WANG Wenjing1a，DONG Haoqi2b，LU Jie1a，LI Wei2，ZHU Lei2，GUO Lisheng1a，
ZHANG Chenhua1a，WEI Yuxue1a，SUN Song1a
（1a. School of Chemistry and Chemical Engineering，1b. School of Materials Science and Engineering， Anhui University，
Hefei 230601， China；2. Anhui Tanxin Technology Co. ， Ltd， Huaibei，235141， China）
Abstract
Objective The energy attenuation of wave-absorbing materials primarily occurs through two mechanisms： dielectric loss and magnetic loss. Conventional wave-absorbing materials are less effective because they cannot simultaneously use both electrical and magnetic losses to attenuate microwave interference. Iron nitride， characterized by magnetic properties， such as high saturation magnetization， low density， large surface area， and environmental friendliness， has applications in various high-tech fields. However， its widespread use is limited due to 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. These core-shell wave-absorbing materials exhibit excellent stability. The incorporation of carbon increases the dielectric loss of iron nitride， generating composites that exhibit high dielectric and magnetic losses， thereby improving the microwave absorption of Fe2N@C， Fe3N@C， and Fe4N@C. Further investigations will explore the microwave absorption 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 analyzed using X-Ray diffraction （XRD）. Their micro-morphology was analyzed using ultra-high-resolution scanning electron microscopy （SEM） and high-resolution transmission electron microscopy （TEM）. The micro-morphology of Fe2N@C， Fe3N@C， and Fe4N@C was determined through the successful synthesis of carbon-encapsulated iron nitride. Raman spectroscopy and X-ray photoelectron spectroscopy （XPS） were also employed for this purpose. XPS techniques were used to characterize and investigate their conformational relationships. Microwave absorption properties， as well as the imaginary parts of the complex dielectric constant and complex permeability， were analyzed using a vector network analyzer （VNA）. Their magnetic loss properties were quantified using a Vibrating Sample Magnetometer （VSM）.
Results and Discussion As shown in Fig. 1， Fe2N， Fe3N， and Fe4N were synthesized using MOFs as precursors. Additionally， Fig. 2 showed 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 showed that Fe3N@C had a relatively low degree of graphitization， resulting in a low permittivity. In contrast， Fig. 6 demonstrated that Fe2N@C and Fe4N@C exhibited poor wave absorption properties， while Fe3N@C displayed good microwave absorption. Therefore， it could be concluded that Fe3N@C was a better candidate for microwave absorption compared to Fe2N@C and Fe4N@C. Fig. 7 showed that Fe2N@C and Fe4N@C had significantly greater dielectric loss than magnetic loss due to their high imaginary dielectric constant， resulting in an imbalancd impedance matching. On the other hand， Fe3N@C had a lower imaginary dielectric constant， providing a better impedance matching due to its balanced dielectric constant and magnetic permeability.
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
Get Citation: 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.
Received:2024-02-03.Revised:2024-03-26,Online:2024-04-26。
Funding Project: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
First Author:王文敬（1998—），女，硕士生，研究方向为化工新材料。E-mail：wwjfp1015@163. com。
Corresponding Author: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。
DOI：10.13732/j.issn.1008-5548.2024.03.004
CLC No:TM25； TB4 Type Code:A
Serial No:1008-5548（2024）03-0039-12
