Fe_3O_4磁流体制备及磁性能研究

采用共沉淀法制备了3种不同粒径的Fe3O4纳米粒子,并分别将其分散在水中制备成磁流体.采用超导量子干涉仪分别测量了不同粒径磁粒子及其磁流体的磁性能.实验结果显示:粉末状Fe3O4粒子的比饱和磁化强度和矫顽力均随粒径的增加而增大;磁流体中的磁粒子比饱和磁化强度也随着粒径的增加而增大,但3种样品的矫顽力均为零,显示出超顺磁性;相同粒径的Fe3O4粒子,在磁流体中的比饱和磁化强度较粉末状态时为低.     

微波辐射乳液聚合制备磁性高分子微球

用化学共沉淀法制备了Fe3O4纳米粒子,并用油酸和十二烷基硫酸钠对Fe3O4纳米粒子进行表面修饰,得到了稳定的水分散性纳米Fe3O4磁流体。在Fe3O4磁流体存在下,以苯乙烯和丙烯酰胺为单体,采用微波辐射乳液聚合法制备了Fe3O4/聚(苯乙烯-丙烯酰胺)磁性高分子微球,表征了磁性高分子微球的形态与结构,研究了磁性高分子微球的粒径、热稳定性、磁含量与饱和磁化强度。研究发现,在选定合适的聚合条件下,通过微波辐射乳液聚合法可以制得粒径为70 nm~80 nm、磁含量为18.2%的磁性高分子微球。     

表面活性剂对磁流体稳定性及外层包覆结构的影响

采用化学共沉淀法制备粒径分布均匀的纳米Fe3O4颗粒,用油酸钠和聚乙二醇4000(PEG4000)对纳米Fe3O4颗粒进行表面修饰,制得分散稳定的纳米Fe3O4磁流体,通过电动电位(Zeta电位)、粒径测试、离心沉淀、红外光谱分析(FT-IR)和热分析(TG)对修饰后的纳米Fe3O4颗粒进行了稳定性能评价与结构表征。结果表明,油酸钠与纳米Fe3O4颗粒存在两种不同类型的化学键作用;增大油酸钠加入量不会改变Fe3O4颗粒表面包覆结构,但是,其在纳米Fe3O4颗粒表面的吸附量呈先增加后降低的趋势;PEG4000物理吸附于油酸钠包覆的纳米Fe3O4颗粒表面,PEG4000的加入会进一步提高磁流体的稳定性。     

油酸钠基纳米Fe3O4磁流体制备、表征及应用

采用化学共沉淀法制备了Fe3O4磁性纳米粒子。以油酸钠为基体的Fe3O4磁流体具有良好的分散效果。利用X衍射仪（XRD）和透射电镜（TEM）分别对磁性粒子的物相、结构及粒径进行了分析，证实其为纯相Fe3O4粒子且粒径约为8nm。采用振动样品磁强计（VSM）测得包覆油酸钠前后的Fe3O4粒子饱和磁化强度（Ms）分别为60...     

纳米Fe3O4/聚苯胺复合粒子的制备及其磁性能研究

用水解沉淀法制备纳米Fe3O4,然后在其溶液中原位合成聚苯胺,得到纳米Fe3O4/聚苯胺复合粒子.通过XRD、TEM、JDM等测试对纳米复合粒子的形态、结构及磁性能进行了研究.实验制备的纳米Fe3O4粒子粒径为30nm左右,在其表面沉积聚苯胺后,复合粒子的粒径达到了50nm左右.与纳米Fe3O4粒子相比,纳米Fe3O4/聚苯胺复合粒子的XRD峰形变得更为明锐.纳米复合粒子的磁性能表现出软磁性,与纳米Fe3O4粒子相比,矫顽力减小为0,这可以大大减小材料的磁滞损耗和退磁难度,性能得到改善.     

单分散Fe3O4纳米粒子的制备与改性的研究进展

Fe3 O4纳米粒子作为纳米材料的一种,由于其独特的光、电、磁、热性能而备受关注.综述了近几年Fe3 O4纳米粒子的制备方法,如共沉淀法、热分解法、微乳液法、水热法、氧化沉淀法、超声辅助法、溶胶-凝胶法等,同时论述了目前较受关注、研究较多的Fe3O4纳米粒子的表面修饰,以及水、油基Fe3O4纳米粒子的相转移,并展望了其进一步的研究.     

多聚磷酸钠改性水基Fe_3O_4磁流体的制备与表征

采用多聚磷酸钠(STPP)对Fe3O4磁性纳米粒子进行表面改性,制备稳定的水基磁流体。通过傅里叶变换红外光谱(FTIR)、热重分析(TG)、透射电镜(TEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)、振动样品磁强计(VSM)及Zeta电位仪对所制备的磁流体进行表征。结果表明,STPP包覆于Fe3O4磁性纳米粒子的表面,当pH>3时,粒子表面带有负电荷;磁性测试结果表明,STPP/Fe3O4磁性纳米粒子具有超顺磁性,其饱和磁化强度为62.3 A.m2.kg-1。     

油酸对微波水热法制备的纳米Fe_3O_4的影响

采用微波水热法制备纳米Fe3O4,并用油酸对其进行表面改性,获得油酸包覆的Fe3O4纳米粒子。利用XRD、FT-IR、TEM和振动样品磁强计对Fe3O4纳米粒子的结构、形貌、磁性能进行表征。结果表明:表面改性使得油酸分子中—COOH和Fe离子形成化学键;改性后的纳米Fe3O4粒子为粒度均匀的球形,具有良好的分散性,平均粒径约8nm;该产物具有超顺磁性,饱和磁化强度为61.8emu/g。     

磁性羧甲基化壳聚糖纳米粒子的制备与表征

以化学共沉淀法制备了Fe3O4纳米粒子,壳聚糖经羧甲基化改性后接枝在Fe3O4颗粒表面,得到了磁性羧甲基化壳聚糖(Fe3O4/CMC)纳米粒子.利用透射电镜(TEM)、X射线衍射(XRD)、傅立叶红外光谱(FT-IR)及磁性测试对产物进行了表征.TEM表明Fe3O4纳米粒子被CMC包覆,粒径约10 nm;XRD分析表明复合纳米粒子中磁性物质为Fe3O4;FT-IR表明壳聚糖发生羧甲基反应以及在Fe3O4表面的接枝反应.Fe3O4/CMC纳米粒子具有超顺磁性,比饱和磁化强度25.73 emu/g,有良好的磁稳定性.     

相反转工艺制备Fe_3O_4/P(St-BA)复合微球的研究

采用共沉淀法制备了油酸修饰的Fe3O4纳米粒子,并采用相反转工艺制备了Fe3O4/P(St-BA)复合微球。用透射电镜(TEM)和热失重(TGA)方法表征了Fe3O4纳米粒子、Fe3O4/P(St-BA)复合微球的形貌和Fe3O4含量。TEM显示大部分Fe3O4粒子被包覆在复合微球内部,同时有部分Fe3O4粒子嵌在微球表面。研究表明:Fe3O4/P(St-BA)复合微球具有良好的磁响应性,油酸量为0.4g修饰的Fe3O4粒子在混合单体中分散效果好。粒度测试结果显示转相水体系中聚乙烯醇和十二烷基硫酸钠复配制备的微球粒径较小且分布较窄;转相过程提高转速微球平均粒径变小,粒度分布变窄。     

Measurement of the Viscosity of Dilute Magnetic Fluids

The capillary tube viscometer is used to measure the viscosity of aqueous magnetic fluids under the influence of parallel and perpendicular magnetic fields. The effects of the volume fraction of the suspended magnetic particles, the concentration of surfactants, and the external magnetic field strength, as well as the orientation, on the viscosity of the magnetic fluid are analyzed. The experimental results show that the viscosity of the sample magnetic fluids increases with increases in the concentrations of suspended magnetic particles and surfactants. The external magnetic field is also an important factor that affects the viscosity of the magnetic fluid. The viscosity first increases with the magnetic field and finally approaches a constant as the magnetization attains a saturation state. For the same magnetic fluid, the viscosity in a perpendicular magnetic field is larger than that in a parallel magnetic field for the same magnetic field.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China     

Strengthening liberation and separation of magnetite ore via magnetic pulse pretreatment: An industrial test study

Performing ore pretreatment before grinding is particularly crucial for improving mineral liberation and conserving energy. This study proposed an innovative magnetic pulse pretreatment (MPP) technology that primarily used the magnetostrictive effect in an alternating magnetic field to enhance mineral liberation. The effect of MPP on the liberation degree and magnetite separation for magnetite ore were systematically investigated. The results show that the size and volume of the magnetic mineral particles in the ore due to the stretching effect of the alternating magnetic field resulted in microcracks at the interface between different minerals. Compared with the unpretreated process in an industrial test, increment in the −0.043 mm content of the ball mill discharge increased by 3.33 percentage points, increment in the liberation degree of magnetite across the entire particle size range increased by 5.82 percentage points, and increment in the iron concentrate grade increased by 1.22 percentage points, with an error range of 0.1%, due to MPP. The industrial application of MPP brings an enormous economic benefit potential to iron ore utilization.     

包覆双层表面活性剂Fe3O4纳米粒子的制备及性能研究

为制备稳定的水基磁流体,分别以月桂酸、油酸钠、十二烷基苯磺酸钠作为外层表面活性剂,对包油酸的Fe3O4粒子进行了再包覆.将得到的双层包覆的Fe3O4粒子分别分散在水中,发现以十二烷基苯磺酸钠为外层表面活性剂的磁粒子制成的水分散液的稳定性最佳.利用IR研究其吸附机理,结果显示:内层的油酸通过化学键合吸附在磁粒子表面,外层的十二烷基苯磺酸钠通过物理作用吸附在包油酸的Fe3O4粒子表面.     

Heating Effect in Biocompatible Magnetic Fluid

This work is devoted to the study of heating of a biocompatible magnetic fluid due to time-varying magnetic induction. The adsorption of dextran on magnetite particles was confirmed by IR spectroscopy. A considerable thickness of the surfactant layer (oleate sodium + dextran) of about 4.3 nm prevents the formation of clusters made of nanomagnetic particles as evidenced by the fact that no maxima of the ultrasound wave absorption coefficient corresponding to cluster formation have been detected. The results show that the observed heating effect may be applied in hyperthermia treatments especially in the preferable region of 500 – 800 kHz. An “H ²– law” observed for the dependence of the SAR on the square of the amplitude of the magnetic field demonstrates the presence of superparamagnetic particles in the ferrofluid. Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5-8, 2005, Bratislava, Slovak Republic.     

尖劈状磁场中磁流体磁性微粒的受力分析

通过有限元方法对尖劈形磁场中磁流体磁性微粒所受的磁场力进行了数值分析,分别给出了磁场气隙处磁通量和磁场强度随不同气隙宽度和夹角的变化规律.在此基础上,利用虚位移法和麦克斯韦应力张量法计算磁流体磁性微粒在气隙上方所受的磁场力.结果表明,随着气隙宽度的减小,磁通量、磁场强度和磁场力明显增加;随着气隙夹角的增加,磁通量、磁场...     

Control of nonmagnetic particles using a magnetic field

Abstract

A force and/or torque are induced in a material under the imposition of a magnetic field. Their magnitudes are different from those acting on the surrounding materials because of the difference in their physical properties. Therefore, a magnetic field is a powerful tool for controlling a second phase in a mother phase such as particles suspended in a liquid. In this paper, we focus on two processes. The first one is a novel method of magnetic filtration in which schwertmannite particles in wastewater are controlled using a magnetic field. The second one is a refining process for a metallic alloy structure during solidification in which solid particles suspended in the liquid phase are controlled using the force excited by the simultaneous imposition of a magnetic field and alternating current.     

Adsorption of polymer coated magnetite composite particles onto carbon nanotubes and their magnetorheology

Polymer coated nano-sized magnetite (Fe₃O₄) particles with multiwalled carbon nanotube (MWNT) nanohybrid were prepared by four step procedures in this study. Initially, magnetic particles were synthesized by a co-precipitation method with ammonium hydroxide and oleic acid, and then the produced particles were coated with polyacrylamide (PAAm). Finally PAAm coated magnetite particles (Mag-PAAm) were physically adsorbed onto multiwalled carbon nanotubes (MWNT) under ultrasonication. Transmission electron microscopy (TEM) was used to investigate the formation of Mag-PAAm-MW nanohybrids nanostructure, confirming that prepared Mag-PAAM particles were well adsorbed onto the surfaces of MWNT. In addition, MR characteristics of PAAm coated magnetite particles with MWNT (Mag-PAAm-MW) nanohybrids were investigated under six different external magnetic field strengths via a rotational rheometer, exhibiting typical MR behavior of yield stress and shear stress.     

磁场诱导和晶种联合法制备链状Fe_3O_4

以粒径为700nm的球形Fe3O4为晶种,将晶种加入到含有FeSO4.7H2O、FeCl3.6H2O与尿素的混合溶液中,在磁场诱导下制备链状Fe3O4。研究了磁场强度、晶种添加量、分散剂聚乙烯吡咯烷酮(PVP)质量浓度以及反应时间对产品形貌的影响。研究结果表明,随着磁场强度的增大、晶种量的增加,链状粒子数目显著增多;适量的PVP能使链状粒子分散平行排列。合成链状Fe3O4粒子的最佳工艺条件为磁场强度0.35T,晶种用量10%,PVP质量浓度7.5g/L,反应18h。磁性能测试表明,该链状Fe3O4粒子具有亚铁磁性,磁饱和强度为72.3emu/g,矫顽力为381Oe。     

不同粒径超顺磁性氧化铁纳米粒子的合成及其在交变磁场中的磁热效应

采用多醇热解法制备3种不同粒径的超顺磁性氧化铁纳米粒子(SPIONs),合成的SPIONs含Fe_3O_4晶相,分散性好,平均粒径分别为8.7,12.6nm和15.3nm,且在300K下,3种SPIONs均呈超顺磁性。将不同粒径、不同浓度的SPIONs水分散液置于频率为425kHz、磁场强度为5.3kA·m^-1的交变磁场(ACMF)中进行升温实验。探讨比能量吸收率值与SPIONs粒径之间的关系,计算布朗弛豫时间及尼尔弛豫时间。结果表明:SPIONs水分散液的升温速率随SPIONs的粒径增大而增大,初始温度为20℃时,粒径为8.7,12.6nm和15.3nm的SPIONs水分散液(2mg·mL^-1)在480s内温度分别升高了25,27,35℃。尼尔弛豫时间比布朗弛豫时间小,说明磁热效应主要来自于尼尔弛豫损耗。SPIONs粒径越大,比能量吸收率SAR值越高,最高可达810W·g^-1,且SAR值与SPIONs水分散液的浓度呈负相关关系。     

Numerical simulation of chainlike cluster movement of feeble magnetic particles by induced magnetic dipole moment under high magnetic fields

In this paper, the motion of a chainlike cluster of feeble magnetic particles induced by high magnetic field is discussed on the basis of the results of numerical simulations. The simulations were performed on glass particles with a diameter of 0.8 mm; and the viscosity, applied magnetic field and magnetic properties of the surrounding medium were changed. In addition to the magnetic field and the difference in magnetic susceptibility between the particles and the surrounding medium, the obtained results indicate that the viscosity is an essential factor for the formation of the chainlike alignment of feeble magnetic particles. We also carried out simulations using glass particles with a smaller diameter of 0.1 mm. Chainlike clusters were produced similar to those of ferromagnetic particles formed in a ferromagnetic fluid.