JP2926196B2 - Manufacturing method of magnetic shield - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic shield, and more particularly to a method for manufacturing a magnetic shield using an oxide-based high-temperature superconductor.

[0002]

2. Description of the Related Art A magnetic shield using a superconductor shields an internal space of a magnetic shield placed in a magnetic field from an external magnetic field, or arranges a magnetic field source inside the magnetic shield to provide a magnetic shield. It is used to prevent magnetic leakage outside.

In recent years, as the magnetic shield, an oxide-based high-temperature superconductor exhibiting superconductivity at a temperature of liquid nitrogen or higher has been studied intensively.

As a method of manufacturing a magnetic shield using an oxide-based high-temperature superconducting material, a method of filling a powder to be an oxide-based high-temperature superconductor into a mold and then firing it under pressure (hot press method) )Met.

[0005]

However, it is difficult to shield a high magnetic field by the hot pressing method. This is due to the following reasons.

When a magnetic field is applied to the magnetic field shield, an opposite magnetic field is generated to cancel the applied magnetic field.
A current is induced inside the magnetic shield. Here, if the induced current (density) is high, it is possible to shield a high magnetic field. However, in the method using the hot press method, the pressure is uniformly transmitted to the inside of the sintered body during pressing. For this reason, there is a problem that a portion where the high-temperature superconducting particles are not uniformly oriented in a specific direction is generated, a current (density) at the portion is reduced, and a magnetic field leaks.

[0007]

Means for Solving the Problems As a result of repeated studies to solve the above problems, the present inventors stacked green sheets composed of oxide-based high-temperature superconducting particles oriented in a specific direction, and fired under pressure. By doing so, it was possible to obtain a magnetic shield capable of shielding a high magnetic field in which the high-temperature superconducting particles were uniformly oriented in a specific direction.

[0008] That is, the present invention is characterized in that a green sheet of an oxide-based high-temperature superconducting material is cut into a required cross-sectional shape, and then a molded body obtained by degreasing is stacked and fired under pressure. It is a manufacturing method of a shield body.

The magnetic shield of the present invention comprises an oxide-based high-temperature superconducting material, a binder, a plasticizer, a dispersant, a solvent (water,
An organic solvent, etc.) is mixed with the slurry or kneaded material to form a sheet by a method such as a doctor blade method or an extrusion molding method to form a green sheet in which high-temperature superconducting particles are oriented in a specific direction. It is cut and degreased to remove a binder or the like to form a thick film molded body, and the obtained thick film molded bodies are stacked and fired while being pressed.

(Oxide-based high-temperature superconductor material) Here, the oxide-based high-temperature superconductor material used in the present invention is an oxide-based high-temperature superconductor that exhibits superconductivity at a temperature of liquid nitrogen or higher by firing. Material, such a high-temperature superconductor,

Ba ₂ YCu ₃ O _y (calcination temperature 900-950 ° C.) Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _y (calcination temperature 800-900 ° C.) Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _y (calcination temperature 800- 900 ° C) Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _y (Baking temperature 900-1000 ° C) Bi _2-x Pb _x Sr ₂ Ca ₂ Cu ₃ O _y (Baking temperature 800-900 ° C.) Bi _2-x Pb _x Sr ₂ Ca ₁ Cu ₂ O _y (calcination temperature 800 to 900 ° C.).

(Green Sheet) In the present invention, in order to make the above-mentioned material into a green sheet, a powder of the above-mentioned material is mixed with a binder, a solvent and the like and formed into a sheet.

The molding method can be a conventional method such as a press method, and is not particularly limited. However, using a doctor blade method or an extrusion method is simple,
Since the density of the obtained sheet is high and the crystal form of the powder of the oxide-based high-temperature superconducting material is a plate-like crystal, the green sheet in which the high-temperature superconducting particles are oriented in a specific direction (C-axis oriented) Is particularly suitable for the present invention.

Doctor blade method The green sheet obtained by the doctor blade method includes a binder such as PVB (polyvinyl butyral) and an acrylic resin, a plasticizer such as DBP (dibutyl phthalate), a dispersant such as ethyl oleate, xylene, ethanol and water. Such a solvent and the raw material powder are mixed by a ball mill or the like,
It is obtained by pulverizing and forming the obtained slurry into a sheet having a predetermined thickness using a doctor blade device and drying.

Extrusion molding method The green sheet obtained by the extrusion molding method is obtained by kneading methylcellulose as a binder, water as a solvent, etc. and raw material powder using a kneader or the like, and kneading the mixture to a predetermined thickness using an extruder. By extruding into a sheet and drying.

The thickness of the green sheet may be designed according to the finally required shape, and is not particularly limited. However, due to the characteristics of the molding method, it is preferably about 25 to 2000 μm in the doctor blade method. In the molding method, the thickness is preferably about 50 to 5000 μm.

(Processing) The obtained green sheet is processed according to the cross section of the finally required shape. For example, in the case of a tubular magnetic shield, it is processed into a ring shape having a predetermined dimension.

(Degreasing) The obtained processed sheet is degreased at about 500 ° C. in order to remove a binder and the like, to obtain a thick film molded body.

(Pressing and sintering)
After stacking to have a predetermined shape, they are fired at a temperature suitable for each high-temperature superconductor composition while applying pressure. The resulting fired body has no seams between the thick film fired bodies and is integrated.

The pressure applied during firing is 150 kg / cm
^The number is not particularly limited as long as it is ² or more, but is preferably 200 kg / cm ² or more to improve the orientation of the high-temperature superconducting particles.

The shape of the magnetic shield may be, for example, a cylindrical or rectangular tube. When used as a magnetic shield, it may be machined after firing to have a predetermined shape, if necessary.

[0022]

The present invention will be described below in detail with reference to examples.

Example 1 As a raw material powder, Bi: Pb: Sr: Ca: Cu = 1.92: 0.48:
2.0: 2.0: 3.2, Bi ₂ O ₃ , PbO, SrCO ₃ , Ca
After blending CO ₃ and CuO, adding ethanol, mixing using a resin mill and a resin ball, drying, and calcining the obtained powder at 850 ° C. for 50 hours, Bi _1.8 Pb _0.2 Sr ₂ Ca ₂ Cu _{3 Oy} oxide high temperature superconducting powder was prepared.

100 g of this powder and 4 g of PVB as a binder
, 3 g of DPB as a plasticizer, 1 g of ethyl oleate as a dispersant and 50 ml of ethanol and 15 ml of xylene as a solvent
Was mixed using a resin mill and a resin ball to produce a slurry.

The slurry was applied to a thickness of 1500 μm using a doctor blade device and dried to obtain a green sheet having a thickness of 1000 μm.

The obtained green sheet has an outer diameter of 40 mm and an inner diameter of 40 mm.
It was processed into a 10 mm ring-shaped disc, heated to 500 ° C. at a rate of 1 ° C./min in air atmosphere, and degreased to obtain a ring-shaped thick film molded article having a density of 4.8 g / cm ³ .

The obtained ring-shaped thick film molded bodies are stacked in a stack of 60 pieces having the same inner diameter, and then baked at 850 ° C. for 48 hours in an air atmosphere under a pressure of 200 kg / cm ² , Outline
A tubular magnetic shield having a diameter of 40 mm, an inner diameter of 10 mm, a length of 50 mm, and a density of 6.2 g / cm ³ was obtained.

While the obtained magnetic shield was cooled in liquid nitrogen, a DC magnetic field was applied from the outside, and the magnetic shield characteristics at the center of the tubular magnetic shield were measured using a Hall element. When the internal magnetic flux density at the center of the body exceeds 1 Gauss, the external magnetic flux density is 1
It was 40 gauss.

When the cross section of the crystal was observed by an electron microscope, it was found that the superconducting plate-like crystal grains were uniformly oriented perpendicular to the side surface of the tubular magnetic shield.

Example 2 As a raw material powder, Bi: Pb: Sr: Ca: Cu = 1.92: 0.48:
2.0: 2.0: 3.2 Bi ₂ O ₃ , PbO, SrCO ₃ , CaCO
_3, CuO was blended resin mill using ethanol, was mixed with the resin ball dried, the resulting powder at 850 ° C.
And 50 hours calcined to prepare a _{Bi 1.8 Pb 0.2 Sr 2 Ca 2} Cu 3 O y oxide high temperature superconductor powders.

1 kg of this powder, 30 g of methylcellulose as a binder, and 150 g of water as a solvent are mixed and kneaded using a kneader.
It was extruded to a thickness of 00 μm and dried to obtain a green sheet.

The obtained green sheet was made to have an outer diameter of 40 mm and an inner diameter of 40 mm.
Processed into 10mm, 500 ℃ at 1 ℃ / min in air atmosphere
The temperature was increased to degrease to obtain a ring-shaped thick film molded article having a density of 4.8 g / cm ³ .

After stacking 60 of the obtained ring-shaped thick film molded bodies, they are baked at 850 ° C. for 72 hours in an air atmosphere under a pressure of 300 kg / cm ² , and have an outer diameter of 40 mm, an inner diameter of 10 mm, and a length of Sa
A tubular magnetic shield having a diameter of 50 mm and a density of 6.2 g / cm ³ was obtained.

While the obtained magnetic shield was cooled in liquid nitrogen, a DC magnetic field was externally applied, and the magnetic shield characteristics at the center of the tubular magnetic shield were measured using a Hall element. As a result, the internal magnetic flux density at the center inside the tubular magnetic shield body exceeded 1 Gauss when the external magnetic flux density was 135 Gauss.

Comparative Example 1 As a raw material powder, Bi: Pb: Sr: Ca: Cu = 1.92: 0.48:
2.0: 2.0: 3.2 Bi ₂ O ₃ , PbO, SrCO ₃ , CaCO
_3, CuO and the formulation was mixed using a resin mill and resin balls adding ethanol, dried and the resultant powder
And 50 hours and calcined at 850 ° C., to produce a _{Bi 1.8 Pb 0.2 Sr 2 Ca 2} Cu 3 O y oxide high temperature superconductor powders.

This powder was baked at 850 ° C. for 100 hours in an air atmosphere while pressing at a pressure of 300 kg / cm ² ,
A tubular magnetic shield having an inner diameter of 10 mm, a length of 50 mm, and a density of 5.5 g / cm ³ was obtained.

While the obtained magnetic shield was cooled in liquid nitrogen, a DC magnetic field was applied from the outside, and the magnetic shield characteristics at the center of the tubular magnetic shield were measured using a Hall element. As a result, the internal magnetic flux density at the center inside the tubular magnetic shield body exceeded 1 Gauss when the external magnetic flux density was 75 Gauss.

Further, as a result of observing the cross section of the sintered body with an electron microscope, it was found that superconducting plate-like crystal grains grew in an arbitrary direction near the center of the tubular magnetic shield, and had a rough structure.

[0039]

According to the method of the present invention, a green sheet made of oxide-based high-temperature superconducting particles oriented in a specific direction is cut, and then a thick film formed by degreasing is stacked.
Since firing is performed while applying pressure, the resulting magnetic shield has high-temperature superconducting particles uniformly oriented in a specific direction, and the current density induced by an external magnetic field has a large limit. It is possible and can greatly expand the application field of the oxide-based superconductor.

Continuation of the front page (56) References JP-A-63-234569 (JP, A) JP-A-1-260894 (JP, A) JP-A-2-275779 (JP, A) JP-A-3-80115 (JP) , A) (58) Fields surveyed (Int. Cl. ⁶ , DB name) H05K 9/00 ZAA

Claims (3)

(57) [Claims] 1. A method for manufacturing a magnetic shield, comprising cutting a green sheet of an oxide-based high-temperature superconducting material into a required cross-sectional shape, stacking degreased compacts, and firing under pressure. Method. 2. The method according to claim 1, wherein the green sheet of the oxide-based high-temperature superconducting material is a sheet comprising high-temperature superconducting particles oriented in a specific direction. 3. The production method according to claim 1, wherein the green sheet of the oxide-based high-temperature superconducting material is a sheet produced by a doctor blade method or an extrusion molding method.