JP2004189906A - Cold storage material, method for producing the same and cold storage type refrigerator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cold storage material capable of stably exhibiting remarkable freezing ability over a long period in a cryogenic area and to provide a cold storage type refrigerator, etc., by using the cold storage material. <P>SOLUTION: The cold storage material is composed of a rare earth acid sulfide in which minimum value of reflectance obtained when irradiated with rays having 400-600 nm wavelength is ≥30% and ≤95%. The rare earth acid sulfide is preferably a magnetic material compound represented by general formula (1): R<SB>2</SB>O<SB>2</SB>S (wherein R is at least one kind of rare earth element selected from Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a regenerator material, a method for manufacturing the same, and a regenerative refrigerator, and more particularly to a regenerator material capable of exhibiting a remarkable refrigerating ability in an extremely low temperature range of 20 K or less, a method for producing the regenerator, a regenerator using the regenerator material, and the like. About.
[0002]
[Prior art]
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.
[0003]
For example, in a superconducting MRI apparatus or a cryopump, a refrigerator using a refrigeration cycle such as a Gifford McMahon (GM) system or a Stirling system is used. In addition, 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 in a superconducting power storage device (SMES), a single crystal pulling device in a magnetic field for producing a high quality silicon wafer, and the like.
[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 supplies the thermal energy to the regenerator material, and the expanded operation medium 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.
[0005]
Conventionally, Cu, Pb, or the like has been mainly used as a regenerator material to be filled in the regenerator of the refrigerator as described above. 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 function sufficiently. Cannot store enough heat energy, and the working medium cannot receive enough heat energy from the cold storage material. As a result, there is a problem that a refrigerator having a regenerator filled with the regenerator material cannot reach extremely low temperatures.
[0006]
Therefore, recently, in order to improve the recuperation characteristics at extremely low temperatures of the regenerator and to realize a refrigerating temperature closer to absolute zero, the regenerator has a maximum value of the volume specific heat particularly in an extremely low temperature region of 20 K or less, and A magnetic regenerative material mainly composed of an intermetallic compound composed of a rare earth element and a transition metal element, such as Er ₃ Ni, ErNi, HoCu _2, and the like, is used. By using such a magnetic regenerator in a GM refrigerator, refrigeration at 4K is realized.
[0007]
As the application of such a refrigerator to various systems is studied, technical requirements for stably cooling a larger cooling object have resulted in further improvement of the refrigerating capacity of the refrigerator. It has been demanded. In order to respond to the request, recently, an attempt has been made to improve the refrigerating capacity by replacing a part of the conventional metal magnetic regenerator with an oxysulfide containing a rare earth element such as GdO ₂ S.
[0008]
According to the findings of the present inventor, the rare earth oxysulfide represented by GdO ₂ S has a steep and large volume specific heat peak in a cryogenic region of about 5 K, while a volume on a high temperature side of about 6 K or more is high. Specific heat is small. Therefore, improvement of the refrigerating capacity is realized to some extent by laminating and using a metal-based cold storage material such as HoCu ₂ having a large volume specific heat in a temperature range of 6 K or more.
[0009]
Generally, the regenerator material is processed into spherical particles having a particle size of about 0.2 mm in order to efficiently carry out heat exchange with a working medium such as He gas and to enhance the efficiency of filling a regenerator of a refrigerator. Used. For example, in the case of a metal regenerator material such as HoCu ₂ , for example, a raw material having a predetermined composition is melted, and the molten metal is finely dispersed by an atomizing method such as a centrifugal spray method, and at the same time, spheroidized by the surface tension of the molten metal. In many cases, it is cooled and solidified and processed into a spherical shape.
[0010]
[Problems to be solved by the invention]
However, rare earth oxysulfides such as GdO ₂ S have a high melting point and are difficult to dissolve, and the spheroidization method by the molten metal quenching method as described above cannot be applied. Then, after the fine powder of GdO ₂ S is granulated into granules by a rolling granulation method or the like, the granulated powder is formed into a sphere, and then sintered at a high temperature to be processed into spherical magnetic particles. It has been implemented. In the state of being sintered in a spherical shape, defects such as minute cracks remain on the surface of the magnetic particles, and the mechanical strength of the spherical magnetic particles is inevitably insufficient. In addition, there has been a problem that the magnetic particles are easily broken, and the refrigerating function is reduced in a short period of time.
[0011]
As a solution to the above problem, an effective measure is to remove the defective portion by polishing the particle surface layer in which a portion having a relatively low strength due to a residual defect or the like is formed. However, when a mechanical stress is applied to a rare earth oxysulfide such as GdO ₂ S at the time of polishing, the sulfur (S) existing on the particle surface is liable to be volatilized and dropped, and the composition of the regenerator material is stoichiometric. There is a problem that the composition deviates greatly from the composition, and the specific heat characteristics of the cold storage material deteriorate.
[0012]
The present invention has been made in order to solve the above problems, and particularly has a large volume specific heat in a limited temperature range around 4 to 6K, and has a remarkable refrigeration capacity in a very low temperature range for a long period of time. It is an object of the present invention to provide a regenerative material that can be used as a regenerator, a method for producing the regenerative material, and a regenerative refrigerator using the regenerative material. Further, the use of the regenerative refrigerator as described above enables an MRI apparatus, a superconducting magnet for a magnetic levitation train, a cryopump, and a magnetic field applying type single crystal, which can exhibit excellent performance over a long period of time. It is an object to provide a pulling device.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the present inventor prepares regenerator materials having various compositions and specific heat characteristics and fills the regenerator with the refrigerating machine. The effects on the service life and durability of the steel were compared by experiments.
[0014]
As a result, the refrigerating capacity of the refrigerator in the 4K temperature range is filled by filling the regenerator with a large volume specific heat in a limited temperature range around 4 to 6K in accordance with the specific heat characteristic of the high temperature side. Was found to be significantly improved. For example, when using a regenerator material having a high specific heat at 4K and a low specific heat at 10K, only the low temperature side of the regenerator is filled with the regenerator material in consideration of the temperature distribution inside the regenerator. As a result, it was found that the performance of the refrigerator was greatly improved by utilizing the high specific heat characteristics at 4K of the cold storage material.
[0015]
Further, the present inventor conducted a detailed comparative study of various characteristics of the rare earth oxysulfide regenerator material whose specific heat characteristics were reduced by the above-described polishing treatment. As a result, it has been found that there is a certain correlation between the specific heat characteristics of the cold storage material made of oxysulfide and the reflectance when the cold storage material is irradiated with light having a wavelength of 400 to 600 nm. In other words, the sulfur (S) component on the surface of the cold storage material volatilizes or falls off due to the mechanical stress due to the polishing treatment, and the composition of the cold storage material shifts, resulting in a decrease in specific heat characteristics. found. That is, the surface of the cold storage material is colored due to the atomic vacancies after the sulfur component (S) is volatilized, and the coloring lowers the reflectance of the surface of light having a wavelength of 400 to 600 nm on the surface to less than 30%. It is thought that it was.
[0016]
However, by subjecting the particles of the rare earth oxysulfide regenerator material after the polishing treatment to a predetermined heat treatment in an atmosphere containing a sulfur oxide such as SO ₂ , a portion where the sulfur component (S) is deficient can be effectively treated. It has been found that since the sulfur component can be replenished and the original stoichiometric composition can be recovered, the volume specific heat of the regenerator material also recovers. Then, the reflectance is improved by recovering the deficiency of the sulfur component (S), and the minimum value of the reflectance of light having a wavelength range of 400 to 600 nm at the surface of the cold storage material is 30% or more and 95% or less. It was found that the specific heat characteristic of the regenerator material was recovered to a level where there was no problem in practical use. The present invention has been completed based on the above findings.
[0017]
That is, the regenerative material according to the present invention is characterized by comprising a rare earth oxysulfide having a minimum reflectance of 30% or more and 95% or less when irradiated with light having a wavelength of 400-600 nm.
[0018]
If the cold storage material particles are made of a rare earth oxysulfide having a minimum reflectance of 30% or more and 95% or less when irradiated with visible light having a wavelength of 400-600 nm, the sulfur component is missing from the surface of the particles. Is small even after the polishing treatment, the stoichiometric composition of the regenerator particles is properly maintained, and good specific heat characteristics can be exhibited.
[0019]
The method of measuring the reflectance is not particularly limited, but can be easily measured by a spectrophotometer using an integrating sphere having an aperture ratio of 7.8%. However, in this measurement method, it is necessary to remove errors caused by the apparatus such as the influence of the reflectance from the container filled with the sample, and measure the reflectance of the sample itself. For example, when the depth of the sample container is shallow or when the packing density of the sample is low, the reflectance from the inner surface of the sample container is also measured. In such a case, the measurement is performed in a state where a sufficiently deep container is filled with the sample at a high density. Specifically, the container preferably has a depth of 2 cm and a packing density of 55% or more. In the present invention, BaSO ₄ was used as a reference for the method for measuring the reflectance.
[0020]
When the minimum value of the reflectance at the time of irradiation with the light having a wavelength of 400 to 600 nm is less than 30%, coloring due to volatilization or omission of the sulfur component (S) is remarkable, and the composition of the surface of the cold storage material particles is reduced. This means that the composition has shifted from the stoichiometric composition, and good specific heat characteristics cannot be obtained. On the other hand, in order to set the minimum value of the reflectance to 95% or more, it is necessary to perform a heat treatment operation for recovering the sulfur component lost due to volatilization or loss to the surface of the cold storage material particles for an extremely long time. It is not industrially preferable. A particularly preferable range for the minimum value of the reflectance of visible light at the wavelength of 400 to 600 nm is from 50% to 90%. A more preferable range is 60% or more and 85% or less.
[0021]
Further, in the cold storage material, the rare earth oxysulfide,
General formula: R ₂ O ₂ S (1)
(Wherein, R represents at least one rare earth element selected from Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er). The oxysulfide represented by the above general formula is preferable because it has a large specific heat in an extremely low temperature range.
[0022]
Further, in the above cold storage material, particularly when the R component in the above general formula is gadolinium (Gd), it is particularly preferable because it shows a large specific heat in a low temperature region around about 5K.
[0023]
It is more preferable that the regenerator material according to the present invention strictly satisfies the stoichiometric composition shown in the general formula (1), but the composition represented by the general formula shown in the following formula (2) based on the O component. May be formed.
[0024]
General formula: R _{2 ± 0.1} O ₂ S _{1 ± 0.1} (2)
[0025]
Further, the regenerator material having the composition shown in the general formulas (1) and (2) may contain unavoidable impurities.
[0026]
In the cold storage material, the cold storage material is preferably made of magnetic compound particles, and the magnetic compound particles preferably have a particle size of 0.01 to 3 mm.
[0027]
Further, in the cold storage material, the ratio of the major axis to the minor axis (aspect ratio) is 5 or less and the particle diameter is 0.01 mm or more and 3 mm or less with respect to all the magnetic compound particles constituting the cold storage material. It is desirable that the ratio of the magnetic compound particles is 70% by mass or more.
[0028]
Further, the regenerative refrigerator according to the present invention has a plurality of cooling stages each composed of a regenerator filled with a regenerator material, and flows the operating medium from a high temperature side upstream of the regenerator of each cooling stage, thereby allowing the operating medium and the regenerator material to flow. In the regenerative refrigerator that obtains a lower temperature on the downstream side of the regenerator by heat exchange with the regenerator, at least a part of the regenerator material to be filled in the low-temperature side space of the regenerator in the final cooling stage is the general type. Formula: R ₂ O ₂ S It is characterized by comprising a cold storage material represented by the formula (1) or (2). In addition, it is preferable that the cold storage material of this invention is filled in the low-temperature side downstream of a regenerator.
[0029]
Further, the MRI (Magnetic Resonance Imaging) device, the superconducting magnet for a magnetic levitation train, the cryopump, and the magnetic field application type single crystal pulling device according to the present invention are all provided with the regenerative refrigerator according to the present invention described above. Features.
[0030]
As is clear from the general formula, the regenerator material according to the present invention is made of a magnetic material composed of a rare earth element (R component), oxygen (O), and sulfur (S).
[0031]
The R component is at least one rare earth element selected from Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er. When any of these R components is added as a cold storage material component, the temperature position of the volume specific heat peak of the magnetic substance is shifted to a lower temperature side, the half width of the peak is expanded, or the R component is adjusted according to the design specifications of the refrigerator. It is added in order to realize specific heat characteristics effective as a cold storage material by adjusting the specific heat characteristics.
[0032]
By appropriately selecting the rare earth element as the R component, the temperature position of the specific heat peak of the magnetic material can be set to a target temperature, that is, a 4 to 6K region.
[0033]
The R component represents at least one kind of rare earth element as described above, and Gd is particularly preferable.
[0034]
In addition to smoothing the flow of the working medium such as helium gas flowing through the regenerator filled with the cold storage material, increasing the heat exchange efficiency between the working medium and the cold storage material, and stably maintaining the heat exchange function. The regenerative material may be composed of spherical magnetic particles having a uniform particle size. Specifically, as described above, the ratio of the major axis to the minor axis (aspect ratio) is 5 or less, and has a particle diameter of 0.01 mm or more and 3 mm or less with respect to all the magnetic particles constituting the cold storage material. It is preferable to adjust the ratio of the magnetic particles to be 70% by weight or more.
[0035]
The particle size of the magnetic particles is a factor that greatly affects the strength of the particles, the cooling function of the refrigerator, and the heat transfer characteristics.When the particle size is less than 0.01 mm, the packing density when filling the regenerator becomes high. In addition, the passage resistance (pressure loss) of He gas, which is a cooling medium, rapidly increases, and in addition to the flowing He gas, it enters the compressor and wears components and the like at an early stage.
[0036]
On the other hand, when the particle size exceeds 3 mm, segregation occurs in the crystal structure of the particles, and the particles become brittle, and the heat transfer area between the magnetic particles and the He gas serving as the cooling medium decreases, resulting in remarkable heat transfer efficiency. There is a possibility that it will decrease. Moreover, when such coarse particles exceed 30% by weight, there is a possibility that the cold storage performance is reduced. Therefore, the average particle size is set to 0.01 mm or more and 3 mm or less, more preferably in the range of 0.05 to 1.0 mm, and further preferably 0.1 mm to 0.5 mm. In order to sufficiently exhibit the cooling function and strength in practical use, the particles having the average particle diameter of 0.01 mm or more and 3 mm or less are at least 70% by weight or more, preferably 80% by weight, based on the whole magnetic regenerator particles. %, More preferably 90% or more.
[0037]
The ratio of the major axis to the minor axis (aspect ratio) of the magnetic regenerator particles is adjusted to 5 or less, preferably 3 or less, more preferably 2 or less, and even more preferably 1.3 or less. The aspect ratio of the magnetic particles has a great effect on the strength of the particles and the packing density and uniformity when filling the regenerator. When the aspect ratio exceeds 5, the magnetic particles are deformed by mechanical action. It is easy to cause destruction, and it is difficult to uniformly and densely fill the regenerator so that the voids are homogeneous. If such particles exceed 30% by weight of all the particles of the regenerator, the efficiency of the regenerator decreases. May be caused.
[0038]
Even when the prepared magnetic particles have variations in particle diameter and variations in the ratio of the major axis to the minor axis, they can be easily classified and used as appropriate. In this case, the ratio of the magnetic particles having an aspect ratio within the above range to 70% or more, preferably 80% or more, more preferably 90% or more, of all the magnetic particles filled in the regenerator, is sufficiently practical. Can be used as a cold storage material.
[0039]
The surface roughness of the magnetic particles is a factor that has a great effect on mechanical strength, cooling characteristics, cooling medium passage resistance, cold storage efficiency, and the like. In general, the maximum height Rmax of irregularities defined by JIS B0601 is 10 μm or less, Preferably, it is set to 5 μm or less, more preferably 2 μm or less. The surface roughness can be measured with a scanning electron microscope (SEM roughness meter).
[0040]
When the surface roughness exceeds 10 μmRmax, micro-cracks, which are the starting points of destruction, are likely to occur in the particles, and the passage resistance of the cooling medium increases to increase the load on the compressor. The contact area increases, the transfer of cold heat between the magnetic particles increases, and the cold storage efficiency decreases.
[0041]
Practically, the proportion of magnetic particles having minute defects with a length of 10 μm or more that affects the mechanical strength of the magnetic particles is 30% or less, preferably 10% or less, and more preferably 10% or less of the whole. desirable.
[0042]
The method for producing a cold storage material according to the present invention includes a step of preparing magnetic compound particles comprising a rare earth oxysulfide, a step of polishing the magnetic compound particles into a spherical shape, and a step of polishing the spherical magnetic compound particles. Heat treatment at a temperature of 900 to 1200 ° C. for 1 to 12 hours in a sulfur oxide atmosphere.
[0043]
In the method for producing a cold storage material, as a raw material powder for forming the magnetic compound particles, a raw material powder having an average particle diameter of 0.3 to 30 μm in order to form a denser and high-strength cold storage material particle. It is preferred to use More preferably, it is desirable to use a raw material powder having a size of 0.5 to 20 μm, and more preferably, a raw material powder having an average particle size of 1 to 10 μm.
[0044]
The method for preparing the magnetic compound particles composed of the rare earth oxysulfide is not particularly limited. For example, a mixture of oxide fine particles having a predetermined composition is formed into a spherical shape by a rolling granulation method or the like. Then, a method of synthesizing and preparing particles of a predetermined oxysulfide by sintering the obtained spherical molded body under predetermined temperature conditions can be adopted. The sintering temperature is preferably in the range of 1200 to 1800 ° C. The sintering time is preferably 1 hour or more and 48 hours or less.
[0045]
However, in the case of the oxysulfide particles as sintered, the surface roughness of the particle surface may be large, which may increase the airflow resistance to the refrigerant gas and lower the refrigeration efficiency. Further, fine powder adheres to the particle surface, and the powder is detached by an impact acting during operation of the refrigerator to cause clogging of the refrigerator component, which causes deterioration of the performance of the refrigerator. Further, fine defects remaining on the particle surface may cause cracks, shortening the life of the cold storage material, or causing clogging as described above.
[0046]
Therefore, the surface layer of the sintered body particles obtained by sintering is polished to further increase the sphericity of the particles, and the powder fixed to the surface of the magnetic compound particles is removed, and the processing is performed with relatively weak strength. A step of removing a defective portion (scratch) is performed.
[0047]
However, when the above-mentioned polishing step is performed, the sulfur (S) existing on the particle surface is liable to be volatilized and dropped off due to the impact force (mechanical stress), and the composition of the cold storage material is largely shifted from the stoichiometric composition. As a result, the specific heat characteristic of the cold storage material is reduced.
[0048]
Therefore, in the method of the present invention, a predetermined heat treatment is performed after the above-mentioned polishing to recover the sulfur component (S) as described above. That is, by subjecting the particles of the rare earth oxysulfide regenerator material after the polishing treatment to a predetermined heat treatment in an atmosphere containing a sulfur oxide such as SO ₂ , a portion where the sulfur component (S) is deficient can be effectively treated. Since the sulfur component can be replenished and the original stoichiometric composition can be restored, the volume specific heat of the regenerator can also be restored. Then, the reflectance is improved by recovering the deficiency of the sulfur component (S), and the minimum value of the reflectance of light having a wavelength range of 400 to 600 nm at the surface of the cold storage material is 30% or more and 95% or less. By recovering the heat storage material, the specific heat characteristic of the cold storage material can be recovered to a level that does not cause any practical problem.
[0049]
The atmosphere during the heat treatment is preferably an atmosphere containing, for example, about 1 to 5% by volume (vol)% of SO ₂ gas, but the same effect can be obtained even when SO ₃ gas is used. Alternatively, heat treatment may be performed in an atmosphere in which SO ₂ or SO ₃ is mixed with another gas such as O ₂ or N ₂ . In the atmosphere having the above sulfur component gas concentration, the heat treatment temperature is preferably in the range of 900 to 1200 ° C. The heat treatment time is preferably from 1 hour to 24 hours from the viewpoint of processing efficiency.
[0050]
A regenerative refrigerator according to the present invention includes a refrigerator having a plurality of cooling stages, wherein at least a part of a regenerator in a final cooling stage is filled with the magnetic regenerator particles. For example, in the two-stage expansion refrigerator, the magnetic field according to the present invention is provided on the low-temperature end side of the second-stage regenerator, and in the three-stage expansion refrigerator, on the low-temperature end side of the third-stage regenerator. While the cold storage material particles are filled, the other cold storage material filling space is filled with another cold storage material having a specific heat characteristic according to the temperature distribution.
[0051]
When the filling amount of the magnetic regenerator material particles of the present invention in the low-temperature side space of the regenerator in the final cooling stage described above is too small at a volume ratio of less than 3%, no improvement in the regenerative efficiency of the refrigerator is observed, and Machine capacity is not improved. On the other hand, when the filling amount is excessively larger than 70% by volume, the above-mentioned drawback of the specific heat characteristics of the magnetic regenerator material particles becomes remarkable, and similarly, the cold storage efficiency is lowered. In other words, a relatively small volume specific heat in a temperature range other than the temperature at which the volume specific heat reaches a peak, particularly in a high temperature range, adversely affects the entire regenerator, resulting in a decrease in cool storage efficiency. Therefore, the filling volume ratio of the magnetic regenerator particles of the present invention to the total volume of the regenerator in the final cooling stage is in the range of 3 to 70% by volume, preferably in the range of 5 to 50% by volume, Further, the range of 10 to 30% by volume is particularly desirable.
[0052]
According to the regenerator material according to the above configuration, since the regenerative material is made of a rare earth oxysulfide-based magnetic material (R ₂ O ₂ magnetic material) having a steep volume specific heat peak in an extremely low temperature range, the temperature position of the volume specific heat peak Is shifted to a lower temperature side, the half-value width of the specific heat peak is expanded, and a regenerator material having good specific heat characteristics is obtained. Then, by filling the regenerator material into the low-temperature end of the regenerator constituting the final cooling stage of the refrigerator, the refrigerating capacity in the temperature 4K region is high and stable refrigerating performance can be maintained for a long period of time. A refrigerator can be provided.
[0053]
The MRI apparatus, the cryopump, the superconducting magnet for the magnetic levitation train, and the magnetic field applying type single crystal pulling apparatus all use the above-described refrigerator because the performance of the refrigerator affects the performance of each apparatus. The MRI apparatus, the cryopump, the superconducting magnet for the magnetic levitation train, and the magnetic field applying type single crystal pulling apparatus of the present invention can exhibit excellent performance over a long period of time.
[0054]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be specifically described based on examples shown below.
[0055]
(Example 1)
A raw material powder of Gd ₂ O ₂ S having an average particle diameter of 3 μm was charged into a tumbling granulator and granulated to prepare granulated particles having a particle diameter of about 0.1 to 0.4 mm. Magnetic particles were prepared by sintering the granulated particles at a temperature of 1800 ° C. for 2 hours in an Ar atmosphere. Next, the sintered magnetic particles are placed on a rotating disk containing diamond abrasive grains and rolled to polish the surface layer of each particle to form a spheroid, and the adhesion formed on the surface layer Powder and defective portions were removed. The removal amount in this polishing step was about 3% of the particle size of the magnetic particles. Then, about 3 vol. The heat storage material according to Example 1 was prepared by performing a heat treatment at a temperature of 1100 ° C. for 5 hours in an N ₂ gas atmosphere containing% SO ₂ gas. When the reflectance of the obtained regenerator material particles was measured, the minimum value in the wavelength range of 400 to 600 nm was 72% at the wavelength of 460 nm.
[0056]
On the other hand, 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. 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 coaxially connected to the first cylinder 11 are installed. Have. The first cylinder 11 has a first regenerator 14 arranged reciprocally, and the second cylinder 12 has a second regenerator 15 arranged reciprocally. Seal rings 16 and 17 are arranged between the first cylinder 11 and the first regenerator 14 and between the second cylinder 12 and the second regenerator 15, respectively.
[0057]
The first regenerator 14 contains a first regenerator 18 such as a Cu mesh. The low-temperature side of the second regenerator 15 is filled with the extremely low-temperature regenerative material of the present invention as the second regenerative material 19 at a predetermined ratio. Each of the first regenerator 14 and the second regenerator 15 has a passage for a working medium such as He gas provided in a gap between the first regenerator 18 and the cryogenic regenerator 19.
[0058]
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.
[0059]
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 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 cooled by supplying thermal energy to each of the cold storage materials 18 and 19. The working medium that has passed between the cold storage materials 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 between the cold storage materials 18 and 19 in the opposite direction. The working medium is discharged after receiving heat energy from each of the cold storage materials 18 and 19. In such a process, as the recuperation effect becomes better, the thermal efficiency of the working medium cycle is improved, and a lower temperature is realized.
[0060]
Then, 100 g of the cold storage material according to Example 1 prepared as described above was charged into the lowest temperature side of the second-stage regenerator of the two-stage expansion GM refrigerator. Further, 150 g of HoCu ₂ was charged on the high temperature side, and 250 g of Pb was further charged on the high temperature side, thereby assembling the refrigerator according to Example 1.
[0061]
Then, the refrigerator according to Example 1 assembled as described above was subjected to a refrigeration test at an operation frequency of 1 Hz, and the refrigeration capacity after continuous operation for 3000 hours was measured. As a result, the refrigeration capacity at 4.2K was 1.11 W. was gotten.
[0062]
Note that the refrigerating capacity in the present embodiment 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 rise in the second cooling stage stopped at 4.2K.
[0063]
(Comparative Example 1)
Gd ₂ O ₂ S raw material powder having an average particle size of 3 μm was charged into a tumbling granulator to perform granulation, and granulated particles having a particle size of about 0.1 to 0.4 mm were prepared. Magnetic particles were prepared by sintering the granulated particles at a temperature of 1800 ° C. for 2 hours in an Ar atmosphere. Next, the sintered magnetic particles are placed on a rotating disk containing diamond abrasive grains and tumbled to polish the surface layer of each particle to form a spheroid, and to adhere to the surface layer. Powder and defective portions were removed. The removal amount in this polishing step was about 3% of the particle size of the magnetic particles. Thereafter, the heat storage material according to Comparative Example 1 was directly used without performing heat treatment in an atmosphere containing a sulfur component. When the reflectance of the obtained regenerator material particles was measured, the minimum value in the wavelength range of 400 to 600 nm was 28% at the wavelength of 460 nm.
[0064]
Then, 100 g of the obtained regenerator particles were charged into the lowest temperature side of the second regenerator of the two-stage expansion GM refrigerator. The high-temperature side was filled with 150 g of HoCu ₂ cold storage material, and the high-temperature side was further filled with 250 g of Pb cold storage material to assemble the refrigerator according to Comparative Example 1. Then, a refrigeration test was performed at an operation frequency of 1 Hz as in Example 1, and a refrigeration capacity at 4.2 K of 0.53 W was obtained.
[0065]
(Example 2)
The magnetic particles according to the _second embodiment were subjected to a heat treatment at a temperature of 1000 ° C. for 5 hours in a N ₂ atmosphere containing 3 vol% of SO ₂ gas for the magnetic particles whose surface was polished in the same manner as the first embodiment. Materials were prepared. When the reflectance of the obtained regenerator particles was measured, the minimum value in the wavelength range of 400 to 600 nm was 44% at the wavelength of 460 nm.
[0066]
Next, 100 g of the obtained regenerator particles were charged into the lowest temperature side of the second stage regenerator of the two-stage expansion GM refrigerator. The refrigerator according to Example 2 was assembled by filling 150 g of HoCu ₂ cold storage material on the high temperature side and 250 g of Pb cold storage material on the high temperature side. Then, a refrigeration test was performed at an operation frequency of 1 Hz in the same manner as in Example 1. As a result, 0.89 W was obtained as the refrigeration capacity at 4.2 K.
[0067]
(Example 3)
The magnetic particles subjected to the surface polishing in the same manner as in Example 1 were subjected to a heat treatment at a temperature of 1100 ° C. for 3 hours in an N ₂ gas atmosphere containing 3 vol% of SO ₂ gas, thereby obtaining Example 3 of the present invention. A cold storage material was prepared. When the reflectance of the obtained regenerator particles was measured, the minimum value in the wavelength region of 400 to 600 nm was 53% at the wavelength of 460 nm.
[0068]
Next, 100 g of the obtained regenerator particles were charged into the lowest temperature side of the second stage regenerator of the two-stage expansion GM refrigerator. The refrigerator according to Example 3 was assembled by filling 150 g of HoCu ₂ regenerator material on the high temperature side and 250 g of Pb regenerator material on the high temperature side. Then, as in Example 1, a refrigeration test was performed at an operating frequency of 1 Hz. As a result, 0.77 W was obtained as a refrigeration capacity at 4.2 K.
[0069]
Next, embodiments 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.
[0070]
FIG. 2 is a sectional view showing a schematic configuration of a superconducting MRI apparatus to which the present invention is applied. The superconducting MRI apparatus 30 shown in FIG. 2 includes a superconducting static magnetic field coil 31 for applying a spatially uniform and temporally stable static magnetic field to a human body, and a correction coil (not shown) for correcting non-uniformity of a generated magnetic field. , A gradient magnetic field coil 32 for giving a magnetic field gradient to the measurement area, 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 drawing, reference numeral 35 denotes a cryostat, and reference numeral 36 denotes a radiation insulation shield.
[0071]
In the superconducting MRI apparatus 30 using the regenerative refrigerator 34 according to the present invention, since the operating temperature of the superconducting static magnetic field coil 31 can be stably ensured over a long period of time, it is spatially uniform and time-dependent. A stable static magnetic field can be obtained for a long period of time. Therefore, the performance of the superconducting MRI apparatus 30 can be stably exhibited over a long period of time.
[0072]
FIG. 3 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 part of a superconducting magnet 40 for a magnetic levitation train. The superconducting magnet 40 for a magnetic levitation train shown in FIG. 3 includes a superconducting coil 41, a liquid helium tank 42 for cooling the superconducting coil 41, a liquid nitrogen tank 43 for preventing the volatilization of the liquid helium tank, 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.
[0073]
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 stably guaranteed for a long period of time, so The required magnetic field 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 refrigerating capacity for a long period of time even when the acceleration acts. Greatly contribute to the long-term stabilization of Therefore, the magnetic levitation train using such a superconducting magnet 40 can exhibit its reliability over a long period of time.
[0074]
FIG. 4 is a sectional view showing a schematic configuration of a cryopump using the regenerative refrigerator according to the present invention. A cryopump 50 shown in FIG. 4 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.
[0075]
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.
[0076]
FIG. 5 is a perspective view showing a schematic configuration of a magnetic field application type single crystal pulling apparatus using the regenerative refrigerator according to the present invention. The magnetic field applying type single crystal pulling apparatus 60 shown in FIG. 5 includes a crucible for melting a raw material, 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 section 61 is configured by a lifting mechanism 63 and the like. 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.
[0077]
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 that suppresses convection can be obtained over a long period of time. Therefore, the performance of the magnetic field applying type single crystal pulling apparatus 60 can be stably exhibited over a long period of time.
[0078]
【The invention's effect】
As described above, according to the regenerator material of the present invention, the regenerative material is composed of a rare earth oxysulfide-based magnetic material (R ₂ O ₂ S-based magnetic material) having a steep peak in volume specific heat in an extremely low temperature region. In addition, the temperature position of the volume specific heat peak shifts to a lower temperature side, and the half width of the specific heat peak is expanded, so that a regenerator material having excellent specific heat characteristics can be obtained. Then, by filling the regenerator material into the low-temperature end of the regenerator constituting the final cooling stage of the refrigerator, the refrigerating capacity in the temperature 4K region is high and stable refrigerating performance can be maintained for a long period of time. A refrigerator can be provided.
[0079]
The MRI apparatus, the cryopump, the superconducting magnet for the magnetic levitation train, and the magnetic field applying type single crystal pulling apparatus all use the above-described refrigerator because the performance of the refrigerator affects the performance of each apparatus. The MRI apparatus, the cryopump, the superconducting magnet for the magnetic levitation train, and the magnetic field applying type single crystal pulling apparatus of the present invention can exhibit excellent performance over a long period of time.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a configuration of a main part of a regenerative refrigerator (GM refrigerator) according to the present invention.
FIG. 2 is a sectional view showing a schematic configuration of a superconducting MRI apparatus according to one embodiment of the present invention.
FIG. 3 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. 4 is a sectional view showing a schematic configuration of a cryopump according to one embodiment of the present invention.
FIG. 5 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.
[Explanation of symbols]
10 GM refrigerator (cool storage 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 for extremely low temperature)
Reference Signs List 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 Cool storage refrigerator 35 Cryostat 36 Radiation Heat insulation shield 40 Superconducting magnet (magnet)
41 superconducting coil 42 liquid helium tank 43 liquid nitrogen tank 44 regenerative refrigerator 45 laminated heat insulator 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 Cold storage refrigerator 65 Current lead 66 Heat shield plate 67 Helium container

Claims (11)

A cold storage material comprising a rare earth oxysulfide having a minimum reflectance of 30% or more and 95% or less when irradiated with light having a wavelength of 400 to 600 nm. The cold storage material according to claim 1, wherein the rare earth oxysulfide is:
General formula: R ₂ O ₂ S (1)
(Wherein R represents at least one rare earth element selected from Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er). Wood. The cold storage material according to claim 2, wherein the R component in the general formula is gadolinium (Gd). 2. The regenerator material according to claim 1, wherein the regenerator material is made of magnetic compound particles, and the particle diameter of the magnetic compound particles is 0.01 to 3 mm. 5. The regenerator material according to claim 4, wherein the ratio of the major axis to the minor axis (aspect ratio) is 5 or less and the particle diameter is 0.01 mm or more and 3 mm or less with respect to all the magnetic compound particles constituting the cold storage material. The ratio of the magnetic compound particles having the following is 70 mass% or more. A step of preparing magnetic compound particles comprising a rare earth oxysulfide; a step of polishing the magnetic compound particles into a spherical form; A heat treatment at 1 ° C. for 1 to 12 hours. It has a plurality of cooling stages composed of regenerators filled with regenerator material, and the working medium flows from the upstream high-temperature side of the regenerators of the respective cooling stages to the downstream side of the regenerator by heat exchange between the operating medium and the regenerator materials. In a regenerative refrigerator that obtains a lower temperature, at least a part of the regenerator material filled in the low-temperature side space of the regenerator in the final cooling stage is a regenerator material according to any one of claims 1 to 5. A regenerative refrigerator comprising: A superconducting magnet comprising the regenerative refrigerator according to claim 7. An MRI (nuclear magnetic resonance imaging) apparatus comprising the regenerative refrigerator according to claim 7. A cryopump comprising the regenerative refrigerator according to claim 7. A magnetic field applying type single crystal pulling apparatus comprising the regenerative refrigerator according to claim 7.

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