corrosion resistance characteristics.For this purpose,this paper chooses multiple carbon coated FeNi nanocapsules,and selects FeNi with high magnetic permeability as the core phase for modification.The FeNi magnetic nanoparticles with multiple shells were prepared by arc-plasma method and sol gel method.The polyvinyl alcohol(PVA)particles adsorbed on the FeNi@C surface were converted to amorphous carbon by annealing treatment.These carbon particles form multiple interfaces and provide more active sites for electric dipoles.The optimized ratio of PVA to nanocapsules significantly enhanced the real(ε’)and imaginary(ε")parts of the dielectric constant and the dielectric loss(tanδε),which leads to polarization relaxation.The multiple carbon shells FeNi magnetic nanoparticles prepared in this work are multifunctional absorbers with good corrosion resistance.When the thickness of the absorber is 2.9 mm,the minimum reflection loss(RL)-63.26 dB can be obtained at 11.45 GHz.When the thickness is 2.5 mm,the absorption bandwidth is 6.57 GHz(RL<-10 dB).After 30 days of immersion,the |Z|0.01Hz(impedance modulus)value of the coating remains at 4.53×104 Ω,which indicates its remarkable barrier performance.In addition,there are still few reports on organic corrosion-resistant absorbent materials in 5G devices that can be used in hospital biological laboratories,except for the improvement of seawater corrosion resistance against inorganic corrosion.As for the natural antibacterial material Cu,core-shell structure can be constructed to coat Fe3O4 nanoparticles with both dielectric and magnetic properties,which can be used in organic corrosion resistance.In this paper,the surface of Cu@C nanocapsules was partially broken by annealing treatment,and Fe3O4 particles were coated on the surface of porous Cu@C nanocapsules by sol gel and Ar/H2 heat treatment.Then,a broadband wave absorber with antibacterial properties was prepared.Due to the large number of surface defects on the internal and external surfaces of partially cracked Cu@C nanocapsules,the surface of nanocapsules has a large number of non-interacting electric dipoles,resulting in their enhanced broadband strong wave absorption characteristics.Compared with conventional Fe-Cu nanocapsules,the electromagnetic wave absorption characteristics of Cu@C nanocapsules coated with Fe3O4 are significantly improved in the 2-18 GHz.When the absorber thickness is 1.8 mm,the absorption bandwidth with reflection loss higher than 90%(RL<-10 dB)can reach 5.87 GHz.Cu coated with porous carbon nanocapsules enable Cu ions to be released into solution in a limited way,showing good long-term sustained release and synergistic antibacterial activity.