Papers by Keyword: Magnetic Composites

Abstract: The fabrication of gold-loaded magnetite/silica core-shell particles was presented in this paper. First, 250 nm of magnetic Fe₃O₄ nanoparticles were prepared by solvothermal reaction. Then, the Fe₃O₄ particles were coated by SiO₂, and Au nanoparticles (AuNPs), respectively. The core-shell structure of these microspheres was confirmed by transmission electron microscopy (TEM) and Power X-ray diffraction (XRD). The magnetic property of the core-shell microspheres was investigated at room temperature. The results indicated that the core-shell composites had a well-retained high magnetic intensity, thus it can be easily separated from the mixture in less than a few minutes by simply using a magnet.

Abstract: Several samples of magnetic hydrogels (also known as ferrogels) are prepared, and their magnetic properties are examined. Polyacrylamide gel is used as the base. Gel matrices are filled with the nanopowder: iron particles with the mean size about 30 nm. The magnetization curves of the samples are measured at different stages of de-swelling. The dependencies of such parameters of magnetization curves as coercive field, remanent magnetization from concentration of magnetic particles in the sample along the process of drying were investigated.

Abstract: Several species of magntic hydrogels (ferrogels) are prepared, and their magnetic and magnetoelastic properties are examined. Three substance are used as the bases: agarose, polyacrylamide and Pluronic. All the gel matrices are filled with the same nanopowder: iron particles with the mean size about 30 nm. The critical concentrations of the magnetic phase, above which the normal gel networks cease to form, are estimated. The magnetization curves of the samples are measured at different stages of de-swelling, and their elastic properties are tested under a uniform magnetic field. The results indicate field-induced rigidity of magnetic hydrogels

Abstract: Magnetic composites, especially ferrite composites, are of great interest for embedded inductor applications. In this paper, the Ni-Zn ferrite particles (Ni1-xZnxFe2O4, x=0.2～0.8) with different zinc contents were synthesized via chemical coprecipitation method followed by modification with γ-glycidoxypropyl trimethoxysilane (KH-560). The particles were investigated by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The results show that the prepared Ni1-xZnxFe2O4(x=0.2～0.7) have good spinel structures, higher saturation magnetization (35.18～77.69 emu/g) and smaller hysteresis hoops, while Ni0.2Zn0.8Fe2O4 grains exhibit some paramagnetic behaviors, such as almost zero hysteresis and non-saturated magnetization. Next Ni1-xZnxFe2O4 magnetic/epoxy composites with different volume fraction of ferrite were prepared and their magnetic performances at high frequencies were characterized by an Agilent E4991A impedance analyzer (USA). It is found that with zinc content in Ni1-xZnxFe2O4 increasing from 0.2 to 0.7, the real part of the complex permeability (μ′) of these composites increase first and then decrease with the frequency increasing gradually from 10 MHz to 1 GHz. Of all, the epoxy composites with filler of Ni0.6Zn0.4Fe2O4 or Ni0.5Zn0.5Fe2O4 ferrite show good frequency stability, and the composites including Ni0.4Zn0.6Fe2O4 ferrite have the highest permeability, and the maximal value at the frequency of 100 MHz is 5.55 when the volume faction is 42.75%. The imaginary part of the complex permeability (μ′′) of all magnetic composites is low For the Ni0.2Zn0.8Fe2O4/epoxy composites, they have very low real permeability (μ′～1) and imaginary permeability (μ″≤0.2).

Abstract: Methyl tert-butyl ether (MTBE) is the most prevalent contaminant found in soil and groundwater and classified as a suspect carcinogen by Environmental Protection Agency (USEPA). Due to high water solubility, MTBE is not easy to be removed from contaminated groundwater. This study aimed to develop a novel and simple method to coat TiO2 photocatalyst on magnetic particles, evaluate its photocatalytic degradation effect on MTBE irradiated under visible (λ= 419 nm), and recollect easily from hydroponic systems with magnet. Iron nanoparticles are synthesized and added to TiO2 sol-gel followed by 500 oC calcinations. The results showed that the novel magnetic composite TiO2/Fe3O4 had significantly efficiency of photocatalytic degradation (91.6 %) for 10 ppm of MTBE under visible light irradiation and the recovery rate was relatively high as we recollected easily from recycled water using magnet.

Abstract: The frequency profile of complex permeability (μr) and permittivity (εr) and their relationship with microwave absorbing properties are investigated in soft magnetic metal-polymer composite materials. The Fe-Si-Al alloy powder was forged by an attrition mill to get the flaky shape. The composite sheet was fabricated in which the flaky powder was dispersed in the polymer and aligned in the direction perpendicular to the electromagnetic wave propagation. We found that dielectric loss (εr") spectra for composite sheets can be controlled by combining the aspect ratio of the flaky powder and the contents of the filler. The permittivity (εr). of magnetic composite was increased with attrition milling time. The maximum attenuation peak of reflection loss is shifted to lower frequency ranges as the aspect ratio increased, while the value of the maximum attenuation peak gets smaller gradually. From these results, we could design a noise absorber sheet (t=1.0 ㎜) for a quasi-microwave band, which is impedance matched at 1.8 ㎓ with respect to -7.7 ㏈ reflection loss.