【作者】 杨勇；

【导师】 李发伸；

【作者基本信息】 兰州大学 ， 凝聚态， 2010， 硕士

【摘要】 随着科技的飞速发展,人们对材料的研究已深入到纳米级别。纳米磁性材料由于其独特的性质在生物医学、磁流体、电磁波吸收、磁记录等领域有着广阔的应用前景。众所周知,化学方法是制备磁性纳米颗粒的最有效的方法之一,这不仅因为其设备简单且成本低廉,而且还容易得到新颖的结构。因此,纳米磁性材料的化学法制备及性质研究也就越来越多地受人们关注。本文通过化学法制备了单分散FeNi合金纳米颗粒、枝状CoNi微米花和FeCo合金纳米片,并对其磁性进行了研究。主要结果如下：1.高温液相还原法制备单分散FeNi合金纳米颗粒及其磁性研究通过高温液相还原法制备出了单分散FeNi合金纳米颗粒。颗粒大小可以在5-13 nm之间通过改变表面活性剂TOP(三辛基膦)的用量来调控,粒径分布均匀,饱和磁化强度为20-40 emu/g。还原剂的种类影响产物中Fe的含量,当用1,2-十二烷二醇做还原剂时,产物中Fe的含量要远少于反应前投入的量。较长的反应时间(>5小时)会导致大量的氧化物的形成,不利于合成FeNi合金。2.枝状CoNi微米花的制备及其磁性、晶体结构研究通过水合肼还原法制备出了大小在5μm左右的单晶枝状Co0.96Ni0.04合金微米花,且微米花由大小在2μm左右长、500 nm左右厚且具有枝状结构的“叶片”所组成。XRD结果表明微米花中同时存在HCP和FCC相,由室温磁滞回线得出磁化强度(Ms)和矫顽力(Hc)分别为153 emu/g和166 Oe。反应温度影响着产物的结晶,温度越高结晶越好,枝状结构更加明显,当反应温度为76℃时出现部分六角对称的雪花状微米颗粒。Co1-xNix中Ni的含量x决定了样品的形貌和相成分。随着x由0增加到0.5时,样品的晶体结构由HCP和FCC的混合相转变为纯的FCC相,枝状结构逐渐消失并且形貌由枝状微米花转变为球形颗粒。通过超声可以破坏Co0.96Ni0.04颗粒的花状结构,同时得到具有(0 002)取向的2μm左右长、500 nm左右厚的枝状结构微米片。3.片状FeCo纳米颗粒的制备及FeCo合金纳米片/石蜡复合样品的微波吸收性质研究通过水合肼还原法在66℃下制备出了被轻度氧化、厚度在24 nm左右、直径在100 nm左右的FeCo合金纳米片,矫顽力(Hc)为76 Oe,饱和磁化强度(Ms)为143 emu/g。同时研究了反应温度对反应产物形貌和相成分的影响,当反应温度为86和76℃下,得到了FeCo合金微米多面体和纳米片的混合物,而在56℃下得到了被严重氧化的FeCo合金纳米片研究了包含10 vol.%、35 vol.%、60 vol.%FeCo纳米片的FeCo合金纳米片/石蜡复合物的微波电磁性质和微波反射吸收性质。复合物的复介电常数和磁导率随着体积分数的增加而增加。同时比较了不同体积分数下的微波反射吸收性质。体积比为10 vol.%的样品在11.1 GHz处、4.0 mm的厚度下得到了-4.6 dB的最小反射吸收,体积比为35 vol.%的样品在13.4 GHz处、1.5 mm的厚度下得到了-35.0 dB的最小反射吸收,在频率为9.9-16.6 GHz、厚度1.3-1.8 mm的范围内得到了小于-20 dB的反射吸收。体积比为60 vol.%的样品在8.8 GHz处、1.5 mm的厚度下得到了-35.4 dB的最小反射吸收,在频率为6.3-9.9 GHz、厚度1.4-2.0 mm的范围内得到了小于-20 dB的反射吸收。更多还原

【Abstract】 With the rapid development of technology, the research work on materi-als has touched nano-scale. Owing to the distinct properties, Magnetic nano-scaled materials have an extensive prospect on biomedicine, magnetic fluid, electromagnetic wave absorption, magnetic recording, and so on. It is known that chemical method is the most effective way for the fabrication of mag-netic nanoparticles due to the simple device, low cost and the possibility of obtaining novel structure. Therefore, the chemical synthesis and investigation of magnetic nano-scaled materials are drawing more and more attention. In this work, monodisperse FeNi nanoparticles, dendritic CoNi microflowers and FeCo nanoplates were synthesized by chemical method and their magnetic properties were investigated as well. The main results are as follows:1. Synthesis of monodisperse FeNi nanoparticles by high temperature solution reduction method and investigation of their magnetic propertiesmonodisperse FeNi nanoparticles were synthesized by high tempera-ture solution reduction method. The size of particles could be tuned by changing the amount of surfactant TOP (trioctylphosphine) from 5-13 nm with the Ms variation from 20-40 emu/g.The content of Fe in FeNi nanoparticles is influenced by the type of reductant. There is much less Fe in the product than that in the original solvent when 1,2-Dodecanediol is used as reductant.A long time (more than 5 hours) of reaction lead to a large amount of oxidant and is not good to form FeNi particles.2. fabrication, investigation of magnetic properties and crystal structure of den-dritic CoNi microflowers Dendritic Co0.96Ni0.04 microflowers with the size of 5μm were fab-ricated by chemical reduction method using hydrazine as reductant. The microflowers were composed of dendritic "leaves" (2μm in length,500 nm in thickness). The XRD results revealed the coexistence of HCP and FCC phase. The Saturation magnetization (Ms) and coercivity (Hc) of as pre-pared flowers are 153 emu/g and 166 Oe respectively obtained form room temperature hysteresis loop.The crystallization are affected by the reaction temperature, a higher temperature benefits the crystallization and dendritic structure. Sixfold-symmetric snowflake were formed at the reaction temperature of 76℃.The Ni content of Co1-xNix plays a crucial role in morphology control. With the decrease of x from 0 to 0.5, the coexistence of HCP and FCC phase was replaced by pure fcc phase, accompanied by a transition from dendritic micro-flowers to aggregated spheric particles.The flower-like structure could be decomposed by the ultrasonic. Den-dritic "leaves" (2μm in length,500 nm in thickness) were obtained after a ultrasonic process. 3. Fabrication of FeCo nanoplates and the microwave absorption properties of FeCo nanoplates/paraffine wax compositesFeCo nanoplates (24 nm in thickness,100 nm in diameter) containing slight amount oxidation were synthesized at 66℃by chemical reduction method using hydrazine as reductant. The Saturation magnetization (Ms) and coercivity (Hc) of as prepared nanoplates are 143 emu/g and 76 Oe re-spectively. Additionally, the influence of reaction temperature on morphol-ogy were investigated. The mixture of micro-polyhedron and nanoplates were obtained at 76 and 86℃, while nanoplates seriously oxidized were obtain at 55℃.The microwave electromagnetic properties and microwave absorption properties of FeCo nanoplates/paraffine wax composites with the metalic volume fraction of 10 vol.%、35 vol.%、60 vol.%were investigated. The relative permittivity and permeability of the composites increase with the volume fraction increasing. Meanwhile, the dependence of microwave ab-sorption properties on volume fraction was also explored. For the composite with the volume fraction of 10 vol.%, a minimum reflection loss value of-4.6 dB was obtained at 11.1 GHz with the matching thickness of 4.0 mm. For the composite with the volume fraction of 35 vol.%, a minimum reflec-tion loss value of-35.0 dB was obtained at 13.4 GHz with the matching thickness of 1.5 mm, the bandwith of frequency corresponding to the re-flection loss less than-20 dB is 9.9-16.6 GHz with the matching thickness from 1.3-1.8 mm.For the composite with the volume fraction of 60 vol.%, a minimum reflection loss value of-35.4 dB was obtained at 8.8 GHz with the matching thickness of 1.5 mm, the bandwith of frequency correspond-ing to the reflection loss less than-20 dB is 6.3-9.9 GHz with the matching thickness from 1.4-2.0 mm.更多还原