JP7246712B2 - Functional composite material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a functional composite material having magnetic refrigeration performance and superconductivity performance.

A superconducting material exhibits a phenomenon in which the electrical resistance becomes zero when cooled to the superconducting transition temperature.
Investigations are being made in various fields such as powerful electromagnets, low-loss power transmission, and low-loss electronic devices that apply such superconductivity phenomena.

Superconducting materials include low-temperature superconducting materials that become superconducting at liquid helium temperature (-269°C) and high-temperature superconducting materials that become superconducting at liquid nitrogen (-196°C).
In fields where superconducting materials are used, when a portion of a conductor transitions from a superconducting state to a normal conducting state for some reason, a large amount of local heat is generated, causing the surrounding conductors to rapidly lose their superconducting properties. .
This phenomenon is called quenching, and there is a risk that cryogen at extremely low temperatures will boil and be released explosively, or the superconductor will be damaged by heat generation.

As a method of cooling to the superconducting transition temperature, a method of compressing and expanding a refrigerant using the Joule-Thomson effect is currently used, but it has the technical problem of large energy loss and low cooling effect.
In recent years, as a new refrigeration technology, magnetic refrigeration technology using the magnetocaloric effect caused by the magnetic field dependence of the entropy and temperature of magnetic materials has been studied.
However, the magnetocaloric effect and the superconducting properties are said to have a contradictory relationship, and no examples have been found that have been sufficiently investigated so far.
Another problem is that materials exhibiting the magnetocaloric effect generally have low thermal conductivity.

For example, Non-Patent Document 1 describes a sintered material using tantalum with high thermal conductivity in the matrix in order to improve the refrigeration performance of the magnetocaloric material, but internal defects due to sintering is likely to occur, and does not have superconducting properties.
Although the present applicant previously proposed a composite material having superconductivity (Patent Document 1), the magnetocaloric effect was not considered at this time.

Japanese Patent No. 5483078

Microstructure, magnetic properties and thermal conductivity of LaFe11.2Si1.8/Ta magnetocaloric composite Qiming Wu, Naikun Sun, Xiangjie Wang, Lingwei Li J. Magn. Mang. Mater. Vol. 476 (2019) No.15

An object of the present invention is to provide a functional composite material that is a superconducting material that can be cooled using the magnetocaloric effect and that is also effective in preventing quenching.

A functional composite material according to the present invention is characterized in that particles exhibiting a magnetocaloric effect and particles exhibiting a superconducting effect are dispersed in a metal substrate.

Here, a particle exhibiting magnetocaloric effect means that when a magnetic field is applied at a constant temperature, the magnetic moment aligns in the direction of the magnetic field, and the entropy decreases. It refers to particles, and the refrigeration technology that uses this property is called magnetic refrigeration.
The greater the magnetocaloric effect, the greater the cooling effect.
It is presumed that the present invention can use not only presently known particles exhibiting magnetocaloric effects, but also those proposed in the future.
Gd compounds and La--Fe--Si compounds are typical examples of substances currently known to exhibit a large magnetocaloric effect. Specific _examples include Gd, _{Gd5Si2Ge2 , Gd5Si1.8Ge1.8Sn0.4 , La} ( _Fe0.88Si0.12 ) _{13 , and} the like _.

Particles exhibiting a superconducting effect are not limited to those currently reported as long as they are substances that exhibit a superconducting phenomenon when cooled to the superconducting transition temperature. Examples of compounds include MgB ₂ , Nb ₃ Ge, Nb ₃ Sn, NbTi, etc. Examples of copper oxides include Y—Ba—Cu—O system, La—Sr—Cu—O system, Hg—Ba—Ca—Cu— O type etc. are mentioned.

A characteristic feature of the present invention is that the particles exhibiting the magnetocaloric effect and the particles exhibiting the superconducting effect are dispersed in a metal substrate (matrix) such as magnesium or aluminum so that their functions are exhibited. The point is that the functions have been combined.
Here, magnesium includes its alloys, and aluminum also includes its alloys.
By using such a light metal as a base material, it becomes possible to reduce the weight.

A method for producing a functional composite material according to the present invention is characterized by infiltrating molten or semi-molten metal into a mixture of particles exhibiting a magnetocaloric effect and particles exhibiting a superconducting effect under pressure.
Here, a mixture obtained by mixing particles exhibiting a magnetocaloric effect and particles exhibiting a superconducting effect and molding the mixture into a preform may be used.

By combining the magnetocaloric properties and the superconducting properties of the present invention, it is possible to cool the metal base material to below the superconducting transition temperature by magnetic refrigeration. The conductivity is expected to prevent the occurrence of quenching.

An example of forming a functional complex is shown. A cross-sectional photograph of the composite is shown. Magnetic entropy change at external magnetic field 0-5T is shown. Relative cooling power (RCP) and ratio RCP values are shown. The distribution map of specific gravity and RCP is shown. 4 shows the electrical resistance measurement results of the composite material. Figure 2 shows thermal conductivity measurement results for composite materials. A comparison table of heat conduction is shown.

A functional composite according to the present invention was prototyped and compared with other materials for evaluation, which will be described below.

As particles exhibiting a magnetocaloric effect, a Gd ₅ Si _1.8 Ge _1.8 Sn _0.4 compound was prepared by an arc melting method and used.
In addition, you may manufacture by the casting method, or you may use what is marketed.
In this example, the Gd ₅ Si _1.8 Ge _1.8 Sn _0.4 produced by the arc melting method was pulverized in a mortar to obtain a powder having a particle size of 10 to 200 μm.

As particles exhibiting a superconducting effect, _MgB2 powder (manufactured by Kojundo Chemical Laboratory Co., Ltd.) having an average particle size of about 50 μm was used.
The particles preferably have an average particle diameter of 20 to 100 μm.

Magnesium with a purity of 99.99% was used for the metal substrate.

<Production of preform body>
A cylindrical mold with a detachable bottom is used, and the inner wall is covered with wrapping paper, and particles exhibiting a magnetocaloric effect (hereinafter referred to as magnetocaloric particles) and particles exhibiting a superconducting effect (hereinafter referred to as superconducting particles) are placed. The mixture was mixed in a predetermined ratio, put into the mold little by little, and pressed lightly with a push rod while repeating the process to produce a powder preform of about 100 g.

<Preparation of composite by three-dimensional molten metal penetration method>
As shown in FIG. 1, a preform body P is placed in a mold 1, and a lid body 2 made of graphite having an outer diameter slightly smaller than the outer diameter of the preform body P is placed thereon.
On top of that, the diaphragm 3 was supported on the stepped portion of the mold.
This diaphragm 3 has a hole in its central portion.
Magnesium as a base material was arranged on the diaphragm 3 .
The temperature of the mold 1 was raised to about 700° C. while blowing a mixed gas of CO ₂ and SF ₆ to prevent burning of magnesium from the surroundings.
After confirming that the magnesium had melted, a graphite punch 4 was placed on the preform body P and pressurized to permeate the preform body P with the molten magnesium.
In addition, it is preferable that the bottom of the mold 1 can be cooled.

As a functional composite material (hereinafter referred to as a composite material), a composite A having a volume ratio of Gd ₅ Ge _1.8 Si _1.8 Sn _0.4 :MgB ₂ :Mg=40:40:20 and Gd ₅ Ge _{1 .8} Si _1.8 Sn _0.4 :MgB ₂ :Mg=25:50:25 Composite B was prepared.
A photograph of the cross section is shown in FIG.
No internal defects such as blowholes were observed, and it was confirmed from the SE image that each particle was uniformly dispersed.
FIG. 3 shows the change in magnetic entropy when the external magnetic field is excited from 0T to 5T.
In the figure, Δ indicates composite A, □ indicates composite B, and ◇ indicates the value of Gd ₅ Ge _1.8 Si _1.8 Sn _0.4 for reference.
As an index indicating how much heat can be pumped out in one cooling cycle based on the magnetic entropy change, RCP (Relative Cooling Power) and a ratio RCP value obtained by dividing the value by the specific gravity of the sample. are shown in the table of FIG.
In the table, the values reported in other literatures are referred to, except for the value of Sn _{0.4 of} composites A and B and Gd ₅ Si _1.8 Ge 1.8.
FIG. 5 shows a scatter diagram of specific gravity and magnetocaloric effect.
4 and 5, the composite material according to the present invention has a ratio RCP value RCP/ρ of Gd ₅ Si ₂ Ge ₂ or La (Fe _0.88 Si _{0 .12} ) showed a value of ₁₃ levels.
FIG. 6 shows the electrical resistance measurement results, and FIG. 7 shows the heat conduction measurement results.
Also, FIG. 8 shows a comparison table of thermal conductivity with other materials.
Comparing these, the composite according to the present invention has improved thermal conductivity by 2 to 20 times due to the use of metal as the base material.
Magnetic refrigeration is possible by the magnetocaloric effect, and high thermal conductivity at low temperatures is expected to prevent quenching in superconducting materials.
Also, when comparing the composite materials A and B in the graph of FIG. It was also revealed that they exhibited excellent superconducting properties.
This presumes that the superconducting particles are preferably larger than the magnetocaloric particles by volume.

1 mold 2 lid 3 diaphragm 4 punch P preform body

Claims (5)

A functional composite material comprising particles exhibiting a magnetocaloric effect and particles exhibiting a superconducting effect dispersed in a metal substrate. 2. The functional composite material according to claim 1, wherein said metal substrate is magnesium or aluminum. 3. The functional composite material according to claim 1, wherein the particles exhibiting the magnetocaloric effect are Gd compounds or La--Fe--Si compounds. The functional composite material according to any one of claims 1 to 3, wherein the particles exhibiting superconductivity are intermetallic compounds or copper oxides. 1. A method for producing a functional composite material, characterized in that a molten or semi-molten metal is impregnated under pressure into a mixture of particles exhibiting a magnetocaloric effect and particles exhibiting a superconducting effect.

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