GB1574671A - Manufacture of super conductive cables - Google Patents

Description

(54) MANUFACTURE OF SUPERCONDUCTIVE CABLES (71) We, GOSUDARSTVENNY NAUCHNO ISSLEDOVATELSKY ENERGETICHESKY INSTI TUT IMENI G.M. KRZHIZHANOVSKOGO, a USSR corporate body of Leninsky prospekt, 19, Moscow, USSR, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method of manufacturing a multisection cable including an intermetallic compound superconductive coating.

According to the present invention there is provided a method of manufacturing a multisection cable core provided with a superconductive layer comprising an intermetallic compound, by joining end-to-end a plurality of cable core sections each comprising a layer of the higher melting-point component of said intermetallic compound, which method comprises applying a barrier layer to end portions of each cable core section, producing a superconductive layer on each of the core sections by thermal diffusion, stripping the barrier layers from the sections, welding the ends of adjacent sections together, and forming a superconductive layer at the welded joints and the adjoining end portions of the sections, by thermal treatment in the presence of the lower melting-point component of the intermetallic compound.

It is expedient that while forming a superconductive layer on internal surfaces of said core sections and prior to welding the sections together an insert comprising a compacted powdered mixture of the components of the intermetallic compound should be interposed between the end faces of adjacent cable core sections, and that the inserts should be initially enclosed within a sheath of the higher melting-point component of the intermetallic compound.

It is preferable that the heat treatment should be carried out in the presence of a molten metallic alloy comprising the lower melting-point component of the intermetallic compound.

The proposed method for manufacturing a multisection cable core with a superconductive coating comprising an intermetallic compound produces improved strength and superconductivity characteristics at the places where individual core sections are welded together; the method also makes it possible to work out a universally acceptable process for assembling and welding together cable core sections of different types and thus improve the reliability of cables.

Preferred features and advantages of the present invention will become more apparent from the following detailed description of a preferred embodiment thereof to be read in conjunction with the accompanying drawings, wherein: Figure 1 is a sectional elevation view of a diffusion chamber, accommodating a coaxial core section with a superconductive coating, which may be used to perform the invention; Figure 2 is a partial sectional view of a joint' between cable core sections with an internal superconductive coating prior to welding the sections together; and Figure 3 is a partial sectional view of the joint of Figure 2 after the sections have been welded together.

According to the method of the invention for manufacturing a multisection cable core with a superconductive coating comprising an intermetallic compound between components of higher and lower melting points, internal and external superconductive layers 1 (Figure 1) are produced by liquid diffusion on respective tubular core blanks 2 and 3 comprising a stabilizing copper layer 4 and a layer 5 of the higher melting-point component of the intermetallic compound used as the superconductive layer.

According to the embodiment here considered, the superconductive layer 1 on the external surface of the smaller-diameter tubular blank 2 and on the internal surface of the larger-diameter tubular blank 3- is produced in a diffusion chamber 6. The stabilizing copper layer 4 of the blanks 2 ánd 3 is provided in advance with dia phra -' 7 and 8 arranged to protect the làyer4 from the effects of a molten metal bc' - lloy 9 'containing the' lower melting- point component of the intermetallic compound.

-nor 'to the formation of the super onduct'ive' I' aye? 1, a barrier layer 10 is ap pMèd to the ends of the blanks 2 and 3, which is done in an air-tight sputtering chamber. As the superconductive layer is being produced, the barrier layer 10 prevents diffusion processes occurring in the layer 5 of the higher melting-point component of the intermetallic compound. Upon withdrawal of the section from the diffusion chamber 6, the barrier layer 10 is removed.

The sections are joined together along their perimeter by electron beam welding; this operation is accompanied by welding of the copper layer 4 to the layer 5- of the.

higher melting-point component of the in termetallic compound. A molten metallic alloy 9 containing the lower melting-point component of the intermetallic compound is used to produce a superconductive layer at the w' ded 'j6ints and the adjoining portions of the sections, freed from the barrier layer.

This process is carried out in a diffusion, chamber different in design from the cham ber. 6.

While producing the superconductive layer 1 (Figure 2) on the internal surface of the sections, but before welding- the sections togethr along their perimeter, there is interpqsed between the abutting end faces 11 of the sections, which are provided with annular grooves 12, an insert 13 of a powdered mixture of the components of the intermetallic compound. The insert 13 is initially enclosed in a 'sheath 14 of the higher melt ing-point component of the intermetallic compound, which makes it possible to joint the sections together without prior evacua tion and ensures a homogenous structure of the superconductive layer both within the sections and at the joints.

Xn the embodiment here considered, cold welding is primarily used to joint the sec- tións along their perimeter; cold welding lidices a region 15 (Figure 3) in which the higher melting-point component of the intermetallic compound of the section and the insert 13 are fused together.

The tightness of the joint is improved by using electron beam welding along an edge 16 of the sections' perimeter An a.c. energized inductor 17 is applied to the welding zone to heat the sections. The heating trans 'forms the structure of the material of the insert 13' ,into that of a superconductor.

In order to ensure adequate superconductivity of welded joints between sections with an internal superconductive layer 1, the amount of the lower melting-point component of the intermetallic compound in the insert 13 exceeds the amount required to ensure a stoichiometric composition of the superconductor formed by the insert 13, which is necessary because part of the lower melting-point component diffuses into the region 15 to fuse the superconductive layer 1 with the superconductor of the insert 13.

The proposed method for manufacturing a multi-section cable core with a superconductive coating comprising an intermetallic compound makes it possible to dispense with placing the cable under vacuum, while assembling. and welding its sections to getter; the method of this invention further makes it possible to prepare welded joints whose strength and superconductive characteristics are as good as those of the sections. Finally, the method makes it possible to, provide a universally applicable process for assembling and welding together sections of different types of cables and improve the operating reliability of cables.

The invention will now be explained in greater detail with reference to some examples listing specific conditions under which the proposed method is realized, and specific components of the intermetallic compound.

EXAMPLE 1 A barrier layer of tantalum (Ta) is applied to cable core blanks 2 and 3 (Figure 1) comprising a stabilizing layer 4 of copper (Cu) and a layer 5 of niobium (Nb) which is the higher melting-point component of the intermetallic- compound (Nb3Sn). A superconductive layer 1 of Nb3Sn is then formed in a diffusion chamber 6 by thermal treatment in the presence of a molten metallic alloy 9 of stannous bronze.

The thermal treatment is carried out under a vacuum of 10-4 to 10-s of mercury at a temperature of 6500C to 800 C for a period of 20 to 50 hours.

The superconductive layer in the weldedjoints between sections with an internal superconductive layer 1 is formed by induction heating of the welding zone and the insert 13 to a temperature of 650 C to 800 C for a period of 15 to 50 hours. The powdered mixture of components of the intermetallic compound comprises niobium (Nb) and tin (Sn). The above-mentioned temperature range at which the superconductive layer is formed is due to the presence of copper (Cu) in the molten metallic alloy and the introduction of copper as powder to the mixture of the components that make up the material of the insert 13. The enclosing sheath 14 of the insert 13 is of niobium (Nb).

EXAMPLE 2 A barrier layer of tantalum (Ta) is applied to cable core blanks 2 and 3 (Figure 1) comprising a stabilizing layer 4 of copper (Cu) and a layer 5 of vanadium (V) which is the higher melting-point component of the intermetallic compound V5Ga. A superconductive layer 1 of VSGa is then formed in a diffusion chamber 6 by thermal treatment in the presence of a molten metallic alloy 9 comprising gallium (Ga).

The thermal treatment is carried out at a temperature of 6000C to 900"C for a period of 5 to 200 hours in an inert medium.

The superconductive layer in the welded joints between sections with an internal superconductive layer 1 is formed by induction heating of the welding zone and the insert 13 to a temperature of 600 C to 900"C for a period of 5 to 200 hours. The powdered mixture comprises vanadium (V) and gallium (Ga). The sheath of the insert 13 is of vanadium (V).

WHAT WE CLAIM IS:- 1. A method of manufacturing a multisection cable core provided with a superconductive layer comprising an intermetallic compound, by joining end-to-end a plurality of cable core sections each comprising a layer of the higher melting-point component of said intermetallic compound, which method comprises applying a barrier layer to end portions of each cable core section, producing a superconductive layer on each of the core sections by thermal diffusion, stripping the barrier layers from the sections, welding the ends of adjacent sections together, and forming a superconductive layer at the welded joints and the adjoining end portions of the sections by thermal treatment in the presence of the lower melting-point component of the intermetallic compound.

2. A method in accordance with claim 1, wherein while forming the superconductive layer on internal surfaces of said core sections, prior to the welding of the sections together, there is interposed between the end faces of the adjacent sections an insert comprising a compacted powdered mixture of the components of the intermetallic compound, which insert is initially enclosed within a sheath of the higher melting-point component of the intermetallic compound.

3. A method in accordance with claim 1 or claim 2, wherein the thermal treatment is carried out in the presence of a molten metallic alloy comprising the lower meltingpoint component of the intermetallic compound.

4. A method for manufacturing a multisection cable core with a superconductive coating formed by an intermetallic compound, substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. EXAMPLE 2 A barrier layer of tantalum (Ta) is applied to cable core blanks 2 and 3 (Figure 1) comprising a stabilizing layer 4 of copper (Cu) and a layer 5 of vanadium (V) which is the higher melting-point component of the intermetallic compound V5Ga. A superconductive layer 1 of VSGa is then formed in a diffusion chamber 6 by thermal treatment in the presence of a molten metallic alloy 9 comprising gallium (Ga). The thermal treatment is carried out at a temperature of 6000C to 900"C for a period of 5 to 200 hours in an inert medium. The superconductive layer in the welded joints between sections with an internal superconductive layer 1 is formed by induction heating of the welding zone and the insert 13 to a temperature of 600 C to 900"C for a period of 5 to 200 hours. The powdered mixture comprises vanadium (V) and gallium (Ga). The sheath of the insert 13 is of vanadium (V). WHAT WE CLAIM IS:-

1. A method of manufacturing a multisection cable core provided with a superconductive layer comprising an intermetallic compound, by joining end-to-end a plurality of cable core sections each comprising a layer of the higher melting-point component of said intermetallic compound, which method comprises applying a barrier layer to end portions of each cable core section, producing a superconductive layer on each of the core sections by thermal diffusion, stripping the barrier layers from the sections, welding the ends of adjacent sections together, and forming a superconductive layer at the welded joints and the adjoining end portions of the sections by thermal treatment in the presence of the lower melting-point component of the intermetallic compound.

2. A method in accordance with claim 1, wherein while forming the superconductive layer on internal surfaces of said core sections, prior to the welding of the sections together, there is interposed between the end faces of the adjacent sections an insert comprising a compacted powdered mixture of the components of the intermetallic compound, which insert is initially enclosed within a sheath of the higher melting-point component of the intermetallic compound.

3. A method in accordance with claim 1 or claim 2, wherein the thermal treatment is carried out in the presence of a molten metallic alloy comprising the lower meltingpoint component of the intermetallic compound.

4. A method for manufacturing a multisection cable core with a superconductive coating formed by an intermetallic compound, substantially as hereinbefore described with reference to the accompanying drawings.