【作者】 单云刚；

【导师】 王钧； 徐任信；

【作者基本信息】 武汉理工大学 ， 复合材料学， 2009， 硕士

【摘要】 铁酸钻（CoFe₂O₄）是性能优良的磁性材料,具有较强的磁各向异性、较高的矫顽力、适中的磁饱和强度、显著的化学稳定性及机械强度,已被广泛应用于催化剂、磁记录材料、铁流体等领域。此外,由于其在微波频段C波段和Ku波段可以保持高的复磁导率实部和虚部,可以用作微波吸收材料。纳米颗粒具有小尺寸效应、表面效应、量子尺寸效应和宏观量子隧道效应等,同时由于与磁相关的特征物理长度恰好处于纳米量级（1-100nm）,如磁单畴尺寸、超顺磁性临界尺寸、交换作用长度及电子平均自由路程等,当磁性材料的尺寸与这些特征物理长度相当时,其多种电磁特性或物理特性即发生变化。因此,对于铁酸钴纳米颗粒的制备方法的研究具有非常重要的意义。目前制备纳米磁性材料的方法主要有高能机械研磨法、自蔓延燃烧合成法、溶胶-凝胶法、共沉淀法、水热法、微乳液法等。其中,水热法具有方法简单、所需温度低、易通过改变反应条件控制产物粒径大小和分布、减少或避免团聚、产物纯度高、且无需高温煅烧等优点,从而成为制备纳米磁性材料最具有潜力的方法之一。本文以FeCl₃·6H₂O和CoCl₂·6H₂O为原料,分别以二次去离子水、聚乙二醇水溶液、丙三醇水溶液以及丙三醇/聚乙二醇水溶液为介质,采用水热法成功制备了CoFe₂O₄纳米粉体。利用XRD、FESEM、VSM分别研究了不同反应介质、溶液pH值、反应时间、反应温度、丙三醇体积浓度对水热法合成CoFe₂O₄颗粒结构、形貌和磁性能的影响。结果表明,四种介质条件下均能生成尖晶石型CoFe₂O₄纳米颗粒。以二次去离子水和聚乙二醇水溶液为介质时,得到的CoFe₂O₄球形纳米颗粒粒径较小,粒度分布狭窄,但晶体结构很不完善,饱和磁化强度和剩余磁化强度均较低;以丙三醇水溶液及丙三醇/聚乙二醇水溶液为介质时,得到的CoFe₂O₄纳米颗粒粒径较大,晶体结构较为完善,饱和磁化强度和剩余磁化强度均较高;溶液pH值的增加、反应时间的延长、反应温度的提高、丙三醇体积浓度的增加都有利于CoFe₂O₄纳米颗粒的生成、晶体结构的完善和磁性能的提高;当pH值大于11、反应温度200℃以上,反应时间8h以上,丙三醇和水的体积比大于1时,生成的CoFe₂O₄纳米颗粒多为八面体结构,晶体结构比较完善,且粒度分布较窄。更多还原

【Abstract】 Cobalt ferrite（CoFe₂O₄） is a magnetic material which has good performance, such as strong magnetic anisotropy, high coercive force, moderate intensity magnetic saturation, remarkable chemical stability and mechanical strength, which has been widely used in catalyst, magnetic recording materials, iron fluids, etc.. In addition, it can be used as microwave absorbing material because of it can keep high real and imaginary parts of complex permeability in C-band and Ku-band of microwave. Nanoparticles have small size effect, surface effect, quantum size effect and the macro-quantum tunneling effect, etc., and at the same time magnetic related characteristic physical length is just in nano class（1-100nm）, such as magnetic single domain size, the super-paramagnetic critical size, length of the exchange, as well as the average e-free journey, etc., when the size of magnetic materials equal to the characteristic physical length, some electromagnetic properties or physical characteristics will change. So it is very important to research the preparation methods of cobalt ferrite nanoparticle. At present, the methods that prepare nano-magnetic material mainly include mechanical grinding, self-propagating combustion synthesis, sol - gel method, co-precipitation, hydrothermal method, micro-emulsion method, etc.. Among them, the hydrothermal method become one of the most potential ways to prepare nano-magnetic materials with some advantages such as simple, low-temperature requirement, easily controll particle size and distribution of products by changing the reaction conditions, reduce or avoid reunion, high purity and needn’t high temperature calcination, etc..In this paper, CoFe₂O₄ nano-powder was successfully prepared by hydrothermal method using FeCl₃·H₂O and CoCl₂·6H₂O as raw materials in second deionized water, aqueous solution of polyethylene glycol, aqueous solution of glycerin and aqueous solution of glycerol/polyethylene glycol resepctivily. X-ray diffraction （XRD）, field-emission scanning electron microscopy （FESEM） and vibrating sample magnetometer （VSM） were used to study the effect of different reaction medium, pH of solution, reaction time, temperature, the ratio of glycerol and water on the structure, morphology and magenetic properties of CoFe₂O₄ nano-particles. The results showed that spinel CoFe₂O₄ nanoparticles can be prepared in the four medium conditions. when using the second deionized water and polyethylene glycol solution as medium, the as-prepared CoFe₂O₄ spherical nanoparticles are smaller and the distribution of particle size is narrow, but the crystal structure is not perfect and the Ms, Mr are lower; when using glycerol solution and glycerol / polyethylene glycol solution as medium, the as-prepared CoFe₂O₄ nanoparticle is larger, and its crystal structure is better, the Ms, Mr are higher; The growth of CoFe₂O₄, crystal structure and magnetic properties will be enhanced with the increasing of pH, reaction time, temperature and the ratio of glycerol and water; when the pH value is morer than 11, the reaction temperature above 200℃, reaction time more than 8h, the ratio of glycerin and water more than 1, most CoFe₂O₄ nanoparticles are the octahedral structure, and the crystal structure is more perfect, the distribution of particle size is narrow.更多还原