MgB 2 superconducting thin wires sheathed with stainless steel (SS) and pure iron (Fe) have been prepared by in situ powder in tube process. Using Magnesium hydride MgH 2 and amorphous B powders with and without SiC nano sized powder addition, SS/Fe/MgB 2 composites have been fabricated through grooved rolling and drawing to form the round wires of 0.53~ 0.10 mm in diameter. Both SS and Fe sheaths were hardened to be a Vickers hardness of around Hv 650 and Hv 510 through cold working at room temperature. The transport critical current (I c ) at 4.2 K for the MgB 2 wire increases with decreasing the amount of SiC addition in lower magnetic field than 1 T. The I c at 4.2 K and self field for the MgB 2 wire of 0.10 mm in diameter without SiC addition is 14 A, which corresponds to the critical current density ( J c ) of around 1×10 4 A/mm 2 . The present MgB 2 thin wires are promising as current leads and level sensor for liquid hydrogen.
Synthesis of c axis oriented MgB 2 bulks was attempted by magnetic orientation technique combined with the electrophoretic deposition (EPD) and the hot pressing (HP) method. Using home made or commercialized MgB 2 powder, EPD was performed under 10 T at room temperature. The EPD processed films were inserted in SUS316 sheath, uniaxially pressed into a tape shape and sintered at 900°C for 24 h in evacuated quartz ampoules. In addition, HP samples were made by heating at 900°C for 6 h in Ar flow under 30 and 100 MPa. X ray diffraction analysis revealed that the EPD processed film in 10 T showed ~15 times higher intensity ratio, I 002 /I 101 , than those of randomly grain oriented ex situ bulks. This suggests EPD under field is a promising way to synthesize c axis oriented MgB 2 tapes. The c axis oriented tapes showed much higher critical current density J c than randomly oriented bulks and excellent high J c of 6.9×10 5 A/cm 2 was recorded at 20 K. Our study shows a combination of c axis orientation and an increase in bulk density is a quite effective way to synthesize ex situ MgB 2 tapes and bulks with dramatically enhanced critical current properties. Keywords: magnesium diboride bulk, ex situ method, polycrystal bulks, magnetic orientation, texturing, c axis alignment, electrophoretic deposition, hot pressing, critical current density, anisotropy, irreversibility field
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