TiC和SiC纳米材料的制备及微波吸收性能研究

发布时间：2018-02-22 12:04

本文关键词： TiC纳米材料 SiC/SiO2复合材料介电性能微波吸收损耗机制　出处：《西北工业大学》2015年博士论文　论文类型：学位论文

【摘要】：随着电子设备和无线通讯的快速发展，电磁干扰和辐射污染问题已经严重影响了人们生活和国家安全，尤其是雷达波隐身技术已经成为军事战略的制高点之一。目前，电磁波吸收材料的研究依然立足于传统的吸波材料，对于新型吸波材料的研究开发明显不足，特别是高温和高频段的微波吸收材料。因此，研究新型微波材料不仅对丰富和扩大吸收材料的种类和应用领域具有现实意义，还具有较高的理论价值。基于多重微波损耗机制，纳米吸波材料显示出优良的微波吸收性能。作为典型的无氧陶瓷，TiC和SiC具有高熔点、低密度、良好导电和导热性、优异的环境稳定性等特性，结合这些优异的特性和纳米结构使得TiC和SiC纳米材料成为潜在的微波吸收材料。本论文以纳米材料的制备和应用为背景，采用氯气辅助碳热还原反应法、热化学反应法和纳米铸造法，分别系统地研究了TiC纳米线、TiC纳米颗粒/Ti和有序内部填充结构SiC/SiO2纳米材料的可控制备及其微观结构，并分析了它们在X波段(8.2~12.4GHz)的室温和高温微波吸收性能和相应的损耗机理。主要研究内容与结果如下： (1)研究了以氯气辅助碳热还原法制备TiC纳米线。研究表明，以Ni(NO3)2·6H2O为催化剂、NaCl为辅助剂、蔗糖为碳源和TiO2纳米粉为Ti源，成功制备了面心立方结构的单晶TiC纳米线，其长径比和比表面积分别为80~100和186.7m2/g。TiC纳米线的初始生长机理为VSL机理，并给出了可能的化学反应方程式。 (2)以丙酮为碳源，研究了在金属Ti颗粒表面原位生长TiC纳米颗粒。结果表明，当载气Ar流量为50ml/min，通过鼓泡方式携带0oC的丙酮进入反应腔体，反应温度和反应时间分别为800°C和2.0h时，大小约为300nm的TiC纳米颗粒均匀且稠密地分布在金属Ti颗粒表面，其晶体结构为多晶面心立方结构，晶粒大小约为8.0nm。热力学计算表明，丙酮在高温下热解产生的小分子气体CHx优先与Ti发生热化学反应得到TiC。 (3)以聚碳硅烷(PCS)和有序介孔氧化硅SBA-15为前驱体和硬模板，采用纳米铸造和冷压成型工艺制备有序内部填充结构SiC/SiO2块体陶瓷复合材料。结果表明，PCS转化生成的SiC纳米颗粒几乎完全填满了有序介孔SBA-15的纳米孔道。复合材料的结晶度随着反应温度的升高而增大，其晶型为β-SiC。在反应温度不高于1400oC时，SiC/SiO2复合材料不仅能够保持有序内部填充结构，而且具有一定的机械强度。 (4)详细表征了TiC纳米线、TiC纳米颗粒/Ti和有序填充结构SiC作为吸波剂与石蜡或SiO2的复合材料在X波段的常温和高温微波吸收性能。结果表明，在常温环境中，掺比量为30wt%的TiC纳米线与石蜡混合材料具有最强的吸收强度：厚度为1.7mm时，其最小反射损耗约为-51.0dB；而1400oC制备的SiC/SiO2复合材料显示出最大的吸收宽度：厚度为3.0mm时，有效吸收宽度(RL-10dB)覆盖整个X波段。在高温环境中，掺比量为7.5wt%的TiC纳米线/SiO2复合材料在300oC具有最强的吸收强度：厚度为3.0mm时，最小反射损耗数值为-61.0dB；而1300oC制备的SiC/SiO2复合材料具有优异的吸收宽度，在25~500oC范围内始终存在一个匹配的厚度，使其有效吸收宽度(RL-10dB)为整个X波段。 (5)研究了上述三种材料的微波损耗机理，结合四分之一波长定律和阻抗匹配定律分析了单层吸收体的微波吸收性能。结果表明，三种材料优异的吸收性能主要源于多重损耗机制：长径比较大的TiC纳米线分散在透波基体中容易形成复杂网状电子导电结构，进而导致较大的导电损耗；TiC纳米颗粒/Ti复合材料具有异质材料微结构，其电磁损耗以界面损耗和介电弛豫损耗为主；有序内部填充结构SiC/SiO2复合材料使电磁波经过有序结构多重反射和网状导电结构而损耗。单层吸收材料具有优异的微波吸收性能，主要归因于其几何厚度遵循干涉相消原理和电磁参数满足阻抗匹配，，这为设计单层吸收体提供了依据。
[Abstract]:With the rapid development of electronic devices and wireless communication, electromagnetic interference and radiation pollution has seriously affected people's life and national security, especially the radar stealth technology has become one of the commanding heights of military strategy. At present, the research of electromagnetic wave absorbing materials is still based on the traditional absorbing materials, absorbing materials research for new is obviously insufficient, especially in high temperature and high frequency microwave absorbing materials. Therefore, the research of new microwave materials not only to enrich and expand the absorption type and application field of materials is of practical significance, theoretical value is higher.
Multiple microwave loss mechanism based on nano absorbing materials exhibit excellent microwave absorption properties. As a typical anaerobic ceramic, TiC and SiC have high melting point, low density, good electrical and thermal conductivity, excellent environmental stability and other characteristics, combined with the excellent properties and nano structure makes the TiC and SiC nano materials become absorbed the potential of microwave materials. In this paper, the preparation of nano materials and the application background of reduction method using chlorine assisted carbothermal thermochemical reaction method and nano casting method were systematically studied TiC nanowires, controllable preparation and microstructure of TiC /Ti nanoparticles and ordered nano materials filled with structure of SiC/SiO2. And analyzes them in the X band (8.2~12.4GHz) performance and the corresponding loss mechanism of microwave absorption at room temperature and high temperature. The main research contents and results are as follows:
(1) study on the preparation of TiC nanowires by chlorine assisted carbothermal reduction. The results show that the Ni (NO3) 2 - 6H2O as catalyst, NaCl as auxiliary agent, sucrose as carbon source and TiO2 nanoparticles as Ti source, single crystalline TiC nanowires with fcc structure were successfully prepared, its long and the initial diameter ratio were 80~100 and 186.7m2/g.TiC nanowires than the surface area of the growth mechanism of VSL mechanism, and gives the possible chemical reaction equation.
(2) using acetone as carbon source on the growth of TiC nanoparticles on the surfaces of metal Ti particles. The results show that when the flow rate of the carrier gas Ar 50ml/min, carrying 0oC acetone by bubbling way into the reaction chamber, reaction temperature and reaction time were 800 ~ C and 2.0h, the size is about on the surface Ti TiC metal particle distribution of 300nm particles is uniform and dense, the crystal structure of polycrystalline face centered cubic structure, the grain size is about 8.0nm. thermodynamic calculation indicates that the gas molecules CHx acetone produced by high temperature pyrolysis of the priority and the chemical reactions taking place in TiC. Ti
(3) using polycarbosilane (PCS) and ordered mesoporous silica SBA-15 as precursor and hard template, using nano casting and cold pressing process for preparing ordered internal packing structure of SiC/SiO2 bulk ceramic composite materials. The results showed that SiC nanoparticles PCS transformed almost completely filled with ordered mesoporous SBA-15 the nano pores. The degree of crystallinity of the composites increases with the increase of the reaction temperature, the crystal type of beta -SiC. is higher than that of 1400oC in the reaction temperature, SiC/SiO2 composite materials can not only maintain an orderly internal filling structure, but also has a certain mechanical strength.
(4) the detailed characterization of TiC nanowires, TiC nanoparticles and /Ti ordered structure SiC as absorbing composite filling agent and paraffin or SiO2 wave absorption properties in the X band microwave at room temperature and high temperature. The results showed that at room temperature, the proportion of TiC doped 30wt% nanowires with paraffin mixed material with absorption intensity the strongest: the thickness is 1.7mm, the minimum reflection loss is about -51.0dB; and the SiC/SiO2 composite materials prepared by 1400oC showed the absorption maximum width: thickness of 3.0mm, the effective width of absorption (RL-10dB) covering the entire X band. In a high temperature environment, mixed proportion of TiC nanowires of 7.5wt% composites with /SiO2 the strongest absorption intensity in 300oC: the thickness of 3.0mm, numerical minimum reflection loss is -61.0dB; and the SiC/SiO2 composite materials prepared by 1300oC have excellent absorption width in the range of 25~500oC, there is always a match The thickness of its effective absorption width (RL-10dB) is the whole X band.
(5) to study the microwave loss mechanism of these three kinds of materials, combined with 1/4 wavelength law and impedance matching law of microwave absorbing properties of single-layer absorber. The results showed that three kinds of materials with excellent absorption performance is mainly due to the multiple loss mechanism: TiC nanowires with high aspect ratio dispersed in the matrix to form transparent conductive structure of complex network electronics, which led to the loss of conductivity; TiC nano particles /Ti composite materials with microstructure of heterogeneous materials, the electromagnetic loss to interface loss and dielectric relaxation loss; ordered structure of SiC/SiO2 composite filled with electromagnetic wave through the ordered structure of multiple reflection and mesh structure and conductive loss. Single layer absorbing materials with excellent microwave absorption properties, mainly due to the geometric thickness following destructive interference and electromagnetic parameters meet the principle of impedance matching for the design The monolayer absorbers provide the basis.

【学位授予单位】：西北工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB383.1;TB34

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