A rolling (Durston, UK) and pressing. Tapes have

A single core MgB2 tape has been fabricated by powder-in-tube technology. TheMgB2 powder, supplied by Alpha Aesar (92 % MgB2, 5% wt. MgO, 3% wt. Mg – asestimated by Rietveld analysis), was loaded into a Fe tube. The tube has an outer diameter of3 mm and the inner one of 1.8 mm. Two tubes loaded with MgB2 powder were submitted toidentical steps of cold rolling (Durston, UK) and pressing. Tapes have a width of 6.9 mm,thickness of 0.48 mm, and a length of ~ 30 mm. One as-processed tape was labeled as openendstape (OT). Second tape (CT) was closed at the terminations by folding two times themetal-sheath-ends followed by uniaxial pressing. Tapes of about 15 mm in length wereimmersed in hexagonal BN powder within a graphite/punches die system (?2 cm innerdiameter). The arrangement was placed in a spark plasma sintering (SPS) furnace (FCTSysteme GmbH HP D 5, Germany). The parameters of the SPS procedure were: heating rate110 °C/min, sintering temperature 1050 ?C for a dwell time of 3 min and under a maximumuniaxial pressure of 96 MPa. The initial vacuum in the SPS chamber was ~ 30 Pa. SPS12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364656chamber was washed with Ar for two times. SPS processing parameters were selected basedon our previous optimization experiments for bulks 15 and Fe-sheathed PIT tapes 14.Apparent densities (g/cm3) of the MgB2 cores were determined by the Archimedesmethod (KERN ALT 220-4M density balance, toluene) (Table 1) after peeling the Fe-metalsheath. The theoretical density (g/cm3) of the composite was estimated according to Ref. 16considering that samples contain MgB2 (2.63 g/cm3), MgO (3.58 g/cm3) and MgB4 (2.49g/cm3). The weight fraction of each phase was extracted by applying Rietveld refinement(MAUD software 17 – version 2.31) on the X-ray diffraction (XRD) data. XRD patternswere taken with a Bruker AXS D8 Advance diffractometer (CuK?1 radiation, ? = 1.5406 Å)on the MgB2 core. From XRD data, crystallite size and residual strain of MgB2 weredetermined by Williamson Hall 18 method and by Rietveld analysis. Surfaces of the peeledcores were observed by scanning electron microscopy (SEM) and energy dispersivespectroscopy (EDS) with a Tescan electronic microscope.


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