JPS63259928A - Manufacture of superconductive wire - Google Patents

Abstract

PURPOSE:To make it possible to manufacture a superconductive wire economically and effectively by heating part of a preform of superconductive matter up to around its fusing point and draw the wire from the heated part. CONSTITUTION:Part of a preform of superconductive matter is suspended in an oven 26 by means of a chuck 24. A resistance coil 44 is connected with a power source to generate heat, which is transmitted to the preform 14 by radiation, so the preform 14 is heated up to around its fusing point. A fusing point range M is produced at a point of a neck range 13 of the preform 14, so the starting point into superconductive wire 36 is formed. After the wire 36 is formed, it is desirable to apply annealing by means of an annealing device 28. By coating the wire 36 by means of a coater 30 after annealing, ductility, durability, etc., of the wire 36 can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates generally to electric wires, and particularly to superconducting electric wires.

[Prior art and its problems]

Superconductivity is a well-known phenomenon. For example, as early as 1911
In 2013, K, H,0nne
It was experimentally confirmed that when mercury is cooled to a temperature of about 4 Kelvin (K), the electrical resistance decreases to zero.

Superconductivity has many potential applications. For example, superconducting power lines can avoid the loss of large amounts of energy that would otherwise occur during power transmission. Superconducting magnets, generators, and motors can be made small and extremely powerful. Superconducting devices, known as Josephson junction devices, are very fast electronic switches that consume negligible power. In other words,
The potential uses of superconducting materials are extremely diverse, and the list of possible uses can grow almost infinitely.

Despite all the potential benefits of superconducting devices and structures, we currently find very few of them outside of laboratories. The main reason for this is that most materials are extremely difficult and expensive to cool down to their superconducting transition temperature Tc.

This is because most materials have transition temperatures within a few Kelvin of absolute zero, requiring the use of liquid helium, which is expensive and difficult to maintain, as a coolant. Until now, the use of superconductors has been impractical for most purposes because the cost of creating and maintaining liquid helium systems has been astronomical.

March 2, 1987, M.K.Wu
) et al., Physical Review Let
ters, Vol. 58, No. 9, “New mixed phase Y at atmospheric pressure”
-Ba-Cu-0 compound system (Superconduct
ivity at 93 K in a NewMix
ed-Phase Y-Ha-Cu-OCompoun
d System at Am-bient Pres.
In a paper entitled ``sure)'', superconductivity in multiphase YBaCuO at temperatures exceeding the temperature of liquid nitrogen was announced.For the first time, a superconducting material that can use liquid nitrogen as a coolant has been discovered. This announcement caused considerable excitement in the scientific community, as liquid nitrogen cooling systems are at least an order of magnitude cheaper than liquid helium cooling systems, and since the discovery by Wu et al.
The application of superconductors in all sorts of ways suddenly became practical.

After the publication by Wu et al., superconductor researchers rapidly became divided into two groups. One group is using bulk YBaC to discover and clarify its properties.
Experiments were started with uO. The other group began experimenting with thin films of YBaCuO, focusing on integrated circuit technology and the aforementioned Josephson junction devices.

Research into other applications of this relatively high temperature superconductor appears to be slow; for example, there is no literature describing practical methods for making superconducting wires or cables using YBaCuO.

This is probably because multiphase YBaCuO is a fragile ceramic type material that is difficult to form into macrostructures such as wires and cables.

However, some other brittle materials are molded into fibers. For example, glass
It is formed into a long fiber for optical transmission.

A description of how optical fibers could be manufactured was published in the winter of 1980. The West
ern 1E1electric Engineer 49
Page of D H Smith Gall (D, H, Ssit
“Drawing of optical guiding fibers” by Dr.
awing Li-ghtguide Fiber)''
Published in a paper entitled. However, glass is a very different material from superconducting YBaCuO, and the methods used to make glass into fibers are quite different from the methods used to make YBaCuO into wires.

[Problems to be Solved and Solution Means] An object of the present invention is to provide practical and economical superconducting wires and cables.

The method of making superconducting wire in accordance with the present invention involves sintering superconductor powder to form a solid superconductor preform (
forming a preform (hereinafter also referred to as a preform); suspending the preform in an open and heating a portion of the preform to near its melting point; molten portion of the preform; The process involves stretching the wire to form a superconducting wire. Additional methods include annealing the wire to enhance the superconducting phase of the wire and applying a coating to the wire to increase ductility, durability, and/or room temperature electrical conductivity. It will be done.

The method of making superconducting cables involves threading together a number of separate superconducting wires. moreover,
It involves screwing together a wire made of a material that is electrically conductive at normal room temperature and a superconducting wire. It is also possible for one or both of the superconducting wire and the conductive wire to be a capillary tube and serve as a conduit for the fluid coolant.

These and other objects and advantages of the invention will become apparent to those skilled in the art from reading the following description and studying the various figures in the drawings.

〔Example〕

The description of embodiments of the present invention will be made with reference to the new YBaCuO class of high temperature superconductors discovered by Wu. However, it will be apparent to those of ordinary skill in the art that the methods and structures described herein can be implemented with a wide variety of superconducting materials, many of which have yet to be discovered. be.

YBaC, as detailed in the paper by Wu et al.
uO is L=Y, M=Ba, A==Cu.

When D=0, x=0.4, a-2, b=1, y≦4, (
A specific example of a system of compounds generally represented by L,-,M,l),AkD. Other relevant high transition temperature Tc superconductors within the above-membrane designation range include LaBaC
There are uO and La5rCuO.

In the conventional technology, high purity Y! 01,BaC0,,
YBaCuO samples were prepared from a mixture of CuO powders. This powder is mixed in a solvent such as methanol or water, and then heated to 100°C to evaporate the solvent. The resulting mixture was then heated for 6 hours.
Heating at 850° C. in air gives a dark green powder. This dark green powder was further applied for 10 hours over a period of 6 hours.
Heated at 0°C to form a black porous solid. superconducting YB
A detailed description of each step of the method for the production of aCuO and a description of some of its properties is provided by J, Z, et al., Department of Applied Physics, Stanford University, PACS#: 74.3Q.
, -E,? 4.70. - B's "Superconductivity and magnetism in the high transition temperature superconductor YBaCuO (Super-
conductivity and magnetis
min in High-Tc 5upper-conduc
tor YBaCuO)”.

Referring to FIG. 1, the method for manufacturing a superconducting wire according to the present invention begins by supplying a superconductor 10 in a continuous manner. For materials based on YBaCuO, YtO
s, B a CO *, Cu O at 24: 42:
By mixing the compound in a ratio of 34 to 34, kneading this compound for 1 to 12 hours, and further exploding (i.e., turning it into powder by heating) the kneaded compound at a temperature of 750 to 900 ° C. for 4 to 8 hours, It can be made into a powdered superconductor.

Other compatible mix ratios include 15:53:32
and 18.5: 65: 16.5. The smoldered powder is then treated with a binder (e.g. polyvinyl alcohol) in a suitable solvent (e.g. isopropyl alcohol).
5%) to form a mixture. This mixture can be further milled in a ball mill for about 1 to 12 hours to form a refined homogeneous slurry. After ball milling, it is possible to remove the solvent by filtration and remove the wet precursor (prec
ursor precursor) is dried into a fine powder.

Once the powdered superconductor precursor 10 is prepared, it is placed in a preforming device 12 . A type of preforming device 12
utilizes a cold press process to form the powdered precursor into a rod, and uses an oven to form the powdered precursor into a rod.
950 to 1,1 for varying lengths of time depending on the specific application
This rod is sintered at a temperature of 00°C.

This sintering converts the rod-shaped superconductor precursor into a superconductor phase as described above. In the case of another type of preforming device 12, 950-1.100°C
Using high-temperature compression at temperatures of , the rods are formed and the superconductor precursor is simultaneously sintered to create the superconductor phase.

At the bottom of FIG. 1, a typical rod or preformed bacteria 14 produced in a preformed bag R12 is shown.

This preformed bacterium 14 includes a main body portion 16, a neck portion 1
8 and a head portion 20.

The process of converting superconductor preforming bacteria into superconductor wires must take into account a number of factors. First, to ensure that wires made from superconductor preformers are actually superconductors, it is necessary to create a continuous superconductor phase from the molten portion of the superconductor preformers. It is important to perform crystallization. Chemical analysis shows that such a superconducting phase is characterized by the formula Ba, YCu, 06-, which exhibits superconductivity at temperatures below 88'K. Second, in order to maintain the purity of the wire produced and to prevent undesirable chemical reactions, the molten portion of the preformed bacteria must not come into contact with other materials. High reactivity has been observed between YBaCuO and many common contaminants, even at relatively low temperatures. Third, superconducting materials are strong and hard (approximately 620
Tsukwell) is also extremely fragile. Therefore, in order to maintain flexibility, it is desirable to keep the diameter of the wire small (for example, 50 mils; however, ■ mils are 2.54 x 10-' m).

Here, a method and apparatus for manufacturing a superconducting wire will be described with reference to FIG. The superconducting wire forming device 22 includes a feed mechanism 24, an open 26,
An annealer 28, a coater 30, a drawing (hereinafter also referred to as "pulling") mechanism 32, and a spooler 34 are provided.

Various configurations of wires 36 are shown in their respective positions.

The feed mechanism 24 includes a column 38 and a post 40° chuck 42. Post 40 and chuck 42
can be moved up and down relative to the column 38 and the open 26. For example, column 38 could be a hydraulic or pneumatic cylinder, while post 40 could be a piston. Alternatively, it is also possible to drive the post up and down by an electric motor, such as a step morph, with a suitable transmission.

The chuck 42 is suitable for suspending the superconductor preformed bacteria within the opening 26. The open 26 includes an enclosure 43 and a resistance coil 44.

Resistive coil 44 is coupled to a power source (not shown) to generate heat, which is transferred to superconductor preformer 14 primarily by radiation. The enclosure 43 can be evacuated or filled with gas (preferably an inert gas);
Convection can further heat the superconductor preformed bacteria. What should be noted is that the temperature within the oven 26 is non-linear, as shown in the temperature graph G0. This is made possible, for example, by increasing the winding density of the resistance coils close to the neck 18 of the superconductor preform 14. By properly adjusting the temperature in the oven 26, the temperature at the neck 18 of the preformed bacteria 14 can be brought close to the melting temperature Ts of the superconductor preform 14. This results in a molten region M at a point in the neck region 18 of the superconductor preform, forming the entry point to the superconducting wire 36.

Once superconducting wire 36 is initially formed in oven 26, it can be wound onto reel 46 of spooler 34.

However, to improve the properties of the superconducting wire 36, it is desirable to perform an annealing process. To this end, the superconducting wire 36 is passed through an annealer 28 that includes an enclosure 48 and a resistance coil 50. Resistive coil 50 is coupled to a power source (not shown) such that resistive coil 50 heats superconducting wire 36 primarily by radiation.

As previously discussed, it is desirable that no contact between superconducting wire 36 and enclosure 48 occur to prevent undesirable contamination and/or reactions.

The enclosure 48 may be evacuated or filled with a gas (preferably inert as described above) in which case the superconducting wire 36
will also be heated to some extent by convection.

Referring to graph GA, the temperature within the annealer 28 is fairly linear (ie, has a more constant temperature zone) compared to the temperature within the open 26.

The temperature TA in the annealer 28 is preferably kept below the melting temperature 19 of the wire 36 and high enough to ensure continuous crystallization of the superconducting phase. A suitable temperature for the annealer is approximately 1.000"C. However, it should be noted that the annealing step does not have to occur immediately after the wire forming step, but can be done much later if desired. The point is that it is also possible.

The bare annealed wire exiting the annealer 28 may be wound onto a reel 46 of the spooler 34. However, in some cases, the wire 36 may be coated by applying a coating to the superconductor core. It becomes possible to further improve the characteristics.

For this reason, the superconductor 36 can also be passed through the coater 30.

The type of coating applied to superconducting wire 36 by coater 30 can vary depending on the end use of superconducting wire 36. For example, the superconducting wire 36 may be provided with a hermetic insulating coating to improve the wire's resistance and prevent contamination or reaction of the superconducting portion of the wire. Alternatively, the core of the superconducting wire 36 can be coated with a metal, such as copper or silver, to increase the ductility of the wire and reduce the resistance of the wire at normal room temperatures. In some applications, it may be desirable to apply a semiconducting coating, which may or may not exhibit semiconductivity at temperatures near the Tc (transition temperature) of superconducting wire 36.

Tensioning mechanism 32 may include a pair of pinch rollers 52 and 54 that rotate in opposite directions as shown. One or both of pinch rollers 52 and 54 are driven by a drive mechanism, such as a motorized step morph (not shown).

As superconducting wire 36 emerges from pinch rollers 52 and 54, it is wound onto reel 46 of spooler 34. The drive mechanism for reel 46 may be any device such as a motorized step morph.

It should be noted that spooler 34 can also be used to pull superconducting wire 36 directly from superconductor preform 14. However, it is desirable to utilize a separate tensioning mechanism 32 because the tensioning speed can be maintained more constant and the reel 46 of the spooler 34 can be replaced without interrupting the wire manufacturing process.

When first starting the wire manufacturing process, the resistive coil 1 sill 44 raises the melting point M of the neck i8 to or near the melting temperature Ts-. The head 20 of the superconductor preform 14 will then pull the superconducting wire 36 from the melting point M under the influence of gravity. When the superconducting wire 36 becomes long enough,
The head 20 is removed and the wire is pulled by the pulling mechanism 32 and spooler 32! Continued.

It is important to note that in the case of the apparatus 22 of the present invention, the superconducting wire 36 is formed without contacting either the open or annealed enclosure. As mentioned above, this is due to YB at high temperatures.
This is because aCuO becomes extremely reactive. For example, YBaCuO exhibits high reactivity towards platinum, aluminum oxide, and other common container materials even at temperatures as low as 1,000°C. melting temperature T,
(1,600~2゜ooooC), YBa
It is impossible to find a container material that does not react with CuO. Therefore, this non-contact method for pulling superconducting wire 36 is superior to conventional methods for making wire, such as extrusion, because purity is maintained and the chance for superconducting wire 36 to react is minimized. much better than.

It is also noteworthy that the method described above allows the production of both solid wires and hollow wires (capillary tubes). Solid preforms are used to make solid wires. To form a capillary,
A hollow preform (ie, one with a circular cross section) is used. For a description of how to make capillaries from preforms, see Bente III.
I [I] et al. U.S. Patent No. 4.293.415 i 19
April 1972, App-1ied Physics711
" by S tone published on pages 1-79
° Optical transmission in liquid-core quartz fibers (Opti
cal Transmission in Liqui
d Core Qua-rlz pipers)”;1
February 960, Analytical Chemistry
"Con-struction of Long L Glass Capillary" by De-Sty et al.
lengths of Co11ed GlassCap
illary )”.

As previously mentioned, an annealing step in the wire manufacturing process can be utilized to increase the purity of the superconducting wire 36, but is not absolutely necessary. Microstructural studies have shown that the superconducting phase of the superconducting wire 36 has a cylindrical or, for example, spaghetti-like structure, which is easy to crystallize from the melting point M in the open 26. Ta. From this molten phase M, wire 3
6 thereby superconducting wire 36
This is important in that it imparts a directionality to the superconducting phase that will greatly improve its efficiency.

Referring now to FIG. 3, a structure for superconducting wire 36 is illustrated.

The initial structure 36A is simply a length of solid superconducting material with a roughly circular perimeter. Another structure 36
B is similar to the structure shown in 36A, but with a plurality of transverse passageways 54 for channeling cooling fluid to the superconducting wire. The transverse passageway 54 can be formed using, for example, a laser boring tool.

Another superconducting wire structure, shown at 36C in FIG. 3, includes a longitudinally extending passageway 56, thus making the superconducting wire 36 a capillary tube.

As a capillary, the superconducting wire 36 carries its own cooling fluid (eg, liquid or gaseous nitrogen), requiring additional conduits to enclose the cooling fluid around the superconducting wire.

Another superconducting wire structure, shown at 36D, consists of a superconductor core 58 and a surrounding coating 60. As previously mentioned, coating 60 can be an insulator, a semiconductor, or a conductor at normal room temperatures.

Yet another structure of superconducting wire is shown at 36E in Figure 3.
is shown. In this case, the wire has a conductive core wire 62.
and a superconducting coating 64.

This structure has several advantages, including good ductility, malleability, and low resistance at normal room temperatures. The superconducting coating 64 has a relatively high resistance at normal room temperature, and therefore, when the superconducting wire is connected to a constant current power source, or when the wire temperature exceeds the superconducting transition temperature Tc, it will burn out due to heating. This low resistance at normal room temperature is important because there is a possibility that the superconducting material could break, and by combining the superconducting material with a normal good conductor, this possibility can be reduced.

Referring to FIG. 4, superconducting cable 66 is comprised of multiple twisted wires 68. Apparatus and methods for twisting individual wires into cables are well known to those skilled in the cable manufacturing arts and will not be described here.

FIG. 5 shows that wire 68 can take on a variety of shapes and combinations. For example, in the case of 66A, the wires 68 are all 36A in FIG.
It can be made using a solid superconducting wire 68' as shown at A. As an alternative, 66B, the superconducting wire 68° can be provided with longitudinal passages for cooling fluid, such as the wire shown at 36C in FIG. The remaining wire 68°' can be a good normal conductor (e.g. wire) at room temperature, preventing the melting problem described above.

As shown at 66C, the cable can also be constructed from a combination of solid superconducting wire 68° and capillary tubes 68' for cooling fluid flow.

The capillary tube 68'' of the cable 66C can be made of ordinary good conductor for the reasons discussed above, or alternatively it can be made of other materials such as plastic.

Referring now to FIG. 6, the superconducting power transmission line 69 includes a tubular core wire 70 and a superconducting layer 7 wound around the outer surface of the core wire 70.
2, a heat insulating layer 74 wound on the superconducting IJ 72, and a protective layer 76 wound on the heat insulating layer 74. A coolant 78, such as liquid or gaseous nitrogen (N2), is applied to the core 7.
0 to cool the superconducting layer to its transition temperature T.

Core wire 70 can be made from a variety of materials including metal, plastic, glass, and the like. However, if the core wire 70 is made of metal, for example, the power transmission line 69 will always have good electrical conductivity, even with the loss of coolant 78. Also, making the core wire 70 from copper or a copper alloy makes it easier to deposit the copper oxide based superconducting layer 72 due to the chemical similarity between the materials.

It should be noted that the superconducting layer 72 can be applied to the inner surface of the core wire 70 instead of or in addition to being wrapped around the outer surface as shown. However, from a process control perspective, coating the inner surface of the tube is often more difficult than the outer surface.

There are many ways to apply superconducting layer 72 to core wire 70. One such method is the well-known thermal spraying technique, also referred to as flame spraying or plasma spraying. For example, Ceran+, Int, (Italy)
Bee Chagnon (P, Chagnon) in Volume 10, No. 4
“Thermal Spraying of Ceramics” by
ray-ing, of Ceramics)” ; Applied Physics (Japan) 52@No. 10 (1983) Nagasaka, “Current status of plasma jet spraying (The
Present 5ituation of Plus
"ma of Jet Spraylng)"; and
“Recent Advances in Plasma Spraying” by B.R.Jal-Ihce at the Expert Conference on Plasma Treatment and Heating Applications, May 23, 1979.
pments in Plasma Spraying
), a number of publications describe techniques for thermal spraying of ceramic materials.

Insulating layer 74, which can also be made of plastic foam, minimizes heat transfer between superconducting power line 67 and the surrounding environment. A protective layer 76, which can also be plastic or rubber, protects the thermal insulation layer 74 from the external environment.

Although the present invention has been described in connection with several preferred embodiments, reading the foregoing description and studying the drawings will show you that:
It is intended that various modifications and alterations to the invention may become apparent to those of ordinary skill in the art. Accordingly, the scope of the present invention should be determined by the scope of the claims set forth above.

〔effect〕

Since the present invention has the above-described configuration and operation, it is possible to solve the above-described problems and provide an economical and efficient superconducting wire.

[Brief explanation of the drawing]

The drawings relate to embodiments of the present invention; FIG. 1 is a diagram showing a manufacturing process of a superconductor preform, FIG. 2 is a diagram showing an apparatus for manufacturing a superconducting wire from a superconductor preform, and FIG. Figure 3 is a partial longitudinal cross-sectional side view showing multiple types of structures of superconducting wires, Figure 4 is a perspective view of a superconducting cable, and Figure 5
The figures are cross-sectional views showing several embodiments of the superconducting cable taken along arrow 5-5 in FIG. 4, and FIG. 6 is a vertical cross-sectional view of the superconducting power transmission line according to the present invention.

Claims (1)

[Scope of Claims] 1. A method for producing a superconducting wire, which comprises heating a part of a superconductor preform to approximately the melting point temperature, and drawing the wire from the heated part. 2. The method of manufacturing a superconducting wire according to claim 1, wherein the method of manufacturing the superconducting wire includes a step of annealing the drawn wire. 3. The method of manufacturing a superconducting wire according to claim 1 or 2, wherein the method of manufacturing the superconducting wire includes a step of coating the drawn wire. 4. The method for manufacturing a superconducting wire according to claim 1, wherein the preform is at least partially hollow, and the drawn wire is a capillary tube. 5. The method of manufacturing a superconducting wire according to claim 4, wherein the method of manufacturing a superconducting wire includes the step of introducing a non-superconducting material into the drawn capillary-shaped superconducting wire.