【作者】 陈映杉；

【导师】 冯旺军；

【作者基本信息】 兰州理工大学 ， 凝聚态物理， 2011， 硕士

【摘要】 具有吸收电磁波特性的材料,在近几年,已成为材料研究和应用的热点。对于理想的吸波材料,对材料特性要求是具有强吸收、吸收频段宽、材料厚度薄、重量轻等特点。但是,到目前为止,还没有找到一种吸波材料能够满足这些特性要求。因此,对现有吸波材料进行恰当设计和改性就成了吸波材料研究的重点。六角晶M型锶铁氧体吸波材料,因其自然共振频率较高,在高频下不容易产生趋肤电流,介电常数也比较小,可与其它吸波材料混合使用来对吸波涂层的电磁参数进行适当调节等优点而成为极其重要的一类电磁波吸波剂。另一方面,它的不足之处是吸波性能对制备工艺的敏感性很强。要进一步显著提高单一铁氧体材料的磁导率μr很困难。而尖晶石型铁氧体吸波材料具有良好的温度稳定性,具有最高的饱和磁化强度ΜS,其微波磁导率较大,优点非常明显。但是尖晶石型铁氧体吸波材料在微波波段频率下,因为受“趋肤效应”的限制,粒度不能太大,而且粒度要分布均匀,其体积分数也不能过大。由此可知,磁铅石型铁氧体吸波材料与尖晶石型铁氧体吸波材料相比较,电磁特性具有很强的互补性,如果把二者有效和适当地结合起来,有可能制备出高效的吸波剂。为此,本文着重讨论了设计和制备新一类型软磁尖晶石型铁氧体包覆硬磁锶铁氧体的“核壳型”电磁波吸波材料。设计和制备这种吸波材料的“核壳型”复合粒子的出发点,就是利用二者在其电磁性能上的互补性,并且希望能够充分发挥复合形式的作用,即“核壳型”结构以及“核”和“壳”的各种特殊界面效应,使这种复合结构也能对电磁波的吸收做出明显贡献。本文首先通过不同制备方法之间的对比,得出溶胶凝胶法的优越性。然后在传统制备工艺方法的基础上进行了改进,制备出了尖晶石型铁氧体和磁铅石型铁氧体纳米粉;之后分别以两种不同材料作为核,以另外一种材料作为壳,采用改进后的凝胶工艺方法,制备出了包覆型纳米复合颗粒。对样品用XRD、SEM、TEM和VSM以及矢量网络分析仪等分析方法和手段,对颗粒的形貌和吸波性能进行了检测和分析。检测和分析结果显示:1.采用共沉淀法和传统的溶胶凝胶法这两种不同方法制备出的纳米颗粒,其粒径都会着随温度的升高而增大,但是,溶胶凝胶法制备出的样品的颗粒粒径小、且分布均匀;在溶胶凝胶法制备过程中,对比以硝酸盐为原料和以乙酸盐为原料制备出的样品,后者的粒径比较小。2.在溶胶凝胶法制备过程中,加入葡萄糖和丙烯酰胺后,制备出磁铅石型SrFe₁₂O₁₉纳米粉,虽然纳米颗粒的粒径也会随温度升高而增大,但是,与改进前相比较,样品的颗粒粒度均匀、粒径小、分散性也得到较大改善。3.采用改进后的网络凝胶法,以磁铅石型SrFe₁₂O₁₉为核,制备出系列核/壳结构SrFe₁₂O₁₉/AFe₂O₄纳米粉,在实验中发现,在核/壳质量比为1:2、退火温度为1050℃条件下热处理10小时、升温速率保持在10℃/min时,得到的颗粒呈球形、分散性好、粒径在30-45nm左右,且分布均匀。随着复合材料中核材料SrFe₁₂O₁₉质量的减小,质量磁化强度（Ms）的值从SrFe₁₂O₁₉核心材料的42.6emu/g增加到SrFe₁₂O₁₉/NiFe₂O₄纳米复合材料的51.4emu/g。而SrFe₁₂O₁₉/NiFe₂O₄纳米复合材料的内稟矫顽力（Hc）是336Oe,在SrFe₁₂O₁₉（5395Oe）和NiFe₂O₄（160Oe）之间。当SrFe₁₂O₁₉/NiFe₂O₄纳米复合粉体的质量比为1:2时,吸波性能达到最大值9dB,是一种性能优良的吸波剂。4.以AFe₂O₄为核,制备出核/壳结构AFe₂O₄/SrFe₁₂O₁₉（A为Ni、Zn、Co）纳米粉。分析结果显示粉体的纯度高、粒径小、颗粒度均匀、分散性好。当核材料发生改变时,质量磁化强度（Ms）和内稟矫顽力（Hc）也会发生不同趋势和不同程度的改变,分析发现,发生这些变化的原因都与核壳结合处的原子替换有关。更多还原

【Abstract】 In recent years, It has become the electromagnetic wave absorption material study and application of hot spots. On the material property requirements is a strong absorption, absorption spectrum width, material thickness thin, light weight characteristics etc. But so far, has not found any kind of material can meet these requirements. So to existing materials appropriate modification and design became the focus of research. Hexagonal crystal M type strontium ferrite because of its natural resonant frequency in high frequencies higher, not easy to generate hasten skin current, dielectric constant is lesser, can be mixed with other absorbing materials for absorbing coatings used to adjust the electromagnetic parameters etc and become a kind of very important electromagnetic wave absorbing agent. Its defect is absorbing properties on the preparation process is very sensitive. To further improve the single ferrite materials magnetic conductivity is difficult. But spinel ferrite absorbing material has good stability, the highest temperature of saturation magnetization intensity, the microwave magnetic conductance larger, the advantage very obvious. But spinel ferrite absorbing material in microwave frequency is restricted by "because skin effect" and granularity cannot too big, and distribution uniformity, volume fraction can not be too big. Thus, magnetic lead stone type ferrite absorbing material and spinel ferrite absorbing material electromagnetic characteristics have strong complementary, effectively combines the two may create efficient absorbing agent. In this paper a new dedicated to design and preparation spinel ferrite magnetic hard magnetic strontium coated the "nuclear shell mould manganese-zinc electromagnetic wave absorbing materials". Design and preparation such "core-shell type" composite particle starting point is to use both electromagnetic properties of complementary, and still hope to be able to play compound form also is "core-shell type" structure and "nuclear" and the "shell" of various special interface effect effect, make they can also contribute to the electromagnetic wave absorption.This paper first through the contrast between the different processing methods, it is concluded that the superiority of sol-gel method. Then in traditional preparation process methods improved, based on prepared the spinel ferrite and magnetic lead stone type ferrite nano powder; Later in two different materials respectively, nuclear power as in a different material as the shell, using modified sol-gel process, prepared the coated nanostructured composite particles. Samples by XRD, SEM of VSM, TEM and network analyzer and vector analysis method and means, of particle morphology and absorbing properties are tested and analyzed.Test and analysis results show:1. The total precipitation and traditional by sol-gel method of the two different methods of preparation out, its size will nanoparticle since the temperature increases and increase, however, sol-gel process) out of the samples of particle size is small, and distributes uniformly; In the process of sol-gel process), contrast nitrate as raw materials and acetic acid salt as raw material with a sample preparation, the latter size smaller.2. In sol-gel process) process, join acrylamide and glucose and preparing a magnetic lead stone type SrFe₁₂O₁₉ nanometer powder, although nanoparticles size will also increases with temperature rise, however, and improved compared samples before the grain size, particle size uniform, small, dispersion also get improved considerably.3. Using the improved polymer network sol-gel method, SrFe₁₂O₁₉ by magnetic lead stone type for nuclear, preparation of a series of SrFe₁₂O₁₉ / AFe₂O₄ core/shell structure nanoparticles, in experiments found in core/shell mass ratio of 1:2, annealing temperature of 1050℃conditions heat treatment 10 hours, heating rate remained in 10℃/ min, get a spherical shape, the granules dispersion of good size in 30 - about 45nm, distribution and evenly. With nuclear materials in composite materials SrFe₁₂O₁₉quality and decreasing quality of magnetic intensity （Ms） SrFe₁₂O₁₉ value from the core material emu/g per increased to SrFe₁₂O₁₉/NiFe₂O₄ nanocomposites emu/g am. And SrFe₁₂O₁₉/NiFe₂O₄ nanocomposites intrinsic coercive force （Hc） is SrFe₁₂O₁₉ (5395Oe 336Oe, in NiFe₂O₄ （160Oe） and in between. When SrFe₁₂O₁₉/NiFe₂O₄nano powder quality than for 1:2, 9dB maximum absorbing properties, is a fine performance absorbing agent.4. The AFe₂O₄/SrFe₁₂O₁₉ （A is Ni, Co, Zn） core/shell structure powders, which were prepared use spinel AFe₂O₄ as nuclear materials, have high purity, uniformity of particle size, small size, and good dispersion. The results show that particle high purity, spheroidization small, even, good dispersion particle degree. When the nuclear material change, quality magnetized intensity （Ms） and intrinsic coercive force （Hc） will also happen different trends and different degree of change, analysis found that, as the cause of the changes with core-shell attaches to replace the atoms concerned.更多还原