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Rapid Synthesis of W–Cr Solid–Solution by Dielectric-Barrier Discharge-Plasma-Assisted Ball Milling
S. F. Hong,Z. C. Lu,Y. H. Liu,Q. M. He,W. Jiang,M. Q. Zeng 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.12
Supersaturated solid–solutions in a W–Cr alloy system were fabricated by conventional milling and plasma milling. The differentextension mechanisms of the solid solubility that were created by ball milling with and without discharge plasma werestudied. The solid–solubility of Cr in W for the P-milling W–Cr alloy system was higher, which indicates that plasma millingpromotes the formation of W(Cr) solid–solution more easily than conventional milling. According to Miedema’s model, inthe W–Cr alloy system, the free-energy change to form a W(Cr) solid solution by plasma milling is reduced compared withconventional milling because of the heating effect of the discharge plasma. Therefore, a higher stored energy in the grainboundaries and dislocations of the W–Cr nanograins during plasma milling makes it easier to overcome the thermodynamicbarrier in the formation of a solid–solution, when compared with conventional milling.
Loss-Separation Study on Silica-insulated Gas-atomized Fe-Si-Al Soft Magnetic Composites
T. T. Xu,B. W. Zhang,Z. Shi,W. W. Guan,K. Wan,X. Y. Shi,W. Liu,H. L. Su,Z. Q. Zou,Y. W. Du 한국자기학회 2020 Journal of Magnetics Vol.25 No.2
Fe-Si-Al soft magnetic composites were composed of gas-atomized Fe-9.6wt.%Si-5.4wt.%Al alloy powders insulated with silica nanoparticles. The influence of silica insulation content on the core’s magnetic properties was studied. It was found that increasing the silica mass ratio deteriorated the effective permeability and core loss in the frequency range of 40-120 kHz, while improved the quality factor at 100 kHz and DC-bias performance. The effective demagnetizing field reflected by density and the core’s volume resistivity may cause the variations of these magnetic parameters. Loss separation fitting was performed using the Bertotti formula, indicating that silica insulation increased the hysteresis loss and reduced the eddy-current loss. The hysteresis loss took over at the frequency lower than 120 kHz in this work. With increasing the frequency, the eddy-current loss grew more quickly than the hysteresis loss. Therefore, different methods should be adopted to reduce the core loss according to the core’s application frequency.
W. Q. Liu,C. Chang,M. Yue,J. S. Yang,D. T. Zhang,Y. Q. Liu,J. X. Zhang,X. F. Yi,J. W. Chen 한국자기학회 2013 Journal of Magnetics Vol.18 No.4
Grain boundary diffusion technique with DyH₃ nanoparticles was applied to fabricate Dy-less sintered Nd-Fe-B permanent magnets with high coercivity. The magnetic properties and microstructure of magnets were systematically studied. The coercivity and remanence of grain boundary diffusion magnet were improved by 60% and reduced by 7% compared with those of the original magnet, respectively. Meanwhile, both the remanence temperature coefficient (α) and the coercivity temperature coefficient (β) of the magnets were improved after diffusion treatment. Investigation shows that Dy is preferentially enriched as (Nd, Dy)₂Fe14B phase in the surface region of the Nd₂Fe14B matrix grains indicated by the remarkable enhancement of the magneto-crystalline anisotropy field of the magnet. As a result, the magnet diffused with a small amount of Dy nanoparticles possesses enhanced coercivity without remarkably sacrificing its magnetization.
M. Q. Zeng,J. L. Tu,M. Zhu,W. Wang,J. W. Liu,Z. C. Lu 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.9
The effects of plasma discharge intensity on the microstructure evolution of ball-milled tungsten (W)–carbon (C)–cobalt (Co)mixtures and the formation mechanism of ultrathin plate-like tungsten carbide (WC) grains prepared by ball milling with andwithout plasma discharge were investigated. It was found that increasing the plasma discharge intensity during ball millingobviously promoted the formation of a thin flake-like W phase because of the electroplasticity effect and simultaneouslylowered the carburization temperature between W and C. A combination of high hardness and transverse rupture strength of92.9 HRA and 3659 MPa, respectively, was obtained for the WC–8Co alloy fabricated by plasma milling at a gas pressure of5 × 103 Pa with a dielectric barrier discharge layer thickness of 3 mm. These properties were mainly attributed to the markedlylowered activation energy of the WC phase and generation of highly oriented ultrathin plate-like WC grains by plasma milling. The combination of the flake-like structure of the plasma-milled W aggregate and high specific interfacial area and shortdiffusion distance of W/C were readily inherited by the ultrathin plate-like WC grains in the sintered WC–Co hardmetals.
Y. Q. Li,M. Yue,J. H. Zuo,D. T. Zhang,W. Q. Liu,J. X. Zhang,Z. H. Guo,W. Li 한국자기학회 2013 Journal of Magnetics Vol.18 No.3
A finite element model was built for MnBi/α-Fe nanocomposite permanent magnets, and the demagnetization curves of the magnets were simulated by micro-magnetic calculation. The microstructure of the cubic model is composed of 64 irregular grains with an average grain size of 20 nm. With the volume fraction of soft magnetic phase (t vol. %) ranged from 5 to 20 vol. %, both isotropic and anisotropic nanocomposite magnets show typical single-phase permanent magnets behavior in their demagnetization curves, illustrating good intergranular exchange coupling effect between soft and hard magnetic phases. With the increase of volume fraction of soft magnetic phase in both isotropic and anisotropic magnets, the coercive force of the magnets decreases monotonically, while the remanence rises at first to a peak value, then decreases. The optimal values of maximum energy products of isotropic and anisotropic magnets are 84 and 200 kJ/m3, respectively. Our simulation shows that the MnBi/α-Fe nanocomposite permanent magnets own excellent magnetic properties and therefore good potential for practical applications.
( Lei Zhang ),( Ji T Gong ),( Hu Q Zhang ),( Quan H Song ),( Guang H Xu ),( Lei Cai ),( Xiao D Tang ),( Hai F Zhang ),( Fang E Liu ),( Zhan S Jia ),( Hong W Zhang ) 대한소화기기능성질환·운동학회 2015 Journal of Neurogastroenterology and Motility (JNM Vol.21 No.2
Background/Aims There are increasing evidences for gastrointestinal motility disorder (GIMD) and gastric stress ulcer induced by noise stress. The present study was to investigate the reversed effect of melatonin on GIMD and gastric stress ulcer induced by noise stress and potential mechanism. Methods Noise stress was induced on rats, and melatonin (15 mg/kg) was administered to rats by intraperitoneal injection. Differences were assessed in gastric residual rate (GRR), small intestine propulsion rate (SPR), Guth injury score, cortisol, gastrointestinal hormones (calcitonin-gene-related peptide and motilin) and oxidative stress markers (superoxide dismutase and malondialde hyde) in blood plasma as well as gastric mucosa homogenate with or without melatonin. The pathological examination of gastric mucosa was also performed. Results The GRR and SPR were improved by noise stress compared with control (P < 0.05). The pathological examination and Guth injury score revealed gastric stress ulcer. Moreover, the levels of cortisol, motilin and malondialdehyde in blood plasma and malondialdehyde in gastric mucosa homogenate were increased by noise stress (P < 0.05). CGRP and superoxide dismutase activity in both of blood plasma and gastric mucosa homogenate were significantly decreased (P< 0.05). Furthermore, melatonin reversed changes in GRR, SPR, pathological examination, Guth injury score, cortisol, motilin, CGRP, superoxide dismutase activity and malondialdehyde (P < 0.05). Conclusions Melatonin is effective in reversing the GIMD and gastric stress ulcer induced by noise stress. The underlying mechanism may be involved in oxidative stress and gastrointestinal hormones. (J Neurogastroenterol Motil 2015;21:189-199)
A CMOS Frequency divider for 2.4/5GHz WLAN Applications with a Simplified Structure
Q. Yu,Y. Liu,X.P. Yu,W. M. Lim,F. Yang,X. L. Zhang,Y. Peng 대한전자공학회 2011 Journal of semiconductor technology and science Vol.11 No.4
In this paper, a dual-band integer-N frequency divider is proposed for 2.4/5.2 GHz multistandard wireless local area networks. It consists of a multi-modulus imbalance phase switching prescaler and two all-stage programmable counters. It is able to provide dual-band operation with high resolution while maintaining a low power consumption. This frequency divider is integrated with a 5 GHz VCO for multi-standard applications. Measurement results show that the VCO with frequency divider can work at 5.2 GHz with a total power consumption of 22 mW.