Modern superconductive materials for electrical machines and devices working on the principle of levitation (original) (raw)
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Journal of Materials Processing Technology, 2007
Additions of Zr can increase critical current density (j c ) of high-pressure synthesized MgB 2 (HPS-MgB 2 ) in the same manner as additions of Ta or Ti, i.e. due to the absorption of impurity hydrogen (to form ZrH 2 ). The formation in HPS-MgB 2 of ZrB 2 phase at higher synthesis temperatures (about 950 • C) does not result in the j c increase. Some increase in j c of HPS-MgB 2 at 10 K in the fields higher than 8 T was observed when nano-SiC was added. The additions of Zr, Ta or Ti can prevent the harmful MgH 2 impurity phase from appearing and may prevent hydrogen from being introduced into the material structure and besides, their presence in HPS-MgB 2 promotes the formation of a higher amount of Mg-B (most likely MgB 2 ) inclusions in the Mg-B-O material "matrix" that in turn leads to the increase of j c in magnetic fields. The high level of superconductive (SC) and mechanical characteristics attained for HPS-MgB 2 and the possibility to manufacture large samples make its application in the superconductive electromotors, generators, pumps, etc., very promising.
Arxiv preprint arXiv: …, 2009
and Mg-B-O (MgB 2 -based materials) systems with high superconducting performance, which can be attained due to the formation of regularly distributed nanostructural defects and inhomogenities in their structure can be effectively used in cryogenic technique, in particular in fault current limiters and electrical machines (electromotors, generators, pumps for liquid gases, etc.). The developed processes of high-temperature (900-800 o C) oxygenation under elevated pressure (16 MPa) of MT-YBCO and high-pressure (2GPa) synthesis of MgB 2 -based materials allowed us to attain high SC (critical current densities, upper critical fields, fields of irreversibility, trapped magnetic fields) and mechanical (hardness, fracture toughness, Young modulus) characteristics. It has been shown that the effect of materials properties improvement in the case of MT-YBCO was attained due to the formation of high twin density (20-22 m -1 ), prevention of macrockracking and reduction (by a factor of 4.5) of microcrack density, and in the case of MgB 2 -based materials due to the formation of oxygen-enriched as compared to the matrix phase fine-dispersed Mg-B-O inhomogenities as well as inclusions of higher borides with near-MgB 12 stoichiometry in the Mg-B-O matrix (with 15-37 nm average grain sizes). The possibility is shown to obtain the rather high T c (37 K) and critical current densities in materials with MgB 12 matrix (with 95 % of shielding fraction as calculated from the resistant curve).
High-pressure synthesis of pure and doped superconducting MgB2 compounds
Superconductor Science & Technology, 2003
Superconducting properties of bulk, dense, pure MgB2 and doped (Mg1-xAx)B2 samples with A = Na, Ca, Cu, Ag, Zn and Al were studied for compositional ranges 0 < x < 0.20. The effect on pinning properties and critical current were investigated, particularly for A = aluminium. The samples were sintered and/or synthesised at high pressure - high temperature in a cubic multi-anvils press (typically : 3.5-6 GPa, 900-1000C). They were characterised by x-ray diffraction, scanning electron microscopy and their superconducting properties were investigated by a.c. susceptibility, magnetisation (VSM and SQUID) and transport measurements under magnetic field. Only Al substitutes really on the Mg site. The other elements form secondary phases with B or Mg which do not act as pinning centres. No positive effect is observed on the superconducting properties of the bulk MgB2 samples added with these doping elements : Tc, jc critical current, Hirr and Hc2. For Al, the effect on Hc2 remains small, and the irreversibility line does not move, thus not improving the critical current of the Al-doped MgB2 samples.
Superconducting and levitation force characterisation of pyrene added MgB2 bulk superconductors
Cryogenics, 2020
This research presents the influence of pyrene (C 16 H 10) addition (0, 2, 4, 6, 8, 10 wt%) on the superconducting properties of bulk MgB 2. For C 16 H 10 added MgB 2 samples, a shrinkage in a-lattice parameters was determined, whereas c-lattice parameters remained practically unchanged. The (1 1 0) peak observed at 2θ ≈ 59.9 • slightly shifted to higher angles, the lattice strain increased and the crystallite size reduced after C 16 H 10 addition. By virtue of induced stronger pinning force, the in-field critical current density (J c) increased after C 16 H 10 addition. The J c value at 20 K and 4 T was obtained about two times higher (8.54 × 10 3 A/cm 2) for 4 wt% C 16 H 10 added MgB 2 sample than that of the pure one. In addition, the variation of levitation force characteristic of MgB 2 with increasing C 16 H 10 content was determined at 20, 25 and 30 K. The best vertical levitation force performance in zero-field-cooled regime was obtained as 7.09 N/g at 20 K for 4 wt% C 16 H 10 added MgB 2 sample with 13 mm in diameter.
Physica C: Superconductivity, 2008
The minor Cu (<3 at%) addition could significantly reduce the amount of MgO impurity in the in situ sintered MgB 2 samples and thus improve the critical current density (J c) at low field and the critical transition temperature (T c). The formation of local Mg-Cu liquid at about 485°C could wrap the neighboring Mg particles and thus protect them from the oxidation during the sintering process. Our results provide a possible route to further improve the superconductive properties of pure or doped MgB 2 samples through decreasing the amount of MgO impurity with minor Cu addition.
Superconductivity in High-Pressure Synthesized Pure and Doped MgB 2 Compounds
Journal of Superconductivity, 2002
Dense pure and doped (Mg1 − x Ax )B2 samples with A = Na, Ca, Cu, Ag, Zn, and Al were synthesized at high pressure–high temperature in a multi-anvils press (3.5–6 GPa, 900–1000°C) for 0 < x ≤ 0.20. They were studied by X-ray diffraction, scanning electron microscopy and their superconducting properties were investigated by AC susceptibility, magnetization, and transport measurements. Only Al is really substituted on the Mg site. The other elements form secondary phases with B or Mg. No large effect is observed on the superconducting properties T c, j c critical current, H irr, and H c2.
Pinning and trapped field in MgB2- and MT-YBaCuO bulk superconductors manufactured under pressure
Journal of Physics: Conference Series
View the article online for updates and enhancements. You may also like Low-temperature liquid-phase epitaxy of YBa 2 Cu 3 O y films by the molten KOH method Shuhei Funaki, Yasuji Yamada, Ryota Okunishi et al.-Oxygenation of bulk and thin-walled MT-YBCO under controllable oxygen pressure T A Prikhna, X Chaud, W Gawalek et al.-A novel 2-dimensional artificial pinning center M Takamura, M Mukaida, S Horii et al.-Recent citations Reproducibility of small Ge2C6H10O7added MgB2 bulks fabricated by ex situ Spark Plasma Sintering used in compound bulk magnets with a trapped magnetic field above 5 T P. Badica et al
Electrical and mechanical properties of superconducting MgB2/Mg metal matrix composites
Superconductor Science & Technology, 2006
MgB 2 /Mg composites were prepared using a metal matrix composite fabrication method that offers the potential to produce superconducting wires as an alternative approach to the powder in tube process. To obtain composites, MgB 2 and Mg powders were mixed at different weight fractions and uniaxially pressed in a cylindrical die under the pressure of 0.5 and 1.0 GPa for two hours at various temperatures. The x-ray diffraction technique was used for phase identification. Temperature dependence of resistivity and magnetization measurements were carried out to determine superconducting properties. The effects of composite fabrication temperature and the addition of the Mg on the mechanical properties of MgB 2 /Mg composites were investigated. For this purpose, the compressive mechanical testing was performed to measure the elastic modulus and fracture strength values of the composites. It was found that the relative weight fraction of the Mg and the fabrication conditions of the composites have considerable effect on the superconducting and mechanical properties of the composites.
Journal of Physics: Conference Series, 2009
We have investigated various characteristic properties depending on sintering conditions of MgB2 samples prepared by the standard solid state reaction method. It is inferred from experimental results that the crystallinity of samples were improved when the pressure of the Ar ambient increased. Also, it was found that the sintering temperature above 850 °C caused extremely high amount of decomposition of the superconductor phase. Finally, it was considered that the sintering process of MgB2 must be carried out under the pressure of Ar ambient higher than 8 bar to impede the volatility of Mg in the structure of MgB2. The Jc values of samples systematically enhanced with the increase of sintering time and in particular, the sample sintered for 180 min. exhibited the highest Jc (0) of 4.9 × 103 A cm-2 at 30 K. The obtained results demonstrate that the sintering conditions of MgB2 have a significant influence on Tc (onset) and Jc, which are directly related to practical applications of MgB2 based superconductor components.
MgB2 superconductors for applications
Physica C: Superconductivity, 2003
The paper presents up to date results on MgB 2 filamentary conductors and coated conductors from the point of view of their possible applications. Basic physical parameters of MgB 2 compound relevant to conductor design are introduced. The correlation between the slope of the irreversibility line, critical temperature and critical current density is discussed with respect to the conductor performance and applicability. The possible origin of the observed anomalous decrease of ac susceptibility at 50 K in copper clad in situ powder-in-tube MgB 2 wires is presented. Some numerical results on critical currents, thermal stability and ac losses of the MgB 2 multifilamentary and coated conductors with magnetic cladding of their filaments are given.