Key Takeaways & Executive Findings
- •• • The optimal composite RmCT-5.4-700 achieves RLmin of -30.2 dB at 14.0 GHz and EAB of 5.3 GHz at 2.0 mm thickness, demonstrating superior microwave absorption suitable for thin coating applications. • • The synthesis employs red mud as raw material and starch as carbon source via sol-gel and carbothermal reduction, enabling cost-effective and scalable production from industrial waste. • • The composite leverages multiple loss mechanisms: dipole polarization from defects, conductive loss from graphitized carbon network, interfacial polarization from heterogeneous interfaces, and magnetic loss from Fe3O4/Fe, leading to enhanced attenuation and impedance matching. • • The material achieves high absorption performance with a low filler loading (implied by coating thickness), indicating potential for lightweight and high-efficiency electromagnetic wave absorbers.
Abstract
Red mud, an industrial solid waste from alumina production, poses severe environmental challenges. This study presents a resource-efficient strategy to convert red mud into high-performance microwave absorbing materials. FexOy/TiO2/C composites were synthesized via a sol-gel method using starch as carbon source, followed by carbothermal reduction. The phase composition and microstructure were optimized by adjusting calcination temperature and raw material ratio. The optimal sample, RmCT-5.4-700, exhibited a minimum reflection loss (RLmin) of -30.2 dB at 14.0 GHz with an effective absorption bandwidth (EAB) of 5.3 GHz at a coating thickness of 2.0 mm. The superior absorption performance is attributed to the synergistic effects of dielectric components (TiO2, graphitized carbon) and magnetic components (Fe3O4/Fe). Carbothermal reduction introduces defects that induce dipole polarization, while the conductive network formed by graphitized carbon and Fe3O4/Fe particles enhances conductive loss. Heterogeneous interfaces between Fe3O4, Fe, TiO2, and the red mud matrix promote interfacial polarization. The magnetic loss of Fe3O4/Fe improves impedance matching, facilitating electromagnetic wave penetration and absorption. This work not only provides a novel route for red mud valorization but also contributes to the high-value utilization of solid wastes.
1. Introduction
Electromagnetic pollution has escalated with the proliferation of 5G devices, demanding absorbers with thin thickness, light weight, strong absorption, broad bandwidth, and facile fabrication. Ferrites, such as Fe3O4, offer magnetic loss but suffer from narrow absorption bandwidth and thermal instability. Carbon-based composites combining ferrites with dielectric carbon materials address these limitations by synergizing magnetic and dielectric losses. However, conventional carbon sources like graphene and carbon nanotubes are costly, hindering commercial scalability.
Red mud, a byproduct of alumina production, is an abundant and hazardous solid waste. Its high iron oxide content and porous structure make it a promising precursor for magnetic absorbers. This study pioneers the use of red mud as the iron source and starch as a carbon source to fabricate FexOy/TiO2/C composites via sol-gel and carbothermal reduction. By optimizing calcination temperature and composition, the resulting material achieves excellent microwave absorption, offering a sustainable and economically viable solution for both waste management and high-performance absorber production.
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LI Guomin, GUO Yujie, LI Lingxiao, JIA Kun, LIANG Liping (2026). Fabrication and Microwave Absorption Performance of FexOy/TiO2/C Composites Derived from Red Mud. Journal of Fuel Chemistry and Technology. https://doi.org/10.3724/2097-213X.2025.JFCT.0021
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Frequently Asked Questions
What is the maximum effective absorption bandwidth (EAB) achieved and at what thickness?
The optimal sample RmCT-5.4-700 exhibits an EAB of 5.3 GHz at a coating thickness of 2.0 mm, covering a significant portion of the Ku band (12-18 GHz).
How does the calcination temperature affect the phase composition and microwave absorption performance?
Calcination temperature influences the reduction of iron oxides and graphitization of carbon. The optimal temperature (700°C) yields a balanced composition of Fe3O4, Fe, TiO2, and graphitized carbon, maximizing synergistic loss mechanisms. Deviations lead to inferior impedance matching or reduced magnetic/dielectric losses.
What are the primary loss mechanisms contributing to the absorption performance?
The composite utilizes multiple loss mechanisms: dipole polarization from defects introduced by carbon consumption, conductive loss from the graphitized carbon network, interfacial polarization at heterogeneous interfaces (Fe3O4/Fe/TiO2/red mud), and magnetic loss from Fe3O4/Fe particles. These mechanisms collectively enhance attenuation and impedance matching.
Is the synthesis method scalable for industrial production?
The sol-gel method combined with carbothermal reduction is relatively simple and cost-effective. Red mud is an abundant waste, and starch is a low-cost carbon source. The process can be scaled up with standard industrial equipment, making it viable for large-scale production.
What is the significance of using red mud in terms of environmental impact?
Red mud is a hazardous solid waste from alumina production. Its utilization in this composite not only provides a high-value application but also mitigates environmental pollution, aligning with circular economy principles.
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