JP2010077447A - Cold accumulating material and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cold accumulating material having a high strength, being nearly free from the risk of being pulverized into fine particles, being excellent in thermal shock resistance and durability, and exhibiting a significant refrigerating performance at a low-temperature region, and a method for manufacturing the same. <P>SOLUTION: The cold accumulating material comprises a number of magnetic particles with diameters of 0.01-3 mm, wherein the magnetic particles include rare earth elements, and each magnetic particle has ≥0.7 of the circularity factor R defined by 4πA/L<SP>2</SP>where A is the area of a projection image of each magnetic particle on a plane and L is the peripheral length of the projection image and the standard deviation of the circularity factors R is ≤0.1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a regenerator material and a method for producing the regenerator material, and more particularly to a regenerator material that is less likely to be pulverized, has excellent mechanical strength and durability, and can exhibit a remarkable refrigerating ability in a low temperature range, and a method for producing the regenerator material.

  In recent years, the development of superconducting technology has been remarkable, and the development of compact and high-performance refrigerators has become indispensable as the field of application expands. 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 a superconducting MRI apparatus, a cryopump, and the like, a refrigerator using a refrigeration cycle such as a Gifford McMahon (GM) system, a Stirling system, or a pulse tube refrigerator is used. Further, a high-performance refrigerator is indispensable in order to generate a magnetic force using a superconducting magnet in a magnetic levitation train. Furthermore, recently, high-performance refrigerators are also used in superconducting power storage devices (SMES) and single-crystal pulling devices in a magnetic field for producing high-quality silicon wafers. The development and commercialization of pulse tube refrigerators that are expected to have higher reliability are also being actively promoted.

  In such a refrigerator, a working medium such as compressed He gas flows in one direction in the regenerator filled with the regenerator material, supplies the heat energy to the regenerator material, and the operation expanded here. The medium flows in the opposite direction and receives heat 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, etc. have been mainly used as the regenerator material used in the refrigerator as described above. However, such a regenerator material has a remarkably small specific heat at an extremely low temperature of 20K or less, so that the above-described recuperation effect does not function sufficiently, and the regenerator material is operated every cycle at a very low temperature when operating in a refrigerator. Sufficient heat energy cannot be stored, and the working medium cannot receive sufficient heat energy from the cold storage material. As a result, there has been a problem that a refrigerator incorporating a regenerator filled with the regenerator material cannot reach an extremely low temperature.

Therefore, recently, in order to improve the recuperation characteristics at the cryogenic temperature of the regenerator and realize a refrigeration temperature closer to absolute zero, it has a maximum volume specific heat particularly in an extremely low temperature region of 20K or less, and Magnetic regenerators mainly composed of intermetallic compounds composed of rare earth elements and transition metal elements such as Er ₃ Ni, ErNi, and HoCu ₂ having large values are used. By using such a magnetic regenerator material for a GM refrigerator, refrigeration at 4K is realized.

  As the above-mentioned refrigerators are actually applied to various cooling systems, it is necessary to stably cool larger-scale objects to be cooled. Improvement is demanded.

International Publication No. 96/06315 JP-A-8-226718 JP 2000-199650 A

  However, in refrigerators that operate at high speed, such as Stirling refrigerators and pulse tube refrigerators, the pressure loss in the regenerator filled with magnetic regenerator particles increases, and sufficient refrigeration capacity cannot be realized. It was. In GM refrigerators, etc., the magnetic particles are damaged or pulverized by the pressure vibration of the high-pressure helium gas that acts during operation of the refrigerator, various stresses, and impact force, and the ventilation resistance of the refrigerant gas is increased. There is a problem that defects such as abrupt decrease are likely to occur.

  In particular, in the case of a GM refrigerator, the stress due to the reciprocating motion of the displacer (refrigerant compression piston) acts on the cold storage material, and the influence is great. In addition, when the refrigerator is started, the temperature drops in a short time from near room temperature to a cryogenic temperature near 4K, so a large thermal shock acts on the cold storage material.

  However, in general, magnetic particles exhibit brittleness, mechanical strength is not sufficient, and they are also vulnerable to thermal shock, so the regenerator material breaks down during operation of the refrigerator, or a part of the regenerator material surface peels off. Then, fine powder is generated. This fine powder damages the seal part of the refrigerator, and as a result, there is a problem that the capacity of the refrigerator is significantly reduced in a short operation.

  The present invention has been made to solve the above-mentioned problems, and has particularly high strength, low risk of pulverization, excellent thermal shock resistance and durability, and a remarkable refrigeration capacity in a low temperature range for a long time. It aims at providing the cool storage material which can be exhibited over a long time, and its manufacturing method.

In order to achieve the above object, a regenerator material according to the present invention is a regenerator material composed of a large number of magnetic particles having a diameter of 0.01 to 3 mm, wherein the magnetic particles contain a rare earth element, and each magnetic particle The average value of the circularity coefficient R defined by 4πA / L ² is 0.7 or more when the area of the projected image on the plane of A is A and the peripheral length of the projected image is L, The standard deviation of the circularity coefficient R is 0.1 or less.

  In the cold storage material, the magnetic particles preferably include a rare earth element.

  Further, the refrigerator to which the present invention is applied has a lower temperature on the downstream side of the regenerator by heat exchange between the refrigerant gas and the regenerator material filled in the regenerator by flowing the refrigerant gas from the upstream high temperature side of the regenerator. In the refrigerator for obtaining the above, at least a part of the regenerator material filled in the regenerator is the regenerator material of the present invention.

  Furthermore, an MRI (Magnetic Resonance Imaging) device to which the present invention is applied, a superconducting magnet for a magnetic levitation train, a cryopump, and a magnetic field application type single crystal pulling device each include the above-described refrigerator according to the present invention. It is said.

The composition of the cold storage material according to the present invention is not particularly limited, but it is preferable that at least a part of the particulate cold storage material contains a rare earth element. Specifically, the particulate regenerator material is
General formula RMz (1)
(However, R is at least one rare earth element selected from Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, and M is Ni. , Co, Cu, Ag, Al, Ru, In, Ga, Ge, Si, and Rh, and z is an atomic ratio satisfying 0 ≦ z ≦ 9.0.) It is preferable to comprise a rare earth element represented by the formula or an intermetallic compound containing a rare earth element. Of the cold storage materials, HoCu ₂ is particularly preferable.

  The regenerator material according to the present invention may be 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 20K or less. As the oxide constituting the magnetic particles, for example, compositions represented by the following general formulas (2), (3), and (4) can be preferably used.

That is, the general formula: RMO ₃ (2)
(However, R is at least one rare earth element selected from Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, and M is A perovskite-based oxide represented by at least one element selected from Group 3B elements;
General formula: AB ₂ O ₄ (3)
(Wherein A is at least one element selected from Group 2B elements, and B is a transition metal element containing at least Cr); and a general formula: CD ₂ O ₆ ...... (4)
An oxide or the like represented by (wherein C is at least one element selected from Mn and Ni, and D is at least one element selected from Nb and Ta) is preferably used.

  The regenerator material composed of these rare earth element-based magnetic particles has a maximum specific heat of 20K or less, and the value is sufficiently large as the specific heat per unit volume (volume specific heat), so it can reach a much lower temperature. Therefore, the cold storage material is suitable for the present invention.

The average value of the circularity coefficient R of the magnetic particles constituting the cold storage material according to the present invention is set to a range of 0.7 or more. Here, the circularity coefficient R is defined as a value given by 4πA / L ² where A is the area of the projected image of the magnetic particles on the plane and L is the peripheral length of the projected image.

The circularity coefficient R (= 4πA / L ² ) is a coefficient representing the degree of roundness of the magnetic particles. The closer the coefficient value is to 1, the closer the particle cross-sectional shape is to a perfect circle, and the particle shape is completely In the case of a sphere, the value is 1. However, when a fine protrusion is formed on the surface of a substantially spherical magnetic particle, a certain degree of circularity coefficient R can be obtained, but the vibration and impact force that the protrusion acts during operation of the refrigerator. There is still a high possibility that the seal part of the refrigerator is damaged by acting like the pulverized powder of magnetic particles.

  The presence or absence of the protrusion is measured as the degree of variation in the circularity coefficient R. Therefore, in the regenerator material according to the present invention, in order to prevent pulverization and increase the mechanical strength and durability, the average value of the circularity coefficient R of a large number of magnetic particles constituting the regenerator material is set to a predetermined value (0.7 ) And the standard deviation of the circularity coefficient R is specified to be 0.1 or less. The standard deviation of the circularity coefficient R is a value indicating variation in the degree of roundness of the magnetic particles, and the smaller the standard deviation, the more uniform the magnetic particle group is.

  And the structure as a regenerator when the projected image shape on the plane of each magnetic particle is close to a perfect circle, and there are few protrusions and recesses that are the starting point of destruction and the standard deviation is small. The strength is increased, and the durability as an aggregate of magnetic particles in a state where the regenerator is filled is also increased.

  When the average value of the circularity coefficient R is less than 0.7, the shape of the magnetic particles constituting the regenerator material is irregularly separated from the true spherical state. For this reason, the contact area between the magnetic particles is not constant, it becomes difficult to uniformly fill the regenerator with a high packing density, and the contact efficiency with the refrigerant gas also becomes uneven, so that the efficiency of cold heat exchange is reduced. In addition, the capacity as a refrigerator is reduced. Therefore, the average value of the circularity coefficient R is defined as 0.7 or more, more preferably 0.8 or more, and further preferably 0.9 or more.

  In addition, the ratio of the magnetic particles having a circularity coefficient R of 0.7 or more to the total magnetic particles constituting the cold storage material is preferably 70% by mass or more. Furthermore, 80 mass% or more is more preferable, and 90 mass% or more is desirable.

  In addition, the magnetic particles in which the variation in the circularity coefficient R is large so that the standard deviation σ of the circularity coefficient R of the magnetic particles constituting the cold storage material exceeds 0.1 are formed with protrusions or the like that are the starting points of fracture. Is. When such a magnetic particle is filled in a regenerator, a tendency to form a bridge (crosslinked structure) in a spherical magnetic particle is high, and in an aggregate including such a bridged magnetic particle, breakage occurs at the bridge portion. Is likely to occur, and the reliability as a cold storage material is reduced. For this reason, the standard deviation of the circularity coefficient R is defined to be 0.1 or less. However, in order to ensure durability and strength as a cold storage material, the standard deviation is more preferably 0.06 or less, and further 0 0.03 or less is more preferable.

  The circularity coefficient R of the magnetic particles and the standard deviation σ thereof are obtained by photographing a projected image with an optical microscope in a state where about 100 randomly selected magnetic particles are placed on a flat plate. Can be measured quickly by image processing. As an image processing apparatus for performing the image processing, for example, an image processing apparatus manufactured by Pierce (model number: PIAS-III) can be preferably used.

  In addition, since the particle size of the magnetic particles constituting the cold storage material has a great influence on the heat transfer characteristics and the like, in the present invention, 70% by weight or more of the whole particle has a particle size of 0.01 to 3 mm. It is preferable to comprise cold storage material particles. Here, the particle diameter referred to in the present invention means the diameter of the smallest sphere that can enclose the particles. If the particle size of the regenerator material particles is less than 0.01 mm, the packing density becomes too high, which may cause an increase in pressure loss. If the particle size exceeds 3.0 mm, the heat transfer area is small. Therefore, the heat transfer efficiency is likely to be lowered. Therefore, when such particles exceed 30% by weight of the whole granules, there is a risk of causing a decrease in cold storage performance. A more preferable particle size is in the range of 0.03 to 1.0 mm. More preferably, it is the range of 0.05-5 mm. The ratio of the particles having a particle size in the range of 0.01 to 3.0 mm in the whole particle is more preferably 80% by weight or more, and still more preferably 90% by weight or more.

  Also, in the regenerator material of the present invention comprising a large number of magnetic particles, the mass 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 20% or less. Is preferred.

  If there are a plurality of cracks on the surface of the magnetic particles constituting the cold storage material, the cracks are likely to develop due to vibrations or impact forces acting during the operation of the refrigerator, and the possibility that the particles are destroyed increases. Specifically, when the abundance ratio (number ratio) of magnetic particles in which two or more cracks having a length of 10 μm or more are present on the surface of the magnetic particles exceeds 20%, the fracture ratio of the particles increases. As a result, the generated fine powder damages the seal part of the refrigerator, and the performance of the refrigerator is significantly reduced.

  Accordingly, the abundance ratio of particles having two or more cracks having a length of 10 μm or more 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.

  In the regenerator material composed of a large number of magnetic particles, it is preferable that the mass ratio of the magnetic particles having a maximum surface roughness of the magnetic particles of 10 μm or more to the total magnetic particles is defined as 30% or less.

  When the surface roughness of the magnetic particles is large, stress concentration is likely to occur at the portions where the protrusions and steps are formed, and the particles are destroyed starting from the stress concentration portions. In order to prevent this phenomenon, it is preferable to regulate the ratio of magnetic particles having a maximum height indicating the degree of surface roughness of 10 μm or more to 30% or less. The proportion of particles having the maximum height of 10 μm or more is preferably 20% or less, and more preferably 10% or less. Further, 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 Standard (JIS-B0601) from a cross-sectional curve of the surface texture obtained by photographing the surface texture with observation means such as an electron microscope.

  The method for producing the regenerator material according to the present invention is not particularly limited, and a rotating disk method, a rotating electrode method, a gas atomizing method, a water atomizing method, a twin roll method, which are conventionally used when preparing metal powders, It can be produced by a melt rapid solidification method such as a single roll method. In addition, according to the molten metal rapid solidification method, magnetic particles having a relatively high degree of circularity (sphericity) can be obtained. However, depending on manufacturing conditions, magnetic particles having a large variation (standard deviation) in the circularity factor R are formed. It is easy to be done. In this case, shape selection is performed on the magnetic particles obtained as appropriate, and a particle group having a circularity coefficient R and a standard deviation only within a predetermined range is selected as the cold storage material according to the present invention.

Specifically, the step of preparing magnetic particles by the centrifugal spray quenching method, the shape of the obtained magnetic particles are selected by an inclined belt conveyor, and the area of the projected image of each magnetic particle on the plane is A When the perimeter of the projected image is L, the average value of the circularity coefficient R defined by 4πA / L ² is 0.7 or more, and the standard deviation of the circularity coefficient R is 0.1 or less. And a step of selecting the shape of certain magnetic particles.

In addition, another method for producing a regenerator material according to the present invention includes a step of preparing magnetic particles by sintering rolling granulated particles, and shape selection of the obtained magnetic particles by an inclined belt conveyor. Then, when the area of the projected image of each magnetic particle on the plane is A, and the perimeter of the projected image is L, the average value of the circularity coefficient R defined by 4πA / L ² is 0. And a step of selecting the shape of magnetic particles having a standard deviation of the circularity coefficient R of 0.1 or less.

Furthermore, another method for producing a regenerator material according to the present invention includes a step of preparing magnetic particles by rapidly solidifying after granulated particles are melted by a thermal plasma apparatus, and forming the obtained magnetic particles by an inclined belt conveyor. When the area of the projected image on the plane of each magnetic particle is A and the perimeter of the projected image is L, the average value of the circularity coefficient R defined by 4πA / L ² is 0. And a step of selecting the shape of magnetic particles whose standard deviation of the circularity coefficient R is 0.1 or less.

  That is, the regenerator material according to the present invention can be manufactured according to the following powder metallurgy method. For example, raw material powder is mixed using a ball mill to prepare a raw material mixture, and the obtained raw material mixture is tumbled granulated, stirred granulated, extruded, sprayed (sprayed), or press molded. After forming into a spherical shape (granulation) by a method or the like, it can be produced by sintering the obtained spherical molded body.

  The raw material powder used in the above production method is desirably a powder having a particle size of 0.3 to 30 μm. A more preferable particle size range is 0.4 to 10 μm, and a particle size range of 0.5 to 8 μm is more preferable.

  Note that particles formed by various granulation methods such as the rolling granulation method, the stirring granulation method, the extrusion method, and the spraying method (spray method) have a low molding density and are excellent when sintered as they are. It may be difficult to tie.

  Therefore, in the present invention, the following manufacturing method can be adopted.

  That is, the raw material powder is granulated to form granulated particles, and the resulting granulated particles are subjected to cold isostatic pressure (CIP) pressure treatment to prepare spherical densified particles, and the obtained dense particles It is also possible to employ a method for manufacturing a regenerator material such as preparing a regenerator material composed of a large number of magnetic particles by sintering the activated particles.

  In the said manufacturing method, you may implement a hot isostatic pressure (HIP) pressurization process as a sintering process. That is, the density of the compact can be further improved by subjecting the granulated particles to cold isostatic pressing (CIP) treatment or hot isostatic pressing (HIP) treatment. Furthermore, by sintering this high-density molded body, magnetic particles with high density and few cracks and voids can be effectively obtained.

  Moreover, in the said manufacturing method, it is possible to raise a shaping | molding density more by granulating by adding 5-30 weight% of binders with respect to oxide powder.

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

  When the amount of the binder added to the 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, when the addition amount is excessive so as to exceed 30% by weight, the ratio of the regenerator material powder in the molded body becomes excessively low, and the molding density decreases. Therefore, the addition amount of the binder is specified in the range of 5 to 30% by weight.

  The added binder is removed by degreasing treatment of the molded body after granulation, and further, the cold storage material according to the present invention is prepared by sintering the degreased molded body.

As a method for preparing spherical magnetic particles, in addition to the method in which the raw material powder is granulated spherically by the rolling granulation method as described above and then sintered, the following thermal plasma is used to spheroidize It is also possible to adopt a method of

  That is, a method for producing a regenerator material that prepares a regenerator material composed of a large number of magnetic particles by melting raw material powder through thermal plasma and solidifying it in a spheroidized state by the surface tension of the melt. Can also be adopted.

  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. This thermal plasma device 80 is a powder that opens to face a reaction vessel 81, a high-frequency transmitter 82, a coil 83, a plasma generation unit outer cylinder 86, and a plasma frame 85 generated at the top of the reaction vessel 81. A body supply port 86, a carrier gas supply cylinder 88 transported to a reaction container 81 stored in a powder supplier 87, a plasma generating gas source 89, a cyclone 90 for separating generated particles, and a reaction container 81 And a cooling gas source 91 for cooling.

  In the thermal plasma device 80, the electromagnetic wave transmitted from the high-frequency transmitter 82 is amplified by the coil 83, while high temperature plasma is generated at the top of the reaction vessel 81 by the discharge of the gas supplied from the plasma generating gas source 89. A frame 85 is formed. The gas temperature of the frame portion 85 reaches several thousand degrees Celsius to about 10,000 degrees Celsius. When the raw material powder supplied from the powder supplier 87 together with the carrier gas is put into the plasma flame 85 in a high temperature state, the whole particle or a part including the surface is melted. The melted raw material powder is spheroidized by its surface tension. Then, it is rapidly 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. In this way, at least part of it is melted and spheroidized and rapidly solidified, so there is no crack on the particle surface, the surface is smooth, the surface roughness is small, and there is no void inside Particles are obtained.

  Even in the case of magnetic particles formed by the powder metallurgy method or the thermal plasma method as described above, depending on the manufacturing conditions, magnetic particles having a large variation (standard deviation) in the circularity coefficient R may be formed. In that case, shape selection may be performed on the obtained magnetic particle group using a shape separation device using an inclined belt conveyor as shown below.

  That is, the shape separation device has a configuration in which a belt conveyor inclined so that the conveyor belt is driven obliquely upward is arranged in a plurality of stages as necessary, and rolls according to the shapes of the spherical object and the deformed object. A spherical object and a deformed object are separated based on the difference in ease. In addition, a vibration device that attaches vibration to a spherical object and a deformed object, which are objects to be processed, in a direction different from the rolling direction is attached. That is, when a magnetic particle group in which spherical objects and irregular shapes are mixed is supplied onto a conveyor belt driven obliquely upward, spherical magnetic particles having a larger circularity coefficient R and easier to roll roll down on the conveyor belt surface. On the other hand, irregularly shaped magnetic particles having a small circularity coefficient R that are difficult to roll are transported upward by frictional force with the transport belt. Even when the circularity coefficient R is large, the magnetic particles having protrusions on the surface are caught upward between the protrusions and the transport belt and are transported upward. As a result, the spherical object and the deformed object are separated on the lower side and the upper side of the conveyor. In particular, the separation accuracy can be changed by appropriately adjusting the inclination angle of the belt conveyor, the number of arrangement stages, the material of the conveyance belt, the conveyance speed, and the like. By carrying out shape selection using the above-described shape sorting device, a group of magnetic particles having the circularity coefficient R defined by the present invention and its standard deviation can be selected as the regenerator material.

  A regenerator type refrigerator to which the present invention is applied is configured by using a regenerator filled with the regenerator material as at least a part of the regenerator material. In addition, while the regenerator filled with the regenerator material according to the present invention is loaded as the regenerator of the predetermined cooling stage, as the other regenerator, another regenerator material having specific heat characteristics according to its temperature distribution is filled. A regenerator may be used in combination.

  According to the regenerator material according to the above configuration, the circularity coefficient and standard deviation of the magnetic particles are defined within a predetermined range, so that the mechanical strength and thermal conductivity are high, the thermal shock resistance is excellent, and the pulverization is performed. There is little fear of it. Therefore, even when used as a regenerator material for a refrigerating machine that performs high-speed operation such as a Stirling refrigerating machine or a pulse tube refrigerating machine, a regenerator material that exhibits low pressure loss and stable refrigerating characteristics over a long period of time can be obtained. And by using the cool storage material as at least a part of the cool storage material of the refrigerator, it is possible to provide a refrigerator having a high refrigeration capacity and capable of maintaining a stable refrigeration performance over a long period of time.

  The MRI apparatus, the cryopump, the superconducting magnet for the magnetic levitation train, and the magnetic field application type single crystal pulling apparatus all use the refrigerator as described above because the refrigerator performance affects the performance of each device. The MRI apparatus, cryopump, magnetic levitation train superconducting magnet, and magnetic field application type single crystal pulling apparatus can all exhibit excellent performance over a long period of time.

  As described above, according to the regenerator material according to the present invention, since the circularity coefficient of the magnetic particles and the standard deviation thereof are defined within a predetermined range, the mechanical strength and thermal conductivity are high, and the thermal shock resistance is high. Excellent and less pulverized. Therefore, even when used as a regenerator material for a refrigerating machine that performs high-speed operation such as a Stirling refrigerating machine or a pulse tube refrigerating machine, a regenerator material that exhibits low pressure loss and stable refrigerating characteristics over a long period of time can be obtained. And by using the cool storage material as at least a part of the cool storage material of the refrigerator, it is possible to provide a refrigerator having a high refrigeration capacity and capable of maintaining a stable refrigeration performance over a long period of time.

  The MRI apparatus, the cryopump, the superconducting magnet for the magnetic levitation train, and the magnetic field application type single crystal pulling apparatus all use the refrigerator as described above because the refrigerator performance affects the performance of each device. The MRI apparatus, cryopump, magnetic levitation train superconducting magnet, and magnetic field application type single crystal pulling apparatus can all exhibit excellent performance over a long period of time.

Sectional drawing which shows the principal part structure of a cool storage type refrigerator (GM refrigerator). The figure which shows typically the element structure and temperature distribution of a pulse tube refrigerator. The figure which shows the structure of a thermal plasma apparatus. Sectional drawing which shows schematic structure of the superconducting MRI apparatus to which the cool storage material by one Example of this invention is applied. The perspective view which shows the principal part schematic structure of the superconducting magnet (for magnetic levitation train) to which the cool storage material by one Example of this invention is applied. Sectional drawing which shows schematic structure of the cryopump to which the cool storage material by one Example of this invention is applied. The perspective view which shows the principal part schematic structure of the magnetic field application type single crystal pulling apparatus to which the cool storage material by one Example of this invention is applied.

  Next, embodiments of the present invention will be specifically described based on the following examples.

[Examples 1 to 5]
A raw material alloy having a composition of HoCu ₂ was melted by a high frequency melting method, and the obtained molten alloy was processed by a centrifugal spray quenching method to prepare spherical magnetic particles. The obtained magnetic particles were sieved by a sieving method to obtain magnetic particles having a particle size range as shown in Table 1.

  Subsequently, the magnetic particles were supplied onto a conveyor belt of a shape separation device in which three inclined belt conveyors as described above were arranged in series. In order to change the circularity coefficient R and the standard deviation of the magnetic particles obtained at this time, the shape sorting of the magnetic particles is performed by adjusting the inclination angle of the belt conveyor and the belt conveying speed of the shape separation device, Cold storage materials according to Examples 1 to 5 made of spherical magnetic particles were produced.

[Example 6]
A cold storage material according to Example 6 was manufactured by processing under the same conditions as in Example 1 except that a raw material alloy having a composition of Er ₃ Ni was used.

[Example 7]
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 diameter of 1.5 μm in ethyl alcohol using a ball mill for 24 hours. Next, after drying the obtained raw material mixture, GdAlO ₃ as an oxide sintered body was synthesized by pre-sintering at a temperature of 1500 ° C. for 12 hours.

  Next, the obtained sintered body was further pulverized in ethyl alcohol for 6 hours using a ball mill. The pulverized powder was dried and then granulated using a rolling 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 12 hours to produce a cold storage material according to Example 7 made of substantially spherical magnetic particles.

[Comparative Example 1]
On the other hand, except that the magnetic particles prepared by the centrifugal spray quenching method were employed as they were without carrying out the shape fractionation treatment, the treatment was performed under the same conditions as in Example 1 to obtain the cold storage material from the magnetic particle group according to Comparative Example 1. Was prepared.

[Comparative Example 2]
Granulated particles having a particle size of 0.1 to 0.4 mm were prepared by granulating HoCu ₂ alloy powder having an average particle size of 10 μm using a rolling granulator. Further, the obtained granulated particles are supplied into a plasma flame generated by the thermal plasma apparatus shown in FIG. 3 and melted, and further rapidly cooled and solidified in a spherical state, so that Comparative Example 2 composed of substantially spherical magnetic particles. The cold storage material which concerns on was manufactured.

[Comparative Example 3]
A cold storage material according to Comparative Example 3 was manufactured by treating HoCu ₂ alloy powder having an average particle size of 10 μm with a gas atomizing method.

  Next, 100 magnetic particles were randomly selected from the regenerator materials according to each of the examples and comparative examples prepared as described above, and a projection image was taken with an optical microscope in a state where the magnetic particles were placed on a flat glass. About each obtained projection image, the circularity coefficient (R) and its standard deviation ((sigma)) were measured by implementing an image analysis using an image processing apparatus (Pierce company make, model number: PIAS-III). The measurement results are shown in Table 1.

  Next, in order to evaluate the characteristics of the regenerator material prepared as described above, a two-stage expansion GM refrigerator as shown in FIG. 1 was prepared. A two-stage GM refrigerator 10 shown in FIG. 1 shows an embodiment of a refrigerator to which the cold storage material of the present invention is applied. A two-stage GM refrigerator 10 shown in FIG. 1 includes a vacuum vessel 13 in which a large-diameter first cylinder 11 and a small-diameter second cylinder 12 connected coaxially to the first cylinder 11 are installed. Have. A first regenerator 14 is disposed in the first cylinder 11 so as to be able to reciprocate, and a second regenerator 15 is disposed in the second cylinder 12 so as to be capable of reciprocating. Seal rings 16 and 17 are disposed between the first cylinder 11 and the first regenerator 14, and between the second cylinder 12 and the second regenerator 15, respectively.

  The first regenerator 14 accommodates a first regenerator material 18 such as Cu mesh. In the second regenerator 15, a plate-like cryogenic regenerator material used in the regenerator of the present invention is accommodated as the second regenerator material 19. The first regenerator 14 and the second regenerator 15 each have a passage for a working medium (refrigerant gas) such as He gas provided in a gap 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. A second expansion chamber 21 is provided between the second regenerator 15 and the tip 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 temperature lower than that of the first cooling stage 22 is formed at the bottom of the second expansion chamber 21.

  A high-pressure working medium (for example, He gas) is supplied from the compressor 24 to the two-stage GM refrigerator 10 as described above. The supplied working medium passes between the first regenerators 18 accommodated in the first regenerator 14, reaches the first expansion chamber 20, and is further stored in the second regenerator 15. (Second cool storage material) 19 passes through and reaches the second expansion chamber 21. At this time, the working medium is cooled by supplying heat energy to the regenerator materials 18 and 19. The working medium that has passed between the regenerators 18 and 19 expands in the expansion chambers 20 and 21 to generate cold, and the cooling stages 22 and 23 are cooled. The expanded working medium flows in the opposite direction between the regenerator materials 18 and 19. The working medium is discharged after receiving thermal energy from each of the cold storage materials 18 and 19. As the recuperating effect is improved in such a process, the thermal efficiency of the working medium cycle is improved, and an even lower temperature is realized.

And each cold storage material which concerns on the Example prepared as mentioned above and a comparative example was filled into the 2nd-stage regenerator (inner diameter 38mm) of the 2-stage expansion type GM refrigerator 10 shown in FIG. That is, in Examples 1 to 5 and Comparative Examples 1 to 3 was filled with cold accumulating material made of the HoCu ₂ alone. On the other hand, in Example 6, 200 g of Er ₃ Ni regenerator material was filled on the high temperature side of the regenerator, while 200 g of HoCu ₂ regenerator material prepared in Example 1 was filled on the low temperature side. Further, in Example 7, 200 g of the HoCu ₂ regenerator material prepared in Example 1 is filled on the high temperature side, while 200 g of the GdAlO ₃ regenerator material is filled on the low temperature side, according to Examples and Comparative Examples. The refrigeration units were assembled and the refrigeration test was performed, and the refrigeration capacity at 4.2K was measured.

The refrigerating capacity in this example was defined as a heat load when a heat load was applied to the second cooling stage by the heater during the operation of the refrigerator and the temperature increase of the second cooling stage stopped at 4.2K. The refrigeration capacity was measured by both the initial value immediately after the start of operation and the value after 1000 hours of continuous operation. The measurement results are shown in Table 1 below.

  As is clear from the results shown in Table 1 above, in the cooler filled with the regenerator material of each example composed of a group of magnetic particles prepared with the circularity coefficient R and the standard deviation σ of the magnetic particles in an appropriate range. The initial value of the refrigeration capacity at 4.2 K was high, the refrigeration capacity after 1000 hours of continuous operation was also high, and the refrigeration capacity did not decrease even after long time operation, and stable refrigeration performance could be confirmed. Furthermore, after the operation was completed, the regenerator was disassembled, the regenerator material was taken out and the appearance was observed, but generation of broken magnetic particles and fine powder was not observed.

  On the other hand, in the refrigerator filled with the regenerator material according to each comparative example, in which at least one of the circularity coefficient R of the magnetic particles and the standard deviation σ thereof is outside the range defined in the present invention, The initial value of the refrigerating capacity at 2K was lower than that of the example. In addition, the refrigeration capacity after 1000 hours of continuous operation was significantly reduced, and the refrigeration performance was significantly reduced. Furthermore, when the regenerator material was taken out from the regenerator after the operation was completed and the appearance was observed, generation of broken particles and fine powder was observed. And it was also confirmed that the seal part of some refrigerators was damaged.

  As is clear from the above examples and comparative examples, according to the refrigerator using the regenerator material according to each example in which the average value of the circularity coefficient R and the standard deviation thereof are properly defined, the regenerator material during operation It is possible to realize a refrigerator capable of maintaining a stable refrigeration capacity over a long period of time.

  In each of the embodiments described above, an example in which the regenerator material according to the present invention is applied to a GM refrigerator is shown, but the regenerator material of the present invention can also be applied to a pulse tube refrigerator 70 as shown in FIG. It is.

  FIG. 2 shows the basic configuration of a single-stage pulse tube refrigerator. The greatest structural feature of the pulse tube refrigerator 70 is that it does not have a reciprocating piston for generating cold, which is essential in the GM refrigerator described above. For this reason, it has an advantage 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 generally helium gas is used as a refrigerant gas. As a basic configuration, the refrigerator includes, in addition to the regenerator 1, a pressure vibration source 71 that compresses helium gas, and a phase adjustment mechanism 72 that controls the time difference between the pressure fluctuation and the position fluctuation (displacement) of the refrigerant gas.

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

  Next, examples of a superconducting MRI apparatus, a superconducting magnet for a magnetic levitation train, a cryopump, and a magnetic field application type single crystal pulling apparatus using a regenerative refrigerator filled with a regenerator material according to the present invention will be described.

  FIG. 4 is a cross-sectional view showing a schematic configuration of a superconducting MRI apparatus to which the present invention is applied. A superconducting MRI apparatus 30 shown in FIG. 4 includes a superconducting static magnetic field coil 31 that applies a spatially uniform and temporally stable static magnetic field to a human body, and a correction coil that is not shown to correct nonuniformity of the generated magnetic field. A gradient magnetic field coil 32 that applies a magnetic field gradient to the measurement region, a radio wave transmission / reception probe 33, and the like. In addition, as described above, the regenerative refrigerator 34 according to the present invention is used for cooling the superconducting static magnetic field coil 31. In the figure, 35 is a cryostat, and 36 is a radiation heat shield.

  In the superconducting MRI apparatus 30 using the regenerative refrigerator 34 to which the present invention is applied, the operating temperature of the superconducting static magnetic field coil 31 can be stably guaranteed over a long period of time, so that it is spatially uniform and temporal. A stable static magnetic field can be obtained over a long period of time. Therefore, the performance of the superconducting MRI apparatus 30 can be exhibited stably over a long period of time.

  FIG. 5 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 to which the present invention is applied, and shows a portion of a superconducting magnet 40 for a magnetic levitation train. A superconducting magnet 40 for a magnetic levitation train shown in FIG. 5 includes a superconducting coil 41, a liquid helium tank 42 for cooling the superconducting coil 41, a liquid nitrogen tank 43 for preventing volatilization of the liquid helium tank, and a regenerative type according to the present invention. It is comprised by the refrigerator 44 grade | etc.,. 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 magnetically levitated train using the regenerative refrigerator 44 to which the present invention is applied, the operating temperature of the superconducting coil 41 can be stably ensured over a long period of time, so that the magnetic levitation and propulsion of the train Thus, it is possible to stably obtain a magnetic field necessary for a long period of time. In particular, the superconducting magnet 40 for a magnetic levitation train acts on acceleration, but the regenerative refrigerator 44 to which the present invention is applied can maintain an excellent refrigerating capacity over a long period of time even when the acceleration acts. 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. 6 is a cross-sectional view showing a schematic configuration of a cryopump using a regenerative refrigerator that applies the present invention. A cryopump 50 shown in FIG. 6 includes a cryopanel 51 that condenses or adsorbs gas molecules, a regenerative refrigerator 52 that cools the cryopanel 51 to a predetermined cryogenic temperature, a shield 53 provided between them, and an air inlet. A baffle 54 provided in the ring, and a ring 55 that changes the exhaust speed of argon, nitrogen, hydrogen, or the like.

  In the cryopump 50 using the regenerative refrigerator 52 to which the present invention is applied, 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 exhibited stably over a long period of time.

  FIG. 7 is a perspective view showing a schematic configuration of a magnetic field application type single crystal pulling apparatus using a cold storage type refrigerator to which the present invention is applied. A magnetic field application type single crystal pulling device 60 shown in FIG. 7 includes a raw material melting crucible, a heater, a single crystal pulling unit 61 having a single crystal pulling mechanism, a superconducting coil 62 for applying a static magnetic field to the raw material melt, and It is constituted by an elevating mechanism 63 of the single crystal pulling unit 61 or the like. And the cool storage type refrigerator 64 to which the present invention as described above is applied 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 vessel.

  In the magnetic field application type single crystal pulling apparatus 60 using the regenerative refrigerator 64 to which the present invention is applied, the operating temperature of the superconducting coil 62 can be stably ensured over a long period of time. A good magnetic field that suppresses liquid convection 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 exhibited stably over a long period of time.

1 Regenerator 10 GM refrigerator (cool storage type refrigerator)
11 First Cylinder 12 Second Cylinder 13 Vacuum Container 14 First Regenerator 15 Second Regenerator 16, 17 Seal Ring 18 First Heat Storage Material 19 Second Heat Storage Material (Cryogenic Storage Material)
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 transmitting / receiving probe 34 Regenerative refrigerator 35 Cryostat 36 Radiation Insulation shield 40 Superconducting magnet (magnet)
41 Superconducting coil 42 Liquid helium tank 43 Liquid nitrogen tank 44 Regenerative refrigerator 45 Laminated insulation 46 Power lead 47 Permanent current switch 50 Cryopump 51 Cryopanel 52 Regenerative refrigerator 53 Shield 54 Baffle 55 Ring 60 Magnetic field applied single crystal Pulling device 61 Single crystal pulling unit 62 Superconducting coil 63 Elevating mechanism 64 Regenerative refrigerator 65 Current lead 66 Heat shield plate 67 Helium vessel 70 Pulse tube type refrigerator 71 Pressure vibration source 72 Phase adjustment mechanism 80 Thermal plasma device 81 Reaction vessel 82 High-frequency transmitter 83 Coil 84 Plasma generation unit outer cylinder 85 Plasma frame 86 Powder supply port 87 Powder supply unit 88 Carrier gas supply cylinder 89 Plasma generation gas source 90 Cyclone 91 Cooling gas source

Claims (6)

A regenerator material composed of a large number of magnetic particles having a diameter of 0.01 to 3 mm, wherein the magnetic particles contain a rare earth element, and the area of the projected image on the plane of each magnetic particle is A, while projecting When the perimeter of the image is L, the average value of the circularity coefficient R defined by 4πA / L ² is 0.7 or more, and the standard deviation of the circularity coefficient R is 0.1 or less. Cold storage material characterized by The regenerator material according to claim 1, wherein a standard deviation of the circularity coefficient R is 0.022 to 0.065. The regenerator material according to claim 1, wherein the diameter of the magnetic particles is 0.15 to 0.25 mm. The step of preparing magnetic particles by the centrifugal spray quenching method, and the shape of the obtained magnetic particles are selected by an inclined belt conveyor, and the area of the projected image on the plane of each magnetic particle is set to A, while surrounding the projected image When the length is L, magnetic particles having an average value of the circularity coefficient R defined by 4πA / L ² of 0.7 or more and a standard deviation of the circularity coefficient R of 0.1 or less are formed. A method for producing a regenerator material, comprising a step of sorting. The step of preparing the magnetic particles by sintering the granulated particles obtained by rolling and granulating, and selecting the shape of the obtained magnetic particles by an inclined belt conveyor, the area of the projected image of each magnetic particle on the plane is A On the other hand, when the perimeter of the projected image is L, the average value of the circularity coefficient R defined by 4πA / L ² is 0.7 or more, and the standard deviation of the circularity coefficient R is 0. And a step of selecting the shape of magnetic particles having a size of 1 or less. The process of preparing the magnetic particles by melting and granulating the granulated particles with a thermal plasma device and then rapidly solidifying them, and selecting the shape of the obtained magnetic particles with an inclined belt conveyor, and the area of the projected image of each magnetic particle on the plane Is A, and when the perimeter of the projected image is L, the average value of the circularity coefficient R defined by 4πA / L ² is 0.7 or more, and the standard deviation of the circularity coefficient R is And a step of selecting the shape of magnetic particles having a size of 0.1 or less.

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