Papers by Keyword: MgB2

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Authors: Xian Ping Zhang, Yan Wei Ma, Zhao Shun Gao, Dong Liang Wang, Zheng Guang Yu, Gen Nishijima, K. Watanabe, Jian Dong Guo
Abstract: Fe-sheathed MgB2 tapes were prepared by the in situ powder-in-tube (PIT) technique using nanoscale Si/N/C and SiC whisker as doping materials, respectively. It is found that the doped tapes exhibited superior field performance and higher critical current (JC) values than the undoped tapes in the magnetic field up to 12 T. Moreover, the improvement of JC for the SiC whisker doped samples was more significantly than that in Si/N/C doped tapes, while flux pinning ability enhancements were similar. It is proposed that the difference of impurity content in MgB2 matrix, which affects the grain connectivity, is responsible for JC value difference between Si/N/C and SiC whisker doped samples.
Authors: Pascal Tixador
Abstract: After the emergence of AC NbTi strands, superconducting transformers were successfully built. But the very high cost of 4 K cryogenics made these transformers economically not attractive. The high Tc superconductors (HTS), operating at much higher temperatures, change these conclusions with low cost HTS conductors. The high cost of PIT tapes and the relatively large AC losses remain issues. The second generation HTS wires, the REBCO coated conductors, are under development and achieved substantial progress recently. They operate at higher temperatures and intrinsically show lower AC losses especially for transformers. MgB2 is the third option. The magnetic flux density conditions make possible the operation at 27 K and they show low costs. This paper provides a preliminary design for an on-board 40 MVA transformer using YBCO coated conductors and MgB2 wires. Both superconducting transformers show similar volume and weight. The power density per unit mass and volume is improved by a factor about two, cryogenic included, compared to resistive systems. This makes them very attractive for on-board mobile systems. The economical point of view will be discussed based on some targets price/performance for superconductors and cryocoolers. MgB2 is penalized by its operation at lower temperature (27 K / 77 K), which makes cryogenics very expensive. The advantage of the low cost of MgB2 compared to REBCO may be lost except with very low AC loss MgB2 tapes.
Authors: Wen Xu Sun, Bao Rong Ni, Akiyoshi Matsumoto, Hiroaki Kumakura
Abstract: It is well known that SiC doping in superconducting MgB2 improves the upper critical magnetic field (Bc2) and the critical current density (Jc) under high magnetic field. However, the relationship between SiC doping and the flux pinning mechanism has not been clarified. In this study, several MgB2 samples with and without SiC doping were prepared by the conventional in situ powder-in-tube method. The critical current densities and the force-displacement characteristics of fluxoids in samples were investigated by an ac inductive measurement (Campbell’s method). The Labusch parameter (αL) and the interaction distance (di) were estimated from the obtained force-displacement profile. It was found that SiC doping enhances the values of αL, but does not change the characteristics of the magnetic field dependence of αL apparently. Namely, αL vs. B3/2 characteristics in the pure samples and SiC doped samples are almost the same. Such a result of αL properties implies that the pinning mechanism in the SiC doped samples could be consistent with the conventional pinning theory. On the other hand, di, which is considered to be proportional to the size of pinning potential, decreases rapidly with increasing magnetic field, especially in the pure samples. For high magnetic field region, the variations of di were deduced to be caused by flux creep. The depth of pinning potential, U0, was estimated by using the values of αL and di. The values of U0 give evidence of that SiC doping can prevent the flux bundles moving to another pinning center under high magnetic field.
Authors: Hao Zhu, Shu Mao Wang, Zhi Nian Li, Xiao Peng Liu, Li Jun Jiang
Abstract: High purity MgB2 powders were synthesized by solid sintering reaction. The degradation behavior of MgB2 powders in deionized water was investigated. XRD and SEM analysis indicate that the changes of MgB2 are a function of time. XRD patterns show that the lattice constants are increasing with the time, and MgB2 samples mostly contain amorphous phase after water treated. The decomposition reaction equation was obtained based on the IR and mass spectrum results. The changes of MgB2 exposed to the 10%HCl, 10%H2SO4, 10%NaOH, 1%HCl, 1%H2SO4 and 1%NaOH (mole concentration) were also studied. The variation of phase composition and morphology indicate that the small amount of MgB2 has decomposed on some extent. The results show that acid can catalyze the decomposition of MgB2 but inversely alkali inhibits the decomposition. The decomposition reaction is limited in water, acid and alkali for less than 1h, and it could be said that the stability of MgB2 is better under such conditions.
Authors: Xi Feng Pan, Guo Yan, Xiang Hong Liu, Yong Feng, Ping Xiang Zhang, Yong Zhao, Akiyoshi Mastumoto, Hiroshi Kumakura
Abstract: A series of MgB2 bulks with different porosity have been successfully prepared by in-situ solid-state reaction at ambient pressure with a toluene-treatment boron powder. The mass density reaches 1.86 g cm-3 at the most compact MgB2 bulk, which has an imporous microstructure, excellent grains coupling, clean grain boundaries and nanosized grains (100~200 nm). Our results reveal that the porosity of MgB2 can be significantly depressed by tuning the residual toluene content and heat treatment temperature in this way. Due to the degradation of porosity and thus the enhancement on grains connectivity and grains boundary pinning, the critical current density, Jc and irreversible fields Birr of MgB2 are significantly improved. For the best sample, at 20K, 4T and 10K, 6T, the Jc reach 2400 and 3700 A cm-2, which is higher than normal porous sample by a factor of 20 and 8, respectively; and the Birr at 20 K reaches 5.10 T.
Authors: Simone Sprio, Anna Tampieri, Gian Carlo Celotti, D. Rinaldi
Authors: G. Yan, Ya Feng Lu, Y. Feng, Ping Xiang Zhang, Lian Zhou, Andre Sulpice, Eric Mossang
Authors: W.X. Li, Ying Li, M.Y. Zhu, R.H. Chen, H.M. Jin, S.X. Dou, M.J. Qin, X. Xu
Abstract: Pulsed magnetic field was first employed in the study on MgB2 superconductors. Superconductivity properties and microstructures of Zn and SiC doped MgB2 were discussed in this paper. The superconductors showed different superconductivities after magnetic sintering. Critical current density and flux pinning force were relevant to the dopants properties in MgB2. Grains in the pulsed magnetic processed MgB2 matrix were smaller than those in the normal processed one. The refinement microstructures have caused the critical current density (Jc) anisotropy in both the Zn and SiC doped MgB2.
Authors: Kwee Yong Tan, K.B. Tan, Kean Pah Lim, Abdul Halim Shaari, Soo Kien Chen
Abstract: In this study, as much as 10 and 15 wt.% nanosized silicon and carbon (Si+C) were reacted with (Mg+2B) at 650°C and 850°C, respectively, for 1 hour. The phase formation, surface morphology and superconducting properties of these samples were evaluated. The relative peak intensity as calculated from the XRD patterns indicates the formation of large Mg2Si volume fraction at low sintering temperature. MgB4 phase was detected in the samples sintered at high temperature as a result of Mg deficiency. The C substitution level as estimated from the lattice parameters, was shown to increase in the samples reacted with a higher amount of (Si+C) at high temperature. Scanning electron micrograph showed that (Si+C) co-addition had refined the grain size and improved the grain coupling of MgB2. The superconducting transition temperature was found to decrease with increasing addition level. The superconducting transition width was also broadened because of a large volume fraction of secondary phases. The improved field dependent critical current density at both 5 K and 20 K is accounted to enhanced scattering by C substitution and grain boundary pinning.
Authors: Xi Feng Pan, Guo Yan, Xiang Hong Liu, Yong Feng, Ping Xiang Zhang, Yong Zhao, Akiyoshi Mastumoto, Hiroshi Kumakura
Abstract: In this paper, we have prepared a series of Fe sheathed MgB2 tapes with SiC, Malic acid and C9H11NO mono-and co-doping by in-situ powder-in-tube (PIT) method, and studied the effects of various C sources co-doping on transport critical current density and flux pinning of MgB2/Fe tapes. The results suggest by various C sources co-doping, the amount of C substitution for boron largely increase, comparing to SiC, Malic acid or C9H11NO mono-doped sample. For MgB2/Fe tapes with 5 mol% SiC+10 wt% Malic acid and 4 wt% C9H11NO+10 wt% Malic acid co-doping, the transport Jc at 4.2 K and 10 T are 14.8 and 13.5 kA/cm2, respectively, which are clearly higher than the Jc of these dopants mono-doped samples. Furthermore, it is found that at the 4 wt.% C9H11NO doped MgB2, the poor in-field Jc should be attributing to the cracks at grains boundary, which results in the bad grains-connectivity.
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