【作者】 周建华；

【导师】 何建平；

【作者基本信息】 南京航空航天大学 ， 材料加工工程， 2010， 博士

【摘要】 本文综合运用嵌入气腔法和分块设计法,制备具有介孔结构的碳/金属（金属氧化物）复合材料,利用这种复合材料丰富的多孔结构和阻抗匹配能力有效衰减雷达波,同时通过成分调整,使这种复合材料在8～14μm波段具有较低的红外发射率,从而为制备轻质、高效的隐身材料提供理论和技术参考。主要内容有:运用分块设计法,制备介孔碳和铁氧体的纳米复合体,实现介观尺度的阻抗匹配。实验过程中采用两步溶剂热法制备葡萄糖基碳包覆铁氧体,经500℃热处理后获得介孔碳为壳、铁氧体为核的微粒,1000℃煅烧后为Fe/C核壳结构粒子。这种葡萄糖基碳包覆铁氧体粒子在8～14μm波段的红外发射率可以降低至0.5以下,且对0.5～18 GHz频段电磁波的吸收较强,有效吸收带宽超过4 GHz。1000℃热处理后,吸波剂的匹配厚度2～9 mm范围内最小反射率均低于-20 dB,其吸收峰主要集中在低频段。提出运用嵌入气腔设计的理念,尝试用三元共组装法制备碳与金属氧化物的复合材料。依据表面活性剂F127的模板导向作用,分别以柠檬酸铁、异丙醇铝、酞酸丁酯为金属源,制备C-Fe₂O₃、C-Al₂O₃和C-TiO₂复合材料。这种复合材料中金属氧化物与碳互为支撑,具有二维六方有序介孔结构。实验发现,加入金属氧化物后,复合材料的红外发射率保持在0.4～0.55之间,较纯介孔碳有明显降低。同时,该复合材料对电磁波的吸收峰明显宽化,有效吸收带宽可达6.7 GHz,最小反射率为-52.4 dB。在嵌入气腔设计理念的基础上,进一步发挥磁性金属具有较大饱和磁化强度的效能。首先采用溶剂蒸发诱导自组装方法获得含磁性金属的有序介孔C-SiO₂纳米复合材料,通过高温热处理在复合材料中实现α-Fe纳米晶原位生长。这种方法增强了复合材料的磁损耗,700℃煅烧后表现出多频段吸收特性,有效吸收带宽可达5.1 GHz。继续添加第二种金属（如Co、Ni、Cu等）,调节匹配厚度可使反射损耗频段涵盖2.8～18 GHz。同时,该复合材料的红外发射率可由纯C-SiO₂的0.677降低至0.498。另外,有序介孔碳中磁性金属的植入还能通过浸渍负载法实现。有序介孔碳粉体浸渍四羧基酞菁铁溶液负载后,经700℃煅烧,通过调节匹配厚度可使该复合材料的电磁波吸收峰覆盖3.1～18 GHz。阻抗匹配和电磁能量的快速损耗是有序介孔复合材料具有较好电磁波吸收性能的主要原因。介孔碳中引入磁性组分形成纳米复合材料,容易实现材料与自由空间的阻抗匹配。另外,复合材料具有丰富的孔道结构、高的比表面积和独特的界面效应,可以发挥磁性组分高损耗的优势,结合介孔碳的电导损耗和介电弛豫,电磁波经介孔结构定向传导后被耗散,得以充分吸收,并能获得较低的红外发射率,形成了符合需要的轻质、高效的隐身复合材料。更多还原

【Abstract】 This dissertation presents ordered mesoporous carbon/metal or metal oxide nanocomposites with the comprehensive use of inserting air cavity and sub-division methods. These nanocomposites can efficiently attenuate electromagnetic wave taking the advantages of robust channel structure and proper impedance matching. They also exhibit low infrared emissivities at 8¹4μm through the component adjustment, which would provide the theory and technology reference for the development of lightweight and highly efficient stealth materials. The main contents are as follows:On the basis of sub-division method, we prepare mesoporous carbon and ferrite nanocomposites to realize meso-scopic impedance matching. Glucose-based carbon coated ferrite was prepared under solvothermal conditions. After heat treatment at 500℃, the composites are composed of mesoporous carbon as shell and ferrite as core. They are tuned into Fe/C core-shell nanoparticles when heat treatment at 1000℃. After carbon coating, the infrared emissivity at 8¹4μm of the ferrite particles can be lowered to 0.5, and the absorption of electromagnetic wave at 0.5¹8 GHz is enhanced. The effective absorption bandwidth can exceed 4 GHz. At the elevated temperature of 1000℃, it presents the minimum reflectivity below -20 dB with the matching thickness of 2⁹ mm, with the absorption peaks focusing on the low frequency bands.We propose the idea of inserting air cavity and attempt to prepare carbon/metal oxide nanocomposites using triconstituent co-assembly method. On the basis of template direction of surfactant F127, C-Fe₂O₃, C-Al₂O₃, and C-TiO₂ nanocomposites were prepared using ferric citrate, aluminum isopropoxide, and titanium isobutoxide as metal precursors, respectively. The metal oxides sustain with carbon in the framework of these nanocomposites with a typical two-dimensional hexagonal mesoporous structure. The results show that the infrared emissivity can be controlled within 0.4⁰.55 after the introduction of metal oxide particles, which is much lower than that of pure mesoporous carbon. Additionally, the absorption peak is also widened. The effective absorption bandwidth can reach 6.7 GHz and the minimum reflectivity is as low as -52.4 dB.In order to further develop the efficiency of the large saturation magnetization of magnetic metal based on the idea of inserting air cavity, ordered mesoporous carbon-silica nanocomposites with magnetic metal constituents were prepared by a facile solvent-evaporation-induced self-assembly approach. Magneticα-Fe nanocrystallines are in situ grown in the nanocomposites through a high temperature heat treatment. This strategy would enhance the magnetic loss. CS-Fe-700 exhibits multi-band absorption characteristics, its effective absorption bandwidth is found to exceed 5.0 GHz. With the addition of the second metal such as Co, Ni, Cu, etc., the frequency of reflection loss could cover 2.8¹8 GHz by changing the matching thickness. In addition, the infrared emissivity could be reduced from 0.677 of pure C-SiO2 to 0.498.Furthermore, magnetic metal embedded into ordered mesoporous carbon can also be realized through impregnation-loading method. Ordered mesoporous carbon powders were used to impregnate tetracarboxy phthalocyanine iron solution for loading. After heat treatment of 700℃, the frequency of reflection loss could cover 3.1¹8 GHz by changing the matching thickness.Impedance matching and fast loss of electromagnetic energy are the main causes to the super microwave absorption property of ordered mesoporous nanocomposites. Ordered mesoporous carbon materials with the introduction of magnetic constituents are easy to realize the impedance matching between the materials and free space. Furthermore, the nanocomposites possess robust channel structure, high surface area, and unique interface effect. It could take the advantages of high loss with magnetic constituents as well as the conductance loss and dielectric relaxation with mesoporous carbon. Electromagnetic wave can be dissipated through the directional conduct of the mesoporus structure and the electromagnetic energy would be fully absorbed. It can also obtain the lower infrared emissivity, meeting the needs of lightweight and highly efficient stealth materials.更多还原