JP4582994B2 - Cold storage material, manufacturing method thereof, and cold storage type refrigerator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a regenerator material, a method for producing the regenerator material, and a regenerator type refrigerator, and in particular, a regenerator material capable of exhibiting remarkable refrigerating capacity in an extremely low temperature region of 20K or less, a production method thereof, a regenerator refrigerator using the regenerator material, and the like. About.
[0002]
[Prior art]
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.
[0003]
For example, in superconducting MRI apparatuses, cryopumps, and the like, refrigerators using a refrigeration cycle such as the Gifford-McMahon (GM) method or the Stirling method are 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.
[0004]
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.
[0005]
Conventionally, Cu, Pb and the like have been mainly used as the regenerator material filled in the regenerator of 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.
[0006]
Therefore, recently, in order to improve the recuperative characteristics at the cryogenic temperature of the regenerator and realize a refrigeration temperature closer to absolute zero, it has a maximum value of volume specific heat particularly in an extremely low temperature region of 20K or less, and Er with a large value₃Ni, ErNi, HoCu₂For example, magnetic regenerators mainly composed of intermetallic compounds composed of rare earth elements and transition metal elements are used. By using such a magnetic regenerator material for a GM refrigerator, refrigeration at 4K is realized.
[0007]
As the application of such refrigerators to various systems is studied, the technical demand for stably cooling larger objects to be cooled has led to further improvements in refrigerator capacity. It has been demanded. Recently, in order to answer that demand, a part of the conventional metal-based magnetic regenerator material is replaced with GdO.₂Attempts have been made to improve the refrigerating capacity by replacing with oxysulfides containing rare earth elements such as S.
[0008]
According to the knowledge of the present inventor, the above GdO₂The rare earth oxysulfide represented by S has a steep and large volumetric specific heat peak in an extremely low temperature region of about 5K, while the volumetric specific heat on the high temperature side of about 6K or more is small. Therefore, HoCu has a large volumetric specific heat in the temperature range of 6K or higher.₂The improvement of the refrigerating capacity is realized to some extent by using it by laminating with a metal-based regenerator material such as.
[0009]
In general, the regenerator material is processed into spherical particles with a particle size of about 0.2 mm in order to efficiently perform heat exchange with a working medium such as He gas and to increase the charging efficiency of the regenerator of the refrigerator. Have been used. For example, HoCu₂For example, in the case of a metal-based regenerator material, 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 spraying method, and at the same time cooled in a spheroidized state by the surface tension of the molten metal. It is often solidified and processed into a spherical shape.
[0010]
[Problems to be solved by the invention]
However, the GdO₂A rare earth oxysulfide such as S is a compound that has a high melting point and is difficult to dissolve, and the spheroidizing method by the molten metal quenching method as described above cannot be applied. So GdO₂After granulating the fine powder of S into granules by the rolling granulation method, etc., the granulated powder is formed into a spherical shape and further processed into spherical magnetic particles by sintering at a high temperature. Has been. In this spherical sintered state, defects such as fine cracks remain on the surface of the magnetic particles, and the mechanical strength of the spherical magnetic particles is inevitably insufficient. In addition, the magnetic particles are easily broken and the refrigeration function is reduced in a short time.
[0011]
As a solution to the above problem, it is an effective measure to remove the defective portion by polishing the particle surface layer in which defects and the like remain and a portion having a relatively low strength is formed. However, GdO₂When mechanical stress is applied to a rare earth oxysulfide such as S during polishing, the sulfur content (S) present on the surface of the particles tends to volatilize and fall off, and the composition of the regenerator deviates greatly from the stoichiometric composition. As a result, there was a problem that the specific heat characteristics of the regenerator material deteriorated.
[0012]
The present invention has been made in order to solve the above-described problems, and particularly has a large volumetric specific heat in a limited temperature range around 4 to 6 K, and can maintain a remarkable refrigerating capacity over a long period of time in an extremely low temperature range. It is an object of the present invention to provide a regenerator material that can be exhibited as a result, a manufacturing method thereof, and a regenerator refrigerator using the regenerator material. Furthermore, the MRI apparatus, the superconducting magnet for the magnetic levitation train, the cryopump, and the magnetic field application type single crystal capable of exhibiting excellent performance over a long period of time by using the above regenerative refrigerator An object is to provide a lifting device.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the present inventor prepared regenerator materials having various compositions and specific heat characteristics and filled them in the regenerator of the refrigerator, so that the composition and specific heat characteristics correspond to the refrigerating capacity and the regenerator material of the refrigerator. The effects on the life and durability of the steels were compared by experiments.
[0014]
As a result, the refrigerating capacity of the refrigerator in the 4K temperature range is obtained by filling the regenerator with a regenerator material having a large volumetric specific heat in a limited temperature range near 4 to 6K according to the specific heat characteristics on the high temperature side. Obtained a significant improvement. For example, when using a regenerator material that has a high specific heat at 4K and a low specific heat at 10K, consider the temperature distribution inside the regenerator and fill the regenerator material only on the low temperature side of the regenerator. Thus, it was found that the refrigerating machine performance is greatly improved by utilizing the high specific heat characteristics at 4K of the cold storage material.
[0015]
Furthermore, the inventor conducted a detailed comparative investigation on various characteristics of the rare earth oxysulfide regenerator material whose specific heat characteristics were reduced by polishing as described above. As a result, it has been found that there is a certain correlation between the specific heat characteristics of the regenerator material made of oxysulfide and the reflectance when the regenerator 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 regenerator material volatilizes or falls off due to mechanical stress due to the polishing treatment, and thus the composition of the regenerator material shifts, resulting in a decrease in specific heat characteristics. found. That is, the surface portion of the regenerator material is colored due to atomic vacancies after the sulfur component (S) has volatilized, and the coloration reduces the reflectance at the surface portion of the 400-600 nm wavelength light to less than 30%. It is thought that.
[0016]
However, for the rare earth oxysulfide regenerator particles after polishing,₂By applying a predetermined heat treatment in an atmosphere containing sulfur oxides such as sulfur component (S), the sulfur component can be replenished effectively and the original stoichiometric composition can be restored. It was found that the volume specific heat of the regenerator material was also recovered. And the reflectance is improved by recovering the deficiency of the sulfur component (S), and the minimum value of the reflectance at the surface of the regenerator material for light having a wavelength range of 400 to 600 nm is in a range of 30% to 95%. It has been found that the specific heat characteristics of the regenerator material can be recovered to such a level that there is no practical problem. The present invention has been completed based on the above findings.
[0017]
  That is, the regenerator material according to the present invention isThe sulfur component is replenished by a step of heat treating the magnetic compound particles made of rare earth oxysulfide in a sulfur oxide atmosphere at a temperature of 900 to 1200 ° C. for 1 to 12 hours,The minimum value of reflectance when irradiating light with a wavelength of 400-600 nm is44% Or more and 95% or less of a rare earth oxysulfide sintered body, wherein the rare earth oxysulfide is
    General formula: R_{2 ± 0.1}O₂S_{1 ± 0.1}
  (Wherein R represents at least one rare earth element selected from Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er), and the regenerator material is magnetic. The magnetic compound particles have a particle diameter of 0.01 to 3 mm, and the ratio of the major axis to the minor axis (aspect ratio) is 5 with respect to all the magnetic compound particles constituting the cold storage material. The ratio of the magnetic compound particles having a particle diameter of 0.01 mm to 3 mm is 70% by mass or more, and the surface of the magnetic compound particles is polished.
[0018]
If the regenerator particles are made of rare earth oxysulfide having a minimum reflectance of 30% to 95% when irradiated with visible light having a wavelength of 400-600 nm, the sulfur component is missing on the surface. However, even after the polishing treatment, the stoichiometric composition of the regenerator particles can be properly maintained, and good specific heat characteristics can be exhibited.
[0019]
The reflectance measurement method is not particularly limited, but can be easily measured by a spectrophotometer using an integrating sphere with an aperture ratio of 7.8%. However, in this measurement method, it is necessary to remove the error caused by the apparatus, such as the influence of the reflectance from the container filled with the sample, and consider that the sample itself measures the reflectance. For example, when the depth of the sample container is shallow or the filling density of the sample is low, the reflectance from the inner surface of the sample container is also measured. In such a case, measurement is performed in a state where a sufficiently deep container is filled with a sample at a high density. Specifically, it is preferable that the container has a depth of 2 cm and a filling density of 55% or more. In the present invention, the reference for the reflectance measuring method includes BaSO.₄It was used.
[0020]
When the minimum value of the reflectance when irradiated with light having a wavelength of 400 to 600 nm is less than 30%, coloring due to volatilization or loss of the sulfur component (S) is remarkable, and the composition of the surface of the regenerator particles is 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 make the minimum value of the reflectance 95% or more, it is necessary to carry out a heat treatment operation for recovering the sulfur component lost due to volatilization or loss to the surface portion of the regenerator material particles for an extremely long time. Yes, industrially unfavorable. A particularly preferable range for the minimum value of the reflectance of visible light at the wavelength of 400 to 600 nm is 50% or more and 90% or less. A more preferable range is 60% or more and 85% or less.
[0021]
In the above regenerator material, the rare earth oxysulfide is
General formula: R₂O₂S ...... (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 a very low temperature region.
[0022]
Furthermore, in the said cool storage material, especially when R component in the said general formula is gadolinium (Gd), since a large specific heat is shown in the low temperature area | region of about 5K vicinity, it is especially preferable.
[0023]
In addition, although it is more preferable that the regenerator material according to the present invention strictly satisfies the stoichiometric composition represented by the general formula (1), the composition represented by the general formula represented by the following formula (2) based on the O component. You may form so that it may have.
[0024]
General formula: R_{2 ± 0.1}O₂S_{1 ± 0.1}    (2)
[0025]
Moreover, the cool storage material which has a composition shown to the said General formula (1), (2) may contain an unavoidable impurity.
[0026]
Moreover, in the said cool storage material, it is desirable that the said cool storage material consists of a magnetic compound particle, and the particle size of this magnetic compound particle is 0.01-3 mm.
[0027]
Further, in the above regenerator material, the ratio of the major axis to the minor axis (aspect ratio) is 5 or less with respect to all the magnetic compound particles constituting the regenerator material, and has a particle size of 0.01 mm or more and 3 mm or less. The ratio of the magnetic compound particles is desirably 70% by mass or more.
[0028]
The regenerator type refrigerator according to the present invention has a plurality of cooling stages composed of regenerators filled with a regenerator material, and the working medium and the regenerator material are flowed from the upstream high temperature side of the regenerator of each cooling stage. 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 filled in the low temperature side space of the regenerator in the final cooling stage is the above general Formula: R₂O₂It consists of the cool storage material represented by S (1) or (2) Formula. In addition, it is preferable that the cool storage material of this invention is filled into the downstream low temperature side of a cool storage.
[0029]
Furthermore, the MRI (Magnetic Resonance Imaging) apparatus, the superconducting magnet for the magnetic levitation train, the cryopump, and the magnetic field application type single crystal pulling apparatus according to the present invention are all provided with the above-described regenerative refrigerator. It is a feature.
[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 these R components are all added as a cold storage material component, the temperature position of the volume specific heat peak of the magnetic material is moved to a lower temperature side, the half width of the peak is expanded, or according to the design specifications of the refrigerator. It is added 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 a predetermined at least one rare earth element as described above, and Gd is particularly preferable.
[0034]
In addition to smooth the flow of working medium such as helium gas flowing in the regenerator filled with regenerator material, to improve the heat exchange efficiency between the working medium and the regenerator material, and to maintain the heat exchange function stably The cold storage 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 the particle size is 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 so that the ratio of the magnetic particles is 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 is high. As a result, the passage resistance (pressure loss) of the He gas, which is the cooling medium, rapidly increases, and is accompanied by the circulating He gas and enters the compressor to quickly wear out the components and the like.
[0036]
On the other hand, when the particle size exceeds 3 mm, the crystal structure of the granule is segregated and becomes brittle and the heat transfer area between the magnetic particles and the He gas as the cooling medium is reduced, so that the heat transfer efficiency is remarkably increased. May decrease. Moreover, when such coarse particle | grains exceed 30 weight%, there exists a possibility of causing the fall of cold storage performance. Accordingly, the average particle diameter 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 or more and 0.5 mm or less. In order to sufficiently exhibit the cooling function and strength practically, the particles having an average particle diameter of 0.01 mm or more and 3 mm or less are at least 70% by weight, preferably 80% by weight with respect to the whole magnetic regenerator material particles. % Or more, 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 still more preferably 1.3 or less. The aspect ratio of the magnetic particles greatly affects 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 becomes difficult to cause destruction, and it becomes difficult to fill the regenerator uniformly and at a high density so that the air gaps are uniform. When such particles exceed 30% by weight of the total regenerator material, the regenerator efficiency decreases. May be incurred.
[0038]
Even in the case where the variation in the particle size of the magnetic particles prepared here and the variation in the ratio of the major axis to the minor axis occur, it is easy to classify and use them appropriately. 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 cold storage part is sufficiently practical. It can be a cold storage material that can withstand.
[0039]
Further, the surface roughness of the magnetic particles is a factor that greatly affects the mechanical strength, the cooling characteristics, the passage resistance of the cooling medium, the cold storage efficiency, and the like. Generally, the maximum height Rmax of the irregularities defined by JIS B0601 is 10 μm or less, The thickness is preferably set to 5 μm or less, more preferably 2 μm or less. In addition, these surface roughness can be measured with a scanning electron microscope (SEM roughness meter).
[0040]
When the surface roughness exceeds 10 μm Rmax, microcracks that are the starting point of breakage are likely to occur in the particles, the passage resistance of the cooling medium increases, the load on the compressor increases, and particularly between the filled magnetic particles A contact area increases, the movement of the cold heat between magnetic particles becomes large, and cold storage efficiency will fall.
[0041]
In practice, the proportion of magnetic particles having a micro defect 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, more preferably 10% or less of the whole. desirable.
[0042]
The method for producing a regenerator material according to the present invention includes a step of preparing magnetic compound particles made of 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. And a heat treatment in a sulfur oxide atmosphere at a temperature of 900 to 1200 ° C. for 1 to 12 hours.
[0043]
In the manufacturing method of the regenerator material, the raw material powder for forming the magnetic compound particles is a raw material powder having an average particle size of 0.3 to 30 μm in order to form a denser and higher-strength regenerator particle. Is preferably used. More preferably, it is desirable to use a raw material powder of 0.5 to 20 μm, and it is more desirable to use a raw material powder having an average particle size of 1 to 10 μm.
[0044]
The method for preparing the magnetic compound particles comprising 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. In addition, a method of synthesizing and preparing particles made of a predetermined oxysulfide by sintering the obtained spherical molded body under a predetermined temperature condition can be employed. The sintering temperature is preferably in the range of 1200-1800 ° C. The sintering time is preferably 1 hour or more and 48 hours or less.
[0045]
However, the as-sintered oxysulfide particles may have a large surface roughness at the particle surface, which may increase the ventilation resistance to the refrigerant gas and lower the refrigeration efficiency. In addition, fine powder is fixed on the particle surface, and this powder is detached due to an impact acting during operation of the refrigerator to cause clogging of the refrigerator parts, which causes a decrease in the performance of the refrigerator. Furthermore, fine defects remaining on the particle surface may cause cracks, reducing the life of the regenerator material and causing clogging as described above.
[0046]
Therefore, the surface layer of the sintered particles obtained by sintering is polished to further increase the sphericity of the particles, and the powder fixed on the surface of the magnetic compound particles is removed, and the strength is relatively low. A step of removing the defective part (scratch) is performed.
[0047]
However, when the above polishing process is performed, the sulfur content (S) present on the surface of the particles tends to volatilize and drop off due to the impact force (mechanical stress), and the composition of the cold storage material deviates greatly from the stoichiometric composition. As a result, the specific heat characteristics of the regenerator material are degraded.
[0048]
Therefore, in the method of the present invention, after the polishing process, a predetermined heat treatment is performed in order to recover the sulfur component (S) as described above. That is, for the particles of the rare earth oxysulfide regenerator material after the polishing treatment, SO₂By applying a predetermined heat treatment in an atmosphere containing sulfur oxide such as sulfur component (S), the sulfur component can be effectively replenished to the site where the sulfur component (S) is lost, and the original stoichiometric composition can be restored. Therefore, the volume specific heat of the cold storage material can be recovered. And the reflectance is improved by recovering the deficiency of the sulfur component (S), and the minimum value of the reflectance at the surface of the regenerator material for light having a wavelength range of 400 to 600 nm is in the range of 30% to 95%. It is possible to recover the specific heat characteristics of the regenerator material to such an extent that there is no practical problem.
[0049]
The atmosphere during the heat treatment is, for example, SO.₂An atmosphere containing about 1 to 5 volume (vol)% of gas is preferable.₃Even when gas is used, the same effect can be obtained. O₂Or N₂SO for other gases such as₂Or SO₃You may heat-process in the atmosphere which mixed. In addition, in the atmosphere of the said sulfur component gas density | concentration, the heat processing temperature has the preferable range of 900-1200 degreeC. The heat treatment time is preferably 1 hour or more and 24 hours or less from the viewpoint of treatment efficiency.
[0050]
The regenerator type refrigerator according to the present invention is configured by filling at least a part of the regenerator in the final cooling stage with the magnetic regenerator particles in a refrigerator having a plurality of cooling stages.
For example, in a two-stage expansion refrigerator, the magnetic property according to the present invention is on the low-temperature end side of the second-stage regenerator, and in a three-stage expansion refrigerator, on the low-temperature end side of the third-stage regenerator. While the regenerator material particles are filled, the other regenerator material filling space is filled with another regenerator material having specific heat characteristics corresponding 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 less than 3% by volume ratio, the improvement of the regenerator efficiency is not recognized, The capacity of the machine is not improved. On the other hand, when the filling amount exceeds 70% by volume, the above-described disadvantage of the specific heat characteristics of the magnetic regenerator particles becomes noticeable, and similarly the regenerative efficiency is reduced. That is, a relatively small volume specific heat in a temperature range other than the temperature at which the volume specific heat reaches a peak, particularly a high temperature side temperature range, adversely affects the entire regenerator, resulting in a decrease in cold 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, Furthermore, the range of 10 to 30% by volume is particularly desirable.
[0052]
  According to the regenerator material having the above configuration, a rare earth oxysulfide-based magnetic material (R) having a steep volume specific heat peak in a cryogenic temperature range.₂O₂ S seriesTherefore, 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 with good specific heat characteristics is obtained. And, by filling the cold storage material on the low temperature end side in 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 over 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 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 of the present invention can all exhibit excellent performance over a long period of time.
[0054]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be specifically described based on the following examples.
[0055]
Example 1
Gd with an average particle size of 3 μm₂O₂The raw material powder of S was filled in a rolling granulator and granulated to prepare granulated particles having a particle size of about 0.1 to 0.4 mm. The granulated particles were sintered in an Ar atmosphere at a temperature of 1800 ° C. for 2 hours to prepare magnetic particles. Next, the sintered magnetic particles are placed on a rotating disk containing diamond abrasive grains and rolled to polish and spheroidize the surface layer of each particle and adhere to the surface layer. Powder and defects were removed. The removal amount in this polishing step was about 3% of the particle size of the magnetic particles. Thereafter, 3 vol. % SO₂N containing gas₂A cold storage material according to Example 1 was prepared by performing a heat treatment at a temperature of 1100 ° C. for 5 hours in a gas atmosphere. When the reflectance of the obtained cold storage material particles was measured, the minimum value in the wavelength region of 400 to 600 nm was 72% at a wavelength of 460 nm.
[0056]
On the other hand, 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. 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 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.
[0057]
The first regenerator 14 accommodates a first regenerator material 18 such as Cu mesh. The low temperature side of the second regenerator 15 is filled with the cryogenic regenerator material of the present invention as the second regenerator material 19 at a predetermined ratio. The first regenerator 14 and the second regenerator 15 each have 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. 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.
[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 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.
[0060]
And the cold storage material 100g which concerns on Example 1 prepared as mentioned above was filled into the lowest temperature side of the 2nd-stage regenerator of the said 2-stage expansion type GM refrigerator. Furthermore, on the high temperature side, HoCu₂150g, and 250g of Pb was filled on the high temperature side to assemble the refrigerator according to Example 1.
[0061]
And as a result of implementing the refrigeration test about the refrigeration machine concerning Example 1 assembled as mentioned above at the operating frequency of 1 Hz, and measuring the refrigeration capacity after continuous operation for 3000 hours, as a refrigeration capacity in 4.2K, 1.11W was gotten.
[0062]
The refrigeration 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.
[0063]
(Comparative Example 1)
Gd with an average particle size of 3 μm₂O₂S raw material powder was filled into a rolling granulator and granulated to prepare granulated particles having a particle size of about 0.1 to 0.4 mm. The granulated particles were sintered in an Ar atmosphere at a temperature of 1800 ° C. for 2 hours to prepare magnetic particles. Next, the sintered magnetic particles are placed on a rotating disk containing diamond abrasive grains and rolled, so that the surface layer of each particle is polished and spheroidized, and the adhesion formed on the surface layer is fixed. Powder and defects were removed. The removal amount in this polishing step was about 3% of the particle size of the magnetic particles. Then, it was set as the cool storage material which concerns on the comparative example 1 as it was, without implementing the heat processing in sulfur component containing atmosphere. When the reflectance of the obtained cold storage material particles was measured, the minimum value in the wavelength region of 400 to 600 nm was 28% at a wavelength of 460 nm.
[0064]
Then, 100 g of the obtained regenerator material particles were filled into the lowest temperature side of the second-stage regenerator of the two-stage expansion GM refrigerator. On the high temperature side, HoCu₂A refrigerator according to Comparative Example 1 was assembled by filling 150 g of the cold storage material and further filling 250 g of the Pb cold storage material on the high temperature side. And similarly to Example 1, when the freezing test was implemented with the operating frequency of 1 Hz, 0.53 W was obtained as a freezing capacity in 4.2K.
[0065]
(Example 2)
For the magnetic particles subjected to surface polishing in the same manner as in Example 1, 3 vol% SO₂N containing gas₂In the atmosphere, a cold storage material according to Example 2 was prepared by performing heat treatment at a temperature of 1000 ° C. for 5 hours. When the reflectance of the obtained cold storage material particles was measured, the minimum value in the wavelength region of 400 to 600 nm was 44% at a wavelength of 460 nm.
[0066]
Next, 100 g of the obtained regenerator material particles were filled into the lowest temperature side of the second-stage regenerator of the two-stage expansion GM refrigerator. On the high temperature side, HoCu₂The refrigerator according to Example 2 was assembled by filling 150 g of the cold storage material and further filling 250 g of the Pb cold storage material on the high temperature side. And similarly to Example 1, when the freezing test was implemented with the operating frequency of 1 Hz, 0.89 W was obtained as a refrigerating capacity in 4.2K.
[0067]
(Example 3)
For the magnetic particles subjected to surface polishing in the same manner as in Example 1, 3 vol% SO₂N containing gas₂A cold storage material according to Example 3 was prepared by performing heat treatment at 1100 ° C. for 3 hours in a gas atmosphere. When the reflectance of the obtained cold storage material particles was measured, the minimum value in the wavelength region of 400 to 600 nm was 53% at a wavelength of 460 nm.
[0068]
Next, 100 g of the obtained regenerator material particles were filled into the lowest temperature side of the second-stage regenerator of the two-stage expansion GM refrigerator. On the high temperature side, HoCu₂The refrigerator according to Example 3 was assembled by charging 150 g of the cold storage material and further charging 250 g of the Pb cold storage material on the high temperature side. And similarly to Example 1, when the freezing test was implemented with the operating frequency of 1 Hz, 0.77 W was obtained as a freezing capacity in 4.2K.
[0069]
Next, examples 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 application 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.
A superconducting MRI apparatus 30 shown in FIG. 2 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 the generated magnetic field inhomogeneity. 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.
[0071]
In the superconducting MRI apparatus 30 using the regenerative refrigerator 34 according to the present invention, the operating temperature of the superconducting static magnetic field coil 31 can be assured stably over a long period of time. 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.
[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 portion of a superconducting magnet 40 for a magnetic levitation train. A 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 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.
[0073]
In the superconducting magnet 40 for a magnetically levitated train using the regenerative refrigerator 44 according to the present invention, the operating temperature of the superconducting coil 41 can be assured stably over a long period of time. A necessary magnetic field can be stably obtained over a long period of time. In particular, the superconducting magnet 40 for a magnetic levitation train acts on acceleration, but the regenerative refrigerator 44 according to the present invention can maintain excellent refrigeration capacity over a long period of time even when acceleration acts, so that the magnetic field strength, etc. 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 cross-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 that condenses or adsorbs gas molecules, a regenerative refrigerator 52 according to the present invention that cools 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 or 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 exhibited stably 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. A magnetic field application type single crystal pulling apparatus 60 shown in FIG. 5 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. Then, as described above, the regenerative refrigerator 64 according to the present invention 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.
[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 guaranteed over a long period of time. A good magnetic field that suppresses the 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.
[0078]
【The invention's effect】
As described above, according to the regenerator material according to the present invention, a rare earth oxysulfide-based magnetic material (R) having a steep volume specific heat peak in an extremely low temperature range.₂O₂Therefore, 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 cold storage material with good specific heat characteristics is obtained. And, by filling the cold storage material on the low temperature end side in 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 over 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 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 of the present invention can all exhibit excellent performance over a long period of time.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a main configuration of a regenerative refrigerator (GM refrigerator) according to the present invention.
FIG. 2 is a cross-sectional view showing a schematic configuration of a superconducting MRI apparatus according to an 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 cross-sectional view showing a schematic configuration of a cryopump according to an 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 type refrigerator)
11 First cylinder
12 Second cylinder
13 Vacuum container
14 1st regenerator
15 Second regenerator
16, 17 Seal ring
18 First heat storage material
19 Second heat storage material (cold storage material for cryogenic temperature)
20 First expansion chamber
21 Second expansion chamber
22 First cooling stage
23 Second cooling stage
24 Compressor
30 Superconducting MRI system
31 Superconducting static magnetic field coil
32 Gradient coil
33 Probe for radio wave transmission / reception
34 Regenerative refrigerator
35 Cryostat
36 Radiation insulation shield
40 Superconducting 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 application type single crystal pulling device
61 Single crystal pulling part
62 Superconducting coil
63 Lifting mechanism
64 Cold storage type refrigerator
65 Current lead
66 Heat shield plate
67 Helium container

Claims (13)

Sulfur components are replenished by a step of heat treating magnetic compound particles made of rare earth oxysulfide at a temperature of 900 to 1200 ° C. for 1 to 12 hours in a sulfur oxide atmosphere, and a light beam having a wavelength of 400 to 600 nm. Is a regenerator material comprising a sintered body of rare earth oxysulfide having a minimum reflectance of 44 % or more and 95% or less when irradiated with the rare earth oxysulfide,
General formula: R _{2 ± 0.1} O ₂ S _{1 ± 0.1}
(Wherein R represents at least one rare earth element selected from Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er), and the regenerator material is magnetic. The magnetic compound particles have a particle diameter of 0.01 to 3 mm, and the ratio of the major axis to the minor axis (aspect ratio) is 5 with respect to all the magnetic compound particles constituting the cold storage material. And a ratio of the magnetic compound particles having a particle diameter of 0.01 mm to 3 mm is 70% by mass or more, and the surface of the magnetic compound particles is polished. . The regenerator material according to claim 1, wherein the rare earth oxysulfide is
General formula: R ₂ O ₂ S
(In the formula, R represents at least one rare earth element selected from Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er.) Wood.   The regenerator material according to claim 2, wherein the R component in the general formula is gadolinium (Gd).   A step of preparing magnetic compound particles made of rare earth oxysulfide, a step of polishing the magnetic compound particles into a spherical shape, and the spherical magnetic compound particles at a temperature of 900 to 1200 in a sulfur oxide atmosphere. And a step of heat-treating at 1 ° C. for 1 to 12 hours.   There are a plurality of cooling stages composed of regenerators filled with regenerator material, and the working medium is flowed from the upstream high temperature side of the regenerators of each cooling stage to the downstream side of the regenerator by heat exchange between the working medium and the regenerator material. The regenerator material according to any one of claims 1 to 3, wherein 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 type refrigerator having a lower temperature. A regenerator type freezer comprising:   A superconducting magnet comprising the regenerative refrigerator according to claim 5.   An MRI (nuclear magnetic resonance imaging) apparatus comprising the regenerative refrigerator according to claim 5.   A cryopump comprising the regenerative refrigerator according to claim 5.   A magnetic field application type single crystal pulling apparatus comprising the regenerator type refrigerator according to claim 5.   The regenerator material according to claim 1, wherein a surface roughness of the polished magnetic compound particles is Rmax of 10 μm or less.   The regenerator material according to claim 1, wherein the minimum value of reflectance when irradiated with light having a wavelength of 400 to 600 nm is 460 nm.   The regenerator material according to claim 1, wherein the minimum value of the reflectance when irradiated with light having a wavelength of 400 to 600 nm is in the range of 50% to 90%. In the manufacturing method of the cool storage material of Claim 4, the said rare earth oxysulfide is,
General formula: R _{2 ± 0.1} O ₂ S _{1 ± 0.1}
(In the formula, R represents at least one rare earth element selected from Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er.) A method of manufacturing the material.

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