基于玉米芯构筑FexOy/C复合材料及吸波性能研究

Construction and microwave absorbing properties of FexOy/C composites based on corncobs

  • 摘要: 玉米芯作为玉米生产加工过程中产生的副产物,具有产量高、来源广、成本低等特点,但废弃玉米芯的潜在价值没有得到充分的利用,随意的丢弃或焚烧造成了严重的资源浪费与环境污染。为了实现废弃玉米芯的高值化利用和碳基复合微波吸收材料的低成本制备,本研究以废弃玉米芯为载体,采用简单的湿化学浸渍法和碳热还原工艺制备FexOy/C复合吸波材料。通过优化焙烧温度和前驱体溶液浓度来探究不同磁性组分及其负载量对复合材料性能的影响。采用XRD、Raman、SEM、BET、VNA多种表征方法对复合材料的物相演变规律、微观形貌、吸波性能进行分析。结果表明,在引入适量的磁性组分时,能有效提高复合材料的吸波性能,Fe/C复合材料仍保持了玉米芯天然的三维孔道结构,比表面积可达126.97 m2/g,孔径为5.40 mm,有助于入射电磁波的多重反射和损耗。当负载量过多时,导致复合材料阻抗失配,不利于吸波性能的优化。其中,FCC-0.3-700和FCC-0.3-900均表现出优异的微波吸收性能,FCC-0.3-700在涂层厚度为2.0 mm时,最低反射损耗值(RLmin)达到−41.4 dB,对应的有效吸收带宽(EAB)达到5.6 GHz;FCC-0.3-900在8.4 GHz处的RLmin达到−41.7 dB,涂层厚度为1.5 mm时EAB达到4.5 GHz。FexOy/C复合材料优异的吸波性能得益于玉米芯中的固定碳被部分消耗产生的缺陷能够增强入射电磁波的多重散射和反射,这些缺陷还可以提供偶极位点进而产生偶极极化,有利于电磁波的衰减。此外,Fe3O4、Fe颗粒均匀的负载于废弃玉米芯孔道内或分散在其碎片间,形成大量的有效界面,增强了界面极化。同时,FexOy/C复合材料中的石墨碳与Fe3O4、Fe颗粒形成的导电网络也可以极大地促进导电损耗。本论文制备的材料不仅符合电磁波吸收材料“薄、轻、宽、强”的发展特点,而且开辟了废弃玉米芯的高值化与功能化利用新途径。

     

    Abstract: As a by-product of corn production and processing, corn cobs have the characteristics of high yield, wide source and low cost, but the potential value of waste corn cobs is often not fully utilized, and the random discarding or incineration has caused serious waste and environmental pollution. In order to realize the high-value utilization of waste corn cobs and the low-cost preparation of carbon-based composite electromagnetic wave absorbing materials (EMWAMs), the waste corn cobs were recycled as the carrier to prepare FexOy/C composite EMWAMs by using the simple wet chemical impregnation method and carbon thermal reduction route. The effects of different magnetic components and their loadings on the properties of the composites were investigated by optimizing the sintering temperature and the concentration of precursor solution. Various characterization methods including XRD, Raman, SEM, BET, VNA were used to analyze the phase composition evolution, microscopic morphology, and microwave absorbing properties of the composites. It was founded that the microwave absorbing properties of the FexOy/C composites could be effectively improved when introducing the moderate amount of magnetic components, under which the Fe/C composite still maintained the natural three-dimensional pore structure of corncobs, with a specific surface area of up to 126.97 m2/g and a pore diameter of 5.40 mm, which benefited for the multiple reflections and losses of incident electromagnetic waves. In the case of excessive loading, it would lead to the impedance mismatch of the composites, which is not conducive to the optimization of the wave-absorbing ability. Among them, FCC-0.3-700 and FCC-0.3-900 exhibited excellent microwave absorption performance, and the minimum reflection loss (RLmin) value reached −41.4 dB at a coating thickness of 2.0 mm for FCC-0.3-700, with an effective absorption bandwidth (EAB) of 5.6 GHz. While the RLmin value was −41.7 dB at 8.4 GHz and the EAB was 4.5 GHz under the coating thickness of 1.5 mm for FCC-0.3-900.The outstanding absorption performance of FexOy/C composites was attributed to the fact that the defects created by the partial consumption of fixed carbon in the corn cores enhanced the multiple scattering and reflection of the incident electromagnetic wave, and these defects could also provide dipole sites for generating dipole polarization, which was beneficial to the attenuation of electromagnetic wave. In addition, Fe3O4 and Fe particles were uniformly embedded in the apertures of the waste corn cobs or dispersed among the fragments, forming a large number of effective interfaces and enhancing the interfacial polarization. At the same time, the conductive network formed by the graphitic carbon and Fe3O4/Fe particles in the FexOy/C composites greatly promoted the conductive loss. The FexOy/C composites prepared in this work are not only accord with the characteristics “thinner thickness, lighter mass, wider absorption bandwidth and stronger absorption intensity” of EMWAMs, but also open the new approach for the high value and functional utilization of waste corn cobs.

     

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