JPH0529787A - Magnetic shield - Google Patents

Abstract

PURPOSE:To provide a magnetic shield possessing high strength and a high magnetic shielding effect. CONSTITUTION:There are provided a silver intermediate layer 2 formed on at least one surface of the material 1 and a coated film 3 comprising a mixture of an oxide superconducting material containing CuxOy-group and 2-30% silver, with the coated being formed on the surface of the intermediate layer 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic shield, and more particularly to a magnetic shield having high strength and high magnetic shield effect.

[0002]

2. Description of the Related Art In the field of biomagnetic measurement for diagnosing a patient based on the weak magnetism generated from the human body, and in the field of magnetic exploration for exploring mineral resources based on the weak magnetism generated from rock, etc. The earth magnetism existing in the environment of the magnetic detection object and the environment of the magnetic detector, and the external magnetism such as the leakage magnetism generated from various electric devices are factors that reduce the detection accuracy of the weak magnetism described above.

Therefore, in order to improve the detection accuracy of weak magnetism, the magnetic substance to be detected and the magnetic detector are protected by an external environment so that external magnetism does not enter the magnetic substance to be detected and the magnetic detector. Need to be magnetically shut off from. Generally, the magnetic shield is made of a ferromagnetic material such as iron or nickel. If a magnetic shield made of a ferromagnetic material covers the magnetic substance to be detected and the magnetic detector, most of the external magnetism will be in the space surrounded by the magnetic shield in which the magnetic substance to be detected and the magnetic detector are placed. Walks along the magnetic shield without penetrating into. Therefore, the weak magnetism is detected with high accuracy without being affected by the external magnetism.

However, the magnetic shield made of a ferromagnetic material is effective in reducing the relatively strong external magnetism to the extent of the intensity of the earth's magnetism. For example, in the case of measuring weak magnetism such as biomagnetism. As described above, when the external magnetism needs to be significantly reduced as compared with the strength of the earth's magnetism, the magnetic shielding effect is not so great. This is because the magnetic shield made of a ferromagnetic material has a residual magnetism.

Therefore, in order to overcome such problems, a base material of stainless steel having no remanence and a Y ₁ formed on at least one surface of the base material by a known plasma spraying method. A magnetic shield composed of a film of a complex oxide superconducting material such as Ba ₂ Cu ₃ O _7- δ can be considered.

According to the magnetic shield described above, Y ₁ Ba ₂ Cu
_A high magnetic shielding effect can be obtained by the Meissner effect of the ₃ O _7- δ film, that is, the diamagnetic effect of completely eliminating external magnetism. Moreover, Y ₁ Ba ₂ Cu ₃ O _7- δ
The critical temperature of the film, that is, the maximum temperature at which the superconducting state occurs (hereinafter simply referred to as Tc) is about 93K. Since the temperature of liquid nitrogen is 77K, liquid nitrogen, which is cheaper than liquid helium, can be used as a coolant for the Y ₁ Ba ₂ Cu ₃ O _7- δ coating.

However, the above-mentioned magnetic shield is
It has the following problems. That is, since the base material is made of stainless steel, Y ₁
During the formation of the Ba ₂ -Cu ₃ O _7- δ film and during the heat treatment of the film after the formation, the base material is likely to chemically react with the film, thus deteriorating the superconducting property of the film.

[0008] Therefore, in order to overcome such a problem, "Materia-ls Research Soci" issued in 1988.
ety Proceedings ", Volume 99, 695-698," Super Co
nduct-ing Tape-Shaped Wire by Y ₁ Ba ₂ Cu ₃ O _7- δ With J
_c 2000A / cm ² "discloses a tape-shaped superconducting wire (hereinafter referred to as the prior art) having excellent superconducting properties.

The prior art superconducting material is composed of a silver base material and a Y ₁ -Ba ₂ Cu ₃ O _7- δ coating formed on the surface of the base material. According to the above-mentioned prior art, the base material is a composite oxide superconducting material containing a Cu _x O _y -group, and silver that is difficult to chemically react with the coating during the formation of the coating and the heat treatment of the coating after the formation. The superconducting properties of the coating do not deteriorate as it is made of

[0010]

However, when the above-mentioned prior art is applied to a magnetic shield, it has the following problems. That is, the base material made of silver has low strength and is expensive. Therefore, it is difficult to manufacture a large magnetic shield capable of accommodating a human body, such as a magnetic shield for biomagnetism measurement. Therefore, an object of the present invention is to provide a magnetic shield which has a high strength and a high magnetic shielding effect and can be manufactured at low cost.

[0011]

The present invention comprises a silver intermediate layer formed on at least one surface of a matrix and a Cu _x O _y -group formed on the surface of said intermediate layer. It is characterized in that it is composed of an oxide superconducting material and a coating film made of a mixture of silver in the range of 2 to 30 wt.

Next, one embodiment of the magnetic shield of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing one embodiment of the magnetic shield of the present invention. First
As shown in the figure, the magnetic shield of the present invention is based on the base material 1
And a silver intermediate layer 2 formed on one surface of the base material 1.
And Cu _x O _y formed on the surface of the intermediate layer 2.
And a coating 3 made of a mixture of a group-containing composite oxide superconducting material and silver. The base material 1 is made of any one of paramagnetic metal, diamagnetic metal, and ceramics, which has high strength and has no residual magnetism. The thickness of the silver intermediate layer 2 is set at the time of forming the coating film 3 by the plasma spraying method and at the time of heat treatment of the coating film 3 after the formation.
In order to reliably prevent the chemical reaction between the base material 1 and the coating 3,
It is preferably in the range of 20 to 200 μm. The silver intermediate layer 2 is formed in a uniform thickness on the surface of the base material 1 by a known method such as a plasma spraying method.

The coating 3 is an Ln-Ba-Cu-O-based complex oxide superconducting material (Ln represents a rare earth element), and Bi-Sr-Ca-.
It is made from any one of Cu-O based complex oxide superconducting materials. Coating 3 contains silver in the range of 2 to 30 wt.%. The reason for adding silver to the coating 3 is as follows. That is, since there is a difference in the coefficient of thermal expansion between the base material 1 and the coating film 3, cracks occur in the coating film 3 during the formation of the coating film 3 by the plasma spraying method and during the heat treatment of the coating film 3 after the formation thereof, and The superconducting property deteriorates. When silver is added to the coating 3, the difference in the coefficient of thermal expansion between the base material 1 and the coating 3 is reduced without impairing the superconducting property of the coating 3, and the coating 3 is not cracked. However, if the silver content is less than 2 wt.%, The desired effect cannot be obtained in the above-mentioned action. On the other hand, if the silver content exceeds 30 wt.%, The magnetic shield characteristics deteriorate. Therefore, the silver content should be limited to the range of 2 to 30 wt.%. The coating 3 is formed in a uniform thickness on the surface of the silver intermediate layer 2 by a known method such as plasma spraying.

According to the magnetic shield of the present invention constructed as described above, the silver intermediate layer 2 is provided on the surface of the base material 1 having high strength and no residual magnetism.
Since the coating 3 made of a mixture of a complex oxide superconducting material containing a Cu _x -O _y -group and silver is formed, high strength and high magnetic shielding effect can be obtained, and the entire base material 1 is made of silver. Since the amount of silver used can be greatly reduced as compared with the case where the magnetic shield is manufactured by, the magnetic shield can be manufactured at a low cost.

【Example】

Next, the magnetic shield of the present invention will be described in more detail by way of embodiments with reference to the drawings. Example 1 First, the ratio of Y to Ba and Cu is Y: Ba: C in a molar ratio.
u = 1: 2: 3 in which Y ₂ O _3, BaCO ₃ and a mixture consisting of CuO, and calcined for 24 hours in air at a temperature of 900 ° C., cooled, and was ground to a powder. Next, the powder of the mixture thus prepared was mixed with Ag ₂ O at a ratio of 20 wt.
Y ₁ Ba having an average particle size of 26 to 44 μm, calcined in air at a temperature of ℃ for 24 hours, cooled and ground into a powder.
A powder raw material for a superconducting coating, which is a mixture of ₂ Cu ₃ O _7- δ and silver, was prepared.

Next, as shown in FIG. 2, inner diameter: 20 mm
A cylindrical base material 4 made of stainless steel defined by JISSUS 316L having dimensions of wall thickness: 1.0 mm and length: 100 mm was prepared. Then, a silver powder having an average particle size of 26 to 44 μm was sprayed on the entire outer surface of the base material 4 by a known plasma spraying method, and the surface of the base material 4 was coated as shown in FIG. Then, a silver intermediate layer 5 having a thickness of 50 μm was formed. Then, Y ₁ Ba ₂ —Cu ₃ O _7- was prepared as described above over the entire surface of the silver intermediate layer 5.
A powder raw material composed of a mixture of δ and silver was sprayed by a known plasma spraying method, and as shown in FIG. 4, Y ₁ Ba ₂ having a thickness of 200 μm was formed on the surface of the silver intermediate layer 5.
A coating 6 consisting of a mixture of Cu ₃ O _7- δ and silver was formed.

Then, the base material 4 on which the coating 6 made of a mixture of Y ₁ Ba ₂ Cu ₃ O _7- δ and silver is formed on the surface of the intermediate layer 5 of silver, the internal atmosphere is set to 7.7. In an electric furnace maintained at a mixed gas of% 0 ₂ and Ar, heated to a temperature of 900 ° C for 2 hours, and then in an electric furnace maintained at an internal atmosphere of 0 ₂ to a temperature of 700 ° C for 4 hours. did. Then, in this manner, a mother film 6 on the surface of which a mixture of Y ₁ Ba ₂ Cu ₃ O _7- δ having excellent superconducting properties and a mixture of silver was formed via the intermediate layer 5 of silver was formed. Material 4 was gradually cooled to room temperature in the electric furnace.

As a result of examining the magnetic shield manufactured in this way, no cracks were found in the coating 6 and
Tc is the critical current density at 89K and 77K, that is,
The maximum current density at which the superconducting state can be maintained (hereinafter, simply J
c) was 2,000 A / cm ² , and it was found to have excellent superconducting properties. Next, the magnetic shielding effect of the magnetic shield was investigated. That is, a magnetometer was placed in the magnetic shield at the center in the axial direction, and the entire magnetic shield was cooled to the temperature of liquid nitrogen. Then, in the direction perpendicular to the axial direction of the magnetic shield, 10 ^-8 T (Tesla) with a frequency of 5 Hz.
Applied a magnetic field. Then, the magnetic strength in the magnetic shield was measured. The magnetometer placed inside the magnetic shield is 5.0
It showed a magnetic strength of × 10 ^-14 T. Example 2 First, the ratio of Bi to Sr, Ca and Cu is B in molar ratio.
A mixture of Bi ₂ O ₃ , SrCO ₃ , SrCO ₃ , CaCO ₃ and CuO with i: Sr: Ca = Cu = 2: 2: 1: 2 was calcined in air at a temperature of 820 ° C. for 24 hours, cooled, Then, the powder was pulverized. Next, Ag ₂ O is added to the powder of the mixture thus prepared in an amount of 10
wt.% mixed, calcined in air at a temperature of 870 ℃ for 24 hours, cooled, and ground to a powder, 26-44μ
A powder raw material for a superconducting coating having a mean particle size of m ₂ and composed of a mixture of Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _{x '} and silver was prepared.

Next, as shown in FIG. 2, as shown in FIG. 2, made of YSZ, that is, yttria-stabilized zirconia, having dimensions of inner diameter: 50 mm, wall thickness: 5.0 mm and length: 200 mm. A cylindrical base material 4 was prepared. Next, base material 4
A silver powder having an average particle diameter of 26 to 44 μm was sprayed on the entire outer surface of the base material by a known plasma spraying method, and as shown in FIG.
An intermediate layer 5 of silver having a thickness of Then, the powder raw material prepared as described above over the entire surface of the silver intermediate layer 5 was sprayed by a known plasma spraying method, and as shown in FIG. 4, on the surface of the silver intermediate layer 5. To
A coating 6 consisting of a mixture of Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _x'and silver having a thickness of 150 μm was formed.

Next, the internal atmosphere of the base material 4 having Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _{x '} and the silver coating 6 formed on the surface of the intermediate layer 5 of silver was maintained as air. It was heated in an electric furnace to a temperature of 870 ° C. for 24 hours. Then, in this way, a coating 6 composed of a mixture of Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _{x '} having excellent superconducting properties and a silver is formed on the surface of the intermediate layer 5 of silver. The base material 4 was gradually cooled to room temperature in the electric furnace.

As a result of examining the magnetic shield manufactured in this manner, no cracks were found in the coating 6 and the magnetic shield
Tc is 103K, and the critical current density at 77K, that is,
The maximum current density at which the superconducting state can be maintained (hereinafter, simply J
c) was 1,000 A / cm ² , and it was found that it has excellent superconducting properties. Next, the magnetic shielding effect of the magnetic shield was investigated. That is, a magnetometer was placed in the magnetic shield at the center in the axial direction, and the entire magnetic shield was cooled to the temperature of liquid nitrogen. Then, in the direction perpendicular to the axial direction of the magnetic shield, 10 ^-8 T (Tesla) with a frequency of 5 Hz.
Applied a magnetic field. Then, the magnetic strength in the magnetic shield was measured. The magnetometer placed inside the magnetic shield is 1.5
It showed a magnetic strength of × 10 ^-13 T.

[0022]

As described above in detail, according to the magnetic shield of the present invention, Cu _x is formed on the surface of the base material having high strength and no residual density through the silver intermediate layer. Since a film made of a mixture of a composite oxide superconducting material containing O _y − group and silver is formed, high strength and high magnetic shielding effect can be obtained, and the magnetic shield can be manufactured at low cost. Thus, an industrially useful effect is brought about.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a magnetic shield of the present invention.

FIG. 2 is a perspective view of a tubular base material that constitutes a magnetic shield in Examples 1 and 2 of the present invention.

FIG. 3 is a perspective view of a cylindrical preform having a silver intermediate layer on its outer surface, which constitutes a magnetic shield in Examples 1 and 2 of the present invention.

FIG. 4 is a perspective view of a magnetic shield in Embodiments 1 and 2 of the present invention.

[Explanation of symbols]

1, 4: Base material, 2, 5: middle layer, 3, 6: Coating.

Claims (3)

[Claims] 1. A silver intermediate layer formed on at least one surface of a base material, and an intermediate layer formed on the surface of said intermediate layer,
Oxide superconducting materials containing Cu _x O _y − groups, and from 2
A magnetic shield comprising a coating made of a mixture of silver in the range of 30 wt.%. 2. The magnetic shield according to claim 1, wherein the mother plate is made of any one of paramagnetic metal, diamagnetic metal and ceramics. 3. The magnetic shield according to claim 1, wherein the intermediate layer has a thickness within the range of 20 to 200 μm.