Methods for forming joints between magnesium diboride conductors

Abstract

In a method for forming joints between MgB.sub.2 filaments of superconducting wires, the MgB.sub.2 filaments from the wires to be joined are exposed, and the exposed filaments are then exposed to a mixture of magnesium powder and boron powder in a furnace, and the MgB.sub.2 filaments and the magnesium and boron powders are pressed together in the furnace. The MgB.sub.2 filaments and the magnesium and the boron powders in the furnace are heated, and oxygen that is present within the furnace is preferentially trapped, and thus removed from the joint, by providing titanium within the furnace.

Claims

1. A method for forming a joint between MgB.sub.2 filaments of superconductive wires, comprising the steps of: at a location of said joint, exposing MgB.sub.2 filaments from the wires to be joined; pressing the exposed M.sub.gB.sub.2 filaments together with a mixture of magnesium powder and boron powder in a mold with the exposed MgB.sub.2 filament being exposed to the mixture of magnesium powder and boron powder in said mold; placing the mold in a furnace and placing titanium in said furnace in proximity to said mold; and heating the MgB.sub.2 filaments and the magnesium and the boron powders in the mold in the furnace, and thereby causing oxygen to be outgassed from magnesium powder in the mold and from the furnace, and gettering the outgassed oxygen with said titanium within the furnace to produce titanium oxide, and thereby preventing the outgassed oxygen from reacting with magnesium in said furnace at said location of said joint.

2. A method according to claim 1 comprising providing the titanium in the furnace as pellets.

3. A method according to claim 1 wherein the furnace is evacuated by a vacuum pump while forming said joint in said furnace.

4. A method according to claim 1 comprising pressing the MgB.sub.2 filaments and the magnesium and the boron powders together by applying a pressure in said mold, and maintaining said pressure during said heating.

5. A method according to claim 1 comprising pressing the MgB.sub.2 filaments and the magnesium and the boron powders together by applying a pressure in said mold, and releasing said pressure before said heating.

Description

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(1) According to the method of the present invention, titanium is provided, preferably in the form of pellets, within the furnace while the joint is formed. The titanium acts as a getter of oxygen, and any oxygen which may be present in the furnace will be preferentially trapped by the titanium to become titanium oxide, rather than reacting with the magnesium. The titanium is placed in close proximity to the jointing mold, so that the oxygen is quickly and efficiently removed from the joint. The entrapment of free oxygen by the titanium avoids any contamination of the joint with magnesium oxides, leading to persistent MgB.sub.2 joints which are acceptably tolerant of background magnetic field strength and current density.

(2) The remaining stages in the method are unchanged. The method of the present invention may be applied in arrangements in which mechanical pressure is maintained during the jointing process, or in arrangements where the mechanical pressure is released during jointing.

(3) The furnace may be evacuated by a vacuum pump, preferably to the order of 10-.sup.7bar (0.01 Pa), or may be provided with an inert flush arrangement to reduce the amount of oxygen which needs to be trapped by the titanium.

(4) Accordingly, the present invention provides the use of titanium pellets to capture any oxygen which may be present during the heat treatment of magnesium and boron powders to realize MgB.sub.2 formation for the jointing of MgB.sub.2 wires. Preferably, a high-vacuum pump is provided for evacuating the furnace, and this will remove some of the oxygen. Remaining oxygen will be preferentially trapped by the titanium, avoiding the formation of magnesium oxides.

(5) Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art.