JPH03222214A - Manufacture of ceramic base superconductive wire-rod - Google Patents

Abstract

PURPOSE:To obtain a ceramic base superconductive wire-rod of high critical current density and of excellent crystal-orienting property by applying plural alternate repetitions of a diameter-reducing process and a unidirectional solidifying process to a ceramic material coated with a metal sheath and then heat- treating the material. CONSTITUTION:A superconductive wire-rod 1 obtained by coating a ceramic material having its superconductivity or its precursory ceramic material with a metal sheath is moved while being taken out from a feed reel 2 and wound round a take-up reel 3. An infrared ray-converging heating-furnace 5 is arranged in the middle of this moving route. After plural alternate repetitions of a diameter-reducing process and a unidirectional solidifying process are then applied to the wire-rod, heat treatment is given to the wire-rod. Processing at this time is carried out preferably at a temperature of not less than 800 degrees centigrade and of less than the melting point of the ceramic material. Thus, a superconductive wire-rod can be obtained with its further excellent crystal-orienting property and its high critical current density.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a ceramic superconducting wire using a ceramic superconducting material.
The present invention relates to a method of manufacturing a ceramic superconducting wire that can be used for superconducting magnets, superconducting cables, etc.

[Prior Art] In order to form a ceramic superconducting material into a wire rod, another material that can be made into a long length is prepared and this and the superconducting material are combined into a composite. A typical example of such compositing is the filling of a metal sheath, for example a metal pipe, with a ceramic material that has superconducting properties or becomes, upon heat treatment, superconducting properties.

In such methods, a sintering method is often employed. That is, a desired ceramic superconducting wire is manufactured by filling a metal pipe with ceramic sintered powder, performing diameter reduction processing and subsequent heat treatment.

In addition, a method using a melting method instead of the sintering method described above has been proposed (ISS '89 Society, Michiya
Okada et al.). In this melting method, ceramic material powder is packed in a gold vibrator, which has been subjected to diameter reduction processing, and then concentrated infrared heating is applied to pass a heating zone along a wire to melt the ceramic material. and coagulation. Here, only one melting and one solidification process is applied to the ceramic material.

[Problems to be Solved by the Invention] However, in both the sintering method and the melting method described above, the diameter reduction process is performed with the metal pipe filled with ceramic material powder, so that the inside of the wire is There was a problem in that voids remained and the superconducting material portion of the obtained superconducting wire lacked density. Because of this, the critical current density of the obtained superconducting wire was not so high.

In addition, in the melting method, after the diameter reduction process, the ceramic material is heated above its melting point, thereby melting and solidifying. However, when such a process is carried out, the above-mentioned voids become even larger, and therefore a high critical current density cannot be expected. Further, due to the high thermal conductivity of the metal pipe, the high temperature gradient caused by concentrated heating is not utilized, and excellent crystal orientation cannot be obtained in the superconducting material portion of the obtained superconducting wire.

Therefore, an object of the present invention is to provide a method for manufacturing a ceramic superconducting wire that can solve the above-mentioned problems.

[Means for Solving the Problem] The present invention is directed to a method for manufacturing a superconducting wire using a ceramic superconducting material, and in order to solve the above-mentioned technical problem, a step of preparing a precursor ceramic material; a step of covering the ceramic material with a metal sheath; and a plurality of alternating diameter reduction processes and unidirectional solidification of the ceramic material covered with the metal sheath. It is characterized by comprising the steps of: repeating the process several times; and then heat-treating the ceramic material coated with the metal sheath.

In the above-described unidirectional solidification process, it is preferable that the wire passing through the heating zone be horizontal.

Further, it is preferable that the ceramic material covered with the metal sheath is in a bulk state previously produced by a unidirectional solidification method.

Further, the temperature T of the heating part during the unidirectional solidification process is preferably selected as follows: A≦TUB (where A is the melting temperature of the ceramic material and B is the melting temperature of the metal sheath).

Preferably, the temperature gradient at the end of the heating zone during the unidirectional solidification process is 10 Kdeg/Cm or more, and the passing speed of the heating zone is 1 mm/h or more. In order to obtain such a temperature gradient, the wire may be actively cooled near the end of passing through the heating zone during the unidirectional solidification process. For cooling, for example, a method of blowing a gas such as nitrogen or air, or a method of impregnating with a liquid such as liquid nitrogen can be adopted.

Further, the metal sheath is preferably composed of gold or a gold alloy, or silver or a silver alloy.

Furthermore, when using a gold alloy, this may be Au-5~40
Preferably, it is a weight percent Pd alloy. If a silver alloy is used, it is preferably an Ag-3 to 30% by weight Pd alloy.

[Operations and Effects of the Invention] In this invention, a ceramic material capable of imparting superconducting properties is covered with a metal sheath, and the diameter of the ceramic material is reduced, thereby achieving a composite of the ceramic superconducting material and the metal sheath. . Furthermore, in the unidirectional solidification process using concentrated heating, the crystal orientation of the ceramic material within the metal sheath can be improved. At this time, if the temperature of the concentrated heating part is lower than the melting temperature of the ceramic material, unidirectional solidification will not be achieved, while if it is higher than the melting temperature of the metal sheath, the ceramic material and the materials constituting the metal sheath will not be able to solidify. Not only will the metal sheath be unable to perform its function, but the crystal orientation of the ceramic material will be greatly disrupted.

In the above-mentioned unidirectional solidification process, when the wire is cooled by injecting, for example, liquid nitrogen, nitrogen gas near 77, or atmospheric air near the end of passage of the concentrated heating zone, the temperature gradient at the end of the heating zone is reduced. becomes even larger, and the crystal orientation of the ceramic material becomes even more excellent.

However, as mentioned above, if unidirectional solidification is performed only once, many voids will exist within the metal sheath, and
For this reason, it has been confirmed that although the crystal orientation is good when viewed partially, the crystal orientation is quite poor when viewed as a whole. Therefore, a diameter reduction process is performed again to eliminate the voids, and then at least a second unidirectional solidification process is performed. In this way, by alternately repeating diameter reduction processing and unidirectional solidification at least twice, the ceramic material portion becomes more dense and high crystal orientation can be obtained.

The higher the number of repetitions, the better; however, when the filling rate of the ceramic material in the metal sheath reaches 100%, the metal sheath will bulge during the next melting process, so there is a preferable upper limit to the number of repetitions. . In practice, three repetitions are desirable and sufficient.

Moreover, in the process of unidirectional solidification, it is preferable that the wire passing through the heating zone be oriented in a horizontal direction. This is because if the wire is oriented vertically, the molten liquid may fall into the voids created in the ceramic material portion, causing the crystal orientation to collapse.

Further, in the process of unidirectional solidification, the passing speed of the heating zone is preferably slow, but if it is less than 1 mm/h, the productivity is low and it is not suitable for industrial use.

In addition, if the ceramic material to be covered with the metal sheath is previously melted and solidified, especially in the bulk state produced by the unidirectional solidification method, a high filling rate can be obtained from the beginning, and diameter reduction processing and Not only can the number of unidirectional solidification cycles be reduced, but the inherent high orientation of the bulk can be utilized as is within the metal sheath, making it possible to create superconducting wires with even better crystal orientation and higher critical current density. Obtainable.

As described above, heat treatment is performed after diameter reduction processing and unidirectional solidification are repeated multiple times. The temperature at this time is
Preferably, the temperature is 800° C. or higher and lower than the melting point of the ceramic material. The heat treatment atmosphere and cooling rate are
It varies depending on the ceramic material used.

If gold or gold alloy or silver or silver alloy is used as the material constituting the metal sheath, it will react with the ceramic material. In particular, if a Y-Ba-Cu-0 based material is used as the ceramic material, It has the advantage that oxygen can easily permeate during the final heat treatment. Further, after being made into a wire, the metal sheath made of gold or gold alloy, silver or silver alloy has low electrical resistance and excellent heat conduction, and therefore can also serve as a stabilizing material. In addition, in order to improve the strength during diameter reduction processing and the heat resistance during heat treatment, when using an alloy, it is necessary to use a complete solid solution with gold or silver as the metal for alloying gold or silver. However, it is preferable to use palladium, which has the effect of raising the melting point. In this case, in particular Au-5 to 40% by weight Pd alloy or Ag-
3-30% by weight Pd alloys are superior. This is because if the addition of palladium is less than 5% by weight in the case of gold alloys and less than 3% by weight in the case of silver alloys, the rate of increase in strength and melting point will be small; on the other hand, if the addition of palladium exceeds 40% by weight in the case of gold alloys In the case of a silver alloy, if the content exceeds 30% by weight, a reaction between palladium and the ceramic material tends to occur.

As described above, according to the present invention, it is possible to manufacture a ceramic superconducting wire in which the metal sheath is filled with ceramic superconducting material at a filling rate of almost 100% and is given high crystal orientation. I can do it. therefore,
Such a superconducting wire can provide a high critical current density.

Therefore, the superconducting wire obtained in this way is effective when used in superconducting magnets, superconducting cables, and the like.

[Example] Fig. 1 is a front view showing a state in which unidirectional solidification included in the method for manufacturing a ceramic superconducting wire according to the present invention is performed, and also shows a state in which unidirectional solidification is performed in the longitudinal direction of the superconducting wire to be obtained. shows the temperature distribution given by

A superconducting wire 1 obtained by coating a ceramic material having superconducting properties or its precursor with a metal sheath is drawn out from a supply reel 2 and taken up by a winding reel 3.
It is moved in the four directions of arrows while being wound up. An infrared concentrated heating furnace 5 is placed in the middle of this movement route.

Note that the superconducting wire 1 may include ceramic materials that do not yet have superconducting properties, but for convenience of explanation, the term "superconducting wire" will be used to include such cases.

Is the infrared central heating furnace 5 light? yi, 6 and a reflecting mirror 7, thereby centrally heating a specific portion of the superconducting wire 1 to form a heating zone 8. As can be seen from FIG. 1, the superconducting wire 1 passing through the heating zone 8 is oriented in the horizontal direction.

In order to cool the superconducting wire 1, a cooling gas 9 is introduced near the end of the passage of the heating zone 8, and this is used to cool the superconducting wire 1.
A conduit 10 is arranged for spraying in the direction of travel of the vehicle.

When the superconducting wire 1 passes through the heating furnace 5, a temperature distribution as shown in the lower part of FIG. 1 is given to the superconducting wire 1 in its longitudinal direction. That is, when passing through the heating zone 8, the temperature reaches the highest temperature, for example, 970° C., but immediately after that, the cooling gas 9 is blown onto the material and the material is rapidly cooled down.

Next, we will introduce some experimental examples carried out in completing this invention.

Experimental Example 1 A bulk material having a diameter of 5 mm and having a composition of Bi2 Sr2 Ca, Cu20X and whose longitudinal direction was oriented perpendicular to the C axis was prepared by the floating zone melt method.
It was charged into an Au-10 wt% Pd alloy vibrator with an inner diameter of 4.5 mm and an outer diameter of 7 mm, and was swaged, wire drawn, and rolled to a width of 5 mm.

It was made into a tape-shaped wire rod with a thickness of 0.2 mm.

Infrared concentrated heating as shown in FIG. 1 was applied to this wire. That is, a part of this wire is heated by concentrated infrared heating to a temperature below the melting point of the above-mentioned gold alloy vibrator and above the melting point of the bulk material, and the wire is moved horizontally at a speed of 3 mm/h to form a bulk material. Unidirectional solidification of the material was performed. At this time, about 100 ml of nitrogen gas was blown in the direction of movement of the wire at a distance of 5 mm from the solidification location of the bulk material in the opposite direction to the heating zone. In this way, a sample was obtained in which the diameter reduction process, more specifically, the rolling process and the unidirectional solidification were repeated "one time". From then on,
The rolling process and the unidirectional solidification were alternately repeated, and samples were obtained in which the number of repetitions was "2" to "4". For each of these samples, a final
Heat treatment was performed for 4 hours to obtain the desired superconducting wire.

For each of the superconducting wires thus obtained, the cross-sectional dimensions and critical current density in a zero magnetic field at liquid nitrogen temperature were measured, and the results shown in Table 1 below were obtained.

Table 1 Experimental Example 2 Experimental Example 1 except that during the unidirectional solidification process, the wire was moved vertically at a speed of 3 m m / h.
A similar experiment was conducted.

The critical current densities of the wires obtained in this experiment in a zero magnetic field at liquid nitrogen temperature are as shown in Table 2 below. Note that the cross-sectional dimensions of each sample are the same as those in Experimental Example 1.

Table 2 Experimental Example 3 An experiment similar to Experimental Example 1 was conducted by changing the temperature gradient at the end of the heating zone of the wire during unidirectional solidification.

Note that the temperature distribution was measured using an infrared radiation thermometer.

The critical current densities in zero magnetic field at liquid nitrogen temperature of samples obtained by heat treatment after repeating diameter reduction and unidirectional solidification three times are shown in Table 3 below.

Table 3: Temperature gradient r8/cmJ ~ r500/cmJ
, no active cooling is performed. In this case, the temperature gradient r500/cm'' is the upper limit of the temperature gradient achieved in the heating furnace used. temperature gradient r1
000/cmJ, cooling was performed with nitrogen gas.

Experimental Example 4 An experiment similar to Experimental Example 1 was conducted by changing the material constituting the metal pipe used. That is, Au-
Pd alloys with different weight percentages of Pd;
and Ag-Pd alloys with different weight percentages of Pd were used as metal pipes to investigate the behavior that occurs during unidirectional solidification. The results are shown in Table 4 below.

Table 4 Pdvt%

[Brief explanation of drawings]

FIG. 1 is a front view showing the unidirectional solidification process included in the method for manufacturing a ceramic superconducting wire according to the present invention, and also shows the temperature distribution given in the longitudinal direction of the superconducting wire 1. . In the figure, 1 is a superconducting wire, 5 is an infrared concentrated heating furnace,
8 is a heating zone, and 9 is a cooling gas.

Claims (9)

[Claims] (1) A method for producing a superconducting wire using a ceramic superconducting material, comprising: preparing a ceramic material having superconducting properties or a precursor thereof; covering the ceramic material with a metal sheath; Alternately repeating diameter reduction processing and unidirectional solidification multiple times on the ceramic material covered with a metal sheath, and then heat-treating the ceramic material covered with the metal sheath. A method for manufacturing a ceramic superconducting wire. (2) The method for manufacturing a ceramic superconducting wire according to claim 1, wherein in the unidirectional solidification process, the wire passes through the heating zone in a horizontal direction. (3) The method for manufacturing a ceramic superconducting wire according to claim 1 or 2, wherein in the step of preparing the ceramic material, the ceramic material is a bulk produced by a unidirectional solidification method. (4) Temperature T of the heating section during the unidirectional solidification process
The method for manufacturing a ceramic superconducting wire according to any one of claims 1 to 3, wherein A≦T<B (where A is the melting temperature of the ceramic material and B is the melting temperature of the metal sheath). (5) The temperature gradient at the end of the heating zone during the unidirectional solidification process is 10 Kdeg/cm or more, and the heating zone passing speed is 1 mm/h or more. A method for manufacturing ceramic superconducting wire. (6) The method for manufacturing a ceramic superconducting wire according to any one of claims 1 to 5, further comprising the step of cooling the wire near a place where the heating zone ends in the unidirectional solidification process. (7) The method for manufacturing a ceramic superconducting wire according to any one of claims 1 to 6, wherein the metal sheath is made of gold or a gold alloy, or silver or a silver alloy. (8) The method for manufacturing a ceramic superconducting wire according to claim 7, wherein the metal sheath is made of an alloy of gold and 5 to 40% by weight palladium. (9) The method for manufacturing a ceramic superconducting wire according to claim 7, wherein the metal sheath is made of an alloy of silver and 3 to 30% by weight palladium.