Synthesis and characteristics of carbon encapsulated magnetic nanoparticles produced by a hydrothermal reaction

A novel process to synthesize carbon encapsulated magnetic nanoparticles was developed by heating an aqueous glucose solution containing Fe@Au (Au coated Fe nanoparticles) or Ni nanoparticles at 160–180 °C for 2 h. In comparison with traditional methods, such a hydrothermal approach is not only simple but also able to provide functional groups such as –OH on the surface of carbon sphere. Only pure Fe nanoparticles did not favor the formation of carbon encapsulated magnetic nanoparticles due to the oxidation of Fe nanoparticles by H₂O during the reaction and their surfaces had to be coated by an Au shell in advance. The results of TEM, HRTEM, XRD, XPS and vibration sample magnetometer characterization show that uniform carbon spheres containing some embedded Fe@Au nanoparticles with a saturation of 14.6 emu/g are obtained and the size of a typical product is 200 nm. Carbon encapsulated Ni nanoparticles have been successfully prepared in the same way.     

Synthesis, characterization, and crystal structures of two new polyoxomolybdate wheel clusters

Two new polyoxomolybdates Na₅(NH₄)₁₆[Mo₅₇Mn₆(NO)₆O₁₇₄ (OH)₃(H₂O)₂₄] · 44H₂O (1) and (NH₄)₂₁[Mo₅₇Cu₆(NO)₆O₁₆₈(OH)₃(H₂O)₂₄] · 53H₂O (2) were synthesized in aqueous solution and characterized by elemental analysis, IR, TG analysis and single-crystal X-ray diffraction. They represent interesting examples of integrating and embedding magnetic 3d metal ions into the diamagnetic polyoxomolybdate host structure.     

磁放大器控制硅弧焊整流器性能的研究

本文针对硅弧焊整流器的控制性能,在分析铁磁材料特性的基础上,分别对单铁芯磁放大器和双铁芯磁放大器的结构和工作原理进行了深入的研究,提出了单铁芯磁放大器所存在的缺点以及双铁芯磁放大器的优点,使得硅弧焊整流器的设计采用双铁芯磁放大器,能够避免焊接时焊接电流波形的畸变,对提高焊接质量是有利的。     

基于磁通门传感器的铁磁探测系统设计

在核磁共振检查前需要进行无磁化确认,针对核磁共振检查所处的环境背景磁场复杂、干扰较多,系统出现误报警高、探测失效等问题,设计了基于磁通门传感器的铁磁探测系统。系统使用二次谐波法测量磁场信号,设计模拟电路进行信号相敏检测。通过积分反馈提高闭环系统的线性度和抗干扰性,探头工作在稳定的状态。采用卡尔曼滤波对背景磁场和磁异信号进行处理,提高信号信噪比,同时设计能量检测器对磁异信号进行检测。试验测试结果表明,系统在核磁共振室外复杂磁场环境可以减少设备工作时的误报警,有效探测出铁磁性物质。     

MAGNETIC MEASUREMENTS ON FERROFLUIDS

Magnetic measurements on ferrofluids can be used to determine the magnetic concentration which may be as large as 15% by volume in a very viscous fluid. Additional information on the particle size distribution parameters and the mode of magnetisation can be obtained from an analysis of the magnetisation curve. Magnetic studies are also invaluable for a correct interpretation of the magnetic dichroism, birefringence and small angle neutron scattering (SANS) data. Measurements on a ferrofluid after freezing enables the shape anisotropy to be determined and the degree of particle elongation (∼15%) calculated.     

Synthesis and characterization of a new water-soluble endohedral metallofullerene for MRI contrast agents

Water-soluble amino acid derivatives of gadolinium (Gd) endohedral metallofullerenes (AAD-EMFs), Gd@C₈₂O_m(OH)_n(NHCH₂CH₂COOH)_l (m ≈ 6, n ≈ 16 and l ≈ 8) are synthesized by a direct reaction of the pure endohedral metallofullerene Gd@C₈₂ with an excess of alkaline solution of β-alanine. The structure of the AAD-EMFs is characterized by FTIR, XPS and laser-desorption time-of-flight (LD-TOF) mass spectrometries. Water proton relaxivity analysis indicates that the longitudinal relaxivity R₁ (the effect on 1/T₁, 9.1 mM⁻¹ s⁻¹) of AAD-EMFs is higher than that of the commercial MRI contrast agent, Magnevist (gadolinium-diethylenetriaminepentaacetic acid, Gd-DTPA, 5.6 mM⁻¹ s⁻¹). The MRI phantom studies are performed to confirm the high efficiency of this sample as MRI contrast agents.     

Extraction of 2-hydroxyphenol by surfactant coated nanosized magnetic particles

A colloidal suspension of magnetic particles coated with double layer surfactant molecules was prepared, characterized and used for separation of some chemicals. The aqueous magnetic fluid was prepared by chemical precipitation method and characterized by total organic carbon analyzer (TOC), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). The TOC and TGA measurements indicate that the prepared magnetic particles are coated with surfactant molecules in double layers. The outer surfactant layer has free polar heads. TEM measurement results show that magnetic particles are nanosized. A mixture of 2-hydroxyphenol (strong polar) and 2-nitrophenol (weak polar) was chosen as the target system. Results show that the magnetic fluid can selectively adsorb 2-hydroxyphenol from the mixture, whereas the adsorption of 2-nitrophenol is insignificant. For 2-hydroxyphenol, the adsorption equilibrium can be described well by Langmuir isotherm, and the adsorption kinetic can be fitted well by a linear driving force mass transfer model.     

基于渔船监测系统的近海捕捞水产品溯源

通过对渔船监测系统的船位、航向、航速等信息挖掘,可以进行水产品溯源,保障海洋水产品的食品安全。基于渔船监测系统数据,结合渔场、沿海区划等信息,构建近海捕捞水产品溯源模型,研究渔船溯源、渔区和渔场溯源、渔获溯源,为水产品安全保障提供参考依据。     

磁力驱动器涡流损失的研究

对磁力驱动器金属隔离套在交变磁场中引起的涡流损失进行了理论计算 ,并与实测结果进行了对比。指出合理选择金属隔离套的相关参数 ,可以有效控制涡流损失的大小     

Surface-initiated atom transfer radical polymerization of methyl methacrylate on magnetite nanoparticles

The synthesis of magnetite nanoparticles coated with a well-defined graft polymer is reported. The magnetite nanoparticles with an initiator group for copper-mediated atom transfer radical polymerization (ATRP), 2-(4-chlorosulfonylphenyl) ethyltrichlorosilane (CTCS) chemically bound on their surfaces were prepared by the self-assembled monolayer-deposition method. The surface-initiated ATRP of methyl methacrylate (MMA) was carried out with the CTCS-coated magnetite nanoparticles in the presence of free (sacrificing) initiator, p-toluenesulfonyl chloride. Polymerization proceeded in a living fashion, exhibiting first-order kinetics of monomer consumption and a proportional relationship between molecular weight of the graft polymer and monomer conversion, thus providing well-defined, low-polydispersity graft polymers with an approximate graft density of 0.7 chains/nm². The molecular weight and polydispersity of the graft polymer were nearly equal to those of the free polymer produced in the solution, meaning that the free polymer is a good measure of the characteristics of the graft polymer. The graft polymer possessed exceptionally high stability and remarkably improved dispersibility of the magnetite nanoparticles in organic solvent.