Elsevier

Materials Letters

Volume 308, Part B, 1 February 2022, 131168
Materials Letters

Facile synthesis of Co/SC microwave absorbents by recycling coal hydrogasification residue

https://doi.org/10.1016/j.matlet.2021.131168Get rights and content

Highlights

  • The composite microwave absorbents was prepared by recovering the residue of coal hydrogasification.

  • The Co/SC composites possess excellent performance.

  • Impedance matching and interfacial polarization play a key role to MA property.

  • This method realizes the recycling of coal hydrogasification residue and reduces the cost of carbon based carrier.

Abstract

A coal hydrogasification residue, semi-coke (SC), was recycled to prepare SC-based composites for microwave absorption by a facile method. This mainly involved loading an ethanol solution of cobalt nitrate onto SC and then conducting in-situ carbothermal reduction. The results showed that, a Co/SC composite could be obtained at a carbothermal temperature of 700 ℃ (denoted by CoSC700). The CoSC700 composite exhibited excellent performance with a minimum reflection loss value of − 40.1 dB and an effective absorption bandwidth of 5.0 GHz at a coating thickness of 2 mm. This is the combined effect of good impedance matching and strong intrinsic dissipation capacity, which benefit from the effective adjustment of input impedance by Co as well as strong conduction and interfacial polarization relaxation losses caused by the effects of graphite carbon and SC-Co interfaces.

Introduction

Carbon-based composite microwave absorption (MA) materials have the advantages of adjustable impedance, multi-frequency and broadband absorption, low density and excellent stability. Accordingly, they have drawn extensive attention in the prevention of electromagnetic radiation pollution and in stealth technology [1], [2], [3]. Current researches are mainly focused on carbon materials with special structures, such as nanofibers, nanotubes, porous graphite nanosheets and reduced graphene oxide [4], [5], [6]. The synthesis of these carbon materials is costly and time-consuming, which greatly limits their large-scale application.

Coal gasification residue (CGR) is a new type of solid waste generated in the coal gasification process. So far, much effort has been made to utilize its inorganic component and well-developed pore structure to produce adsorbents, soil modification materials and building materials [7], [8]. Generally, CGR also contains a large amount of carbon with a certain degree of graphitization. Therefore, CGR may be a promising candidate as a carbonaceous carrier in the economical construction of carbon-based composite microwave absorbents.

In this work, coal hydrogasification residue (semi-coke, SC, a type of CGR) was recycled to construct Co/SC composite MA materials. The residual carbon in SC acts as a reductant of the cobalt species and dielectric component in the MA composites. This research provides a new pathway for the facile synthesis of MA materials and the high-efficiency utilization of CGR.

Section snippets

Experimental section

Raw SC material (Sino US New Energy Technology R & D Co., Ltd., China) was ground and passed through a 150-mesh screen. The screen underflow was collected and dried at 120 ℃. Some 30 g of dried SC powder was impregnated with 150 mL of a 0.7 M solution of cobalt nitrate in ethanol for 12 h at room temperature. After removing most of the liquid, the precursor powder was dried at 120 ℃ for 8 h, then heat-treated at 300–800 ℃ for 2 h in an Ar atmosphere to finish the carbothermal reaction. The

Composition and microstructure

X-ray diffraction (XRD) analysis was carried out to ascertain the optimal heat-treatment temperature. As shown in Fig. 1 (a), with increasing temperature, the cobalt species of Co3O4, CoO, and Co appeared in sequence, and the cobalt oxides largely disappeared after calcination at 700 ℃ as a result of the sufficiently high temperature. Thus, the optimal heat-treatment temperature was determined to be 700 ℃. Inevitably, there is still a certain amount of cobalt oxide on the surface due to the

Conclusions

By loading Co onto the surface of SC, effective microwave absorbents were successfully prepared. The SC-based composite showed excellent MA performance, which benefited from the good impedance matching and strong intrinsic dissipation capacity originating mainly from the dielectric losses. The present work provides a new way for the economical synthesis of microwave absorbents and the high-efficiency disposal of SC.

CRediT authorship contribution statement

Fei Gao: Methodology, Investigation, Formal analysis, Writing-original draft. Yuyan Li, Lutao Mao, Yake Wang and Baoshun Zhu: Methodology, Investigation, Formal analysis. Rong Zhang: Writing-review & editing. Liping Liang and Guomin Li: Conceptualization, Supervision, Visualization, Project administration, Writing-review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the National Nature Science Foundation of China (51802212) and the National College Students’ Innovation and Entrepreneurship Training Program (2021465).

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