多尺度蜂窝状TiO2材料结构设计与电磁波吸收效应研究

Recently, the microwave absorption properties of TiO2 materials have captured numerous interests. It is well accepted that the microwave absorption properties were closely related to their microstructure. Especially, the hot-topic is the complicated porous structure because they can tune electromagnetic impedance match. Moreover, they can also constrain the electromagnetic waves into porous structures to prolong the travel path, leading to multiple reflection or scattering of electromagnetic waves, as well as the lightweight feature. In this project, the honeycomb-like TiO2 materials were successfully prepared by using spherical polystyrene as template, and various multi-scale honeycomb TiO2 materials with different pore density, different pose size, gradient pore structure and different TiO2 crystals were fabricated by monitoring experimental parameters. We addressed the key problems regarding the uniform pore formation in high temperature, the design and control of multi-scale honeycomb structure, and the electromagnetic absorption characteristics of various structured TiO2 materials. We conducted in depth investigation on the various electromagnetic effects in various structured TiO2 materials, such as the size effect, the volume effect, the gradient distribution effect, and the structure effect, which are generated under the alternated electromagnetic fields. The influences of the various electromagnetic effects on the impedance match, interfacial dissipation, and local thermal transportation were also studied. The key factors of the design and control of honeycomb structured TiO2 materials and the formation mechanism of various electromagnetic effects were exploited. The influences of the intrinsic dielectric loss, dielectric loss, gradient compensation, interfacial polarization, multiple reflection and microwave coupling thermal on the absorption location and intensity were explored. Finally, we also proposed the electromagnetic wave absorption mechanisms of multi-scale honeycomb structured TiO2 materials, which is under the synergistic action of alternated electromagnetic fields.

TiO2材料的电磁波吸收性能是近年来国际重点关注的新领域。而吸波性能与结构有很大关系，尤其是多孔结构，既调控电磁阻抗匹配性，又延长电磁波传输路径，同时有质轻等特点，是当前电磁波吸收领域研究的热点。本项目以聚苯乙烯球作为模板，制备孔体积、孔径尺度、梯度孔结构和TiO2晶型可控的蜂窝状材料。重点解决高温下气孔形成与均一化机理、多尺度蜂窝结构设计与调控机理、不同结构TiO2材料的电磁波吸收特征等关键科学问题；研究不同结构TiO2蜂窝材料与电磁波相互作用过程中各类电磁效应如尺寸效应、体积效应、梯度效应、结构效应及其对阻抗匹配性、界面耗散、区域热扩散等影响规律；分析TiO2蜂窝状结构设计与调控原理、各类电磁效应产生机理与关键影响要素，揭示本征介电损耗、梯度补偿、界面极化、多级反射、电磁耦合热效应等对电磁波吸收频率和强度的影响；提出多尺度蜂窝结构TiO2材料在电磁波耦合下的多级杂化电磁波吸收机理。

模板法是近年来发展起来的合成新型纳米材料的方法，它具有结构易控制、孔径大小均匀等优点，已经成为制备多孔材料的通用方法。本项目以聚苯乙烯球（PS球）为模板，对具有梯度孔径大小的蜂窝状SnO2相关电磁波吸收性能进行研究；其次，对不同晶型蜂窝状TiO2基多孔材料进行制备与表征，研究晶型对复合材料性能的影响。此外，基于前期研究结果，还制备出了碗状和蜂窝状的TiO2/CNT复合材料，并对其进行表征和性能研究；最后，除了模板法制备多孔材料以外，本项目还对具有天然多孔结构的木材、秸秆此类生物质碳材料做了相关电磁性能研究。本项目通过以上工作的研究，揭示了材料的组分、晶型结构、导电/磁性填料含量、孔径结构密度等诸多因素对多孔材料电磁波吸收性能的影响规律；分析复合材料体系中电损耗与磁损耗的协同作用对材料吸波性能的影响；提出用模板法制备碗状、蜂窝状不同形貌的多孔材料，为此类材料的制备提供了通用的设计方法，为多孔材料的性能研究提供了一定的理论支撑。以PS球为模板制备的蜂窝状SnO2材料，当厚度为2mm时，在17.1GHz频率时，最佳反射损耗为-37.6 dB，且有效吸波带宽达到了5.6 GHz(12.4-18 GHz)。以PS球作为模板，采用混合过滤和分层真空辅助过滤的方法制备了碗状和蜂窝状的TiO2/CNT复合材料。碗状结构具有大的比表面积，增加了材料体内部的界面，有助于增强的多重反射和散射。蜂窝复合材料由于其低电导率和大孔隙体积分数，表现出优异的阻抗匹配性。当CNT含量为5 mg所制备的碗状TiO2/CNT复合材料在1.5 mm条件下的最小反射损耗为−38.6 dB，有效吸波带宽达4.2 GHz。当CNT 含量为10 mg所制备的蜂窝状TiO2/CNT复合材料在2.1 mm条件下的最小反射损耗值为−34.8 dB，吸波频宽达4.3 GHz。本项目的实施为多孔材料中“结构-性能”调控在吸波材料领域的设计与制备提供了理论基础与技术支持。