Patent GB-1029424-A (GB)
Title: Improvements in superconductors
IPC: H01L39/24
Filed: 1963-02-18
Abstract: A non-brittle and bendable superconductor is formed by mechanically reducing a planer Nb supporting member, e.g. by rolling or by using swaging apparatus or dies, simultaneously or thereafter applying a layer of Sn to the Nb supporting surface, heating the Sn and Nb, e.g. at 800 to 1100 DEG C., and controlling the duration of heating and controlling the temperature above the melting point of Sn to form a Nb3Sn stratum at the Nb-Sn interface.  The mechanical reduction increases the wettability of the Nb to molten Sn.  Wettability may be further improved by using a reducing agent such as Mg as part of the Sn coating.  Nb may be rolled down to foil and clad with Sn foil by cold rolling reductions. Reduction in thickness may be in excess of 95% e.g. 98%.  The cladded combination of Nb and Sn which may be in ribbon form may be folded along its centre line to sandwich the Sn and wound into a tight spiral for heating in an inert gas. Afterwards, the spiral is unwound ready for fabrication. To prevent Sn leaking during heating, the ribbon, prior to winding into a spiral and heating, may be coated at least in part with a refractory wash such as MgO.  In Example 1, vacuum annealed Nb foils are sandwiched with Sn foils, rolled and heated in argon at 950 DEG C. for 30 minutes.  In Example 2, a Nb foil is placed over the Sn of a Nb foil clad with Sn. The product is locked between ceramic blocks and heated in a vacuum furnace at 973 DEG C. for 60 minutes. The Nb3Sn may be used in making solenoids or in shielding and containing magnetic fields.ALSO:A non-brittle and bendable superconductor is formed by mechanically reducing a planar Nb supporting member, e.g. by rolling or by using swaging apparatus or dies, simultaneously or thereafter applying a layer of Sn to the Nb supporting surface, heating the Sn and Nb, e.g. at 800 DEG  to 1100 DEG  C., and controlling the duration of heating and controlling the temperature above the melting point of Sn to form a Nb3Sn stratum at the Nb-Sn interface.  The mechanical reduction increases the wettability of the Nb to molten Sn.  Wettability may be further improved by using a reducing agent such as Mg as part of the Sn coating.  Nb may be rolled down to foil and clad with Sn foil by cold rolling reductions.  Reduction in thickness may be in excess of 95%, e.g. 98%.  The cladded combination of Nb and Sn which may be in ribbon form may be folded along its centre line to sandwich the Sn and wound into a tight spiral for heating in an inert gas. Afterwards, the spiral is unwound ready for fabrication.  To prevent Sn leaking during heating, the ribbon, prior to winding into a spiral and heating, may be coated at least in part with a refractory wash such as MgO.  In Example 1, vacuum annealed Nb foils are sandwiched with Sn foils, rolled and heated in argon at 950 DEG  C. for 30 minutes.  In Example 2, a Nb foil is placed over the Sn of a Nb foil clad with Sn.  The product is locked between ceramic blocks and heated in a vacuum furnace at 973 DEG  C. for 60 minutes. The Nb3Sn may be used in making solenoids or in shielding and containing magnetic fields.