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Transport Critical Current Density of Bi1.6Pb0.4Sr2Ca2Cu3O10)/Ag Superconductor Tapes with Addition of 50 and 70 nm MgO
摘要： added size 50 average particle and 70 nm were MgO nanoparticles with into Bi1.6Pb0.4Sr2Ca2Cu3O10(MgO)x/Ag superconductor tapes and sintered at 845 oC for 50 and 100 h. The effect of sintering time on the transport critical current density (Jc) was investigated. Jc of the tapes were measured in zero-field between 30 and 77 K and under magnetic fields at 77 K. The phase and microstructure of the tapes were examined by X-ray diffraction method and scanning electron microscopy, respectively. All tapes showed plate-like grains and a larger plate-like grain was observed in the tapes sintered for 100 h. Jc of the MgO added tapes was higher than those of the non-added tapes. Jc of the non-added tape sintered for 100 h was 10820 A/cm2 at 30 K and 1262 A/cm2 at 77 K. Jc of the tapes sintered for 100 h was higher than the tapes sintered for 50 h. The 50 nm MgO added tapes showed a higher Jc than the 70 nm MgO added tapes. Jc for the 100 h sintered MgO (50 nm) added tape was 22710 and 3070 A/cm2 at 30 and 77 K, respectively which are higher than that of the 100 h sintered MgO (70 nm) added tape. The improved Jc was attributed to the increase in flux pinning potential and improvement in the microstructure due to the addition of nano-sized MgO. This work showed the importance of the size of the added nanoparticles to the transport current properties of these superconductors.
关键词： flux pinning,transport critical current density,nano MgO,size effect
更新于2025-09-04 15:30:14
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Surface treeing and segmented worm model of tracking behavior in MgO/Epoxy nanocomposites
摘要： Surface tracking experiments were conducted on MgO/epoxy nanocomposites according to IEC60112. Treeing phenomenon, which was commonly observed in bulk insulators, was detected on the surface of tracked samples via optical microscopy. Tree branches were further found to be segmented tracking channels by scanning electron microscopy, which consisted of a series of ablation holes along electric field, i.e. wormholes. According to distribution of surface trees, tracking area was divided into three typical regions. Region A, close to electrodes, was barely ablated. Region B, which directly connects electrodes, exhibited paralleled tracking channels. Region C, which is the outer annular ablated region, is full of crossed tracking channels. At the beginning, the initial tracking channels were demonstrated to appear at the triple junction of Region A, B and C, where electric field was supposed to be the highest. Then tracking regions spread from the junction to Region B and Region C with tracking channels segmentally growing longer and wider, indicating a segmented energy accumulation process. Tracking trees were finally formed connecting two electrodes, leading to sample failure. With addition of nano-MgO particles, wide and deep channels turned into slight but dense ones. Correspondingly, comparative tracking index (CTI) increased from 400 to 475 V with increasing nano-MgO from 0 to 10 wt%. Improved tracking resistance was obtained in nanocomposites while reduced thermal conductivity and pyrolysis characteristics were observed. Combining with results above, a segmented worm model was thus proposed to explain surface tracking performance in MgO/epoxy nanocomposites.
关键词： epoxy nanocomposites,nano-MgO,surface tracking,surface treeing
更新于2025-09-04 15:30:14