A sol-gel method for growing superconducting MgB2 films

In this paper we report a new sol-gel method for the fabrication of MgB2 films. Polycrystalline MgB2 films were prepared by spin-coating a precursor solution of Mg(BH_4)_2 diethyl ether on (001)Al2O3 substrates followed with annealing in Mg vapor. In comparison with the MgB2 films grown by other techniques, our films show medium qualities including a superconducting transition temperature of Tc ~ 37 K, a critical current density of Jc(5 K, 0 T) ~ 5 {\times} 10^6 A cm^{-2}, and a critical field of H_{c2}(0) ~ 19 T. Such a sol-gel technique shows potential in the commercial fabrication of practically used MgB2 films as well as MgB2 wires and tapes.Comment: 8 pages, 5 figure

Formation of MgB2 at low temperatures by reaction of Mg with B6Si

Formation of MgB2 by reactions of Mg with B6Si and Mg with B were compared, the former also producing Mg2Si as a major product. Compared to the binary system, the ternary reactions for identical time and temperature were more complete at 750 C and below, as indicated by higher diamagnetic shielding and larger x-ray diffraction peak intensities relative to those of Mg. MgB2 could be produced at temperatures as low as 450 C by the ternary reaction. Analyses by electron microscopy, x-ray diffraction, and of the upper critical field show that Si does not enter the MgB2 phase.Comment: Submitted to Supercond. Sci. Techno

Solenoidal Coils Made from Monofilamentary and Multifilamentary MgB2 strands

Three solenoids have been wound and with MgB2 strand and tested for transport properties. One of the coils was wound with Cu-sheathed monofilamentary strand and the other two with a seven filament strand with Nb-reaction barriers, Cu stabilization, and an outer monel sheath. The wires were first S-glass insulated, then wound onto an OFHC Cu former. The coils were then heat treated at 675C/30 min (monofilamentary strand) and 700C/20 min (multifilamentary strand). Smaller (1 m) segments of representative strand were also wound into barrel-form samples and HT along with the coils. After HT the coils were epoxy impregnated. Transport Jc measurements were performed at various taps along the coil lengths. Measurements were made initially in liquid helium, and then as a function of temperature up to 30 K. Homogeneity of response along the coils was investigated and a comparison to the short sample results was made. Each coil contained more than 100 m of 0.84-1.01 mm OD strand. One of the 7 strand coils reached 222 A at 4.2 K, self field, with a Jc of 300 kA/cm2 in the SC and a winding pack Je of 23 kA/cm2. At 20 K these values were 175 kA/cm2 and 13.4 kA/cm2. Magnet bore fields of 1.5 T and 0.87 T were achieved at 4.2 K and 20 K, respectively. The other multifilamentary coil gave similar results.Comment: 22 pages, 8 figures, 2 table

Yb-123 superconducting film coating on Gd2O3 buffered nickel substrate by sol-gel method

Surface coated Yb-123 superconductor was produced by a non-vacuum sol-gel technique. Nickel tape, which was used as substrate, was annealed in reducing atmosphere to get texture. To prevent Ni reaction with Yb-123 and transfer the texture to superconductor layer, Gd2O3 buffer layer was coated on Ni tape by sol-gel method. Yb-123 was coated on top of buffer layer by using non-vacuum sol-gel technique. Crystallographic and surface properties of Ni tape, buffer layer and the superconductor film were examined by; X-ray and ESEM. Critical transition temperature of 77 K was measured by four-point method

ANOMALOUS INCREASES IN THE CRITICAL CURRENTS OF MULTIFILAMENTARY NB3SN WIRES PREPARED BY THE BRONZE ROUTE

Several heat treatment processes have been suggested to improve the critical currents of multifilamentary Nb3Sn wires prepared by the bronze route1. In this paper we describe the results obtained on wires heat treated under high pressure argon gas. This heat treatment process improves both the mechanical2 and the electrical properties by suppressing the formation of Kirkendall3 porosity which, in turn, enhances the Nb3Sn layer growth. The latter effect results in anomalous increases in the overall critical current density of the wires

ANOMALOUS INCREASES IN THE CRITICAL CURRENTS OF MULTIFILAMENTARY Nb3Sn WIRES PREPARED BY THE BRONZE ROUTE

Plusieurs procédés de traitement thermique ont été proposés pour améliorer les courants critiques des fils multifilamentaires de Nb3Sn préparés par la voie bronze. Dans ce papier nous décrivons les résultats obtenus avec des fils traités à chaud sous argon à haute pression. Cette opération de traitement thermique améliore à la fois les propriétés mécaniques et électriques, en supprimant la formation de porosités de Kirkendall ce qui augmente la croissance des couches de Nb3Sn. Ceci a pour effet une augmentation importante des courants critiques dans les fils.Several heat treatment processes have been suggested to improve the critical currents of multifilamentary Nb3Sn wires prepared by the bronze route1. In this paper we describe the results obtained on wires heat treated under high pressure argon gas. This heat treatment process improves both the mechanical2 and the electrical properties by suppressing the formation of Kirkendall3 porosity which, in turn, enhances the Nb3Sn layer growth. The latter effect results in anomalous increases in the overall critical current density of the wires