粉煤灰磁珠Fe含量和研磨粒径对Fe3C@C-CNTs复合材料结构和吸波性能的影响

以粉煤灰磁珠作为原料，采用化学气相沉积(CVD)方法制备纳米结构铁/碳复合材料。该复合材料呈现良好的吸波性能，但存在磁珠性质不均一、结构调控难等问题。本文采用摇床方法对磁珠进行分选，并进行研磨处理，考察了磁珠Fe含量和研磨粒径对CVD生成产物的影响。结果表明，富铁磁珠CVD生成产物为碳包覆磁性颗粒与碳纳米管组成的复合材料(Fe₃C@C-CNTs)，该复合材料呈现多孔团簇球形结构。磁珠Fe含量增加，复合材料的相对碳沉积量(C/Fe值)减小，石墨化程度降低(D峰和G峰面积比I_D/I_G值升高)，导致材料阻抗匹配值升高，吸波性能获得提升。磁珠Fe含量为71.43wt%时，复合材料有效吸收频带达到4.5 GHz，最小反射损耗(RLmin)达到-16.1 dB。对磁珠进行研磨后，CVD生成产物的C/Fe值不变，但碳沉积速率增大，I_D/I_G值升高，电磁波衰减常数下降，但阻抗匹配明显提高，吸波性能大幅度提升。研磨粒径为18.23μm时，复合材料有效吸收频带达到4.8 GHz,RLm_i...

Impact of Fe content of coal fly ash magnetospheres and the grinding size upon microstructure and microwave absorption properties of Fe3C@C-CNTs nanocomposites

Nano-structured iron/carbon composites can be prepared by chemical vapor deposition (CVD) using coal fly ash magnetospheres as raw materials, showing good microwave absorption properties. However, there are problems such as uneven properties of magnetospheres and difficulty in structural regulation. In this paper, the magnetospheres were separated by the shaking bed method, and then were grinded. The effects of the magnetospheres Fe content and the grinding particle size on the CVD products were investigated. The results show that the CVD product of Fe-rich magnetospheres is Fe₃C@C-CNTs, and the composite exhibits a porous cluster spherical structure. With the increase of magnetic bead Fe content, the relative carbon deposition (C/Fe value) of the composite decreases, and the graphitization degree decreases (Higher D/G peak intensity ratio I_D/I_G value increases), resulting in the increase of impedance matching value and the improvement of wave absorption performance. When the Fe content is 71.43wt%, the effective absorption band of the composite reaches 4.5 GHz, and the minimum reflection loss (RL_min) reaches ?16.1 dB. After grinding the magnetospheres, the C/Fe value of CVD products is unchanged, but the carbon deposition rate increases, the I_D/I_G value increases, and the electromagnetic wave attenuation constant decreases, but the impedance matching is significantly improved, and the microwave absorption performance is greatly improved. When the grinding particle size is 18.23 μm, the effective absorption band of the composite is 4.8 GHz, and the RL_min can reach ?34.7 dB. The excellent microwave absorption properties of the composites benefit from the synergistic absorption of CNTs and Fe₃C@C. Multiple reflections of microwave are supposed to be enhances in the porous cluster aggregated spheres, and the promoted interface polarization is also attributed to the excellent microwave absorption properties.