Controllable Preparation Of Fe₃O₄-based Composites And Its Microwave Absorbing Performance

Fe3O4 material is an attractive candidate for microwave absorption due to its appropriate saturation magnetization,high permeability and low cost.However,its application is limited by poor high frequency magnetic property,large density and narrow bandwidth.In this paper,we focus on the morphology control of Fe3O04 and the preparation of Fe3O4-based composites to obtain the materials with strong absorbing ability and low density through the synergistic effect between components of composite materials,and systematically discuss the electromagnetic loss mechanism of Fe3O4/C composites.The main contents are as follows:(1)The short X-shaped and long X-shaped FeOOH precursors that were synthesized by hydrothermal method have been calcined in an argon/hydrogen mixed atmosphere to obtain short X-shaped and long X-shaped Fe3O4 materials.Spherical Fe3O4 material synthesized by solvothermal method was used as a contrast.And then the influence of shape on the electromagnetic parameters and microwave absorption propertie of Fe3O4 were investigated in detail.The X-shaped configuration endows Fe3O4 with large shape anisotropy,which effectively improves the magnetic properties in high frequency of Fe3O4.X-shaped Fe3O4 with different sizes exhibit the better microwave absorption performance than spherical Fe3O4.The short X-shaped Fe3O4 obtain the reflection loss of-52.5 dB at a thickness of 2.5 mm.When the thickness is adjusted between 1.5 and 5.5 mm,the effective absorption bandwidth less than-10 dB can reach 15.12 GHz.(2)By heat treatment of FeOOH@PDA-x(x=5,30,60)core-shell precursor,controllable preparation of porous X-shaped Fe3O4@C-x(x=5,30,60)core-shell composite with adjustable carbon shell thickness have been realized.The effects of different thickness of carbon shell on the electromagnetic parameters and absorbing performance of Fe3O4@C-x are investigated.It is found that with the increase of carbon shell thickness,the dielectric loss increases while the magnetic loss decreases.For the Fe3O4@C-60 composite with carbon shell thickness of 29 nm,the reflection loss reaches the optimal value of-64.9 dB and the effective bandwidth is up to 4.64 GHz(13.04-17.68 GHz)with a thickness of only 1.75 mm.The morphology,structure and electromagnetic properties of FeOOH@PDA-60 products at different heat treatment temperatures have been systematically studied.It is found that X-shaped FeOOH is reduced to X-shaped Fe3O4 at 450-700℃,and is reduced to amorphous Fe at 800℃by polydopamine-derived carbon.The crystallinity of the polydopamine-derived arbon shell increases significantly at 700℃,resulting a significant increase in the dielectric loss of the composites.