Electrospining Machine: The Nitriding Treatment of Ternary Nanofibers toward Outstanding Electromagnetic Wave Absorption Performance (Professor Yu Meijie and Professor Wang Chengguo's team)

Background

Recently, the team of Professor Yu Meijie and Professor Wang Chengguo from Shandong University published their latest research results "The Nitriding Treatment of Ternary Nanofibers toward Outstanding Electromagnetic Wave Absorption Performance" in the journal Composites Part B: Engineering (impact factor: 11.1).

Method

The researchers prepared ternary composite nanofibers (Fe4N/ZrO2/CNFs) by electrospinning and gas nitriding. Compared with Fe3O4/ZrO2/CNFs fibers without nitriding, Fe4N-based nanofibers achieved high efficiency and broadband electromagnetic wave absorption performance.

Research highlights

The nitrided Electrospun Nanofbers exhibited superior electromagnetic wave absorption performance:

The synthesis of Fe4N promoted the enhancement of multiple attenuation mechanisms including conductive loss, magnetic loss and polarization relaxation; in addition to phase change, a large number of defects and functional groups were introduced into the carbon Electrospun Nanofbers during the nitridation process, which enhanced the loss capacity while suppressing the excessive increase of conductivity, thereby optimizing the impedance matching properties of the material. With the help of the synergistic effect between all components, Fe4N/ZrO2/C exhibited superior electromagnetic wave absorption performance, with a minimum reflection loss of -63.7 dB and an effective absorption bandwidth of up to 7.0 GHz.

Nitriding nanofibers 1

The nitriding process induces the generation of defects and promotes polarization relaxation loss:

 As shown in Figure 2a-c, one-dimensional fibers with ultra-high aspect ratios overlap and stack to form a three-dimensional conductive network, which can promote the contact between the material and the incident wave and increase the multiple scattering of microwaves inside the material. On the other hand, it can serve as a carrier of Fe4N and ZrO2 to promote the uniform dispersion of components. It is worth noting that charges tend to accumulate at the heterogeneous interface between ZrO2 and Fe4N, and reciprocate with the change of the alternating electric field phase, thereby consuming electromagnetic energy (Figure 2d and e). At the same time, a large number of different types of defects are widely present inside the material, confirming that the nitriding process will induce the generation of defects and promote polarization relaxation loss. (Figure 2f).

Nitriding nanofibers 2

The nitriding treatment optimizes the impedance matching properties of the material: 

Through the analysis of electromagnetic parameters, it can be seen that the dielectric loss and magnetic loss of Fe4N/ZrO2/CNFs are better than those of Fe3O4/ZrO2/CNFs (Figure 3a-d). With the help of the results of the spatial electric field distribution simulation, it can be seen that when the incident wave acts on the composite nanofibers, the dipoles inside the material are polarized to form polarized charges. Compared with ferrites, polarized charges are more likely to accumulate at the heterojunction interface between Fe4N and other phases, resulting in a more obvious spatial electric field distribution. The periodic change of the phase angle of the alternating electric field continuously induces repeated polarization and rearrangement of dipoles, as well as changes in the electric field distribution inside the material. In the process, electromagnetic energy is consumed (Figure 3e-f). In addition to super strong loss capacity, the achievement of perfect impedance matching is a prerequisite for achieving efficient electromagnetic wave absorption. The inhibitory effect of nitriding on the electrical conductivity of carbon Electrospun Nanofbers and the introduction of low dielectric ZrO2 helped Fe4N/ZrO2/CNFs achieve this condition (Figure 3g-j).

Nitriding nanofibers 3

Compared with traditional ferrites, Fe4N/ZrO2/C ternary nanocomposites have higher conductivity and saturation magnetization than traditional ferrites, which will greatly improve the various loss mechanisms of the material, including conductive loss, magnetic loss and polarization relaxation. This work will surely provide inspiration for the design, development and microwave absorption applications of other nitride hybrid materials.

Paper link:

https://www.sciencedirect.com/science/article/pii/S1359836824007340