JPH0832599B2 - Cylindrical structure of oxide superconductor - Google Patents

Description

The present invention relates to a tubular structure of an oxide superconductor.

[Conventional technology]

Oxide superconductors have a high critical temperature and are attracting attention because they are expected to be used in various fields such as electric power fields, nuclear magnetic resonance devices, and magnetic shields. In particular, weak biomagnetism can be measured with a simple cooling device using liquid nitrogen by using an oxide superconductor, and future applications in the medical and medical fields are expected.

In the measurement of biomagnetism, the measuring device needs to be able to accommodate a living body and at the same time obtain an extremely low magnetic field space, and a tubular structure has been generally proposed as a container for the living body.

To obtain an extremely low magnetic field space in a tubular structure,
It is necessary that the superconducting current sufficient to shield the earth's magnetic field uniformly flows over the entire tubular body. For this reason, it has been conventionally said that a tubular body containing a living body must be obtained by integral manufacturing.

[Problems to be Solved by the Invention]

However, the cylindrical body that serves as a container for biomagnetic measurement requires a minimum diameter of about 1 m and a length of about 3 m for diagnostic measurement of the human body.

In order to integrally manufacture such a large tubular body,
In addition to requiring a large-scale electric furnace and not being practical, it is predicted that it is extremely difficult with the current technology to make the entire region of the tubular body made of an oxide superconductor uniform.

As a result of intensive investigations by the inventors for the purpose of obtaining a container for biomagnetism measurement that can be industrially put to practical use, conventionally, a container for a homogeneous oxide superconductor produced by integral molding, etc. While it was said that it is possible to obtain an extremely low magnetic field space by shielding, the present invention is a tube of a long oxide superconductor obtained by joining after manufacturing a large tubular body by dividing. The present invention has been completed by specifying a part to be divided and a joining state in order to obtain a tubular body having a high magnetic shielding ability even in the case of a tubular body.

[Means for solving the problem]

According to the present invention, in a tubular structure of an oxide superconductor used as a magnetic shield for biomagnetism measurement, there is one or two or more joints that traverse the axial direction, and the joints are of the tubular body. The oxide superconductors are arranged at intervals of 1/10 or more of the diameter, and the relationship between the thickness (t: mm) of the oxide superconductor and the critical current density (Jc) is such that t × Jc is 4 A / cm or more, at the joint, t × Jc is 0.4 A / cm or more, and the width of the joint is 0.5
There is provided a tubular body structure of an oxide superconductor characterized by being less than or equal to mm.

 Hereinafter, the present invention will be described in detail.

Examples of the oxide superconductor in the present invention include M-
Ba-Cu-O-based compound (where M is Sc, Tl, Y and La, Eu, G
Represents one or more selected from lanthanides such as d, Er, Yb and Lu. ) And Bi-Sr-Ca-Cu-O based compounds having a multi-layer perovskite structure.

The oxide superconductor of the present invention may be composed only of the above oxide superconductor, or may be one in which the above oxide superconductor is composited by coating or the like on a substrate such as a metal to form a superconductor.

The tubular body structure of the present invention is obtained by dividing the tubular body in the axial direction into 1 or 2 or more pieces, producing divided tubular bodies each shorter than 1 m, and joining the divided tubular bodies. is there. The length of the tubular body is not particularly limited, but is generally applied to a tubular body of 1 m or more.

The division of the tubular body in the axial direction may be preferably performed at a right angle, but may be within ± 10 ° from the vertical. When dividing at an angle of 10 ° or more from the vertical, the magnetic shield is not sufficient, and when the cylindrical body is used as a biomagnetic measurement container, a very low magnetic field space cannot be obtained.

In the tubular body of the present invention, the joint portion has a diameter of the tubular body.
Make sure they are placed at 1/10 intervals. Therefore, the divided tubular body used in the present invention generally has a diameter of about 1 m and a length of 0.1 to 1.0 m, and the diameter is the same as the diameter constituting the tubular body structure. If the length is less than 0.1 m, the joints having a low critical current density will be present at intervals of less than 0.1 m, and the effect of shielding the geomagnetism will be reduced, which is not suitable as a biomagnetic measuring container. In addition, the length of the divided tubular body is 1.0 m
If it exceeds, it is not practical and is not preferable.
For example, those with a diameter of 1 m and up to a length of 1 m can be fired in an existing electric furnace, and if the length is 0.5 m or less, it can be fired using a relatively small electric furnace that has been conventionally used. It is more preferable because it is possible to easily manufacture a tubular body which is an oxide superconductor having a uniform whole area.

The critical current density (Jc) at the joint portion of the present invention may be lower than Jc of the oxide superconductor forming the tubular structure.
Jc in the joint portion varies depending on the thickness of the oxide superconductor (which is a layer having the oxide superconducting property in the oxide superconductor compounded with a substrate such as a metal) forming the tubular body, For example, when the thickness of the oxide superconductor is 1 mm, the junction is made of a superconductor having Jc of 4 A / cm ² or more, and the width of the junction is 0.5 mm or less, sufficient magnetic shielding can be achieved.

Generally, in order to completely shield the earth's magnetism, it is necessary to attenuate the external magnetic field by about 5 gauss in consideration of the fluctuation of the earth's magnetism and the safety factor. In this case, for example, in a cylindrical tubular structure having a diameter of 1 m and a length of 3 m, it is necessary to have a diamagnetic current of about 4 A per 1 cm of the axial direction of the tubular body, that is, a superconducting current in the circumferential direction of the tubular body. Requirements. In order to satisfy this requirement, for example, the thickness of the superconductor that constitutes the tubular body
If it is 1 mm, it has a Jc of 40 A / cm ² , and the thickness is 10
If it is 0 μm, it must have a Jc of 400 A / cm ² .

Further, it has been considered that, when the tubular body is obtained by joining the divided bodies in the manufacturing process, there is a possibility that the external magnetic field may enter from the joined portion and the external magnetic field cannot be attenuated.

On the other hand, according to the knowledge of the inventors, when the joint is installed across the axial direction of the tubular body, for example, with a diameter of 1 m,
In a cylindrical body structure consisting of a 3.0 m long cylindrical 1 mm thick oxide superconductor, two divided cylindrical bodies are installed so that the joint part is installed almost vertically at a 1.5 m long site. Gap width 0.5 mm
When the intrusion magnetic field was measured by arranging and arranging, the intrusion of the external magnetic field into the inside of the cylindrical body was about 10%.
Therefore, as described above, when the thickness of the oxide superconductor is 1 mm, Jc at the joint width of 0.5 mm is 4 A / cm ²
The above is enough.

In the present invention, the joining of the divided tubular bodies is a method of joining the divided tubular bodies as they are and locally heating and melting them, and when joining the divided tubular bodies, a superconductor of the tubular body is formed. After applying the raw material slurry to the joining surface of the divided tubular body, the method of joining the joining portion by partially firing, and a joining portion different from the tubular body between the joining divided tubular bodies, preferably having a lower melting point Such as a method of arranging a thin cylindrical body of an oxide superconductor that forms a film, locally heating and melting and joining, or applying a raw material slurry that constitutes the oxide superconductor and then partially firing and joining. It can be performed by various methods.

The partial heating melting or firing in the above joining method can be performed by using, for example, a local heating furnace.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to this embodiment.

Example Y ₂ O ₃ powder (average particle size 0.4 μm), BaCO ₃ powder (average particle size 0.8 μm) and CuO powder (average particle size 2.5 μm) having a purity of 99.9%
m) was prepared in a molar ratio of 1: 4: 6, and
It was calcined at 40 ° C. for 10 hours to synthesize YBaCu ₃ O ₇ powder.

Then, 2 g of this YBaCu ₃ O ₇ powder was mixed with 50 g of polyvinyl butyral (PVB) as a binder and 5 g of a nonionic dispersant, and 1 g of zirconia cobblestone was placed in 2 l of toluene in a polypot container and pulverized with a rotary mill for 16 hours. -Slurry was prepared by mixing. This slurry was granulated with a spray dryer to an average particle size of 50 μm.

This powder was press-molded with a hydrostatic pressure of 2.5 ton / cm ² to obtain a cylindrical molded body (A) having an outer diameter of 110 mm, a height of 350 mm and a thickness of 8 mm, and an outer diameter of 110 mm, a height of 120 mm and a thickness of 120 mm. Three cylindrical shaped bodies (B) having a length of 8 mm were produced.

Each of the formed compacts was fired in an oxygen atmosphere at 250 ° C for 6 hours, 880 ° C for 10 hours, and further at 960 ° C for 6 hours,
Then, the mixture was gradually cooled at 1 ° C./min to obtain a cylindrical sintered body.

The obtained sintered body is a compact (A) with an outer diameter of 100 mm and a height of 3 mm.
A cylindrical sintered body (A) with a thickness of 00 mm and a thickness of 6 mm, and a molded body (B)
Was a cylindrical sintered body (B) having an outer diameter of 100 mm, a height of 100 mm and a thickness of 6 mm.

Then, after three end faces of the sintered body (B) are smoothed with SiC paper, the YBaCu ₃ O ₇ slurry is applied to the joint surface, and the _three joints are combined in an oxygen atmosphere in the same manner as above. Was fired and gradually cooled to obtain a cylindrical sintered body (B ') having a joint and having a height of 300 mm. Jc of the joint in this case is
In 20A / cm ^2, it was lower than Jc100A / cm ² of sintered body.

The sintered bodies (A) and (B ') obtained above were immersed in liquid nitrogen in a minute magnetic field space (10 ^-4 Gauss) magnetically shielded with a permalloy alloy to make them superconducting. After that, take out the sintered body into the geomagnetism in a state of being immersed in liquid nitrogen,
The magnetic field strength at the center of each cylindrical sintered body was measured with a magnetometer.

As a result of the measurement, the magnetic field strength in the direction parallel to the cylindrical axis of the sintered body was 10 ⁻³ Gauss or less for both the sintered bodies (A) and (B ′), and both of them completely shielded the earth's magnetic field.

Comparative Example By the same manufacturing method as in the example, the outer diameter is 110 mm and the height is
Six semi-cylindrical compacts (C) each having a size of 8 mm and a thickness of 8 mm and having a shape obtained by cutting a cylinder into two in the axial direction were prepared, and six sintered compacts (C) were obtained. Thereafter, six sintered bodies were bonded and fired in the same manner as in the example so as to form a cylindrical body, and a cylindrical sintered body (C ′) having a joint portion and a height of 300 mm was obtained.

The magnetic shielding ability of the sintered body (C ') was measured in the same manner as in the example. As a result, the magnetic field strength in the direction parallel to the cylindrical axis of the sintered body (C ′) was 10 ⁻² Gauss, and it was confirmed that the geomagnetism partially penetrated.

From the results of these examples and comparative examples, in the cylindrical body of the oxide superconductor having the joint portion in the axial direction, there is a partial invasion of the geomagnetism, whereas in the present invention, there is a joint portion traversing the axial direction of the present invention. In the tubular body of the oxide superconductor in which the divided tubular bodies are joined as described above, a minute magnetic field at the same level as that of the tubular body of the integrally molded oxide superconductor can be obtained, and the magnetic flux from the joint portion can be obtained. It was confirmed that no leakage occurred.

〔The invention's effect〕

The present invention is a tubular body structure of an oxide superconductor, which is manufactured by dividing a large-sized tubular body into pieces and then providing a joint portion, and is an oxide superconductor tubular body having a joint portion. Even so, it is possible to obtain a shield effect of geomagnetism.

Conventionally, it is said that the shield effect can be obtained only by integral molding, etc., and in view of the fact that practical application has been a problem, particularly in the industrial production of a large oxide superconductor container used for biomagnetic measurement, Extremely useful.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01B 13/00 HCU Z 7244-5L

Claims (1)

[Claims] 1. A tubular structure of an oxide superconductor used as a magnetic shield for biomagnetism measurement, which has one or more joints traversing the axial direction, and the joints have a diameter of the tubular body. The distance between the oxide superconductor and the critical current density (Jc: A / cm ² ) is 1/10 or more, and the relation between the critical current density (Jc: A / cm ² ) is t × A tubular body structure of an oxide superconductor characterized in that Jc is 4 A / cm or more, t × Jc is 0.4 A / cm or more at the joint, and the width of the joint is 0.5 mm or less.