【作者】 张绍强；

【导师】 邓文礼；

【作者基本信息】 华南理工大学 ， 材料物理与化学， 2013， 博士

【摘要】 在先进的磁性功能材料中,稀土-铁超磁致伸缩材料(GMM)和磁性纳米材料这两类磁性材料占据着重要的位置。GMM由于其优异的磁致伸缩性能以及大的机电耦合系数,在声纳换能器、防震装置、位移器等精密仪器领域有着关键的应用。而磁性纳米材料则在磁记录、磁流体、医学成像、靶向药物、催化等方面有着广泛的应用。对于GMM材料,其昂贵价格是阻碍其广泛应用的主要因素之一。而对磁性纳米材料来说,探索合适的制备工艺,研究其生长机理,实现纳米晶粒的尺寸与形貌的可控合成和性能调控,是当前磁性材料的研究热点与难点。基于上述问题,本学位论文成功地采用价格相对便宜的Pr元素部分取代了(Tb, Dy)Fe2中的Dy元素,制备出(Tb, Dy, Pr)Fe2化合物。采用水热法制备了尺寸小于10纳米的Fe304与CoFe2O4磁性纳米粒子,并研究其性能和晶粒生长的机理。本学位论文的主要研究内容与结果如下：1.通过电弧炉法成功制备了Tbo.3(Dy1-xPrx)o.7Fe1.96(x=0,0.1,0.2,…,0.6)化合物合金锭。XRD粉末衍射结果显示了化合物的结构与晶格常数随着Pr含量增加的变化规律。SEM-BSD和热磁曲线的检测结果验证了材料物相的变化。磁性能测试表明,随着Pr含量增加,化合物的居里点和磁化强度都发生了下降。本实验的结果,为TbDyPrFe材料的成分控制与性能提高提供了必要的实验依据。2.首次通过籽晶引导的定向凝固区熔法,制备具有一定择优取向的Tbo.3(Dy1-xPrx)o.7Fe1.96定向凝固样品。材料检测表明,随着Pr含量的增加,化合物的取向发生变化。同时,材料的磁致伸缩性能发生下降,微分磁致伸缩系数d33逐渐下降且趋向于变为一个常数,而磁致伸缩滞后也逐渐减少。研究发现,在一定的成分范围内,热处理能够有效提高材料的磁致伸缩值,其λ值最高能比相应的铸态样品提高一倍。最后,论文利用SEM-BSD和能谱对铸态样品的物相结构进行了测量,并分析了材料性能与结构变化的关系。本研究首次发现TbDyPrFe化合物的定向凝固参数需要根据Pr含量作适当调整,并阐明了Pr含量与定向凝固样品的磁致伸缩性能的关系,以及热处理对材料结构与性能之间的影响规律。这些研究结果将有助于使TbDyPrFe化合物成为实用化的新型超磁致伸缩材料。3.以Fe(acac)3和Fe粉为前驱体,在正己烷-表面活性剂体系中通过水热法制备了不同晶粒尺寸的磁性纳米晶粒。XRD和拉曼光谱证实所制得的材料为Fe304。 HRTEM分析表明,随不同的反应时间,样品的晶粒尺寸在5.3-6.8nm之间分布。从晶粒形貌的变化对样品的生长机理进行分析,本文认为在表面活性剂的调控下,纳米晶的形貌从无规则形状过渡到三角形和四边形,最后生长为六边形。磁性测量表明,所制得的样品都具有超顺磁性,最大的饱和磁化强度为62.65emu/g。本研究结果可以为Fe304磁性纳米材料的可调控制备与应用提供技术支持与理论参考。4.利用水热法,以Fe(acac)3和CoCl2·6H20为前驱体,分别在正己烷-水-表面活性剂(标记为A1)和乙醇-表面活性剂(标记为B1)两个反应体系中成功制备了CoFe2O4纳米粒子。利用Scherrer公式对XRD数据进行估算,结果显示所制备的样品尺寸均小于5纳米。磁性能检测表明,A1和B1样品的Ms分别为60.95emu/g和61.20emu/g,Hc分别为1860.90Oe和423.32Oe。经过热处理后,样品的Ms、Mr,Hc和剩磁比R均有不同程度的变化。最后,论文初步分析了两个体系的反应机理,并讨论了反应体系对晶粒尺寸以及磁性能的影响规律。更多还原

【Abstract】 Rare earth-iron giant magnetostrictive material (GMM) and nano-magnetic material play an important role in advanced magnetic functional materials. Because of its excellent magnetostrictive properties and large electromechanical coupling factor, GMM has critical applications in some precision instruments, such as sonar transducer, anti-vibration mounting, positioning device, and etc. Meanwhile, the nano-magnetic materials have been widely exploited in many fields, such as magnetic recording, magnetic fluid, magnetic resonance imaging, drug targeting, and catalysts.For GMM, its expensive price is one of the main factors hindering its wider application. For nano-magnetic material, it has become the research focus and challenge to explore the preparation technology and to study the crystal growth mechanism, in order to precisely control the grain size, morphology and property. Based on the above-described problems,(Tb, Dy, Pr)Fe2compound is successfully prepared by partial substituting the relatively inexpensive rare earth element, Pr, for the expensive metal element, Dy, in the (Tb, Dy)Fe2alloy in this dissertation. Also, Fe3O4and CoFe2O4magnetic nanopatticles with the grain size less than10nm are synthesized by hydrothermal method. Their properties and the mechanism of grain growth are studied in details. In this dissertation, the main researches and results are as follows:1. The Tb0.3(Dy1-xPrx)0.7Fe1.96compound ingots with x=0,0.1,0.2,…,0.6are prepared by arc melting method. The powder XRD results of the powder show the evolution regulation of the compounds microstructure and lattice constant with the increase of Pr content. The measurement results of SEM with BSD mode and thermo-magnetic curves confirm the change of phase composition. The magnetic test indicates that the Curie point and the magnetization of the compound decrease with the increase of Pr element. The results of this experiment will provide the necessary reference data for the controlling of material composition and performance improving for TbDyPrFe materials.2. The directionally solidified Tb0.3(Dy1-xPrx)0.7Fei.96rods with some preferred orientation are first prepared by the zone melting method with the guidance of seeds. The results of measurement indicate that, with the increase of Pr element, the orientation of samples is changed, the magnetostrictive properties decrease, the value of differential magnetostrictive coefficient (d33) reduces gradually and tends to become a constant. The magnetostrictive hysteresis of the samples is also reduced gradually. It is found that in a range of Pr content, heat treatment could effectively improve the magnetostrictive property of samples. After heat treatment, the maximum value increases about one times than the as-cast ones. At last, the relationship between the properties and the phase composition of samples is analyzed by the measurement of as-cast samples by SEM-BSD and EDS. In summary, the study of this dissertation first finds that the directional solidification parameters of TbDyPrFe compounds need to be adjusted according to the Pr content. The effects of Pr content, magnetostrictive properties of the directionally solidified samples and heat treatment on the structure and properties of materials are clarified. The results of these studies will be beneficial to make TbDyPrFe compounds to be a series of practical new giant magnetostrictive materials.3. Magnetic nanocrystals with different size are prepared by hydrothermal method at different reaction-times in N-hexane-surfactant system. The precursors are Fe(acac)3and iron powder. The results of XRD and Raman spectrum confirm these samples are Fe3O4. HRTEM measurement shows the grain size distributes from5.6to6.8nm with the reaction time. The grain growth mechanism is analyzed based on the crystal morphologies. It is considered that in the regulation of surfactant, the morphology of the Fe3O4magnetic nanocrystals change from the irregular crystal form to triangles and quadrilaterals, and finally to the hexagonal nanoparticles. The Magnetic measurement results show that the prepared samples are of superparamagnetic, and the maximum saturation magnetization is62.65emu/g. The results in these investigations could provide technical support and theoretical reference for the regulation preparation and its application of the Fe3O4magnetic nanocrystals.4. By the hydrothermal methods, CoFe2O4nanoparticles are successfully synthesized in the hexane-water-surfactants system (sample Al) and the ethanol-surfactants system (sample B2). The precursor are Fe(acac)3and CoCl2·6H2O. The results of XRD estimated by Scherrer formula indicate that the crystal size of all the samples is less than5nm. Magnetic measurement indicates that the saturation magnetizations (Ms) of sample A1and B1are60.95emu/g and61.20emu/g, the coercivities (Hc) are1860.90Oe and423.32Oe, respectively. After heat treatment, Ms, Mr, Hc, and remanence ratio R of samples are changed in some degree. At last, the reaction mechanism of these two systems is analyzed, and the effects of these reaction systems on the crystal size and magnetic properties are discussed.更多还原