Cold storage particle, cold storage particle group, regenerator, refrigerator, cryopump, superconducting magnet, nuclear magnetic resonance imaging apparatus, nuclear magnetic resonance apparatus, magnetic field application-type single crystal pulling-out apparatus, and helium recondensing apparatus

Abstract

A cold storage particle of an embodiment including: at least one first element selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu); nickel (Ni); at least one second element selected from the group consisting of silicon (Si) and germanium (Ge); a SmNiGe3-type crystal phase; and at least one of a CeNiSi2-type crystal phase and a CaF2-type crystal phase.

Description

COLD STORAGE PARTICLE, COLD STORAGE PARTICLE GROUP, REGENERATOR, REFRIGERATOR, CRYOPUMP, SUPERCONDUCTING MAGNET, NUCLEAR MAGNETIC RESONANCE IMAGING APPARATUS, NUCLEAR MAGNETIC RESONANCE APPARATUS, MAGNETIC FIELD APPLICATION-TYPE SINGLE CRYSTAL PULLING-OUT APPARATUS, AND HELIUM RECONDENSING APPARATUS

[0001] Embodiments of the present invention relate to a cold storage particle, a cold storage particle group, a regenerator, a refrigerator, a cryopump, a superconducting magnet, a nuclear magnetic resonance imaging apparatus, a nuclear magnetic resonance apparatus, a magnetic field application-type single crystal pulling-out apparatus, and a helium recondensing apparatus.

[0002] In recent years, superconducting technologies have remarkably developed, and expansion of application fields of the superconducting technologies has led to an indispensable demand for development of small and high-performance cryogenic refrigerators. Cryogenic refrigerators need to be lightweight, compact, and highly thermally efficient. Cryogenic refrigerators have been put into practical use in various application fields.

[0003] A cryogenic refrigerator includes a regenerator filled with a plurality of cold storage particles. For example, cooling is performed by heat exchange between the cold storage particles and helium gas passing through the regenerator.

[0004] Examples of the cold storage particles include magnetic cold storage particles containing a rare-earth element and a metal. An example of the magnetic cold storage particles containing a rare-earth element and a metal includes HoCu2. In order to improve the performance of a cryogenic refrigerator, realization of cold storage particles having good specific heat characteristics is anticipated.

[0005] WO 2022 / 224783

[0006] Fabiana R. Arantes et al., ”Structure, magnetism, and transport of single-crystalline RNiSi3 (R=Y,Gd-Tm,Lu)”, Physical Review Materials 2,044402(2018)

[0007] An object of the present invention is to provide a cold storage particle having good specific heat characteristics.

[0008] There is provided a cold storage particle of an embodiment including: nickel (Ni); at least one first element selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu); at least one second element selected from the group consisting of silicon (Si) and germanium (Ge); a SmNiGe3-type crystal phase; and at least one of a CeNiSi2-type crystal phase or a CaF2-type crystal phase.

[0009] FIG. 1 is a schematic cross-sectional view of a cold storage particle of a first embodiment.FIG. 2 is a schematic cross-sectional view of a cold storage particle of a second embodiment.FIG. 3 is a schematic cross-sectional view of a cold storage particle of a modification example of the second embodiment.FIG. 4 is a schematic cross-sectional view illustrating a configuration of a main part of a refrigerator of a fourth embodiment.FIG. 5 is a cross-sectional view illustrating a schematic configuration of a cryopump of a fifth embodiment.FIG. 6 is a perspective view illustrating a schematic configuration of a superconducting magnet of a sixth embodiment.FIG. 7 is a cross-sectional view illustrating a schematic configuration of a nuclear magnetic resonance imaging apparatus of a seventh embodiment.FIG. 8 is a cross-sectional view illustrating a schematic configuration of a nuclear magnetic resonance apparatus of an eighth embodiment.FIG. 9 is a perspective view illustrating a schematic configuration of a magnetic field application-type single crystal pulling-out apparatus of a ninth embodiment.FIG. 10 is a schematic view illustrating a schematic configuration of a helium recondensing apparatus of a tenth embodiment.

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same or similar members and the like are denoted by the same reference numerals, and the description of the members and the like which have been described once may be appropriately omitted.

[0011] In the present specification, a cryogenic temperature is, for example, a temperature range in which a superconducting phenomenon can be industrially used. The cryogenic temperature is, for example, in a temperature range of 25 K or lower.

[0012] (First Embodiment) A cold storage particle of a first embodiment includes at least one first element selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu); nickel (Ni); at least one second element selected from the group consisting of silicon (Si) and germanium (Ge); a SmNiGe3-type crystal phase; and at least one of a CeNiSi2-type crystal phase or a CaF2-type crystal phase.

[0013] FIG. 1 is a schematic cross-sectional view of a cold storage particle of the first embodiment. A cold storage particle 100 of the first embodiment is a magnetic cold storage particle containing a rare-earth element and a metal.

[0014] As illustrated in FIG. 1, the cold storage particle 100 is polycrystalline. The cold storage particle 100 contains a plurality of crystal grains. The plurality of crystal grains include first crystal grains 10a, second crystal grains 10b, and third crystal grains 10c. A grain boundary phase may be present between the plurality of crystal grains.

[0015] The cold storage particle 100 includes a SmNiGe3-type crystal phase. The cold storage particle 100 includes at least one of a CeNiSi2-type crystal phase or a CaF2-type crystal phase. The cold storage particle 100 may include only one of the CeNiSi2-type crystal phase and the CaF2-type crystal phase. The cold storage particle 100 may include both the CeNiSi2-type crystal phase and the CaF2-type crystal phase.

[0016] For example, the first crystal grain 10a has the SmNiGe3-type crystal phase. For example, the second crystal grain 10b has the CeNiSi2-type crystal phase. For example, the third crystal grain 10c has the CaF2-type crystal phase.

[0017] For example, of the crystal phases included in the cold storage particle 100, the SmNiGe3-type crystal phase is a main crystal phase. The fact that the SmNiGe3-type crystal phase is the main crystal phase means that a percentage of the SmNiGe3-type crystal phase in the cold storage particle 100 is higher than percentages of the other crystal phases. The percentage of the SmNiGe3-type crystal phase in the cold storage particle 100 is preferably 30% or higher, and more preferably 50% or higher.

[0018] Whether or not the cold storage particle 100 includes the SmNiGe3-type crystal phase, the CeNiSi2-type crystal phase, or the CaF2-type crystal phase can be identified by powder X-ray diffraction (PXRD). In addition, whether or not the SmNiGe3-type crystal phase is the main crystal phase of the crystal phases included in the cold storage particle 100 can be determined, for example, by comparing peak intensities of crystal phases obtained by powder X-ray diffraction. In addition, a weight proportion of a crystal phase present in a sample is analyzed by Rietveld analysis of a diffraction pattern obtained by XRD, and whether or not the SmNiGe3-type crystal phase is the main crystal phase can be determined by comparing values obtained through the analysis.

[0019] In addition, whether or not the SmNiGe3-type crystal phase is the main crystal phase of the crystal phases included in the cold storage particle 100 can be determined, for example, by observing a backscattered electron image of a cross section of the cold storage particle 100 with a scanning electron microscope (SEM). For example, the determination can be made by comparing an occupied area of the crystal grains identified as the SmNiGe3-type crystal phase on the backscattered electron image with an occupied area of other crystal grains by using image processing software. Whether or not a crystal grain is the SmNiGe3-type crystal phase can be determined by, for example, energy dispersive X-ray spectroscopy (EDX).

[0020] The cold storage particle 100 contains at least one first element selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). The first elements are rare-earth elements.

[0021] The cold storage particle 100 contains at least one second element selected from the group consisting of silicon (Si) and germanium (Ge).

[0022] A chemical composition of the SmNiGe3-type crystal phase included in the cold storage particle 100 can be represented as, for example, R1±xNi1±x(SiyGe1-y)3±x(R represents at least one rare-earth element selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu), 0 ≦ x ≦ 0.5, and 0 ≦ y ≦ 1). The chemical composition of the SmNiGe3-type crystal phase included in the cold storage particle 100 is, for example, HoNiSi3or HoNiGe3.

[0023] A chemical composition of the CeNiSi2-type crystal phase included in the cold storage particle 100 can be represented as, for example, R1±xNi1±x(SiyGe1-y)2±x(R represents at least one rare-earth element selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu), 0 ≦ x ≦ 0.5, and 0 ≦ y ≦ 1). The chemical composition of the CeNiSi2-type crystal phase included in the cold storage particle 100 is, for example, HoNiSi2or HoNiGe2.

[0024] The chemical composition of the CaF2-type crystal phase included in the cold storage particle 100 is, for example, Ni1±xSi2±x(0 ≦ x ≦ 0.5).

[0025] Detection of an element contained in the cold storage particle 100 and measurement of an atomic concentration of the element can be performed by using, for example, inductively coupled plasma atomic emission spectroscopy (ICP-AES). For example, the cold storage particles 100 are dissolved in a liquid, and the dissolved cold storage particles 100 are measured by inductively coupled plasma atomic emission spectroscopy.

[0026] Detection of an element contained in the cold storage particle 100, the first crystal grain 10a, the second crystal grain 10b, or the third crystal grain 10c, and measurement of an atomic concentration of the element can be performed by using, for example, energy dispersive X-ray spectroscopy (EDX) or wave dispersive spectroscopy (WDX).

[0027] A peak intensity of a peak corresponding to a (131) plane of the SmNiGe3-type crystal phase obtained from the cold storage particle 100 by powder X-ray diffraction is defined as a first peak intensity (Ia), a peak intensity of a peak corresponding to a (131) plane of the CeNiSi2-type crystal phase is defined as a second peak intensity (Ib), and a peak intensity of a peak corresponding to a (111) plane of the CaF2-type crystal phase obtained by powder X-ray diffraction is defined as a third peak intensity (Ic). A ratio ((Ib + Ic) / Ia) of a sum of the second peak intensity (Ib) and the third peak intensity (Ic) to the first peak intensity (Ia) is equal to or higher than 0.01 and equal to or lower than 0.3.

[0028] When the cold storage particle 100 is measured by powder X-ray diffraction, for example, the cold storage particle 100 is pulverized in an agate mortar. Then, powder that has passed through a 500 mesh sieve is used as a measurement sample.

[0029] A particle size of the cold storage particles 100 is, for example, equal to or larger than 50 μm and equal to or smaller than 3 mm. A shape of the cold storage particle 100 is, for example, spherical.

[0030] In the present specification, the particle size of the cold storage particle is an equivalent circle diameter. The equivalent circle diameter is a diameter of a true circle corresponding to an area of a figure observed in an image such as an optical microscope image or a scanning electron microscope image. The particle size of the cold storage particle can be obtained, for example, by image analysis of the optical microscope image or the scanning electron microscope image.

[0031] When a perimeter of a projection image of the cold storage particle 100 is denoted by L and an actual area of the projection image is denoted by A, a circularity R represented by 4πA / L2is higher than 0.5. The circularity R of the cold storage particle 100 can be obtained, for example, by the image analysis of the optical microscope image or the scanning electron microscope image.

[0032] An aspect ratio of the cold storage particle 100 is, for example, equal to or higher than 1 and equal to or lower than 5. The aspect ratio of the cold storage particle 100 is a ratio of the major axis to the minor axis of the cold storage particle 100. The aspect ratio of the cold storage particle 100 can be obtained, for example, by the image analysis of the optical microscope image or the scanning electron microscope image.

[0033] A maximum value of volumetric specific heat of the cold storage particle 100 in a temperature range of 25 K or lower is equal to or larger than 0.38 J / (cm3K).

[0034] Next, an example of a method for manufacturing the cold storage particles of the first embodiment will be described. Hereinafter, a case where the first element is holmium (Ho) and the second element is silicon (Si) will be described as an example.

[0035] First, a HoNiSi3master alloy is prepared by high-frequency induction dissolution. Next, the HoNiSi3master alloy is melted, and the melted alloy is dropped on a rotating disk in an argon atmosphere and is rapidly solidified. The cold storage particles are manufactured through the rapid solidification of the melted alloy.

[0036] A cooling rate of the melted alloy can be controlled by controlling a rotation speed of the rotating disk. For example, the cooling rate of the melted alloy can be increased by increasing the rotation speed of the rotating disk. In addition, for example, the cooling rate of the melted alloy can be decreased by decreasing the rotation speed of the rotating disk.

[0037] A ratio ((Ib + Ic) / Ia) of a sum of the second peak intensity and the third peak intensity to the first peak intensity of the manufactured cold storage particle can be controlled to a desired value by controlling the cooling rate of the melted alloy. For example, the ratio ((Ib + Ic) / Ia) can be decreased by increasing the cooling rate of the melted alloy. In addition, the ratio ((Ib + Ic) / Ia) can be increased by decreasing the cooling rate of the melted alloy.

[0038] The cold storage particles 100 of the first embodiment can be manufactured by the above-described manufacturing method.

[0039] The cold storage particle 100 of the first embodiment includes the SmNiGe3-type crystal phase and includes the first element, nickel (Ni), and the second element. A chemical composition of the SmNiGe3-type crystal phase included in the cold storage particle 100 can be represented as, for example, RNi(SixGe1-x)3(R represents at least one rare-earth element selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu), and 0 ≦ x ≦ 1).

[0040] The cold storage particle 100 of the first embodiment can realize, for example, higher volumetric specific heat than HoCu2can.

[0041] In addition, in the cold storage particle 100 of the first embodiment, for example, an atomic proportion of the contained rare-earth elements is smaller than that in HoCu2. Since the atomic proportion of the expensive rare-earth elements is small, manufacturing costs of the cold storage particle 100 can be reduced.

[0042] The cold storage particle having the circularity R equal to or lower than 0.5 has, for example, unevenness on a surface thereof. For example, when a regenerator of a refrigerator is filled with the cold storage particles having the unevenness on the surfaces thereof, a void fraction in the regenerator becomes non-uniform, or fillability in the regenerator becomes unstable. Therefore, for example, when a working medium flows into the regenerator, the cold storage performance of the regenerator deteriorates.

[0043] In addition, for example, due to stress applied to the cold storage particles at the time of filling of the cold storage particles or at the time of operating the refrigerator, the cold storage particles are moved, or the cold storage particles are broken to form fine particles that may clog voids in the regenerator. The clogging of the voids degenerates refrigeration performance or long-term reliability of the refrigerator.

[0044] Hence, the cold storage particles with which the regenerator is filled are preferably spherical. In other words, the circularity R of the cold storage particles 100 is preferably high, and the circularity R is preferably approximate to 1. The circularity R of the cold storage particles 100 is preferably higher than 0.5, more preferably equal to or higher than 0.7, and still more preferably equal to or higher than 0.9.

[0045] In the cold storage particle 100 of the first embodiment, the peak intensity of the peak corresponding to the (131) plane of the SmNiGe3-type crystal phase obtained by powder X-ray diffraction is defined as the first peak intensity (Ia), the peak intensity of the peak corresponding to the (131) plane of the CeNiSi2-type crystal phase is defined as the second peak intensity (Ib), and the peak intensity of the peak corresponding to the (111) plane of the CaF2-type crystal phase obtained by powder X-ray diffraction is defined as the third peak intensity (Ic). The ratio ((Ib + Ic) / Ia) of the sum of the second peak intensity and the third peak intensity to the first peak intensity is equal to or higher than 0.01 and equal to or lower than 0.3.

[0046] When the ratio ((Ib + Ic) / Ia) is equal to or higher than 0.01 and equal to or lower than 0.3, it is easy to form the cold storage particles 100 into spherical particles. When the ratio ((Ib + Ic) / Ia) is equal to or higher than 0.01 and equal to or lower than 0.3, it is easy to increase the circularity R of the cold storage particles 100. When the ratio ((Ib + Ic) / Ia) is equal to or higher than 0.01 and equal to or lower than 0.3, it is easy to have the circularity R of the cold storage particles 100 which is approximate to 1.

[0047] The maximum value of the volumetric specific heat of the cold storage particles 100 in the temperature range of 25 K or lower is preferably equal to or larger than 0.38 J / (cm3K), more preferably equal to or larger than 0.4 J / (cm3K), and still more preferably equal to or larger than 0.45 J / (cm3K).

[0048] A cold storage particle group can include the cold storage particles 100 of the first embodiment in a particle number percentage equal to or higher than 90%.

[0049] As described above, according to the first embodiment, it is possible to provide the cold storage particles having good specific heat characteristics. In addition, according to the first embodiment, it is possible to provide the cold storage particles which are easily formed into spherical particles.

[0050] (Second Embodiment) A cold storage particle of the second embodiment includes nickel (Ni); at least one first element selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu); at least one second element selected from the group consisting of silicon (Si) and germanium (Ge); a SmNiGe3-type crystal phase; and a first phase in which an atomic concentration of the second elements is higher than 70 at%. The cold storage particle of the second embodiment differs from the cold storage particle of the first embodiment in that the phase in which the atomic concentration of the at least one second element is higher than 70 at% is included. Hereinafter, the repeated descriptions of the details described in the first embodiment may be partially omitted.

[0051] FIG. 2 is a schematic cross-sectional view of the cold storage particle of the second embodiment. Cold storage particles 200 of the second embodiment are a magnetic cold storage material containing a rare-earth element and a metal.

[0052] As illustrated in FIG. 2, the cold storage particles 200 are polycrystalline. The cold storage particle 200 includes a plurality of crystal grains. The plurality of crystal grains include first crystal grains 10a. In addition, the cold storage particle 200 includes grains 10x.

[0053] The cold storage particle 200 includes a SmNiGe3-type crystal phase. For example, the first crystal grain 10a has the SmNiGe3-type crystal phase.

[0054] For example, of the crystal phases included in the cold storage particle 200, the SmNiGe3-type crystal phase is a main crystal phase. The fact that the SmNiGe3-type crystal phase is the main crystal phase means that a percentage of the SmNiGe3-type crystal phase in the cold storage particle 200 is higher than percentages of the other crystal phases. The percentage of the SmNiGe3-type crystal phase in the cold storage particle 100 is preferably 30% or higher, and more preferably 50% or higher.

[0055] Whether or not the cold storage particle 200 includes the SmNiGe3-type crystal phase can be identified by powder X-ray diffraction. In addition, whether or not the SmNiGe3-type crystal phase is the main crystal phase of the crystal phases included in the cold storage particle 200 can be determined, for example, by comparing peak intensities of crystal phases obtained by powder X-ray diffraction.

[0056] In addition, whether or not the SmNiGe3-type crystal phase is the main crystal phase of the crystal phases included in the cold storage particle 200 can be determined, for example, by observing a backscattered electron image of a cross section of the cold storage particle 200 with a scanning electron microscope. For example, the determination can be made by comparing an occupied area of the crystal grains identified as the SmNiGe3-type crystal phase on the backscattered electron image with an occupied area of other crystal grains by using image processing software. Whether or not the crystal grains have the SmNiGe3-type crystal phase can be determined by, for example, the energy dispersive X-ray spectroscopy.

[0057] The cold storage particle 200 includes a first phase in which an atomic concentration of the second elements is higher than 70 at%. The second elements are at least one element selected from the group consisting of silicon (Si) and germanium (Ge). The second element may be only one of silicon (Si) or germanium (Ge). The second element may be both of silicon (Si) and germanium (Ge). For example, the grains 10x have the first phase.

[0058] The first phase is, for example, crystalline or amorphous. The grains 10x are, for example, crystalline or amorphous. The atomic concentration of the second elements contained in the first phase is, for example, equal to or lower than 100 at%. In addition, a second phase and a third phase are, for example, crystalline or amorphous.

[0059] An area percentage of the first phase in a cross section of the cold storage particle 200 is, for example, equal to or higher than 0.01% and equal to or lower than 45%.

[0060] Whether or not the cold storage particle 200 includes the first phase can be determined by using, for example, the energy dispersive X-ray spectroscopy or the wave dispersive spectroscopy.

[0061] In addition, the area percentage of the first phase included in the cold storage particle 200 can be determined, for example, by observing a backscattered electron image of a cross section of the cold storage particle 200 with the scanning electron microscope. For example, an area occupied by grains identified as the first phase in the backscattered electron image is measured using the image processing software. Whether or not the grains have the first phase can be determined by, for example, the energy dispersive X-ray spectroscopy.

[0062] The cold storage particle 200 contains at least one first element selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). The first elements are rare-earth elements.

[0063] The cold storage particle 200 contains at least one second element selected from the group consisting of silicon (Si) and germanium (Ge).

[0064] A chemical composition of the SmNiGe3-type crystal phase included in the cold storage particle 200 can be represented as, for example, RNi(SixGe1-x)3(R represents at least one rare-earth element selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu), and 0 ≦ x ≦ 1). The chemical composition of the SmNiGe3-type crystal phase included in the cold storage particle 200 is, for example, HoNiSi3or HoNiGe3.

[0065] Detection of an element contained in the cold storage particle 200 and measurement of an atomic concentration of the element can be performed by using, for example, inductively coupled plasma atomic emission spectroscopy. For example, the cold storage particles 200 are dissolved in a liquid, and the dissolved cold storage particles 200 are measured by inductively coupled plasma atomic emission spectroscopy.

[0066] Detection of an element contained in the cold storage particle 200, the first crystal grain 10a, or the grain 10x, and measurement of an atomic concentration of the element can be performed by using, for example, energy dispersive X-ray spectroscopy or wave dispersive spectroscopy.

[0067] A particle size of the cold storage particles 200 is, for example, equal to or larger than 50 μm and equal to or smaller than 3 mm. A shape of the cold storage particle 200 is, for example, spherical.

[0068] When a perimeter of a projection image of the cold storage particles 200 is denoted by L and an actual area of the projection image is denoted by A, a circularity R represented by 4πA / L2is higher than 0.5.

[0069] The aspect ratio of the cold storage particle 200 is, for example, equal to or higher than 1 and equal to or lower than 5.

[0070] A maximum value of volumetric specific heat of the cold storage particles 200 in a temperature range of 25 K or lower is equal to or larger than 0.38 J / (cm3K).

[0071] Next, an example of a method for manufacturing the cold storage particles of the second embodiment will be described. Hereinafter, a case where the first element is holmium (Ho) and the second element is silicon (Si) will be described as an example.

[0072] First, a HoNiSi3master alloy is prepared by high-frequency induction dissolution. Next, the HoNiSi3master alloy is melted, and the melted alloy is dropped on a rotating disk in an argon atmosphere and is rapidly solidified. The cold storage particles are manufactured through the rapid solidification of the melted alloy.

[0073] A cooling rate of the melted alloy can be controlled by controlling a rotation speed of the rotating disk. For example, the cooling rate of the melted alloy can be increased by increasing the rotation speed of the rotating disk. In addition, for example, the cooling rate of the melted alloy can be decreased by decreasing the rotation speed of the rotating disk.

[0074] The area percentage of the first phase in the manufactured cold storage particle can be controlled to a desired value by controlling the cooling rate of the melted alloy. For example, the area percentage of the first phase can be decreased by increasing the cooling rate of the melted alloy. For example, the area percentage of the first phase can be increased by decreasing the cooling rate of the melted alloy.

[0075] The cold storage particles 200 of the second embodiment can be manufactured by the above-described manufacturing method.

[0076] The cold storage particle 200 of the second embodiment includes the SmNiGe3-type crystal phase and includes the first element, nickel (Ni), and the second element. A chemical composition of the SmNiGe3-type crystal phase included in the cold storage particle 200 can be represented as, for example, RNi(SixGe1-x)3(R represents at least one rare-earth element selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu), and 0 ≦ x ≦ 1).

[0077] The cold storage particle 200 of the second embodiment can realize, for example, higher volumetric specific heat than HoCu2can.

[0078] In addition, in the cold storage particle 200 of the second embodiment, for example, an atomic proportion of the contained rare-earth elements is smaller than that in HoCu2. Since the atomic proportion of the expensive rare-earth elements is small, manufacturing costs of the cold storage particle 200 can be reduced.

[0079] The cold storage particle having the circularity R equal to or lower than 0.5 has, for example, unevenness on a surface thereof. For example, when a regenerator of a refrigerator is filled with a plurality of cold storage particles of which the cold storage particles having the unevenness on the surfaces thereof are more than 5%, a void fraction in the regenerator becomes non-uniform, or fillability becomes unstable. Therefore, for example, when a working medium flows into the regenerator, the cold storage performance of the regenerator deteriorates.

[0080] In addition, for example, due to stress applied to the cold storage particles at the time of filling of the cold storage particles or at the time of operating the refrigerator, the cold storage particles are moved, or the cold storage particles are broken to form fine particles that may clog voids in the regenerator. The clogging of the voids degenerates refrigeration performance or long-term reliability of the refrigerator.

[0081] Hence, the cold storage particles with which the regenerator is filled are preferably spherical. In other words, the circularity R of the cold storage particles 200 is preferably high, and the circularity R is preferably approximate to 1. The circularity R of the cold storage particles 200 is preferably higher than 0.5, more preferably equal to or higher than 0.7, and still more preferably equal to or higher than 0.9.

[0082] In the cold storage particle 200 of the second embodiment, the area percentage of the first phase in which the atomic concentration of the second elements is higher than 70 at% is preferably equal to or higher than 0.01% and equal to or lower than 45%.

[0083] When the area percentage of the first phase is equal to or higher than 0.01% and equal to or lower than 45%, it is easy to form the cold storage particles 200 into spherical particles. When the area percentage of the first phase is equal to or higher than 0.01% and equal to or lower than 45%, it is easy to increase the circularity R of the cold storage particles 200. When the area percentage of the first phase is equal to or higher than 0.01% and equal to or lower than 45%, it is easy to have the circularity R of the cold storage particles 200 which is approximate to 1.

[0084] From the viewpoint of forming the cold storage particles 200 into spherical particles, the area percentage of the first phase is more preferably equal to or higher than 0.1% and equal to or lower than 30%, and still more preferably equal to or higher than 1% and equal to or lower than 20%.

[0085] From the viewpoint of making the cold storage particles 200 into the spherical particles, the atomic concentration of the second elements contained in the first phase is more preferably equal to or higher than 75%.

[0086] The maximum value of the volumetric specific heat of the cold storage particles 200 in the temperature range of 25 K or lower is preferably equal to or larger than 0.4 J / (cm3K), and more preferably equal to or larger than 0.5 J / (cm3K).

[0087] (Modification Example) A cold storage particle of a modification example of the second embodiment differs from the cold storage particle of the second embodiment in that at least one of a CeNiSi2-type crystal phase or a CaF2-type crystal phase is included.

[0088] FIG. 3 is a schematic cross-sectional view of the cold storage particle of the modification example of the second embodiment. cold storage particles 210 of the modification example of the second embodiment are a magnetic cold storage material containing a rare-earth element and a metal.

[0089] As illustrated in FIG. 3, the cold storage particles 210 may be polycrystalline. In the case of the polycrystalline cold storage particle, the cold storage particle 210 includes a plurality of crystal grains. The plurality of crystal grains include first crystal grains 10a, second crystal grains 10b, and third crystal grains 10c. In addition, the cold storage particle 210 includes grains 10x.

[0090] The cold storage particle 210 includes a SmNiGe3-type crystal phase. The cold storage particle 210 includes at least one of a CeNiSi2-type crystal phase or a CaF2-type crystal phase. The cold storage particle 210 may include only one of the CeNiSi2-type crystal phase and the CaF2-type crystal phase. The cold storage particle 210 may include both the CeNiSi2-type crystal phase and the CaF2-type crystal phase.

[0091] For example, the first crystal grain 10a has the SmNiGe3-type crystal phase. For example, the second crystal grain 10b has the CeNiSi2-type crystal phase. For example, the third crystal grain 10c has the CaF2-type crystal phase.

[0092] The cold storage particle 210 includes a first phase in which an atomic concentration of the second elements is higher than 70 at%. The second elements are at least one element selected from the group consisting of silicon (Si) and germanium (Ge). For example, the grains 10x have the first phase.

[0093] The cold storage particle 210 of the modification example of the second embodiment has the same effects as the cold storage particle 200 of the second embodiment.

[0094] A cold storage particle group can include the cold storage particles 200 of the second embodiment in a particle number percentage equal to or higher than 90%.

[0095] As described above, according to the second embodiment and the modification example, it is possible to provide the cold storage particles having good specific heat characteristics. In addition, according to the second embodiment and the modification example, it is possible to provide the cold storage particles which are easily formed into spherical particles.

[0096] (Third Embodiment) A regenerator of a third embodiment is a regenerator filled with a plurality of the cold storage particles of the first or second embodiment. In the regenerator of the third embodiment, for example, when the perimeter of the projection image of the plurality of filled cold storage particles of the first or second embodiment is denoted by L and the actual area of the projection image is denoted by A, a percentage of the cold storage particles having the circularity R equal to or lower than 0.5 which is represented by 4πA / L2is equal to or lower than 5%.

[0097] The circularity R can be obtained by performing image processing on the shapes of the plurality of cold storage particles in an image obtained using an optical microscope. The cold storage particle having the circularity R equal to or lower than 0.5 has, for example, unevenness on a surface thereof.

[0098] For example, when the regenerator is filled with a plurality of cold storage particles of which the cold storage particles having the unevenness on the surfaces thereof are more than 5%, a void fraction in the regenerator becomes non-uniform, or fillability in the regenerator becomes unstable. Therefore, for example, when a working medium flows into the regenerator, the cold storage performance of the regenerator is deteriorated.

[0099] In addition, for example, due to stress applied to the cold storage particles at the time of filling of the cold storage particles or at the time of operating the refrigerator, the cold storage particles are moved, or the cold storage particles are broken to form fine particles that may clog voids in the regenerator. The clogging of the voids degenerates refrigeration performance or long-term reliability of the refrigerator.

[0100] Hence, the cold storage particles having the circularity R equal to or lower than 0.5 with which the regenerator is filled is preferably equal to or lower than 2%, and more preferably 0%.

[0101] As described above, according to the third embodiment, it is possible to realize the regenerator having good characteristics by using the cold storage particles having good characteristics.

[0102] (Fourth Embodiment) A refrigerator of a fourth embodiment is a refrigerator including the regenerator of the third embodiment filled with a plurality of the cold storage particles of the first or second embodiment. Hereinafter, the repeated descriptions of the details described in the first, second, and third embodiments are partially omitted.

[0103] FIG. 4 is a schematic cross-sectional view illustrating a configuration of a main part of the refrigerator of the fourth embodiment. FIG. 4 is a schematic cross-sectional view illustrating a configuration of a main part of a GM refrigerator which is an example of the refrigerator of the fourth embodiment. The GM refrigerator which is an example of the refrigerator of the fourth embodiment includes the regenerator of the third embodiment filled with the plurality of cold storage particles of the first or second embodiment.

[0104] The refrigerator of the fourth embodiment is a two-stage regenerative cryogenic refrigerator 300 used for cooling a superconducting machine or the like. The refrigerator may be, for example, a Stirling refrigerator or a pulse tube refrigerator.

[0105] The regenerative cryogenic refrigerator 300 (refrigerator) includes a first cylinder 111, a second cylinder 112, a vacuum container 113, a first regenerator 114, a second regenerator 115 (regenerator), a first seal ring 116, a second seal ring 117, a first cold storage material 118, a second cold storage material 119 (cold storage particles), a first expansion chamber 120, a second expansion chamber 121, a first cooling stage 122, a second cooling stage 123, and a compressor 124.

[0106] The regenerative cryogenic refrigerator 300 includes the vacuum container 113 in which a first cylinder 111 having a large diameter and a second cylinder 112 having a small diameter which is coaxially connected to the first cylinder 111 are provided. The first regenerator 114 is disposed in the first cylinder 111 to freely perform reciprocating motion. In the second cylinder 112, the second regenerator 115 which is an example of the regenerator of the fourth embodiment is disposed to freely perform reciprocating motion.

[0107] The first seal ring 116 is disposed between the first cylinder 111 and the first regenerator 114. The second seal ring 117 is disposed between the second cylinder 112 and the second regenerator 115.

[0108] The first regenerator 114 is filled with a first cold storage material 118 such as Cu mesh. The second regenerator 115 is filled with a plurality of the cold storage particles of the first or second embodiment as the second cold storage material 119.

[0109] The second regenerator 115 may be divided by a metal mesh material and may include a plurality of cold storage material filling layers. In a case where the second regenerator 115 is divided into a plurality of filling layers, at least one filling layer is filled with a cold storage particle group including a plurality of cold storage particles of the first or second embodiment. Then, for example, a combination with at least one cold storage particle group selected from a rare-earth oxide cold storage particle group, a rare-earth oxysulfide cold storage particle group, a lead cold storage particle group, a bismuth cold storage particle group, a tin cold storage particle group, a holmium copper cold storage particle group, an erbium nickel cold storage particle group, an erbium cobalt cold storage particle group, and a gadolinium aluminum oxide cold storage particle group is used.

[0110] In the combination of the cold storage materials, the one having a higher peak temperature of specific heat is defined as a first cold storage particle group, the one having a lower peak temperature of specific heat is defined as a second cold storage particle group, and the combination is performed so that the peak temperature of specific heat is sequentially lowered.

[0111] The first regenerator 114 and the second regenerator 115 each have a passage of a working medium which is provided in a gap or the like between the first cold storage material 118 and the second cold storage material 119. The working medium is helium gas.

[0112] The first expansion chamber 120 is provided between the first regenerator 114 and the second regenerator 115. In addition, the second expansion chamber 121 is provided between the second regenerator 115 and a distal end wall of the second cylinder 112. The first cooling stage 122 is provided at the bottom of the first expansion chamber 120. In addition, the second cooling stage 123 having a temperature lower than that of the first cooling stage 122 is formed at the bottom of the second expansion chamber 121.

[0113] A high-pressure working medium is supplied from the compressor 124 to the above-described two-stage regenerative cryogenic refrigerator 300. The supplied working medium passes through the first cold storage material 118, with which the first regenerator 114 is filled, and reaches the first expansion chamber 120. Then, the working medium passes through the second cold storage material 119, with which the second regenerator 115 is filled, and reaches the second expansion chamber 121.

[0114] At this time, the working medium is cooled by supplying thermal energy to the first cold storage material 118 and the second cold storage material 119. The working medium passing through the first cold storage material 118 and the second cold storage material 119 expands in the first expansion chamber 120 and the second expansion chamber 121, and cooling is performed. Then, the first cooling stage 122 and the second cooling stage 123 are cooled.

[0115] The expanded working medium flows in an opposite direction through the first cold storage material 118 and the second cold storage material 119. The working medium receives thermal energy from the first cold storage material 118 and the second cold storage material 119 and then is discharged. The regenerative cryogenic refrigerator 300 is configured such that thermal efficiency of the working medium cycle is enhanced as a recuperative effect is improved in such a process, and a lower temperature is realized.

[0116] In the regenerator included in the regenerative cryogenic refrigerator 300 of the fourth embodiment, the second regenerator 115 is filled with the plurality of cold storage particles of the first or second embodiment as the second cold storage material 119. At least a part of the second cold storage material 119 is the cold storage particles of the first or second embodiment.

[0117] Regarding the plurality of cold storage particles of the first or second embodiment, when the perimeter of each projection image of the cold storage particles is denoted by L and the actual area of the projection image is denoted by A, the cold storage particles having the circularity R equal to or lower than 0.5 which is represented by 4πA / L2are preferably equal to or lower than 5%.

[0118] In order to improve the refrigerating capacity of the refrigerator, it is desirable to improve specific heat per unit volume of the cold storage material and improve thermal conductivity and a heat transfer coefficient. The regenerative cryogenic refrigerator 300 of the fourth embodiment includes a cold storage material or cold storage particles which maintain volumetric specific heat and are improved in the thermal conductivity and the thermal conductivity. The regenerative cryogenic refrigerator 300 of the fourth embodiment includes a cold storage material or cold storage particles enabling the manufacturing costs to be reduced.

[0119] For example, by using the regenerative cryogenic refrigerator 300 of the fourth embodiment in a magnetic levitation train, the long-term reliability of the magnetic levitation train can be improved.

[0120] As described above, according to the fourth embodiment, it is possible to realize the refrigerator having good characteristics by using the cold storage particles having good characteristics.

[0121] (Fifth Embodiment) A cryopump of a fifth embodiment includes the refrigerator of the fourth embodiment. Hereinafter, the repeated descriptions of the details described in the fourth embodiment are partially omitted.

[0122] FIG. 5 is a cross-sectional view illustrating a schematic configuration of the cryopump of the fifth embodiment. The cryopump of the fifth embodiment is a cryopump 500 including the regenerative cryogenic refrigerator 300 of the fourth embodiment.

[0123] The cryopump 500 includes a cryopanel 501 that condenses or adsorbs gas molecules, the regenerative cryogenic refrigerator 300 that cools the cryopanel 501 to a predetermined cryogenic temperature, a shield 503 provided between the cryopanel 501 and the regenerative cryogenic refrigerator 300, a baffle 504 provided at an inlet, and a ring 505 that changes an exhaust velocity of argon, nitrogen, hydrogen, or the like.

[0124] According to the fifth embodiment, it is possible to realize the cryopump having good characteristics by using the refrigerator having good characteristics.

[0125] (Sixth Embodiment) A superconducting magnet of a sixth embodiment includes the refrigerator of the fourth embodiment. Hereinafter, the repeated descriptions of the details described in the fourth embodiment are partially omitted.

[0126] FIG. 6 is a perspective view illustrating a schematic configuration of the superconducting magnet of the sixth embodiment. The superconducting magnet of the sixth embodiment is a superconducting magnet 600 for a magnetic levitation train, the superconducting magnet including the regenerative cryogenic refrigerator 300 of the fourth embodiment.

[0127] The superconducting magnet 600 for a magnetic levitation train includes a superconducting coil 601, a liquid helium tank 602 for cooling the superconducting coil 601, a liquid nitrogen tank 603 for preventing liquid helium from volatilizing, a multi-layer insulation material 605, a power lead 606, a permanent current switch 607, and the regenerative cryogenic refrigerator 300.

[0128] According to the sixth embodiment, it is possible to realize the superconducting magnet having good characteristics by using the refrigerator having good characteristics.

[0129] (Seventh Embodiment) A nuclear magnetic resonance imaging apparatus of a seventh embodiment includes the refrigerator of the fourth embodiment. Hereinafter, the repeated descriptions of the details described in the fourth embodiment are partially omitted.

[0130] FIG. 7 is a cross-sectional view illustrating a schematic configuration of the nuclear magnetic resonance imaging apparatus of the seventh embodiment. The nuclear magnetic resonance imaging (MRI) apparatus of the seventh embodiment is a nuclear magnetic resonance imaging apparatus 700 including the regenerative cryogenic refrigerator 300 of the fourth embodiment.

[0131] The nuclear magnetic resonance imaging apparatus 700 includes a superconducting static magnetic field coil 701 that applies a spatially uniform and temporally stable static magnetic field to a human body, a correction coil (not illustrated) that corrects nonuniformity of a generated magnetic field, a gradient magnetic field coil 702 that gives a magnetic field gradient to a measurement region, a radio wave transmission / reception probe 703, a cryostat 705, and a radiation adiabatic shield 706. The regenerative cryogenic refrigerator 300 is used for cooling the superconducting static magnetic field coil 701.

[0132] According to the seventh embodiment, it is possible to realize the nuclear magnetic resonance imaging apparatus having good characteristics by using the refrigerator having good characteristics.

[0133] (Eighth Embodiment) A nuclear magnetic resonance apparatus of an eighth embodiment includes the refrigerator of the fourth embodiment. Hereinafter, the repeated descriptions of the details described in the fourth embodiment are partially omitted.

[0134] FIG. 8 is a cross-sectional view illustrating a schematic configuration of the nuclear magnetic resonance apparatus of the eighth embodiment. The nuclear magnetic resonance (NMR) apparatus of the eighth embodiment is a nuclear magnetic resonance apparatus 800 including the regenerative cryogenic refrigerator 300 of the fourth embodiment.

[0135] The nuclear magnetic resonance apparatus 800 includes a superconducting static magnetic field coil 802 that applies a magnetic field to a sample such as an organic substance placed in a sample tube 801, a high frequency oscillator 803 that applies a radio wave to the sample tube 801 in a magnetic field, and an amplifier 804 that amplifies an induced current generated in a coil (not illustrated) around the sample tube 801. In addition, the nuclear magnetic resonance apparatus 800 includes the regenerative cryogenic refrigerator 300 that cools the superconducting static magnetic field coil 802.

[0136] According to the eighth embodiment, it is possible to realize the nuclear magnetic resonance apparatus having good characteristics by using the refrigerator having good characteristics.

[0137] (Ninth Embodiment) A magnetic field application-type single crystal pulling-out apparatus of a ninth embodiment includes the refrigerator of the fourth embodiment. Hereinafter, the repeated descriptions of the details described in the fourth embodiment are partially omitted.

[0138] FIG. 9 is a perspective view illustrating a schematic configuration of the magnetic field application-type single crystal pulling-out apparatus of the ninth embodiment. The magnetic field application-type single crystal pulling-out apparatus of the ninth embodiment is a magnetic field application-type single crystal pulling-out apparatus 900 including the regenerative cryogenic refrigerator 300 of the fourth embodiment.

[0139] The magnetic field application-type single crystal pulling-out apparatus 900 includes a single crystal pulling-out unit 901 having a raw material melting crucible, a heater, a single crystal pulling-out mechanism, and the like, a superconducting coil 902 that applies a static magnetic field to raw material melt, a lifting-lowering mechanism 903 of the single crystal pulling-out unit 901, a current lead 905, a heat shield plate 906, and a helium container 907. The regenerative cryogenic refrigerator 300 is used for cooling the superconducting coil 902.

[0140] According to the ninth embodiment, it is possible to realize the magnetic field application-type single crystal pulling-out apparatus having good characteristics by using the refrigerator having good characteristics.

[0141] (Tenth Embodiment) A helium recondensing apparatus of a tenth embodiment includes the refrigerator of the fourth embodiment. Hereinafter, the repeated descriptions of the details described in the fourth embodiment are partially omitted.

[0142] FIG. 10 is a schematic view illustrating a schematic configuration of the helium recondensing apparatus of the tenth embodiment. The helium recondensing apparatus of the tenth embodiment is a helium recondensing apparatus 1000 including the regenerative cryogenic refrigerator 300 of the fourth embodiment.

[0143] The helium recondensing apparatus 1000 includes the regenerative cryogenic refrigerator 300, an evaporation pipe 1001, and a liquefaction pipe 1002.

[0144] The helium recondensing apparatus 1000 can recondense helium gas evaporating from a liquid helium apparatus into liquid helium. The liquid helium apparatus is, for example, the superconducting magnet, the nuclear magnetic resonance (NMR) apparatus, the nuclear magnetic resonance imaging (MRI) apparatus, a physical property measurement system (PPMS), or a magnetic property measurement system.

[0145] Helium gas is introduced from the liquid helium apparatus (not illustrated) into the helium recondensing apparatus 1000 through the evaporation pipe 1001. The helium gas is cooled to 4 K equal to or lower than the liquefaction temperature of helium by the regenerative cryogenic refrigerator 300. The condensed and liquefied liquid helium returns to the liquid helium apparatus through the liquefaction pipe 1002.

[0146] According to the tenth embodiment, it is possible to realize the helium recondensing apparatus having good characteristics by using the refrigerator having good characteristics.

[0147] Hereinafter, examples of the embodiments, comparative examples, and evaluation results thereof will be described.

[0148] (Example 1) An HoNiSi3master alloy was prepared by high-frequency induction dissolution. Next, the HoNiSi3master alloy was melted at about 1500°C. Next, the melted alloy was dropped onto a rotating disk in an argon atmosphere at a pressure of about 101 kPa and is rapidly solidified. The rotation speed of the rotating disk was controlled to have a rapid cooling rate of the melted alloy of about 1000°C / s, and the cold storage particles of Example 1 were manufactured.

[0149] In the cold storage particles of Example 1, the first element is holmium (Ho), and the second element is silicon (Si). In addition, in the cold storage particles of Example 1, the first phase is a phase in which the atomic concentration of silicon (Si) is higher than 70 at%.

[0150] The manufactured cold storage particles were measured by powder X-ray diffraction. Rietveld analysis was performed on a diffraction pattern obtained by the measurement. From Rietveld analysis, the ratio ((Ib + Ic) / Ia) of the sum of the second peak intensity and the third peak intensity to the first peak intensity was calculated, in the case of the first peak intensity (Ia) corresponding to the (131) plane of the SmNiGe3-type crystal phase, the second peak intensity (Ib) corresponding to the (131) plane of the CeNiSi2-type crystal phase, and the third peak intensity (Ic) corresponding to the (111) plane of the CaF2-type crystal phase.

[0151] The cold storage particles were pulverized in an agate mortar, and powder having passed through a 500 mesh sieve was used as a measurement sample of powder X-ray diffraction.

[0152] Regarding the manufactured cold storage particles, the area percentage of the first phase was measured. A backscattered electron image of a cross section of the cold storage particle from the scanning electron microscope was observed. An area occupied by grains identified as the first phase in the cross section was measured using the image processing software ImageJ. Whether or not the grains were the first phase was determined by the energy dispersive X-ray spectroscopy.

[0153] The maximum value of the volumetric specific heat of the manufactured cold storage particles was measured. The measurement was performed using a physical property measurement system (PPMS).

[0154] From an optical microscope image of the plurality of manufactured cold storage particles, a percentage of the cold storage particles having the circularity R equal to or lower than 0.5 was measured. For the measurement, the image processing software ImageJ was used.

[0155] The results of the above-described measurement are provided in Table 1. In Table 1, in a case where the percentage of the cold storage particles having the circularity R equal to or lower than 0.5 was equal to or lower than 5%, the spheroidizing of the particles was evaluated as “Good”. In addition, in a case where the percentage of the cold storage particles having the circularity R equal to or lower than 0.5 was higher than 5%, the spheroidizing of the particles was evaluated as “No Good”.

[0156] (Examples 2 to 5) The cold storage particles were manufactured in the same method as in Example 1 except that the rotational speed of the rotating disk was changed to change the rapid cooling rate of the melted alloy. The rotation speed was increased in a case where the rapid cooling rate of the melted alloy was increased, and the rotation speed was decreased when the rapid cooling rate of the melted alloy was decreased.

[0157] The same measurement as in Example 1 was performed. The results are provided in Table 1.

[0158] (Examples 6 to 9) The cold storage particles were manufactured in the same method as in Example 1 except that a dissolution temperature is changed, in addition to the change of the rotational speed of the rotating disk to change the rapid cooling rate of the melted alloy. The rotation speed was increased in a case where the rapid cooling rate of the melted alloy was increased, and the rotation speed was decreased when the rapid cooling rate of the melted alloy was decreased.

[0159] The same measurement as in Example 1 was performed. The results are provided in Table 1.

[0160] (Example 10) The cold storage particles were manufactured in the same method as in Example 1 except that the HoNiGe3master alloy was used.

[0161] In the cold storage particles of Example 10, the first element is holmium (Ho), and the second element is germanium (Ge). In addition, in the cold storage particles of Example 10, the first phase is a phase in which the atomic concentration of germanium (Ge) is higher than 70 at%.

[0162] The same measurement as in Example 1 was performed. The results are provided in Table 1.

[0163] (Example 11) The cold storage particles were manufactured in the same method as in Example 1 except that the GdNiSi3master alloy was used.

[0164] In the cold storage particles of Example 11, the first element is gadolinium (Gd), and the second element is silicon (Si). In addition, in the cold storage particles of Example 11, the first phase is a phase in which the atomic concentration of silicon (Si) is higher than 70 at%.

[0165] The same measurement as in Example 1 was performed. The results are provided in Table 1.

[0166] (Example 12) The cold storage particles were manufactured in the same method as in Example 1 except that the DyNiSi3master alloy was used.

[0167] In the cold storage particles of Example 12, the first element is dysprosium (Dy), and the second element is silicon (Si). In addition, in the cold storage particles of Example 12, the first phase is a phase in which the atomic concentration of silicon (Si) is higher than 70 at%.

[0168] (Comparative Example 1) The cold storage particles were manufactured in the same method as in Example 1 except that the rotational speed of the rotating disk was decreased to decrease the rapid cooling rate of the melted alloy.

[0169] The same measurement as in Example 1 was performed. The results are provided in Table 1.

[0170] (Comparative Example 2) The cold storage particles were manufactured in the same method as in Example 1 except that the rotational speed of the rotating disk was increased to increase the rapid cooling rate of the melted alloy.

[0171] The same measurement as in Example 1 was performed. The results are provided in Table 1.

[0172]

[0173] In all of Examples 1 to 12, the particle size of the cold storage particles having the circularity R equal to or higher than 0.5 was in the range of 50 μm or larger to 3 mm or smaller. In addition, in all of Examples 1 to 12, the aspect ratio of the cold storage particles having the circularity R equal to or higher than 0.5 was in the range of 1 or higher to 5 or lower.

[0174] As is clear from Table 1, in the range in which the ratio ((Ib + Ic) / Ia) of the sum of the second peak intensity and the third peak intensity to the first peak intensity is equal to or higher than 0.01 and equal to or lower than 0.3, the maximum value of the volumetric specific heat is equal to or larger than 0.4. For example, the maximum value of the volumetric specific heat of HoCu2is about 0.4, and the maximum value of the volumetric specific heat larger than HoCu2is obtained in the range in which the ratio ((Ib + Ic) / Ia) is equal to or higher than 0.01 and equal to or lower than 0.3.

[0175] As is clear from Table 1, within the range in which the ratio ((Ib + Ic) / Ia) of the sum of the second peak intensity and the third peak intensity to the first peak intensity is equal to or higher than 0.01 and equal to or lower than 0.3, the percentage of the cold storage particles having the circularity R equal to or lower than 0.5 is equal to or lower than 5%. Hence, in the range in which the ratio ((Ib + Ic) / Ia) is equal to or higher than 0.01 and equal to or lower than 0.3, the spheroidizing of the cold storage particles becomes easy.

[0176] As is clear from Table 1, when the area percentage of the first phase is in the range of 0.01% or higher and 45% or lower, the maximum value of the volumetric specific heat is equal to or larger than 0.4. In the range in which the area percentage of the first phase is equal to or higher than 0.01% and equal to or lower than 45%, the maximum value of the volumetric specific heat larger than that of HoCu2is obtained.

[0177] As is clear from Table 1, in the range in which the area percentage of the first phase is equal to or higher than 0.01% and equal to or lower than 45%, the percentage of the cold storage particles having the circularity R equal to or lower than 0.5 is equal to or lower than 5%. Hence, in the range in which the area percentage of the first phase is equal to or higher than 0.01% and equal to or lower than 45%, the spheroidizing of the cold storage particles becomes easy.

[0178] Although some embodiments of the present invention have been described, these embodiments have been presented as examples, and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. For example, a component of one embodiment may be replaced with or changed into a component of another embodiment. These embodiments and modifications thereof are included in the scope or gist of the invention and are included in the invention described in WHAT IS CLAIMED IS: and the scope of equivalents thereof.

[0179] Hereinafter, technical proposals of the present invention will be described. The following technical proposals are included in the scope of the present invention.

[0180] (Technical Proposal 1) A cold storage particle including: at least one first element selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu); nickel (Ni); at least one second element selected from the group consisting of silicon (Si) and germanium (Ge); a SmNiGe3-type crystal phase; and at least one of a CeNiSi2-type crystal phase and a CaF2-type crystal phase.

[0181] (Technical Proposal 2) The cold storage particle according to Technical Proposal 1, in which, in a case where a peak intensity of a peak corresponding to a (131) plane of the SmNiGe3-type crystal phase obtained by powder X-ray diffraction is defined as a first peak intensity, a peak intensity of a peak corresponding to a (131) plane of the CeNiSi2-type crystal phase obtained by powder X-ray diffraction is defined as a second peak intensity, and a peak intensity of a peak corresponding to a (111) plane of the CaF2-type crystal phase obtained by powder X-ray diffraction is defined as a third peak intensity, a ratio of a sum of the second peak intensity and the third peak intensity to the first peak intensity is equal to or higher than 0.01 and equal to or lower than 0.3.

[0182] (Technical Proposal 3) A cold storage particle including: at least one first element selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu); nickel (Ni); at least one second element selected from the group consisting of silicon (Si) and germanium (Ge); a SmNiGe3-type crystal phase; and a first phase in which an atomic concentration of the at least one second element is higher than 70 at%.

[0183] (Technical Proposal 4) The cold storage particle according to Technical Proposal 3, in which an area percentage of the first phase in a cross section is equal to or higher than 0.01% and equal to or lower than 45%.

[0184] (Technical Proposal 5) The cold storage particle according to any one of Technical Proposals 1 to 4, in which, when a perimeter of a projection image is denoted by L and an actual area of the projection image is denoted by A, a circularity R represented by 4πA / L2is higher than 0.5.

[0185] (Technical Proposal 6) The cold storage particle according to any one of Technical Proposals 1 to 5, in which a particle size is equal to or larger than 50 μm and equal to or smaller than 3 mm.

[0186] (Technical Proposal 7) The cold storage particle according to any one of Technical Proposals 1 to 6, in which a maximum value of volumetric specific heat in a temperature range of 25 K or lower is equal to or larger than 0.38 J / (cm3K).

[0187] (Technical Proposal 8) A cold storage particle group including the cold storage particles according to any one of Technical Proposals 1 to 7 by an amount equal to or higher than 90%.

[0188] (Technical Proposal 9) A regenerator filled with a plurality of the cold storage particles according to any one of Technical Proposals 1 to 7.

[0189] (Technical Proposal 10) A refrigerator including the regenerator according to Technical Proposal 9.

[0190] (Technical Proposal 11) A cryopump including the refrigerator according to Technical Proposal 10.

[0191] (Technical Proposal 12) A superconducting magnet including the refrigerator according to Technical Proposal 10.

[0192] (Technical Proposal 13) A nuclear magnetic resonance imaging apparatus including the refrigerator according to Technical Proposal 10.

[0193] (Technical Proposal 14) A nuclear magnetic resonance apparatus including the refrigerator according to Technical Proposal 10.

[0194] (Technical Proposal 15) A magnetic field application-type single crystal pulling-out apparatus including the refrigerator according to Technical Proposal 10.

[0195] (Technical Proposal 16) A helium recondensing apparatus including the refrigerator according to Technical Proposal 10.

[0196] 100 Cold storage particle 115 Second regenerator (regenerator) 200 Cold storage particle 210 Cold storage particle 300 Regenerative cryogenic refrigerator (refrigerator) 500 Cryopump 600 Superconducting magnet 700 Nuclear magnetic resonance imaging apparatus 800 Nuclear magnetic resonance apparatus 900 Magnetic field application-type single crystal pulling-out apparatus 1000 Helium recondensing apparatus

Claims

1. A cold storage particle comprising: nickel (Ni); at least one first element selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu); at least one second element selected from the group consisting of silicon (Si) and germanium (Ge); a SmNiGe3-type crystal phase; and at least one of a CeNiSi2-type crystal phase or a CaF2-type crystal phase.

2. The cold storage particle according to claim 1, wherein, in a case where a peak intensity of a peak corresponding to a (131) plane of the SmNiGe3-type crystal phase obtained by powder X-ray diffraction is defined as a first peak intensity (Ia), a peak intensity of a peak corresponding to a (131) plane of the CeNiSi2-type crystal phase obtained by powder X-ray diffraction is defined as a second peak intensity (Ib), and a peak intensity of a peak corresponding to a (111) plane of the CaF2-type crystal phase obtained by powder X-ray diffraction is defined as a third peak intensity (Ic), a ratio ((Ib + Ic) / Ia) of a sum of the second peak intensity and the third peak intensity to the first peak intensity is equal to or higher than 0.01 and equal to or lower than 0.3.

3. A cold storage particle comprising: nickel (Ni); at least one first element selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu); at least one second element selected from the group consisting of silicon (Si) and germanium (Ge); a SmNiGe3-type crystal phase; and a first phase in which an atomic concentration of the at least one second element is higher than 70 at%.

4. The cold storage particle according to claim 3, wherein an area percentage of the first phase in a cross section is equal to or higher than 0.01% and equal to or lower than 45%.

5. The cold storage particle according to claim 1 or 3, wherein, when a perimeter of a projection image is denoted by L and an actual area of the projection image is denoted by A, a circularity R represented by 4πA / L2is higher than 0.5.

6. The cold storage particle according to claim 1 or 3, wherein a particle size is equal to or larger than 50 μm and equal to or smaller than 3 mm.

7. The cold storage particle according to claim 1 or 3, wherein a maximum value of volumetric specific heat in a temperature range of 25 K or lower is equal to or larger than 0.38 J / (cm3K).

8. A cold storage particle group comprising the cold storage particle according to claim 1 or 3 by an amount equal to or higher than 90%.

9. A regenerator filled with a plurality of the cold storage particle according to claim 1 or 3.

10. A refrigerator comprising the regenerator according to claim 9.

11. A cryopump comprising the refrigerator according to claim 10.

12. A superconducting magnet comprising the refrigerator according to claim 10.

13. A nuclear magnetic resonance imaging apparatus comprising the refrigerator according to claim 10.

14. A nuclear magnetic resonance apparatus comprising the refrigerator according to claim 10.

15. A magnetic field application-type single crystal pulling-out apparatus comprising the refrigerator according to claim 10.

16. A helium recondensing apparatus comprising the refrigerator according to claim 10.

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