Research On Low-frequency Broadband Core-shell Structure Nano-absorbent Material

Core-shell nanostructured composite materials can integrate the excellent properties of multiple materials into a single structure.Through research on material combination optimization design,coupling behavior between core-shell interface,and core-shell spatial construction methods,its comprehensive performance can be far superior to other materials.In recent years,the rapid development of radar detection,especially the breakthrough in broadband technology,has brought enormous challenges to the field of stealth material research.Currently,practical microwave absorbing materials generally have good microwave absorption performance in the frequency range above 8 GHz,while relatively few have good microwave absorption performance in the low frequency（1.2-8 GHz）range,and there are few materials that can achieve broadband absorption.This paper proposes the research of nano core-shell structure microwave absorbing materials,using low dimensional strong magnetic nano metals as the core and multi-level multi-dimensional carbon-based nano materials as the shell,to design microwave absorbing materials with low frequency and broadband characteristics,the main research content and conclusions are as follows:（1）A novel pinecone shaped nanoscale multi-level structure microwave absorbing material was prepared by a new process.Based on the Kirkendall diffusion effect,an in-situ anisotropic oriented growth strategy was established during the pyrolysis of Prussian blue to prepare a new type of carbon based magnetic composite material（γ-Fe₂O₃@N-r GO/MWCNTs）.The material has a multi-level structure composed of pinecone shaped nanoflowers and a porous carbon skeleton.The nanoflower is a core-shell structure withγ-Fe₂O₃magnetic nanoparticles as the core and nitrogen-doped reduced graphene oxide as the shell.Porous carbon skeletons include entangled multi-walled carbon nanotubes and disordered carbon.When the pyrolysis temperature is 650℃and the holding time is 3 h,the sample has the optimal reflection loss of–59.2 d B;When the sample thickness is 4.5 mm,the effective absorption bandwidth of the low frequency band is 3.23 GHz（4.74-7.97 GHz）.（2）Preparation of rhombic dodecahedron and spindle shaped nanosheet ZIF-67 and their derived absorbing materials.By changing the solvent to change the deporotonation ability of the reaction solution,ZIF-67 with rhombus dodecahedron and spindle shaped nanosheet morphologies was prepared,in which two-dimensional spindle shaped nanosheets coexisted to form three-dimensional nanoflower structures.A carbon-based magnetic composite（Co₃O₄@N-C）with core-shell structure was prepared by pyrolysis of ZIF-67 as precursor in air.By changing the pyrolysis temperature to control the composition ratio and graphitization degree of carbon in the composite,when the pyrolysis temperature is 600℃,the sample has the optimal reflection loss of–39.68 d B;When the sample thickness is 5.0 mm,the effective absorption bandwidth of the low frequency band is 2.12 GHz（6.87-8.99 GHz）;When the absorption rate is 70%,the absorption bandwidth reaches 4.16 GHz（5.68-9.84 GHz）.（3）ZIF-8 with multi-dimensional（rodlike,sheet-like,flower-like）structures and its derived absorbing materials were prepared.By selectively isotropic and anisotropic nanoscale growth,using surfactant CTAB to precisely regulate morphology,ZIF-8 crystals with one-dimensional to three-dimensional（rodlike,sheet-like,flower-like）structures were prepared.A carbon-based magnetic composite（Zn O@N-C）with core-shell structure was prepared by pyrolysis of ZIF-8 as precursor in air.By changing the pyrolysis temperature to control the composition ratio and graphitization degree of carbon in the composite,when the pyrolysis temperature is 700℃,the sample has the optimal reflection loss of–47.64 d B;When the sample thickness is 5.0 mm,the effective absorption bandwidth at low frequency band is 3.15 GHz（5.59-8.74 GHz）;When the absorption rate is 70%,the absorption bandwidth reaches 7.73 GHz（3.81-11.54 GHz）.