JP3425966B2 - Manufacturing method of magnetic shielding container made of oxide superconducting material - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molded article made of an oxide superconducting material having few defects, and more particularly to a method for producing a magnetic shielding container utilizing the Meissner effect.

[0002]

2. Description of the Related Art Conventionally, when a bulk is made of an oxide superconducting material, it is most commonly carried out by packing and sintering a powder. HIP this sintering
(Hot isostatic pressing) is often used to create a dense material or to melt a part of the composition to increase the density (sometimes called partial melt). .

Further, as a method for improving the drawbacks of the powder sintering method, there is a method of using a paste in which a powder made of an oxide superconducting material is dissolved in an appropriate dispersion medium. These pastes or slurries are directly formed into a plate shape by a doctor blade method or the like, or the paste or slurry is applied onto a substrate having a desired shape and baked to produce an oxide superconducting material having a considerably free shape. Is becoming possible.

[0004] Further, a method of coating a thin film and a thick film made of an oxide superconducting material on a suitable substrate or substrate by using a method such as CVD is also being studied mainly for wires.

[0005]

Despite considerable research being conducted, it is difficult to say that the conventional method for producing an oxide superconducting material is practical. For example, in the powder sintering method, there is almost no degree of freedom in shape, and it is a technically difficult method to create a large sintered body even if it is not an oxide superconducting material. Is almost impossible to perform with an oxide superconducting material. Further, the molded product obtained by HIP or the like has a high density and a dense product, but it cannot be increased in size.

The method using a paste or the like is also used for producing a superconducting magnetic shielding container whose sample shipment is about to start, and is a method having a high degree of freedom in shape and excellent. However, these are inevitably porous because organic substances and the like in the dispersion medium are removed during firing, and in many cases the quality is insufficient for the purpose of magnetic shielding.

The material produced by coating by the CVD method or the like has a high quality, but in order to obtain a certain magnetic shielding ability, a certain volume as a bulk, that is, the thickness of the container is required. At present, it is insufficient considering the film speed.

Therefore, there has been a demand for a method for solving the above-mentioned problems and for producing a molded product of high quality as well as flexibility of shape and productivity.

[0009]

SUMMARY OF THE INVENTION The present invention combines the advantages of a method of using a paste and coating such as CVD in order to produce a molded product of high quality together with the freedom of shape and productivity. Is. The structure of the present invention will be described below.

The present invention is characterized in that when a molded product (a magnetic shielding container as a main object) is obtained, it is roughly divided into two steps.

The first step is a step of forming a molded product to be a matrix having a rough shape, and this part is basically the same as the method using a conventional paste or the like. That is, an oxide superconducting material is mixed with an organic binder or the like to form a slurry, which is formed into a sheet shape, which is wound or formed into a tile shape, and then pasted using a paste or the like, or YSZ or the like. The sintered body is formed into a desired shape by a method such as applying a paste onto the sintered body as a base, and firing the formed body.
However, the conventional method using a paste has been trying to obtain a relatively dense molded product by itself, so that the essential advantage such as simplicity has been lost. More specifically, it was necessary to perform temperature management very severely. However, in the present invention, it is only for forming a matrix, and even if it is porous to some extent, there is no problem, so there is a secondary effect that this step can be simplified. That is, in this step, if there are no large cracks or large defects that cannot be blocked, such high density is not required. Also, the magnetic shielding ability is largely related to the pinning force of the constituent materials, and therefore it is effective to add a material that will serve as a pinning center when forming the matrix.

In the second step, a film is formed by using CVD or the like in order to fill the gaps in the molded product obtained in the first process, that is, the matrix, and to form a denser and higher quality molded product. It is a process to do. At that time, an oxidizing gas is introduced from either the inside or the outside of the molded product, and the raw material gas of the oxide superconducting material, that is, for example, each organometallic complex is introduced from the other, and the two kinds of gases are It has a great feature in forming an oxide superconducting material so as to close the holes of the matrix by adjusting the flow rate and the pressure. In other words, the higher the gas permeability, the more preferentially the film grows,
As a whole, it goes toward a dense molded product. This principle will be briefly described with reference to FIG.

First, the matrix obtained by sintering the slurry or the like is porous and has many pores 1 (FIG. 1.a). When the oxidizing gas 3 is supplied from one side and the source gas 2 is supplied from the other side, both of them are mixed in the vicinity of the above-mentioned holes and react with each other to easily form an oxide (FIG. 1.b). When kept at a high temperature in this state, the two gases react to form the oxide superconducting material 4,
Deposit near the holes. And, as this deposition site, by sufficiently lowering the rate of gas permeation through the holes,
It is possible to deposit directly on the pores, that is, so as to close the pores (FIG. 1.c).

By switching the above-mentioned two kinds of gas midway, it is possible to obtain a dense film on both surfaces of the molded product. In the present invention, the method of CVD does not matter. That is, MOCVD using an organometallic complex as a raw material
Alternatively, halide CVD using a halide salt of a constituent metal as a raw material may be used. Of course, it is natural that there is a limitation that an oxidizing gas suitable for it is used. In addition, when the film is formed, the pressure is not limited, but considering that the high-quality film used in a device or the like is not necessary and that the higher the film forming rate is, the normal pressure process or the low vacuum process is sufficient. It has been confirmed that there is.

Further, as described above, one of the major characteristics of the CVD process of the present invention is that the film growth proceeds so as to close the defects. However, it has been considered that this method cannot be used after defects and the like are completely closed, and therefore further growth of the film cannot be expected.

Unexpectedly, however, when a film is continuously formed after a molded product which is dense enough to prevent gas permeation is obtained, the film formation rate is remarkably reduced, but a very hard and dense film is formed on the surface. It turned out to coat the whole. This is due to the very high oxygen ion transport number of the oxide superconducting material itself, and corresponds to EVD which has been partially put into practical use in other fields. This principle will be briefly described with reference to FIG.

When the oxygen superconducting material 5 has a high oxygen partial pressure and a low oxygen partial pressure (in FIG. 2, the upper oxygen partial pressure is lower and the lower oxygen partial pressure is higher). (As shown), a kind of densified cell is formed and an electromotive force is generated, resulting in an ionic current flow. That is, oxygen 8 becomes an oxide ion at the interface with the high concentration side of oxygen partial pressure and moves in the oxide superconducting material (oxide ion 7), and oxygen is again oxygenated at the low concentration side of the other oxygen partial pressure. 6 is formed (Fig. 2.a). The oxygen thus generated reacts with the raw material gas 9 of the oxide superconducting material in the vicinity of the surface of the matrix to form a dense and good quality thin film 10 so as to cover the entire surface (FIG. 2.b).

In order to confirm that this step is EVD, it suffices to confirm whether or not an ionic current is flowing.
By forming a porous electrode made of platinum on the inner and outer surfaces of a molded article that is dense enough not to have gas permeability, and observing the current between them, it is possible that an ionic current will flow,
It was confirmed that the above principle was correct.

This can also be applied to an oxide superconducting material formed on a substrate having oxide ion conductivity. The thin film obtained by the process corresponding to this EVD is a more dense and high-quality product than the thin film obtained by the process (CVD process) prior to the present invention. Therefore, by adding this process, The molded product has almost no pinholes and can be sufficiently used for magnetic shielding.

It is sufficiently possible to exhibit superconductivity by controlling the atmosphere for film formation and firing only by the above series of steps, but if necessary, anneal the whole in an arbitrary atmosphere. Is valid.

[0021]

According to the present invention, it becomes possible to obtain a molded article made of an oxide superconducting material having both productivity and compactness. Also, since it does not require a particularly complicated device and process and is realized by a combination of commonly used technologies at present, it is also important that the versatility is high.

Hereinafter, the present invention will be described in more detail by showing examples.

[0023]

【Example】

Example 1 As an example of the present invention, a yttrium-based oxide superconducting material (typically, as an oxide superconducting material)
An example of using YBa ₂ Cu ₃ O ₇ ) to make a magnetic shielding container having a cylindrical shape is shown.

First, each raw material powder was wet mixed so that Y: Ba: Cu = 1: 2: 3. In practice, it is possible to achieve a higher critical current density by shifting the weak crown composition so that the so-called 221 phase precipitates.This time, only Y was slightly increased, and the platinum Material with a small amount of addition was used. This was calcined, crushed, fired and annealed to confirm superconductivity. Next, the obtained oxide superconducting material was finely pulverized and mixed with an organic binder to obtain a slurry. Here, it should be noted that if the organic binder is too much, large voids may be formed in the obtained molded product.

Next, the obtained slurry was spread on a Teflon sheet so as to have a thickness of about 5 mm, and this was rolled into a cylindrical shape to obtain a molded product. A sheet having the same thickness was also used to seal one end by pasting together with a paste.

After drying, these were baked in oxygen at 960 ° C. for 6 hours, and then gradually cooled at a rate of 100 ° C./hour to sufficiently absorb oxygen to obtain a molded product. At the time of firing, in order to maintain the shape, it is necessary to take care so that the stress distribution is not biased, that is, is not bent. The dimensions of the container after firing are about 100 mm in diameter and about 500 mm in length. As a result of measuring the molded product by the Archimedes method, it was about 70% of the theoretical density, which was expected to be slightly porous, and it was confirmed that a considerable amount of voids were actually contained due to gas permeation.

Next, the baked container was similarly fixed to the tip of an alumina tube 17 having a diameter of 100 mm. An inorganic adhesive mainly composed of alumina was used for fixing. This alumina part is fixed to gauge ports 15 and 16, and as a whole,
The configuration is as follows.

This time, the container 13 made of oxide superconducting material
Oxygen was introduced from the inside, and a raw material composed of a β-diketone (DPM) complex of each constituent metal was flown from the outside, and the film formation was performed at a reaction pressure of 100 Torr. The composition of the raw materials was controlled by different cell temperatures, and the raw materials were transported to the reaction vessel by argon gas. Also, a container made of oxide superconducting material 13
Was heated to 750 ° C. this time by a hot-wall type reaction vessel 12 with a heater 14 to form a film.

In order to confirm the change in firing, a zirconia-type oxygen concentration meter was installed in front of the rotary pump on the exhaust 19 side to start film formation.

In the initial setting, the flow rate of the source gas 11 was 200 sccm, the flow rate of oxygen 18 was 10 sccm, and the supply pressure was 100 sccm.
APC by controlling the conductance on the exhaust side
By (auto pressure control), the pressure inside the reaction vessel was kept constant and film formation was started.

It was confirmed that the amount of oxygen sensed by the oximeter decreased slightly from about 3 hours after the start of film formation. This is probably because the voids and the like of the container made of the oxide superconducting material have been filled. Therefore, when the flow rate was further reduced and the film formation was continued, the oxygen pressure obviously decreased from 8 hours after the start of the film formation. From around this time, it can be construed that the direct supply of oxygen through the voids and the like has substantially disappeared.
In other words, at this point, the transition from the CVD process in the present invention to the EVD process is performed.
Therefore, the flow rate of the raw material gas was further reduced to 50 sccm, and then the film was formed for another 5 hours.

After the film formation was completed, the raw material gas was stopped, oxygen was supplied instead, and the furnace was cooled at an oxygen pressure of 1 atm both inside and outside, cooled to room temperature, and then taken out.

The container made of the oxide superconducting material taken out had a smooth surface, and its morphology was greatly different from that of the case of only the matrix prepared from the slurry.

Finally, the portion joined to the alumina tube and the portion having one end sealed were cut to obtain a magnetic shielding container having both ends open. When the superconductivity was confirmed by the direct current 4-terminal method using the cut portion, it was confirmed that the resistance became completely zero at 91K.

The finally remaining magnetically shielded container has a diameter of approximately
It had a cylindrical shape of 50 mm and had a thickness of about 4.5 mm.

Finally, the magnetic shielding ability of the magnetic shielding container using the oxide superconducting material thus obtained will be described. When the magnetic field was applied in the axial direction of the cylinder, the magnetic shielding ability was about 14 Gauss. By the way, in the case of the sintered body made from the slurry prepared previously (the one used this time as the matrix), it was about 5 gauss, which was proved to have a considerable effect.

[Example 2] As Example 2, an example in which the thin film made of an oxide superconducting material coated only on the outside in Example 1 is also coated on the inside will be described.

Before the voids are completely closed, that is, EVD
In the previous CVD process, the thin film was coated not only on the outer side but also on the inner side by changing the inner gas species and the outer gas species at regular intervals, this time every 30 minutes. Naturally, it took an extra time, which was about 1.4 times longer than the case of only one side. The apparatus used for film formation is the same, and in this embodiment as well, from CVD to E
The transfer to VD was performed by observing the amount of oxygen permeation.

In the subsequent EVD process, the film formation was performed for 5 hours on one side, for a total of 10 hours, as in Example 1. As a result, the magnetic shielding ability was improved to about 17 gauss.

Example 3 This time, instead of directly forming an oxide superconducting material in a cylindrical shape, a substrate having oxide ion conductivity, specifically, YSZ (yttrium partially stabilized zirconia) was used. An example is shown in which a sintered body is used as a base, and a magnetic shield portion made of an oxide superconducting material is formed thereon by a paste coating method. Yttrium-based oxide superconducting materials (typically YB
a ₂ Cu ₃ O ₇ ) was used, but the composition and the like were exactly the same as in Example 1, and the method of making the paste was also based on the slurry of Example 1.

The sintered body of YSZ (yttrium partially stabilized zirconia) was not porous but was intentionally made porous. The shape is a one-end seal like a protective tube with a diameter of 50 mm and a length of about 1000 mm. On top of this, paste of oxide superconducting material is spread over a length of 500 mm,
It was applied from the tip. Instead of applying the coating thickly at one time, coating, drying and sintering were performed several times to form a film having a thickness of about 2 mm.

After the thick film was formed by the paste, coating was performed by the same process as in Example 1 (the film forming time and the like are slightly different because the thickness is different).

Finally, the magnetic shielding ability of the magnetic shielding container using the oxide superconducting material thus obtained will be described. When a magnetic field was applied in the axial direction of the cylinder, a magnetic shielding ability of about 8 Gauss was obtained. It is considered that the magnetic shielding ability is lower than that of Examples 1 and 2 because the thickness of the portion made of the oxide superconducting material is small.

[Embodiment 4] As an embodiment of the present invention, a bismuth oxide superconducting material (typically, 2212 phase called 80K phase) is used as the oxide superconducting material. An example of producing a magnetic shielding container having a simple cylindrical shape will be shown.

First, wet mixing was carried out so that Bi: Sr: Ca: Cu = 2: 2: 1: 2, and these were calcined, crushed, fired and annealed to confirm superconductivity. Further, fine silver powder was added for the purpose of increasing the critical current density. Next, the obtained oxide superconducting material was finely pulverized and mixed with an organic binder to obtain a slurry. Also here, as in Example 1, if too much organic binder is used, large voids may be formed in the obtained molded product, so care must be taken.

Then, in the same manner as in Example 1,
Shielded containers of the same size were formed.

Next, regarding the method for coating these with a thin film, the atmospheric pressure CVD method was adopted this time, and an attempt was made to increase the film forming speed. As a raw material, a DPM complex of each constituent metal was used, heated to 120 to 270 ° C., and transported to a reaction chamber using argon gas. The pressure during film formation is about 1 atm, and the apparatus configuration and the like are exactly the same as in the first embodiment. The oxygen supply pressure was about 1 atm. The flow rate was set to 500 sccm for the source gas and 100 sccm for the oxygen in the initial settings, aiming for high-speed film formation. Deposition temperature is 750 ℃
Is.

Basically, the behavior during film formation was also in accordance with Example 1, but since the film formation rates differ greatly,
After about 3 hours, a transition from CVD to EVD was observed, and film formation was continued for about 3 hours thereafter. After the film formation, unlike the yttrium system, this time, after annealing in a slightly reduced state with a mixed gas of argon and oxygen, furnace cooling was performed. At the time of cooling, it was necessary to be careful to slow the cooling rate so that cracks and the like would not occur.

In the same manner as in Example 1, the joined portion with the alumina tube and the portion having one end sealed were cut to obtain a magnetic shielding container having both ends open. Superconductivity was confirmed by the direct current 4-terminal method using the cut portion, and when analyzed by XRD, it was confirmed that most of them consisted of 80K phase, although 110 K phase was partially included.

The finally obtained cylindrical magnetic shielding container had a magnetic shielding ability of about 35 Gauss when a magnetic field was applied in the axial direction of the cylinder. It is considered that the magnetic shielding ability is higher than that of the yttrium-based material of Example 1 while having exactly the same dimensions, probably because of the difference in critical current density.

[0051]

Industrial Applicability According to the present invention, it becomes possible to rapidly manufacture a magnetic shielding container or the like made of an oxide superconducting material having good characteristics while having an arbitrary shape which has been impossible up to now. It was The method can be sufficiently applied within the category of conventional technology, and the cost is relatively low.

Although the cylindrical shape is shown this time, it is needless to say that it is easy to form another magnetic shield plate, for example, in the form of a plate. It was possible to further improve the characteristics by using an oxidizing gas having a strong oxidizing power other than oxygen, and steam oxidation was possible depending on the raw material.

That is, the present invention is very promising and is therefore considered to be very useful.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a process of filling voids by a gas supply method of the present invention.

FIG. 2 is a schematic diagram of an EVD process according to the present invention.

FIG. 3 is a schematic view of hot wall type CVD used in the examples.

[Simple explanation of symbols]

1 Void 2 Raw material gas 3 Oxidizing gas 4 Oxide superconducting material 5 Moldings made of oxide superconducting materials 6 oxygen molecules 7 Oxide ion flow 8 oxygen molecules 9 Raw material gas 10 Oxide superconducting thin film 11 Raw material gas flow 12 Reaction chamber 13 Molded product made of oxide superconducting material 14 heater 15 gauge port 16 gauge port 17 Alumina tube 18 Oxidizing gas flow 19 Exhaust gas flow

Claims (8)

(57) [Claims] 1. An oxide superconducting material is mixed with a binder.
Slurry, shape the slurry into the desired shape, and bake
The step of forming a porous container by heating, and one of the inside and the outside of the container in a heated state.
Introducing oxidizing gas from one side, and introducing the oxidizing gas
Either the outside or the inside of the container opposite to the
Introduce the raw material gas of the oxide superconducting material from the side of
The oxidizing gas and the oxide superconductor through the holes of the container.
Reacts with the source gas of the material to cause the oxidation near the holes.
A step of depositing a magnetic superconducting material , and a magnet made of an oxide superconducting material.
A method for manufacturing an air shielding container . 2. An oxide superconducting material is mixed with a binder.
There is a slurry, and the slurry is rolled into a sheet shape.
Or tile to form the desired shape
Form a porous container by molding and firing
And the heated state, either inside or outside the container.
Introducing oxidizing gas from one side, and introducing the oxidizing gas
Either the outside or the inside of the container opposite to the
Introduce the raw material gas of the oxide superconducting material from the side of
The oxidizing gas and the oxide superconductor through the holes of the container.
Reacts with the source gas of the material to cause the oxidation near the holes.
A step of depositing a magnetic superconducting material , and a magnet made of an oxide superconducting material.
A method for manufacturing an air shielding container . 3. Mixing an oxide superconducting material with a binder
As a paste, YSZ (yttrium partially stabilized zirconia
Apply the paste on the base consisting of the sintered body of a).
By forming it into a desired shape and firing it to make it porous
Quality container and, when heated, either inside or outside the container.
Introducing oxidizing gas from one side, and introducing the oxidizing gas
Either the outside or the inside of the container opposite to the
Introduce the raw material gas of the oxide superconducting material from the side of
The oxide superconducting and the oxidizing gas to through holes of the serial container
Reacts with the source gas of the material to cause the oxidation near the holes.
A step of depositing a magnetic superconducting material , and a magnet made of an oxide superconducting material.
A method for manufacturing an air shielding container . 4. A step of depositing the oxide superconducting material.
In the process of depositing the oxide superconducting material,
The introduction of the reactive gas and the raw material gas of the oxide superconducting material
Switch from inside to outside or outside to inside of each container
This allows the oxide superconductivity to grow inside and outside the container.
4. A conductive material is deposited according to claim 1.
A magnetic shield made of the oxide superconducting material according to any one of the above.
A method for manufacturing a shielding container . 5. A step of depositing the oxide superconducting material
Therefore, it is characterized in that the holes of the porous container are closed.
A method for manufacturing a magnetic shielding container made of the oxide superconducting material according to claim 1 . 6. A step of depositing the oxide superconducting material.
And deposit the oxide superconducting material using the CVD method.
6. The method according to claim 1, wherein
Of the magnetic shielding container made of the oxide superconducting material described in
Manufacturing method. 7. A step of depositing the oxide superconducting material
And deposit the oxide superconducting material using the CVD method.
The oxidizing gas and the oxide superconducting
A molded product that is dense enough not to pass the raw material gas of the conducting material
After the formation, the oxide superconductivity is continuously applied to the surface of the molded product.
A method comprising the step of forming a film of a conductive material.
Item 5. The oxide superconducting material according to any one of Items 1 to 5.
A method for manufacturing a magnetic shielding container. 8. The oxidizing gas and the oxide superconducting material
To form a compact molded product that does not allow the raw material gas of
After that, the oxide superconducting material is continuously applied to the surface of the molded article.
A step of performing film formation is characterized by a EVD method
A magnetic shield made of the oxide superconducting material according to claim 7.
How to make a container.