Structural, Electromagnetic and Microwave Properties of Magnetite Extracted from Mill Scale Waste via Conventional...

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.