【作者】 郭睿倩；

【导师】 李洪桂； 孙培梅；

【作者基本信息】 中南大学 ， 冶金科学与工程， 2001， 博士

【摘要】 本研究是在前人工作的基础上，同时从制备方法和掺杂元素两方面着手，以保证制备的粉体材料具有优异的性能，即首次利用溶胶—凝胶湿化学合成法和低温燃烧合成法相结合的一种兼具二者优点的超细粉末新型合成技术——溶胶-凝胶燃烧合成法来完成稀土元素掺杂钡铁氧体BaRE_xFe_12-xO₁₉（RE为La、Nd、Sm、Gd）超细粉末的制备。在深入进行了理论分析和大量实验研究的基础上，以稀土La元素掺杂为代表，首次查明了各种工艺条件（包括溶胶组成、中间产物种类、溶液浓度、络合剂配比、阴离子种类、分散剂、自蔓延燃烧和热处理制度）对稀土掺杂钡铁氧体粉末物相结构、粒度、形貌及磁学性能影响的规律性，确定了最佳制备工艺。 首次对溶胶-凝胶燃烧合成法热处理过程中稀土掺杂钡铁氧体的生成机理进行了深入研究，同时初步查明了过程中络合剂（柠檬酸）和分散剂（乙二醇）的作用机理。 首次查明了钡铁氧体粉末的磁性能（包括比饱和磁化强度、比剩余磁化强度和内禀矫顽力）随稀土元素种类及其掺杂量的变化规律。 利用X射线衍射仪（XRD）确定样品物相，振动样品磁强计（VSM）进行磁性测量，综合热分析仪研究凝胶的燃烧和析晶过程，扫描电子显微镜（SEM）和透射电子显微镜（TEM）观察粉末的形貌与粒度。本研究的成果和结论如下： 1)查明了稀土掺杂钡铁氧体的生成机制，即： 有机前驱物（凝胶）→γ-Fe₂O₃+B²⁺→BaFe₂O₄ BaFe₂O₄+5γ-Fe₂O₃→BaFe₁₂O₁₉ 因此，制备性能优异、粒度均匀的稀土掺杂钡铁氧体超细粉末，其关键是反应过程中应尽量避免中间产物α-Fe₂O₃的生成。这一关键对稀土掺杂钡铁氧体的其他制备方法，如化学共沉淀法、气溶胶法、低温化学法和水热法等也同样适用。 2)根据理论分析和实验研究，提出了选用柠檬酸作络合剂，乙二醇为分散剂，且将溶液起始PH值调至弱酸性（7.0左右）以及将凝胶预燃烧后再进行高温煅烧的两步热处理制度是保证γ-Fe₂O₃中间物相、避免α-Fe₂O₃中间物相生成的两个关键步骤，可保证在较低的煅烧温度下形成稀土掺杂磁铅石型钡铁氧体超细粉末。 3)在查明了最佳工艺条件的基础上，制备了纯净单一、粒径细小（30～70nm左右）、粒度均匀且磁性能优良的稀土掺杂磁铅石型钡铁氧体超细粉末。其比饱和磁化强度达65.54A·m²/Kg，接近Blirk和Buessem所报道的aaFe₁₂O₁₉单晶的理论值（72A·m²/kg），矫顽力为437kA/m，接近根据Stoner和Wohlfarth理论所推算的无定向的单轴单畴BaFe₁₂O₁₉颗粒在室温的理论预期值（533kA/m），其作为永磁材料的磁学性能指标与前人合成的样品相比也有了较大的改善。 4)查明了稀土掺杂对钡铁氧体微粒磁性能的影响规律。随着稀土掺杂量的增加，样品的比饱和磁化强度和比剩余磁化强度均随之下降，且掺杂各种不同稀土元素的下降幅度大体相同。样品的矫顽力在掺杂量较低的范围内出现一个极值（La和Sm掺杂时为极小值，Nd和Gd掺杂时为极大值）；在掺杂量较高的范围内，矫顽力随掺杂量的增加而大幅度增大。更多还原

【Abstract】 The hexagonal BaRExFe,2.xO,,(RE denote La^ Nd> Sm and Gd) ultrafine powders with M-typestructure were firstly synthesized by a novel technique ------ sol-gel combustion synthesis methodwhich combines sol-gel method with low temperature combustion synthesis method.Based on theoretical analysis and experimental study, the effects of the composition of the gel, the different kinds of intermediate, strength of solution, the amount of complexing agent, the different kinds of anions, the adding of dispersant, auto - propagating combustion and the condition in heat treatment of the gel on crystal phase, particle size, morphology and magnetic properties of BaRE^Fe^O,, ultrafine powders were firstly investigated systematically to clarify the optimum forming conditions.The formation mechanism of BaRExFe12_xOl9in heat treatment was firstly deeply discussed, and the action mechanism of complexing agent (citrate) and dispersant (glycol) during the formation of the gel was also firstly studied.The effects of the different kinds of rare earths and the doping amount of them on magnetic properties of BaFe,2O19 ultrafine powders (including the specific saturation magnetization, the specific remanent magnetization and coercive force) were firstly discussed systematically.The composition of sample was identified by means of X-ray diffractometer(XRD). Magnetic properties were measured by vibrating sample magnetometer (VSM). The combustion behavior and crystallization process of the gel were studied by means of differential thermal analysis-thermogravimetric analysis (DTA-TG). Scan electron microscope (SEM) and transmission electron microscope (TEM) were used to examine the morphology. Some important results are concluded as follows:1) This investigation presents the formation mechanism of BaREiFe^Oi,, that is,organic precursor (gel) - Y -Fe2O3+Ba2+-BaFe204BaFe2O4+5 y -Fe2O3-BaFe,2O19Therefore, only when the formation of a -Fe2O3 intermediate is prevented, can the pure BaRExFe,2.xOI9 particles be obtained at relatively lower calcining temperature. This conclusion can also be applied in other synthesis methods such as chemical co-precipitation, aerosol synthesis, cryochemical method and hydrothermal synthesis.2) The results show that controlling the pH value of starting precursor solution at 7.0 or so and preprocessing the gel (that is, igniting the gel) into y -Fe^ before calcining are two key steps which can prevent the formation of a -Fe2O3 intermediate, thus the pure BaRE^Fe^O,, particles can be obtained at lower calcining temperature (850 "C).3) The BaRExFel2.x019 ultrafine powders with single phase, small size (about 30~70nm), narrow size distribution and high magnetic properties with coercive force (437kA/m) and specificmagnetization (65.54A ?m2/kg) that are similar to the theoretically predicted values and far more than those of barium ferrite produced by others without doping.4) The rule about the influence of rare earths (La, Nd, Sm, Gd) doping on magnetic properties of barium ferrite is concluded. With the increasing of the doping amount of these four rare earths, both the specific saturation magnetization and the specific remanent magnetization decrease gradually to the same extent. When the doping amount of these four rare earths is lower, coercive force of La and Sm-doped barium ferrite powders shows a similar regularity, that is, there exists a minimum, whereas there exists a maximum in Nd and Gd-doped barium ferrite powders. When the doping amount is higher, coercive force increases greatly with the increasing of the doping amount更多还原