【作者】 赵文俞；

【导师】 张清杰； 官建国；

【作者基本信息】 武汉理工大学 ， 材料学， 2004， 博士

【摘要】 吸波材料是一种能够衰减电磁波能量的功能材料，广泛用于军事、微电子等领域。M型铁氧体和羰基铁是两种研究程度最高、性能优异、应用广泛的吸波剂，但均存在无法克服的局限性，均不能多频谱、宽频带吸收电磁波。目前，球磨处理对微米级M型铁氧体的结构和性能影响、化学共沉淀法合成亚微米级M型铁氧体的共沉淀机理及其影响因素、钡过量M型铁氧体的结构和性能、稳定结构单相纳米级M型铁氧体的合成条件、晶粒尺寸效应对M型铁氧体吸波性能的影响是M型铁氧体尚需深入研究的基础性问题，羰基铁／M型铁氧体复合体系中电、磁相互作用机制及其对吸波性能的影响并不清楚且尚无报道，羰基铁易氧化而影响吸波性能仍是有待解决的应用问题。 本文的研究内容包括两个部分：（1） 微米、亚微米和纳米级单相BaCoTiFe₁₀O₁₉（即“多尺度M型铁氧体”）的合成、表征和性能研究，（2） SiO₂／M型铁氧体纳米壳铁核复合粒子的合成、表征和性能研究。前者系统研究了M型铁氧体目前尚需深入研究的基础性问题，同时探索在羰基铁和SiO₂纳米壳铁核复合粒子表面建造M型铁氧体纳米壳的工艺条件；后者首次研究了羰基铁／M型铁氧体复合体系中电、磁相互作用规律，并为提高羰基铁的抗氧化能力提供了新的方法。得到的主要结论如下： 一、多尺度M型铁氧体的合成、表征和性能研究 1．首次系统地研究了Fe³⁺、Ti⁴⁺、Co²⁺和Ba²⁺离子的共沉淀机理，发现化学共沉淀法制备BaCoTiFe₁₀O₁₉前驱体的共沉淀反应中同时存在阳离子的协同共沉淀效应和阴离子（或络合离子）的配位效应。这一发现对研究其它多离子的共沉淀条件具有重要的指导意义。 2．采用化学共沉淀法首次在900℃煅烧2 h条件下合成出了一系列单相钡过量非化学计量M型铁氧体Ba_1+xCoTiFe₁₀O_19+x（x=0.00，0.05，0.10，0.15，0.20），发现x=0.05时σ_s几乎不变而σ_r，和H_c出现极大值，x=0.10时以过量钡离子为中心的“带电畴结构”极化共振可在12.48和15.28 GHz附近产生共振型介电损耗。这些结果对在GHz频段开发具有多频带吸收电磁波功能的吸波材料具有重要的意义。 3．采用陶瓷法、化学共沉淀法和溶胶-凝胶工艺分别合成出了微米、亚微米和纳米级单相BaCoTiFe₁₀O₁₉。2-18GHz频段的介电谱表明：BaCoTiFe₁₀O₁₉在2-8GHz频段的内储藏电能与晶粒尺度成反比关系，纳米级BaCoTiFe₁₀O₁₉在武权理工大学博士论文 15只GF比附近出现共振型极化峰，并认为该极化峰和微米级BaCO石Fe:。O，9 球磨48h后在1 6.24 GHz附近的共振型极化峰都是BaCoTIFeloo:，纳米粒子 极化共振形成的.与微米级BacOTIFel0O19相比，亚微米级和纳米级 BaCoTIF。:。019在4-6 GHz附近的自然共振损耗峰几乎消失，在2一12 GHz频 段的磁损耗稳定;在12一18GHz频段的吸波性能受纳米粒子极化共振影响。4:优化了纳米级Bac。五Fel0O:9的溶胶一凝胶合成工艺，并在900℃缎烧Zh的条 件下合成出了结构稳定、粒径为5压65nm的单相BaC。五Fe:。ol，.工艺研究 表明，采用消除cl.和Na+离子的共沉淀预处理工艺可大大提高BaConFe:。ol， 柠株酸盐溶胶的稳定性，600℃下形成的纳米级M型铁氧体实际是多种原子 构成的具有一定内在联系的亚稳原子团簇，700℃下可形成粒径为3小35 nm 的单相BaCo五Fe一0019。二、5102月吐型铁叙体纳米壳铁核复合粒子的制备、表征和性能研究1.成功制备出了510:纳米壳和5102刀以型铁氛体纳米壳两种铁核复合粒子，并 首次采用XPS技术研究了5102纳米壳和M型铁氛体纳米壳的电子结构。5102 纳米粒子的si和0元素化学状态的定t分析表明，与Fe键合的盆为Q3硅 签团中的叙，叙与Fe键合后会导致电子结合能降低;BaCoTIFelool，纳米粒 子的Fe、Ti和。元素化学状态的定t分析表明，co2+、Ti’+离子取代了 BaCOT扭el.ol，中自旋向上的12k磁晶位和自旋向下的4fl与4几磁晶位上的 F产离子，且12k磁晶位上的F产离子被取代t最大.这些结果坟补了510: 和BaCOT扭eloo:，纳米粒子电子结构方面的研究空白.2.5102纳米壳铁核复合粒子的静磁特性和2一18 GHz频段的介电、磁谱表明，随 着5102纳米壳厚度增大，氏降低，价、Hc和凡均在△R=8 nm时出现极大值; si仇纳米壳的隔离作用不仅导致si仇纳米壳铁核复合粒子之间的磁相互作用 减弱，而且使复合粒子之间产生类似于超交换作用的磁偶合共振效应;在8.72 和10.72 GHz附近的弛豫型极化峰与拨基铁在6 GHz附近的弛豫型极化峰均 是固有电偶极子的取向极化形成的，在巧.04和14.48 GHz附近的弛豫型极 化峰与拨基铁在15.68 GHz附近的弛豫型极化峰均是界面极化形成的.3.5102舰型铁氧体纳米壳铁核复合粒子的静磁特性和2一18 GHz频段的介电、 磁谱表明，随着M型铁氧体纳米壳厚度的增大，几减小，ar和Hc呈反“S” 型变化趋势，由此推断拨基铁微米核与M型铁氧体纳米壳之间存在超交换作 用:产在13 GHz附近的谐振峰与M型铁氧体Bac。五Fe:。O:9的自然共振无关， 可能是拨基铁微米核和M型铁氧体纳米壳之间的超交换作用形成的。关锐词:多尺度M型铁氧体，共沉淀机理?更多还原

【Abstract】 Electromagnetic-wave absorbing materials. are functional materials that may attenuate electromagnetic-wave energy, have been widely used in military and micro-electronic industries. M-type hexaferrite and carbonyl iron are two kinds of electromagnetic-wave absorbers with excellent property, which have been extensively studied and widely applied. However, they both have some insuperable disadvantages and cannot intensively absorb multi-frequency electromagnetic waves in a broad frequency band. There are some basic issues for M-type hexaferrite to need to study systematically such as effects of ball-milling on the structure and properties of micro-sized M-type fexaferrite, precipitation mechanism and its affecting factors during synthesizing submicro-sized M-type hexaferrite by chemical coprecipitation method, structure and properties of non-chiometric M-type hexaferrite with barium surplus, synthesis condition of single-phase nano-sized M-type hexaferrite with stable structure, and effects of crystal grain size on electromagnetic-wave absorbing property of M-type hexaferrite. In addition, it is also an unclear and unreported issue that electric and magnetic interaction mechanisms take place in the composite of M-type hexaferrite and carbonyl iron and how they affect electromagnetic-wave absorbing property of the composite. At the same time, how to improve the oxidation resistance of carbonyl iron is still not resolved.The thesis has investigated above-mentioned basic issues by two special studies: (1) Synthesis, characterization and properties of micro-, submicro- and nano-sized single-phase BaCoTiFe10O19 (namely multi-scale M-type hexaferrite), (2) Synthesis, characterization and properties of iron-SiO2/M-type hexaferrite core-nanoshell composite particles. The first one has mainly discussed some basic issues relative to M-type hexaferrite microwave absorber, and searched for process conditions of fabricating M-type hexaferrite nanoshell on the surface of carbonyl iron and iron-SiO2 core-nanoshell composite particles. The second one has for the first time studied the electric-magnetic interaction mechanism in the composite of carbonyl iron and M-type hexaferrite. The main results from these studies are summarized as following:1. Synthesis, characterization and properties of multi-scale M-type hexaferrite (1) The synergetic coprecipation effect of cations and coordination effect ofanions or complex ions, occurring during the coprecipitation reaction of preparing BaCoTiFe10O19 precursor, was for the first time discovered by systemically investigating the coprecipitation mechanism of Fe3+, Ti4+, Co2+ and Ba2+ cations. The conclusion has important guiding significance in studying coprecipitation condition of other multi-cations system.(2) A series of single-phase non-chiometric M-type hexaferrite with barium surplus Ba1+xCoTiFe10O19+x(x=0.00, 0.05, 0.10, 0.15, 0.20) have been for the first time successfully synthesized at 900℃ heating for 2 h by chemical coprecipitation method. It was discovered that specific saturation magnetization value (σs) of Ba1+xCoTiFe10O19+x are almost no change and remnant magnetization (σr) and coercivity (Hc) reach maxima when x=0.05, and that the electric domain polarization around excess barium may result in resonance dielectric loss at about 12.48 and 15.28 GHz. These results have important significance in manufacturing new electromagnetic-wave absorbing materials with multi-frequency bands in the range GHz.(3) Micro-, submicro-, and nano-sized single-phase BaCoTiFe10O19 were synthesized by conventional ceramic method, chemical coprecipiation method, and sol-gel process, respectively. The dielectric properties in the range 2-18 GHz show that the intrinsic electric energy of BaCoTiFe10O19 is inversely proportional to grain diameter in the range 2-8 GHz, and that a polarization resonation peak of BaCoTiFe10O19 nanoparitcles, whose formation mechanism is the same as that of micro-sized BaCoTiFe10O19 at about 16.24 GHz after having been ball-milled for 48 hours, occurs at ab更多还原