Recycling of red mud to Fe/C-based composite microwave absorbents by coal gasification semi-coke
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摘要: 基于煤加氢气化半焦(简称半焦,SC)与赤泥(RM)高温固相反应一步回收赤泥制备Fe/碳基复合微波吸收材料,调节体系组成以优化吸波性能。研究发现,在Ar气氛、900 ℃条件下,源自SC与RM质量比为0.4∶1−0.7∶1的复合物均显示了优良的性能;且当SC与RM质量比为0.6∶1时,复合物性能最优。其最低模拟反射损耗为−48.3 dB,相应的有效吸收带宽为4.6 GHz。材料强的本征衰减能力源于石墨化碳及大量相界与缺陷引起的介电损耗;其良好的波阻抗匹配得益于体系组成调变对复合物电磁参数的有效调控。此外,Na2O、Al2O3与SiO2之间的高温固相化合一定程度上削弱了赤泥引起的强碱性。Abstract: Fe/C-based composite microwave absorption (MA) materials were prepared by high temperature solid phase reaction between coal hydrogasification semi-coke (SC for short) and solid waste red mud (RM). In order to optimize MA performance, initial system composition was changed. It was found that, under an argon atmosphere and reaction temperature of 900 ℃, the composites obtained from systems with mass ratio of SC to RM (MRSR) at 0.4∶1−0.7∶1 all showed excellent performance, and that corresponding to MRSR of 0.6∶1 was the best. At a coating thickness of 1.5 mm, the simulated minimum reflection loss and effective absorption bandwidth could reach −48.3 dB and 4.6 GHz, respectively. The strong intrinsic attenuation ability mainly resulted from the dielectric loss due to the presence of graphite carbon as well as a large number of phase boundaries and defects. And the impedance matching between material and free space was attributed to the effective regulation on electromagnetic parameters of the initial system composition. Moreover, the solid phase combination reaction among Na2O, Al2O3 and SiO2 could weaken the strong alkalinity caused by RM.
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Key words:
- microwave absorption /
- coal gasification semi-coke /
- red mud /
- carbon /
- iron
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图 4 不同MRSR条件下制备样品的反射损耗(RL)与阻抗匹配特性参数(Z)模拟曲线 (a)−(e)及衰减常数(α)曲线 (f)
Figure 4 Simulated reflection loss (RL) and impedance matching characteristic (Z ) curves (a)−(e) as well as attenuation constant (α) curves (f) of the samples obtained at different MRSR
(a): SCRM900-0.4; (b): SCRM900-0.5; (c): SCRM900-0.6; (d): SCRM900-0.7; (e): SC900
表 1 热处理过程中的主要化学反应与其热力学数据
Table 1 Major reactions during heat treatment and their thermodynamic data
No. Reaction ΔrGT θ /(J·mol−1) ts /℃ tf /℃ (a) 3Fe2O3 + C = 2Fe3O4 + CO 125275−222.53T 289.8 (b) Fe3O4 + C = 3FeO + CO 191743−227.79T 568.6 (c) FeO + C = Fe + CO 161519−158.46T 746.2 (d) 3Fe2O3 + CO = 2Fe3O4 + CO2 −47184−46.67T any temperature (e) Fe3O4 + CO = 3FeO + CO2 19284−51.92T 98.3 (f) FeO + CO = Fe + CO2 −10940 + 17.41T 355.2 (g) CO2 + C = 2CO 172459−175.87T 707.5 (h) C = [C] 22590−42.26T 261.4 (i) 2CO = [C] + CO2 −143960 + 128.7T 845.4 (j) [Na6Al6Si6O24]·[Na2CO3]= 6NaAlSiO4 + Na2O + CO2 − − − (k) Na2O + Al2O3 + 2SiO2 = 2NaAlSiO4 −168483−30.58T any temperature ΔrGTθ is the standard Gibbs free energy change of the reaction, T is thermodynamic temperature, ts and tf are the thermodynamic initial and terminational temperatures in the standard state, [C] represents carbon in intermetallic of Fe and carbon, “−” represents no data obtained 表 2 相关材料的微波吸收性能
Table 2 Microwave absorption performance data for the related materials in current literatures
Absorption materail RLmin /dB Matching frequency /GHz EAB /GHz Simulating thickness /mm Ref. C/Fe3O4 nanoparticles −58.5 14.9 5.6 (12.4−18.0) 2.0 [3] C/MnFe2O4/MnO2 heterojunction −72.1 10.5 5.0 (8.4−13.4) 2.8 [4] Fe@C microspheres −37.7 13.4 7.5 (10.5−18.0) 3.0 [30] FeCo/C (from bamboo) −40.0 14.1 4.7 (6.6−11.3) 1.9 [14] Fe3O4@C (from walnut shell) −40.3 17.5 4.3 (13.7−18.0) 2.0 [31] Fe/C (from coal gasification slag) −47.1 5.5 5.3 (12.4−17.7) 1.5 [16] SCRM900-0.6 −48.3 15.1 4.5 (12.9−17.4) 1.5 this work -
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