Method of producing multifilament lengths of superconductor from

Details Method of producing multifilament lengths of superconductor from Method of producing multifilament lengths of superconductor from

1985-06-06

1986-06-10

Lechert, Jr., Stephen J.

Powder metallurgy processes

Powder metallurgy processes with heating or sintering

Making articles of indefinite length

29 33F, 295274, 57 9, 72286, 140 71R, 148 315, 174126S, 228126, 427117, 428558, B22F 300

Patent

active

045942188

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to lengths of superconductor constituted from superconducting filaments based on ternary chalcogenides of molybdenum, and assembled within a stabilizing metallic matrix which is not superconducting, is based on copper, and serves to evacuate the heat generated, and which constitutes and electrical shunt for regions of superconducting filaments which have lost their superconducting state by virtue of local heating.
Attempts have been made to make superconductive filaments from ternary chalcogenides of molybdenum of the form M.sub.x Mo.sub.6 X.sub.8 (often called "Chevrel phases"), in which M may be a 3d element, an alkali, an alkali earth, a rare earth, silver, cadmium, indium, tin, or lead, in which x varies in the range 1 to 4 depending on the element M, and in which X is one of the elements sulfur, sodium, selenium, or tellurium. These materials are used because of their extremely high critical field which is much higher than that of niobium titanium. The attempts have mostly been performed on the highest performance compound PbMo.sub.6 S.sub.8, but they have not led to the critical current densities that could be expected from the superconducting properties shown by solid samples.
Because of their special crystallographic structure, Chevrel phases are not ductile, and they must be used in the form of a powder when making superconducting filaments. Further, they are polluted by copper and must be protected therefrom by an appropriate metal sheath. Various tests have been performed in which PbMo.sub.6 S.sub.8 powder has been compacted in sheaths made of silver, molybdenum, niobium, lead, or tantalum which sheaths are surrounded on the outside by copper and are then drawn or swaged by conventional cable-making techniques. During these operations, the Chevrel phase loses its superconducting properties, but it recovers them in the grains of the powder after heat treatment at 800.degree. C. for a few hours. It seems that the current density in a filament remains low because of voids between the grains of powder. This defect could theoretically be removed by sintering; however the sintering temperature (greater than 1100.degree. C.) is incompatible with the presence of copper in the stabilizing matrix.
The aim of the present invention is to mitigate the above defect and to provide lengths of superconductor based on Chevrel phases having high critical current densities without requiring a final heat treatment that is incompatible with the presence of copper.
The present invention provides a method of manufacturing lengths of superconductor, the method consisting of mixing a second powder with the Chevrel phase powder used for making the superconducting filaments, the second powder having a smaller granulometry than the Chevrel phase powder and being chosen from the components of the Chevrel phase being used or from the group of metals consisting of aluminum, silver, gallium, rhenium and titanium, in sheathing this powder mixture in a metal wall to protect the Chevrel phase from copper, the wall metal being chosen from the group of metals consisting of molybdenum, niobium, tantalum and vanadium, and in subjecting the length of superconductor obtained after swaging the superconductive filaments within a copper based stabilizing matrix to a final heat treatment consisting of heating to a temperature of about 800.degree. C. for a period of at least twenty hours.
The metal wall enclosing the outer mixture and protecting the Chevrel phase from the copper of the stabilizing matrix is advantageously coated on the inside with a metal layer for ensuring good electrical contact, said layer metal being chosen from the group of metals consisting of aluminum, silver, gallium, rhenium, and titanium.
Other characteristics and advantages of the invention appear from the following description of an example of manufacturing a length of superconductor constituted by superconducting filaments based on the Chevrel phase of the PbMo.sub.6 S.sub.8 type with silver powder added thereto and existing within

REFERENCES:
patent: 2873518 (1959-02-01), Schilling et al.
patent: 2888740 (1959-06-01), Danis
patent: 3066407 (1962-12-01), Toensing
patent: 3271849 (1966-09-01), Price et al.

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