JP2615079B2 - Superconducting film manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a superconducting film, and more particularly, to a method for producing a superconducting film having a high film-forming speed and a surface having an arbitrary shape, for example, a surface of various molded products or a surface of a wire. The present invention relates to an industrial method for manufacturing a superconducting film capable of forming a superconducting film at a high film forming speed.

[Prior art and its problems] In recent years, superconducting materials have been attracting attention due to their Meissner effect, zero resistance when a critical temperature is reached, and the Josephson effect, and development of their industrial production methods and their applications. Is being done.

In particular, as a superconducting material that can be used for industrial applications, a supercritical material that has a high critical temperature and is easy to process is being searched for. Alternatively, the development of the molding method is being studied day and night.

At present, as a method of forming a yttrium-based superconducting material, basic research has been conducted on sintering a yttrium-based superconducting material to form, for example, a disk, or forming a thin film or a wire rod. It is no exaggeration to say that superconducting material deposition technology has not yet been established.

For example, when a technique for forming a ceramic superconductor into a thin film and a wire is developed, the use of the superconductor is dramatically expanded.

As a general ceramic thinning technique, a plasma CVD method, a sputtering method, an ion beam method and the like are known.

However, in the plasma CVD method, a plasma obtained by activating a raw material ceramic is brought into contact with a substrate (base material) to form a ceramic thin film. Therefore, a film forming speed is, for example, about 0.3 μm / min. The target or practical film forming speed is considerably low. Moreover, in the plasma CVD method, the plasma entrained by the carrier gas is brought into contact with the base material placed on the holder in the decompression chamber, so that a thin film can be formed on the flat surface of the base material. However, it is difficult to form a thin film on the entire circumference of a curved surface such as a wire.

Also, in the sputtering method and the ion beam method, the film forming rate is low as in the case of the plasma CVD method.

On the other hand, there is a thermal spraying method as a ceramic coating technique for imparting heat resistance and corrosion resistance to the base material surface. This thermal spraying method has not yet been put to practical use as a technique for thinning a superconducting material.

As a result of investigations by the present inventors, a thin film of a superconducting material was not obtained even if this thermal spraying method was simply diverted as a technique for thinning an oxide ceramic as a superconducting material.

This is because when spraying oxide ceramics,
It is presumed that the oxygen content required for the oxide-based ceramic to exhibit superconductivity was reduced, and even if a thin film was formed, the thin film no longer exhibited superconductivity.

 The present invention has been made based on the above circumstances.

An object of the present invention is to provide a simple method for manufacturing a superconducting film, which realizes film formation of a superconducting material at a high film forming speed by a thermal spraying method.

Another object of the present invention is to provide a method for manufacturing a superconducting film capable of forming a superconducting film on any surface such as a flat surface and a curved surface such as a peripheral surface of a wire. is there.

[Means for Achieving the Object] The inventors of the present invention studied to achieve the object, and applied a thermal spraying method, which could not be conventionally applied as a method for forming a superconducting film, to a specific ceramic. Further, the inventors have found that, when a specific treatment is performed after the specific ceramic is sprayed, a thin film exhibiting superconductivity can be formed on a surface having an arbitrary shape, for example, a flat surface or a peripheral side surface of a wire.

That is, the constitution of the present invention is obtained by (1) subjecting a raw material oxide to heat treatment as a pretreatment, spraying fine particles of a substance having superconductivity onto a substrate, and then forming a film on the substrate surface. High temperature heat treatment maintained at 800-950 ° C for 8-10 hours,
Then, a method for producing a superconducting film is characterized by performing a low-temperature heat treatment at 300 to 550 ° C. for 10 to 20 hours, (2)
The method according to (1), wherein the base material according to (1) is preheated before fine particles of a substance having superconductivity are sprayed.

In the method of the present invention, first, fine particles of a substance having superconductivity (hereinafter, sometimes referred to as raw material fine particles) obtained by subjecting a raw material oxide to a heat treatment as a pretreatment are formed on the surface of a substrate. Spray.

In this case, having the superconductivity means that, as shown in FIG. 1, in a first equation showing an inductance L when a core material formed of powder of a target substance is inserted into a coil, L = K (Μπa ² ) N / l (1) (where K is a constant, μ is the magnetic permeability, a is the radius of the coil, N is the number of turns of the coil, l is Is the length of the coil.) When a is 4 mm, N is 50, and l is 10 mm, the decrease in the inductance L (compared to when no core material is inserted) is 1 μH or more. Say the nature.

In the present invention, in the first formula, L
Is difficult to form a superconducting film on the surface of the base material even when spraying a substance having a value of less than 2 μH.

In the present invention, the material having superconductivity obtained by subjecting a raw material oxide to heat treatment as a pretreatment is not particularly limited as long as it complies with the above definition, and includes various oxides. Specific examples include an yttrium-based oxide, a strontium-based oxide, a europium-based oxide, and a lanthanum-based oxide.

As an example, yttrium-based oxides are usually YBa ₂ Cu
₃ O _7-X (where X is 7-X from 6.5 to 6.
The number is in the range of 8. In the above formula, all or part of Ba may be substituted with an atom such as strontium.

Depending on conditions, for example, Y-
In the Ba-Cu-O system, it may be good to use an excess amount of a copper component raw material such as copper oxide so as to have a composition ratio of Cu; 3 or more with respect to Y; 1 and Ba; 2.

Which oxide is suitable for the present invention can be appropriately determined by experiment, but an yttrium-based oxide is one of the preferable oxides.

In the case of producing an yttrium-based oxide (although the same applies to the case of producing other oxides), it is preferable to classify the average particle size of the raw material oxide to 0.7 to 1 μm or less.

In any case, a substance having superconductivity obtained by performing a heat treatment as a pretreatment on the raw material oxide can impart superconductivity by performing an appropriate pretreatment on the raw material oxide. .

As the pre-treatment, the raw material oxide is blended at a ratio such that the atomic ratio in the above formula is obtained.
It is desirable to perform the heat treatment at a temperature within the range of 970970 ° C. for 1 hour to 10 hours, and repeat this heat treatment 2 to 4 times.

If the temperature at the time of the heat treatment is less than 900 ℃, it is obtained by performing a heat treatment as a pre-treatment on the raw material oxide, it may not be possible to obtain a substance having superconductivity,
On the other hand, when the temperature exceeds 970 ° C., the crystal structure changes and the raw material oxide is obtained by performing a heat treatment as a pretreatment, and a substance having superconductivity may not be obtained in some cases.

In the present invention, a substance having superconductivity obtained by subjecting a raw material oxide to a heat treatment as a pretreatment is supplied as fine particles.

The material having superconductivity, which is obtained by subjecting the raw material oxide to a heat treatment as a pretreatment, has an average particle diameter of usually 20 to 120 μm, preferably 30 to 60 μm. When the particle size is smaller than 30 μm, clogging may occur in a nozzle or a feeder pipe during the thermal spraying described below, and when the particle size is larger than 120 μm, a dense superconducting film may not be manufactured. .

To obtain a material having superconductivity, which is obtained by performing a heat treatment as a pretreatment on the raw material oxide and having a superconducting ability within the above range, for example, a lump solid is pulverized according to a known method, and then sieved or the like. You only need to classify it.

In the present invention, the raw material fine particles are sprayed to bring the plasma into contact with the surface of the base material.

As the thermal spraying method, a plasma thermal spraying method and a flame jet thermal spraying method are preferable, and both can provide substantially the same effect.

Specifically, for example, a DC arc is generated between the cathode and the anode of, for example, a water-cooled nozzle by DC arc discharge, the working gas to be supplied is heated by this arc, and the ultra-high temperature plasma generated by this is used as a plasma jet as a nozzle. By supplying the raw material fine particles into the direct current arc with a carrier gas, the raw material fine particles are melted, blown into this plasma jet, and accelerated and jetted from a nozzle by a so-called plasma spraying method. Alternatively, the plasma containing the raw material fine particles can be brought into contact with the substrate.

In the case of the plasma spraying method, argon, helium, nitrogen, hydrogen, or a mixed gas thereof can be used as the working gas. Although the plasma jet may be reduced depending on the type of the working gas, in the present invention, it is preferable to add an oxygen gas to the working gas to form an oxidizing plasma jet.

When the plasma jet is made oxidizable, a reduction in the oxygen content in the ceramic substance formed on the substrate surface can be prevented, and the superconducting film can be advantageously formed. In other words,
In the case of a reversible plasma jet, a superconducting film may not be formed on the substrate surface in some cases.

In addition, as the carrier gas, for example, argon,
Oxygen or the like can be used.

When a superconducting film is formed on a substrate surface by thermal spraying, care must be taken in the distance between the tip of the nozzle that emits plasma and the substrate surface.

In the present invention, it is desirable that the distance between the tip of the nozzle and the surface of the substrate is maintained at 85 mm or more, preferably 85 to 140 mm.

If the distance is shorter than 85 mm, a superconducting film may not be formed on the substrate surface. Although the reason for this has not been clarified yet, if the distance between the nozzle tip and the substrate surface is too short, the raw material fine particles ejected from the nozzle do not incorporate enough oxygen to show superconductivity. It is estimated from. If the distance between the tip of the nozzle and the substrate surface exceeds 140 mm, the adhesion of the superconducting film adhered to the substrate surface to the substrate decreases, and the film tends to be easily peeled.

The thermal spraying may be performed in the air or in a closed container. However, in order for the film formed on the obtained substrate surface to exhibit good superconductivity, the thermal spraying may be performed in the air. It is preferable to perform thermal spraying.

The base material is not particularly limited as long as it is a member having heat resistance to a high-temperature jet. For example, metals such as iron, cobalt, nickel, titanium, copper, zinc, and aluminum and alloys of these metals such as stainless steel ,
Alternatively, mention may be made of semimetals such as silicon, glass, ceramics such as nitrides such as silicon nitride and carbides such as silicon carbide, and carbon fibers. In some cases, a heat-resistant synthetic resin can be used as the base material.

The shape of the base material is appropriately determined depending on what kind of application the base material with a superconducting film is provided for, for example,
It may be flat or linear.

In some cases, it is preferable to preheat the substrate during thermal spraying. Preheating may be effective in taking in oxygen or densifying the superconducting film.

The thickness of the film formed on the surface of the substrate by thermal spraying differs depending on the application of the substrate with the film.

In the present invention, a high-temperature heat treatment and a low-temperature heat treatment can be performed after forming a film of a substance having superconductivity obtained by performing a heat treatment as a pretreatment on a raw material oxide on a base material surface by thermal spraying. is important.

If the high-temperature heat treatment and the low-temperature heat treatment are omitted, the film on the base material often does not show superconductivity, and a film with good adhesion is not formed.

The temperature in the high-temperature heat treatment is usually 800 to 950 ° C., and the high-temperature heat treatment time is usually 8 to 10 hours.

If the temperature at the time of the high-temperature heat treatment is lower than 800 ° C., or if the processing time is shorter than 8 hours, the adhesion of the film to the substrate may be poor and the film may be easily peeled off. If the temperature is higher than 950 ° C., there is a tendency that oxygen deficiency tends to occur, and if the processing time exceeds 10 hours, the effect of taking much time cannot be obtained.

The high-temperature heat treatment is usually performed in the air, but may be performed in an inert gas.

The temperature in the low-temperature heat treatment is usually 300 to 550 ° C., and the low-temperature heat treatment time is usually 10 to 20 hours.

If the temperature during the low-temperature heat treatment is lower than 300 ° C., or if the processing time is shorter than 10 hours, the film formed on the substrate surface may not show superconductivity, and the adhesion of the film to the substrate And may be easily peeled off. 550
If the temperature is higher than ℃, there is a tendency to cause transformation,
If the processing time exceeds 20 hours, the effect of taking a long time cannot be obtained.

Further, the film does not show superconductivity only by forming a film on the surface of the substrate by thermal spraying, but the film on the substrate becomes superconductive by performing the above-described high-temperature heat treatment and low-temperature heat treatment. It is very interesting to show.

I'm not sure why it shows superconductivity,
It is presumed that by performing the high-temperature heat treatment and the low-temperature heat treatment, oxygen necessary for exhibiting superconductivity is taken into the film.

Therefore, the high-temperature heat treatment and the low-temperature heat treatment are preferably performed in an oxygen-containing atmosphere.

The oxygen-containing atmosphere may be under air or an atmosphere in which the amount of oxygen is forcibly increased.

[Examples] Next, the present invention will be described more specifically by showing Examples and Comparative Examples of the present invention.

Example 1 Cuprous oxide having an average particle size of 1 μm, yttrium oxide having an average particle size of 0.7 μm, and barium carbonate having an average particle size of 0.7 μm were mixed at a weight ratio of 1: 2: 3. 9 of this mixture
High temperature heat treatment of heating at 50 ° C. for 8 hours was performed twice.

The mixture after the high-temperature heat treatment was packed into an elongated glass container, which was used as a core. The coil device shown in FIG. 1 was used to examine the change in inductance between when the core was not inserted and when the core was inserted. There was a decrease in inductance.

That is, this mixture after heat treatment has superconductivity.

Next, this mixture was classified so that the average particle diameter became 32 to 52 μm, and the classified mixture was subjected to a stainless steel substrate (length and width) using a thermal spraying apparatus Plasmatron [manufactured by Plasmadyne Corporation].
(5 cm, thickness 1.2 mm) was plasma sprayed.

 Thermal spraying conditions were as follows.

Working gas type Argon, helium Carrier gas type Oxygen spray thickness 100μm Distance between nozzle tip and substrate 140mm After thermal spraying, perform high temperature heat treatment to heat film coated substrate to 950 ° C for 8 hours, then return to normal temperature once Then, a low-temperature heat treatment of heating to 500 ° C. for 15 hours was performed.

When the substrate with a film was cooled to 77K and placed on a magnet, the substrate with a film floated in the air, and the Meissner effect was confirmed.

Also, after cutting the base material with a film into a strip shape so that it can be inserted into the coil shown in FIG. 1,
When a strip-shaped substrate with a film was inserted into the coil and the decrease in inductance was examined, a characteristic curve of superconductivity was obtained as shown in FIG. 2, and the inductance became extremely small at 90K.

As a result, it was confirmed that the film formed on the surface of the substrate was a superconductive film.

(Comparative Example 1) Example 1 except that the heat treatment after thermal spraying was not performed.
In the same manner as described above, the surface of the substrate was formed into a film.

When the superconductivity of the obtained base material with a film was evaluated in the same manner as in Example 1 above, the base material with a film did not show a Meissner effect such as floating above a magnet at 77 K, and the temperature was lower. Did not change the inductance at the time.
Therefore, the film on this substrate was not a superconducting film.

[Effects of the Invention] According to the present invention, (1) using a specific ceramic material to form a superconducting film that cannot be realized by the thermal spraying method by a special combination of the thermal spraying method and the heat treatment. Can be.

(2) The method of the present invention is an industrial film-forming method because the film-forming speed is higher than that of a CVD method, a sputtering method or the like.

(3) The film of the present invention cannot be formed on the surface of the wire by the CVD method or the like, whereas the film of the present invention can be formed on the surface of an arbitrary shape, for example, the surface of the wire. Opens the way for superconducting materials to be made into wires.

It has excellent technical effects such as.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a coil device for measuring an inductance, and FIG. 2 is a graph showing a decrease in inductance at a critical temperature of a thin film obtained in an example.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Jiro Kawarahata 3-43-2 Ebisu, Shibuya-ku, Tokyo Inside Jikiso Co., Ltd. (72) Inventor Toshiaki Noda 3-4-2-3 Ebisu, Shibuya-ku, Tokyo No. Jikso Co., Ltd. (56) References JP-A-1-93007 (JP, A)

Claims (2)

(57) [Claims] (1) After spraying fine particles of a substance having superconductivity onto a substrate obtained by subjecting a material oxide to heat treatment as a pretreatment, a film on the substrate surface is heated to 800 to 950 ° C. ~Ten
Perform high-temperature heat treatment to maintain the time, then
A method for producing a superconducting film, comprising performing low-temperature heat treatment for 20 hours. 2. The method according to claim 1, wherein the base material is sprayed with fine particles of a substance having superconductivity.
The method for producing a superconducting film according to claim 1, wherein the superconducting film is preheated.