JP2767773B2 - Manufacturing method of magnetic shield - Google Patents

Description

Description: 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 for eliminating externally mixed magnetic noise in micromagnetic measurement. It is.

[Background Art] Weak magnetic measurements are susceptible to the effects of geomagnetism and leakage magnetism from other measuring instruments, and these effects become measurement noise and make the measurement of weak magnetism inaccurate. In order to eliminate this noise, a magnetic shield is used to block the leakage magnetism or to shield the magnetic field of the measuring equipment.The magnetic shield is made of a soft magnetic material with high magnetic permeability and low coercive force in the required shape. Used.

[Problems to be Solved by the Invention] However, the molded article made of the above soft magnetic material may cause a leakage magnetic field from the joint of the magnetic shield or the like. To prevent this, a large volume of the shielding material is required to increase the shielding effect. A method of increasing the size was adopted, and as a result, the problem that the shield was large and the weight increased was inevitable.

[Means for Solving the Problems] As a result of repeated studies to solve the above problems, the present inventor has made use of the perfect diamagnetic property of the oxide-based high-temperature superconductor to form such a superconductor. The present inventors have found a method of manufacturing a magnetic shield having a small size and a large shield characteristic by applying a solution containing a constituent metal and firing the solution.

That is, the present invention dissolves in a solvent an organic compound of a metal that is soluble in an organic solvent and becomes a superconductor at a temperature of liquid nitrogen or higher by firing, and the dissolved solution is to form a magnetic shield. Coating, drying and calcining a metal in a shape, repeating the application, drying and calcination several times or more, and firing with the metal to obtain a seamless integrated magnetic shield. A method for manufacturing a shield is provided.

The magnetic shield obtained in the present invention is used while cooling with liquid nitrogen.

(Oxide Superconductor Composition) As the composition of the oxide superconductor used in the present invention, a composition exhibiting superconductivity above liquid nitrogen is used. For example, Ba ₂ YCu ₃ O
_y (sintering temperature 900-950 ° C), Bi ₂ Sr ₂ Ca ₂ Cu ₃ O (sintering temperature
800-900 ° C), Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _y (firing temperature 900-100
0 ℃), Bi _2-x Pb _x Sr ₂ Ca ₂ Cu ₃ O _y (firing temperature 800-900 ℃)
And the like.

(Metal Organic Compound) In the present invention, each metal constituting the oxide superconductor is used as a raw material in the form of an organic compound soluble in a solvent. Such a metal organic compound is soluble in an organic solvent, and any one can be used as long as it becomes a metal oxide by firing, for example, a fatty acid salt such as naphthenate, octylate, and stearylate. And acetylacetonate and alkoxide.

(Solvent) As a solvent for dissolving the metal organic compound, toluene, xylene, mineral spirit, butanol, or the like is used. Depending on the metal compound to be dissolved, it is used alone or as a mixture.

(Solution) The dissolution method is not particularly limited. Each metal compound may be mixed and dissolved in a solvent so that the amount of each metal component becomes the composition ratio, or the specific metal compound may be dissolved in a specific solvent and mixed with a solution. The concentration of the solution is not particularly limited, but may be 1 based on the number of moles of the target oxide superconductor.
A concentration of about × 10 ⁻³ to 1 × 10 ⁻⁴ mol / g is selected.

A dispersing agent, a spreading agent, a thickener, and the like, which are decomposed and removed when heated, can be added to the solution as needed to impart adhesiveness and spreadability upon application.

(Metal container) As the shape of the metal container, one made in a target shield shape such as a cylindrical shape or a cube is used. Since the material of the metal container is processed at the sintering temperature together with the applied metal compound, any material having a melting point higher than the sintering temperature for the oxide superconductor may be used, and copper, silver, etc. are particularly suitable. . Further, the thickness may be any shape as long as the shape can be maintained, and it can be formed by processing a normal plate material or the like according to the shape of the final magnetic shield. In the case of a small shield, a foil may be used.

(Applying and Drying) After firing, the metal organic compound solution having a composition to be a superconductor is applied to a metal container. The coating is performed by a usual method such as brushing, spraying, dipping, and the like. Coating is performed as needed. After the coating film is dried at 100 ° C., it is calcined at about 500 ° C. to decompose and remove organic components in the coating film. Re-coating the solution after calcination and then repeating the drying and calcination steps increase the density of the oxide superconductor obtained by firing the coating, prevent cracks from occurring, and reduce the leakage magnetic field. It is effective in preventing occurrence.

The thickness of the coating film and, consequently, the thickness of the superconductor film are preferably as large as possible, but usually the desired shielding effect can be achieved if the oxide film has a thickness of 10 to 50 μm.

(Firing) The coating film from which organic components have been decomposed and removed by calcination at 500 ° C. is then fired at a firing temperature suitable for each superconductor composition in the presence of an oxygen partial pressure for a necessary time, and the metal container is fired. A sintered body coating of an oxide superconductor is formed on the surface, and used as a seamless integrated magnetic shield together with a metal container while being cooled in liquid nitrogen.

[Example] Example Naphthenic acid Bi, naphthenic acid Pb, naphthenic acid Sr, naphthenic acid Ca, and naphthenic acid Cu (all of Nippon Chemical Industry Co., Ltd.)
Was mixed and dissolved in toluene so that the metal atomic ratio was Bi: Pb: Sr: Ca: Cu = 1.4: 0.6: 2.0: 2.0: 3.0 to obtain a mixed solution having a superconductor composition. . Its concentration was 1.5 × 10 ^-4 mol / g, considering the superconductor composition as one molecule.

This mixed solution was prepared in advance using a 1 mm thick silver plate with a diameter of 100 mm.
The inner surface of a shield support having a height of 100 mm mm was uniformly applied by spraying. Then after drying at about 100 ℃, 500
Heat treatment was performed at 10 ° C. for 10 minutes. The solution was again spray-coated on the inner surface of the shield support, and the spray-drying-calcination operation was repeated 15 times.

The obtained calcined body was fired in an electric furnace at 830 ° C. for 24 hours in the air to obtain an integrated magnetic shield.

This magnetic shield is made of 1mm thick stainless steel outer diameter 110
The magnetic shield was cooled by being housed between double walls of a container having a diameter of 90 mmφ, an inner diameter of 90 mmφ, and a height of 120 mm, and further filled with liquid nitrogen.

In this state, a DC magnetic field was applied from the outside of the stainless steel container using a normal conduction coil, and the magnetic field strength inside the stainless steel container was measured with a Gauss meter using a Hall element probe. When 1000 gauss was applied as the external magnetic field, the internal magnetic field was less than 1 gauss and was hardly detected.

[Effects of the Invention] According to the method of the present invention, a superconductor sintered body of a required thickness is formed on the surface of a metal container as a shape holder, and the Meissner effect based on diamagnetism is obtained at liquid nitrogen temperature. , A magnetic shield body having a seamless and integral structure can be manufactured.

In addition, since the metal container is only used as a support for the magnetic shield, the number of metal members can be reduced as the magnetic shield, and the magnetic shield can have any desired shape. Thus, it is possible to obtain a shield body having no shield magnetic field and having an excellent shield effect.

Claims (1)

(57) [Claims] An organic compound of a metal, which is soluble in an organic solvent and becomes a superconductor at a temperature of liquid nitrogen or higher by firing, is dissolved in the organic solvent, and the dissolved solution is formed into a shape for forming a magnetic shield. A magnetic shield characterized by obtaining a seamless integrated magnetic shield by repeating the application, drying and calcination several times or more and then firing with the metal to obtain a seamless integrated magnetic shield. Manufacturing method.