Strontium ferrites/graphene (SrFe12O19/G) composites were synthesized by a facile one-step surfactant assisted hydrothermal method. The structure, magnetic properties and electromagnetic parameters of the as-prepared composites were evaluated. Uniform SrFe12O19 nanoparticles with a diameter of 60–70 nm were well distributed on the graphene. The formation of SrFe12O19 nanoparticles and the reduction of graphene oxide were accomplished simultaneously. The re-stacking of graphene sheets and the aggregation of SrFe12O19 nanoparticles were inhibited. The as-obtained composites exhibited better absorbing properties than the pristine SrFe12O19 particles due to the synergistic effect of SrFe12O19 and graphene. The minimum reflection loss (RL) of SrFe12O19/G composites with the thickness of 3 mm reached −34.8 dB at 13.6 GHz, and the effective absorption bandwidth (RL < −10 dB) was 5.7 GHz. However, the minimum RL of the SrFe12O19 particles only reached −13.5 dB, and the effective absorption bandwidth was 4.6 GHz. A possible mechanism for the enhanced absorbing performance was proposed.
Yanhui Wei,Mingyue Liu,Jiaxing Wang,Guochang Li,Chuncheng Hao,Qingquan Lei
For high voltage direct current (HVDC) cable, a semi-conductive layer lies between the conductor and the insulation layer; as the charge migrates the path from the conductor to the insulation material, it will affect space charge injection. In this work, the research idea of changing the injection path of moving charges within semi-conductive layer by magnetic particles was proposed. Semi-conductive composites with different SrFe12O19contents of 1 wt.%, 5 wt.%, 10 wt.%, 20 wt.%, and 30 wt.% were prepared, and the amount of injected charges in the insulation sample was characterized by space charge distribution, polarization current, and thermally-stimulated depolarization current. The experimental results show that a small amount of SrFe12O19can significantly reduce charge injection in the insulation sample, owing to the deflection of the charge migration path, and only part of the electrons can enter the insulation sample. When the content is 5 wt.%, the insulation sample has the smallest charge amount, 0.89 × 10−7C, decreasing by 37%, and the steady-state current is 6.01 × 10−10A, decreasing by 22%. When SrFe12O19content exceeds 10 wt.%, the charge suppression effect is not obvious and even leads to the increase of charge amount in the insulation sample, owing to the secondary injection of charges. Most moving charges will deflect towards the horizontal direction and cannot direct access to the insulation sample, resulting in a large number of charges accumulation in the semi-conductive layer. These charges will seriously enhance the interface electric field near the insulation sample, leading to the secondary injection of charges, which are easier to inject into the insulation sample.Keywords:HVDC cable;semi-conductive composites;SrFe12O19;space charge accumulation
This study attempts to prompt the formation of microorganism films on flexible textile-based anodes and enhances the performance of living microorganisms by introducing magnetic properties to the anodes. A magnetic and electrically conductive anode for a microbial fuel cell is designed and fabricated by encapsulating uniformly dispersed SrFe 12 O 19 nanoparticles into the poly(vinyl alcohol- co -ethylene) (PVA- co -PE) nanofibers and forming a three-dimensional (3D) polypyrrole (PPy) network on the surface of flexible composite nanofiber based fabric. A dual-chamber MFC equipped with the magnetized anode shows a maximum power density of 3317 mW m −2 , which is significantly larger than that of the non-magnetized anode (2471 mW m −2 ). This study demonstrates that the hard-magnetic anode providing an inherent magnetic field can greatly promote bio-electrochemical reaction rates of E. coli , and decrease the anode charge transfer resistance in a MFC system.
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