JP2004075884A - Rare earth oxysulfide ceramic regenerator material, method for producing the same, and cryogenic regenerator using the regenerator material - Google Patents

Abstract

[Constitution] Crystal particles of rare earth oxysulfide such as Gd ₂ O ₂ S are used as primary particles, and a porous body in which the primary particles are sintered together at a neck is used as a constituent particle. In order to obtain such constituent particles, granular rare earth oxysulfide is HIP-baked at 1150 to 1350 ° C. and HIP-baked at a relatively low temperature so that the primary particles grow and the constituent particles are densified. It is preferable to grow the neck between the primary particles while suppressing.
[Effect] A ceramic regenerator material having a high refrigerating capacity with less destruction of constituent particles and generation of fine powder during operation of the refrigerator can be obtained.
[Selection diagram] Fig. 1

Description

【００４２】
表１から明らかなように、ｘの値を変化させても、無負荷時の最低到達温度及び４．２Ｋにおける冷凍能力に著しい変化は見られなかった。試料１と同様に連続１０００時間冷凍機を運転しても、安定した出力を得ることができた。尚、希土類元素をＧｄ及びＴｂを他の希土類元素に変更した場合でも、同様の傾向が見られた。実施例ではＧｄ_ｘＴｂ_２−ｘＯ_２Ｓを中心に説明したが、他の希土類オキシ硫化物セラミックス蓄冷材でも同様である。
【図面の簡単な説明】
【図１】実施例のＧｄ_２Ｏ_２Ｓセラミックス蓄冷材での構成粒子の粒子構造を示す、ＳＥＭ型の電子顕微鏡写真で、下部の水平なバーは５μｍ長を示す。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a compound represented by the general formula R ₂ O ₂ S (R is Y containing La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. The present invention relates to a rare earth oxysulfide regenerative material represented by the following formula, and a method for producing the regenerative material, and a regenerator using the regenerative material. More specifically, the present invention relates to a regenerator material which is less likely to be pulverized during operation of a refrigerator, has excellent durability, and has excellent refrigerating capacity in an extremely low temperature region, a method for producing the same, and a regenerator using the same.
[0002]
[Prior art and its problems]
Liquid helium is indispensable for cooling superconducting magnets and sensors, and liquefaction of helium gas requires enormous compression work, which requires a large refrigerator. However, it is difficult to use a large refrigerator for a small device utilizing superconductivity such as a linear motor car or an MRI (magnetic resonance diagnostic device). Therefore, it is essential to develop a compact and high-performance refrigerator capable of generating a liquid helium temperature (4.2 K). Such refrigerators are required to be lightweight and small and have excellent thermal efficiency. For example, in a superconducting MRI apparatus, for example, a GM refrigerator (a small helium refrigerator of the Gifford McMahon type) is used. The GM refrigerator mainly includes a compressor for compressing a working medium such as He gas, an expansion unit for expanding the compressed working medium, and a cryogenic regenerator for maintaining a cooling state of the working medium cooled in the expansion unit. It is configured. Then, at about 60 cycles per minute, the working medium compressed by the compressor is expanded and cooled by the refrigerator, and the system to be cooled is cooled through the distal end of the expansion section of the refrigerator.
[0003]
The cooling capacity and the minimum attainable temperature of the small refrigerator depend on the cold storage material incorporated in the refrigerator, and the cold storage material needs to have a large heat capacity and high heat exchange efficiency. With a conventional metal regenerative material such as Pb, the heat capacity drops sharply at a low temperature of 10K or less. Therefore, a regenerative material for rare earth intermetallic compounds such as HoCu ₂ and ErNi having a large heat capacity up to the vicinity of the liquefied helium temperature (4.2 K) has been developed (Japanese Patent No. 2609747). However, the heat storage capacity of the rare earth intermetallic compound regenerator material is significantly reduced below 7K, and the heat capacity in the extremely low temperature region around 4.2K is less than 0.3 J / cc · K. In order to sufficiently maintain the refrigerating capacity in the cryogenic temperature range, the heat capacity of the cold storage material at that temperature is required to be 0.3 J / cc · K or more, and the cold storage material of a rare earth intermetallic compound such as HoCu ₂ ErNi is used in the cryogenic temperature range. Refrigeration capacity is insufficient. In addition, rare earth intermetallic compounds are extremely expensive, and cold storage materials using them in the order of several hundred grams are also extremely expensive.
[0004]
The rare earth intermetallic compound cold storage material is prepared by quenching and solidifying a molten metal as disclosed in Japanese Patent No. 2609747 and the like. Naturally, it is a solid, dense granular material having an average particle size of 0.01 to It is about 3 mm. When the average particle size of the granules is increased, the gas flow resistance of the He gas decreases, but the heat exchange efficiency decreases. When the average particle size is reduced, the heat exchange efficiency increases, but the gas flow resistance sharply increases.
[0005]
It has been studied to fix the particles of the rare earth intermetallic compound to each other to increase the strength of the cold storage material and improve the air permeability. For example, Japanese Patent Application Laid-Open No. H11-264618 proposes that a surface of a particle of a rare earth intermetallic compound is coated with a low melting point metal such as Pb, In, or Sn, and the particles are fixed to each other by liquid phase sintering. I have. However, it is difficult to obtain fine particles of the rare earth intermetallic compound, and the average particle diameter of the particles is, for example, 100 to 250 μm. Since the average particle diameter is large, the heat exchange efficiency is limited.
[0006]
[Problems of the Invention]
An object of the present invention is to improve the refrigeration capacity of a refrigerator,
・ It is possible to improve the permeability of high pressure He gas and reduce pressure loss,
Sufficiently withstands vibration and shock due to reciprocating motion of a working medium such as high-pressure He gas during operation of the refrigerator, or hydrodynamic stress due to high-pressure He gas passing inside the regenerator;
It is an object of the present invention to provide a rare earth oxysulfide ceramic regenerator material capable of maintaining excellent refrigerating capacity in a cryogenic region for a long time, a method for producing the same, and a regenerator.
[0007]
Configuration of the Invention
Rare earth oxysulfide ceramic regenerator material of the present invention,
General formula R ₂ O ₂ S (R is at least one rare earth element selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu containing Y In a cold storage material using a rare earth oxysulfide represented by
The crystal particles of the rare earth oxysulfide are primary particles, and the primary particles are porous particles sintered together at a neck as constituent particles.
[0008]
Preferably, the average crystal grain size of the crystal grains is 0.2 to 5 μm, more preferably 0.5 to 3 μm, most preferably 0.9 to 2 μm (Claim 2).
[0009]
The relative density of the porous body is preferably 60 to 85%, more preferably 65 to 80%, and most preferably 70 to 75% (Claim 3).
[0010]
The rare earth element constituting the rare earth oxysulfide is optional, but has a specific heat peak temperature of about 4 to 7 K lower than the rare earth intermetallic compound, and is suitable for cooling to liquid helium temperature, such as Gd or Tb, or Dy, Ho, or the like, which has a specific heat peak temperature of about 2 to 4 K and is suitable for cooling to a temperature lower than the liquid helium temperature, is preferable. The rare earth oxysulfide regenerator material need not be one type of constituent rare earth elements, for example, as _{Gd x Tb 2-x O 2} S, may be used two or more types of constituent rare earth elements. Preferably, at least 80 atomic% of the constituent rare earth elements in the rare earth oxysulfide are Gd, Tb, Dy, or Ho (claim 4).
[0011]
The method for producing a rare earth oxysulfide ceramic regenerator material of the present invention comprises:
General formula R ₂ O ₂ S (R is at least one rare earth element selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu containing Y In the method for producing a cold storage material using a rare earth oxysulfide represented by
Granulate the rare earth oxysulfide powder into granules,
The granules are subjected to HIP baking at 1150 to 1350 ° C. to form rare earth oxysulfide crystal particles as primary particles, and the primary particles are used as a cold storage material composed of a porous body sintered together at a neck. (Claim 5).
[0012]
The HIP temperature is more preferably set to 1200 to 1300 ° C.
Preferably, the pressure in the HIP is set to 50 to 200 MPa, and the firing time is set to 1 to 10 hours (claim 6).
[0013]
The cryogenic regenerator according to the present invention uses the rare earth oxysulfide ceramic regenerative material according to any one of claims 1 to 4 (claim 7).
[0014]
Function and Effect of the Invention
In the rare earth oxysulfide ceramic cold storage material of the present invention, a porous body (secondary particle) obtained by sintering primary particles made of crystal particles with each other at a neck is used as constituent particles. In ceramics, the particle size of primary particles can be extremely small, for example, about 0.2 to 5 μm. For this reason, He gas flows inside the porous body and exchanges heat with the primary particles, so that the heat exchange efficiency can be improved. The fine primary particles are sintered together at the neck, making the porous body as a whole a strong material. It is also possible for a plurality of crystal particles to be present in one primary particle, but a plurality of crystal particles closely adhered in the primary particle are fused during the sintering process, and in principle, one crystal particle is formed. Growing into particles.
[0015]
As described above, according to the present invention, a regenerator or a regenerator having high heat exchange efficiency and low pressure loss can be obtained because the constituent particles are porous and the gas permeability of He gas is high. Moreover, since the primary particles are sintered at the neck of each other, the cold storage material and the animal cooler of the present invention have high strength of constituent particles and can withstand vibration, impact, stress, etc. in the refrigerator. Therefore, excellent refrigeration capacity can be maintained for a long time (claims 1 and 7). On the other hand, in the case of metal, it is difficult to obtain fine primary particle powder itself, and even if the primary particles are sintered together to form a porous body, the size of the primary particles is large, so that heat exchange is not possible. It is difficult to improve efficiency.
[0016]
The average crystal grain size of the rare earth oxysulfide ceramic regenerator is preferably 0.2 to 5 μm as an average crystal grain size after HIP firing, because it is involved in improving the permeability of high-pressure He gas and reducing pressure loss. The thickness is more preferably 0.5 to 3 μm, and still more preferably 0.9 to 2 μm. When the average crystal grain size exceeds 5 μm, the heat exchange efficiency between the high-pressure He gas and the primary particles decreases, and when the average crystal grain size is less than 0.2 μm, the permeability of the high-pressure He gas inside the constituent particles is remarkable. And the pressure loss increases. The airflow resistance inside the constituent particles is a viscous resistance, and the viscous resistance is inversely proportional to the size of the void through which the high-pressure He gas flows. The size of the void is proportional to the size of the primary particles.
[0017]
The average crystal grain size of the primary particles is also restricted by the preparation of ceramics. Considering the particle size of the primary particles in the ceramic powder before sintering, it is difficult to make the average crystal particle size of the primary particles in the cold storage material after sintering smaller than this. It is difficult to make the average particle size of the primary particles sufficiently smaller than 0.2 μm from the viewpoint of powder handling properties. Making the average crystal grain size of the primary particles 0.2 μm or more in this way also means that the raw material powder of the ceramic regenerator can be easily obtained (Claim 2).
[0018]
The relative density of the constituent particles in the rare earth oxysulfide ceramic regenerator is preferably from 60 to 85%, more preferably from 65 to 80%, further preferably from 70 to 75%. The strength of the constituent particles depends on the relative density. For example, when the relative density is about 50%, it is difficult to withstand vibration, impact, and stress due to the movement of the high-pressure He gas. The strength of the constituent particles increases exponentially with the relative density when the relative density is in the range of about 50 to 70%. On the other hand, the air permeability in the constituent particles rapidly decreases with the relative density. Particularly, when the relative density exceeds 80%, the air permeability decreases exponentially with the density, and when the relative density exceeds 85%, the air permeability extremely decreases. Therefore, when the relative density of the constituent particles is set to 60 to 85%, the strength of the constituent particles can be secured, and the air permeability in the constituent particles can be secured (claim 3).
[0019]
When the constituent rare earth elements in the rare earth oxysulfide ceramics are Gd and Tb, a specific heat peak appears at about 4 to 7 K, which is lower than the specific heat peak of the rare earth intermetallic compound, and is necessary for cooling to the liquid He temperature. Are suitable. Note that the specific heat peak (magnetic phase transition temperature) of Gd ₂ O ₂ S is 5.2K, that of Tb ₂ O ₂ S is 6.3K, and that Gd _x Tb _2-x O ₂ S (0 ≦ X ≦ 1.8) In this case, a peak of specific heat appears at about 4.2 to 5.3K. Further, when the rare earth intermetallic compound cold storage material is arranged on the high temperature side of the rare earth oxysulfide ceramic cold storage material, it can be efficiently cooled to the liquid He temperature. When the constituent rare earth element of the rare earth oxysulfide ceramic regenerator material and Dy and Ho, the peak of the specific heat at _Dy 2 _{O 2} S becomes 2.2K at 4.6K, _{Ho 2 O} 2 S. Thus _Gd 2 _{O 2} S and _{Tb 2 O 2 S, Gd x} Tb 2-x O 2 S a (0 <X <2) disposed on the high temperature side, _{Dy 2 O} 2 S and _Ho 2 O in the cold side When placing the _{2 S,} cooling is facilitated to a lower temperature (claim 4).
[0020]
To produce the rare earth oxysulfide cold accumulating material of the present invention, for example, raw materials of rare earth oxide powder, H _{2 S} under heating by flowing a gas containing an oxidizing number -2 sulfur atoms, such as CH 3 _SH reaction Thus, a rare earth oxysulfide powder is produced, and this powder is granulated. Alternatively, the rare earth oxide powder may be granulated and then reacted with a gas containing a sulfur atom having an oxidation number of -2 to form a rare earth oxysulfide. The method of granulation itself is arbitrary, and may be, for example, tumbling granulation, a combination of extrusion and tumbling granulation, fluidized granulation, spray drying granulation, embossing granulation, and the like.
[0021]
In order to obtain a rare earth oxysulfide ceramic regenerator material, it is preferable to fire the granulated particles by HIP (hot isostatic pressure). In the conventional normal pressure firing method, when high-temperature firing is performed, a neck between primary particles grows. At the same time, however, grain growth and densification occur. I can not secure it. On the other hand, when low-temperature firing is performed to suppress grain growth and densification, necks between primary particles do not grow, and the strength of constituent particles cannot be obtained. An inert gas such as argon is used as a firing atmosphere (pressure medium) of the HIP, a firing temperature is 1150 to 1350 ° C., particularly 1200 to 1300 ° C., and a firing time is a holding time to a peak temperature of 1 to 10 hours. Is preferably 50 to 200 MPa. These are experimentally obtained under the conditions that the relative density of the constituent particles is 60 to 85%.
[0022]
The diameter of the sphere (circumscribed sphere) containing the constituent particles affects the air permeability, the heat exchange efficiency, and the strength, and the average diameter is preferably 0.01 to 2 mm. The aspect ratio (the ratio of the major axis to the minor axis) of the constituent particles is preferably 3 or less, more preferably 2 or less, and particularly preferably 1.2 or less. This is because, as the aspect ratio is smaller, uniform filling is easier, and the generation of fine powder due to vibration, impact, and stress due to the movement of the high-pressure He gas is smaller. However, the aspect ratio of the primary particles themselves is arbitrary, and it is preferable that non-spherical primary particles be bonded to each other inside the constituent particles to obtain a large void.
[0023]
The regenerator of the present invention is a regenerator having the above-described rare earth oxysulfide ceramic regenerator filled in a regenerator cylinder. For example, the regenerator may be divided into a plurality of layers and each layer may be filled with another regenerator. Further, it is preferable that the high-temperature side of the rare-earth oxysulfide ceramic regenerator is filled with a rare-earth intermetallic regenerative material such as HoCu ₂ so that the specific heat is continuous from the high-temperature side to the lowest temperature.
[0024]
【Example】
Examples will be described below.
[0025]
[Sample 1]
The average particle diameter of gadolinium oxide Gd ₂ O ₃ was 0.46 μm according to the Fisher method. This gadolinium oxide is filled in a quartz boat and reacted at 650 ° C. while flowing hydrogen sulfide gas H 2 S through a quartz reaction tube. When the X-ray diffraction of the reaction product was measured, only a peak of gadolinium oxysulfide Gd ₂ O ₂ S alone was recognized, and the reaction yield with respect to the rare earth oxide was 100%. The obtained Gd ₂ O ₂ S powder (average particle size 0.46 μm) was tumbled and granulated. The tumbled and granulated powder was filled in an alumina crucible, and the furnace was sufficiently evacuated to perform HIP firing. After that, the inside of the furnace was sufficiently evacuated, and argon gas was introduced and firing was performed in an argon atmosphere. By setting the firing temperature to 1250 ° C., the pressure to 150 MPa, and the firing time to 5 hours, constituent particles having a relative density of 72% of the theoretical density by a pycnometer method were obtained.
[0026]
The fired constituent particles, nylon-based media, and 10 wt% alumina slurry were charged into a processing tank, and surface processing was performed by a rotary barrel processing method. When the processing time was set to 2 hours, crystal particles existing as protrusions on the surface of the constituent particles could be removed. The observation of the surface state was performed by a scanning electron microscope (SEM). The surface-processed constituent particles are sieved with a filter net, and the sieved constituent particles are rolled on an iron plate (polished to a mirror surface) inclined at about 25 °, and the rolling-down constituent particles are collected and classified. Was performed. For 100 constituent particles, the average diameter of the spheres containing the constituent particles was 0.4 mm, and the average aspect ratio of the constituent particles was 1.1. The average particle diameter and the average aspect ratio of the constituent particles were measured from images taken using a video high scope system. The constituent particles after shape classification are referred to as Sample 1.
[0027]
The constituent particles were fixed in plastic, cut, and the primary particles inside were observed by SEM. An SEM photograph is shown in FIG. Observation with an SEM revealed that the average particle size of the crystal particles constituting the constituent particles was 1.1 μm. The relative density was 72% as described above. The crystal grains were sintered and fixed to each other at the neck, and voids were left between the crystal grains, and the voids communicated to form open pores. Further, the constituent particles did not adhere to each other.
[0028]
Next, in order to examine the strength of the constituent particles, 100 constituent particles were put into a rectangular plastic bag having a side of 5 cm and the other side of 10 cm, and shaken for 120 minutes / minute with a shaker for 5 minutes. Inspection of the crushed state of the sample showed no destruction of constituent particles or generation of fine powder.
[0029]
After the thus obtained constituent particles are filled in the cooling section of the GM refrigerator in a close-packed manner, He gas having a heat capacity of 25 J / K is supplied at a mass flow rate of 3 g / sec and a gas pressure of 16 atm under the GM conditions. The refrigeration cycle was continued for 1000 hours and 3000 hours. The constituent particles after 1000 hours and 3000 operation were observed, but no broken constituent particles or fine powder were observed. The refrigeration characteristics of the above constituent particles were examined using a two-stage GM refrigerator with a power consumption of 3.4 kW. Pb was used for the first-stage regenerator on the high-temperature side, and 50 vol% of HoCu ₂ was placed on the high-temperature side of the second-stage regenerator, and 50 vol% of constituent particles of sample 1 was placed on the low-temperature side of the second-stage regenerator. After loading, the refrigeration capacity was checked. The refrigerating capacity at 4.2 K was 1.94 W, and the minimum temperature at the time of no load was 2.62 K. Even if the refrigerator was operated continuously for 1000 hours or 3000 hours, there was no change in the refrigerating capacity or the minimum attained temperature.
[0030]
The sintering method and the sintering conditions were changed for the granulated by rolling in Sample 1, and the strength and refrigerating characteristics of the regenerator material were evaluated. The rolled granules of Gd ₂ O ₂ S used in Sample 1 were filled in an alumina crucible and fired at a firing temperature of 1250 ° C. for 5 hours in an argon atmosphere at normal pressure. When this sample was subjected to rotary barrel processing in the same manner as Sample 1, a large amount of fine powder was generated during the processing, so that no further test was carried out because it was not usable as a cold storage material (Sample 2). In the SEM, the neck was slightly growing between the primary particles and the relative density of the secondary particles (sintered individual granules) by the pycnometer method was 52%. .
[0031]
Since the sintering temperature of Sample 2 was too low, the sintering temperature was changed to 1350 ° C and 1500 ° C by normal pressure sintering. At 1350 ° C., the secondary particles were porous, but the formation of necks between the primary particles was slight, and a large amount of fine powder was generated by rotating barrel processing. After sintering at 1500 ° C., the relative density of the secondary particles was 99.9%, and the average crystal grain size was 3.2 μm. This sample was subjected to surface processing, sieving, and shape classification in the same manner as Sample 1, and charged into a refrigerator as a regenerator material, and the refrigerator was operated continuously for 1000 hours. The refrigerating capacity at 4.2 K was 1.69 W, the minimum temperature reached 2.62 K, and the refrigerating capacity was reduced to 85% as compared with Sample 1.
[0032]
In the normal pressure sintering, a sample having sufficient permeability of He gas and durability with respect to continuous operation of the GM refrigerator was not obtained because the sample was porous and the primary particles were bonded by a neck. The sintering conditions in sintering were studied. The rolled granulated particles of Gd ₂ O ₂ S prepared in Sample 1 were filled in an alumina crucible, and HIP firing was performed in an argon atmosphere (150 MPa) at a firing temperature of 1000 ° C. and a firing time of 3 hours. The average crystal grain size of the primary particles is 0.1 μm, the relative density of the constituent particles is 56%, and the neck is slightly growing between the primary particles within the constituent particles. Was. When this sample was subjected to rotary barrel processing in the same manner as Sample 1, some of the constituent particles were broken during the processing. Except for the sample destroyed through the filter, the refrigerator was operated continuously for 1000 hours in the same manner as in Sample 1, and a large amount of fine powder was generated.
[0033]
The rolling granulated particles used in Sample 1 were fired under the conditions of HIP firing at 1200 ° C., an Ar pressure of 200 MPa, and a firing time of 8 hours. The relative density of the constituent particles was 67%, the average crystal grain size of the primary particles was 0.8 μm, and the primary particles were connected to each other by a neck. This sample was subjected to rotary barrel processing in the same manner as Sample 1, subjected to sieving and shape classification, and was continuously operated as a cold storage material by a refrigerator for 1000 hours and 3000 hours. No destruction of the constituent particles was observed in the rotary barrel processing, and no fine powder was generated even after continuous operation for 1000 hours or 3000 hours, and the initial value of the refrigerating capacity was similar to that of Sample 1.
[0034]
The rolling granules used in Sample 1 were fired under the conditions of HIP firing at 1300 ° C., an Ar pressure of 60 MPa and a firing time of 3 hours. The relative density of the constituent particles was 73%, and the average crystal grain size of the primary particles was 1.1 μm. The primary particles were connected to each other by a neck. This sample was subjected to rotary barrel processing in the same manner as Sample 1, subjected to sieving and shape classification, and was continuously operated as a cold storage material by a refrigerator for 1000 hours. No destruction of the constituent particles was observed in the rotary barrel processing, no fine powder was generated during continuous operation for 1000 hours, and the initial value of the refrigerating capacity was 2.63K at the lowest temperature and 4.2F at 4.2K. It was 91W.
[0035]
The rolling granules used in Sample 1 were fired under the conditions of HIP firing at 1180 ° C., an Ar pressure of 200 MPa, and a firing time of 8 hours. The relative density of the constituent particles was 66%, the average crystal grain size of the primary particles was 0.7 μm, and the primary particles were connected to each other by a neck. This sample was subjected to rotary barrel processing in the same manner as Sample 1, subjected to sieving and shape classification, and was continuously operated as a cold storage material by a refrigerator for 1000 hours and 3000 hours. No destruction of the constituent particles was observed in the rotating barrel processing, no fine powder was generated during continuous operation for 1000 hours, and the initial value of the refrigerating capacity was similar to that of Sample 1. However, in the continuous operation for 3000 hours, generation of fine powder was observed.
[0036]
The rolling granules used in Sample 1 were fired under the conditions of HIP firing at 1330 ° C., an Ar pressure of 100 MPa, and a firing time of 6 hours. The relative density of the constituent particles was 78%, the average crystal grain size of the primary particles was 2.3 μm, and the primary particles were connected to each other by a neck. This sample was subjected to rotary barrel processing in the same manner as Sample 1, subjected to sieving and shape classification, and was continuously operated as a cold storage material by a refrigerator for 1000 hours. No destruction of the constituent particles was observed in the rotary barrel processing, no fine powder was generated during continuous operation for 1000 hours, and the initial value of the refrigerating capacity was 1.62 K at the lowest attained temperature and 1. at the refrigerating capacity at 4.2 K. It was 90W.
[0037]
The rolled granulated particles of Gd ₂ O ₂ S prepared in Sample 1 were filled in an alumina crucible, and HIP firing was performed in an argon atmosphere (100 MPa) at a firing temperature of 1500 ° C. and a firing time of 3 hours. The obtained sample was subjected to surface processing, sieving and shape classification in the same manner as Sample 1. The relative density of the constituting particles was 89%, and the average crystal grain size was 5.3 μm. When a test on the refrigerating capacity was performed in the same manner as in Sample 1, the initial value of the refrigerating capacity at 4.2 K was 1.51 W, and the lowest temperature was 2.63 K.
[0038]
Dysprosium oxide having an average particle size of 0.6 μm was sulfurized and molded in the same manner as in Sample 1. The obtained granular secondary particles were treated under the same conditions as Sample 1 (Sample 3), and a refrigerator test similar to that of Sample 1 was performed. As a result, even if the refrigerator was operated continuously for 1000 hours and 3000 hours, no broken constituent particles or fine powder could be confirmed. As for the refrigerating capacity, the refrigerating capacity at 4.2 K was 1.75 W, and the minimum temperature was 2.65 K. On the other hand, the rolling granules of Dy ₂ O ₂ S used in Sample 3 were filled in an alumina crucible, and fired at 1500 ° C. in argon under normal pressure (Sample 4). Was done. As a result, even if the refrigerator was operated continuously for 1000 hours, no broken constituent particles or fine powder could be confirmed, but the initial value of the refrigerating capacity was reduced to about 85% as compared with Sample 3. A similar tendency was observed when the rare earth element was changed from Gd or Dy to another rare earth element.
[0039]
After subjecting the gadolinium oxide Gd ₂ O ₃ used in Sample 1 to tumbling granulation, a sulfidation reaction was performed in the same manner as in Sample 1. The particles after the sulfidation reaction (granular secondary particles) were treated under the same conditions as in Sample 1 to obtain the same constituent particles as Sample 1. The refrigerating capacity and the lowest temperature reached at 4.2 K were the same as those of Sample 1, and a stable output could be obtained even when the refrigerator was operated continuously for 1000 hours and 3000 hours.
[0040]
Sulfidation, molding, and HIP sintering were performed in the same manner as in Sample 1, except that gadolinium oxide used in Sample 1 and terbium oxide (average particle size: 0.69 μm) were mixed. In this way, the porous particles composed of the porous secondary particles in which the primary particles of gadolinium-terbium-based oxysulfide (Gd _x Tb _2-x O ₂ S, 0 ≦ X ≦ 2) are bonded to each other at the neck. A cold storage material was obtained (Sample 5). The refrigerating capacity of the obtained regenerator material was evaluated in the same manner as in Sample 1. The results are shown in Table 1, and the refrigerating capacity is shown by an initial value and two values after continuous operation for 1000 hours.
[0041]
[Table 1]

[0042]
As is clear from Table 1, even when the value of x was changed, no remarkable change was observed in the minimum attained temperature at no load and the refrigerating capacity at 4.2K. Even when the refrigerator was operated continuously for 1000 hours in the same manner as in Sample 1, a stable output was obtained. Note that the same tendency was observed when the rare earth element was changed from Gd and Tb to another rare earth element. In the embodiment, Gd _x Tb _2-x O ₂ S has been mainly described, but the same applies to other rare earth oxysulfide ceramic regenerator materials.
[Brief description of the drawings]
FIG. 1 is an SEM-type electron micrograph showing the particle structure of constituent particles of a Gd ₂ O ₂ S ceramic regenerator according to an example. The lower horizontal bar shows a length of 5 μm.

Claims (7)

General formula R ₂ O ₂ S (R is at least one rare earth element selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu containing Y In a cold storage material using a rare earth oxysulfide represented by:
A rare earth oxysulfide ceramic regenerator material, wherein the rare earth oxysulfide crystal particles are primary particles, and the primary particles are porous particles sintered together at a neck. The rare earth oxysulfide ceramic cold storage material according to claim 1, wherein the average crystal grain size of the crystal grains is 0.2 to 5 µm. The rare earth oxysulfide ceramic cold storage material according to claim 1 or 2, wherein the porous body has a relative density of 60 to 85%. The rare earth oxysulfide ceramic regenerator according to any one of claims 1 to 3, wherein 80% by atom or more of the rare earth element constituting the rare earth oxysulfide is Gd, Tb, Dy, or Ho. General formula R ₂ O ₂ S (R is at least one rare earth element selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu containing Y In the method for producing a cold storage material using a rare earth oxysulfide represented by
Granulate the rare earth oxysulfide powder into granules,
The granules are subjected to HIP baking at 1150 to 1350 ° C. to form rare earth oxysulfide crystal particles as primary particles, and the primary particles are used as a cold storage material composed of a porous body sintered together at a neck. A method for producing a rare earth oxysulfide ceramic cold storage material. The method for producing a cold storage material for rare earth oxysulfide ceramics according to claim 5, wherein the pressure at the HIP is 50 to 200 MPa and the sintering time is 1 to 10 hours. A cryogenic regenerator using the rare earth oxysulfide ceramic regenerative material according to claim 1.

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