JPH10245651A - Magnetic cold storage alloy, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide alloy useful as a lamination type cold storage material in which a sharp specific heat peak is not lost even when powdered and granulized by limiting the content of the impurities fluorine and the content of oxygen in the alloy to the prescribed values, and increasing the specific heat peak due to the phase transfer to the antiferromagnetism at the prescribed low temperature. SOLUTION: Rare earth metals such as Er3 Ru, Er5 Ru2 , and ErHg are alloyed, and melted together with the flux mainly consisting of CaF2 or CaCl2 in which Ca is saturated, and the specific heat peak due to the phase transfer to the antiferromagnetism at the low temperature range of 3-15K is increased to >=0.5J/K.cm<3> by reducing the content of impurity fluorine to be <=0.05wt.%, and the content of oxygen to be <=0.15wt.%. The alloy is granular or powdery with grain size of <=0.6mm. In the melting together with the flux, oxygen contained in the alloy is absorbed in the flux as the rare earth metal oxide. The fluoride is reacted with Ca in the flux, and absorbed and turned into the slag, and removed outside the system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a magnetic regenerator material alloy and a method for producing the same. More specifically, the present invention relates to 10K
The present invention relates to a magnetic regenerator material alloy that has a high specific heat peak at an extremely low temperature (K is an absolute temperature unit) and maintains a high specific heat peak even in a granular or powder form, and a method for producing the same.

[0002]

2. Description of the Related Art Gas cycle refrigerators such as a GM (Keyfort McMahon) refrigerator, a Stirling refrigerator, a pulse tube refrigerator, etc.
In the extremely low temperature range of 20K or less, particularly 10K or less where the specific heat of helium (He) as the refrigerant increases, the refrigerating performance is greatly affected by the performance of the regenerator. So, in recent years,
A magnetic regenerator material having a large specific heat even in a cryogenic region has been developed and used for a regenerator for a cryogenic refrigerator.

[0003] The specific heat of the magnetic regenerator material is one of (1) lattice specific heat, (2) specific heat accompanying magnetic phase transition, and (3) Schottky specific heat.
It is composed of types. Among them, the lattice specific heat is similar to that of a general nonmagnetic regenerator, and the magnetic phase transition specific heat and the Schottky specific heat are caused by magnetism. Initially, the regenerator material was required to exhibit a relatively large specific heat over a wide temperature range, and therefore, a material mainly composed of a Schottky specific heat which exhibited an effect over a wide temperature range was used. However, recently, in order to improve the refrigeration capacity at extremely low temperatures, a regenerator having a structure in which a plurality of magnetic regenerator materials having different specific heat peak temperatures are stacked has been used. In such a laminated regenerator,
The magnitude of the specific heat near the peak apex is more important for performance than the spread of the specific heat peak. For this reason, a magnetic regenerator material having a sharper specific heat peak in the cryogenic temperature range than before has been required.

[0004] In addition, the regenerator material is often produced as a spherical powder having a diameter of 0.6 mm or less in order to enhance the heat exchange efficiency. It is manufactured by spraying into an inert gas. Therefore, it is known that the regenerator material has a rapidly cooled fine metal structure, and its specific heat peak has a gentler shape than that originally possessed by the regenerator material alloy, and the specific heat at the peak decreases. As described above, it has been conventionally required that a relatively large specific heat appears in a relatively wide temperature range, so that even when the specific heat peak is sacrificed to some extent, the specific heat peak gradually changes over a wide range. I liked it,
The regenerator material used for the laminated regenerator has a low specific heat peak, which is not preferable, and a regenerator having a maximum specific heat peak in a narrow range is required.

As an example of such a magnetic regenerator material having a high specific heat peak at an extremely low temperature, the specific heat peak in the vicinity of 7 to 8 K is enhanced by removing impurities such as oxygen and nitrogen from Er ₃ Ni and increasing the purity. (Advances in Cryogenic Engineeri
ng vol.40 p617-624). However, in this report, the concentrations of impurities such as oxygen and nitrogen are not clear. For this reason, although the bulk sample has a specific heat peak close to 0.8 J / K · cm ³ , the powder sample has a specific heat peak. Have a specific heat peak of 0.4 J / K · cm ³ or less.

[0006]

SUMMARY OF THE INVENTION The present invention has solved the above-mentioned problems in the conventional magnetic regenerator material alloy, and has a higher specific heat peak due to a phase transition to antiferromagnetism in a cryogenic temperature range of 0.5 J / It is an object of the present invention to provide a magnetic regenerator material alloy having a K · cm ³ or more and which does not lose this sharp specific heat peak even when powdered.

[0007]

That is, according to the present invention, the following magnetic regenerative alloy material is provided. (1) By limiting the impurity fluorine content to 0.05 wt% or less and the oxygen content to 0.15 wt% or less,
A magnetic regenerator material alloy, wherein the specific heat peak due to the phase transition to antiferromagnetism in a low temperature range of 3 to 15 K is increased to 0.5 J / K · cm ³ or more. (2) The magnetic regenerator material alloy according to (1) above, which is in the form of particles or powder having a particle size of 0.6 mm or less. (3) It is composed of Er ₃ Ru or Er ₅ Ru ₂ ,
The magnetic regenerator alloy according to the above (1) or (2), having a specific heat peak of 6 J / K · cm ³ or more between 6 and 10K.

Further, according to the present invention, the following manufacturing method is provided for the regenerator material alloy. (4) A method for producing a magnetic regenerative alloy according to any one of the above (1) to (3), wherein a melt of the alloy is made of C saturated with Ca.
By melting a flux containing aF ₂ or CaCl ₂ as a main component and absorbing oxygen and fluorine as impurities into the flux, the impurity fluorine content of the alloy is reduced to 0.05.
A method for producing a magnetic regenerator material alloy, characterized in that the content of oxygen is not more than 0.15 wt% or less. (5) CaF ₂ to Ca saturated with Ca
Flux mainly composed of Cl ₂ is melted to reduce impurities such as oxygen and fluorine, and a melt of the alloy is sprayed into an inert gas to form a granular or powder magnetic regenerator having a particle size of 0.6 mm or less. The production method according to the above (4) for producing a material alloy.

[0009]

[Detailed Description] (I) Fluorine content and oxygen content of alloy The magnetic regenerator material is generally formed of an alloy mainly composed of a rare earth metal having a large magnetic moment. Rare earth metals are generally obtained from a fluoride raw material, an oxide or a chloride raw material. In the case of a fluoride raw material, 0.1 wt% or more of fluorine in the raw material remains in a usual refining process. Further, in the oxide or chloride raw material, oxygen in moisture due to moisture absorption remains in addition to oxygen originally contained.

With respect to the amount of impurity fluorine and the amount of oxygen contained in such a rare earth alloy, the present inventors have determined that the amount of fluorine is less than 0.1 wt% and the amount of oxygen is less than 0.3 wt%, preferably 0.1 wt%. By limiting to less than, it was previously proposed to increase the fluidity of the molten metal to facilitate atomization from the nozzle (JP-A-5-48573 and JP-A-5-14857).
No. 4). However, in this case, the change in the specific heat peak is not mentioned.

However, in the course of studying the present invention, if the impurity fluorine content is further reduced to 0.05 wt% while keeping the oxygen content at less than 0.15 wt%, the Schottky specific heat hardly changes, but the antiferromagnetic property is reduced. It has been found that the specific heat peak associated with the magnetic phase transition to A is improved. Such a change in the specific heat peak with respect to the amount of fluorine and the amount of oxygen, which is completely different from the fluidity of melting in the above proposal, has not been known so far.

The present invention is based on this finding,
The content of impurity fluorine is 0.05 wt% or less, preferably 0.5 wt%.
01 wt% or less, and oxygen content of 0.15 wt% or less,
Preferably, the specific heat peak accompanying the phase transition to antiferromagnetism in the low temperature range of 3 to 15 K is increased to 0.5 J / K · cm 3 or more by limiting the content to 0.10 wt% or less.

Further, the magnetic regenerator alloy of the present invention has a small specific heat peak due to rapid cooling even when the molten material is sprayed from a nozzle and granulated, and can maintain a higher specific heat peak than before. . Further, the magnetic regenerator material alloy of the present invention has a sharper specific heat peak than conventional ones, so that the crystal lattice is less disordered and has excellent thermal conductivity. Incidentally, E having a specific heat peak due to a phase transition to ferromagnetism described in the above-mentioned document is used.
r ₃ Ni has a substantially different specific heat peak height (magnitude of specific heat) between bulk and powder even if the amount of impurities is substantially equal, and 0.8 J / K · cm ^{3 in} bulk. Is about 0.4 J / K · cm ^3, which is about half in powder form.

(II) Alloy Composition The rare earth alloy to which the present invention is applied has a specific heat peak accompanying a phase transition to antiferromagnetism in a low temperature range of 3 to 15 K. For example, Er ₃ Ru and Er ₅ Ru ₂ , E
rAg, HoAg ₂ , HoCu _{2 and the} like.

(III) Manufacturing Method The impurities such as fluorine and oxygen contained in the rare earth metal are reduced by melting with a flux mainly composed of CaF ₂ or CaCl _{2 in} which the rare earth metal is alloyed and Ca is saturated. Can be. By melting together with the flux, oxygen (oxide ions) contained in the alloy is absorbed by the flux as a rare earth oxide. Fluorine (fluoride ion) reacts with calcium in the flux to be absorbed and slag, and is removed from the system. Generally, commercially available rare earth metals, especially medium / heavy rare earths (Gd,
Tb, Dy, Ho, Er, Tm, Yb) are extremely active and it is difficult to reduce the oxygen and fluorine concentrations.
Oxygen concentration can be reduced to 50pp if a special method such as solid phase electrolysis is used.
m, but there are reports that
It is not an industrially practical method. In addition, C used in the present invention
Even if an a-based flux is used for refining a simple metal, it is difficult to reduce the amount of oxygen and fluorine to 0.1% or less because Ca evaporates because the melting point of medium and heavy rare earths is as high as about 1300 to 1550 ° C. It is. In the present invention, since the Ca-based flux treatment is performed not on the rare earth metal alone but on the rare earth alloy, a relatively low temperature (1200
° C or lower, preferably 1000 ° C or lower). Further, by such a treatment, the amount of oxygen and fluorine can be relatively easily reduced to 0.1% or less. If a eutectic point exists in a composition different from the target composition, a master alloy having the eutectic point composition is prepared in the presence of Ca-saturated flux, and an alloy element is added thereto to adjust the composition by arc melting or the like. This makes it possible to more effectively prepare a high-purity alloy with reduced contents of fluorine and oxygen. Alternatively, the fluoride of the alloy component is replaced with Ca
The alloy having the desired composition may be produced by melting in the presence of a saturated flux.

A granular or powdered regenerator material can be produced by spraying a rare-earth alloy melt with reduced fluorine and oxygen impurities into an inert gas from a small-diameter nozzle. The particle size of the material used as a cold storage material is 0.1.
6 mm or less is suitable, and 0.2 to 0.5 mm is preferable. Conventional rare earth alloys have a low specific heat peak when quenched by such spraying.However, in the case of the present invention in which the amount of fluorine and oxygen is reduced, the decrease in the specific heat peak due to quenching is extremely small, and the specific heat characteristic is low. A good granular or powder magnetic regenerative alloy can be obtained.

[0017]

The embodiments of the present invention will be described below. In addition, these are illustrations and do not limit the scope of the present invention.

Example 1 and Comparative Example 1 81 g of commercially available erbium (Er) metal and ruthenium (Ru)
19 g was alloyed by argon arc melting. The X-ray diffraction pattern of the obtained alloy coincided with the pattern of Er ₅ Ru ₂ . The alloy had an oxygen concentration of 0.30 wt% and a fluorine concentration of 0.12 wt%. Figure 1 shows the specific heat characteristics of this alloy.
(Comparative Example 1: broken line). This alloy was put in a tantalum crucible together with ₁₀ g of Ca and 30 g of CaCl ₂ , heated and melted at 1200 ° C. under an argon atmosphere, and stirred with a tungsten blade for 20 minutes. After cooling, the flux was removed. The resulting alloy had an oxygen concentration of 0.09 wt% and a fluorine concentration of 0.01 wt%. The X-ray diffraction pattern was the same as in Comparative Example 1. The specific heat characteristics of this alloy are shown in FIG. 1 (Example 1: solid line).

As shown in the figure, the rare earth alloy of this embodiment has a large specific heat peak near 8K. The specific heat peak of Comparative Example 1 in which oxygen and fluorine were not removed was 0.5 J / K · cm ³ near 8 K, while the specific heat peak of this example was about 0.8 J / Kcm ³ , which was about 1 J / K · cm ^3. .5 times the size.
The reason why the specific heat of the comparative example is slightly higher than that of the example in the portion of 5 K or less is considered to be that Er ₃ Ru ₂ is present to the extent that it cannot be confirmed by X-ray diffraction (10 wt% or less). Also,
From the above figures, it can be seen that, in the present invention, the effect of not only sharpening the specific heat peak but also increasing the area of the entire specific heat peak is realized. Generally, when the amount of impurities contained in the alloy is about several percent or less, the magnitude of the magnetic moment decreases almost proportionally according to the amount of impurities. This principle is almost valid for Schottky specific heat caused by the state inside the rare earth. However, in the cryogenic temperature range targeted by the present invention, the specific heat accompanying the magnetic phase transition is greatly advantageous. In this case, since the lattice disorder due to the impurities greatly extends around the impurities, the impurity amount of about 0.1% is reduced. It is considered that the difference causes a difference of about several tens% in the specific heat peak area.

Each of the alloys (ErRu) of Example 1 and Comparative Example 1 was arc-melted in an argon gas atmosphere, and this alloy was introduced from a tungsten nozzle (nozzle diameter: 0.1 mm) into a helium atmosphere of about 1 atm. Was sprayed with helium gas to obtain a spherical powder having an average particle diameter of 0.4 mm. When the specific heat characteristics of this powdery alloy were measured, the alloy of Example 1 had a specific heat peak of 0.7 J / K · cm ³ at 8K. Almost unchanged. on the other hand,
The powdered alloy of Comparative Example 1 had a specific heat peak of 0.45 J / K · cm ³ at 8K, and the height of the specific heat peak was almost halved as compared with the bulk.

Examples 2 to 4 and Comparative Examples 2 to 4 HoCu ₂ , HoAg ₂ , and ErAg were prepared in the same manner as in Example 1 except that the alloy compositions were changed as shown in Table 1. An oxygen / fluorine reduction treatment was performed. Before treatment (Comparative Examples 2 to 4) and after treatment (Examples 2 to 4)
Table 1 also shows changes in the impurity concentration and the specific heat characteristic of 4). In any case, the specific heat peak is improved by reducing the oxygen amount and the fluorine amount of the impurities to a predetermined amount or less. These alloys were re-melted under an argon atmosphere, sprayed and granulated. Table 1 also shows the results of measuring the specific heat characteristics of this granular alloy.

Example 5 120 g of erbium fluoride, 10 g of Ru, 38 g of Ca and 70 g of CaCl ₂ were placed in a tantalum crucible, heated to 1150 ° C. under an argon atmosphere to dissolve, and stirred with a tantalum blade for 30 minutes. After cooling, the flux was exfoliated and then arc melted to recover 99 g of the alloy. To this was added 11.6 g of Ru, and argon arc melting was performed again. Insert this alloy into a tungsten nozzle (nozzle diameter: 0.1m
m) into a helium atmosphere of about 1 atm with helium gas at 3 atm to obtain a spherical powder having an average particle size of 0.4 mm. The alloy powder has an oxygen concentration of 0.09 wt% and a fluorine concentration of 0.09 wt%.
It was 01 wt% (analysis limit). The powder X-ray diffraction pattern almost coincided with Er ₅ Ru ₂ . Further, the specific heat characteristic shows the same profile as before the granulation (bulk) of Example 1, and the specific heat peak also shows a maximum value of 0.8 J / K · cm ³ at 8K,
Almost no decrease in peak due to granulation was observed.

[0023]

[Table 1]

[0024]

According to the present invention, a large peak specific heat in a low temperature range, which cannot be realized by the conventional magnetic regenerator material alloy, can be realized. The magnetic regenerator material alloy of the present invention has a sharp peak and a specific heat peak hardly decreases even when fine powder is formed by a melt spraying method, or a decrease in the specific heat peak is small, and the specific heat peak is high in an extremely low temperature region of 6 K or less. Having. Therefore, it is particularly useful as a laminated cold storage material, and is suitable for use in a gas cycle refrigerator for realizing an extremely low temperature around 4K level.

[Brief description of the drawings]

FIG. 1 is a graph showing specific heat characteristics before and after performing an oxygen / fluorine reduction treatment of the present invention.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masashi Nagao 8-1-1, Tsukaguchi-Honcho, Amagasaki-shi, Hyogo Sanrio Electric Co., Ltd. Advanced Technology Research Institute (72) Inventor Kooki Naka 8 Tsukaguchi-Honcho, Amagasaki-shi, Hyogo Chome 1-1, Mitsubishi Electric Corp. Advanced Technology Laboratory (72) Inventor Takashi Inaguchi 8-1-1, Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture Mitsubishi Electric Corporation Advanced Technology R & D Center

Claims (5)

[Claims] By limiting the content of impurity fluorine to 0.05 wt% or less and the content of oxygen to 0.15 wt% or less, a specific heat peak due to a phase transition to antiferromagnetism in a low temperature range of 3 to 15 K is obtained. A magnetic regenerator alloy characterized by increasing to 0.5 J / K · cm ³ or more. 2. The magnetic regenerator material alloy according to claim 1, which is in the form of particles or powder having a particle size of 0.6 mm or less. 3. The magnetic regenerator material alloy according to claim 1, which is composed of Er ₃ Ru or Er ₅ Ru ₂ and has a specific heat peak of 0.5 J / K · cm ³ or more between 6 and 13K. . 4. The method for producing a magnetic regenerative alloy according to claim 1, wherein a melt of the alloy is melted with a flux containing CaF ₂ or CaCl ₂ saturated with Ca as a main component. A magnetic regenerator material characterized in that the flux contains oxygen and fluorine as impurities to reduce the fluorine content of the alloy to 0.05 wt% or less and the oxygen content to 0.15 wt% or less. Alloy manufacturing method. 5. A molten alloy of CaF ₂ saturated with Ca.
Or melting a flux containing CaCl ₂ as a main component to reduce impurities such as oxygen and fluorine, and further spraying a melt of the alloy into an inert gas to form a granular or powdery magnetic material having a particle size of 0.6 mm or less. The method according to claim 4, wherein the cold storage material alloy is manufactured.