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Yu J.,Dalian University of Technology | Gao J.,Dalian University of Technology | Xue F.,Dalian University of Technology | Yu X.,Dalian University of Technology | And 7 more authors.
RSC Advances | Year: 2015

Silicon nanoparticles (Si NPs), silicon nanosheets (Si NSs), and silicon nanoribbons (Si NRs) were fabricated by means of DC arc-discharge under diverse atmospheres (hydrogen, mixtures of hydrogen and inert gas). It is shown that these as-prepared Si NPs are approximately 5-50 nm in diameter, Si NSs are about 10-30 nm in width and about 2.8 nm in thickness, and Si NRs consist of fine sheets with a length as long as 200 nm, width of 13 nm, and thickness of 3.1 nm. BET measurements reveal that the specific surfaces are 110.9, 108.8, and 164.2 m2 g-1 for Si NPs, Si NSs, Si NRs, respectively. Formation mechanisms for polymorphic Si nanostructures are elucidated, revealing that the anisotropic or isotropic growth of Si nanostructures is greatly induced by high energetic inert gas and hydrogen atoms, and finally results in the formation of polymorphic Si nanostructures. A visible down-shift of Raman frequency for these Si nanostructures is mainly attributed to the size effect. The band gaps are experimentally measured as 2.89 eV (Si NPs), 2.92 eV (Si NSs), and 3.02 eV (Si NRs) for direct transition, and 1.99 eV (Si NPs), 1.26 eV (Si NSs), and 1.36 eV (Si NRs) for indirect transition. These are noticeably enlarged with respect to bulk Si (1.1 eV). © The Royal Society of Chemistry 2015. Source


Shah A.,Dalian University | Ding A.,Dalian University | Ding A.,Ningbo Branch of China Academy Ordnance Science | Wang Y.,Dalian University | And 7 more authors.
Carbon | Year: 2016

Influences of the arrayed carbon fibers (CFs) and gradiently dispersed Fe nanoparticles (NPs) inside epoxy resin (ER) matrix on the microwave absorption and mechanical properties were investigated. As a microwave absorbent, the Fe NPs were synthesized by an arc discharge plasma method and subsequently surface-modified by using of silane coupling agent (KH-550) to improve their dispersion in organic ER matrix. To measure the naturalistic electromagnetic and mechanical properties of such nanocomposite plates, a series of square plates (20 × 20 cm2) were fabricated by filling the modified Fe NPs (30 wt.%) with/without orientated CFs at different mass percentages (0, 1.38 wt.%, 2.76 wt.% and 5.52 wt.%) into the ER matrix. The excellent microwave absorption of nanocomposite plate occurred as the direction of CFs was vertical to that of incident microwave, in such case the multi-reflections of microwave were caused by CFs and favors to create a great absorption probability to Fe NPs. A well matched input impedance of the plate to air is necessary for the effective entrance of incident microwave and to be attenuated by the structural resonance and electromagnetic losses. The input impedance of nanocomposite plate is mainly determined by the content of absorbent (Fe NPs with a gradient dispersion), CFs (with orientations to incident microwave, i.e. vertical, parallel or perpendicularly cross-linked to each other) and the geometric configuration (sizes of the plate, distribution of each components, etc.). It was figured out that the nanocomposite plate (30 wt.% of Fe NPs, 5.52 wt.% of CFs vertical to incident microwave) exhibits a higher reflection loss (RL) of -26.8 dB at 4.9 GHz, in which the structural resonances, appropriate conductivity, dielectric polarization and impedance matching were involved. The effects of gradiently dispersed Fe NPs and the arrayed CFs with orientations on the electromagnetic and mechanical properties were emphasized and investigated. © 2015 Elsevier Ltd. Source


Qian K.-M.,Ningbo Branch of China Academy Ordnance Science | Hao J.,Ningbo Branch of China Academy Ordnance Science | Ji S.,Ningbo Branch of China Academy Ordnance Science | Zhang Y.-S.,Ningbo Branch of China Academy Ordnance Science | And 4 more authors.
Advanced Materials Research | Year: 2014

The composition and microstructure of nanocrystalline soft magnetic materials with different components were analyzed and calculated in detail by using the method of micro-structural analysis and thermal magnetic analysis. The results show that the micro-structural parameters of the nanocrystalline soft magnetic materials are closely related to their chemical composition. The internal mechanism of the chemical composition affecting on the micro-structural parameters were explained by the crystallization process of amorphous materials and the phase transition kinetics, respectively. © (2014) Trans Tech Publications, Switzerland. Source


Qian K.M.,Ningbo Branch of China Academy Ordnance Science | Hao J.,Ningbo Branch of China Academy Ordnance Science | Hao J.,Zhejiang University | Ji S.,Ningbo Branch of China Academy Ordnance Science | And 5 more authors.
Advanced Materials Research | Year: 2013

The new Nd-Fe-B magnets were prepared by powder metallurgical processing. The thermal stability and magnetic properties were found to be remarkably improved after annealing at 680 °C for 2 h. The Br, and Hc, BH of annealed magnets were improved by -0.04 T, 132 KA·m-1, 22 KJ·m-3, from 1.25 T, 882 KA·m-1, 286 KJ·m-3 of the as-sintered magnets, respectively. The losses and average temperature coefficients of magnetic properties were very low at 373 K. Compare with the as-sintered magnets, the magnetic property losses of the annealed magnets decreased by half at different temperature. Scanning electron microscopy on magnets did reveal a noticeable difference in phase-morphology, and found that the improvements of thermal stability and magnetic properties can be attributed to the change of magnetic domain wall motion, composition, stray demagnetizing fields, and microstructure. The new Nd-Fe-B preferment magnets are promising to use in the all-electric bus hub direct drive motor © (2013) Trans Tech Publications, Switzerland. Source

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