Study On Microwave Absorption Properties Of Nickel-Based Absorbing Materials

Nickel-based microwave absorbing materials have attracted extensive attention due to their excellent microwave absorption properties,and have been widely used as military absorbing materials and civil absorbing materials.For traditional nickel-based absorbing materials,their reflection loss values are generally distributed in the high-frequency phase,and few studies have reported that a strong absorption,wide-band nickel-based absorbing material can be realized in the low-frequency phase.This master’s thesis mainly focuses on the use defects of absorbing materials in practical applications.Metal nickel nanoparticles are prepared by self-developed metal nano-powder industrial production equipment,based on this high-quality core-shell nickel nanoparticles.Nickel-based composite absorbing materials with different morphologies were prepared.The microwave absorption properties of these materials were studied.The relationship between the structure and microwave absorption properties of these materials was discussed.The research content of this paper is summarized as follows:1.Preparation and microwave absorption properties of Ni/C porous nanofibers.The cross-linked network of Ni/C porous nanofibers was successfully prepared by using polyacrylonitrile（PAN）,vegetable oil and N,N-dimethylformamide（DMF）as raw materials,combined with electrospinning technology and subsequent heat treatment steps.The morphological characterization results show that the diameter of the fiber is about 300 nm,and there are many small pores with a pore size of 50 nm.Since the carbon fiber itself has good electrical conductivity,and electromagnetic waves can undergo multi-level reflection in the porous fiber,the Ni/C porous nanofiber has a strong microwave absorption value and a wider range in the low frequency range（especially in the C band）.In addition,the role of nanopores in improving the dielectric loss properties of composite porous carbon fibers is highlighted,and the interfacial polarization relaxation loss and dipole relaxation loss can significantly improve the microwave absorption properties of the materials.Therefore,the Ni/C porous nanofiber is expected to be a microwave absorbing material excellent in absorbing properties in a low frequency range.2.Preparation and microwave absorption properties of Ni@GO binary composite absorbing materials.The graphene oxide（GO）was prepared by the modified Hummers method,and the Ni@GO binary composite was prepared by hydrothermal synthesis.In a high-temperature closed reaction environment,ion exchange occurs between the functional groups on the surface of nickel ions and graphene oxide,so that the nickel nanoparticles and the graphene oxide are well compounded.Graphene oxide is regarded as a carrier of nickel nanoparticles by utilizing the large specific surface area of the graphene oxide and the fact that the nickel nanoparticles are easily dispersed.Nickel nanoparticles themselves have a strong magnetic loss.In addition,polarization occurs at the interface between nickel nanoparticles and graphene oxide in the composite,causing strong polarization loss.Microwave absorption properties studies show that the Ni@GO binary composite exhibits superior microwave absorption properties compared to nickel nanoparticles.3.Preparation and microwave absorption properties of Ni/ZnFe₂O₄/GO ternary composite absorbing materials.Ni@GO binary composites exhibit excellent microwave absorption properties,but this material also has obvious shortcomings.The biggest shortcoming is that the reflection loss values are distributed in the high frequency range,which will greatly limit the application of these material in the low frequency range.In this regard,we introduced ZnFe₂O₄,utilizing the dielectric properties and magnetic properties of ZnFe₂O₄ to compensate for the shortcomings of Ni@GO binary composite absorbing materials in the low frequency range.Hollow spherical ZnFe₂O₄ particles with a particle size of 300 nm were prepared by a hydrothermal method.Ni/ZnFe₂O₄/GO ternary composite absorbing materials were prepared by blending method.Compared with the Ni@GO binary composite absorbing material,the dielectric constant of Ni/ZnFe₂O₄/GO ternary composites becomes significantly larger,so the introduction of ferrite improves the dielectric loss.Morever,the microwave absorption properties of Ni/ZnFe₂O₄/GO ternary composites are significantly improved.Microwave absorption results show that the microwave absorption values of ternary composites can be distributed in the low frequency range.This novel ternary composite material has practical application value in the low frequency range.4.Preparation and microwave absorption properties of Ni@C composites.A Ni@C composite absorbing material was prepared by self-polymerization combined with heat treatment using dopamine hydrochloride as a carbon source.The amorphous carbon coating on the periphery of the magnetic nickel core provides a protective layer for the nickel core while increasing the dielectric loss of the composite.Compared with nickel nanoparticles,the microwave absorption performance of Ni@C composite absorbing materials is significantly improved in the high frequency range,and the loss of electromagnetic waves comes from the magnetic loss of the magnetic nickel core and the dielectric loss of the peripheral amorphous carbon layer.Finally,by comparing the above research results,nickel/carbon porous nanofibers and Ni/ZnFe₂O₄/GO ternary composite absorbing materials can achieve broadband,strong absorption in the low frequency range（especially in the C band 4-8 GHz）.The microwave absorption performance can meet the practical application requirements of the absorbing material in the low frequency range.