纳米氧化铁的热稳定性及其磁性能的研究

发布时间：2019-06-16 19:35

【摘要】：纳米氧化铁材料聚集了越来越多的研究目光,主要是因为它的用途比较广范。纳米氧化铁各种各样的应用与氧化铁材料的热稳定性和磁性有着重要的关系。本文中,我们选取了不同形貌的α-Fe2O3纳米颗粒和空心结构的Fe_3O_4纳米粒子及17nm左右的Fe_3O_4纳米颗粒作为研究对象。利用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、和综合物理测试系统(PPMS)对样品进行表征,分别对样品的形貌、结构及磁性能进行了研究。同时也研究了提高Fe_3O_4磁性纳米粒子热稳定性的方法。本文的主要研究成果如下:(1)我们通过水热法合成了不同形貌的(片状,鼓状,梭状)α-Fe2O3纳米颗粒。在高真空(9.5×10-6 Torr)下通过对磁学性能的测量来确定不同形貌的α-Fe2O3纳米颗粒的热稳定性。实验结果发现,在高温高真空下存在一个α-Fe2O3到Fe_3O_4的相变过程,而且这个转变过程受纳米粒子形貌的影响。低温下的磁性测量结果表明,三种形貌的Morin转变温度被完全抑制,这个结果也说明了Morin转变受纳米粒子形貌的影响。(2)我们通过两步合成了具有空心结构的Fe_3O_4纳米环和纳米管,在高真空下测量空心纳米结构的磁性能。纳米环与纳米管的居里温度随着平均壁厚的减少而降低。空心磁性纳米结构的居里温度遵从尺寸效应,拟合出的标度指数为ν=1.04±0.03。通过比较零维的Fe_3O_4粒子和准二维的Fe_3O_4薄膜不同尺寸下的居里温度,我们发现Fe_3O_4空心结构的尺寸关系与准二维的尺寸效应吻合的更好。(3)我们通过两步法成功制备了Fe_3O_4@C纳米颗粒。与纯的Fe_3O_4纳米颗粒相比,Fe_3O_4@C纳米颗粒表现出了更好的热稳定性。在高真空(9.5×10-6 Torr)下通过300K到920K之间的磁学性能的测量来确定Fe_3O_4@C的热稳定性。实验结果发现,高温高真空下Fe_3O_4@C纳米颗粒是非常稳定的。这对于有限尺寸的尺寸效应的研究是有很大意义的。(4)我们将水热法合成的Fe_3O_4粒子与球磨过的NaCl颗粒充分混合,探究NaCl对Fe_3O_4粒子尺寸和热稳定性影响。实验结果表明,NaCl的存在抑制了Fe_3O_4粒子的聚合,并提高了Fe_3O_4到α-Fe2O3的起始相转化温度。这种方法简单、无毒、比较经济,有很好的应用前景。
[Abstract]:Nano-iron oxide materials have attracted more and more research attention, mainly because of its wide use. Various applications of nano-iron oxide are closely related to the thermal stability and magnetic properties of iron oxide materials. In this paper, 伪-Fe2O3 nanoparticles with different morphology, Fe_3O_4 nanoparticles with hollow structure and Fe_3O_4 nanoparticles with about 17nm were selected as the research objects. The samples were characterized by scanning electron microscope (SEM), X-ray diffractometer (XRD), and comprehensive physical test system (PPMS). The morphology, structure and magnetic properties of the samples were studied. At the same time, the methods to improve the thermal stability of Fe_3O_4 magnetic nanoparticles were also studied. The main results of this paper are as follows: (1) different morphologies (flake, drum, fusiform) 伪-Fe2O3 nanoparticles were synthesized by hydrothermal method. The thermal stability of 伪-Fe2O3 nanoparticles with different morphologies was determined by measuring the magnetic properties of 伪-Fe2O3 nanoparticles in high vacuum (9.5 脳 10 脳 6 Torr). The experimental results show that there is a phase transition process from 伪-Fe2O3 to Fe_3O_4 in high temperature and high vacuum, and this transition process is affected by the morphology of nanoparticles. The magnetic measurement results at low temperature show that the Morin transition temperature of the three morphologies is completely suppressed, which also shows that the Morin transition is affected by the morphology of nanoparticles. (2) Fe_3O_4 nanorings and nanotubes with hollow structure were synthesized by two steps, and the magnetic properties of hollow nanostructure were measured in high vacuum. The Curie temperature of nanoparticles and nanotubes decreases with the decrease of average wall thickness. The Curie temperature of hollow magnetic nanostructures obeys the size effect, and the fitted scale index is v = 1.04 卤0.03. By comparing the Curie temperature between zero-dimensional Fe_3O_4 particles and quasi-two-dimensional Fe_3O_4 thin films at different sizes, we find that the size relationship of Fe_3O_4 hollow structures is in good agreement with the quasi-two-dimensional size effect. (3) Fe_3O_4@C nanoparticles were successfully prepared by two-step method. Compared with pure Fe_3O_4 nanoparticles, Fe_3O_4@C nanoparticles show better thermal stability. The thermal stability of Fe_3O_4@C was determined by measuring the magnetic properties between 300K and 920K in high vacuum (9.5x10 脳 6 Torr). The experimental results show that Fe_3O_4@C nanoparticles are very stable at high temperature and high vacuum. This is of great significance to the study of the size effect of finite size. (4) We fully mix the Fe_3O_4 particles synthesized by hydrothermal method with the ball-milled NaCl particles to explore the effect of NaCl on the size and thermal stability of Fe_3O_4 particles. The experimental results show that the existence of NaCl suppresses the polymerization of Fe_3O_4 particles and increases the initial phase transition temperature from Fe_3O_4 to 伪-Fe2O3. This method is simple, non-toxic, more economical, and has a good application prospect.
【学位授予单位】：宁波大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB383.1;O614.811

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