JP2003073661A - Rare earth oxysulfide cold storage medium and cold storing machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cold storage medium having a large heat capacity at an extreme low temperature of around 4.2 K and generating no abrasion powder during the operation of a refrigerator. SOLUTION: A rare earth oxysulfide represented by general formula: R2 O2 S (wherein R represents at least a rare earth element including Y and others selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) is made into a spherical granule. The granule's average particle diameter is 0.05-1 mm, and its relative density is not lower than 96%. This granule is used as a cold storage medium at the temperature of liquid helium.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a rare earth oxysulfide regenerator and a regenerator using the same. More specifically, the present invention relates to a highly functional regenerator or regenerator that has a large heat capacity in the cryogenic region around 4.2K required for liquefying helium gas and that does not generate abrasion powder during refrigerator operation.

[0002]

2. Description of the Related Art Liquid helium is indispensable for cooling superconducting magnets, sensors and the like, and enormous compression work is required for liquefying helium gas, which requires a large refrigerator. However, it is difficult to use a large refrigerator in a small device that uses superconductivity such as a linear motor car or MRI (magnetic resonance diagnostic device). Therefore, a small, high-performance refrigerator capable of generating liquid helium temperature (4.2K) is essential.

The cooling efficiency and the minimum attainable temperature of the small refrigerator depend on the regenerator material that is the filling material of the regenerator. The regenerator material needs to have a sufficiently large heat capacity for the helium refrigerant passing through the regenerator and have high heat exchange efficiency. In metal regenerator materials such as Pb that have been used conventionally,
Since the heat capacity sharply decreases below 10K, the cooling efficiency below 10K decreases. So more liquid helium temperature (4.2K)
A cold storage material having a large heat capacity at a temperature close to is developed. This cold storage material is formed of a rare earth intermetallic compound such as HoCu ₂ or ErNi (Patent 2609747, USP 5449,416), and has a large heat capacity near 20 to 7K as shown in FIG. 1, but a heat capacity below 7K It is small and has insufficient cooling capacity at cryogenic temperatures. Further, the regenerator material is required to have durability against thermal shock and vibration during operation of the refrigerator.

[0004]

An object of the present invention is to provide a regenerator material having a large heat capacity near the temperature of liquefied helium and having high durability against thermal shock and vibration, and a regenerator using the same. An additional object of the present invention is to provide a regenerator material or a regenerator suitable for freezing to 4 to 7K. An additional object of the present invention is also to provide a regenerator material or regenerator suitable for freezing to 2 to 4K.

[0005]

The regenerator material of the present invention has the general formula R ₂ O ₂ S (R
Is Y including La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, E
It represents one or more rare earth elements selected from r, Tm, Yb and Lu. ) Is a rare earth oxysulfide. The rare earth element is preferably Gd, Tb, D
It is at least one member of the group consisting of y, Ho and Er, and more preferably Gd or Tb. For example, if the rare earth oxysulfide is Gd _2-x Tb _x O ₂ S (x = 0.2 to 2), the peak temperature of the specific heat can be changed from around 6K to around 4K, and especially the x value is 1.6 When it is set to ˜2, preferably 1.8 to 2, and more preferably 1.9 to 2, a regenerator material having a peak of specific heat slightly higher than Gd ₂ O ₂ S can be obtained. When this cold storage material is combined with a cold storage material containing Gd as the main component of the rare earth element, 4
A broad and large specific heat is obtained in the range of up to 7 K, which is particularly suitable for cooling to near the liquid helium temperature. Moreover, when the rare earth oxysulfides are Ho or Dy oxysulfides, they have a specific heat peak at a temperature lower than that of Gd oxysulfides, and thus are particularly suitable for freezing to 2 to 4K. And, for example, if a cool storage material containing Gd as a main component of a rare earth element is placed on the high temperature side, and a cool storage material made of oxysulfide of Ho or Dy is placed on the low temperature side, Gd is a rare earth element that is frozen up to 4K. The cold storage material containing the main component is used, and the freezing of 4k or less is performed with the cold storage material containing Ho or Dy as the main component of the rare earth element, and the freezing to 4K or less can be efficiently performed.

Preferably, the rare earth oxysulfide is used as granules, and particularly preferably, the average particle diameter of the granules is from 0.05 mm to
1 mm, or preferably, the average aspect ratio of the granules is 3 or less, and preferably the relative density of the granules is 96% or more. The rare earth oxysulfide in the granule preferably has an average crystal grain size of 100 μm or less, and the granule preferably has a surface roughness of 10 μm or less on the basis of the maximum height R _max .
The excess sulfur content in the granules is preferably 10,000 wtppm or less. And it is preferable that the granules have a maximum value of the volume specific heat at 2 to 7K.

Further, the regenerator of the present invention is one in which the above-mentioned rare earth oxysulfide regenerator material is filled in an appropriate cylinder or the like. Rare earth oxysulfide is excellent in specific heat at 7K below, placing the cold accumulating material mainly composed of HoCu ₂ on the high temperature side, refrigeration down to 7K in HoCu _2, rare earth oxysulfide frozen to 7K or less It can be refrigerated to 7K or less efficiently by using a cold storage material. The oxysulfide cold storage material containing Gd as the main component of the rare earth element has a peak of specific heat at 5 to 4K, and the specific heat at 7 to 5K is insufficient. Therefore, it is preferable to use Tb on the high temperature side as the main component of the rare earth element. An oxysulfide cold storage material is placed. In the case of freezing to 4K or less, an oxysulfide cold storage material containing Gd as a main component of a rare earth element is placed, and an oxysulfide storage cold storage material containing Ho or Dy as a main component of a rare earth element is placed on the low temperature side. . Freezing to 2-4K is effective for increasing the sensitivity by cooling the X-ray detector in the inspection of semiconductors through transmitted X-rays, and for cooling the adiabatic degaussing refrigerator in the previous stage. The display of the rare earth element in the rare earth oxysulfide will be described here. Gd
The oxysulfide or oxysulfide cold storage material containing Gd as the main component indicates that, for example, 50 atomic% or more of the metal component is Gd. For example, as shown in Table 1, Gd ₁ Tb ₁ O ₂ S Gd ₂ O ₂
It is a material that has a specific heat peak on the lower temperature side than S and is more similar to Gd ₂ O ₂ S than Tb ₂ O ₂ S. In the case of Tb, Dy, Ho, etc., these oxysulfides or oxysulfides containing these as the main components mean that 80 atomic% or more of the metal components are these elements. For example, 10 atoms of metal component
% Substitution from these elements does not cause a large difference in the specific heat characteristics of oxysulfide.

[0008]

The effect of the present invention The rare earth oxysulfide regenerator material of the present invention undergoes a magnetic phase transition in the range of about 7 to 2K and has a large heat capacity which is 2 to 5 times that of the conventional regenerator materials such as HoCu ₂ and ErNi. For this reason, it is possible to easily obtain a small-sized regenerator having a high refrigerating efficiency, having a high refrigerating capacity in an extremely low temperature environment around 4.2K, having a lower minimum temperature than the existing regenerator material. INDUSTRIAL APPLICABILITY The regenerator material or regenerator of the present invention can be used for a superconducting magnet, an MRI cooling refrigerator, or the like. By selecting the kind of rare earth element and using a plurality of rare earth elements, it is possible to obtain a desired magnetic phase transition temperature and further widen the width of the specific heat peak near the magnetic phase transition temperature. Further, by using spherical rare earth oxysulfide cold storage material granules, it is possible to reduce the passage resistance of the cooling medium while increasing the packing density of the cold storage material.
By reducing the roughness of the granule surface, generation of fine powder can be prevented and the life of the regenerator material can be extended.

In the regenerator, it is necessary that the specific heat is continuous from the high temperature side to the low temperature side, and that the distribution of the specific heat near the freezing target temperature is broad. The former has the property of efficiently refrigerating to the target temperature, and the latter has the property of being able to select the target temperature from a wide range. Since the rare earth oxysulfide regenerator material has a small specific heat at 7 K or more, it is preferable to arrange the regenerator material such as HoCu ₂ on the high temperature side. Further, since the distribution of the specific heat is narrow in a single rare earth oxysulfide cold storage material, it is preferable to arrange the rare earth oxysulfide cold storage material in layers for low temperature and high temperature to have a continuous specific heat as a whole. . In particular, since the oxysulfide containing Gd as the main component lacks the specific heat at 6 to 7 K, it is preferable to arrange the oxysulfide containing Tb as the main component on the high temperature side. In the case of refrigeration to 4K or less, Ho and Dy are added to the low temperature side of oxysulfide mainly composed of Gd.
It is preferable to dispose an oxysulfide containing as a main component.

The rare earth oxysulfide is, for example, a rare earth oxide powder contained in a reaction tube such as quartz and heated under heating to H ₂ S, C.
It is obtained by causing a gas containing a sulfur atom having an oxidation number of −2, such as H ₃ SH, to flow and react. The reaction temperature varies depending on the particle size of the rare earth oxide powder of the raw material powder, but if the particle size is about 1 μm, which is easily available, 500 to 800 ° C. is preferable, and 600 to 700 ° C. is more preferable. If it is less than 500 ° C, it takes a long time to complete the reaction, and if it exceeds 800 ° C, sulfides start to form. The reaction time is preferably 1 to 9 hours,
1 to 3 hours is more preferable.

It is preferable that the regenerator material is in the form of granules in order to withstand the compression pressure at the time of filling the regenerator and the thermal shock and vibration during the operation to prevent generation of fine powder, and particularly the granules are spherical. The average value of the ratio of the major axis to the minor axis of the granule
The (average aspect ratio) is preferably 3 or less, more preferably 2 or less, and further preferably around 1 to approximate a true sphere. Since rare earth oxysulfides are more brittle than rare earth intermetallic compounds, if the average aspect ratio exceeds 3, fracture tends to occur, and if the average aspect ratio exceeds 3, it becomes difficult to uniformly fill the regenerator. Become.

The average particle size of the granules is preferably in the range of 0.05 to 1 mm. If the average particle size is less than 0.05 mm, the packing density becomes high, and the helium refrigerant cannot pass through the regenerator sufficiently,
Heat exchange efficiency decreases. On the other hand, when the average particle size exceeds 1 mm, the contact area with the helium refrigerant becomes small, and the heat exchange efficiency decreases. Therefore, the average particle size is preferably 0.05 to 1 mm, more preferably 0.1 to 0.7 mm, and further preferably 0.1 to 0.3 mm.

The relative density of granules of the regenerator material is preferably 96% or more, more preferably 98% or more, and further preferably 9% or more.
It is preferably 9% or more and close to the theoretical density. When the relative density is less than 96%, the mechanical strength is lowered because many open pores are present. In order to increase the mechanical strength of the granules, the average crystal grain size is preferably 100 μm or less, more preferably 50 μm or less, further preferably 10 μm or less and 1 μm or less.
m or more If the average crystal grain size of the granules exceeds 100 μm, the mechanical strength decreases. Since the unevenness of the granule surface becomes the starting point of fracture, the surface roughness of the granule is preferably 10 μm or less based on the maximum unevenness height Rmax defined by JIS B0601.

The excess sulfur content in the granules is 1000
It is preferably 0 wtppm or less, particularly preferably 5000 wtppm or less, and most preferably 2000 wtppm or less. The presence of a large amount of sulfur in the granules causes sintering inhibition and reduces the mechanical strength. The control of the excess sulfur content can be easily performed, for example, by controlling the flow rate of the H ₂ S gas at the time of sulfiding the rare earth oxide.

Granules can be prepared from rare earth oxysulfide powder by various methods, for example, rolling granulation method, combination of extrusion method and rolling granulation method, fluidized granulation method, spray drying method, embossing method, etc. May be used, and it is preferable to mold into a spherical shape.
After molding, it is adjusted to the optimum particle size and aspect ratio by sieving and shape classification. Alternatively, the rare earth oxide powder may be granulated in advance by the above method, and then the sulfurization reaction may be performed. Sulfurization conditions are the same as when using the oxide powder raw material.

The rare earth oxysulfide compact is sintered.
In atmospheric pressure sintering, the sintering atmosphere is vacuum (10 ^-3 torr or less) or an inert gas such as argon or nitrogen so that the rare earth oxysulfides are not oxidized, and the sintering temperature is 1100 to 1600 ° C. The time is preferably 1 to 10 hours. When the sintering temperature is low or the sintering time is short, the relative density does not reach 96% or more, and the mechanical strength decreases. If the sintering temperature is too high or the sintering time is too long, the average crystal grain size of the granules becomes large and the mechanical strength decreases.

It is also effective to improve the mechanical strength by promoting densification by using HIP treatment after sintering. Argon, for example, is used for the sintering atmosphere (pressure medium) at the time of HIP processing, the processing temperature is 1200 to 1500 ° C., and the pressure is 50 to 20.
It is preferably 0 MPa. When the treatment temperature is low or the pressure is low, the mechanical strength is almost the same as that in normal pressure sintering. On the other hand, if the treatment temperature is too high or the pressure is too high, the average crystal grain size of the granules becomes large and the mechanical strength decreases.

In order to make the surface roughness of the granules, for example, 10 μm or less on the basis of the maximum height R _max , the sintered granules are preferably polished. For example, put the granules of the regenerator material and the free abrasive material in the processing tank, and if the processing liquid is needed, load it with the media,
A processing tank or a workpiece placed in the tank is moved, and polishing is performed by relative movement of the workpiece and the abrasive or media. For example, rotary barrel processing, centrifugal flow barrel processing, vibrating barrel processing, gyro processing, reciprocating processing, linear flow processing and the like may be used.

[0019]

EXAMPLES Examples and comparative examples will be described below, but the present invention is not limited to these examples. The regenerator was filled with the regenerator at a filling pressure of 100 KPa, and the helium gas passage resistance was measured by the pressure difference between the upper and lower ends of the regenerator. The average aspect ratio was determined by microscopically photographing the granules after sintering and measuring the ratio of the length of the major axis to the length of the minor axis with an image recognition device. The degree of dust generation was determined by visually inspecting the regenerator material collected from the regenerator and determining the proportion of broken granules. Further, the content of excess sulfur is obtained by comparing the chemical analysis value of Gd and the S content by the combustion method, and its unit is wtppm.

[0020]

[Preparation and heat capacity of oxysulfide] 10 g of gadolinium oxide having an average particle size of 0.46 μm by the Fischer method was filled in a quartz boat and housed in a quartz reaction tube, and hydrogen sulfide gas H ₂ S was supplied.
The mixture was reacted at 650 ° C for 2 hours while flowing at a flow rate of 0.2 L / min. When the reaction product was measured by X-ray diffraction, only the peak of the gadolinium oxysulfide Gd ₂ O ₂ S was observed, and the reaction yield with respect to the rare earth oxide was 100%. The obtained Gd ₂ O ₂ S powder was molded into a disk shape with a diameter of 12 mm at a pressure of 30 MPa, isostatically pressed at a pressure of 200 MPa, and then subjected to atmospheric pressure sintering at 1500 ° C. for 6 hours in an argon atmosphere to give Gd. _{A 2} O ₂ S sample was obtained (Example 1).

The density of the Gd ₂ O ₂ S sintered body of Example 1 was 99.9% of the theoretical density by the Archimedes method, and the average crystal grain size was 3.2 μm as calculated from the following formula. d = 1.56C / (MN) (d: average grain size, C: length of line arbitrarily drawn in high resolution image such as SEM, N: number of crystal grains on line arbitrarily drawn, M: image The excess sulfur content of the Gd ₂ O ₂ S sintered body of Example 1 was 1000 wtppm as determined by comparison between the chemical analysis value of Gd and the S content by the combustion method.

FIG. 1 shows the results of measuring the heat capacity of the Gd ₂ O ₂ S sintered body of Example 1, and Table 1 shows the magnetic phase transition temperature and the heat capacity at that time. In addition to this, Fig. 1 also shows Tb ₂ O ₂ S, Dy ₂ O ₂ S, and Ho ₂ O ₂ S.
Helium (He-0.5MPa) for reference
The heat capacities of Pb, ErNi, and HoCu ₂ , which are general cold storage materials, are shown. The Gd ₂ O ₂ S regenerator material of Example 1 has a magnetic phase transition temperature around 5K, and the heat capacity at the magnetic phase transition temperature is 1.2 J / c.
At c · K, the heat capacity was 3 to 5 times higher than that of conventional HoCu ₂ or ErNi near the temperature of liquefied helium.

[0023]

[Table 1] Sample composition Magnetic phase transition temperature / K Heat capacity / J / cc · K Example 1 Gd ₂ O ₂ S 5.2 1.2 Example 2 Ho ₂ O ₂ S 2.2 1.25 Dy ₂ O ₂ S 4.6 1.0 Example 3 Gd _1.8 Tb _0.2 O ₂ S 4.8 0.84 Gd ₁ Tb ₁ O ₂ S 4.2 0.61 Tb _1.8 Gd _0.2 O ₂ S 5.3 1.3 Tb ₂ O ₂ S 6.3 1.7 Example 4 Dy _1.8 Ho _0.2 O ₂ S 4.3 0.8 Ho _1.8 Dy _0.2 O ₂ S 2.4 0.85 Example 5 Gd _1.8 Y _0.2 O ₂ S 4.6 0.75 Gd _1.8 La _0.2 O ₂ S 4.6 0.85 Gd _1.8 Ce _0.2 O ₂ S 4.7 0.74 Gd _1.8 Pr _0.2 O ₂ S 4.7 0.69 Gd _1.8 Nd _0.2 O ₂ S 4.8 0.77 Gd _1.8 Sm _0.2 O ₂ S 4.8 0.63 Gd _1.8 Eu _0.2 O ₂ S 4.9 0.76 Gd _1.8 Dy _0.2 O ₂ S 4.9 0.82 Gd _1.8 Ho _0.2 O ₂ S 4.9 0.71 Gd _1.8 Er _0.2 O ₂ S 5 0.81 Gd _1.8 Tm _0.2 O ₂ S 5 0.73 Gd _1.8 Yb _0.2 O ₂ S 5.1 0.76 Gd _1.8 Lu _0.2 O ₂ S 5.2 0.8

Gadolinium oxide Gd ₂ O used in Example 1
₃ was prepared as a sintered body under the same conditions as in Example 1, but without being sulfurized as an oxide (Comparative Example 1). This sample is 1K
It was found that it has a magnetic phase transition temperature in the vicinity and its heat capacity around 4.2K is extremely small, so it cannot be used as a regenerator material for liquefying helium gas.

Homium oxide having an average particle size of 0.36 μm and dysprosium oxide having an average particle size of 0.6 μm were sulfided, molded, hydrostatically pressed and sintered in the same manner as in Example 1 to give Ho ₂ O.
_{A 2} S, Dy ₂ O ₂ S sintered body was obtained (Example 2). The heat capacity of the obtained sintered body is shown in FIG. 1, and the magnetic phase transition temperature and the heat capacity at that temperature are shown in Table 1. In a wide area near the temperature of liquid helium,
It showed a larger amount of heat than HoCu ₂ and ErNi.

A mixture of the gadolinium oxide powder used in Example 1 and the terbium oxide powder having an average particle size of 0.69 μm was prepared,
Sulfurization, molding, isostatic pressing and sintering were carried out in the same manner as in Example 1 to obtain gadolinium-terbium oxysulfide (G
A d _x Tb ₂ -xO ₂ S) sintered body was obtained (Example 3). Four types of sintered bodies (x = 0.2,1.0,
1.8, 2.0) X-ray diffraction was measured, and when x = 2.0, Tb ₂ O ₂
Only S peak is observed, and G at x = 0.2, 1.0, 1.8
Solid solution Gd _x Tb belonging to neither d ₂ O ₂ S nor Tb ₂ O ₂ S
A peak corresponding to _2-x O ₂ S was obtained.

The heat capacity measurement results of the Gd _x Tb _2-x O ₂ S sintered body of Example 3 are shown in FIG. 2, and the magnetic phase transition temperature and the heat capacity at that time are shown in Table 1. The heat capacity at the magnetic phase transition decreases as the value of x decreases to 1.8, 1, but the magnetic phase transition temperature shifts to the low temperature side compared to Gd ₂ O ₂ S, and the peak width of the specific heat widens, At the liquid helium temperature, it exceeds the heat capacity of Gd ₂ O ₂ S. On the other hand, as shown in Table 1 and FIG. 3, as the composition of Tb ₂ O ₂ S approaches, the magnetic phase transition temperature shifts to a higher temperature side than Gd ₂ O ₂ S.

Generally, in a rare earth magnetic atom in a crystal, the magnetic interaction depends on the interatomic distance, and if the interatomic distance is the same in a perfect crystal, the magnetic interaction can be represented by a single parameter, The entire magnetic spin system of the crystal undergoes a sharp phase transition. In that case, as in Example 1, the peak of the specific heat due to the phase transition becomes large and sharp. On the other hand, when a plurality of rare earth elements are solid-dissolved as in Example 3, the distance between magnetic atoms is locally changed, the crystal field is locally disturbed, and the homogeneity of the magnetic interaction of the entire crystal is impaired. Be done. As a result, local disorder appears in the magnetic phase transition of the magnetic spins in the crystal, and the peak of the specific heat is dispersed in a certain temperature range to widen the width of the specific heat peak. To the low temperature side in Gd, Tb, and Dy systems.

The dysprosium-holmium composite oxysulfide Dy was prepared by mixing the holmium oxide powder and the dysprosium oxide powder used in Example 2 and subjecting them to sulfide / molding / isostatic pressing / sintering in the same manner as in Example 1. _A sintered body of _x Ho _{2 -x} O ₂ S was obtained (Example 4). Figure 4 shows the heat capacity of this sintered body.
Table 1 shows the magnetic phase transition temperature and the heat capacity at that temperature. By changing the value of x, an intermediate magnetic phase transition temperature between Dy ₂ O ₂ S and Ho ₂ O ₂ S can be obtained, and the peak width of the specific heat can be obtained from Dy ₂ O ₂ S and Ho ₂ O ₂ S. I was able to spread

Gadolinium oxide (90 mol%), Y, La, Ce,
The rare earth oxides of Pr, Nd, Sm, Eu, Dy, Er, Tm, Yb and Lu (10 mol%) were treated in the same manner as in Example 3 to obtain a composite rare earth oxysulfide sintered body (implementation). Example 5). Table 1 shows the magnetic phase transition temperature (Tc) and the heat capacity at that temperature.
By using the composite rare earth oxysulfide, various magnetic phase transition temperatures can be obtained, and the peak value of the specific heat at the magnetic phase transition temperature also changes variously. The rare earth oxides used in Examples 3 and 5 were treated in the same manner as in Example 3 with the oxides remaining unsulfurized to obtain sintered bodies, but the heat capacity at around 4.2K was extremely small (comparison). Example 2).

[0031]

[Regenerator granules] The Gd ₂ O ₂ S powder obtained in Example 1 was formed into a spherical shape by the rolling granulation method, and the obtained granules were mixed with two different nylon meshes (A mesh (opening 308 μm)). B mesh
(Opening of 190 μm)). The sieved granules were rolled on an iron plate (polished to a mirror surface) tilted at about 25 °, and the rolled-down granules were collected, which was subjected to shape classification. The average particle size and average aspect ratio of 100 granules were 0.25 mm and 1.1. The average particle size and the average aspect ratio of the Gd ₂ O ₂ S granules were measured from images taken by using a video high scope system.

The obtained Gd ₂ O ₂ S granules were filled in an alumina crucible and placed in a sintering furnace to carry out normal pressure sintering, and the inside of the furnace was sufficiently evacuated and then argon gas was introduced. And sintered in an argon atmosphere. The desired Gd ₂ O ₂ S regenerator material was obtained by setting the firing temperature to 1500 ° C. and the firing time to 6 hours. Gd ₂ O
The density of ₂ S regenerator material is calculated by the pycnometer method.
It was 99.2%. The average crystal grain size and the sulfur content were the same as in Example 1.

Nylon type media and 10 wt% concentration of alumina slurry were loaded into a processing tank, Gd ₂ O ₂ S regenerator material was placed therein, and surface processing was performed by a rotary barrel processing method.
Granules of a cold storage material were obtained (Example 6). When the processing time was 6 hours, the surface roughness of the granules became 1 μm. The surface roughness was measured with a scanning tunneling microscope (STM roughness meter).
After filling the obtained Gd ₂ O ₂ S regenerator material in the cooling section of the GM refrigerator at a filling rate close to the closest packing, He gas with a heat capacity of 25 J / K was added at 3 g / se.
The GM refrigeration operation cycle was continued for 500 hours continuously under the condition of mass flow rate of c and gas pressure of 16 atm. When the passage resistance of the helium gas flowing through the cold storage section was measured at this time, no increase in the passage resistance from the start of the operation was observed. 1000 in succession
After the Hr operation, the Gd ₂ O ₂ S regenerator material was taken out and observed, and no finely divided granules were observed.

In each of the following samples, the rare earth oxysulfide granules were sulfided, molded, classified, and subjected to the same conditions as in Example 6.
It was prepared by sintering and polishing. The preparation conditions are the same as in Example 6 except as noted. Note that the sample numbers are shown in the order of succession with Example 1 as Sample 1.

Granules were prepared, sintered and polished under the same conditions as in Example 6 except that the tilt angle of the iron plate was changed (Samples 2 and 3). In addition, the remainder of the shape classification in Example 6,
Granules having an aspect ratio of more than 3 were sintered and polished (Sample 4). Then, the passage resistance of helium gas and the degree of generation of dust were evaluated by the GM refrigeration operation cycle used in Example 6, and the results are shown in Table 2. When the average aspect ratio is less than 3, good results are obtained as in Example 6, but when the average aspect ratio exceeds 3, the helium gas passage resistance increases by 30 to 40% after continuous operation for 500 hours, and continuous 1000 Hr. After operation, the proportion of finely crushed granules reached about 20-30%.

[0036]

[Table 2] Sample classification angle / ° Average aspect ratio He gas passage Degree of dust generation Resistance increase rate 1 25 1.1 No problem No 2 30 1.3 No problem No 3 40 1.8 No problem 4 − 3.2 After 500 hours, 20% to 30% % Granule 30-40% destroyed

Sintered granules were produced under the same conditions as in Example 6 except that the crystal grain size was changed by changing the sintering temperature or the sintering time (Samples 5 to 9). The helium gas passage resistance and the degree of generation of dust due to the difference in crystal grain size were measured in Example 6
The GM refrigerating operation cycle used in 1. was evaluated, and the results are shown in Table 3. Good results were obtained with granules having a crystal grain size of 100 μm or less like Samples 1 to 5-7. However, in the case of granules with a crystal grain size of more than 100 μm like Samples 8 and 9, the helium gas passage resistance increased by 20 to 30% after continuous operation for 500 hours, and
The percentage of finely crushed granules reached about 10 to 15% after 000 hours of operation.

[0038]

[Table 3] Sample Sintering temperature / Sintering time / Average Crystal He gas passage Dust generation ℃ Hr Particle size / μm Resistance increase rate Degree 1 1500 6 3.7 No problem No 5 1550 6 23 No problem No 6 1600 6 85 No problem None 7 1600 3 37 None No problem 8 1650 6 110 10 to 15% 20 to 30% after operation 500hr, granule destruction 9 1600 15 121 10 to 15% after operation 500hr 10 to 15% 20 to 30% granule destruction

The surface processing time was changed, and the helium gas passage resistance and the degree of dust generation due to the difference in surface roughness were evaluated in the GM refrigeration operation cycle used in Example 6, and the results are shown in Table 4. Good results were obtained when the surface roughness was 10 μm or less as in Samples 1, 10, and 11. But sample 1
When the surface roughness exceeds 10 μm, as in 2, continuous operation 500
The helium gas passage resistance increased by 20 to 30% as the time continued, and the proportion of finely crushed granules reached about 15 to 20% in continuous 1000Hr operation.

[0040]

[Table 4] Sample surface processing time Surface roughness / μm He gas passage Dust generation rate Resistance increase rate 1 6 1 No problem No 10 4 5 No problem No 11 2 8 No problem 12 0 12 15% to 20% after 500 hours of operation 20% to 30% granule destruction

Gd ₂ O ₂ S prepared by changing the sulfide gas flow rate
Granules were prepared and sintered in the same manner as in Example 6 using the powder. The excess sulfur content affects the relative density, and also affects the helium gas passage resistance and the degree of dust generation. Therefore, the helium gas passage resistance and the degree of generation of dust are determined in Example 6
Table 5 shows the results of evaluation by the GM refrigeration operation cycle used in. Good results were obtained with granules having a relative density of 96% or more as in Samples 1, 13, and 14. In the case of granules having a relative density of less than 96% as in Sample 15, the increase rate of helium gas passage resistance at the time of continuous operation for 500 hours reaches 15 to 20%,
Regarding the state of destruction of granules after continuous operation for 1000 hours, the proportion of finely crushed granules reached about 5-10%. In order to make the relative density 96% or more, the content of excess sulfur is preferably 10,000 wtppm or less, more preferably 500 to make the relative density 98% or more.
It is 0 wtppm or less, and most preferably 1000 wtppm or less in order to make the relative density 99% or more.

[0042]

[Table 5] Sample H ₂ S gas flow rate Sulfur content / Relative density /% He gas passage Dust generation rate (L / min) wtppm Resistance increase rate 1 0.2 1000 99.2 No problem 13 1 5000 98.3 No problem 14 1.25 7000 97.6 None No problem 15 2.5 12500 95.1 After 500 hours of operation 5-10% Granules 15-20% Destruction

[0043] The refrigeration properties of the Gd _1.8 Tb _{0 .2} O ₂ S cold accumulating material was prepared in the same manner as Gd ₂ O ₂ S regenerator material and Example 6 prepared in Example 6, regenerative power consumption 3.3kW It investigated by the pulse tube refrigerator. This refrigerator has a two-stage regenerator,
Pb was used for the first stage regenerator on the high temperature side, and the second stage regenerator was filled with regenerator material. FIG. 5 (A) shows the configuration of the second-stage regenerator in the conventional example. The regenerator is filled with Pb, Er ₃ Ni and HoCu _{2 in} order from the higher temperature side, and the volume ratio of each is 2: 1: 1. The freezing characteristics of the conventional example are shown in FIG. The output of this refrigerator at 4.2K was about 165mW, and the minimum temperature reached at no load was about 2.9K.

On the other hand, 25% by volume of the HoCu ₂ regenerator material on the low temperature side of this regenerator was replaced with a Gd ₂ O ₂ S regenerator material, a Gd _1.8 Tb _0.2 O ₂ S regenerator material or the like to examine the regenerator characteristics. The configuration of the regenerator in the example is shown in FIG. 5 (B). Figure 6 shows the freezing characteristics of the Gd ₂ O ₂ S regenerator material.
Fig. 6 (c) shows the freezing characteristics of the Gd _1.8 Tb _0.2 O ₂ S regenerator material in (b). With Gd ₂ O ₂ S regenerator, output at 4.2K is about 300m
The minimum temperature reached at W and no load was about 2.7K. Gd _1.8 Tb
_{When 0.2} O ₂ S regenerator material was used, the output at 4.2K was about 340mW, and the minimum temperature reached at no load was about 2.65K.

The conventional regenerator of FIG. 6 (a) is referred to as FIG.
Fig. 7 shows the ratio of the refrigerating capacity of the regenerator using the Gd ₂ O ₂ S and Gd _1.8 Tb _0.2 O ₂ S regenerator materials in (b) and (c). The regenerator filled with Gd ₂ O ₂ S regenerator material (broken line a) had about twice the refrigerating capacity at 4.2K, and the ratio of the refrigerating capacity increased as the temperature decreased and reached 4 times at 3K. Gd _1.8 Tb _0.2 O ₂ S with cold storage material (solid line b) at 4.2K
It has more than twice the refrigerating capacity, and the ratio of the refrigerating capacity increased with the temperature decrease, reaching 4.5 times at 3K.

Except that the size of the mesh used for sieving was changed to change the average particle size of the granules,
Under the same conditions as in Example 6, cold storage material granules were prepared. The frozen characteristics of the produced granules were evaluated in the same manner as above, and the results are shown in Table 6.
Shown in. Like Samples 16-18, the average particle size of the granules is 0.
A high output was obtained at 4.2K in the range of 05 mm or more and 1 mm or less, but when the average particle size of the granules was out of this range as in Samples 19 and 20, the output at 4.2K decreased. Therefore, the average particle size of the granules is preferably 0.05 mm or more and 1 mm or less, more preferably
The thickness is 0.1 to 0.7 mm, more preferably 0.1 to 0.3 mm, and most preferably 0.2 to 0.3 mm.

[0047]

[Table 6] Average particle size of sample granules / mm 4.2 Output power at 4.2K / mW 16 0.25 300 17 0.77 290 18 18 0.071 285 19 19 200 200 0.045 185

[0048]

Comparative Example 3 The freezing characteristics of Gd ₂ O ₃ granules produced under the same molding, classifying and sintering conditions as in Example 6 were evaluated in the same manner as above. The output at 4.2K was about 100mW, and the minimum temperature reached at no load was about 3.5K. This result is lower than the conventional example (HoCu ₂ ) in both the output of the regenerator and the minimum reached temperature.

The volume ratio of the HoCu ₂ regenerator material to the rare earth oxysulfide regenerator material is preferably 20 to 80% HoCu _{2 and} 80 to 20% rare earth oxysulfide. Further, even when the Tb-based oxysulfide is arranged on the high temperature side of the Gd-based oxysulfide, it is preferable to arrange HoCu ₂ on the high temperature side to secure the refrigerating capacity up to 7K. As oxy sulfides mainly comprised of Tb, was prepared _{Gd 0.1 Tb 1.9 O 2 S,} Tb 2 O 2 S
The specific heat peak shifts slightly to the low temperature side, and
A cold storage material similar to ₂ O ₂ S was obtained.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing heat capacities of a rare earth oxysulfide regenerator material and helium of an example and a regenerator material of a conventional example.

FIG. 2 is a characteristic diagram showing heat capacities of Gd-rich Gd _2-x Tb _x O ₂ S rare earth oxysulfide cold storage materials in Examples.

FIG. 3 is a characteristic diagram showing a heat capacity of a Tb-rich Gd _2−x Tb _x O ₂ S rare earth oxysulfide cold storage material in an example.

FIG. 4 is a characteristic diagram showing the heat capacity of the Ho-Dy composite rare earth oxysulfide cold storage material of the example.

FIG. 5 is a diagram showing the configurations of a conventional regenerator (A) and an example regenerator (B).

FIG. 6 is a characteristic diagram showing the refrigerating capacity (a) of the conventional regenerator and the refrigerating capacity (b) and (c) of the regenerator of the embodiment.

FIG. 7 is a characteristic diagram showing a ratio of refrigerating capacities of a conventional regenerator and an example regenerator.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Katsunori Kagawa             Kamijima Kagaku 80 Kada, Omagama-cho, Mitoyo-gun, Kagawa Prefecture             Industrial Co., Ltd. Takuma Factory

Claims (16)

[Claims] 1. The general formula R ₂ O ₂ S (R is Y containing La, Ce,
Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Y
Represents one or more rare earth elements selected from b and Lu. ) A rare earth oxysulfide cold storage material consisting of a rare earth oxysulfide. 2. The rare earth oxysulfide is Gd _2-x Tb _x O ₂
The rare earth oxysulfide cold storage material according to claim 1, wherein S (x = 0.2 to 2). 3. The rare earth oxysulfide Gd _2-x Tb _x O ₂ S
3. The rare earth oxysulfide cold storage material according to claim 2, wherein the x value in is 1.6 to 2. 4. The rare earth oxysulfide is Ho or Dy.
2. The regenerator material of rare earth oxysulfide according to claim 1, which is an oxysulfide of 5. The regenerator material of rare earth oxysulfide according to claim 1, wherein the rare earth oxysulfide is granular. 6. The rare earth oxysulfide regenerator material of claim 5, wherein the granules of the rare earth oxysulfide regenerator material have an average particle size of 0.05 mm to 1 mm. 7. The rare earth oxysulfide cold storage material according to claim 5, wherein the average value (average aspect ratio) of the ratio of the major axis to the minor axis of the granule is 3 or less. 8. The rare earth oxysulfide cold storage material according to claim 5, wherein the relative density of the rare earth oxysulfide granules is 96% or more. 9. The cool storage material for rare earth oxysulfide according to claim 5, wherein the rare earth oxysulfide granules have an average crystal grain size of 100 μm or less. 10. The rare earth oxysulfide cold storage material according to claim 5, wherein the surface roughness of the granules is 10 μm or less based on the maximum height R _max . 11. Excessive sulfur content in the granules of 1000
The rare earth oxysulfide cold storage material according to claim 5, characterized in that the content is 0 wtppm or less. 12. The regenerator material for rare earth oxysulfides according to claim 5, wherein the granules have a maximum value of volume specific heat at 7 to 2K. 13. The general formula R ₂ O ₂ S (R is Y containing La, Ce,
Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Y
Represents one or more rare earth elements selected from b and Lu. ) A regenerator filled with a rare earth oxysulfide cold storage material composed of a rare earth oxysulfide. 14. The regenerator is filled with a regenerator material in layers in the order from a high temperature material to a low temperature material, and a HoCu ₂ regenerator material is filled on the high temperature side of the rare earth oxysulfide regenerator material. The regenerator according to claim 13, wherein: 15. The regenerator is filled with the regenerator material in layers in the order from the high temperature material to the low temperature material, and the high temperature side of the Gd oxysulfide regenerator material is filled with the Tb oxysulfide regenerator material. The regenerator according to claim 13, which is provided. 16. The regenerator is filled with a regenerator material in layers from a high temperature material to a low temperature material in this order, and Ho or Dy oxysulfide regenerator material is provided on the low temperature side of the Gd oxysulfide regenerator material. The regenerator according to claim 15, wherein the regenerator is filled with.