JPH05203272A - Cryogenic cold accumulation material and cryogenic cold accumulator using same - Google Patents

Abstract

PURPOSE:To provide a cryogenic cold accumulation material and a cold accumulator using the same in which gaps among cold accumulation substance particles can be stably held even if a stress, a thermal impact, etc., is applied to gas flow during operation and performance of the accumulator can be maintained for a long period. CONSTITUTION:A cryogenic cold accumulation material has particles of cold accumulation substance having a specific heat of 0.1j/cm<3>K or more at 30K or lower such as magnetic intermetallic compound containing Pb, Pb alloy and rare earth element. The particles of the substance are fixed thereamong by sintering the substance at a temperature lower than its melting point. A cryogenic cold accumulator uses the sintered material at least as part of the material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryogenic regenerator material used in refrigerators and the like, and a cryogenic regenerator using the same.

[0002]

2. Description of the Related Art In recent years, the development of superconducting technology has been remarkable, and with the expansion of its application fields, it has become essential to develop a small-sized and high-performance refrigerator. Such refrigerators are required to be lightweight, compact and have high thermal efficiency.
For these reasons, research on refrigerators using a new refrigeration system (magnetic refrigeration) such as a heat cycle using a magnetocaloric effect instead of gas refrigeration has been actively conducted.

For example, in a superconducting MRI apparatus or the like,
For example, a Gifford McMahon type small helium refrigerator (GM refrigerator) is used. This GM refrigerator
It is mainly composed of a compressor for compressing the working medium such as He gas, an expansion section for expanding the compressed working medium, and a cryogenic regenerator for maintaining the cooling state of the working medium cooled by the expansion section. .. Then, the working medium compressed by the compressor is expanded and cooled by the refrigerator at a cycle of about 60 times per minute, and the system to be cooled is cooled through the tip of the expansion part of the refrigerator.

The cryogenic regenerator incorporated in the refrigerator as described above is constructed by filling the regenerator cylinder with the cryogenic regenerator material. Here, Cu, Pb, etc. have been mainly used conventionally as a constituent material of the cryogenic regenerator material. Further, recently, in order to realize a temperature closer to absolute zero, rare earth element-based magnetic regenerator materials such as Er ₃ Ni, which show a large volume specific heat in an extremely low temperature range, have been used.

Of these, Cu and Cu alloys are excellent in drawability, and therefore, extra fine wires can be produced, and by knitting the fine wires into a mesh shape, a cool storage material having stable durability is constructed. Is common.

On the other hand, when a rare earth element magnetic regenerator material such as Pb or Pb alloy or Er ₃ Ni is used, it is made into a particle shape close to a sphere in order to increase the filling rate (for example, JP-A-3-174486). (See, for example, the gazette), a regenerator is constructed by filling such a regenerator with a regenerator and then covering the regenerator with an appropriate lid so that the grains do not move. The function of such a regenerator is to cause a gas such as He to flow through the voids remaining between the constituent particles and to perform heat exchange by the temperature difference between the regenerator material and the gas.

[0007]

By the way, in the use state of the regenerator using the spherical regenerator material as described above, the gas such as He is high in pressure and at a high speed, and its flow direction is frequently changed. In addition, since the cold storage substance particles pass through the voids, a complicated stress such as vibration is applied to the cool storage substance particles.

[0008] For example, when a cold storage material in which Cu is woven into a mesh shape is used, the stress is generated almost symmetrically from the center of the wire, so that the relative positions of the wires do not change. However, in a regenerator composed of a spherical body such as Pb or a rare earth magnetic regenerator material, an unequal stress may be seen from one particle. For this reason, at the beginning of filling, the cold storage material particles that were packed in the closest packed state generated a gap between the particles with the passage of operating time, causing a change in the gas flow of the working medium, and There is a problem that the performance of the regenerator is adversely affected by the generation of fine powder due to the friction of.

Here, it is effective to avoid the above-mentioned inconveniences by making the shape of the particles of the cold storage material spherical and eliminating the variation in the particle diameter size, but it is impossible from an industrial point of view. Or it is very expensive and not a realistic solution. For this reason, in the conventional regenerator, disassembly repair and replacement of the regenerator are performed every time a certain operating time elapses, and even during operation during that period, operation is performed according to the time change of temperature. Complex driving operations were forced, such as having to adjust the conditions.

The present invention has been made in order to solve such a problem, and keeps the voids between the cold-storing substance particles stable even if stress or thermal shock due to the gas flow is added during operation. It is an object of the present invention to provide a regenerator material for cryogenic temperature and a regenerator using the same, which is capable of maintaining the performance of the regenerator.

[0011]

Means for Solving the Problem That is, the cryogenic regenerator material of the present invention is a cryogenic regenerator material using granules of a regenerator material having a specific heat of 0.1 J / cm ³ K or more at a temperature of ³⁰ K or less. In the above, the particles of the regenerator material are fixed by sintering at a temperature lower than the melting point of the regenerator material.

The cryogenic regenerator of the present invention is a cryogenic regenerator filled with a cryogenic regenerator material, wherein the sintered cold accumulator is used as at least a part of the cryogenic regenerator material. It is characterized by

The cold storage material used in the present invention includes 3
Various substances can be used as long as they have a specific heat of 0.1 J / cm ³ K or more at a temperature of 0 K or less, and examples thereof include lead, lead alloys, and magnetic intermetallic compounds containing rare earth elements. It

As the rare earth element-based magnetic intermetallic compound, RM _z (R is Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, T
At least 1 selected from b, Dy, Ho, Er, Tm and Yb
R is a rare earth element, M is at least one metal element selected from Ni, Co and Cu, and z is a number in the range of 0.001 to 9.0). An intermetallic compound etc. are illustrated. These rare earth element-based magnetic intermetallic compounds have the maximum value of specific heat below 20K, and the value is sufficiently large as the specific heat per unit volume (volume specific heat), so that it is possible to reach a very low temperature. To do.

The cryogenic regenerator material of the present invention comprises the particles of the regenerator material described above, and these particles are fixed by sintering. Here, the particles of the cold storage material, the shape is close to spherical, and the more uniform the particle size,
Since the flow of gas can be smoothed, 70
The ratio of the major axis to the minor axis (aspect ratio) is more than weight%
It is preferable that the regenerator material particles are 5 or less, and that 70% by weight or more of all the particles are regenerator material particles having a particle diameter of 0.01 to 3.0 mm.

The aspect ratio of the particles of the regenerator material has a great influence on the strength and packing density of the granules. If the aspect ratio exceeds 5, deformation fracture tends to occur and uniform voids should be formed. Difficult to fill. Therefore, if such particles exceed 30% by weight of the whole particles, the cold storage performance is deteriorated. A more preferable aspect ratio is 3 or less, and more preferably 2 or less, and it is desirable that the aspect ratio be as close to a true sphere as possible. The ratio of particles with an aspect ratio of 5 or less in the whole particle is 80
It is more preferably at least wt%, and even more preferably at least 90 wt%.

Further, the particle size of the cold storage material particles has a great influence on the strength and heat transfer characteristics of the particles, and the particle size is
If it is less than 0.01 mm, the packing density becomes too high, which leads to an increase in pressure loss, and if the particle size exceeds 3.0 mm, the heat transfer area becomes small, resulting in a decrease in heat transfer efficiency. It will be. Therefore, if such particles exceed 30% by weight of the whole particles, the cold storage performance is deteriorated. A more preferable particle size is in the range of 0.1 to 2 mm. The ratio of particles having a particle size of 0.01 to 3.0 mm in the whole particle is more preferably 80% by weight or more, and further preferably 90% by weight or more.

The particles of the cold-storing substance as described above can be produced by various methods. However, when the particles of the rare earth element-based magnetic intermetallic compound which are essentially brittle are manufactured, the rare earth element is used. It is preferable to apply a method of spheroidizing by rapidly quenching and solidifying the molten metal containing s by a rotating disk method, a single roll method, a twin roll method, an inert gas atomizing method, a rotating nozzle method, or the like. After that, the particle size and shape are made uniform by sieving, shape classification and the like.

The cold accumulating material in the present invention is obtained by sintering the particles of the cold accumulating substance as described above at a temperature lower than the melting point thereof to fix the particles. The degree of sintering may be such that particles are fixed to each other, and the sintering conditions are preferably set so that the porosity is about 15 to 80%. If the porosity after sintering is less than 15%, the gas flow is obstructed, and the cold storage performance deteriorates.
If it exceeds 80%, it becomes impossible to actually manufacture it structurally.

Further, the fixation due to the sintering of the cold storage material granules is
It may be performed directly between the particles of the cold storage material, or the surface of the particles of the cold storage material may be previously covered with a material that liquefies, softens or self-bonds at a temperature lower than the melting point of the cold storage material, and then liquid phase baking is performed through such a material. You may carry out by binding. Examples of such intervening substances include lead, silver, tin, indium,
Examples are low melting point alloys made of zinc or the like. By performing liquid phase sintering through the substance as described above, the cold storage substance particles can be fixed at a lower temperature and the fixing strength can be improved.

The cryogenic regenerator material of the present invention is manufactured, for example, as follows. That is, first, the cold storage substance granules as described above are housed in a sintering container made of a material that does not easily react with the cold storage substance, and pressure is applied to the cold storage substance particles so that the cold storage substance particles appropriately contact with each other. Hold down the above granules,
In this state, heat treatment is performed to sinter. As the above-mentioned sintering container, in order not to fuse the container and the cool storage material particles, spray fine particles of oxide, Ni, Co
It is also an effective method to carry out plating with a metal or the like, or to use an oxide container. The firing atmosphere is preferably performed in vacuum or in an inert gas so that the cold storage material is not oxidized. The sintering temperature and time are appropriately set so that the porosity as described above can be obtained depending on the presence or absence of the cool storage material and inclusions used. In addition, this sintering process,
It also functions as a stabilizing treatment for cold storage materials, especially rare earth intermetallic compounds.

Further, the cryogenic regenerator of the present invention is one in which a regenerator material in which particles are fixed by the above-mentioned sintering (hereinafter referred to as a sintered regenerator material) is filled in a regenerator cylinder. Not all of the materials have to be composed of the above-mentioned sintered regenerator material, but it is also possible to fill them as a mixture of the sintered regenerator material and granules. Further, various forms can be adopted, such as a cold regenerator for cryogenic temperature can be configured by filling a plurality of sintered regenerator materials.

[0023]

In the cryogenic regenerator material of the present invention, the particles of the regenerator material are sintered and the particles are fixed. Therefore, even if stress or thermal shock due to the gas flow is applied, it is possible to prevent the vibration and movement of the cool storage material particles, so that the voids between the cool storage material particles are kept stable, and the change in the gas flow and the generation of fine powder. The generation can be effectively suppressed. In addition, the heat transfer area can be sufficiently ensured because particles of the cold storage substance are basically used. A regenerator using such a cryogenic regenerator material can greatly improve stability. That is, after the temperature change is stable and the operating conditions are optimally adjusted, it is possible to always operate without adjusting the stable conditions and the maximum output conditions. In particular, in the case of a rare earth-based cool storage material, its melting point is relatively high, and when spherical powder is made, its particle size distribution becomes quite wide. However, according to the cool storage material of the present invention, its particle size distribution The adverse effect of can be completely eliminated, and a long-life regenerator can be constructed.

[0024]

EXAMPLES Examples of the present invention will be described below.

Example 1 First, an Er ₃ Ni mother alloy (melting point: 850 ° C.) was produced by high frequency melting. This Er ₃ Ni mother alloy was melted at approximately 1150 ° C., and this molten metal was dropped onto a rotating disk in an Ar atmosphere and rapidly solidified. The obtained granules were appropriately classified and sieved to obtain Er ₃ Ni granules having a particle size of 200 to 300 μm. This Er ₃ N
When the aspect ratio of the i grain was measured, particles having an aspect ratio of 5 or less were present in a proportion of 95% by weight or more of the whole grain. Such Er ₃ Ni granules were filled in a graphite crucible while applying vibration, and placed so that the force of lightly pressing the graphite lid was exerted, and placed in the firing furnace in this state. .. The filling rate when filling granules is approx.
It was set to 62%. Then, evacuate the furnace sufficiently and then
A gas was introduced, the mixture was baked in this Ar atmosphere at a temperature of 750 to 800 ° C. for 30 to 60 minutes, cooled to room temperature, and then taken out from the crucible to obtain the target sintered Er ₃ Ni regenerator material.

The sintered Er ₃ Ni regenerator material thus obtained is
It had a porosity of about 30%. Further, the outer shape was contracted by about 5% in terms of the size ratio compared to the inner diameter of the crucible used. To investigate the strength of this sintered Er ₃ Ni regenerator material, it was dropped onto a bakelite plate from a height of about 30 cm, and it was found that the corners did not break and had sufficient strength. did. This means that it has sufficient resistance to gas flow.

Next, a cryogenic regenerator was constructed using the sintered Er ₃ Ni regenerator material, and its stability and refrigerating capacity were evaluated as follows. First, it polished together the outer diameter of the sintered Er ₃ Ni cold accumulating material to the inner diameter of the cold accumulating cylinder, after full dropped pulverized by ultrasonic, pressed into cold storage cylinder roughly a pressure of 1 kg / cm ² did. This was incorporated into a GM refrigerator and a freezing test was conducted. As a result, the refrigerating capacity at 4.2K was about 200-400mW, and stable output could be obtained during continuous 3000 hours operation, and good results were obtained.

Further, as a comparison with the present invention, a cryogenic regenerator was constructed by directly using the Er ₃ Ni particles produced in Example 1 as a regenerator material without sintering. The filling rate of Er ₃ Ni particles in the cold storage cylinder was set to 65%. This cryogenic regenerator was incorporated into a GM refrigerator, and a freezing test was conducted in the same manner as in the above-mentioned examples. As a result, the refrigeration capacity at 4.2K was about 150-300mW.

Example 2 The Er ₃ Ni particles produced in the same manner as in Example 1 were sintered under the same conditions as in Example 1 except that an alumina crucible was used. The obtained sintered Er ₃ Ni regenerator material had the same strength as that of Example 1, and the same good result as that of Example 1 was obtained in the freezing test.

Example 3 The Er ₃ Ni particles produced in the same manner as in Example 1 were sintered under the same conditions as in Example 1 except that a crucible having Ni plated therein beforehand was used. The obtained sintered Er ₃ Ni regenerator material is
It has the same strength as that of Example 1, and the same good result as that of Example 1 was obtained in the freezing test.

Example 4 First, the surface of an Er ₃ Ni grain produced in the same manner as in Example 1 was preliminarily plated with Sn to a thickness of 5 to 10 μm. Then, the Er ₃ Ni particles having this Sn plating film were filled into the crucible made of graphite while applying vibration, and the crucible made of graphite was placed thereon so that the force of gently pressing the lid made of graphite would work.
It was placed in the firing furnace in this state. The filling rate when filling the granules was about 65%. Then, the furnace was evacuated to 5 × 10 ^-3 Torr, fired at a temperature of about 300 ° C for 30 minutes, cooled to room temperature, and then taken out of the crucible.
A sintered Er ₃ Ni cold storage material having a plated layer was obtained.

The sintered Er ₃ Ni regenerator material having the Sn plating layer thus obtained had a porosity of about 33%. Further, the strength of the sintered Er ₃ Ni cold accumulating material is equivalent to the sintering Er ₃ Ni cold accumulating material according to Example 1, even when dropped onto a Bakelite plate from a height of 50 cm, any problem did not occur.

Sintered Er ₃ Ni having the above Sn plating layer
The cold storage material is press-fitted into the cold storage cylinder in the same manner as in Example 1 to form a cryogenic regenerator, and the cryogenic regenerator is incorporated into a GM refrigerator, and a freezing test is performed in the same manner as in Example 1. It was As a result, the refrigeration capacity at 4.2K was good at about 150-200mW.

Example 5 First, lead spheres having a particle size of 250 to 300 μm were prepared, and the lead spheres were filled in a graphite crucible while applying vibration, and a force for gently pressing the graphite lid was exerted on it. And placed in a firing furnace in this state. The filling rate when filling the lead balls was about 68%. Then, in the furnace 5 ×
After evacuating to 10 ^-3 Torr, 2
After firing at a temperature of 70 ° C for 10 to 30 minutes and cooling to room temperature, it was taken out from the crucible to obtain the desired sintered Pb cold storage material.

The sintered Pb regenerator material thus obtained has a content of about 28%.
Had a porosity of. In addition, the outer shape was contracted by about 4% in terms of the size ratio compared to the inner diameter of the crucible used. Further, the strength test of this sintered Pb cold storage material was conducted in the same manner as in Example 1, and it was confirmed that there was no problem in strength.

Further, the sintered Pb regenerator material was press-fitted into the regenerator cylinder in the same manner as in Example 1 to form a cryogenic regenerator, and this cryogenic regenerator was incorporated into the GM refrigerator. A freezing test was conducted in the same manner as in 1. As a result, the refrigeration capacity at 10K was good at about 3W.

As described above, it is understood that the regenerator using the regenerator material of the present invention can be stably operated for a long period of time. This means that the number of man-hours required for maintenance of the regenerator can be significantly reduced, and the operating cost of the refrigerator can be reduced.

[0038]

As described above, according to the present invention, the durability against stress and thermal shock due to gas flow is excellent, the vibration and movement of the particles of the cold storage material can be prevented, and the voids between the particles of the cold storage material are kept stable. It is possible to provide an extremely low temperature regenerator material. Therefore, it is possible to effectively suppress the change of the gas flow and the generation of fine powder, and thus it is possible to provide a regenerator that can stably maintain its performance for a long period of time.

[0039]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomohisa Arai 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Incorporated Toshiba Toshiba Office

Claims (3)

[Claims] 1. A regenerator material for cryogenic use, comprising particles of a regenerator material having a specific heat of 0.1 J / cm ³ K or more at a temperature of ³⁰ K or less, wherein the space between the regenerator material particles is less than the melting point of the regenerator material. An extremely low temperature regenerator material characterized by being fixed by sintering at the temperature. 2. The cryogenic regenerator material according to claim 1, wherein the particles of the regenerator material are liquid phase fired through a substance that liquefies, softens or self-bonds at a temperature lower than the melting point of the regenerator material. A cryogenic regenerator characterized by being fixed by binding. 3. A regenerator filled with a cryogenic regenerator material, wherein at least a part of the cryogenic regenerator material is a grain of a regenerator material having a specific heat of 0.1 J / cm ³ K or more at a temperature of ³⁰ K or less. A cryogenic regenerator characterized by using a regenerator material having a body fixed by sintering at a temperature lower than the melting point of the regenerator material.