The design of microwave absorbing materials requires low reflection and high absorption of radiation simultaneously. Low reflection of electromagnetic waves can be achieved inducing porous faces which minimize the impedance mismatch. High absorption can be obtained by increasing the conductivity of the material. We report the preparation of highly porous scaffolds from a combination of graphene and carbon nanotubes. The bimodal porous structure was controlled making use of the surface properties of graphene oxide that are able to stabilize hexane droplets in aqueous dispersions of graphene oxide and carbon nanotubes. After hydrothermal and two step freeze-drying processes, macro-(220 microns) and mesoporous (10 microns) structures, due to hexane droplets and freeze drying, respectively, were obtained. DC conductivities of 8.2, 14.7, 33.2, and 60.7 S m(-1) were obtained for graphene scaffolds containing 0, 10, 20 and 40% of carbon nanotubes respectively. An electromagnetic characterization was performed on scaffolds infiltrated with epoxy resin; using appropriate models, the electromagnetic properties of the conducting phase have been obtained. Scaffolds with a thickness of 9 mm were able to absorb up to 80% of the incident radiation keeping the reflection as low as 20%.
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机译:微波吸收材料的设计要求同时具有低反射和高辐射吸收率。可以实现电磁波的低反射,从而感应出可将阻抗失配降至最低的多孔面。通过增加材料的电导率可以获得高吸收。我们报告了从石墨烯和碳纳米管的组合制备高度多孔的支架。利用能够稳定氧化石墨烯和碳纳米管的水分散体中的己烷液滴的氧化石墨烯的表面性质来控制双峰多孔结构。经过水热和两步冷冻干燥过程后,分别由于己烷液滴和冷冻干燥,获得了大(220微米)和中孔(10微米)结构。对于分别包含0%,10%,20%和40%碳纳米管的石墨烯支架,获得的直流电导率为8.2、14.7、33.2和60.7 S m(-1)。在渗透了环氧树脂的支架上进行了电磁表征。使用适当的模型,可以获得导电相的电磁特性。厚度为9毫米的支架能够吸收多达80%的入射辐射,从而使反射率低至20%。
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