【作者】 向军；

【导师】 沈湘黔；

【作者基本信息】 江苏大学 ， 材料学， 2011， 博士

【摘要】 近年来,一维磁性纳米材料如纳米管、纳米带、纳米线和纳米纤维等因其新奇的物理和化学性质以及在基础研究和应用技术方面的重要价值而受到人们的广泛关注。它们不但具有普通纳米粒子的各种特殊效应,而且还具有独特的形状各向异性和磁各向异性,可以突破各向同性粉体材料对电磁性能的限制,被认为是构筑新型电磁光功能材料与器件的重要组元,有望在高密度磁记录、磁传感器、磁性复合材料、微纳功能器件、自旋电子器件、电磁波吸收、催化以及生物医学等方面得到实际应用。在制备一维微纳米结构材料的众多方法中,高压静电纺丝技术不仅具有制备过程简单、成本低、可大量生产等优势,更重要的是应用范围广泛,而且所得的纤维均匀、连续、直径可控、长度可达宏观尺度。尖晶石铁氧体是一种在工业和日常生活中应用非常广泛的磁性材料,它们的性质与其化学组成和形貌及微观结构有着密切的联系。目前有关尖晶石铁氧体一维微纳米结构的研究主要集中在单元尖晶石铁氧体方面,而对性能优越和应用范围更为广泛的多元尖晶石铁氧体的研究较少。为此,多元尖晶石铁氧体一维微纳米结构及其相关复合材料的研究将具有非常重要的科学价值和现实意义。本论文以高压静电纺丝技术为基础,与溶胶-凝胶技术和热处理过程控制相结合,围绕着一维多元尖晶石铁氧体微纳米纤维及其相关复合材料的可控制备、结构调控与磁性能进行研究,主要工作和创新成果如下：1.多元尖晶石铁氧体微纳米纤维。以PVP为络合剂,分别与相关无机盐反应制得前驱体溶液,利用静电纺丝技术先制备出PVP/无机盐的复合微纳米纤维,然后将得到的PVP/无机盐复合微纳米纤维经适当的高温焙烧处理获得了所需要的无机物微纳米纤维。(1)我们可控制备了二元尖晶石型Mn0.5Zn0.5Fe2O4、Ni1-xZnxFe2O4 (x= 0.0～0.8)> Co0.5Ni0.5Fe2O4、Co1-xZnxFe2O4 (x= 0.0～0.5)、Li0.5-0.5xZnxFe2.5-0.5xO4 (x=0.0-0.8)以及三元尖晶石型Ni0.5-xCuxZno.5Fe2O4 (x= 0.0～0.5)铁氧体微纳米纤维。(2)采用TG-DTA、FTIR、XRD、SEM(HR)TEM、SAED、EDS和VSM等技术对所制备的微纳米纤维进行了表征,系统研究了焙烧温度和化学组成对纤维的结构、微观形貌和宏观磁性能的影响,并对其原因进行了分析和讨论。(3)初步认识和揭示了一维或准一维多元尖晶石铁氧体的组成、结构与性能之间的关系,发现Co1-XZnxFe2O4微纳米纤维的晶格常数随Zn含量的变化呈一种非单调行为,不满足Vegard定律,而Ni1-XZnxFe2O4和Li0.5-0.5XZnXFe2.5-0.5X4微纳米纤维的晶格常数则随Zn含量的变化基本符合Vegard定律；确定了多元尖晶石铁氧体微纳米纤维Nio.5Zno.5Fe2O4、Coo.5Zno.5Fe2O4、Coo.5Nio.5Fe2O4、Li0.35Zn0.3Fe2.3504及Nio.3Cuo.2Zno.5Fe2O4的单磁畴临界尺寸,分别在33、39、30、35和53 nm左右；在单畴范围内,建立了Coo.5Zno.5Fe2O4、Coo.5Ni0.5Fe2O4及Nio.3Cuo.2Zno.5Fe2O4微纳米纤维的矫顽力与其晶粒尺寸的依赖关系,分别与其平均晶粒尺寸的0.65、0.70和0.71次方成正比,验证了随机各向异性模型对一维纳米体系所预测的结果(即Hc∝D2/3)。(4)此外,我们还分别探讨和表征了Nio.5Zno.5Fe204和Nio.3Cuo.2Zn05Fe2O4微纳米纤维的磁各向异性以及纤维与其相应粉体在磁学行为上的差异,并合理解释了引起这种差异的原因。2.多元尖晶石铁氧体/非磁性氧化物复合微纳米纤维。在成功制备出NiZn铁氧体微纳米纤维的基础上,结合溶胶-凝胶技术,采用静电纺丝法合成了Nio.5Zno.5Fe2O4/Si02和Nio.5Zno.5Fe2O4/A1203复合微纳米纤维。研究了Si02和A1203对Nio.5Zno.5Fe2O4微纳米纤维的物相、微观结构及形貌和宏观磁性能的影响规律,并探讨了相关的物理机制。发现引入非晶Si02和A1203非磁性氧化物是调控尖晶石铁氧体微纳米纤维微观结构及磁性能的一条有效途径。3.尖晶石铁氧体／磁性合金复合微纳米纤维。结合部分还原过程控制技术,利用静电纺丝法制备了平均直径约为170 nm的镍铁氧体/Fe-Ni合金微纳米纤维,研究了它们的晶体结构、物相组成、微观形貌和宏观磁性能,并与还原前的纯镍铁氧体微纳米纤维进行了比较。发现所制备的复合微纳米纤维由面心立方(FCC)、体心立方(BCC)结构Fe-Ni合金和尖晶石结构镍铁氧体所构成,Fe-Ni合金与镍铁氧体两相间具有较好的磁交换耦合,使之表现出了更为优良的磁性能,比饱和磁化强度和矫顽力分别由还原前的49.5 emu/g和17.4 kA/m提高到还原后的103.9 emu/g和36.6 kA/m。该制备新方法可扩展用于构筑其他类型的磁性金属或合金／铁氧体复合微纳米纤维。更多还原

【Abstract】 In recent years, one-dimensional (1D) magnetic nanomaterials, such as nanotubes, nanobelts, nanowires and nanofibers, have attracted an intensive attention because of their distinctive physical and chemical properties from their bulk and nanoparticle counterpartes due to their large specific surface area, high aspect ratio and unique shape anisotropy, leading potential applications in high-density magntic recording, magnetic sensors, micro-nano functional devices, magnetic composites, spintronic devices, electromagnetic wave absorbing materials, calalyst, biomedicine, etc. Among the vaious methods for preparation of 1D micro-nanostructured materials, the electrospinning due to simple, low cost and high yield is proved to be a versatile and the most popular technique utilized in fabrication of functional micro/nanofibers with both solid and hollow interiors that are exceptionally long in length, uniform in diameter, and diversified in composition. Spinel ferrites are a kind of widely used soft magnetic materials in both industry and daily life, and their performances are found to be directly related to their stoichiometric composition, microstructure and morphology. Up to now, the researches on spinel ferrite 1D micro-nanostructures have been mainly focused on some simple spinel ferrites and a few for the complex spinel ferrites with excellent performances and wide applications. Therefore, there is important scientific interests and practical applications to develop 1D micro-nanostructured materials of the complex spinel ferrites and relative composites.In this dissertation, we combined electrospinning technique with sol-gel and heat treatment processes and carried out abundant research work on the controlled fabrication, structural adjustment and magnetic property characterization of the 1D complex spinel ferrite micro/nanofibers and relative composite materials. The main works and innovative results are as follows:1. Fabrication, structure and magnetic properties of the complex spinel ferrite micro/nanofibers. (1) We successfully prepared Mn0.5Zn0.5Fe204, Ni1-xZnxFe2O4(x= 0.0-0.8), Co0.5Ni0.5Fe2O4, Co1-xZnxFe2O4 (x= 0.0～0.5) and Li0.5-0.5xZnxFe2.5-0.5x04 (x= 0.0～0.8) binary spinel ferrite micro/nanofibers as well as Ni0.5-xCuxZn0.5Fe2O4 (x=0.0-0.5) ternary spinel ferrite micro/nanofibers with a narrow diameter distribution and uniform cross-section by calciantion of the electrospun PVP/inorganic component composite micro/nanofibers. (2) These micro/nanofiber samples were characterized using TG-DTA, FT-IR, XRD, SEM, (HR)TEM, SAED, EDS and VSM techniques. The effects of calcination temperature and chemical composition on the structures, micromorphologies and macro-magnetic properties of samples were systematically investigated and the reasons were analyzed and discussed. (3) We revealed and preliminarily understood the relationship between structure and performance of the investigated complex spinel ferrite in the one-dimensional or quasi one-dimensional case. It finds that the variation of the lattice constant with Zn content shows a nonmonotonic behavior and deviates from the Vegard’s law for the Co1-xZnxFe2O4 nanofibers, but for Ni1-xZnxO4 and Li0.5-0.5xZnxFe2.5-0.5xO4 micro/nanofibers, this variation relationship basically complies with the Vegard’s law. The single-domain critical sizes for Ni0.5Zn0.5Fe204, Co0.5Zn0.5Fe2O4, Co0.5Ni0.5Fe204, Lio.35Zno.3Fe2.35O4 and Nio.3Cu0.2Zn0.5Fe2O4 micro/nanofibers are estimated to be about 33,39,30,35 and 53 nm, respectively. Futhermore, the dependent relationships of the coercivity (Hc) on the average crystalline size (D) in a D range below the critical size are obtained for Coo.5Zno.5Fe204, Co0.5Ni0.5Fe2O4 and Ni0.3Cu0.2Zn0.5Fe204 micro/nanofibers. It is showed that Hc of these fiber samples follows a D power law with an exponent of 0.65, 0.70 and 0.71, respectively, which verifies the predicted results (i.e. Hc～D2/3) for 1D nanosystems based on the random anisotropy model. (4) In addition, we investigated the magnetic anisotropy and difference in magnetic behaviors between the fiber and the corresponding powder samples for the prepared Ni0.5Zn0.5Fe204 and Ni0.3Cuo.2Zno.5 Fe2O4 micro/nanofibers and reasonably explained the reason for the observed phenomena.2. Fabrication, structure and magnetic properties of the complex spinel ferrite/non-magnetic oxide composite micro/nanofibers. Based on the successful preparation of NiZn ferrite micro/nanofibers, we fabricated the non-magnetic Nio.5Zno.5Fe204/Si02 or Al2O3 micro/nanofibers by electrospinning technique combined with sol-gel process. The effects of SiO2 or Al2O3 additives on the phase, microstructure and morphology as well as macro-magnetic properties were studied in detail, and the related physical mechanisms were also discussed. The results indicate that the addition of amorphous non-magnetic oxides is an effective way to control and tune the microstructure and magnetic performances of spinel ferrite micro/nanofibers.3. Fabrication, structure and magnetic properties of the spinel ferrite/magnetic alloy composite micro/nanofibers. We successfully synthesized the Fe-Ni alloy/nickel ferrite composite micro/nanofibers with an average diameter of 170 nm by electrospinning and subsequent partial reduction process control technology for the first time. The crystal structure, phase composition, micromorpholgy and macro-magnetic properties of these micro/nanofibers were studied, in comparison with the pristine nickel ferrite micro/nanofibers before reduction. It finds that the synthesized composite micro/nanofibers consist of Fe-Ni alloy with the face centered cubic (FCC) and body centered cubic (BCC) mixed structures and nickel ferrite with the spinel structure. The two phases of the Fe-Ni alloy and nickel ferrite are well magnetic exchange-coupled, and consequently the prepared composite micro/nanofibers exhibit enhanced magnetic properties compared to the pristine nickel ferrite micro-nanofibers. The saturation magnetization and coercivity are increased from 49.5 emu/g and 17.4 kA/m before reduction to 103.9 emu/g and 36.6 kA/m after reduction, respectively. This new synthetic route can be conveniently expanded to prepare other types of magnetic metal or alloy/spinel ferrite composite micro/nanofibers as well.更多还原