JPH0471279A - Manufacture of oxide superconducting material - Google Patents

Abstract

PURPOSE:To improve the freedom in profile by a method wherein the title manufacture is composed of the process bringing about the amorphous alloy state comprising the stoichiometric composition of metallic elements comprising the objective oxide superconducting material and the process oxidizing the amorphous alloy. CONSTITUTION:In order to manufacture an amorphous alloy out of yttrium base superconducting material (Y1Ba2Cu3O7-y) by single rolling process, a metallic powder mixed in the ratio of Y:Ba:Cu=1:2:3 is fed into a crucible 1 to be heated and melted down using high-frequency coils 2 and then high pressure argon gas is led into the crucible l by a pressure regulator 5 to spray a melted solution over a roll 4 from a stopper nozzle 3. This roll 4 is structured to be driven at high speed so that cooling water may be fed to the inside. The ribbon type amorphous alloy is processed while being pressurized in vacuum atmosphere at relatively low temperature to relieve the structure and successively this film is heat-treated in oxygen atmosphere to form a superconductor layer. Through these procedures, the superconducting layer can take the specific shape while keeping the superconductivity.

Description

[Detailed description of the invention] (a) Field of application of the invention The present invention relates to a method for making oxide superconducting materials.

(b) Prior Art Conventional methods for producing oxide superconducting materials, since they are oxides, have been carried out in the same manner as for other ceramics. The method basically involved mixing raw powders of oxides and carbonates and firing them. The most common mixing method is a method using a mortar or the like, and a coprecipitation method is used to further improve uniformity. Subsequently, semiconductor manufacturing processes were introduced to create better quality films.

The methods include the CVD method and the sputtering method, and these methods are still the mainstream. Furthermore, for wire rods that are considered important for producing superconducting magnets, etc., the current common method is to fill powder inside a sheath material, draw the wire, and then fire it.

(c) Problems with conventional technology In order for a substance to be usable as a material, it must first have a desired shape and have sufficient functionality in that shape, and secondly, it must be low cost or necessary. At present, it is difficult to say that this has been fully achieved using conventional production methods.

Using the powder method, it is extremely difficult to obtain materials that have a complex shape and still have sufficient superconductivity.
Furthermore, even if they were obtained, they would have poor crystal orientation and would be difficult to control grain boundaries, resulting in low reliability. C
Even in the production of thin films using the VD method, films grown epitaxially on substrates do not seem to have sufficient functionality for practical use.They have a low degree of freedom in shape, and the starting materials and equipment are expensive. However, there are problems in that it takes a long time to form a film and is expensive in practice. Although wire rods still have a degree of freedom in shape, most of the sheath material used is silver, which poses a cost problem, and the surface is covered with a non-superconducting material. Therefore, there is a problem that it is not suitable for things that flow as surface current, such as high frequency waves.

(d) Purpose of the Invention The purpose of the present invention is to develop a method for producing an oxide superconducting material that allows it to have a desired shape while ensuring practically sufficient superconductivity. Another object of the present invention is to produce an oxide superconducting material using an inexpensive method that can withstand industrial practical use, rather than using a costly method such as the CVD method.

(e) Structure of the invention The present invention provides, in the process of creating an oxide superconducting material,
It is characterized by comprising a step of taking an amorphous alloy state containing metal elements constituting the target oxide superconducting material in a stoichiometric ratio, and a step of oxidizing the amorphous alloy. In the present invention, amorphous is used to mean that it has only short-range order and medium-range order, unlike crystals that have long-range order, and its microstructure is microcrystalline or phase-split. I don't care if there is.

The use of an amorphous process in the production process of oxide superconducting materials may not be that new, or the amorphous process of oxides has traditionally been carried out, and they are designed to improve the crystal orientation. That was the main purpose. However, the amorphous process in the present invention is an amorphous process for the constituent metals, and its purpose is essentially different in that the purpose is to provide a desired shape by utilizing the degree of plasticity possessed by the metal. Further, the following reasons can be cited for making the alloy amorphous instead of crystallizing it. First of all, it is extremely difficult to create alloys containing multi-component metal elements in complete solid solution, such as superconducting materials. Even if the material is crystallized, it is possible to obtain a uniform material from a macroscopic perspective.Next, by making it amorphous, the plasticity increases.In addition, the material that has been crystallized is stable, so the original crystal is While cutting bonds and recrystallizing requires a large amount of energy, the amorphous state is a metastable state with high energy, so it has the advantage of being easy to crystallize through oxidation treatment. The amorphous process in the present invention does not matter as long as it involves melting and quenching the component metals.For example, metal powders are mixed in a stoichiometric ratio, and the raw material formed into a pellet is used as a target for sputtering. The amorphous alloy can be made by quenching using a general roll method, etc. In addition, the process of oxidizing the amorphous alloy is performed by heat treatment at an appropriate temperature in an oxygen atmosphere for a relatively short period of time to make it superconducting. As in the case of firing other oxides, it is possible to pass an electric current through the oxidation process (Japanese Patent Application Laid-Open No. 63-233068), or heat it in a furnace with a temperature gradient (Japanese Patent Application No. -25526), it is possible to align the crystal orientation and improve its properties.Also, by leaving metal parts inside in this oxidation process, it is possible to improve structural stability and reliability. be.

EXAMPLES The present invention will be explained in more detail with reference to Examples below.

(f) Example 1 Yttrium-based superconducting material (YIBa2Cu30□-
7) was selected as a superconducting material, and an amorphous alloy was created by a single roll method. Figure 1 shows an outline of the apparatus used to create the amorphous alloy. Y:Ba:Cu=1:2:3
The mixed metal powder was put into an alumina crucible 1, and heated to 1500°C or higher by a high frequency coil 2 to melt it. The temperature of the melt was measured by a thermocouple 9. After the metal was completely melted, high-pressure argon gas was introduced into the crucible 1 by the pressure controller 5, and the molten liquid was sprayed onto the roll 4 from the stopper nozzle 3. This stopper nozzle 3 was also made of alumina like the crucible 1, and the hole diameter of the nozzle was circular with a diameter of 0.5 mm. The roll 4 has a diameter of 250 t+m and a thickness of 20 mm, rotates at a high speed of 800 rpm, and has a structure in which cooling water is flowed inside from a pump 7. The cooling rate in this pickling is approximately 10'/
See, it was possible to create an amorphous alloy without crystallizing the melt. All of the above steps were performed in a state in which the inside of the vacuum container 7 was evacuated to 10-'' Torr or less using a vacuum pump 8 to prevent oxidation, and then filled with an inert gas such as Ar. The obtained sample had a ribbon shape with a width of 1 to 2 mm and a thickness of several tens of μm, and was confirmed to be amorphous by XRD measurement.

The ribbon-shaped amorphous alloy obtained by the above method is subjected to structural relaxation by processing it at a relatively low temperature, for example, 400°C while applying pressure in a vacuum, and the thickness is about 5.
A film of 0 μm and 2t+m square was obtained. This film is heated at 700°C to 900°C in an oxygen atmosphere, e.g. 800"C, 30m1n.
A superconductor layer could be formed by heat treatment for ~3 hours. The critical temperature T was about 90, and the reproducibility was good. XRD measurement revealed that this film was mostly oriented along the C axis, although some portions were oriented along the ab axis. When this film was cut and the cross section was observed using a SEM, it was found that the metal part remained inside the film that had been oxidized to 30 m1n, resulting in a structure like that shown in Figure 2, but the oxidation process took a long time. It was found that this metal region became smaller and eventually became completely oxidized to the inside.

In FIG. 2, numeral 10 indicates a portion that has become a superconductor layer through oxidation treatment, and numeral 11 indicates a metal portion that remains unoxidized. As for the sample in which the metal part remained inside, the oxide layer was polished and the internal metal part was subjected to XRD measurement. As a result, it was found that this metal part had already been crystallized.

(g) Example 2 A ribbon-shaped amorphous alloy obtained by the same method as in Example 1 was subjected to structural relaxation by treatment at a relatively low temperature, for example, 400° C., while applying pressure in vacuum, and then wire-drawn. By doing this, a wire rod having a diameter of about 50 μm was obtained. This wire was oxidized using an apparatus as shown in FIG.

In the method shown in FIG. 4, an amorphous alloy wire 19 is placed on an alumina plate 20 in a quartz furnace tube 21, and the electric furnace 12 is moved by a motor at a constant speed of 5 min/cm, so that the entire wire is heated. was oxidized. Alumina plate 2
0 was used to prevent reaction between the quartz furnace tube 21 and the amorphous alloy wire 19. The temperature of the electric furnace 12 was 850° C., and oxidation was performed while a constant amount of oxygen was supplied by the mass flow controller 16. After the temperature had cooled down enough, I carefully took out the wire and measured its resistivity.
The critical temperature Tc was approximately 90°C. It was found by XRD measurement that it was oriented along the C axis. A cross-sectional SEM observation revealed that a small amount of metal remained inside, and that it had a double structure. As a result of measuring the critical current density in 0 magnetic field, it is approximately 3XlO'A/cnf
The wire rod had a Jc of approximately Also, because the surface of this wire is surrounded by a superconductor layer, the resistance when high frequency waves are applied was lower than that of conventional silver sheath materials with a superconductor layer inside. As shown in FIG. 5, a part of the superconductor layer of this wire was irradiated with a laser to remove oxygen to create a non-superconducting layer 24, and the resistivity of this wire was measured in liquid nitrogen. It was found that the total resistance was approximately equal to the resistance value of the alloy portion 23 determined by calculation. This is considered to indicate that heat generation can be suppressed to a low level by allowing a bypass current to flow through the alloy portion 23, and the influence on other superconductor layers can be reduced.

(h) Example 3 A ribbon-shaped amorphous alloy obtained by the same method as in Example 1 was treated at a relatively low temperature, for example 400°C, in a vacuum while applying pressure to relax the structure and reduce the thickness. A ribbon-shaped amorphous alloy with a length of about 50 μm and a width of about 2 cylinders was prepared. Next, solder having a diameter of 100 μm was wound using the aforementioned ribbon-shaped amorphous alloy, and then drawn to obtain a wire rod having a diameter of approximately 50 μm. Thereafter, the above wire was oxidized to obtain a superconducting wire. The oxidation conditions and the equipment used for oxidation were the same as in Example 2. Note that since solder has a low melting point and will melt during the above oxidation process, only the other parts were oxidized, leaving both ends of the wire, and care was taken to prevent the melted solder from flowing out.

The structure of the superconducting wire thus obtained is shown in FIG. The wire rod in which the oxidation time was short and the alloy part still remained (a in Figure 6) showed superconductivity with a critical temperature Tc of about 90, but the wire rod in which the oxidation time was long and the alloy part still remained (a) showed superconductivity with a critical temperature Tc of about 90. 6th
Figure b) did not exhibit superconductivity. By pressing two wires that exhibited superconductivity and heat-treating them at 200°C, the two wires could be joined. Although this bonded wire had some resistance at the solder portion, the resistance value was sufficiently low.

(i) Effects of the Invention The pickling of the present invention makes it possible to create a superconducting material in a desired shape. Furthermore, when a film is created using this method, the film can be easily obtained by rolling or the like by utilizing the plasticity of the amorphous alloy, and the film has the advantage that it does not require any other substrate. Similarly, if a wire is created using this method, the wire can be easily obtained by utilizing the plasticity of the amorphous alloy, and if the metal part is left inside, the outside is entirely surrounded by superconductor. Therefore, it was particularly effective as a conductor for high frequencies. Also, if it is made in combination with solder etc.
It was easy to join and a sufficiently practical wire rod was obtained. From the standpoint of reliability, this is considered to be excellent in practical terms, as it is possible to reduce heat generation by allowing current to flow through the metal parts when some superconductivity is lost.

From the above, it is believed that the present invention has a very large effect on the practical application of superconducting materials.

[Brief explanation of the drawing]

FIG. 1 schematically shows an apparatus for producing an amorphous alloy. FIG. 2 shows a cross-sectional view of the amorphous alloy after oxidation treatment. FIG. 3 schematically shows an apparatus for oxidizing amorphous alloy wire. FIG. 4 shows a method of arranging the amorphous alloy wire during the oxidation process. FIG. 5 is a diagram schematically showing that a non-superconductor layer is partially formed on a superconducting wire by laser irradiation. FIG. 6 shows the structure of a superconducting wire containing a solder portion inside. 1... Aluminum pot 2... High frequency coil 3 ・ 4 ・ 5 ・ 6 ・ 7 ・ 8 ・ 9 ・ 1O・ 11 ・ 12 ・ 13 ・ 14 ・ 15 ・ 16 ・ 17 ・ 18 ・ 19 ・ 20 ・ 21 ・22. Stopper nozzle roll pressure controller pump (for cooling water) Vacuum vessel vacuum pump thermocouple (for melt temperature measurement) Oxide layer (superconductor layer) Alloy layer (non-superconductor layer) Electric furnace core tube ( Made of quartz) Bogie rail mass 0 - Controller Vacuum pump base Amorphous alloy wire alumina plate Reactor core tube (same as 12 in Figure 3) Superconductor layer Alloy layer (non-superconductor layer) Laser irradiated part (non-superconductor layer) Laser oxide layer (superconductor layer) Alloy layer (non-superconductor layer) Solder layer oxide layer (non-superconductor layer) Solder layer

Claims (1)

[Claims] 1. In the step of creating an oxide superconducting material, a step of taking an amorphous alloy state consisting of a stoichiometric composition of the metal elements constituting the target oxide superconducting material, and A method for producing an oxide superconducting material, comprising a step of oxidizing an amorphous alloy. 2. Claim 1 is characterized in that when an amorphous alloy consisting of a stoichiometric composition of metal elements constituting the target oxide superconducting material is oxidized, an alloy portion is left inside. A method for creating oxide superconducting materials. 3. In the step of creating an oxide superconducting material, there is a step of taking an amorphous alloy state consisting of a stoichiometric composition of the metal elements constituting the desired oxide superconducting material, and a step of forming the aforementioned amorphous alloy into a predetermined state. 1. A method for producing an oxide superconducting material, comprising a step of processing it into a shape and a step of oxidizing it. 4. Claim 3 is characterized in that when an amorphous alloy consisting of a stoichiometric composition of metal elements constituting the target oxide superconducting material is oxidized, an alloy portion is left inside. A method for creating oxide superconducting materials.