JP2002249763A - Cold storage material, method for producing the same, and refrigerator using the cold storage material - Google Patents

Abstract

(57) [Summary] A regenerator material having high strength, less risk of pulverization, excellent thermal shock resistance and durability, and capable of exhibiting remarkable refrigeration ability in a low temperature range, a method for producing the same, and a regenerator thereof Provide a regenerative refrigerator using materials. A regenerator material comprising a large number of magnetic particles mainly composed of an oxide, wherein the average value of equivalent circular diameters of crystal grains constituting the magnetic particles is 0.3 to 20 μm. The area ratio of crystal grains having an equivalent circular diameter of 50 μm or more is preferably 10% or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a regenerator material, a method for producing the regenerator material, and a refrigerator using the regenerator material.
Cold storage material that can demonstrate remarkable refrigeration capacity in low temperature range,
The present invention relates to a manufacturing method thereof, a refrigerator using the cold storage material, and the like.

[0002]

2. Description of the Related Art In recent years, the development of superconducting technology has been remarkable, and the development of a small-sized and high-performance refrigerator has become indispensable as its application field has expanded. Such small refrigerators are required to be lightweight, small and have high thermal efficiency, and are being put to practical use in various application fields.

For example, in superconducting MRI apparatuses and cryopumps, refrigerators using a refrigerating cycle such as a Gifford McMahon (GM) system, a Stirling system, and a pulse tube refrigerator are used. Also, a high-performance refrigerator is required for a magnetic levitation train to generate magnetic force using a superconducting magnet. Further, recently, a high-performance refrigerator has been used also in a superconducting power storage device (SMES) and a single crystal pulling device in a magnetic field for producing high quality silicon wafers and the like.
The development and commercialization of pulse tube refrigerators, which are expected to have higher reliability, are also being actively pursued.

[0004] In such a refrigerator, a working medium such as a compressed He gas flows in one direction in a regenerator filled with a regenerator material, and the heat energy is supplied to the regenerator material. The expanded working medium flows in the opposite direction and receives thermal energy from the cold storage material. As the recuperation effect in such a process becomes better, the thermal efficiency in the working medium cycle is improved, and a lower temperature can be realized.

Conventionally, Cu, Pb, and the like have been mainly used as a cold storage material used in the above-described refrigerator.
However, since such a regenerator material has a remarkably small specific heat at an extremely low temperature of 20 K or less, the recuperation effect described above does not sufficiently function. And the working medium cannot receive sufficient heat energy from the cold storage material. As a result, there is a problem that a refrigerator incorporating a regenerator filled with the regenerator material cannot reach extremely low temperatures.

Therefore, recently, in order to improve the recuperation characteristics of the regenerator at a very low temperature and to realize a refrigerating temperature closer to absolute zero, a maximum value of the volume specific heat is required especially in a very low temperature region of 20 K or less. Er ₃ Ni, E having a large value
Magnetic regenerative materials mainly composed of an intermetallic compound composed of a rare earth element and a transition metal element such as rNi and HoCu ₂ are used. By using such a magnetic cold storage material in a GM refrigerator, refrigeration at 4K is realized.

[0007] With the study of applying such a refrigerator to various cooling systems in practice, the necessity of stably cooling a large-scale object to be cooled has been increasing. There is a demand for improved refrigeration capacity.

In order to respond to such technical requirements,
By replacing a part of the conventionally used metal magnetic regenerator material with an oxide magnetic regenerative material such as GdAlO ₃ containing a rare earth element, the specific heat characteristics of the entire regenerative material are controlled to achieve refrigeration. Attempts have been made to improve their abilities.

The magnetic regenerator material described above usually has a diameter of 0 in order to smooth the flow of He gas as a refrigerant, increase the efficiency of heat exchange with He gas, and maintain the efficiency stably. It is used after being processed into spherical particles having a uniform particle size of about 0.1 to 0.5 mm. In particular, when the magnetic cold storage material (particulate cold storage material) is an intermetallic compound containing a rare earth element, it is processed into a spherical shape by a processing method using a centrifugal spray method or the like.

[0010]

However, since the oxide magnetic regenerator material has a high melting point, the oxide magnetic regenerator material may be processed into a spherical shape by a centrifugal spray method like a conventional metal magnetic regenerator material. Impossible. Therefore, the oxide regenerative material is processed into a nearly spherical shape by a method in which fine raw material powder is granulated to an appropriate size and then sintered.

In a refrigerator operating at a high speed such as a Stirling refrigerator or a pulse tube refrigerator, the pressure loss in the regenerator filled with spherical magnetic regenerator particles becomes large, and sufficient refrigerating capacity is realized. There was a problem that could not be done. In the case of GM refrigerators and the like, the magnetic particles are damaged or pulverized by the pressure vibration of the high-pressure helium gas or various stresses or impact forces acting during the operation of the refrigerator, thereby increasing the flow resistance of the refrigerant gas, thereby increasing the heat exchange efficiency. However, there was a problem that troubles such as abrupt decrease were easily generated.

In particular, in the case of a GM refrigerator, the stress caused by the reciprocating motion of the displacer (refrigerant compression piston) acts on the cold storage material, which has a great influence. In addition, when the refrigerator is started, the temperature falls from a room temperature to an extremely low temperature around 4K in a short time, so that a large thermal shock acts on the cold storage material.

However, in general, oxides exhibit extreme brittleness, lack sufficient mechanical strength, and are also weak against thermal shock. Therefore, during operation of the refrigerator, the oxide-based cold storage material may break down, or the surface of the cold storage material may be damaged. Part of the material is peeled off to generate fine powder.
Since the fine powder damages the seal portion of the refrigerator, there is a problem that the performance of the refrigerator is significantly reduced as a result.

Therefore, in order to improve the mechanical strength of the oxide-based regenerator, attempts have been made to make the crystal structure of the regenerator particles fine. However, when the crystal structure becomes fine, the number of crystal grain boundaries serving as thermal resistance increases, and the thermal conductivity of the cold storage material is impaired. When the heat conductivity decreases, the heat exchange between the cold storage material and the He gas as the refrigerant gas in the refrigeration cycle becomes insufficient, and the cold storage function is not sufficiently exhibited to the inside of the cold storage material particles. There was a problem.

In particular, in the case of the oxide-based regenerator produced by the method of granulating and sintering fine oxide raw material powder as described above, the raw material components are not completely dissolved, It is difficult to make the cold storage material particles dense. In other words, particles with micro cracks on the particle surface,
Many particles having a rough surface due to a step or the like and particles having minute voids formed therein are manufactured. For this reason, pressure vibrations and various stresses acting during the operation of the refrigerator can easily cause breakage and pulverization from defects such as cracks, steps, and voids, and the generated fine powder damages components such as seals of the refrigerator. And the refrigerating capacity is significantly reduced.

The present invention has been made in order to solve the above problems, and in particular, has a high strength, is less likely to be pulverized, has excellent thermal shock resistance and durability, and has a remarkable refrigeration capacity in a low temperature range. It is an object of the present invention to provide a cold storage material capable of exhibiting the above-mentioned characteristics and a cold storage refrigerator using the cold storage material.

[0017]

In order to achieve the above object, a regenerator material according to the present invention comprises a large number of magnetic particles mainly composed of an oxide, and has an equivalent circular diameter of crystal grains constituting the magnetic particles. The average value is 0.3 to 20 μm.

In the regenerative material, the area ratio of crystal grains having an equivalent circular diameter of 50 μm or more to all crystal grains constituting the magnetic particles is preferably 10% or less.

Further, in the regenerative material, it is preferable that the magnetic particles are made of a sintered body and have a sintered density of 86 to 99.8%. The magnetic particles preferably contain at least one of Y, Mg, Al, Ca and a rare earth element different from the constituent elements in an amount of 0.5 to 15% by weight in terms of oxide.

Further, in the cold storage material, the ratio of the magnetic particles having two or more cracks having a length of 10 μm or more on the surface of the magnetic particles to the total magnetic particles is preferably 20% or less.

In the cold storage material, the ratio of the magnetic particles having a maximum surface roughness of the magnetic particles of 10 μm or more to all the magnetic particles is preferably 30% or less.

Further, in the cold storage material, the ratio of the magnetic particles having voids having a maximum width of 20 μm or more inside the magnetic particles to all the magnetic particles is preferably 40% or less.

In the regenerator material, the magnetic particles may contain silicon, sodium and iron in a total amount of 3 ppm to 2 ppm.
It is preferred that the content be regulated so as to be contained by weight.

Further, in the above cold storage material, the magnetic particles may be:
General formula: Gd_1-xR_xA_1-yB _yO₃(Where R is
Ce, Pr, Nd, Sm, Tb, Dy, Ho and Er
At least one rare earth element selected from
Is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Z
Indicates an element selected from n, Ga, Ge, Al, and Si
And when x = 0 and y = 0, at least two elements
Is selected, while if x ≠ 0 or y ≠ 0,
At least one element is selected, and B is Zr, Nb, Mo,
Ag, In, Sn, Sb, Hf, Ta, W, Au, Bi
Represents at least one element selected from the group consisting of:
0 ≦ x ≦ 0.4 in the ratio and y ≦ 0 ≦ y ≦ 0.4 in the atomic ratio
Add. ) May be composed of oxide magnetic particles represented by
preferable.

Further, in the cold storage material, the magnetic particles may be:
Specific heat in the temperature range of 4.0 to 5.0K is 0.3 J / Kcm
³ or more, a specific heat in a temperature range of 4.5 to 5.5 K of 0.35 J / Kcm ³ or more, and 5.5 or more.
It is preferable that the magnetic particles are made of oxide magnetic particles having at least one property of specific heat in a temperature range of 6.0 K of 0.4 J / Kcm ³ or more.

In the method for producing a cold storage material according to the present invention, the oxide powder is granulated to form granulated particles, and the obtained granulated particles are subjected to pressure treatment to prepare spherical densified particles. And
It is characterized in that a regenerator material comprising a large number of magnetic particles is prepared by sintering the obtained densified particles.

[0027] In the above-mentioned production method by the granulation method, the pressurizing treatment of the granulated particles is preferably a cold isostatic pressure (CIP) pressurizing process, and the sintering process is performed by a hot isostatic pressure (HI).
P) It is preferable to be a pressure treatment. Further, it is preferable to granulate by adding 5 to 30% by weight of a binder to the oxide powder.

In another method for producing a regenerative material according to the present invention, a large number of oxide powders are melted by passing them through a thermal plasma and solidified in a spherical state by the surface tension of the melt. It is characterized in that a regenerator made of magnetic particles is prepared.

In the method for producing a regenerator material by the above-mentioned thermal plasma method, it is preferable that the magnetic particles which have been made spherical by passing through thermal plasma are further heat-treated at a temperature of 500 ° C. or more. Further, when the heat treatment temperature is 120
Desirably, the temperature is 0 to 1700 ° C.

In the refrigerator according to the present invention, the refrigerant gas flows from the high temperature side upstream of the regenerator and heat exchange between the refrigerant gas and the regenerator material filled in the regenerator causes a more downstream side of the regenerator. In a refrigerator for obtaining a low temperature, at least a part of the cold storage material filled in the cool storage device is the cold storage material of the present invention.

The high-temperature side of the regenerator is filled with a conventional non-oxide regenerative material, while the low-temperature side of the regenerator is filled with the oxide regenerative material of the present invention. It is possible to suitably adjust the specific heat distribution. The non-oxide regenerative material is not particularly limited, and Pb, HoCu ₂ , Er ₃ Ni, or the like can be used.

Further, the MRI (Magne) according to the present invention
tic Resonance Imaging) device,
A superconducting magnet for a maglev train, a cryopump, and a magnetic field application type single crystal pulling apparatus are all provided with the refrigerator according to the present invention described above.

The regenerator material according to the present invention is composed of a large number of magnetic particles mainly composed of an oxide having a specific heat peak in an extremely low temperature region of 20 K or less. The oxides constituting the magnetic particles include, for example, the following general formulas (1), (2),
The compositions shown in (3) and (4) can be suitably used.

That is, the general formula: RMO ₃ (1) (where R is Y, La, Ce, Pr, Nd, Pm, S
At least one rare earth element selected from m, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb, and M is at least one element selected from Group 3B elements. General formula: AB ₂ O ₄ (2) (where A is at least one selected from Group 2B elements)
B is a transition metal element containing at least Cr. And a general formula: CD ₂ O ₆ (3) (where C is at least one element selected from Mn and Ni, and D is selected from Nb and Ta) An oxide represented by the following formula: is preferably used. Of the above oxides, GdAlO
No. ₃ was preferred because it had a very steep and large specific heat peak in a low temperature range of about 3.9K.
The specific heat on the high temperature side described above has a disadvantage. Therefore, the improvement of the refrigerating capacity at 4.2 K was insufficient for a large specific heat peak.

Therefore, in the present invention, a regenerator material having a composition represented by the following general formula (4) is proposed as a regenerator material having a higher specific heat peak on a higher temperature side than a conventional regenerator material having a composition of GdAlO _3. are doing.

That is, a general formula: Gd _1−x R _x A _{1−y By y} O ₃ (4) (where R is Ce, Pr, Nd, Sm, Tb, Dy, H
o represents at least one rare earth element selected from o and Er, and A represents Ti, V, Cr, Mn, Fe, Co, N
i represents an element selected from Cu, Zn, Ga, Ge, Al, and Si. When x = 0 and y = 0, at least two elements are selected, while x ≠ 0 or y ≠ 0 , At least one element is selected, and B is Zr, N
b, Mo, Ag, In, Sn, Sb, Hf, Ta, W,
X represents at least one element selected from Au and Bi, x represents an atomic ratio of 0 ≦ x ≦ 0.4, and y represents an atomic ratio of 0 ≦ y.
Satisfies ≦ 0.4. ) Is preferably used.

In the cold storage material according to the present invention, the magnetic particles have a specific heat of 0.3 J in a temperature range of 4.0 to 5.0K.
/ Kcm ³ or more, specific heat in a temperature range of 4.5 to 5.5 K of 0.35 J / Kcm ³ or more, and specific heat in a temperature range of 5.5 to 6.0 K of 0.4 J / Kcm
It is preferable that the oxide magnetic particles have at least one of ^three or more characteristics.

The present inventors conducted a refrigerating test by filling a refrigerating material having various specific heat characteristics into a refrigerator. As a result, in order to improve the refrigerating capacity at 4K, it was necessary to use the above-mentioned method.
It has been found that it is preferable to satisfy at least one of the specific heat characteristics in the temperature range. It is preferable to satisfy the above two specific heat characteristics, but it is more preferable to satisfy all the specific heat characteristics.

In the general formula: Gd _1-x R _x A _{1-y By y} O ₃ (4), when x = 0 and y = 0, the general formula is GdAO
_In the case where the A component is only a single element with respect to GdAO ₃ , magnetic particles having a specific heat peak in an extremely low temperature range are generally obtained, while the GdAO ₃ has a specific heat peak of 4 to 6K as described above. It rarely shows a large specific heat peak in the temperature range. Therefore, when x = 0 and y = 0,
At least two elements are selected as the A component. On the other hand, by replacing a part of Gd with another rare earth element or a part of the A component with another element, the specific heat characteristics are adjusted and a high-performance cold storage material is obtained.

The above general formula: Gd _1-x R _x A
In _{1-y B y O 3,} R component is Ce, Pr, Nd,
At least one rare earth element selected from Sm, Tb, Dy, Ho and Er, is a component effective for broadening a steep specific heat peak and controlling a peak temperature position, and a part of Gd. It is added to replace.
When the addition ratio x indicating the replacement amount of the R component exceeds 0.4, the specific heat decreases. Of the above R components, Tb, Dy, H
o and Er are preferable, and Tb and Dy are more preferable.

A component is Ti, V, Cr, Mn, F
e, Co, Ni, Cu, Zn, Ga, Ge, Al, Si
And has the effect of controlling the specific heat peak. When x = 0 and y = 0, at least two elements are selected, while x ≠ 0 or y ≠ 0
Since at least one element is selected in the case of
Part of the Gd or A component in the dAO ₃ system is necessarily replaced by another element. As the A component element, Ti, V, Cr, Mn, Fe, Co, Ni, Ga,
Al is preferable, and Cr, Mn, Fe, Co, N
i, Ga, Al are more preferred.

Further, the component B is an element which improves specific heat characteristics by substituting a part of the above-mentioned component A to adjust the distance between (Gd _1-x R _x ) atoms. The B component is Zr, Nb, Mo, Ag, In, Sn, S
b, at least one element selected from Hf, Ta, W, Au, and Bi. As the B component element, Z
r, Nb, Mo, Sn, Ta, W are preferred, and Ta, W is more preferred. If the ratio y indicating the added amount of the B component exceeds 0.4, it becomes difficult to maintain the perovskite structure, and the specific heat characteristics of the cold storage material composed of magnetic particles deteriorate.

The above general formula: Gd _1-x R _x A _1-y
The atomic ratio of oxygen in the B _y O _3, and the like defects of atoms, which may deviate from the 3 is a stoichiometric ratio. However, if the atomic ratio of oxygen is in the range of 2.5 to 3.5, the specific heat characteristics are not significantly affected.

The average value of the equivalent circular diameter of the crystal grains of the magnetic particles constituting the cold storage material according to the present invention is in the range of 0.3 to 20 μm. Here, as shown in FIG. 16, the equivalent circular diameter D of the crystal grains is a circle having an area A equal to the exposed area or the cross-sectional area of the crystal grains 2 when observing the surface structure or the cross-sectional structure of the magnetic particles. Defined as diameter D. The average value is the average of the equivalent circular diameters of 100 arbitrary crystal grains.

Since the regenerator material of the present invention is composed of magnetic particles mainly composed of an oxide, when the magnetic particles are polished to observe the cross-sectional structure of the magnetic particles, the grain boundary phase becomes an abrasive. Since the crystal grains are crushed, the boundaries of the crystal grains become unclear, and it may be difficult to measure the equivalent circular diameter of the crystal grains. Even in that case, it is possible to measure the size of the crystal grains appearing in the surface structure of the magnetic particles.

When the average value of the equivalent circular diameters of the crystal grains is less than 0.3 μm, the number of crystal grain boundaries serving as thermal resistance increases, and the thermal conductivity of the grains is undesirably deteriorated. On the other hand, when the average value of the equivalent circular diameter of the crystal grains exceeds 20 μm, the mechanical strength of the particles becomes insufficient. Therefore, the average value of the equivalent circular diameter of the crystal grains is in the range of 0.3 to 20 μm, more preferably in the range of 0.5 to 10 μm, and even more preferably in the range of 1 to 7 μm.

In the cold storage material according to the present invention, the area ratio of crystal grains having an equivalent circular diameter of 50 μm or less is 10%.
It is preferable to set the following. If the area ratio exceeds 10%, the magnetic particles are easily cracked due to cracks due to thermal shock accompanying a rapid temperature drop that occurs when the refrigerator is started. This phenomenon is presumed to occur for the following reasons. That is, it is considered that abrupt shrinkage of large crystal grains having an equivalent circular diameter exceeding 50 μm cannot be absorbed and reduced in the entire crystal structure, and cracks are easily generated.

A more preferable range of the area ratio of the crystal grains having an equivalent circular diameter of 50 μm or more is 5% or less, more preferably 1% or less. The equivalent circular diameter is 40 μm
It is more preferable that the area ratio of the crystal grains described above is 10% or less, and it is further preferable that the area ratio of the crystal grains having an equivalent circular diameter of 30 μm or more be 10% or less.

The size of the crystal grains can be adjusted by controlling various manufacturing conditions such as the sintering temperature, sintering time, heating rate, cooling rate after sintering, and impurity content of the raw material compact. . However, these manufacturing conditions affect each other in a complicated manner, and also influence factors specific to a device such as a sintering furnace. Therefore, it is difficult to simply define the manufacturing conditions.

However, in general, when the sintering temperature is increased and the sintering time is extended, the crystal grains tend to become large. Similarly, as the rate of temperature rise during sintering and the rate of cooling after sintering are both reduced, the crystal grains grow and become coarse. In addition, impurities are one factor for generating crystal nuclei, and the smaller the impurity content, the larger the crystal grains are likely to be.

The crystal grain size of the regenerator material is measured and evaluated by observing the surface structure or the crystal structure cross-section of the particles with a scanning electron microscope (SEM) or the like, and processing the structure diagram by image processing. Can be implemented.

When the regenerator material according to the present invention is composed of magnetic particles made of a sintered body of granulated powder, the sintered density (relative density) of the magnetic particles should be in the range of 86 to 99.8%. Is preferred. If the sintering density is less than 86%, the mechanical strength of the magnetic particles becomes insufficient, and the filling amount in the regenerator is not preferable. On the other hand, if the sintering density exceeds 99.8%, cracks tend to occur in the particles due to thermal shock due to a rapid temperature drop at the start of the refrigerator, which is not preferable. More preferred sintering density is 95-9
9.8%, more preferably 98 to 99.8%
It is. On the other hand, when the regenerator material is magnetic particles formed by the thermal plasma method, the density of the magnetic particles is 99 to 1
Reaches 00%.

The magnetic particles constituting the regenerator material contain at least one of Y, Mg, Al, Ca and a rare earth element different from the constituent elements in an amount of 0.5 to 15% by weight in terms of oxide.
It is preferred to contain.

The oxide of the main phase constituting the magnetic particles is 40%.
It has a specific specific heat peak in an extremely low temperature region of K or less, and has a function as a cold storage material. By containing at least one of Y, Mg, Al, Ca and rare earth elements different from the constituent elements of the main phase in an amount of 0.5 to 15% by weight in terms of oxide, the sintered body of the oxide can be more Can be densified. By densifying each magnetic particle, a magnetic regenerator material composed of a composite oxide having high mechanical strength and excellent thermal shock resistance can be realized.

At least one of Y, Mg, Al, Ca and a rare earth element different from the constituent elements of the main phase of the magnetic particles.
The additional component containing the seed is generally added in the form of an oxide, but is not limited to an oxide, and may be added as a compound such as a carbide or a nitride. Among the above-mentioned additional components, Y, Ce, Mg, and Ca are particularly preferable for obtaining the densification effect.

When the amount of the additional component such as Y is less than 0.5% by weight in terms of oxide, the effect of densifying the sintered body is small. On the other hand, when the addition amount exceeds 15% by weight, the ratio of the main phase constituting the magnetic particles relatively decreases, and the cool storage effect is impaired. Therefore, the addition amount is 0.5 to 15% by weight, and a more preferable range is 1 to 10% by weight in terms of oxide. More preferably, it is in the range of 2 to 7% by weight.

Further, in the regenerator material of the present invention comprising a large number of magnetic particles mainly composed of an oxide, the magnetic particles having two or more cracks having a length of 10 μm or more on the surface of the magnetic particles may be used for all the magnetic particles. The ratio is preferably set to 20% or less.

If a plurality of cracks are present on the surface of the magnetic particles constituting the regenerator material, the cracks are likely to develop due to the vibration or impact force acting during the operation of the refrigerator, and the possibility of breaking the particles increases. Specifically, when the presence ratio (number ratio) of the magnetic particles having two or more cracks having a length of 10 μm or more on the surface of the magnetic particles exceeds 20%, the breaking ratio of the particles increases.
As a result, the generated fine powder damages the seal portion and the like of the refrigerator and significantly lowers the performance of the refrigerator.

Therefore, two cracks having a length of 10 μm or more
The abundance ratio of the particles present is preferably 20% or less, more preferably 10% or less, and further preferably 5% or less. The crack to be measured is more preferably a crack having a length of 5 μm or more, and more preferably a crack having a length of 3 μm or more.

A regenerator material composed of a large number of magnetic particles mainly composed of an oxide, wherein the ratio of the magnetic particles having a maximum surface roughness of 10 μm or more to all the magnetic particles is 30% or less. It is preferable to define

If the surface roughness of the magnetic particles is large, stress concentration tends to occur at the portions where the protrusions and steps are formed, and the particles are broken starting from the stress concentration portions. To prevent this phenomenon, the maximum height indicating the degree of surface roughness is 1
The ratio of the magnetic particles having a size of 0 μm or more is 30% or less. The ratio of particles having the maximum height of 10 μm or more is 20
%, More preferably 10% or less. The maximum height of the surface roughness to be evaluated is preferably 5 μm or more, and more preferably 3 μm or more. The surface roughness can be measured in accordance with Japanese Industrial Standards (JIS-B0601) from a cross-sectional curve of the obtained surface texture by photographing the surface texture with an observation means such as an electron microscope.

Further, in the cold storage material of the present invention comprising a large number of magnetic particles mainly composed of an oxide, the ratio of the magnetic particles having voids having a maximum width of 20 μm or more inside the magnetic particles to the total magnetic particles is as follows. It is preferable to set it as 40% or less.

The maximum width of the gap is measured as the length of the short side of the square having the minimum area surrounding the cross-sectional shape of the gap shown in the cross section of the magnetic particles.

Even when voids are formed inside the magnetic particles, the mechanical strength of the particles decreases, and the particles are easily broken during operation of the refrigerator. Therefore, the maximum width inside the particle is 2
The ratio of particles having voids of 0 μm or more is preferably 40% or less, more preferably 30% or less, and 2% or less.
0% or less is more desirable. The width of the void to be measured is preferably 5 μm or more, more preferably 3 μm.
m or more is more preferable.

The method for measuring the ratio of particles having defects such as cracks, surface roughness, and voids as described above is not particularly limited, but can be measured, for example, by the following method. In other words, observation of defects such as cracks, maximum height, voids, etc., using observation means such as an electron microscope, was performed on 20 or more magnetic particles randomly extracted from a cold storage material composed of many magnetic particles, A method of calculating the percentage of particles having defects can be employed. Here, in order to make the ratio of particles having defects higher, the number of particles to be observed is preferably 50 or more.
More preferably, the number is 00 or more.

When observing the cracks, it is sufficient to observe only one surface of each particle. That is, when observing the particle group in a certain visual field, it is not necessary to consider the surface on the opposite side that becomes the shadow of each particle. On the other hand, when measuring the surface roughness or internal defects of magnetic particles, after embedding the target magnetic particles in a substrate such as a resin, the substrate surface is polished to expose the particle cross section and observed with a microscope. The method is preferred. In this case, the average diameter of the magnetic particles is 80 to 120.
% Is set as the object to be measured.

Further, in the cold storage material of the present invention comprising a large number of magnetic particles mainly composed of an oxide, the magnetic particles contain silicon, sodium and iron in a total amount of 3 ppm to 2% by mass.
It is also preferable to configure to contain.

The inventor of the present application has noticed that a minute amount of grain boundary precipitates contained in the sintered body greatly affects the strength of the sintered body. As a result of further studies, silicon (S
It has been found that when compounds such as i), oxides of sodium (Na) and iron (Fe) are precipitated in large amounts at grain boundaries, the strength of the sintered body is reduced. That is. S
It has been found that when the total content of i, Na, and Fe exceeds 2% by mass, the strength as a cold storage material is reduced.

On the other hand, when the total content of Si, Na and Fe is 3
If the amount is less than ppm, the amount of precipitate that suppresses crystal growth is extremely reduced, and the crystal grains become coarse. When the crystal grains become coarse, the mechanical strength of the magnetic particles decreases, and the thermal shock characteristics also deteriorate.

Therefore, the total content of Si, Na and Fe is preferably specified in the range of 3 ppm to 2% by mass, more preferably in the range of 10 ppm to 1% by mass, and further preferably in the range of 50 to 5000 ppm. . However, when at least one of Si and Fe is selected as the A component in the general formula shown in the above formula (4), the total content excluding the amounts of the elements is used.

The method for producing a cold storage material according to the present invention is not particularly limited. For example, raw material powders are mixed using a ball mill or the like to prepare a raw material mixture, and the obtained raw material mixture is rolled. It can be manufactured by forming a spherical body (granulation) by a dynamic granulation method, a stirring granulation method, an extrusion method, a spray method (spray method), a press molding method or the like, and then sintering the obtained spherical molded body.

The raw material powder used in the above production method is as follows:
Desirably, the powder has a particle size of 0.3 to 30 μm. A more preferred particle size range is 0.4 to 10 μm, and a still more preferred particle size range is 0.5 to 8 μm.

The particles formed by various granulation methods such as the above-mentioned tumbling granulation method, stirring granulation method, extrusion method, and spraying method (spray method) have low molding densities. In some cases, it is difficult to obtain a good sintered body.

Therefore, the present invention employs the following manufacturing method.

That is, the oxide powder is granulated to form granulated particles, and the obtained granulated particles are subjected to cold isostatic pressure (CIP) pressure treatment to prepare spherical densified particles. It is also possible to adopt a method of manufacturing a regenerator material in which the obtained densified particles are sintered to prepare a regenerator material composed of a large number of magnetic particles.

In the above manufacturing method, a hot isostatic pressure (HIP) pressurizing process may be performed as the sintering process. That is, by performing cold isostatic pressing (CIP) or hot isostatic pressing (HIP) on the granulated particles, the density of the molded body can be further improved. Further, by sintering the high-density compact, magnetic particles having high density and few cracks and voids can be effectively obtained.

Further, in the above-mentioned production method, by adding 5 to 30% by weight of a binder to the oxide powder and granulating, it is possible to further increase the molding density.

As the above binder, water, ethyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyethylene glycol, polyacrylate and the like can be suitably used.

If the amount of the binder added to the oxide raw material powder is too small, less than 5% by weight, the effect of increasing the density by bonding the powders with high strength becomes insufficient. On the other hand, if the addition amount exceeds 30% by weight, the ratio of the oxide powder in the molded body becomes excessively low, and the molding density decreases. Therefore, the amount of binder added is 5
It is specified in the range of ３０30% by weight.

The added binder is removed by a degreasing treatment of the formed body after granulation, and the degreased formed body is sintered to prepare the regenerator material according to the present invention.

As a method of preparing the spherical magnetic particles, in addition to the method of sintering the raw material powder into a sphere by a rolling granulation method as described above and then sintering, the following thermal plasma is used. Alternatively, a method of spheroidization may be adopted.

That is, the oxide particles having a predetermined composition are granulated and then passed through a thermal plasma to be melted and solidified in a spheroidized state by the surface tension of the molten liquid, whereby a regenerative storage comprising a large number of magnetic particles is formed. A method for producing a cold storage material such as preparing a material can also be employed.

The method for granulating the oxide particles is not particularly limited. For example, a rolling method, an extrusion method,
Various granulation methods such as a spray method are used. As the raw material powder, a powder having an average particle diameter of 0.3 to 30 μm is suitable. More preferable average particle size of the raw material powder is 0.5 to 2
0 μm, and more preferably 1 to 10 μm.

Here, the thermal plasma means a state in which a high-temperature gas is discharged, and can be generated by discharging a gas by a high-frequency electromagnetic wave of several MHz to several GHz or a direct current.

FIG. 3 shows the configuration of the thermal plasma apparatus. The thermal plasma device 80 includes a reaction vessel 81, a high-frequency oscillator 82, a coil 83, a plasma generating unit outer cylinder 86,
Plasma frame 85 generated at the top of reaction vessel 81
Powder supply port 86 opening opposite to
A carrier gas supply cylinder 88 for transporting to the reaction vessel 81 stored in the reactor, a gas source 89 for plasma generation, a cyclone 90 for separating generated particles, and a cooling gas source 91 for cooling the reaction vessel 81. Is done.

In the thermal plasma apparatus 80, the electromagnetic wave transmitted from the high-frequency transmitter 82 is amplified by the coil 83, while the gas supplied from the plasma generating gas source 89 discharges the electromagnetic wave to the top of the reaction vessel 81. A temperature plasma frame 85 is formed. This frame part 8
The gas temperature of 5 reaches several thousand to about 10,000 ° C.

The plasma frame 8 in such a high temperature state
When the oxide particles supplied from the powder supply device 87 together with the carrier gas are introduced into 5, the whole particles or a part including the surface is melted. The molten raw material powder becomes spherical due to its surface tension. Then, it is rapidly cooled and solidified by the cooling gas supplied from the cooling gas source 91. The generated spherical magnetic particles are separated and collected by the cyclone 90. Since at least part of the particles is rapidly solidified by melting and spheroidizing, there is no crack on the particle surface, the surface is smooth, the surface roughness is small, and there are no voids inside. Particles are obtained.

However, since the magnetic particles spheroidized by the above-mentioned thermal plasma method are manufactured by being rapidly cooled from a high temperature of several thousand degrees centigrade, a prosbite structure exhibiting good specific heat characteristics depending on the raw material composition, processing conditions and the like. In some cases, such a crystal structure or structure cannot be obtained, and a complex structure in which an amorphous phase (glass phase) or a crystal phase different from the intended purpose is mixed is formed. For this reason, the original specific heat characteristic cannot be obtained, and there is a problem that the refrigerating capacity is reduced.

Therefore, as one mode of the method for producing a regenerative material according to the present invention, it is preferable to further heat-treat the magnetic particles which have been made spherical by passing through thermal plasma at a temperature of 500 ° C. or higher.

A magnetic particle having a non-equilibrium phase such as an amorphous phase generated by quenching from the high temperature state in the thermal plasma or a crystal phase different from the intended phase is heat-treated at a temperature of 500 ° C. or more to obtain a perovskite phase. It can be re-synthesized to the desired crystal phase.
When the heat treatment temperature is 500 ° C. or lower, the effect of resynthesizing the crystal phase becomes insufficient. The heat treatment temperature is preferably higher, but if the temperature exceeds 50 ° C. lower than the melting point of the magnetic particles,
It is not preferable because a part of the magnetic particles starts to melt. The heat treatment temperature is preferably 1800 ° C. or less from the viewpoint of the treatment time and the restriction on the specifications of the heat treatment furnace. A more preferable range of the heat treatment temperature is 1000 to 1750 ° C,
A more preferable temperature range is 1200 to 1700 ° C. The heat treatment time is not particularly limited.
The range is from 0 minutes to 50 hours. The heat treatment atmosphere is
Air or oxygen is preferred.

The regenerative refrigerator according to the present invention is configured using a regenerator filled with the regenerator as at least a part of the regenerator. In addition, while a regenerator filled with the regenerator material according to the present invention is loaded as a regenerator in a predetermined cooling stage, other Pb, HoCu ₂ , and Pb having specific heat characteristics corresponding to the temperature distribution are used as other regenerators. A regenerator filled with a regenerator material such as Er ₃ Ni may be used in combination.

According to the regenerative material having the above-described structure, the equivalent circular diameter, density, additive amount (composition), impurity amount, and amount of defects such as cracks and voids of the crystal grains of the magnetic particles are defined in a predetermined range. Therefore, the mechanical strength and the thermal conductivity are high, the thermal shock resistance is excellent, and the possibility of pulverization is small. Therefore, even when used as a cold storage material for a refrigerator operating at a high speed such as a Stirling refrigerator or a pulse tube refrigerator, a cold storage material having a small pressure loss and exhibiting stable refrigeration characteristics over a long period of time can be obtained. And by using the cold storage material as at least a part of the cold storage material of the refrigerator,
A refrigerator capable of maintaining high refrigerating capacity and maintaining stable refrigerating performance over a long period of time can be provided.

The MRI apparatus, the cryopump, the superconducting magnet for the magnetic levitation train, and the magnetic field application type single crystal pulling apparatus all have the performance of each apparatus, so that the above-described refrigerators are used. Of the present invention using
The RI device, the cryopump, the superconducting magnet for the magnetic levitation train, and the magnetic field application type single crystal pulling device can all exhibit excellent performance over a long period of time.

[0094]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be specifically described based on the following examples.

Example 1 A raw material mixture was prepared by mixing and pulverizing Al ₂ O ₃ powder and Gd ₂ O ₃ powder having an average particle size of 1.5 μm in ethyl alcohol using a ball mill for 24 hours. Next, after the obtained raw material mixture is dried, it is temporarily sintered at a temperature of 1500 ° C. for 12 hours, so that GdAl as an oxide sintered body is obtained.
The O ₃ were synthesized.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 6 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, by sintering the obtained granulated particles at a temperature of 1700 ° C. for 12 hours, Example 1 consisting of substantially spherical magnetic particles was obtained.
Was produced.

The surface and cross-sectional structure of the obtained regenerator particles were observed with a scanning electron microscope (SEM).
Was obtained. Based on these organization photos,
As a result of image analysis, the average value of the equivalent circular diameter of the crystal grains was 3.3 μm.

The regenerator particles produced by the tumbling granulation method have a substantially spherical shape as shown in FIGS. 4 to 7, but have a large surface roughness and a small number of fine particles inside. Are formed.

Next, in order to evaluate the characteristics of the cold storage material prepared as described above, a two-stage expansion type GM refrigerator as shown in FIG. 1 was prepared. The two-stage GM refrigerator 10 shown in FIG.
1 shows an embodiment of the refrigerator of the present invention. Figure 1
Has a vacuum vessel 13 in which a large-diameter first cylinder 11 and a small-diameter second cylinder 12 coaxially connected to the first cylinder 11 are installed. ing. The first cylinder 11 has a first regenerator 14 arranged reciprocally, and the second cylinder 12 has a second regenerator 15 arranged reciprocally. Between the first cylinder 11 and the first regenerator 14 and the second cylinder 12
The seal ring 1 is provided between the
6, 17 are arranged.

The first regenerator 14 contains a first regenerator 18 such as a Cu mesh. In the second regenerator 15,
A plate-like cold storage material for cryogenic use used in the cool storage device of the present invention is accommodated as the second cold storage material 19. Each of the first regenerator 14 and the second regenerator 15 has a passage for a working medium (refrigerant gas) such as He gas provided in a gap or the like between the first regenerator 18 and the cryogenic regenerator 19. .

A first expansion chamber 20 is provided between the first regenerator 14 and the second regenerator 15. Further, a second expansion chamber 21 is provided between the second regenerator 15 and the end wall of the second cylinder 12. A first cooling stage 22 is formed at the bottom of the first expansion chamber 20, and a second cooling stage 23 having a lower temperature than the first cooling stage 22 is formed at the bottom of the second expansion chamber 21.

The two-stage GM refrigerator 10 as described above is supplied with a high-pressure working medium (for example, He
Gas) is supplied. The supplied working medium passes between the first regenerators 18 accommodated in the first regenerator 14, reaches the first expansion chamber 20, and further reaches the cryogenic regenerator material accommodated in the second regenerator 15. (Second regenerative material) passes through the space 19 and reaches the second expansion chamber 21. At this time, the working medium is each cold storage material 1
8 and 19 are cooled by supplying thermal energy. The working medium that has passed between the cold storage materials 18 and 19 is
21 to generate cold, and each cooling stage 22,
23 is cooled. The expanded working medium is stored in each cold storage material 1
It flows between 8 and 19 in the opposite direction. The working medium is each cold storage material 1
Emitted after receiving thermal energy from 8,19. In this process, as the recuperation effect becomes better, the thermal efficiency of the working medium cycle is improved, and a lower temperature is realized.

Then, 200 g of the cold storage material according to the first embodiment prepared as described above is charged into the low-temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. Was assembled with a refrigerator according to Example 1 by filling 200 g of Pb cold storage material, and a refrigeration test was carried out, and the refrigeration capacity at 4.2K was measured.

The refrigerating capacity in the present embodiment is defined as the heat load when a heat load is applied to the second cooling stage by the heater during the operation of the refrigerator and the temperature rise of the second cooling stage stops at 4.2K. .

As a result of the refrigeration test, 0.76 W was obtained as the initial value of the refrigeration capacity at 4.2 K. Also, 2
The refrigeration capacity after continuous operation for 40 hours was 0.74 W, and stable refrigeration performance was confirmed. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed, but no generation of broken particles or fine powder was observed.

Comparative Example 1 Al ₂ O ₃ powder and Gd ₂ O ₃ powder having an average particle diameter of 30 μm were mixed in ethyl alcohol for 24 hours using a ball mill.
The mixture was pulverized to prepare a raw material mixture. Next, after drying the obtained raw material mixture, it is pre-sintered at a temperature of 1500 ° C. for 12 hours to obtain GdAlO ₃ as an oxide sintered body.
Was synthesized.

Next, the obtained sintered body was further ground in ethyl alcohol using a ball mill for 6 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, by sintering the obtained granulated particles at a temperature of 1800 ° C. for 12 hours, Comparative Example 1 consisting of substantially spherical magnetic particles was obtained.
Was produced.

The sectional structure of the obtained regenerator particles was observed with a scanning electron microscope (SEM) and image analysis revealed that the average value of the equivalent circular diameter of the crystal grains was as coarse as 28 μm.

Then, 200 g of the cold storage material according to Comparative Example 1 prepared as described above is charged into the low-temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. Was assembled with a refrigerator according to Comparative Example 1 by charging 200 g of Pb cold storage material, and a refrigeration test was performed to measure the refrigeration capacity at 4.2K.

As a result of the refrigerating test, 0.74 W was obtained as the initial value of the refrigerating capacity at 4.2 K. Also, 2
The refrigerating capacity after continuous operation for 40 hours was reduced to 0.31 W, and the refrigerating performance was significantly reduced. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed. As a result, generation of broken particles and fine powder was observed.

Comparative Example 2 Al ₂ O ₃ powder and Gd ₂ O ₃ powder having an average particle size of 1 μm were mixed and pulverized in ethyl alcohol using a ball mill for 24 hours to prepare a raw material mixture. Next, after drying the obtained raw material mixture, it was provisionally sintered at a temperature of 1200 ° C. for 6 hours to synthesize GdAlO ₃ as an oxide sintered body.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 6 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, the obtained granulated particles were sintered at a temperature of 1700 ° C. for 3 hours to produce a regenerator material according to Comparative Example 2 composed of substantially spherical magnetic particles.

The cross-sectional structure of the obtained regenerator particles was observed with a scanning electron microscope (SEM) and image analysis revealed that the average equivalent circular diameter of the crystal grains was as small as 0.2 μm.

Then, 200 g of the cold storage material according to Comparative Example 2 prepared as described above is charged into the low-temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. Was assembled with a refrigerator according to Comparative Example 2 by charging 200 g of Pb cold storage material, and a refrigeration test was performed to measure the refrigeration capacity at 4.2K.

As a result of the refrigeration test, 0.42 W was obtained as the initial value of the refrigeration capacity at 4.2 K. Also, 2
The refrigerating capacity after continuous operation for 40 hours was 0.41 W.

Next, an embodiment in which the area ratio of coarse crystal grains is specified will be described.

Example 2 An Al ₂ O ₃ powder and a Gd ₂ O ₃ powder having an average particle size of 1.5 μm were mixed and pulverized in ethyl alcohol using a ball mill for 24 hours to prepare a raw material mixture. Next, after drying the obtained raw material mixture, it is pre-sintered at a temperature of 1600 ° C. for 3 hours to obtain GdAlO as an oxide sintered body.
₃ was synthesized.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 6 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, by sintering the obtained granulated particles at a temperature of 1700 ° C. for 12 hours, Example 2 consisting of substantially spherical magnetic particles
Was produced.

The sectional structure of the obtained regenerator particles was observed with a scanning electron microscope (SEM) and image analysis revealed that no crystal grains having an equivalent circular diameter of 50 μm or more were observed. The equivalent circular diameter of the coarsest crystal grain in the sectional structure was 21 μm. The average value of the equivalent circular diameter of the crystal grains was 3.8 μm.

Then, 200 g of the cold storage material according to the second embodiment prepared as described above is charged into the low-temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. Was assembled with a refrigerator according to Example 2 by filling 200 g of Pb cold storage material, and a refrigeration test was performed, and the refrigeration capacity at 4.2K was measured.

As a result of the freezing test, 0.70 W was obtained as the initial value of the freezing capacity at 4.2K. Also, 2
The refrigerating capacity after continuous operation for 40 hours was 0.69 W, and stable refrigerating performance was confirmed. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed, but no generation of broken particles or fine powder was observed. Therefore, according to the cold storage material according to the present embodiment, it is possible to realize a refrigerator having a high refrigerating capacity in the 4K region and stable characteristics.

Comparative Example 3 Al ₂ O ₃ powder and Gd ₂ O ₃ powder having an average particle diameter of 20 μm were mixed and pulverized in ethyl alcohol using a ball mill for 6 hours to prepare a raw material mixture. Next, after drying the obtained raw material mixture, it was provisionally sintered at a temperature of 1500 ° C. for 12 hours to synthesize GdAlO ₃ as an oxide sintered body.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 6 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, by sintering the obtained granulated particles at a temperature of 1800 ° C. for 24 hours, Comparative Example 3 consisting of substantially spherical magnetic particles was obtained.
Was produced.

The sectional structure of the obtained regenerator particles was observed with a scanning electron microscope (SEM) and image analysis revealed that the area ratio of crystal grains having an equivalent circular diameter of 50 μm or more was 17%.
Was too big. The average equivalent circle diameter of the crystal grains was 24 μm.

Then, 200 g of the cold storage material according to Comparative Example 3 prepared as described above was charged into the low-temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. Was assembled with a refrigerator according to Comparative Example 3 by filling 200 g of a Pb cold storage material, and performed a refrigeration test to measure the refrigeration capacity at 4.2K.

As a result of the refrigeration test, 0.75 W was obtained as the initial value of the refrigeration capacity at 4.2 K. Also, 2
The refrigerating capacity after continuous operation for 40 hours was reduced to 0.28 W, and it was confirmed that the refrigerating performance was significantly reduced. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed. As a result, generation of broken particles and fine powder was observed.

Next, an example in which the sintering density of the magnetic particles is specified will be described.

[0128] 24 hours using a ball mill _Al 2 _{O 3} powder and _Gd 2 _{O 3} powder of Example 3 the average particle diameter of 2μm in ethyl alcohol, the raw material mixture was prepared by mixing pulverized. Next, after drying the obtained raw material mixture, it was temporarily sintered at a temperature of 1400 ° C. for 6 hours to synthesize GdAlO ₃ as an oxide sintered body.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 6 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, the obtained granulated particles were inserted into a bag made of a nylon-polyethylene film, and the inside of the bag was evacuated and then the opening of the bag was heat-sealed. In this state, the whole bag is 600kgf
/ Cm ^{2 at} a pressure of CIP. Next, the granulated particles densified by the CIP treatment were sintered at a temperature of 1700 ° C. for 12 hours, thereby forming substantially spherical magnetic particles.
Was produced.

The sintering density of the obtained regenerator material particles was 96.8%. The average equivalent circle diameter of the crystal grains was 5.2 μm.

Then, 200 g of the cold storage material according to the third embodiment prepared as described above is charged into the low-temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. Was assembled with a refrigerator according to Example 3 by charging 200 g of Pb cold storage material, and a refrigeration test was performed, and the refrigeration capacity at 4.2K was measured.

As a result of the freezing test, 0.77 W was obtained as the initial value of the freezing capacity at 4.2K. Also, 2
The refrigerating capacity after continuous operation for 40 hours was 0.75 W, and stable refrigerating performance was confirmed. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed, but no generation of broken particles or fine powder was observed.

Example 4 An Al ₂ O ₃ powder having an average particle size of 3 μm and a Gd ₂ O ₃ powder were mixed and pulverized in ethyl alcohol using a ball mill for 24 hours to prepare a raw material mixture. Next, after drying the obtained raw material mixture, it was temporarily sintered at a temperature of 1500 ° C. for 3 hours to synthesize GdAlO ₃ as an oxide sintered body.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 6 hours. After drying the ground powder, 10% by weight of carboxymethyl cellulose
, And granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, after degreasing the obtained granulated particles,
By sintering at 0 ° C. for 4 hours, a regenerator material according to Example 4 consisting of substantially spherical magnetic particles was produced.

The sintering density of the obtained regenerator material particles was 97.8%. The average value of the equivalent circular diameter of the crystal grains was 3.6 μm.

Then, 200 g of the cold storage material according to Example 4 prepared as described above is charged into the low-temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. Was filled with 200 g of Pb cold storage material, assembled a refrigerator according to Example 4, performed a refrigeration test, and measured the refrigeration capacity at 4.2K.

As a result of the refrigerating test, 0.74 W was obtained as the initial value of the refrigerating capacity at 4.2 K. Also, 2
The refrigeration capacity after continuous operation for 40 hours was 0.74 W, and stable refrigeration performance was confirmed. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed, but no generation of broken particles or fine powder was observed. Therefore, according to the cold storage material according to the present embodiment, a refrigerator having high refrigerating capacity in the 4K region and stable characteristics can be realized.

Comparative Example 4 Al ₂ O ₃ powder and Gd ₂ O ₃ powder having an average particle size of 50 μm were mixed and pulverized in ethyl alcohol using a ball mill for 2 hours to prepare a raw material mixture. Next, after drying the obtained raw material mixture, it was provisionally sintered at a temperature of 1200 ° C. for 2 hours to synthesize GdAlO ₃ as an oxide sintered body.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 2 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, the obtained granulated particles were sintered at a temperature of 1400 ° C. for 3 hours to produce a regenerator material according to Comparative Example 4 composed of substantially spherical magnetic particles.

When the sintering density of the obtained regenerator material particles was measured, it was as low as 73.6%. The average value of the equivalent circular diameter of the crystal grains was 51 μm.

Then, 200 g of the cold storage material according to Comparative Example 4 prepared as described above was charged into the low-temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. Was assembled with a refrigerator according to Comparative Example 4 by charging 200 g of a Pb cold storage material, and a refrigeration test was performed to measure a refrigeration capacity at 4.2K.

As a result of the freezing test, 0.62 W was obtained as an initial value of the freezing capacity at 4.2K. Also, 2
It was confirmed that the refrigeration capacity after continuous operation for 40 hours was reduced to 0.24 W. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed. As a result, generation of broken particles and fine powder was observed.

Comparative Example 5 Al ₂ O ₃ powder and Gd ₂ O ₃ powder having an average particle diameter of 1 μm were mixed and pulverized in ethyl alcohol using a ball mill for 24 hours to prepare a raw material mixture. Next, the obtained raw material mixture after drying, by 6 hours provisionally sintered at a temperature 1500 ° C., was synthesized GdAlO ₃ as an oxide sintered body.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 6 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, the obtained granulated particles were inserted into a bag made of a nylon-polyethylene film, and the inside of the bag was evacuated and then the opening of the bag was heat-sealed. In this state, the whole bag is 800kgf
/ Cm ^{2 at} a pressure of CIP. Next, the granulated particles densified by the CIP treatment were sintered at a temperature of 1800 ° C. for 6 hours to produce a regenerator material according to Comparative Example 5 composed of substantially spherical magnetic particles.

When the sintering density of the obtained regenerator material particles was measured, it was 99.7%, which was excessive. The average equivalent circular diameter of the crystal grains was 23 μm.

Then, 200 g of the regenerator material according to Comparative Example 5 prepared as described above is charged into the low-temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. Was assembled with a refrigerator according to Comparative Example 5 by charging 200 g of a Pb cold storage material, and a refrigeration test was performed to measure a refrigeration capacity at 4.2K.

As a result of the refrigerating test, 0.73 W was obtained as the initial value of the refrigerating capacity at 4.2 K. Also, 2
The refrigeration capacity after continuous operation for 40 hours decreased to 0.42 W. In particular, it was found that cracks were frequently generated in the cold storage material, and the refrigerating ability was reduced with time.

Next, an embodiment of a regenerative material to which yttria is added as an additive will be described.

Example 5 An Al ₂ O ₃ powder and an Gd ₂ O ₃ powder having an average particle size of 2 μm were mixed and pulverized in ethyl alcohol using a ball mill for 24 hours to prepare a raw material mixture. Next, the obtained raw material mixture after drying, by 6 hours provisionally sintered at a temperature 1500 ° C., was synthesized GdAlO ₃ as an oxide sintered body.

Next, the average particle size of the obtained sintered body was 0.8 μm.
After adding 3% by weight of m ₂ Y ₂ O ₃ powder, the mixture was further ground in ethyl alcohol using a ball mill for 6 hours.
After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm.
Further, the obtained granulated particles were sintered at a temperature of 1700 ° C. for 6 hours to produce a regenerator material according to Example 5 composed of substantially spherical magnetic particles. The average value of the equivalent circular diameter of the crystal grains was 3.6 μm.

Then, 200 g of the cold storage material according to Example 5 prepared as described above is charged into the low-temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. Was filled with 200 g of Pb cold storage material, assembled a refrigerator according to Example 5, performed a refrigeration test, and measured the refrigeration capacity at 4.2K.

As a result of the refrigerating test, 0.74 W was obtained as an initial value of the refrigerating capacity at 4.2 K. Also, 2
The refrigeration capacity after continuous operation for 40 hours was 0.73 W, and stable refrigeration performance was confirmed. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed, but no generation of broken particles or fine powder was observed. Therefore, according to the cold storage material according to the present embodiment, a refrigerator having high refrigerating capacity in the 4K region and stable characteristics can be realized.

Example 6 Al ₂ O ₃ powder and Gd ₂ O ₃ powder having an average particle size of 2 μm were mixed and pulverized in ethyl alcohol using a ball mill for 24 hours to prepare a raw material mixture. Next, after drying the obtained raw material mixture, it was provisionally sintered at a temperature of 1500 ° C. for 6 hours to synthesize GdAlO ₃ as an oxide sintered body.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 6 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, the obtained granulated particles were sintered at a temperature of 1700 ° C. for 6 hours, thereby producing a regenerator material according to Example 6 comprising substantially spherical magnetic particles. The average value of the equivalent circular diameter of the crystal grains was 3.3 μm.

Then, 200 g of the cold storage material according to Example 6 prepared as described above is charged into the low-temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. Was filled with 200 g of Pb cold storage material, assembled a refrigerator according to Example 6, performed a refrigeration test, and measured the refrigeration capacity at 4.2K.

As a result of the refrigeration test, 0.73 W was obtained as the initial value of the refrigeration capacity at 4.2 K. Also, 2
The refrigeration capacity after continuous operation for 40 hours was 0.60 W, and stable refrigeration performance was confirmed. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed, but no generation of broken particles or fine powder was observed.

Next, an embodiment of a regenerative material made spherical by a thermal plasma method will be described.

Example 7 A mixture of raw materials was prepared by mixing and pulverizing Al ₂ O ₃ powder and Gd ₂ O ₃ powder having an average particle size of 3 μm in ethyl alcohol using a ball mill for 24 hours. Next, after drying the obtained raw material mixture, it was provisionally sintered at a temperature of 1500 ° C. for 6 hours to synthesize GdAlO ₃ as an oxide sintered body.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 6 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, the obtained granulated particles are supplied into a plasma flame generated by a thermal plasma apparatus shown in FIG. 3 to be melted, and then rapidly solidified in a spherical state to prepare substantially spherical magnetic particles. The heat storage material according to Example 7 was manufactured by performing a heat treatment at 1700 ° C. for 2 hours in the air.

[0160] 200 particles were randomly extracted from the obtained spherical cold storage material particles, and the surface condition was observed with a scanning electron microscope (SEM). As a result, two cracks having a length of 10 µm or more were found on the particle surface. There were five such particles, and the abundance was 2.5%. The average value of the equivalent circular diameter of the crystal grains was 6.4 μm.

Then, 200 g of the cold storage material according to Example 7 prepared as described above is charged into the low-temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. Was filled with 200 g of Pb cold storage material, assembled a refrigerator according to Example 7, performed a refrigeration test, and measured the refrigeration capacity at 4.2K.

As a result of the refrigerating test, 0.72 W was obtained as the initial value of the refrigerating capacity at 4.2 K. Also, 2
The refrigerating capacity after continuous operation for 40 hours was 0.71 W, and stable refrigerating performance was confirmed. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed, but no generation of broken particles or fine powder was observed.

Example 8 An Al ₂ O ₃ powder and a Gd ₂ O ₃ powder having an average particle size of 3 μm were mixed and pulverized in ethyl alcohol using a ball mill for 24 hours to prepare a raw material mixture. Next, after drying the obtained raw material mixture, it was provisionally sintered at a temperature of 1500 ° C. for 6 hours to synthesize GdAlO ₃ as an oxide sintered body.

Next, the obtained sintered body was further ground in ethyl alcohol using a ball mill for 6 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, the obtained granulated particles were sintered at a temperature of 1700 ° C. for 6 hours to produce a cold storage material according to Example 8 consisting of substantially spherical magnetic particles.

200 particles were randomly extracted from the obtained spherical regenerator particles, and the surface condition was observed by a scanning electron microscope (SEM). As a result, two cracks having a length of 10 μm or more were found on the particle surface. There were 56 such particles, and their abundance was 28%. The average value of the equivalent circular diameter of the crystal grains was 3.1 μm.

Then, 200 g of the cold storage material according to Example 8 prepared as described above is charged into the low-temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. Was filled with 200 g of Pb cold storage material, assembled a refrigerator according to Example 8, performed a refrigeration test, and measured the refrigeration capacity at 4.2K.

As a result of the refrigerating test, 0.73 W was obtained as the initial value of the refrigerating capacity at 4.2 K. Also, 2
The refrigerating capacity after continuous operation for 40 hours was 0.61 W, and stable refrigerating performance was confirmed. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed, but no generation of broken particles or fine powder was observed.

Example 9 Al ₂ O ₃ powder and Gd ₂ O ₃ powder having an average particle size of 8 μm were mixed and pulverized in ethyl alcohol using a ball mill for 24 hours to prepare a raw material mixture. Next, after drying the obtained raw material mixture, it was provisionally sintered at a temperature of 1500 ° C. for 6 hours to synthesize GdAlO ₃ as an oxide sintered body.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 6 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, the obtained granulated particles are supplied into a plasma flame generated by a thermal plasma apparatus shown in FIG. 3 to be melted, and then rapidly solidified in a spherical state to prepare substantially spherical magnetic particles. The obtained spherical particles were subjected to a heat treatment at 1700 ° C. for 2 hours in the air to produce a cold storage material according to Example 9.

200 particles were randomly extracted from the obtained spherical regenerative particles, each particle was embedded in a transparent resin, and polished until the cross section of each particle was exposed. When the surface state of the cross section of each particle was observed with a scanning electron microscope (SEM), the maximum height of the surface roughness of the particle was 1%.
There are four particles having a size of 0 μm or more, and the presence ratio is 2
%Met. The average value of the equivalent circular diameter of the crystal grains is
It was 5.4 μm.

Then, 200 g of the cold storage material according to the ninth embodiment prepared as described above is charged into the low-temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. Was filled with 200 g of Pb cold storage material, assembled a refrigerator according to Example 9, performed a refrigeration test, and measured the refrigeration capacity at 4.2K.

As a result of the refrigerating test, 0.73 W was obtained as an initial value of the refrigerating capacity at 4.2 K. Also, 2
The refrigerating capacity after continuous operation for 40 hours was 0.72 W, and stable refrigerating performance was confirmed. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed, but no generation of broken particles or fine powder was observed.

Example 10 Al ₂ O ₃ powder and Gd ₂ O ₃ powder having an average particle size of 8 μm were mixed and pulverized in ethyl alcohol using a ball mill for 24 hours to prepare a raw material mixture. Next, after drying the obtained raw material mixture, it was provisionally sintered at a temperature of 1500 ° C. for 6 hours to synthesize GdAlO ₃ as an oxide sintered body.

Next, the obtained sintered body was further ground in ethyl alcohol using a ball mill for 6 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, by sintering the obtained granulated particles at a temperature of 1700 ° C. for 6 hours, Example 10 consisting of substantially spherical magnetic particles was obtained.
Was produced.

200 particles were randomly extracted from the obtained regenerator material particles, each particle was embedded in a transparent resin, and further polished until the cross section of each particle was exposed. When the cross section of each particle was observed with a scanning electron microscope (SEM), 70 particles having a maximum surface roughness of 10 μm or more were present, and the abundance was 35%. The average value of the equivalent circular diameter of the crystal grains was 8.5 μm.

Then, Example 10 prepared as described above was used.
200 g of the cold storage material according to Example 1 was charged into the low-temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. The refrigerator was assembled and a refrigeration test was performed to measure the refrigeration capacity at 4.2K.

As a result of the refrigerating test, 0.71 W was obtained as the initial value of the refrigerating capacity at 4.2 K. Also, 2
The refrigeration capacity after continuous operation for 40 hours was 0.59 W, and stable refrigeration performance was confirmed. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed, but no generation of broken particles or fine powder was observed.

Next, the effect of a heat treatment performed on the magnetic particles prepared by the thermal plasma method will be described with reference to the following examples.

Example 11 Al ₂ O ₃ powder and Gd ₂ O ₃ powder having an average particle size of 8 μm were mixed and pulverized in ethyl alcohol using a ball mill for 24 hours to prepare a raw material mixture. Next, after drying the obtained raw material mixture, it was provisionally sintered at a temperature of 1500 ° C. for 6 hours to synthesize GdAlO ₃ as an oxide sintered body.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 6 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, the obtained granulated particles are supplied into a plasma flame generated by a thermal plasma apparatus shown in FIG. 3 to be melted, and then rapidly solidified in a spherical state to prepare substantially spherical magnetic particles. The obtained spherical particles were subjected to a heat treatment in the atmosphere at a temperature of 1700 ° C. for 2 hours to produce a regenerator material according to Example 11 composed of magnetic particles having good surface properties.

From the obtained spherical regenerator particles, 200 particles were randomly extracted, each particle was embedded in a transparent resin, and further polished until the cross section of each particle was exposed. Then, when the surface state and cross-sectional structure of each particle were observed with a scanning electron microscope (SEM), the surface state was observed.
Was obtained. As a result of shape analysis based on these micrographs, no particles having a maximum surface roughness of 10 μm or more were found. The average value of the equivalent circular diameter of the crystal grains was 6.6 μm.

Then, Example 11 prepared as described above was used.
While filling 50 g of the cold storage material according to the above into the lowest temperature side of the second stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. 1, while filling 150 g of the HoCu ₂ cold storage material on its high temperature side, Further, the refrigerator of Example 11 was assembled by filling 200 g of Pb cold storage material on the high temperature side, and a refrigerating test was performed at an operating frequency of 1 Hz, and the refrigerating capacity at 4.2 K was measured.

As a result of the refrigerating test, 0.86 W was obtained as the initial value of the refrigerating capacity at 4.2 K. Also, 2
The refrigeration capacity after continuous operation for 40 hours was 0.85 W, and stable refrigeration performance was confirmed. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed, but no generation of broken particles or fine powder was observed.

Example 12 In Example 11, the heat treatment was not performed on the magnetic particles spheroidized by the thermal plasma method, and
2 was used as the cold storage material.

200 particles were randomly extracted from the obtained regenerator particles, each particle was embedded in a transparent resin, and polished until the cross section of each particle was exposed. When the cross section of each particle was observed by a scanning electron microscope (SEM), two particles having a maximum surface roughness of 10 μm or more were present, and the abundance was 1%. Also,
The average value of the equivalent circular diameter of the crystal grains was 5.2 μm.

Then, Example 12 prepared as described above was used.
While 200 g of the cold storage material according to the above is filled in the lowest temperature side of the second stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. 1, while the high temperature side is filled with 150 g of HoCu ₂ cold storage material, Further, 200 g of Pb cold storage material was filled on the high-temperature side, a refrigerator according to Example 12 was assembled, and a refrigeration test was performed in the same manner as in Example 11, and the refrigeration capacity at 4.2K was measured.

As a result of the freezing test, 0.41 W was obtained as the initial value of the freezing capacity at 4.2K. That is, as is apparent from a comparison between Example 11 and Example 12, by subjecting the magnetic particles spherical by the thermal plasma method to a further heat treatment, non-magnetic particles such as an amorphous phase generated in the particle structure are obtained. Since the equilibrium phase is re-synthesized into a crystalline phase having excellent specific heat properties such as a perovskite phase, 4K
It was found that the refrigerating capacity of the region was high, and the refrigerating capacity was dramatically improved.

Next, an embodiment of a regenerative material in which the proportion of particles having voids is defined will be described.

Example 13 Al ₂ O ₃ powder and Gd ₂ O ₃ powder having an average particle diameter of 6 μm were mixed and pulverized in ethyl alcohol using a ball mill for 24 hours to prepare a raw material mixture. Next, after drying the obtained raw material mixture, it was provisionally sintered at a temperature of 1200 ° C. for 6 hours to synthesize GdAlO ₃ as an oxide sintered body.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 6 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, the obtained granulated particles are supplied to the end of the plasma frame generated by the thermal plasma device shown in FIG.
Further, by solidifying in a spherical state, a cold storage material according to Example 13 consisting of substantially spherical magnetic particles was produced.

From the obtained regenerator particles, 200 particles were randomly extracted, each particle was embedded in a transparent resin, and further polished until the cross section of each particle was exposed. When the cross section of each particle was observed with a scanning electron microscope (SEM), 34 particles having a void having a maximum width of 20 μm or more were present inside the particle, and the abundance ratio was 17%. Also,
The average value of the equivalent circular diameter of the crystal grains was 6.5 μm.

Then, Example 13 prepared as described above was used.
In the thirteenth embodiment, 200 g of the cold storage material according to Example 1 was charged into the low-temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. The refrigerator was assembled and a refrigeration test was performed to measure the refrigeration capacity at 4.2K.

As a result of the refrigerating test, 0.72 W was obtained as the initial value of the refrigerating capacity at 4.2 K. Also, 2
The refrigerating capacity after continuous operation for 40 hours was 0.72 W, and stable refrigerating performance was confirmed. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed, but no generation of broken particles or fine powder was observed.

Example 14 Al ₂ O ₃ powder and Gd ₂ O ₃ powder having an average particle diameter of 6 μm were mixed and pulverized in ethyl alcohol using a ball mill for 24 hours to prepare a raw material mixture. Next, after drying the obtained raw material mixture, it was provisionally sintered at a temperature of 1200 ° C. for 6 hours to synthesize GdAlO ₃ as an oxide sintered body.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 6 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, by sintering the obtained granulated particles at a temperature of 1600 ° C. for 5 hours, Example 14 consisting of substantially spherical magnetic particles was obtained.
Was produced.

From the obtained regenerator particles, 200 particles were randomly extracted, embedded in a transparent resin, and polished until the cross section of each particle was exposed. When the cross section of each particle was observed with a scanning electron microscope (SEM), there were 84 particles having voids having a maximum width of 20 μm or more inside the particles, and the abundance was 42%. Also,
The average equivalent circle diameter of the crystal grains was 6.1 μm.

Then, Example 14 prepared as described above was used.
200 g of the cold storage material according to Example 1 was charged into the low-temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. The refrigerator was assembled and a refrigeration test was performed to measure the refrigeration capacity at 4.2K.

As a result of the refrigerating test, 0.71 W was obtained as an initial value of the refrigerating capacity at 4.2 K. Also, 2
The refrigerating capacity after continuous operation for 40 hours was 0.58 W, and stable refrigerating performance was confirmed. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed, but no generation of broken particles or fine powder was observed.

Next, an embodiment of a regenerative material in which the contents of Si, Na and Fe as additives are specified will be described.

Example 15 The total content of Si, Na and Fe was 230 ppm.
Al ₂ O ₃ powder and Gd ₂ O ₃ powder having an average particle diameter of 1 μm were mixed and pulverized in ethyl alcohol for 4 hours using a ball mill to prepare a raw material mixture. Next, after drying the obtained raw material mixture, it was provisionally sintered at a temperature of 1400 ° C. for 3 hours to synthesize GdAlO ₃ as an oxide sintered body.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 3 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, by sintering the obtained granulated particles at a temperature of 1700 ° C. for 6 hours, Example 15 consisting of substantially spherical magnetic particles was obtained.
Was produced. The above manufacturing steps were performed in a clean room.

The total content of Si, Na and Fe in the obtained regenerator particles was analyzed by ICP method and found to be 540 ppm. The average equivalent circle diameter of the crystal grains was 1.5 μm.

Then, Example 15 prepared as described above was used.
200 g of the cold storage material according to Example 1 was charged into the low-temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. The refrigerator was assembled and a refrigeration test was performed to measure the refrigeration capacity at 4.2K.

As a result of the freezing test, 0.68 W was obtained as an initial value of the freezing capacity at 4.2K. Also, 2
The refrigeration capacity after continuous operation for 40 hours was 0.65 W, and stable refrigeration performance was confirmed. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed, but no generation of broken particles or fine powder was observed.

Example 16 The total content of Si, Na and Fe was 2.3% by weight,
Al ₂ O ₃ powder and Gd ₂ O ₃ powder having an average particle diameter of 1 μm were mixed and pulverized in ethyl alcohol for 4 hours using a ball mill to prepare a raw material mixture. Next, after drying the obtained raw material mixture, it was provisionally sintered at a temperature of 1400 ° C. for 3 hours to synthesize GdAlO ₃ as an oxide sintered body.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 3 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, by sintering the obtained granulated particles at a temperature of 1700 ° C. for 6 hours, Example 16 consisting of substantially spherical magnetic particles was obtained.
Was produced.

The total content of Si, Na and Fe in the obtained regenerator particles was analyzed by ICP method and found to be 2.4% by weight. The average equivalent circle diameter of the crystal grains was 1.3 μm.

Then, Example 16 prepared as described above was used.
200 g of the cold storage material according to Example 1 was charged into the low-temperature side of the second stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. The refrigerator was assembled and a refrigeration test was performed to measure the refrigeration capacity at 4.2K.

As a result of the refrigeration test, 0.75 W was obtained as the initial value of the refrigeration capacity at 4.2 K. Also, 2
The refrigeration capacity after continuous operation for 40 hours was 0.59 W, and stable refrigeration performance was confirmed. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed, but no generation of broken particles or fine powder was observed.

Comparative Example 6 Al ₂ O ₃ powder and Gd ₂ O ₃ powder having a total content of Si, Na and Fe of 1 ppm and an average particle size of 1 μm were mixed in ethyl alcohol for 4 hours by using a ball mill. The mixture was pulverized to prepare a raw material mixture. Next, the obtained raw material mixture after drying for 3 hrs provisionally sintered at a temperature 1400 ° C., was synthesized GdAlO ₃ as an oxide sintered body.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 3 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, the obtained granulated particles were sintered at a temperature of 1700 ° C. for 6 hours to produce a regenerator material according to Comparative Example 6 composed of substantially spherical magnetic particles. The above manufacturing steps were performed in a clean room.

The total content of Si, Na and Fe in the obtained regenerator material particles was measured by ICP method.
ppm. The average value of the equivalent circular diameter of the crystal grains was 24 μm.

Then, 200 g of the cold storage material according to Comparative Example 6 prepared as described above was charged into the low-temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. Was assembled with a refrigerator according to Comparative Example 6 by charging 200 g of a Pb cold storage material, and performed a refrigeration test to measure the refrigeration capacity at 4.2K.

As a result of the refrigerating test, 0.69 W was obtained as the initial value of the refrigerating capacity at 4.2 K. Also, 2
The refrigeration capacity after continuous operation for 40 hours was reduced to 0.44 W, and it was found that the refrigeration performance was reduced with time. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed. As a result, generation of broken particles and fine powder was observed.

[0215]Example 17 The content of sodium (Na) is 14 ppm, and the average
Fe with a particle size of 1 μm₂O₃Powder and SiO₂Powder and Gd₂
O₃Powder and 4: 2: 5 in molar ratio,
Mix for 4 hours using a ball mill in ethyl alcohol
The mixture was pulverized to prepare a raw material mixture. Next, the raw material mixture obtained
After the body is dried, it is temporarily sintered at a temperature of 1400 ° C. for 3 hours.
Thus, GdFe as an oxide sintered body_0.8Si
_0.2O ₃Was synthesized. After drying the synthesized mixture, 15
Sintered at 00 ° C for 6 hours.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 6 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, the obtained granulated particles are supplied to a thermal plasma apparatus shown in FIG. 3, and are melted and rapidly solidified into a sphere to form GdFe _0.8 S
Spherical particles having a composition of i _0.2 O ₃ were obtained. Further, the spherical particles were heat-treated in the atmosphere at a temperature of 1700 ° C. for 2 hours to produce a cold storage material according to Example 17 composed of substantially spherical magnetic particles.

The content of Na as an impurity contained in the obtained regenerator particles having the composition of GdFe _0.8 Si _0.2 O ₃ was analyzed by ICP method and found to be 15 ppm. The average value of the equivalent circular diameter of the crystal grains was 6.1 μm.

Then, Example 17 prepared as described above was used.
Is charged into the lowest temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. 1, while the high-temperature side is filled with 150 g of HoCu ₂ regenerative material. The high-temperature side was filled with 200 g of Pb cold storage material to assemble the refrigerator according to Example 17, and performed a refrigeration test at an operating frequency of 1 Hz, and measured the refrigeration capacity at 4.2K.

As a result of the refrigerating test, 0.79 W was obtained as the initial value of the refrigerating capacity at 4.2 K. Also, 2
The refrigerating capacity after continuous operation for 40 hours was 0.78 W, and stable refrigerating performance was confirmed. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed, but no generation of broken particles or fine powder was observed.

[0220]Example 18 A sodium (Na) content of 2.1% by mass;
Fe with an average particle size of 1 μm ₂O₃Powder and SiO₂Powder and Gd
₂O₃Compounded with powder in a molar ratio of 4: 2: 5
4 hours using a ball mill in ethyl alcohol
The mixture was pulverized to prepare a raw material mixture. Raw materials obtained next
After the mixture is dried, it is temporarily sintered at a temperature of 1400 ° C. for 3 hours.
By doing so, GdFe as an oxide sintered body_0.8
Si_0.2O₃Was synthesized.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 6 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, the obtained granulated particles are supplied to a thermal plasma apparatus shown in FIG. 3, where they are melted and rapidly solidified into a sphere to form GdFe _0.8
Spherical particles having a composition of Si _0.2 O ₃ were obtained. Further, the spherical particles were heat-treated in the atmosphere at a temperature of 1700 ° C. for 2 hours to produce a regenerator material according to Example 18 composed of substantially spherical magnetic particles.

The content of the impurity Na contained in the obtained regenerator particles having the composition of GdFe _0.8 Si _0.2 O ₃ was analyzed by ICP method and found to be 2.1% by mass. The average value of the equivalent circular diameter of the crystal grains is 5.9 μm
Met.

Example 18 prepared as described above
Is charged into the lowest temperature side of the second stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. 1 in the same manner as in the eleventh embodiment, and 150 g of HoCu ₂ regenerative is stored on the high temperature side. The refrigerator was charged with 200 g of Pb cold storage material on the high-temperature side, and the refrigerator according to Example 18 was assembled. A refrigeration test was performed in the same manner as in Example 17, and the refrigeration capacity at 4.2 K was measured. did.

As a result of the freezing test, 0.77 W was obtained as the initial value of the freezing capacity at 4.2K. Also, 2
The refrigeration capacity after continuous operation for 40 hours was 0.63 W, and stable refrigeration performance was confirmed. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed, but no generation of broken particles or fine powder was observed.

Next, the above general formula: Gd _1-x R _x A _1-y
Examples of cold accumulating material having a B _y O ₃ having a composition will be described.

Example 19 Al ₂ O ₃ powder having an average particle diameter of 3 μm, Tb ₂ O ₃ powder and G
d ₂ O ₃ powder and the desired composition: Gd _0.9 Tb
_0.1 AlO ₃ was mixed and pulverized in ethyl alcohol using a ball mill for 24 hours to prepare a raw material mixture. Next, after drying the obtained raw material mixture, it was temporarily sintered at a temperature of 1500 ° C. for 6 hours to synthesize an oxide sintered body.

Next, the obtained sintered body was further pulverized in ethyl alcohol using a ball mill for 6 hours. After the pulverized powder was dried, it was granulated using a tumbling granulator to prepare granulated particles having a particle size of 0.1 to 0.4 mm. Further, the obtained granulated particles were fed into a plasma flame generated in the thermal plasma device shown in FIG. 3 allowed melted, by further rapid solidification remains spherical state consists substantially spherical magnetic particles, Gd ₀ Spherical particles having a composition of _0.9 Tb _0.1 AlO ₃ were prepared. Further, the spherical particles were subjected to a heat treatment at 1700 ° C. for 2 hours in the air to produce a cold storage material according to Example 19.

When the specific heat of the obtained composition of Gd _0.9 Tb _0.1 AlO _{3 at} an extremely low temperature was measured by an adiabatic method, the specific heat at 4.5 K was 0.32 J / Kcm ³ . In addition, 200 particles were randomly extracted from the spherical regenerator particles, and the surface state was observed with a scanning electron microscope (SEM). As a result, particles having two or more cracks with a length of 10 μm or more were found on the particle surface. There are 5 of them, and their presence ratio is 2.5%
Met. The average value of the equivalent circular diameter of the crystal grains is 5.9.
μm.

Example 19 prepared as described above
1 is filled in the lowest temperature side of the second-stage regenerator of the two-stage expansion type GM refrigerator 10 shown in FIG. 1, while 100 g of HoCu ₂ is filled in the high-temperature side thereof. Example 12 was filled with 150 g of Pb cold storage material on the side.
And a refrigeration test was performed at an operation frequency of 1 Hz, and the refrigeration capacity at 4.2K was measured.

As a result of the freezing test, 0.79 W was obtained as the initial value of the freezing capacity at 4.2K. Also, 2
The refrigerating capacity after continuous operation for 40 hours was 0.77 W, and stable refrigerating performance was confirmed. Further, after the operation was completed, the regenerator material was taken out of the regenerator and the appearance was observed, but no generation of broken particles or fine powder was observed.

Example 20 On the other hand, a regenerator material according to Example 20 was prepared by treating under the same conditions as in Example 19 except that the raw material powder was blended so that the composition of the magnetic particles was GdAlO ₃ . The obtained regenerator material was filled in a regenerator of a refrigerator as in Example 19, and a refrigerating test was performed. As a result, the initial value of the refrigerating capacity at 4.2 K was 0.53 W.

Examples 21 to 41 Each of Examples 21 to 41 was treated under the same conditions as in Example 19 except that the metal oxide powder was finally blended to have the composition shown in the left column of Table 1. Such a cold storage material was prepared. For each of the obtained regenerator materials, the specific heat in an extremely low temperature range was measured by an adiabatic method, and the results shown in Table 1 were obtained. The equivalent circular diameter of the crystal grains of the magnetic particles was in the range of 5.0 to 6.3.

Further, 80 g of the cold storage material according to each of the examples was dispensed, filled in the second-stage regenerator of the GM refrigerator in the same manner as in Example 19, and a freezing test was carried out. The initial values of the performance were measured to obtain the results shown in Table 1 below. Table 1 also shows the data of Example 20.

[0234]

[Table 1]

As is clear from the results shown in Table 1 above,
It was found that each of the refrigerators using the regenerator material according to each of the examples prepared by adjusting the composition of the magnetic particles appropriately by the thermal plasma method has a large specific heat in a low temperature region and can exhibit excellent refrigeration ability. The composition of the cold storage material according to Example 29 satisfies the general formula represented by the above formula (4), but has a low specific heat at 4.5 K and is higher due to the combination with the cold storage material having other specific heat characteristics. Refrigeration capacity may be realized. On the other hand, the cold storage material according to Example 30 is out of the composition range of the general formula represented by the formula (4),
High specific heat at 4.5K. On the other hand, the cold storage material according to Example 20 had a low low-temperature specific heat and an insufficient refrigerating capacity.

In each of the embodiments described above, examples are shown in which the cold storage material according to the present invention is applied to a GM refrigerator. However, the cold storage material according to the present invention is applied to a pulse tube refrigerator 70 as shown in FIG. Is also applicable.

FIG. 2 shows the basic structure of a single-stage pulse tube refrigerator. The greatest structural feature of the pulse tube refrigerator 70 is that it does not include a reciprocating piston for generating cold, which is essential in the GM refrigerator described above.
Therefore, it has advantages of excellent mechanical reliability and low vibration, and is particularly expected as a refrigerator for cooling elements and sensors.

The pulse tube refrigerator 70 is a kind of regenerative refrigerator, and helium gas is generally used as a refrigerant gas. As a basic configuration, the refrigerator includes, in addition to the regenerator 1, a pressure vibration source 71 for compressing helium gas, and a phase adjusting mechanism 72 for controlling a time difference between pressure fluctuation and position fluctuation (displacement) of the refrigerant gas.

In a GM refrigerator or a Stirling refrigerator, the phase adjusting mechanism 72 is a reciprocating piston mechanism disposed in a low temperature section, whereas in the pulse tube refrigerator 70, it is disposed in a room temperature section. The low-temperature end of the regenerator 1 and the phase adjusting mechanism 72 at the room temperature are connected by a pipe called a pulse tube, and the phase of the pressure wave of the refrigerant gas is remotely controlled. Then, the entropy transfer between the refrigerant gas and the cold storage material due to the pressure fluctuation proceeds at an appropriate timing with the displacement, so that the entropy is sequentially pumped in one direction, and the cold heat of the cold storage unit 1 is cooled at a lower temperature. Is obtained.

Next, an embodiment of a superconducting MRI apparatus using a regenerative refrigerator according to the present invention, a superconducting magnet for a magnetic levitation train, a cryopump, and a magnetic field applying type single crystal pulling apparatus will be described.

FIG. 12 shows a superconducting MRI to which the present invention is applied.
It is sectional drawing which shows the schematic structure of an apparatus. The superconducting MRI apparatus 30 shown in FIG. 12 includes a superconducting static magnetic field coil 31 for applying a spatially uniform and temporally stable static magnetic field to a human body,
A correction coil (not shown) for correcting non-uniformity of the generated magnetic field, a gradient magnetic field coil 32 for applying a magnetic field gradient to the measurement area,
And a radio wave transmitting / receiving probe 33 and the like. The regenerative refrigerator 34 according to the present invention as described above is used for cooling the superconducting static magnetic field coil 31. In the figure, 35 is a cryostat, 3
Reference numeral 6 denotes a radiation insulation shield.

In the superconducting MRI apparatus 30 using the regenerative refrigerator 34 according to the present invention, the superconducting static magnetic field coil 3
Since the operating temperature can be stably guaranteed for a long period of time, a spatially uniform and temporally stable static magnetic field can be obtained for a long period of time. Therefore, the superconducting MR
The performance of the I device 30 can be stably exhibited over a long period of time.

FIG. 13 is a perspective view showing a schematic configuration of a main part of a superconducting magnet for a magnetic levitation train using a regenerative refrigerator according to the present invention, and shows a portion of a superconducting magnet 40 for a magnetic levitation train. The superconducting magnet 40 for a magnetic levitation train shown in FIG. 13 includes a superconducting coil 41, a liquid helium tank 42 for cooling the superconducting coil 41, a liquid nitrogen tank 43 for preventing the liquid helium tank from volatilizing, and a regenerative storage system according to the present invention. It is constituted by a refrigerator 44 and the like. In the figure, 45 is a laminated heat insulating material, 46 is a power lead, and 47 is a permanent current switch.

In the superconducting magnet 40 for a magnetic levitation train using the regenerative refrigerator 44 according to the present invention, the operating temperature of the superconducting coil 41 can be assured stably for a long period of time. And the magnetic field required for propulsion can be stably obtained over a long period of time. In particular, although the acceleration acts on the superconducting magnet 40 for the magnetic levitation train, the regenerative refrigerator 44 according to the present invention can maintain excellent refrigeration capacity for a long period of time even when the acceleration acts, so that the magnetic field strength etc. Will greatly contribute to long-term stabilization. Therefore, the magnetic levitation train using such a superconducting magnet 40 can exhibit its reliability over a long period of time.

FIG. 14 is a sectional view showing a schematic configuration of a cryopump using a regenerative refrigerator according to the present invention.
A cryopump 50 shown in FIG. 14 includes a cryopanel 51 for condensing or adsorbing gas molecules, a regenerative refrigerator 52 according to the present invention for cooling the cryopanel 51 to a predetermined cryogenic temperature, and a shield provided therebetween. 53, a baffle 54 provided at the intake port, and a ring 55 for changing the exhaust speed of argon, nitrogen, hydrogen and the like.

In the cryopump 50 using the regenerative refrigerator 52 according to the present invention, the operating temperature of the cryopanel 51 can be stably guaranteed over a long period of time.
Therefore, the performance of the cryopump 50 can be stably exhibited over a long period of time.

FIG. 15 is a perspective view showing a schematic configuration of a magnetic field application type single crystal pulling apparatus using a regenerative refrigerator according to the present invention. A magnetic field applying type single crystal pulling apparatus 60 shown in FIG. 15 includes a material melting crucible, a heater, a single crystal pulling section 61 having a single crystal pulling mechanism, a superconducting coil 62 for applying a static magnetic field to the raw material melt, and The single crystal pulling unit 61 includes a lifting mechanism 63 and the like. And
The regenerative refrigerator 64 according to the present invention as described above is used for cooling the superconducting coil 62. In the figure, 65 is a current lead, 66 is a heat shield plate, and 67 is a helium container.

In the magnetic field application type single crystal pulling apparatus 60 using the regenerative refrigerator 64 according to the present invention, the operating temperature of the superconducting coil 62 can be stably ensured over a long period of time. A good magnetic field for suppressing the convection of the raw material melt can be obtained over a long period of time. Therefore,
The performance of the magnetic field application type single crystal pulling apparatus 60 can be stably exhibited over a long period of time.

[0249]

As described above, according to the regenerator material according to the present invention, the equivalent circular diameter of the crystal grains of the magnetic particles, the density, the amount of additives, the amount of impurities, and the amount of defects such as cracks and voids are determined as necessary. Since it is defined in the predetermined range, the mechanical strength and the thermal conductivity are high, the thermal shock resistance is excellent, and the possibility of pulverization is small. Therefore, even when used as a cold storage material for a refrigerator operating at a high speed such as a Stirling refrigerator or a pulse tube refrigerator, a cold storage material having a small pressure loss and exhibiting stable refrigeration characteristics over a long period of time can be obtained. And
By using the cold storage material as at least a part of the cold storage material of the refrigerator, it is possible to provide a refrigerator having a high refrigerating capacity and capable of maintaining stable refrigerating performance for a long period of time.

In the MRI apparatus, cryopump, superconducting magnet for magnetic levitation train, and magnetic field applying type single crystal pulling apparatus, the performance of each apparatus affects the performance of each apparatus. Of the present invention using
The RI device, the cryopump, the superconducting magnet for the magnetic levitation train, and the magnetic field application type single crystal pulling device can all exhibit excellent performance over a long period of time.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a main configuration of a regenerative refrigerator (GM refrigerator).

FIG. 2 is a diagram schematically showing an element configuration and a temperature distribution of the pulse tube refrigerator.

FIG. 3 is a diagram showing a configuration of a thermal plasma device.

FIG. 4 is an electron micrograph showing the surface structure of cold storage material particles formed by the tumbling granulation method.

FIG. 5 is an electron micrograph showing a central portion of the cold storage material particles shown in FIG. 4 in an enlarged manner.

FIG. 6 is an electron micrograph showing a cross-sectional structure of cold storage material particles formed by the tumbling granulation method.

FIG. 7 is an electron micrograph showing an enlarged end portion of the cold storage material particles shown in FIG.

FIG. 8 is an electron micrograph showing the surface structure of cold storage material particles formed by the plasma sphering method.

FIG. 9 is an electron micrograph showing a central portion of the cold storage material particles shown in FIG. 8 in an enlarged manner.

FIG. 10 is an electron micrograph showing a cross-sectional structure of cold storage material particles formed by a plasma sphering method.

11 is an electron micrograph showing an enlarged end portion of the cold storage material particle shown in FIG.

FIG. 12 is a sectional view showing a schematic configuration of a superconducting MRI apparatus according to one embodiment of the present invention.

FIG. 13 is a perspective view showing a schematic configuration of a main part of a superconducting magnet (for a magnetic levitation train) according to an embodiment of the present invention.

FIG. 14 is a sectional view showing a schematic configuration of a cryopump according to one embodiment of the present invention.

FIG. 15 is a perspective view showing a schematic configuration of a main part of a magnetic field application type single crystal pulling apparatus according to an embodiment of the present invention.

FIG. 16 is an explanatory view showing a method for measuring an equivalent circular diameter of a crystal grain of a cold storage material.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 regenerator 2 regenerator crystal grains 10 GM refrigerator (regenerator) 11 first cylinder 12 second cylinder 13 vacuum vessel 14 first regenerator 15 second regenerator 16 and 17 seal ring 18 first heat storage material 19 Second heat storage material (cryogenic material for cryogenic temperature) 20 First expansion chamber 21 Second expansion chamber 22 First cooling stage 23 Second cooling stage 24 Compressor 30 Superconducting MRI apparatus 31 Superconducting static magnetic field coil 32 Gradient magnetic field coil 33 Radio wave transmission / reception Probe 34 regenerative refrigerator 35 cryostat 36 radiation insulating shield 40 superconducting magnet (magnet) 41 superconducting coil 42 liquid helium tank 43 liquid nitrogen tank 44 regenerative refrigerator 45 laminated heat insulating material 46 power lead 47 permanent current switch 50 cryopump 51 Cryopanel 52 Cool storage refrigerator 53 Shield 54 Baffle 55 Ring 60 Magnetic field application type single crystal pulling device 61 Single crystal pulling unit 62 Superconducting coil 63 Elevating mechanism 64 Cold storage refrigerator 65 Current lead 66 Heat shield plate 67 Helium container 70 Pulse tube refrigerator 71 Pressure vibration source 72 phase adjusting mechanism 80 thermal plasma device 81 reaction vessel 82 high frequency oscillator 83 coil 84 plasma generating unit outer case 85 plasma frame 86 powder supply port 87 powder supply device 88 carrier gas supply cylinder 89 plasma generation gas source 90 cyclone 91 Cooling gas source

────────────────────────────────────────────────── ─── of the front page continued (51) Int.Cl. ⁷ identification mark FI theme Court Bu (reference) H01F 1/11 C09K 5/00 F F term (reference) 4G002 AA06 AA12 AB01 AD04 AE02 AE05 4G072 AA35 BB05 BB07 GG01 GG03 HH14 JJ26 MM01 MM37 RR13 TT01 UU30 4G076 AA02 AA18 AB02 BA38 CA02 CA03 CA26 DA30 5E040 AA03 BD01 CA01 HB03 HB05 HB17 NN01 NN06

Claims (24)

[Claims] 1. A cold storage material comprising a large number of magnetic particles mainly composed of an oxide, wherein the average value of equivalent circular diameters of crystal grains constituting the magnetic particles is 0.3 to 20 μm. 2. The cold storage material according to claim 1, wherein an area ratio of crystal grains having an equivalent circular diameter of 50 μm or more to all crystal grains constituting the magnetic particles is 10% or less. 3. The regenerative material according to claim 1, wherein said magnetic particles are made of a sintered body of granulated particles, and the sintered density thereof is 86 to 99.8%. 4. The magnetic particle according to claim 1, wherein at least one of Y, Mg, Al, Ca and a rare earth element different from the constituent elements is contained in an amount of 0.5 to 15% by weight in terms of oxide. Item 8. The cold storage material according to Item 1. 5. The ratio of magnetic particles having two or more cracks having a length of 10 μm or more on the surface of the magnetic particles to 20% or less of all magnetic particles.
Cold storage material as described. 6. A magnetic particle having a maximum surface roughness of 1
2. The cold storage material according to claim 1, wherein the ratio of the magnetic particles having a diameter of 0 μm or more to all the magnetic particles is 30% or less. 7. The regenerative material according to claim 1, wherein the ratio of the magnetic particles having voids having a maximum width of 20 μm or more inside the magnetic particles to all the magnetic particles is 40% or less. 8. The cold storage material according to claim 1, wherein said magnetic particles contain silicon, sodium and iron in a total amount of 3 ppm to 2% by mass. 9. The method according to claim 1, wherein the magnetic particles have a general formula: Gd _1-x R _x
A _{1-y ByO 3} (where R is Ce, Pr, Nd, S
m represents at least one rare earth element selected from the group consisting of Tb, Dy, Ho and Er, and A represents Ti, V, Cr, M
n, Fe, Co, Ni, Cu, Zn, Ga, Ge, A
represents an element selected from 1, Si, x = 0 and y = 0
In the case of at least two elements are selected, while x
When ≠ 0 or y ≠ 0, at least one element is selected, and B is Zr, Nb, Mo, Ag, In, Sn, S
b represents at least one element selected from Hf, Ta, W, Au, and Bi, and x is 0 ≦ x ≦ 0.4 in atomic ratio;
y satisfies 0 ≦ y ≦ 0.4 in atomic ratio. 2. The regenerative material according to claim 1, comprising oxide magnetic particles represented by the following formula: 10. The characteristic that the magnetic particles have a specific heat of 0.3 J / Kcm ³ or more in a temperature range of 4.0 to 5.0K,
Specific heat in the temperature range of 4.5 to 5.5 K is 0.35 J / Kc
The oxide magnetic particles have at least one of a characteristic of m ³ or more and a characteristic of a specific heat of 0.4 J / Kcm ³ or more in a temperature range of 5.5 to 6.0 K. Item 8. The cold storage material according to Item 1. 11. An oxide powder is granulated to form granulated particles, and the obtained granulated particles are subjected to a pressure treatment to prepare spherical densified particles. A method for producing a cold storage material, comprising preparing a cold storage material composed of a large number of magnetic particles by sintering. 12. The pressure treatment of the granulated particles is a cold isostatic pressure (CIP) pressure treatment.
A method for producing the cold storage material according to the above. 13. The method according to claim 13, wherein the sintering process is performed using hot isostatic pressure (HIP).
The method for producing a cold storage material according to claim 11, wherein the method is a pressure treatment. 14. A method according to claim 14, wherein the binder is a binder for the oxide powder.
The method for producing a regenerative material according to claim 11, wherein the granulation is performed by adding up to 30% by weight. 15. A regenerative material comprising a large number of magnetic particles is prepared by passing an oxide powder through a thermal plasma to melt it and solidifying it in a spheroidized state by the surface tension of the melt. Manufacturing method of cold storage material. 16. The method for producing a regenerative material according to claim 15, wherein the magnetic particles which have been made spherical by passing through thermal plasma are further heat-treated at a temperature of 500 ° C. or higher. 17. The method according to claim 16, wherein the heat treatment temperature is 1200 to 1700 ° C. 18. A refrigerator for obtaining a lower temperature downstream of a regenerator by flowing a refrigerant gas from a high temperature side upstream of the regenerator and exchanging heat between the refrigerant gas and a regenerator material filled in the regenerator. 11. A refrigerator comprising at least a part of the regenerator filled in the regenerator is the regenerator according to any one of claims 1 to 10. 19. A refrigerator for obtaining a lower temperature downstream of a regenerator by flowing a refrigerant gas from a high temperature side upstream of the regenerator and exchanging heat between the refrigerant gas and a regenerator material filled in the regenerator. A refrigerating machine characterized in that a high-temperature side of the regenerator is filled with a non-oxide regenerator material, while a low-temperature side of the regenerator is filled with the regenerator material according to any one of claims 1 to 10. 20. The non-oxide regenerative material is P
b, refrigerating machine according to claim 19, wherein the at least one HoCu _{2 and} Er ₃ Ni. 21. A superconducting magnet comprising the refrigerator according to claim 18. 22. An MRI (nuclear magnetic resonance imaging) apparatus comprising the refrigerator according to claim 18. 23. A cryopump comprising the refrigerator according to claim 18. 24. A magnetic field applying type single crystal pulling apparatus comprising the refrigerator according to claim 18.