JP2531186B2 - Recovery method of superconducting powder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for recovering superconducting powder from a sintered body containing a superconducting substance.

[Prior Art] A superconducting material is a material that has an electric resistance of 0 at a critical temperature or lower. In addition to the property that the electric resistance becomes 0, it has complete diamagnetism (Meissner effect) and Josephson effect.

If the fact that the electric resistance of the superconducting material is 0 is used for power transmission, power distribution, and power generation, a large current can be obtained with low loss. Not only energy-related but also widely used in magnetic levitation trains and accelerators that require the generation of high magnetic fields.

Moreover, it can be used as a magnetic shield by utilizing the complete diamagnetism of superconducting materials. In addition, mechanical applications such as actuators and bearings are also conceivable because they always show repulsive force against magnetism.

Furthermore, focusing on the high speed and high sensitivity of the Josephson effect of superconducting materials, it can be applied to various devices such as high-speed computer devices and superconducting interferometers (so-called SQUIDs) that detect trace magnetism.

Superconducting materials are extremely useful materials as described above,
Conventionally known superconducting materials such as Nb-Ti alloys have a very low critical temperature at which they exhibit superconducting properties and need to be cooled with liquid helium (4K), so they have not been put into practical use.

However, in recent years, as a material exhibiting superconductivity at a temperature higher than liquid nitrogen temperature (77 K), for example, Ba—Y—Cu—O-based or Ba—La—Cu—O-based metal oxide sintered bodies have been discovered. The practical application of superconducting materials has come to be expected.

[Problems to be Solved by the Invention] However, since the above-mentioned metal oxide sintered body contains many parts that do not exhibit superconductivity (usually 2/3 to 3/4 or more of the whole), As such, the properties of superconducting materials cannot be fully utilized.

That is, the practical use is hindered because the critical current density is low, the diamagnetic property is not perfect, and the like.

[Means for Solving Problems] The present invention has the following structure for the purpose of solving the above problems.

That is, the gist of the present invention is that a pulverizing step of pulverizing a sintered body containing a superconducting substance into powder and magnetizing the powder obtained in the pulverizing step at a temperature not higher than the critical temperature of the superconducting substance. A method of recovering superconducting powder, comprising: a separation step of magnetically separating a superconducting substance by passing through a passage having a filter medium of a ferromagnetic material.

Here, as the sintered body containing the superconducting conductive material,
Ba-Y-Cu-O system, Ba-Y-Cu-O-F system, or Ba
-La-Cu-O-based metal oxide sintered body, La-Sr-Cu
-O system, Ln-Ba-Cu-O system (where Ln is Lu, Yb, Tm, Er, H
Metal oxide sintered bodies such as o, Dy, Tb, Gd, Eu and Sm) are known, and any of them can be used in the present invention.

In addition, the crushing process of this sintered body, the usual ball mill,
It can be performed by a jet mill or the like.

In this crushing step, if the above-mentioned sintered body is crushed too finely, the crystal structure of the superconducting substance will be broken, so the grain size of the crushed powder is preferably 0.01 μm or more, and conversely the crushing is rough. Since it is difficult to recover only the superconducting substance, it is preferable that the crushed powder has a particle size of 100 μm or less.

The filter media made of a ferromagnetic material used in the above magnetic separation step include a stack of a large number of ferromagnetic fine wires formed in a net, a plurality of similar thin ferromagnetic wires arranged in parallel with the flow, etc. Can be used.

Further, the filter medium made of this ferromagnetic material can be easily magnetized by applying a DC magnetic field from the outside with an electromagnet or the like. It is more preferable to make the direction of this magnetization perpendicular to the flow of the passage because the superconducting substance trapped in the filter medium does not clog the filter medium.

The powder can be passed through the filter medium in a state in which the powder is dispersed in a solvent such as liquid nitrogen or in a state in which the powder is fluidized. In particular, it is preferable to disperse the powder in liquid nitrogen and pass through the filter medium, because the powder can be easily maintained below the critical temperature of the superconducting substance.

The superconducting substance powder recovered by the above means is
A superconducting thin film is formed by pressing and used as a sputtering target for forming a superconducting thin film, or a superconducting powder is packed in a highly ductile metal pipe and stretched to make the superconducting powder adhere to each other to form a superconducting wire. The material powder can be solidified into a superconducting material, or can be further molded and re-sintered to form a superconducting material.

[Operation] A sintered body containing a superconducting substance is pulverized in the above-mentioned pulverizing step, so that the superconducting substance alone or a large amount of superconducting substance (hereinafter referred to as superconducting particle) and the superconducting substance is not contained or the superconducting substance is small. It becomes a powder consisting of particles.

Then, in the separation step, at a temperature below the critical temperature of the superconducting substance, this powder is passed through a passage having a filter medium of a magnetized ferromagnetic material to capture only superconducting particles in the filter medium. , Can be separated into superconducting particles and particles that are not.

Separation of superconducting particles in the above filter medium will be described with reference to FIG. 1 which is an enlarged view of the thin line W of the ferromagnetic material forming the filter medium and its vicinity.

The magnetic force Fm acting on the particles in the vicinity of the magnetized thin wire W is 2
Dimensionally, it is expressed by the following equations (1) and (2).

Fmr = −V × HO ² a ² (a ² / 2r ⁵ + cos 2θ / r ³ ) (1) Fmθ = −V × HO ² a ² sin2θ / r ³ (2) where r and θ are thin wires W In the cylindrical coordinates of the center of the external magnetic field
The orientation of HO is on the x-axis and this is the reference axis. Further, a is the radius of the thin wire W, X is the magnetic susceptibility of the particles, V is the volume of the particles, and HO is the external magnetic field.

The magnetic force Fm to be applied to the superconducting particles exhibiting strong diamagnetism (X≈-1) at the critical temperature or less is obtained from the above equations (1) and (2) and is shown by an arrow in FIG. As is clear from FIG. 1, the superconducting particles are trapped on the surface portion of the thin wire W perpendicular to the external magnetic field.

That is, the above superconducting particles exhibit strong diamagnetism at the critical temperature or lower. Therefore, when the thin wire W constituting the filter medium is magnetized, the thin wire W receives a force as shown in FIG. 1 in the vicinity of the thin wire W and is captured by the thin wire W.

On the other hand, since the particles having no superconducting substance have the magnetic susceptibility X≈0, they are hardly affected by the thin wire W and therefore pass through the filter medium without being captured by the filter medium.

Therefore, the above powder, in a state below the critical temperature,
Only the superconducting particles can be trapped in the filter medium by passing through the passage provided with the magnetized filter medium.

Incidentally, the collection of the trapped superconducting particles from the combined filter medium may be carried out by removing the magnetic field applied to magnetize the thin wires, or by making the filter medium higher than the critical temperature to lose the superconducting property of the superconducting particles. Can be done easily.

[Example] In order to confirm the effect of the present invention, the following experiment was conducted.

First, a sintered body sample containing a superconducting material was manufactured as follows.

Y ₂ O ₃ powder (purity 99.99%, average particle size 1.5 μm, made in Japan Yttria), BaCO ₃ powder (purity 99.9%, average particle size 1 μ
m, manufactured by Furuuchi Chemical Co., Ltd.) and CuO powder (purity 99.9%, average particle size 1 μm, manufactured by Furuuchi Chemical Co., Ltd.) at a ratio of Y ₂ O ₃ : BaO: CuO = 1.129: 3.947: 2.386 (g) and placed in a mortar. Mixed and stirred. The final average particle size was 1.5 μm.

Then, the above mixture was put into an alumina crucible (inner diameter 2.0 m
m, depth 3.3 mm), the temperature is raised to 400 ° C in 1 hour, further raised to 950 ° C at 600 ° C / hr, held for 2 hours, and then cooled to 200 ° C. Went inside.

Then, the obtained calcined product is pulverized again in a mortar, and polyvinyl butyral resin (PVB, polymerization degree 7
00, manufactured by Wako Pure Chemical Industries, Ltd.) was added at a ratio of 1.1 ml to 1 g of the calcined powder. After that, the calcined powder was molded at room temperature with a forming pressure of 1 t.
It was molded into a rectangular parallelepiped having a thickness of 7 mm, a width of 9 mm and a length of 50 mm by a press of / cm ² .

Next, the above rectangular parallelepiped shaped body was fired in the air at 950 ° C. for 6 hours. The heating rate is 100 ° C / hr and cooling is 950.
The furnace was cooled from ℃ to 250 ℃ for 8 hours.

 The color of the obtained sintered body sample was black.

The critical temperature of this sintered sample was 92 K, the magnetic field was 100 Oe (Oersted), and the magnetization at 80 K was 4πl = 18 G (Gauss). The content of the superconducting substance contained in this sintered body is 4πl = -100G if it is completely superconducting.
Therefore, 18/100 = 18% was calculated.

Then, the method for recovering superconducting powder of the present invention was applied to the above-mentioned sintered body sample.

First, the above-mentioned sintered body powder was pulverized by a ball mill to obtain a sample powder having an average particle size of 1 μm and a sample powder having an average particle size of 5 μm.

Next, 0.5 g of this sample powder was suspended in liquid nitrogen 5 having a liquid temperature of 80 K and passed through the magnetic separator shown in FIG. 2 to recover superconducting powder.

This magnetic separation device includes a passage 10 having an inner diameter of 50 mmφ and the passage 10.
The filter medium 20 is made of a ferromagnetic material, and a pair of electromagnets 30 and 40 that magnetize the filter medium 20 are provided in the unit 10. The filter medium 20 is formed by stacking 70 stainless wire nets made of fine wires made of a SUS430 ferromagnetic material having a wire diameter of 1 mmφ.

Further, the electromagnets 30 and 40 are composed of magnetic cores 30h and 40h, magnetic cores 30h and 40h,
A coil 30c, 40c wound around 40h is provided, and a power source (not shown) is connected to a terminal (not shown) of the coils 30c, 40c, so that a DC magnetic field is generated between the magnetic core 30c and the magnetic core 40c. It is configured.

Then, by generating a DC magnetic field shown in Table 1 by the electromagnets 30 and 40, liquid nitrogen (liquid temperature 80K) in which the sample powder is suspended is passed from one end of the passage 10 at a rate of 5/5 min. . The superconducting particles in the liquid nitrogen were captured by the magnetized thin wires constituting the filter medium 20.

Then, the energization of the electromagnets 30, 40 is stopped, the cleaning solvent is circulated in the passage 10, and the filter media 20
The superconducting particles trapped in the thin wire of No. 3 were collected.

Table 1 shows the average particle size of the sample powder used, the external magnetic field used, the amount of collected superconducting powder, the amount of magnetization at 80K in a magnetic field of 100 Oe (Oersted), and the content of the superconducting substance calculated from the amount of magnetization. , And the capture rate of the superconducting substance in the sample powder are shown in Table 1. The capture rate of the superconducting substance in the sample powder was calculated by the following formula.

Capture rate of superconducting substance = (capture amount of superconducting powder x share of the superconducting substance) /
(Sample powder amount (0.5g) x content of the superconducting substance) From Table 1, the following was found.

It was confirmed that the content rate of the superconducting substance was increased in both cases.

The smaller the average particle size of the powder, the higher the content of the superconducting substance.

Contrary to the content of the superconducting substance, the capture rate of the superconducting substance increases as the average particle size of the powder increases.

Therefore, by appropriately selecting the average particle size of the powder, it is possible to obtain a superconducting powder suitable for the intended use.

[Effects of the Invention] The present invention adopts the configuration as described above,
A superconducting powder having a high content of the superconducting substance can be easily obtained.

By using the superconducting powder having a high content of the superconducting substance, it becomes easier to put the superconducting metal oxide sintered body into practical use.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of a separation process of the present invention, and FIG. 2 is an explanatory diagram of a magnetic separation device used in an embodiment of the present invention. W: Magnetic fine wire 10: Passage 20: Filter media 30,40: Electromagnet

Claims (1)

(57) [Claims] 1. A crushing step of crushing a sintered body containing a superconducting substance into powder, and a powder obtained by the crushing step, which is magnetized at a temperature below the critical temperature of the superconducting substance, of a ferromagnetic material filter medium. And a separation step of magnetically separating the superconducting substance by passing it through a passage having the.