Abstract
This study presents the utilization of mill scale waste, which has attracted much attention due to its high content of magnetite (Fe3O4). This work focuses on the extraction of Fe3O4 from mill scale waste via magnetic separation, and ball milling was used to fabricate a microwave absorber. The extracted magnetic powder was ground-milled using two different techniques: (i) a conventional milling technique (CM) and (ii) mechanical alloying (MM) process. The Fe3O4/CM samples were prepared by a conventional milling process using steel pot ball milling, while the Fe3O4/MM samples were prepared using a high-energy ball milling (HEBM) method. The effect of milling time on the structural, phase composition, and electromagnetic properties were examined using X-ray diffraction (XRD) and a vector network analyzer (VNA). XRD confirmed the formation of magnetite after both the magnetic separation and milling processes. The results revealed that Fe3O4 exhibited excellent microwave absorption properties because of the synergistic characteristics of its dielectric and magnetic loss. The results showed that the Fe3O4/CM particle powder had a greater absorption power (reflection loss: <−10 dB) with 99.9% absorption, a minimum reflection loss of −30.83 dB, and an effective bandwidth of 2.30 GHz for 2 mm thick samples. The results revealed the Fe3O4/MM powders had higher absorption properties, including a higher RL of −20.59 dB and a broader bandwidth of 2.43 GHz at a matching thickness of only 1 mm. The higher microwave absorption performance was attributed to the better impedance matching property caused by the porous microstructure. Furthermore, the magnetite, Fe3O4 showed superior microwave absorption characteristics because of the lower value of permittivity, which resulted in better impedance matching. This study presents a low-cost approach method by reutilizing mill scale waste to fabricate a high purity crystalline Fe3O4 with the best potential for designing magnetic nano-sized based microwave absorbers.
Highlights
Microwave absorbing materials (MAMs) are materials that can interact with electromagnetic (EM) waves and dissipate into other forms of thermal energy through their electric and magnetic losses [1,2,3]
The high environmental pollution of electromagnetic (EM) waves produced by the accelerating of variable electronic applications such as wireless communication technologies in mobile phones, remote controls, and Wi-Fi has led to serious harm to human healthcare and has affected the normal operation of electronic equipment and communications systems that operate at super high frequency ranges [9,10,11]
Meng et al fabricated a small size composite of Fe3O4 covered with an ultra-thin carbon layer (Fe3O4/C); the prepared sample displayed the strongest reflection loss of composite NPs with an average particle size of 52 nm; this composite could reach −58.5 dB at 14.88 GHz with a thickness of 2 mm, and the corresponding effective absorption (RL ≤ −10 dB) bandwidth (EAB) was 5.63 GHz (12.37–18 GHz) [35]
Summary
Microwave absorbing materials (MAMs) are materials that can interact with electromagnetic (EM) waves and dissipate into other forms of thermal energy through their electric and magnetic losses [1,2,3]. As a viable solution to tackle this issues, advanced electromagnetic absorptive materials have attracted considerable attention because they exhibit strong absorption, light weight, wide absorption bandwidth, reduced thickness MAMs, strong attenuation, and good impedance match [12,13,14] In addition to their outstanding absorption capacity, these materials can maximize the electromagnetic energy entering a material and convert that energy into thermal energy or dissipate it via an interference-effect based on their dielectric or magnetic loss mechanisms, which are determined by the parameters of electromagnetism, i.e., complex permeability and permittivity during the absorbing process of an electromagnetic wave [15,16,17]. Yan et al obtained magnetite particles (MPs) using the high-energy ball milling of oxidized nickel slag that possessed strong magnetic properties and hetero-interfaces formed by impurities According to their results, magnetite crystals displayed outstanding microwave absorption properties [39]. As part of intensive research to study the microwave absorbing characteristics of magnetite, the authors of this paper aimed to study the effect of different particle sizes and various milling times on Fe3O4 from mill scale waste products
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