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- Prikhna, Tatiana, et al.
(author)
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Spark plasma synthesis and sintering of superconducting MgB 2-based materials
- 2012
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In: Applied Electromagnetic Engineering for Magnetic, Superconducting and Nano Materials. - : Trans Tech Publications Inc.. - 9783037854204 ; , s. 42437-
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Conference paper (peer-reviewed)abstract
- Superconducting (SC) and mechanical properties of spark plasma (or SPS) produced MgB 2 -based materials allow their efficient applications in fault current limiters, superconducting electromotors, pumps, generators, magnetic bearings, etc. The synthesized from Mg and B at 50 MPa, 1050 °C for 30 min material has a density of 2.52 g/cm 3, critical current density, j c = 7.1·10 5 A/cm 2 at 10 K , 5.4·10 5 A/cm 2 at 20 K, and 9·10 4 A/cm 2 at 35 K in zero magnetic field; at 20 K its field of irreversibility B irr(20)=7 T and upper critical field B c2(20)=11 T; microhardness H V=10.5 GPa and fracture toughness K 1C =1.7 MPa·m 1/2 at 4.9 N-load. SPS-manufactured in- situ MgB 2- based materials usually have somewhat higher j c than sintered ex-situ. The pressure variations from 16 to 96 MPa during the SPS-process did not affect material SC characteristics significantly; the j c at 10-20 K was slightly higher and the material density was higher by 11%, when pressures of 50-96 MPa were used. The structure of SPS-produced MgB 2 material contains Mg-B-O inclusions and inclusions of higher borides (of compositions near MgB 4, MgB 7, MgB 12, MgB 17, MgB 20), which can be pinning centers. The presence of higher borides in the MgB 2 structure can be revealed by the SEM and Raman spectroscopy.
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| 2. |
- Prikhna, Tetiana, et al.
(author)
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The effect of oxygen distribution inhomogeneity and presence of higher borides on the critical current density improvement of nanostructural MgB2
- 2010
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In: Advances in Science and Technology. - 1662-0356. ; 75, s. 161-166
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Journal article (peer-reviewed)abstract
- MgB2-based nanostructural materials with rather high oxygen concentration (5-14 wt.%) and dispersed grains of higher borides (MgB12, MgB7) high-pressure (2 GPa or 30 MPa) synthesized (in-situ) or sintered (ex-situ) demonstrated high superconducting characteristics (critical current density, jc, up to 1.8-1.0106 A/cm2 in the self magnetic field and 103 in 8 T field at 20 K, 3-1.5105 A/cm2 in the self field at 35 K, upper critical field up to HC2 = 15 T at 22 K, field of irreversibility Hirr =13 T at 20 K). The additives (Ti, SiC) and synthesis or sintering temperature can affect the segregation of oxygen and formation of oxygen-enriched Mg-B-O inclusions in the material structure, thus reducing the amount of oxygen in the material matrix as well as the formation of higher borides grains, which affects an increase of the critical current density. The record high HC2 and Hirr have been registered for the material high-pressure (2 GPa) synthesized from Mg and B at 600 oC having 17% porosity and more than 7 wt.% of oxygen. The attained values of the critical current, AC losses and thermal conductivity make the materials promising for application for fault current limiters and electromotors. The structural and superconducting (SC) characteristics of the material with matrix close to MgB12 in stoichiometry has been studied and the SC transition Tc=37 K as well as jc= 5×104 A/cm2 at 20 K in the self field were registered, its Raman spectrum demonstrated metal-like behavior.
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