【作者】 徐国亮；

【导师】 朱正和；

【作者基本信息】 四川大学 ， 原子与分子物理， 2005， 博士

【摘要】 碳团簇型微波吸收功能材料的研究,在国内外是一个新方向,这是从理论上根据对分子振转频率与结构之间的关系,通过计算而设计与研制的一种新的微波吸收材料。本文通过微波吸收涂层的结构优化设计,制备得到了密度较低的双层结构及三层结构的碳团簇型微波吸收涂层体系,并讨论了微波吸收涂层中碳团簇材料的碳化温度、含量、混合比例、组合顺序方式等因素对其吸波性能的影响。研究了制备碳团簇型吸波材料原材料的结构特性、电荷分布、电偶极矩、能级分布及其热力学特性。同时研究在外场作用下,甲烷分子、碳分子线的结构、电荷分布、极化率及激发态等特性。 研究结果表明:不同碳化温度处理后得到的碳团簇材料,按不同方式组合成的双层微波吸收涂层体系,其吸波性能差异很大。同时双层结构微波吸收涂层存在明显的方向性,如1000℃碳化的10″材料与700℃碳化的7″材料组合的吸波性能远好于7″材料与10″材料组合的结果。在8.2～12.4GHz频率范围内,其对微波的最小反射率为-31 dB,其中反射率小于-10dB的有效带宽占总频率范围近60%,且质量较轻,密度仅为1.16g/cm~3。改变吸收剂在变换层和吸收层的含量进行研究,低含量的变换层可与不同含量的吸收层组合可得较好的吸收性能,在8.2～12.4GHz频率范围内,对微波的最小反射率可达-33dB,其中有效带宽达78%。理更多还原

【Abstract】 As a new research direction, the study of carbon cluster-like microwave absorbing functional material is designed and developed based on the relationship between structure and the vibration-rotation motion levels of the planar cyclocarbon clusters. The bi-layer and tri-layer structural carbon cluster-like microwave absorbing coating systems with low density were designed and prepared by the optimized structural design for microwave absorbing coating. The effects of carbonization temperature, amount, mixture proportionment and the layer’s combination way on the absorbing properties of carbon cluster-like microwave absorbing coating are discussed in this paper. The structural properties, charge distribution, dipole moment, energy levels and the thermodynamic properties of the polymer raw material for preparing carbon cluster-like microwave absorbing material has been investigated. At the same time, the equilibrium geometry, charge distribution, polarizability and the excited states properties of methane and carbon molecular chains are studied under different external electric fields.There are six chapters in this paper. Chapter one narrates the development on study of the microwave absorbing materials and the significance of this work. Chapter two introduces the interaction of microwave with absorbing material and the physical meaning of electric and magnetic parameters for absorbing materials. The third chapter expatiates upon the processing craft and the testing theory of the microwave absorbing material. The effects of carbonization temperature, amount, mixture proportionment and the layer’s combination way on the absorbing properties of bi-layer structural carbon cluster-like microwave absorbing coating are discussed, and the properties of tri-layer structural carbon cluster-like microwave absorbing coating in the chapter. The geometric properties of the planar cyclocarbon clusters areemphasis in chapter four. At the same time, based on the theory, the absorbing properties of carbon cluster-like material on low frequency microwave has been studied The structural properties of raw material processing for carbon cluster-like material have been investigated systematically in chapter five. The equilibrium geometry, charge distribution, polarizability and the excited states properties of methane and carbon molecular chains are studied under different external electric fields in the sixth chapter, which can help to understand further the loss mechanism of microwave in carbon cluster-like absorbing material.The experiment results indicate that in order to obtain good absorbing property, the bi-layer structural carbon cluster-like microwave absorbing coating must be combined according to the way that the materials heat treated by 1000℃ as the transforming layer and the materials heat treated by 700℃ as the absorbing layer. The absorbing coating with density of 1.16g/cm3 and thickness of 2mm possesses good microwave absorbing property in the frequency range of 8.2-12.4 GHz, its minimum reflectivity is -31dB, and the frequency width with reflectivity under -10dB reaches 60% of the whole frequency range. The effect of the amount of carbon cluster-like absorber on the microwave absorbing coating has been investigated. The microwave absorbing coating achieves maximum absorbing value of -33 dB, and the frequency width with reflectivity under -10dB reaches 78% of the whole frequency range of 8.2-12.4 GHz. Compared the single component, the composite materials mixed by the materials heat treated by 1000℃ and 700℃ improve the absorbing properties, its minimum value of-10dB over the whole frequency ranges of 8.2-12.4 GHz. As for other type absorbing coating composed by mixed materials achieve the maximum absorbing value of -52dB. Moreover, it can be found that the absorbing coating composed by mixed materials has good absorbing property in the frequency ranges of 12.4-18GHz, which will be a new research goal. At the same time, the tri-layer structural carbon cluster-like microwave absorbing coating with gross thickness of 2.1mm has good microwave absorbing property over broadband, its minimum reflectivity is -29dB, and the frequency width with reflectivity under -10dB is over the whole frequency ranges of 8.2~12.4GHz.The present work discovers that the bigger the area of cyclocarbon, the lower the energy of the structure, and rotational constants B and energy level interval will minish continuously, which make cyclocarbon be propitious to absorb microwave of low frequency bands.Moreover, depended on the theoretic instruction, the influences of different carbonized temperatures, thickness and material Ⅱ on the transmissivity are reviewed. The carbon cluster-like absorbing materials AII with thickness of 1mm, obtained the minimum transmissivity value of -35dB, and the frequency width with transmissivity under -10dB was over 92% of the whole frequency ranges 2.0~5.0GHz. The equilibrium geometries of the polyacrylonitrile (PAN) chain has been theoretically studied using the Hartree-Fock method at the STO-3G levels. The present work has obtained the result that the average distance of the C atom couple in main chain is 0.1556nm; the average distance of the C atom couple in branch chain is 0.1496nm; the average distance of C atom bonding with N atom is 0.1154nm. The vibration models have been analyzed to clarify the reaction sequence of dehydrogenation and cyclization during pre-oxidation and carbonization of the polyacrylonitrile. By employing density functional theory (DFT) and single substitute configuration interaction (CIS) approach with basis sets 6-311++G**, excited states of methane under external electric field are investigated. It is shown that the transition between ground state x 1A1, and the high-excitedstate of methane is prone to come into being. The electronic structure properties of Q, (n=3~10) molecular wires are investigated systemically using the B3LYP method. Because of the effect of delocalization, the ground states of all Cn are singlet as n are even, whereas, the triplet are the stable ground states of Cn as n are odd. The relationships between HOMO, LUMO and the carbon atom number n of molecular wires are determined, i.e., EHn-1< EHn< EH n+1, EL n-1> ELn> EL n+1. Therefore, the fermi levels of carbon molecular wires display their own brand of odd-even properties. Excited states, oscillator strength and dipole moment of carbon molecular wire under external electric field were studied using time dependent density functional theory (TDDFr) with the basis set 6-31 l++g**. It is shown that the external electric field along the X, Y and Z axis affect differently on the exited states of carbon molecular wire. The electric field along the carbon molecular wire axis (Z axis) influences the dipole moment much stronger than that of the electric field along the X and Y axis.更多还原