Method for the production of superconductive wires based on hollow filaments made of MgB2

Abstract

A method is described for the production of superconductive wires based on hollow filaments made of MgB 2 , which comprises: a) the formation of a composite billet by means of the coaxial insertion in a tubular metallic container of a cylindrical bar made of metallic magnesium and amorphous boron powder in the interspace between the container and bar, said powder being pressed between the metallic container and the magnesium bar, in such a quantity that the weight ratio magnesium/boron is higher than 1.2; b) at least one plastic deformation treatment of the composite billet thus obtained until a wire with a prefixed diameter is obtained, with the subsequent winding of the wire onto a support; c) a thermal treatment of the filament product thus obtained, at a temperature ranging from 700° C. to 950° C. for a time ranging from 15 minutes to three hours.

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         24 . A superconductor wire based on a hollow monofilament or multifilament made of MgB 2 , which can be obtained by means of the method which comprises: 
 a) the formation of a composite billet by means of the coaxial insertion in a tubular metallic container of a cylindrical bar made of metallic magnesium and amorphous boron powder, in the interspace between the container and bar, said powder being pressed between the metallic container and the magnesium bar, in such a quantity that the weight ratio magnesium/boron is higher than 1.2;    b) at least one plastic deformation treatment of the composite billet thus obtained until a wire with a prefixed diameter is obtained, with the subsequent winding of the wire onto a support;    c) a thermal treatment of the filament product thus obtained, at a temperature ranging from 700° C. to 950° C. for a time ranging from 15 minutes to three hours.    
     
     
         25 . A method of forming superconductor wires for use in making coils, said coils being based on hollow MgB 2  filaments obtained with the thermal treatment comprising: c1) static thermal treatment in a chamber oven, after sealing the ends of the wire in an atmosphere with a low oxygen content, thus generating inside, at a high temperature, a pressure of magnesium vapours higher than atmospheric pressure; or 
 c2) dynamic thermal treatment, by passing the wire continuously through an open tubular oven, containing an atmosphere poor in oxygen.    
     
     
         26 . A method of making superconductor wires based on hollow MgB 2  filaments according to  claim 25 , wherein the superconductor wires are stranded wires or filiform electric conductor wires obtained by means of the thermal treatment described in c2.