【作者】 谢玄；

【导师】 周晓东；

【作者基本信息】 华东理工大学 ， 化学工程， 2012， 博士

【摘要】 本文以雷达隐身材料为应用目的,制备了针对3.8～18GHz的有效吸收剂。空腔共振损耗、介电或电阻损耗、磁损耗是将电磁波吸收转化为其他形式能耗散的主要机制,现有电磁波吸收材料需要克服密度高、厚度大、吸收少和频带窄的缺点。本文拟通过制备多组分复合吸波剂,获得协同增强作用。制备了纳米级的磁性/导电核壳复合材料,并设计了以空心玻璃微珠为基础的多层核壳结构微米级吸波剂,研究了纳/微米材料的制备工艺与性能,主要包括以下内容：采用γ-氨丙基三乙氧基硅烷对空心玻璃微珠表面进行了疏水和氨基化改性,利用供电子氨基与吡咯环中亲电亚氨基的相互作用,在表面富集单体,确保了聚吡咯包覆层的致密性。讨论了溶液体系、引发剂、掺杂剂以及投料比等工艺参数的影响,综合考虑电导率、表面形貌、分散性和热稳定性等因素,选取了吡咯/水/乙醇/5-磺基水杨酸/氯化铁作为聚吡咯化学氧化聚合反应体系,5-磺基水杨酸(SSA)和三价铁离子特殊的络合配位特性能在一定程度上降低反应物与生成物浓度梯度,在反应初期有利于控制反应速率,提高均匀性和致密性。在吡咯/水/乙醇/5-磺基水杨酸/氯化高铁体系中得到的聚吡咯为球形颗粒,大小在200-300nm。少量乙醇有利于吡咯单体的分散,并能消耗部分自由基控制反应速率,改善聚吡咯链结构的均匀性,一定乙醇浓度下聚吡咯与溶液体系的浸润效果较好,有利于掺杂离子的进入提高导电性。SSA和Cl协同掺杂时体系的电导率最高,在前期和后期都存在掺杂竞争和掺杂离子的不稳定性,反应时间过长体系中的乙醇阻聚效应和溶液中氧攻击吡咯链会恶化电导率。产品在通常环境下保持很好的导电性和热稳定性,在水环境中掺杂离子有部分脱离而电导率保持性率为34%,在弱酸条件下具有较好的稳定性,在碱性条件下脱掺杂过程明显。以硫酸亚铁和氯化铁为前驱体,氨水为沉淀剂,油酸钠为表面活性剂,采用化学共沉淀法制备得到了反尖晶石结构的面心立方体型Fe3O4,纳米粒子的平均粒径在16.82nm。讨论了最佳反应条件,搅拌速率、反应温度、加料顺序在形成纳米级粒子过程中起到关键作用；稀土掺杂能诱导晶胞畸变,使晶格常数增大,提高磁性能,实验得到了优选掺杂量。Fe304饱和磁强53.38emu/g,Fe304@聚吡咯饱和磁强12.88emu/g,电导率10.73S/cm。聚吡咯包覆的Fe304复合材料不单防止了纳米磁性粒子的团聚,更提高了产品磁性与导电性的环境稳定性。制备了空心玻璃微珠@铁氧体@聚吡咯三层核壳结构微球。在薄壁的光滑空心玻璃微珠表面沉积了200-600nm粗糙的铁氧体层,包覆300～500nm厚的聚吡咯层后得到紧实致密的表面,表面聚吡咯微粒粒径在50～100nm。醋酸铵与三价铁离子形成[Fe3(μ3_O)(OAc)6(H2O)3]Cl型前驱体,易在空心微珠表面形成反应位点,有利于沉积,醋酸铵既是缓冲剂,又是前驱体的稳定剂,得到的产品包覆均匀性较好、负载量较高。多层复合微球的性能与磁性层的均匀性有很大关系,产品具有超顺磁特性,稀土掺杂使产物的衍射峰和晶间距发生变化,产物饱和磁强为20.61emu/g,电导率16.5S/cm。比较了纳米和微米级吸波剂在3.8～18GHz内的电磁波衰减效果。磁性组分增加使吸收峰红移,导电聚吡咯增加使吸收峰蓝移,一定组分配比的空心微珠@磁性铁氧体@聚吡咯材料能够发生协同作用。稀土Er在0.5%掺杂量下就能增加频带宽度降低反射率,<-10dB区域频带宽度达到了8.17GHz,最大衰减值达到了-27.15dB。稀土掺杂增大了自然共振损耗、极化弛豫损耗和畴壁共振的损耗吸收,聚吡咯凭借介质的电子极化和界面极化衰减和吸收电磁波,合理的组分配比对拓宽频带和增大衰减率有利。7.5wt%添加量厚度为2.5mm的环氧树脂基空心玻璃微珠@Fe304(Er0.5%)@聚吡咯<-5dB的频带宽度达到了8.50GHz,<-10dB的频带宽度达到了7.44GHz,最大衰减值为-28.27dB。更多还原

【Abstract】 The specific aim is to prepare effective absorbing agent for the application in radar absorption used in 3.8-18GHz band. Cavity resonance loss, dielectric or resistance loss, and magnetic loss are the main pathway to convert electromagnetic wave into other energy forms for dissipation. Existent absorbing materials still have disadvantages such as high density, large thickness, low absorption and narrow bandwidth. Therefore in this work, nano-sized core-shell composites with magnetic and conducting component, as well as multi-layer micro-sized spheres basis on hollow glass spheres, were designed and successfully prepared. The synthetic process and properties of both nano and micro spheres were studied and electromagnetic wave absorbing effects were compared. The main contents are listed as follows:y-aminopropyltriethoxysilane was used for the hydrophobic modification and amino-functionalization on the hollow glass sphere(HGS) surface, the strong interaction between electrondonating amino-group and electrophilic nitrogen atom in pyrrole chain led to gathering of monomer and well encapsulation of polypyrrole(PPy) layer. Parameters such as solution, initiator, dopant and raw ratio were discussed, comprehensive concerning conductivity, morphology, dispersibility and stablility, H2O/C2H5OH/pyrrole/5-sulfosalicylic acid(SSA)/FeCl3 was selected as the in situ chemical oxidative polymerization system. The specific SSA-FeCl3 chelation-initiate-doping took effect in the beginning of the reaction to decrease the concentration gradient, so that the reaction speed could be controlled and the uniformity and compactness were increased.Polymerization in H2O/C2H5OH/pyrrole/SSA/FeCl3 system was studied where the obtained polypyrrole spheres with particle size between 200-300nm. Small amount of ethanol conduced good conductivity for good dispersibility of monomer, control of speed by consumption free radical, meanwhile good wettability between polypyrrole and doping solution. The reaction system was insensitive to temperature while raw ratio could be optimized. Good properties were achieved when SSA and Cl ions conducted cooperative doping while other periods competitive doping and unstable doping led to bad performance, long reaction time would bring deterioration of polymer chain by the inhibition of C2H5OH and attack from oxygen in solution. Products kept good conductivity and thermostability under usual conditions, had a conservation rate of 34% immersing in water, had good stability in acid medium while quickly undoped in alkaline medium.Chemical coprecipitation process was conducted using ferric chloride and ferrous sulfate as precursor, ammonia as precipitator, sodium oleate as surfactant. The obtained face centered cubic type inverse spinel Fe3O4 nano particles had average diameter of 16.82nm. The optimum conditions were discussed, stirring speed, temperature and adding sequence played critical roles during the process. Rare earth could lead to lattice distortion, increase lattice constant and achieve good magnetic properties and optimum doping amount was found. Fe3O4 had a saturation magnetization of 53.38emu/g and Fe3O4@PPy of 12.88emu/g with a conductivity of 10.73S/cm. The encapsulation of polypyrrole not only prevented the aggregation but also increased the stability.Multilayer core-shell spheres were synthesized with thin smooth hollow glass inner layer, 200-600nm rough magnetic middle layer and 300-500nm compact conducting outer layer with 50-100 polypyrrole grains on surface. Ammonium acetate and ferric iron generated [Fe3(μ3_O)(OAc) (H2O)]C1 and provide reaction site for the deposition, ammonium acetate was the buffer agent for the system and also stabilizer for precursor to obtain uniform and high mass loading products. The uniformity of magnetic layer had large influence on the properties, superparamagnetic products were obtained and the doping of rare earth changed the diffraction peak and lattice distance. The HGS@Fe3O4@PPy had a saturation magnetization of 20.61emu/g and conductivity of 16.5S/cm.The reflection loss of electromagnetic wave between 3.8-18GHz frequency were detected, varied nano-sized and micro-sized absorbing agent were compared. The increase of magnetic component would bring red shift while conducting component lead to blue shift, certain ratio of hollow glass sphere, Fe3O4 and polypyrrole could bring synergetic effects. Erbium with a doping addition of 0.5wt had increase absorption till-27.15dB with a bandwidth of 8.17GHz under-10dB. Rare earth doping increased natural resonance loss, polarization relaxation loss, domain wall resonance loss while polypyrrole added electronic polarization and interfacial polarization loss, the rational combination could enhance absorption and broaden bandwidth. HGS@Fe3O4(Er0.5%)@PPy in epoxy resin with an addition of 7.5wt% and thickness of 2.5mm, had bandwidth of 8.50GHz under-5dB and 7.44GHz under-10dB, the largest reflection loss reached-28.78dB.更多还原