JPH0531490B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing a superconducting material. [Conventional technology and its problems] Superconducting materials have already been used in high-energy particle accelerators,
In MRI-CT physical property research equipment for medical diagnosis, etc.
It has been put into practical use in the form of superconducting magnets. Applications include generators, energy storage and conversion, linear motor cars, magnetic separation devices for resource recovery, nuclear fusion reactors, power transmission cables, magnetic shielding materials, etc.
Furthermore, superconducting elements using the Josephson effect are expected to be applied to ultra-high-speed computers, infrared detectors, low-noise amplifiers, etc., and if these are put into full-scale practical use, they will have significant industrial and social impact. The magnitude of the impact is still difficult to measure. Nb-Ti alloy is a typical superconducting material developed so far, and is currently widely used as a wire for generating magnetic fields up to 9T. Nb−
Tc of Ti alloy (critical temperature at which superconducting state exists)
is 9K. In addition, compound superconducting materials have been developed as materials with Tc much higher than Nb-Ti alloys, and currently Nb ₃ Sn (Tc: 18K) and V ₃ Ga
(Tc: 15K) has been made into wire and put into practical use. Furthermore, a Tc of 23K has been obtained with Nb ₃ Ge. Although efforts have been made to obtain high Tc superconducting materials for many years, Tc23K has become a major barrier to conventional alloy-based and compound-based superconducting materials. Expensive liquid He is required to cool superconducting materials with Tc below 23K.
This hinders the widespread application of superconducting materials. In 1986, Mr. Muller of IBM Zurich and others proposed Ba-La-
Since the announcement that signs of superconductivity were observed in Cu-O-based oxides, the race to develop oxide-based superconducting materials has accelerated. In 1986, Tc was 40K, but in early 1987, a Y-Ba-Cu-O based superconducting material was developed that exceeded the liquid nitrogen temperature of 77K, and Tc reached approximately 93K. Furthermore, vigorous development has continued since then, and there have been reports of the development of superconducting materials that exhibit superconductivity at room temperature, although there are currently safety issues. The discovery of high-temperature superconducting materials that can be used at liquid nitrogen temperatures has raised expectations for the aforementioned application fields, but for actual application, it is necessary to develop processing techniques such as wire rods and coatings. must be accompanied by [Problems to be solved by the invention] In order to form a film with a superconducting material, it is possible to apply the superconducting material onto a base material by a thermal spraying method or a vapor deposition method. The thickness of the film that can be formed using this method is approximately 1 μm at most, which limits the power supply capacity, and in addition, the film formation rate is slow and it takes a long time to form the desired film. The purpose of this invention is to form a thick film stably,
In addition, it is an object of the present invention to provide a method for producing a superconducting material that can form a film made of a superconducting material on a base material at a high film formation rate. [Means for Solving the Problems] This invention provides a method of spraying onto the surface of a base material by a thermal spraying method.
A film of a composite oxide superconducting material containing a Cu _x O _y group is formed, and then the superconducting material consisting of the base material and the film thus obtained is heated at 500°C to 980°C in an oxygen-containing atmosphere. The method is characterized in that superconducting properties are imparted to the film by heating the film to a temperature of It is something. Next, one embodiment of the method for manufacturing a superconducting material according to the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing one embodiment of the method for manufacturing a superconducting material according to the present invention. Using a plasma spraying apparatus 1 as shown in FIG. 1, Y-Ba-Cu-O
A film 3 of a composite oxide superconducting material containing a Cu _x O _y group such as a Cu x O y group is formed. The thermal spraying device 1 may be other than one that uses plasma as a heat source. The plasma spraying apparatus 1 includes a vacuum vessel 4, a thermal spray nozzle 5 provided in the vacuum vessel 4, a tungsten electrode 6 provided in the thermal spray nozzle 5, and connected between the thermal spray nozzle 5 and the electrode 6. It consists of a plasma power supply 7. A plate-shaped or rod-shaped base material 2 is placed in the vacuum container 4 facing the thermal spray nozzle 5, and while the gas in the vacuum container 4 is sucked, argon,
A working gas such as helium and a powder (10 to 100 μm) of a composite oxide superconducting material containing Cu _x O _y groups are each continuously supplied, and the plasma power supply 7 is activated to flow from the spray nozzle 5 to the electrode 6. Generates a plasma jet towards the enemy. After obtaining the superconducting material 8 consisting of the base material 2 and the film 3 in this way, the superconducting material 8 is heated to a temperature of 500 to 980°C in an oxygen-containing atmosphere, and then, if necessary, , after holding the superconducting material 8 in the temperature range for a predetermined time, the superconducting material 8
Cool at a rate of 20℃/min or less. Here, the heat treatment temperature was set at 500 to 980℃ because
At temperatures below 500℃, it is difficult to obtain homogeneous orthorhombic crystals, and the amount of oxygen vacancies is large, making it difficult to obtain sufficient superconducting properties.
This is because if the temperature exceeds 980°C, the base material and the film will react, the base material will penetrate into the film, and the superconducting property will no longer be exhibited. In addition, the cooling rate was set to 20℃/min or less because
This is because at a cooling rate exceeding 20°C/min, the risk of cracking in the film increases, the film and the base material tend to peel off, and the amount of oxygen vacancies in the crystal increases. The reason why the superconducting material 8 is heat-treated in this way is as follows. When the molten particles of the superconducting material 8 adhere to the surface of the base material 2 by thermal spraying, the molten particles are immediately cooled. Therefore, the crystal structure of most of the film 3 formed on the surface of the base material 2 is orthorhombic, which is stable at high temperatures and is close to tetragonal. Moreover, the amount of oxygen contained in the film 3 also decreases. As a result, the superconducting phenomenon does not sufficiently appear in the film 3. Therefore, when the film 3 is heated to the above-mentioned temperature, the crystal structure of the film 3, which originally has a tendency to form an orthorhombic crystal, easily changes from an orthorhombic crystal close to a tetragonal crystal to an orthorhombic crystal. As a result, the superconducting phenomenon completely appears in the film 3. Next, embodiments of the invention will be described. Vacuum vessel 4 of plasma spraying apparatus 1 shown in FIG.
A copper plate-shaped substrate 2 is set inside the spray nozzle 5, and a mixed gas of argon gas and helium gas (Ar: 20/min, He: 40/min) is continuously supplied as plasma gas into the thermal spray nozzle 5. and plasma power supply 7
A power _of 15 Kw is supplied between the thermal spray nozzle 5 and _{the electrode 6} from Then, the atmospheric pressure inside the vacuum container 4 is
The pressure was reduced to 80 mbar, and a film 3 made of a superconducting material having a film thickness of 150 μm was formed on the surface of the base material 2. Next, the base material 2 and the film 3 obtained in this way
The superconducting material 8 consisting of . Next, another plate-shaped superconducting material was manufactured under the same conditions as in the above example except that the heating temperature of the superconducting material 8 was 800°C. Test piece of superconducting material manufactured in this way (base material thickness: 2 mm, film thickness: 150 μm, width: 5 mm, length:
50mm) was immersed in liquid nitrogen (77K), and the critical current density (Jc) was investigated using a four-terminal resistance measurement method. In addition, the critical temperature (Tc) was similarly measured using the four-terminal resistance measurement method. This result,
When the superconducting material 8 is not subjected to heat treatment, that is,
The results are shown in Table 1 together with the as-sprayed case. In addition,
When as-sprayed, the coating did not exhibit superconducting phenomena.

[Table] As is clear from Table 1, according to the method of the present invention, the crystal structure of the film 3 changes from an orthorhombic crystal close to a tetragonal crystal to a homogeneous orthorhombic crystal due to the heat treatment, so that the superconducting phenomenon occurs. is clearly recognized. Next, the strength of the film 3 was examined. this is,
As shown in Figure 2, a test piece of superconducting material (standard thickness: 2 mm, film thickness: 150 μm, width: 5 mm, length 50
mm) was subjected to a three-point bending test, and evaluated based on the bending angle of the test piece when cracking occurred in the coating 3. The results are shown in Table 2 together with the as-sprayed case.

〔Effect of the invention〕

As explained above, according to the present invention, by forming the coating by thermal spraying, the thickness of the coating can be increased, and moreover, the coating can be formed in a short time. Furthermore, by heat-treating the film, the particles of the superconducting material become stronger, and at the same time, the crystal structure and the amount of oxygen in the crystals can be optimized, making it possible to impart superconducting properties to the film. Useful effects are produced.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing how a film made of superconducting material is formed on the surface of a base material by the method of the present invention, and Figure 2 is a front view showing the three-point bending test method. It is. In the drawings, 1... plasma arc thermal spraying device, 2... base material, 3... film, 4... vacuum vessel,
5...Thermal spray nozzle, 6...Electrode, 7...Plasma power source, 8...Superconducting material.

Claims (1)

[Claims] 1. A film of a composite oxide superconducting material containing a Cu _x O _y group is formed on the surface of a base material by a thermal spraying method, and then a film consisting of the base material and the film obtained in this way is formed. The superconducting material is heated to a temperature of 500°C to 980°C in an oxygen-containing atmosphere and then cooled at a rate of no more than 20°C/min, thus
A method for producing a superconducting material, characterized in that superconducting properties are imparted to the film by controlling the crystal structure and oxygen content of the film.