JPH0765823B2 - Freezing method - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a refrigerating method in which a magnetocaloric effect is used for cooling, and more specifically, it is possible to exert a sufficient cooling effect in a wide range of freezing temperature range. The present invention relates to a freezing method having excellent heat transferability.

[Technical background of the invention and its problems] With the recent remarkable development of superconducting technology, industrial electronics are expected to be applied in a wide range of fields such as the information industry and medical equipment. In order to use superconductivity technology, it is essential to develop a refrigerator that creates a cryogenic environment. There is a gas refrigeration method as a well-known refrigeration method, but its efficiency is extremely low and the device becomes large. Therefore, as a new refrigeration method to replace this, there is a magnetic refrigeration method that uses the magnetocaloric effect of a magnetic material. Research is being actively conducted (Proceedings of ICEC9 (1982, May); 26-29, Ad
vances in Cryogenic Engineering, 1984, Vol, 29,581-58
7) [Proceedings of ICEC9 (May 1982
26-29, Advances in Cryogenic Engineering (1984, Vol. 29, pp. 581-587)].

In short, this method is endothermic due to the change in entropy (ΔS _M ) between the spin alignment state when a magnetic field is applied to a magnetic substance and the disordered state of spins when the magnetic field is released,
The basic principle is to utilize a heat release reaction.
This magnetic substance is called a magnetic working substance. The larger the ΔS _{M of the} magnetic substance used as such a magnetic work substance, the greater the cooling effect.

Fig. 13 is a diagram showing the relationship between ΔS _M and temperature of a magnetic substance. As is clear from the figure, the magnetic substance shows a maximum value of ΔS _{M at} a specific temperature (magnetic transition point), and before and after that. At the temperature of, ΔS _M decreases. Therefore, this magnetic body can obtain a sufficient cooling effect only in a delicate temperature range near the magnetic transition point.

In order to solve the above problem, a magnetic material having a plurality of different magnetic transition points may be used, and as a result, a sufficient cooling effect can be obtained in a relatively wide temperature range.

As a substance capable of forming a magnetic substance having a plurality of magnetic transition points, RAl ₂ Laves type intermetallic compound (R is a rare earth element)
Etc. are known (Proceedings of ICEC (1982, May);
30-33 etc.) [Proceedings of ICEC9 (May 1982); pages 30-33 etc.].

That is, it is considered that a magnetic substance having a plurality of magnetic transition points can be obtained by mixing two or more kinds of the compound powders and sintering the mixture. However, in the magnetic material obtained by the above method, mutual diffusion progresses between different compound powders during the sintering process, and as a result, the maximum value of ΔS _M becomes one.

In addition to the RAl ₂ Laves-type intermetallic compound, Gd ₃ Ga ₅
Garnet-based oxide single crystals containing rare earth elements represented by O ₁₂ and Dy ₃ Al ₅ O ₁₂ are also known, but this substance can obtain a sufficient cooling effect only in a temperature range of 4 K or less. Therefore, it is not effective for the demand for a magnetic material that can obtain a sufficient cooling effect in a wide temperature range of 4K or higher.

Further, the magnetic substance for a magnetic working material is required to efficiently dissipate the absorbed heat to the outside, and therefore it must have excellent heat transfer properties.

However, in magnetic refrigeration intended for a temperature range of about 77K to 15K, a regenerator type cycle such as the Ericsson cycle is desirable because of large contribution of lattice entropy. In such a cold storage type refrigerator, heat transfer between the magnetic substance for magnetic working material and the cold storage material is indispensable. At extremely low temperatures below 77K, there is only solid regenerator material such as lead,
The magnetic working substance and the regenerator material are brought into solid contact, but at that time
It is necessary to form a narrow gap such as a He gas film for heat exchange. Therefore, high-precision machining such as mirror finishing and complex shape machining is required for both magnetic materials for magnetic working materials and regenerator materials (Cryogenic Engineering Society, November 1984). Therefore, it is preferable that the magnetic substance for a magnetic working material has a high density.

[Object of the Invention] The present invention has been made in order to meet the above-mentioned demand, and provides a refrigeration method capable of obtaining a sufficient cooling effect in a wide range of refrigeration temperature range and having excellent heat transferability. With the goal.

[Summary of the Invention] As a result of intensive studies to achieve the above object, the present inventors have found that a magnetic body obtained by molding a coating powder obtained by coating a magnetic alloy powder described below with a metal binder described below is a heat-resistant material. The magnetic substance, which has excellent transmissivity and is composed of a mixed powder containing plural kinds of rare earth elements, does not cause mutual diffusion between different kinds of magnetic alloy powders, and therefore has different magnetic transition points. The present invention has been completed by finding out the fact that the present invention has.

That is, the refrigeration method of the present invention, Y, La, Ce, Pr, Nd, Pm, Sm,
It contains at least one element selected from the group of Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, and the balance metal is substantially from at least one selected from the group of Al, Ni and Co. Is a magnetic alloy powder and a metal binder, and the magnetic binder is present in an amount of 1 to 80% by volume.

First, the magnetic alloy powder used in the present invention is, for example, RA
l _2, RNi _2, rare earth as represented by _{RCo 2 - (Al, Co,} Ni)
It is a magnetic alloy powder of an alloy or a solid solution thereof. Here, R is Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Dy, Ho, Er, Tm,
It is at least one element selected from the group of Yb. In this alloy powder, the content of R (the total content of both when R is two) is preferably as follows. When the content is less than the lower limit below, ΔS _M does not increase at any temperature below room temperature, and a sufficient cooling effect cannot be obtained. Preferably, when the balance metal is Al 60
% By weight, 20% by weight or more for Ni, 40% by weight or more for Co. Further, the upper limit of the content of the element (R) is
It is preferably 99% by weight or less. When the content exceeds 99% by weight
This is because the content of Al, Ni, Co is reduced and the alloy crushing property is significantly deteriorated, making it difficult to produce a fine powder and making it difficult to form a powder compact. An alloy powder satisfying the above content conditions is a ferromagnetic alloy powder.

The above alloy powder can be manufactured as follows.
Thus, for example RAl _2, RNi _2, the RCo ₂ alloy obtained by dissolving Te arc melting furnace. Then, the obtained alloy is pulverized into a fine powder. Since the particle size of this powder affects the filling rate in the molding mold when molding a mixture of this powder and a binder to be described later, it is preferably 1 to 100 μm, preferably 2 to 30 μm.
It is preferably in the range of μm. If the particle size exceeds 100 μm, the filling rate decreases, and if the particle size is less than 1 μm, oxidation tends to occur and the desired cooling effect cannot be obtained.

Next, the magnetic alloy powder obtained by the above method is prepared. At this time, when one kind of alloy powder is used, an excellent heat transfer property is obtained, but when two or more kinds of alloy powders are prepared and molded, a magnetic material having a plurality of different magnetic transition points is also obtained. When two or more alloy powders having different R elements are prepared, the balance metal in each alloy powder may be the same or different. Therefore, the prepared powder is, for example, a combination of DyAl ₂ , ErAl ₂ , HoAl ₂ and DyHoAl ₂ ; DyNi ₂ , D
It looks like a combination of yCo ₂ . In this way, by preparing and mixing and molding two or more kinds of alloy powders, it becomes possible to obtain a magnetic body having two or more magnetic transition points.

The magnetic material used in the present invention comprises the above alloy powder and a metal binder. This binder has the function of improving the heat transfer property in the molded body obtained by the method described below, and the function of binding the above-mentioned various mixed powders in a separated and independent state. As a result, mutual diffusion between powders is suppressed, and a sintered body having a plurality of magnetic transition points is obtained.

As the metal applicable to the binder, there are metals such as Au, Au, and Cu that have excellent heat conduction characteristics at low temperature, or alloys thereof, but the metal whose thermal conductivity at 4.2K is 1 W / kcm or more. If so, it is effective in improving the heat transfer property. Therefore, since the binder itself is made of a metal having excellent thermal conductivity, the heat transfer property of the obtained molded product is significantly improved.

The binder content in the compact is 1 to 80% by volume.
It is preferably 5 to 30% by volume. If the existence ratio is less than 1% by volume, the binder binding ability is small and molding is difficult, and at the same time, at the time of sintering which will be described later, mutual diffusion between alloy powders progresses, and it becomes difficult to achieve the object. Further, if it exceeds 80% by volume, the ratio of the magnetic alloy powder decreases, the cooling effect per unit volume decreases, and the cooling effect remarkably decreases due to heat generation due to eddy current loss during magnetic field control. .

The molded body composed of the binder and the alloy powder having the above-mentioned abundance ratios can be manufactured as follows.

First, the alloy powder is coated with the metal (binder). Examples of this coating method include a plating method (for example, electroless plating method) and a vapor phase growth method such as sputtering. When applying the plating method, it is advisable to subject the alloy powder to a pretreatment such as a sensitizer treatment or an activator treatment before the plating treatment.

At the time of coating, the amount of the coating metal used may be adjusted so that the film thickness of the metal coating film is 0.1 to 1 μm with respect to the particle diameter of the alloy powder of 2 to 30 μm. By thus setting the particle size and the film thickness in a predetermined relationship, it becomes possible to adjust the abundance ratio of the binder in the molded body.

Next, the alloy powder coated with metal is press-molded and then sintered, or an impact pressure molding method is used to obtain a desired molded body.

If by sintering method, pressing pressure 500~10,000kg / cm ² preferably 1,000~10,000kg / cm ^2. Then, the obtained molded body is sintered in a non-oxidizing atmosphere. Examples of the non-oxidizing atmosphere include a vacuum of 10 ^-6 Torr or less and an inert gas such as Ar or N ₂ .

The sintering temperature is 100 to 1100 ° C, preferably 500 to 900 ° C.
If the sintering temperature is less than 100 ° C, a high filling rate cannot be obtained, and if it exceeds 1100 ° C, mutual diffusion between the binder metal and alloy powder proceeds, and a sufficient cooling effect over a wide range of temperatures is obtained. I can't.

The impact pressure molding method is a method of obtaining a high-density molded body by inserting a metal-coated magnetic alloy powder into a capsule and performing impact pressure molding. For example, 10 with a railgun
Impact pressure of 0 to 10,000,000 atmospheres, impact pressure with a rifle gun, and explosive molding using explosives are effective. Also, 10
High-pressure molding with an ultra-high pressure press of 10,000 atm is also effective.

[Examples of the Invention] Example 1 An alloy (A) consisting of 75% by weight of Dy and the balance Al, and an alloy (B) consisting of 75.6% by weight of Er and the balance Al were prepared separately by using an arc melting furnace. Each alloy was pulverized by a ball mill method into fine powder having a particle size of about 30 μm, and then an alloy (A) powder and an alloy (B) powder were obtained, which were mixed with a mixer in an equimolar ratio to obtain a mixed powder.

The mixed powder obtained is subjected to sensitizer treatment (acidic HCl) and activator treatment (acidic HCl), and then TMP ^# 500
Copper plating (NaOH alkaline) by A and B (chemicals used,
Okuno Pharmaceutical Co., Ltd.).

The weight ratio of alloy powder and copper plating at the time of copper plating is 3 to 4: 1.
Is 0.5-1 μm on the surface of the alloy powder due to the plating treatment.
A film was formed.

The copper-plated alloy powder was press-molded at a pressing pressure of 10 t / cm ² and then sintered at 600 ° C. in an Ar gas atmosphere.

The result of X-ray diffraction of the obtained sintered body is shown in FIG.

In addition, as Comparative Example 1, a mixed powder of the alloy (A) powder and the alloy (B) powder was press-molded without being plated, and was sintered at 1100 ° C. to obtain X of a sintered body.
The result of the line diffraction is shown in FIG.

From the result of X-ray diffraction on the (440) plane of the sintered body of Example 1, the lattice constant a of ErAl ₂ was a = 7.793, and the lattice constant a of DyAl ₂ was a = 7.
827 was obtained. On the other hand, the X-ray diffraction result on the (440) plane of Comparative Example 1 was a = 7.817.

As is clear from FIG. 1 and FIG. 2, it was confirmed that ErAl ₂ and DyAl ₂ exist in the magnetic material of the present invention separately and independently in X-ray, but in Comparative Example 1, Progress of mutual diffusion is observed as seen in the decrease in the number of peaks.

Further, in the magnetic field of 2 Tesla of Example 1 and Comparative Example 1, 70
Fig. 3 shows the results of magnetization measurement in the ultra-low temperature region below K. Magnetic transition point of ERAL ₂ around 15K in Example 1 As is apparent from the figure, although the magnetic transition point Dyal ₂ around 60K are observed, the result both in the vicinity of Comparative Example 1, 35K is interdiffusion give Only the magnetic transition point of the obtained substance is observed.

In addition, the filling rate of Example 1 was a high-density sintered body exceeding 95%, and the thermal conductivity was 3 W / cm · k, which was an order of magnitude larger than the 200 mW / cm · K of Comparative Example 1. The binder content in the sintered body was 20 to 25% by volume.

Example 2 Alloy (A) consisting of Dy 75% by weight and balance Al, Er 75.6% by weight, alloy (B) from balance Al, alloy (C) consisting of Dy 37.6% by weight, Ho 38.2% by weight and balance Al , Ho75.4% by weight, balance Al
Alloy (D) consisting of the above is separately produced by using an arc melting furnace, pulverized into a fine powder having a particle size of about 30 μm by a ball mill method, and then the alloy (A), (B), (C), (D) Powders are obtained, and these are 1 mol, 0.38 mol, 0.24 mol and 0.3 mol, respectively.
Mixing was performed with a mixer at a molar ratio of 1 mol to obtain a mixed powder.

The obtained mixed powder was treated in the same manner as in Example 1 to obtain a sintered body. Fig. 4 shows the results of measuring the specific heat (Cp) of the obtained sintered body under a magnetic field of 5 Tesla and in the absence of a magnetic field, and examining the temperature dependence of the amount of change in magnetic entropy (ΔS _M / R). Shown in.

The results of the temperature dependence of the amount of change in magnetic entropy in Comparative Example 1 are also shown in FIG.

As is clear from FIG. 4, the sintered body of the present invention is 10K to 70K.
Thus, the cooling effect can be obtained in a wide range, but in Comparative Example 1, the range of the cooling temperature is as narrow as 30K to 50K.

Example 3 Dy 58% by weight, alloy (E) consisting of balance Ni, Er 59% by weight,
A mixed powder was obtained in the same manner as in Example 1 except that an alloy (F) consisting of the balance Ni was prepared.

The obtained mixed powder was plated as in Example 1. At this time, the alloy powder and the copper plating amount are 5 by weight ratio.
It was ~ 6: 1.

A sintered body was obtained in the same manner as in Example 1 using the copper-plated alloy powder. The result of X-ray diffraction of the obtained sintered body
Shown in the figure. Further, as Comparative Example 2, FIG. 6 shows the result of X-ray diffraction of a sintered body produced in the same manner as in Comparative Example 1 except that the sintering temperature was 980 ° C. using the mixed powder.

Furthermore, the magnetization measurement results of Example 3 and Comparative Example 2 are shown in FIG. As is clear from the figure, in the third embodiment, in the vicinity of 8K
The magnetic transition point of ErNi _{2 and} the magnetic transition point of DyNi ₂ near 20 K are observed.

Further, the filling rate in Example 3 exceeds 98%, and the thermal conductivity is 4 W / cm ·, which is an order of magnitude higher than the 350 mW / cm · K in Comparative Example 3.
It was K. In addition, the binder existence ratio in the sintered body is 20 ~
It was 25% by volume.

Example 4 Dy 58% by weight, alloy (E) consisting of balance Ni, Ho58.5% by weight, alloy (G) consisting of balance Ni, Er 57.5% by weight, balance Ni
An alloy powder was prepared in the same manner as in Example 1 except that the alloy (H) was prepared, and these powders were mixed at a molar ratio of 1 mol, 0.4 mol, and 0.3 mol to obtain a mixed powder.

The obtained mixed powder was treated in the same manner as in Example 3 to obtain a sintered body. Fig. 8 shows the results obtained by measuring the specific heat (Cp) of the obtained sintered body under a magnetic field of 5 Tesla and in the absence of a magnetic field, and examining the temperature dependence of the amount of change in magnetic entropy (ΔS _M / R). Shown in.

The temperature dependence of the magnetic entropy change amount in Comparative Example 2 is also shown in FIG.

Example 5 A mixed powder was obtained in the same manner as in Example 1 except that an alloy (I) containing 58.7 wt% Er and the balance Co and an alloy (J) containing 58.9 wt% Tm and the balance Co were prepared.

The obtained mixed powder was plated as in Example 1. At this time, the alloy powder and the copper plating amount are 4 by weight ratio.
It was ~ 5: 1.

A sintered body was obtained in the same manner as in Example 1 using the copper-plated alloy powder. The result of X-ray diffraction of the obtained sintered body is
Shown in the figure. In addition, as Comparative Example 3, FIG. 10 shows the result of X-ray diffraction of a sintered body produced in the same manner as in Comparative Example 1 except that the sintering temperature was 1000 ° C. using the above mixed powder.

Further, the magnetization measurement results of Example 5 and Comparative Example 3 are shown in FIG. As is clear from the figure, in Example 5, the magnetic transition point of TmCO ₂ is observed at around 10 K, and the magnetic transition point of ErCO ₂ is observed at around 30 K.

Further, the filling rate in Example 5 exceeds 98%, and the thermal conductivity is 2 W / cm · which is one digit larger than 180 mW / cm · K in Comparative Example 5.
It was K. In addition, the binder existence ratio in the sintered body is 20 ~
It was 50% by volume.

Example 6 Alloy (I) consisting of Er 58.7 wt% and balance Co, Tm 58.9 wt% and alloy (J) consisting of balance Co, Ho 38.9 wt% and Er 19.5
An alloy powder was obtained in the same manner as in Example 1 except that an alloy (K) consisting of wt% and the balance Co was prepared, and these were mixed at a molar ratio of 1 mol, 0.5 mol, and 0.7 mol to obtain a mixed powder. .

The obtained mixed powder was treated in the same manner as in Example 5 to obtain a sintered body. The specific heat (Cp) of the obtained sintered body was measured under a magnetic field of 5 Tesla and under no magnetic field, and the temperature dependence of the magnetic entropy change (ΔS _M / R) was examined. Shown in.

The temperature dependence of the magnetic entropy change amount in Comparative Example 3 is also shown in FIG.

[Effects of the Invention] As described above, in the freezing method of the present invention, since the magnetic material used is excellent in heat transfer, it is possible to achieve a sufficient cooling effect in a wide range of freezing temperature range. Moreover, since the magnetic material has a high density, it has excellent workability. In particular, the freezing method of the present invention is particularly effective because good heat transfer can be obtained by using such a magnetic substance as a magnetic working substance used in a cold storage system such as the Ericsson cycle.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1, FIG. 2, FIG. 5, FIG. 6, FIG. 9, and FIG. 10 are views showing the X-ray diffraction results of the obtained sintered bodies, respectively.
Figures 7, 7 and 11 are diagrams showing the relationship between the magnetization and temperature of the obtained sintered body, respectively.
The figure shows the relationship between the magnetic entropy change and the temperature of the obtained sintered body, and FIG. 13 is the view showing the relationship between the entropy change and the temperature of the magnetic body.

Claims (5)

[Claims] 1. Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er,
A magnetic alloy powder containing at least one element selected from the group of Tm and Yb, and the balance metal consisting essentially of at least one selected from the group of Al, Ni and Co, and a metal binder, and A refrigeration method using a magnetic material having a metal binder content of 1 to 80% by volume. 2. The refrigerating method according to claim 1, wherein the magnetic substance is a magnetic working substance for magnetic refrigeration. 3. The refrigerating method according to claim 1 or 2, wherein the magnetic alloy powder is a mixed powder of two or more kinds of alloy powder. 4. The refrigerating method according to claim 3, wherein the two or more alloy powders have different magnetic transition points. 5. The refrigerating method according to claim 1, wherein the metal binder is a metal or an alloy having a thermal conductivity at 4.2 K of 1 W / cm · K or more.