王文敬¹，董浩琪²，卢 洁¹，李 伟³，朱 磊³，郭立升¹，张成华¹，魏宇学¹，孙 松¹（1. 安徽大学 化学化工学院，安徽 合肥 230601；2. 安徽大学 材料科学与工程学院，安徽 合肥 230601； 3. 安徽碳鑫科技有限公司，安徽 淮北 235141）

引用格式：

王文敬，董浩琪，卢洁，等. 碳包裹氮化铁复合材料的制备及微波吸收性能［J］. 中国粉体技术，2024，30（3）：39-50. WANG W J， DONG H Q， LU J， et al. Preparation and microwave absorption properties of carbon-coated iron nitride composites ［J］. China Powder Science and Technology，2024，30（3）：39−50.

DOI：10.13732/j.issn.1008-5548.2024.03.004

收稿日期：2024-02-03，修回日期：2024-03-26，上线日期：2024-04-26。

基金项目：国家自然科学基金项目，编号：21902001，22179001，22102001；安徽省高校杰出青年科研项目，编号：2022AH020007；安 徽高校协同创新项目，编号： GXXT-2023-009；安徽省高等学校自然科学基金项目，编号：2023AH050114

第一作者简介：王文敬（1998—），女，硕士生，研究方向为化工新材料。E-mail：wwjfp1015@163. com。

通信作者简介：魏宇学（1991—），女，副教授，博士，硕士生导师，研究方向为化工新材料。E-mail：weiyuxue@ahu. edu. cn。

摘要：【目的】 研究不同氮化铁复合材料Fe₂N@C、 Fe₃N@C和Fe₄N@C的微波吸收性能。【方法】 采用X射线衍射（X-Ray diffraction，XRD）、超高分辨扫描电子显微镜（scanning electron microscope，SEM）、高分辨透射电子显微镜（transmission electron microscope，TEM）、拉曼光谱（Raman spectra，Raman）和X射线光电子能谱（X-ray photoelectron spectroscopy，XPS） 等技术表征、定性研究 Fe₂N@C、 Fe₃N@C和 Fe₄N@C的结构、形貌以及成分变化，结合矢量网络分析（vector network ana⁃ lyzer，VNA）和振动样品磁强计（vibrating sample magnetometer，VSM）定量分析Fe₂N@C、 Fe₃N@C和Fe₄N@C对微波的反射 损耗能力以及磁性能。【结果】 Fe₂N@C和Fe₄N@C因介电常数远大于磁导率，导致阻抗匹配失衡，而Fe₃N@C介电常数和 磁导率相近，存在较好的阻抗匹配，涂层厚度为 2 mm 的样品，小于反射损耗为−10 dB 的有效吸波宽带达到的频率为 2. 4 GHz，在频率为9. 1 GHz处最小的反射损耗为−14. 1 dB。【结论】 由于3种氮化铁的相结构和碳层的缺陷程度不同， 氮化铁核与碳壳的导电性不同，会在界面间出现电荷聚集，引起界面极化，导致Fe₂N@C和Fe₄N@C的介电常数增加，使得 Fe₂N@C和Fe₄N@C中的介电常数远大于磁导率，最终导致阻抗匹配失衡。

关键词：氮化铁；复合材料；阻抗匹配；微波吸收

Abstract

Objective The energy attenuation of wave-absorbing materials occurs primarily through two mechanisms： dielectric loss and magnetic loss. Conventional wave-absorbing materials are often limited in their effectiveness because they cannot use both electrical and magnetic losses simultaneously to attenuate microwave interference. Iron nitride， characterised by magnetic properties such as high saturation magnetisation, low density， large surface area and environmental friendliness，has found applications in various high-tech fields. However，its widespread use has been hampered by its poor dielectric loss characteristics. Carbon materials， known for their exceptional conductivity and dielectric loss properties，can be combined with iron nitride to form composite materials that exhibit both magnetic and high dielectric losses. To achieve this， metal-organic frameworks （MOFs） are used as precursors for the synthesis of Fe₂N@C， Fe₃N@C and Fe₄N@C through a process involving calcination and nitriding. The resulting core-shell wave-absorbing materials exhibit excellent stability. The incorporation of carbon materials increases the dielectric loss of iron nitride， resulting in composites that exhibit high levels of both dielectric and magnetic losses， thereby improving the microwave absorptivity of Fe₂N@C， Fe₃N@C and Fe₄N@C. Subsequent investigations will further explore the microwave absorptivity variations between different compositions of Fe₂N@C， Fe₃N@C and Fe₄N@C.

Methods The physical composition of Fe₂N@C， Fe₃N@C and Fe₄N@C was analysed using X-Ray Diffraction （XRD）. The micro-morphology of Fe₂N@C， Fe₃N@C and Fe₄N@C was analysed using Ultra-high resolution Scanning Electron Microscope （SEM） and High resolution Transmission Electron Microscope （TEM）. The micro morphology of Fe₂N@C， Fe₃N@C and Fe₄N@C was determined through the successful synthesis of carbon-encapsulated iron nitride. The Transmission Electron Microscope （TEM） was used to analyze the microscopic morphology of Fe₂N@C， Fe₃N@C， and Fe₄N@C to determine the successful synthesis of carbon-coated iron nitride. Raman spectra and X-ray photoelectron spectroscopy （XPS） were also employed for this purpose. Photoelectron spectroscopy （XPS） techniques were used to characterize and investigate the conformational relation⁃ships of Fe₂N@C， Fe₃N@C and Fe₄N@C. The microwave absorption properties， as well as the complex dielectric constant imaginary part and complex permeability imaginary part of Fe₂N@C， Fe₃N@C and Fe₄N@C， were analyzed using a Vector Network Analyzer （VNA）. The magnetic loss properties of Fe₂N@C， Fe₃N@C and Fe₄N@C were quantitatively analyzed using a Vibrating Sample Magnetometer （VSM）.

Results and Discussion Based on Fig. 1， Fe₂N， Fe₃N， and Fe₄N were synthesized using MOFs as precursors. Additionally，Fig. 2 shows that highly dispersed Fe nanoparticles were successfully encapsulated in the carbon layer，confirming the synthesis of Fe₂N@C，Fe₃N@C，and Fe₄N@C. Fig. 4 shows that the degree of graphitization of Fe₃N@C is relatively low，resulting in a low permittivity. In contrast， Fig. 6 demonstrates that Fe₂N@C and Fe₄N@C exhibit poor wave absorption properties，while Fe₃N@C has good microwave absorption ability. Therefore，it can be concluded that Fe₃N@C is a better candidate for microwave absorption compared to Fe₂N@C and Fe₄N@C. Fig. 7 shows that Fe₂N@C and Fe₄N@C have a significantly larger dielectric loss than magnetic loss due to their high dielectric constant imaginary part， resulting in an imbalance in impedance matching. On the other hand， Fe₃N@C has a lower dielectric constant imaginary part， leading to a better impedance matching as the dielectric constant and magnetic permeability are similar.

Conclusion Fe₂N@C， Fe₃N@C， and Fe₄N@C were successfully prepared by nitriding metal-organic frameworks （MOFs） as precursors. Fe₂N@C and Fe₄N@C exhibit an imbalance in impedance matching due to their dielectric constants being much larger than their magnetic permeability. In contrast， Fe₃N@C has similar values for both parameters， resulting in better impedance matching. Samples with a coating thickness of 2 mm have an effective absorbing bandwidth of less than -10 dB， with a reflection loss of -10 dB up to 2. 4 GHz. The minimum reflection loss of -14. 1 dB at 9. 1 GHz indicates better absorbing performance. The reflection loss at 9. 1 GHz is a minimum of -14. 1 dB， indicating good wave-absorbing performance. The electrical conductivity of the iron nitride cores and the carbon shells differs due to the varying phase structures of the three iron nitrides and the degree of defects in the carbon layers. This difference leads to charge aggregation between the interfaces， causing interfacial polarization. As a result， the dielectric constants of Fe₂N@C and Fe₄N@C increase， making them much larger than the magnetic perme-ability. This ultimately leads to an imbalance of the impedance matching.

Keywords：iron nitride；composites；impedance matching；wave-absorbing properties

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