【作者】 张明辉；

【导师】 杜耘辰；

【作者基本信息】 哈尔滨工业大学 ， 化学， 2023， 硕士

【摘要】 随着电磁干扰和电磁辐射问题的日益突出,电磁波吸收材料（简称“吸波材料”）在民用和军事领域受到了广泛的关注。在众多的吸波材料当中,碳材料因来源丰富、化学性质稳定、介电性能可调,被认为是一种极具应用前景的吸波材料。作为一种特殊的碳材料,碳气凝胶具有交联的三维多孔结构,因而能够形成入射电磁波的多重反射,这有利于延长电磁波在吸波材料内部的传播距离,加剧电磁能量的耗散,从而增加材料对电磁波的吸收能力。但是,单纯的碳气凝胶仍然存在损耗机制单一和阻抗失配的问题,因此构建碳气凝胶基复合材料已成为相关领域的研究热点。Mo₂C纳米材料不仅具有优异的介电性能,而且具有较强的抗腐蚀能力,将其引入碳气凝胶有望提升复合材料的吸波性能和环境耐受能力,但是至今仍没有关于碳气凝胶与Mo₂C复合材料的研究报道。本课题采用两种不同的方法制备了碳化钼/碳气凝胶复合材料,并对其吸波性能进行了系统地研究。主要工作如下:以氧化石墨烯、钼酸铵、葡萄糖为原料,通过水热组装、冷冻干燥、高温热解制备了具有三维大孔结构的Mo₂C/GA复合材料。调控葡萄糖与钼酸铵的摩尔比,可以有效调节复合材料的组成,Mo₂C的含量最高可达56.5 wt%。分析测试结果表明,Mo₂C纳米粒子的引入会适当地降低复合材料的孔隙率和碳骨架的相对石墨化程度。相应地,复合材料的介电性能也随着Mo₂C含量的增加而逐渐减小。但是,复合材料的吸波性能却明显优于纯石墨烯气凝胶,Mo₂C含量为27.6、40.8和56.5 wt%时,三个样品最小反射损耗值分别为-21.5d B（18.0 GHz,1.3 mm）、-63.3 d B（7.4 GHz,3.3 mm）和-14.6 d B（17.1GHz,5.0 mm）。其中,样品Mo₂C/GA-1.0不仅给出了最强的反射损耗,其最大有效吸收带宽（反射损耗值<-10 d B的频率范围）在厚度为1.7 mm时,可以达到5.1 GHz。当吸收涂层厚度在1.5-5.0 mm之间时,其有效吸收带宽可覆盖3.8-18.0 GHz。Mo₂C/GA复合材料优异的吸波性能主要来自于碳气凝胶骨架上分布的Mo₂C改善了复合材料的阻抗匹配特性。通过CST模拟结果可知,Mo₂C/GA-1.0对雷达反射截面的缩减效果最好,表明其具有较好的雷达隐身特性。此外,Mo₂C纳米粒子还可以增强碳骨架表面的粗糙度,降低碳骨架的热传导性能,因此Mo₂C/GA-2.0在室温下的水接触角可达134.9°,在200℃加热板上加热30 min,其上表面温度约为65℃。为了进一步增强碳骨架与Mo₂C纳米粒子之间的相互作用,以硝酸锌、钼酸铵和聚乙烯吡咯烷酮（PVP）为原料,采用聚合物发泡合成了Mo₂C/CF复合材料。研究发现,利用该方法得到的复合材料中,Mo₂C纳米粒子的尺寸显著降低,仅为10 nm左右。通过电磁参数分析可知,随着Mo₂C纳米粒子含量的增多,Mo₂C/CF气凝胶表现出了更多的极化损耗过程。当钼酸铵与PVP的质量比为0.2时,Mo₂C/CF复合材料具有最佳的电磁波吸收性能,其最大有效吸收带宽（吸收厚度为2.3 mm时）可达6.7 GHz,最强反射损耗（在16.3GHz处）可达-72.2 d B。CST模拟结果也表明其对雷达反射截面的缩减效果最好,具有较好的雷达隐身特性。此外,Mo₂C纳米粒子尺寸的减小进一步增强了复合材料的绝热性能,在200℃加热板上加热30 min,其上表面温度约为57℃,但其疏水性能呈现了轻微的下降。更多还原

【Abstract】 With the increasing severity of electromagnetic interference and radiation issues,microwave absorbing materials（referred to as“MAMs”）have received extensive attention in civil and military fields.Among the se MAMs,carbon materials are considered to have great application potential due to their abundant sources,stable chemical properties,and adjustable dielectric performance.As a kind of carbon material,carbon aerogel has cross-linked three-dimensional porous structure,which can strengthen the multiple reflection of incident electromagnetic wave.It is conducive to extend the propagation distance of electromagnetic wave inside MAMs and increase the dissipation of electromagnetic energy,and thus enhancing the attenuation ability of MAMs.However,pure carbon aerogel still suffers from single loss mechanism and impedance mismatch.Therefore,constructing carbon aerogel-based composites has become a research hotspot in the related fields.The excellent dielectric properties and strong cor rosion resistance of Mo₂C nanoparticles render them as popular secondary components to combined with carbon aerogel to obtain high-efficiency MAMs.However,the preparation and research related to Mo₂C/carbon aerogel composites have been inaccessible in the field of microwave absorption to date.In this study,two preparation schemes are employed to synthesis Mo ₂C/carbon aerogel composites,and their absorbing properties are systematically studied.The two works are as followed:Mo₂C/GA composites with three-dimensional macroporous are prepared using graphene oxide,（NH₄）₂Mo O₄,and glucose as raw materials through hydrothermal assembly,freeze-drying,and high-temperature pyrolysis.The composition of Mo₂C/GA can be effectively controlled by adjusting the molar ratio of glucose to（NH₄）₂Mo O₄,where the highest Mo₂C content can reach 56.5wt%.The research results show that the introduction of Mo₂C nanoparticles slightly reduced the porosity of Mo₂C/GA and the graphitization degree of carbon skeleton,and correspondingly,the dielectric properties of Mo₂C/GA will gradually decrease with the increasing content of Mo₂C.However,Mo₂C/GA exhibits significantly better microwave absorption properties than pure graphene aerogel.The minimum reflection loss values of Mo₂C/GA-0.5,Mo₂C/GA-1.0 and Mo₂C/GA-2.0 are-21.5 d B（18.0 GHz,1.3 mm）,-63.3 d B（7.4 GHz,3.3 mm）,and-14.6 d B（17.1 GHz,5.0 mm）,respectively,whose Mo₂C contents are 27.6,40.8,and 56.5 wt%,respectively.Among them,Mo₂C/GA-1.0 has the maximum effective absorption bandwidth（reflection loss value<-10 d B frequency range）with 5.1 GHz at thickness of 1.7 mm.When change the thickness of MAMs from1.5 to 5.0 mm,its effective absorption bandwidth can cover 3.8-18.0 GHz.The excellent microwave absorbing properties of Mo₂C/GA composites mainly come from the good impedance matching,which is improved by distributing Mo₂C on the carbon aerogel framework.According to the CST simulation results,Mo₂C/GA-1.0 has the best reduction effect on radar reflection cross-section,indicating its good radar stealth characteristics.In addition,Mo₂C nanoparticles can enhance the roughness and reduce the thermal conductivity of the carbon skeleton surface.As results,the water contact angle of Mo₂C/GA-2.0 at room temperature can reach 134.9°and the upper surface temperature is about 65℃when heated on a 200℃heating plate for 30 minutes.In order to further enhance the interaction between the carbon skeleton and Mo₂C nanoparticles,Mo₂C/CF composites are synthesized by polymer foaming method where polyvinylpyrrolidone（PVP）,Zn（NO₃）₂·6H₂O and H₂₄Mo₇N₆O₂₄ are used as raw materials.It is found that the size of Mo₂C nanoparticles in Mo₂C/CF obtained by polymer foaming method is significantly reduced,only about 10 nm.According to their electromagnetic parameters,Mo₂C/CF aerogels show more polarization loss processes with the increasing content of Mo₂C nanoparticles.When the mass ratio of H₂₄Mo₇N₆O₂₄ to PVP is 0.2,Mo₂C/CF-0.2 has the best microwave absorption performance,with a maximum effective absorption bandwidth（d=2.3 mm）of 6.7 GHz and a minimum reflection loss of-72.2 d B（f=16.3 GHz）.The CST simulation results indicate that Mo₂C/CF-0.2 has the best reduction effect on radar reflection cross-section.In addition,the small size of Mo₂C nanoparticles further enhances the insulation performance of Mo₂C/CF.When heated on a 200℃heating plate for 30 minutes,the upper surface temperature is about 57℃,while its hydrophobicity slightly decreases.更多还原