JP2554660B2 - Method for producing compound superconducting wire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for producing a compound superconducting wire, and
The present invention relates to a method for producing an oxide-based compound superconducting wire.

(Prior Art) Recently, an oxide-based compound superconductor having a composition represented by Y—Ba—Cu—O has been attracting attention. Many of these oxide-based compound superconductors have a critical temperature higher than the temperature of liquid nitrogen. Therefore, it is not necessary to use expensive and difficult-to-handle liquid helium as a refrigerant, and the cooling system can be greatly simplified, so that it is expected that the superconducting technology will be drastically developed.

Meanwhile, the oxide-based compound superconductors which have been published so far are mainly a bulk superconductor and a thin film superconductor. In order to incorporate it into an actual circuit, the shape of a wire, such as a normal lead wire, is preferable because it has some applicability. However, oxide compound superconductors are extremely brittle, and it is difficult to make them into wire shapes. For these reasons, the reality is that compound superconducting wires with high critical temperature and high critical current density have not yet appeared.

(Problems to be Solved by the Invention) As described above, the emergence of an oxide compound superconducting wire having a critical temperature higher than the liquid nitrogen temperature and a high critical current density is desired.

Therefore, an object of the present invention is to provide a method for producing a compound superconducting wire capable of producing an oxide-based superconducting wire satisfying the above-mentioned demand without complicated steps.

[Structure of the Invention] (Means for Solving Problems) In the present invention, a state in which a mixture of a plurality of types of powders containing an element capable of synthesizing an oxide-based compound superconductor is housed in a silver cladding tube The first step of axially compressing the mixture to form a pressure-molded product in which the mixture and the cladding tube are integrated, and the pressure-molded product obtained in this step is subjected to surface-reduction processing to form a wire rod. This is realized by the second step of obtaining and the third step of subjecting the wire formed by this step to heat treatment in an oxygen gas atmosphere.

More specifically, several kinds of powders are yttrium, erbium, dysprosium, samarium, cadolinium, holmium, neodymium, ytterbium,
At least one kind of oxide powder selected from thulium and lutetium, barium carbonate or barium oxide powder, copper oxide powder or a powder obtained by replacing a part of each of the powders with a substitution substance. In addition, in the first step, it is desirable to subject the mixture to calcination treatment in air at 850 to 950 ° C. for 1 to 50 hours.

Furthermore, in the second step, in order to improve the critical current density of the finally obtained superconducting wire, 1000 kg / cm ²
It is desirable to apply the above-mentioned pressure molding force to densify the powder base material and integrate it with the coating tube. In addition, the cladding tube has an important function of holding powder during surface reduction processing and a function of mechanically holding the finally obtained superconductor. In order to increase the amount of oxygen permeation and improve the superconducting properties, it is desirable to reduce the surface in the second step until the wall thickness becomes 500 μm or less. In the third step, it is desirable to perform heat treatment at 850 to 950 ° C. for 24 hours or more.

(Operation) The above-mentioned powder mixture is housed in a silver-made coating tube and subjected to pressure molding to form a pressure molded product, and then the second step and the third step are carried out. .
Therefore, the powder mixture,
That is, the density of the base material of the superconductor can be sufficiently increased, voids in the base material can be eliminated, and the base material and the cladding tube can be integrated. As a result, it is possible to improve the superconducting properties of the obtained superconductor. Also, silver is more permeable to oxygen than other metals.
In the present invention, since the silver coated tube is used, the function of holding the powder at the time of surface-reduction processing and the function of mechanically holding the finally obtained superconductor are not impaired. Oxygen can be sufficiently permeated inside in the process of
It is possible to further improve the superconducting characteristics.

(Example) Y ₂ O ₃ (yttrium oxide) powder, BaCO ₃ (barium carbonate) powder, and CuO (copper oxide) powder in a molar ratio of 0.5: 2.0: 3.
The mixture was mixed at a ratio of 0 to obtain a powder mixture 1 as shown in FIG. This powder mixture 1 was calcined in air at 900 ° C. for 2 hours, pulverized, and then pulverized with a ball mill. Next, this powder mixture is used as shown in FIG.
It is housed in a silver cladding tube 2 with a diameter of 14 mm, an inner diameter of 12 mm, and a length of 70 mm.
An axial pressure of 2000 kg / cm ² was applied to this as indicated by the second thick arrow 3 to obtain a pressure-molded product 4 as shown in FIG. 3 (the above is the first step).

Next, the pressure-molded product 4 was subjected to surface reduction processing to obtain a wire 5 having a diameter of 0.5 mm as shown in FIG. 4 (second step). The thickness of the silver layer 6 as a covering material located on the surface layer of the wire 5 was 300 μm.

Next, the wire 5 whose outer surface is covered with the silver layer 6 is heat-treated at 900 ° C. for 24 hours in an atmosphere in which oxygen gas flows (third step), and then gradually cooled to complete the manufacturing process. finished.

When X-ray spectroscopic analysis was performed on the wire rod manufactured in this way, Y ₁ Ba ₂ Cu ₃ O
It was confirmed that a compound superconducting layer having a composition formula of _7-y was formed. Moreover, when the superconducting characteristics of the superconducting wire manufactured as described above were examined, the critical temperature (Tc) was found to be
The critical current density (Jc) at 97K was 1700 A / cm ² . The reason why such excellent characteristics were obtained is that the powder mixture 1, that is, the base material of the superconductor, is sufficiently increased in density by forming the pressure-molded product 4 by applying sufficient force in the first step. It is believed that this is due to the fact that the base material and the covering tube 2 can be integrated and that the covering tube 2 is made of silver which allows easy permeation of oxygen.

The inventors examined the relationship between the material and wall thickness of the covering material and the critical current density. As a result, it was confirmed that the critical current density decreased as the coating thickness increased under the same heat treatment conditions. This is considered to be due to the fact that the thicker the coating material, the lower the oxygen permeation amount in the heat treatment process performed while flowing oxygen gas. Moreover, when the difference in critical current density due to the difference in material was examined, it was confirmed that silver has far better oxygen permeability than copper or the like. However, it was confirmed that even if silver is used, the effect is small if the thickness exceeds 500 μm. Therefore, it can be said that silver is preferable as the coating material, and that the thickness thereof is as thin as possible within the range where the function as the holding material is not impaired, specifically 500 μm or less.

The present invention is not limited to the above embodiment. That is, at least one oxide powder selected from erbium, dysprosium, samarium, gadolinium, holmium, neodymium, ytterbium, thulium, and lutetium may be used instead of yttrium oxide. In the first step, the powder mixture is calcined at 900 ° C. for 2 hours in air, but the temperature may be 850 to 950 ° C. and the time may be 1 to 50 hours. . In addition, the heat treatment temperature and time for the third step is 850-
The temperature may be 950 ° C for 24 hours or more. It should be noted that good results cannot be obtained even if the temperature is higher or lower than the above temperature. Furthermore, the first
It is desirable that the pressure molding pressure in the step is 1000 kg / cm ² or more. If the pressure molding pressure is less than 1000 kg / cm ² , the effect is small. Also, the electric circuit element may be formed by the wire rod after the second step, and the third step may be performed in this state. Further, the drawing process may be performed in a high temperature atmosphere in the second step.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a method for producing a compound superconducting wire which can easily produce a superconducting wire having a high critical temperature characteristic and a high critical current density characteristic.

[Brief description of drawings]

1 to 4 are views for explaining one embodiment of the manufacturing method of the present invention. 1 …… powder mixture, 2 …… silver cladding tube, 4 …… pressed molding, 5 …… wire rod, 6 …… cladding material.

Claims (7)

(57) [Claims] 1. A mixture of a plurality of kinds of powders containing an element capable of synthesizing an oxide-based compound superconductor is axially compressed in a state of being housed in a silver cladding tube to form the mixture and the cladding tube. A first step of forming a pressure-molded product integrated with
The pressure-molded product obtained by this step is subjected to surface-reduction processing to obtain a wire rod, and a third step of subjecting the wire rod formed by this step to a heat treatment in an oxygen gas atmosphere. A method for producing a compound superconducting wire, which comprises: 2. The powder of the plurality of types is yttrium,
At least one oxide powder selected from erbium, dysprosium, samarium, gadolinium, holmium, neodymium, ytterbium, thulium, and lutetium, and barium carbonate or barium oxide powder,
The method for producing a compound superconducting wire according to claim 1, characterized in that it is a copper oxide powder or a powder obtained by replacing a part of each of the powders with a substitution substance. 3. The method according to claim 1, wherein the first step comprises:
The method for producing a compound superconducting wire according to claim 1, characterized in that it includes a treatment of calcination in air at 850 to 950 ° C for 1 to 50 hours. 4. The pressure molding force in the first step is 100.
The method for producing a compound superconducting wire according to claim 1, characterized in that the content is 0 kg / cm ² or more. 5. In the second step, the cladding tube has a wall thickness of 50.
The method for producing a compound superconducting wire according to claim 1, characterized in that surface reduction processing is performed until it becomes 0 μm or less. 6. The heat treatment condition in the third step is 850.
2. The method for producing a compound superconducting wire according to claim 1, wherein the temperature is not less than 950 [deg.] C. and 24 hours or more. 7. The compound according to claim 1, wherein the third step is performed after the wire rod obtained through the second step is formed into a desired shape of an electric circuit element. Superconducting wire manufacturing method.