Research progress of advanced institute technology in the field of absorbing materials research

Dendritic multilevel iron-based materials and their absorption performance curves

   Beijing Normal University has collaborated with universities such as Beijing Institute of Technology and Delaware State University to achieve phase transition from alpha-Fe2O3 to Fe, Fe3O4, and gama-Fe2O3 through methods such as oxidation-reduction. The transformed iron-based material still retains the dendritic structure of Alpha-Fe2O3 and has excellentElectromagnetic wave absorption performance.

Schematic diagram of two-phase and three-phase heterostructures

   The method of introducing a second phase on the surface/interior of carbon nanotubes (CNTs) and constructing heterostructures is often used to improve the dielectric and magnetic loss capabilities of materials to electromagnetic waves. Professor Cao Maosheng from Beijing Institute of Technology (corresponding author) constructed Fe3O4/multi walled carbon nanotube (MWCNT) two-phase heterostructures and polyaniline (PANI)/Fe3O4/MWCNT three-phase heterostructures, and compared the differences in electromagnetic wave absorption performance between the two, deepening the understanding of the relationship between heterostructures and absorption performance.

   Graphene can be used as a material due to its high dielectric loss characteristicsElectromagnetic wave absorberHowever, the lack of magnetism and magnetic loss capability limits its application. Professor He Jianping (corresponding author) from Nanjing University of Aeronautics and Astronautics used a relatively simple solvothermal method to bond magnetic Fe3O4 onto the surface of graphene, synthesizing layered magnetic graphene. The introduction of Fe3O4 not only improves impedance matching, but also increases magnetic loss capability, resulting in a significant improvement in electromagnetic wave absorption ability.

The influence of temperature and filler content on microwave absorption performance at different thicknesses

    Professor Cao Maosheng's team from Beijing Institute of Technology (corresponding author) has preparedMulti walled carbon nanotubesMWCNT/SiO2 composite materials were studied, and the effects of temperature (100-500 ℃) on the dielectric and microwave loss behavior of the materials were investigated in the X-band (8.2-12.4GHz). The results indicate that the MWCNT content and temperature affect the electromagnetic wave transmission and loss ability of the material by altering electron transfer and conductivity. This article not only provides a technical direction for designing microwave loss materials, but also demonstrates the great application value of CNT based composite materials in microwave loss materials.

NiFe2O4 nanoparticles graphene composite material (a) and NiFe2O4 nanorods-Graphene composite materials(b) The absorption performance

   Zhao Yun (corresponding author) from Beijing Institute of Technology synthesized NiFe2O4 nanorod graphene composite material using a relatively simple one-step hydrothermal method and studied its absorbing properties. The magnetic saturation strength and coercivity of the material are 22.5 emu g-1 and 48.67 Oe, respectively. Compared with NiFe2O4 nanoparticle graphene composite material, NiFe2O4 nanorod graphene composite material has superior microwave absorption performance. When the thickness is 2mm, the material has a minimum reflection loss (RL) of 29.2 dB (at 16.1 GHz) and an effective absorption bandwidth (RL<-10) of 4.4 GHz (13.6-18 GHz).

core-shell structure Fe3O4@C Composite materials and their absorbing properties

    Du Yunchen (corresponding author) from Harbin Institute of Technology first conducted in-situ polymerization on the surface of Fe3O4, coating it with phenolic resin, and then subjected it to high-temperature carbonization treatment to prepare a core-shell structure Fe3O4@C compound material. The thickness of the shell of this material can be controlled by changing the mass fraction of resorcinol during the polymerization process. The research results on the absorption performance of the material show that coating carbon shell on Fe3O4 not only increases the complex dielectric constant, but also improves the impedance matching characteristics, generates multiple relaxation processes, and thus enhances the microwave absorption capacity. In addition, in Fe3O4@C In the core-shell structure, a preferred shell thickness will produce special dielectric behavior, endowing the material with stronger reflection loss.

Morphology and Absorption Properties of γ - Fe2O3/RGO Composite Materials

    The advantages of a huge interface, high dielectric loss, and low density make graphene suitable for use as an electromagnetic wave absorber. However, graphene has high conductivity and electromagnetic parameters, making it difficult to meet impedance matching requirements. Yin Xiaowei (corresponding author) from Northwestern Polytechnical University used solvothermal method to combine reduced graphene oxide (RGO) nanosheets with surface modified γ - Fe2O3 colloidal nanoclusters. The special structure of alternating nanoclusters assembled on the surface of RGO endows this two-dimensional hybrid with lower reflection coefficient and wider effective bandwidth. The absorption of electromagnetic waves mainly comes from the interface polarization between nanoparticle clusters and the conductivity loss of RGO.

Dielectric Properties and Loss Mechanism of Graphene foam

    Professor Huang Yi (corresponding author), Department of Chemical Engineering, Nankai University, prepared three-dimensional graphene foam by freeze-drying and high-temperature carbonization. The three-dimensional conductive network constructed by the porous structure endows the material with an extremely wide effective absorption bandwidth (60.5 GHz) and adjustable microwave absorption characteristics. In addition, the three-dimensional graphene foam also has good compressibility.

Preparation and Mechanism of CoFe2O4 Hollow Sphere/Graphene Composite Materials by Steam Diffusion Method

    Zhao Yun (corresponding author) from Beijing Institute of Technology prepared CoFe2O4 hollow spheres/graphene composite materials using steam diffusion method combined with high-temperature calcination. The diameter of CoFe2O4 hollow spheres is around 500nm, and the shell thickness is about 50nm. This method successfully disperses CoFe2O4 hollow spheres uniformly on the surface of graphene sheets and endows the composite material with good electromagnetic wave absorption properties.