We applied hot pressing to in situ powder-in-tube-processed (PIT-processed) MgB 2 tapes. We enhanced the superconducting properties by adding nanometer-sized SiC powder and ethyltoluene (C 9 H 12 ) to the mixed powder. Hot pressing was performed at 100 MPa and 630 • C in an Ar gas atmosphere for 2-10 h. Hot pressing reduced the cross-sectional area of the MgB 2 tapes from ∼0.55 mm 2 for conventionally heat-treated tapes to ∼0.44 mm 2 . This increased the MgB 2 core density from 50% to 70%. Undoped MgB 2 tapes hot pressed for 5 h exhibited a transport J c of 90 A mm −2 at 4.2 K and 10 T, which is about three times greater than that for a tape heat treated without hot pressing. The value of J c for codoped tape hot pressed for 5 h was 450 A mm −2 at 10 T, which is larger than that for codoped tape heat treated without hot pressing (280 A mm −2 ). These results clearly demonstrate that hot pressing is effective in increasing the MgB 2 core density, and hence in enhancing the J c values of PIT-processed MgB 2 tapes.
MgB 2 superconducting thin wires have been prepared by in-situ powder-in-tube process. Using Magnesium hydride MgH 2 and amorphous B powders with SiC nano-sized powder addition, SS/Fe/MgB 2 / steel composite wires of 0.53 mm ~ 0.19 mm in diameter have been fabricated through grooved rolling and drawing. The stainless steel sheath was hardened to a Vickers hardness of around 600 Hv by cold drawing. The Ic at 4.2 K and self-field for the MgB 2 wire of 0.53 mm in diameter without SiC addition is 200 A, which corresponds to the critical current density (Jc) of 4,300 A/mm 2 . The MgB 2 composite thin wires sheathed with low thermal conductive metals are promising as current leads with small heat leakage in liquid hydrogen.
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