JPH0816214B2 - Regenerator material and regenerator - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a cold storage material.

[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 indispensable to develop a small-sized and high-performance refrigerator. Such a small refrigerator is required to be lightweight, small and have high thermal efficiency.

For this reason, researches on gas refrigeration by the Stirling cycle and magnetic refrigeration by a heat cycle (for example, Carnot, Ericsson) using the magnetocaloric effect have been actively conducted.

In order to improve the performance of the gas refrigeration by the heat cycle such as the Stirling cycle, improvement of the regenerator, the compression section and the expansion section is an important issue. In particular, the performance of the cold storage material, which is the filling substance that constitutes the cool storage device, is greatly affected. In the regenerator, the filling material is conventionally formed of lead or bronze balls, or a wire mesh layer of copper or phosphor bronze. However, such a filling material has a specific heat of 1
Since it rapidly decreases at a low temperature of 0 K or less, there is a problem in the gas refrigeration described above that the gas cooling efficiency significantly decreases at a low temperature (10 K or less).

On the other hand, as a cold storage material, the intermetallic compound (R; Sm) of R · Rh has a maximum value of specific heat of 20 K or less and the value is sufficiently large in specific heat per unit volume (volume specific heat). , Gd, Tb, Dy, Ho, Er, Tm,
It has been proposed to use Yb) (JP-A-51-52378).
issue). However, since Rh (rhodium) which is one component of such a cold storage material is extremely expensive, there is a problem in practical use as a filling material for a cold storage used on the order of several hundred grams.

Further, the heat storage material R · Mz (R; Sc, Y, L, which has a sufficiently large specific heat of 20 K or less and is low in price.
a, Pr, Nd, Sm, Gd, Tb, Dy, Ho, E
r, Tm, Yb, Lu, M; Ni, Co, Cu, A
g, Au, Mn, Fe, Al, Zr, Pd, B, Si,
P, C, z; 0.001 ≦ z ≦ 9.0) has been proposed (JP-A-1-310269).

[0007]

This RMz-based material has an excellent low-temperature specific heat at 20 K or less, and has a specific heat equivalent to Pb at a high temperature of 20 K or less. It is a very promising material because the regenerator can be constructed with a one-stage configuration, which was difficult to use as a regenerator without the two-stage configuration.

However, the rare earth material has a problem that it is not always stable in the air. Simply coating with a protective layer will lower the low temperature specific heat. The present invention has been made in view of the above points, and an object thereof is to provide a chemically stable rare-earth magnetic regenerator material without deteriorating the specific heat characteristics at low temperatures.

[0009]

Means and Actions for Solving the Problems The present invention is directed to a rare earth element or a small amount selected from Ni, Co and Cu.
Both of them have a grain surface composed of a rare earth compound of a metal,
At least one oxide of Nd, Ho, Gd and Er
A cold storage material characterized by being coated and using this
It is a regenerator.

As described above, the rare earth simple substance and the rare earth compound are not always stable in the air. Therefore, the chemical stability can be improved by forming a coating layer made of a chemically stable rare earth oxide on the surface of the cool storage material containing the rare earth element. The coating layer thus obtained not only improves the chemical stability of the above-mentioned cold storage material, but the rare earth oxide (ROx) itself, which is the coating layer, has a relatively large specific heat even at a low temperature (20 K or less). It is desirable from the standpoint of low temperature specific heat. Therefore, according to the present invention, in the heat storage material using a large specific heat at a low temperature (20 K or less), the main phase R or R
By covering Mz and the like with an oxide of rare earth R, it is possible to provide a cold storage material having improved chemical stability without deteriorating the low temperature specific heat characteristic. In addition, in the case of coating, besides the oxidation treatment, an oxide film may be separately coated.

The rare earth element simple substance or the rare earth element compound used in the present invention includes Y, La, Ce, Nd, Sm and E.
Examples thereof include u, Gd, Tb, Dy, Ho, Er, Tm, Yb and compounds of these with Ni, Co, Cu and the like. Examples of this compound include AMz represented by Er ₃ Ni (where A in the formula is Y, La, Ce, Pr, Nd, S
m, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb
At least one rare earth element selected from, M is Ni,
At least one kind of metal selected from Co and Cu, and x represents 0.001 ≦ z ≦ 9.0), and one or more kinds of magnetic substances represented by the formula (1) are included. As the rare earth, Er, Ho, Dy, Tb, Gd and the like are preferable.

Preferably 0.01 ≦ z <2.0 and further z
≦ 1.5 and ⅓ ≦ z ≦ 1.0.

A part of M may be replaced with B, Al, In, Si or the like. Furthermore, Ge, Sn, Pb, Ag, A
u, Mg, Zn, Ru, Pd, Pt, Re, Cs, I
You may add r, Fe, Mn, Cr, Cd, Hg, Os, etc.

Although such a material is filled into a regenerator, it is desirable that the regenerator has an average particle diameter or fiber diameter of 1 to 2000 μm. The reason for this is that if the average particle size or fiber diameter is less than 1 μm, it will easily flow out of the regenerator together with the high-pressure working medium (for example, helium gas) when it is filled in the heat storage device, and the average particle size or fiber diameter will also increase. Is 20
If it exceeds 00 μm, the thermal conductivity of the magnetic material is (magnetic material)-
This is the cause of rate control of heat transfer between the (working media), and the heat transfer performance may be significantly reduced, leading to a reduction in the recuperative effect.

The coating layer made of a rare earth oxide has a thickness of 0.001 to 20 μm in consideration of specific heat and thermal conductivity.
Furthermore, about 0.01 to 0.2 μm is preferable. An oxide composed of the same rare earth element as the main phase inside may be used, or different oxides may be used. This is, for example, after forming the main phase into a desired shape such as a sphere, and then 200 to 400 in an inert gas atmosphere such as Ar having an oxygen partial pressure of about 1 to 8 Pa.
C., 10 to 60 min. Can be easily manufactured by heat treatment in each case. As the rare earth element forming the oxide, Gd, Nd or the like having a large low temperature specific heat is preferable.

[0016]

Embodiments of the present invention will be described below. (Example 1) REP method (Rotating Electrode Process)
The molten metal of neodymium (Nd) having a purity of 99.9% was subjected to a rapid solidification treatment by using a granule producing apparatus according to ss).

Here, in the REP method, a rotating electrode made of a granular raw material in a solid state is prepared, and a high temperature flow such as a plasma arc is caused to act on the end of the rotating electrode rotating at a high speed to melt the granular raw material. Then, the molten metal is formed at the same time as the molten metal is dispersed, and the molten metal is rapidly solidified in an inert gas atmosphere having a large cooling effect such as helium gas to produce granules.

The processing conditions in this embodiment were set as follows. That is, the outer diameter of the rod-shaped rotating electrode is 20
mm, rotating electrode length 150 mm, rotating electrode rotation number 3
Each of them was set to 0000 rpm.

As a result, magnetic particles having a particle diameter of 0.1 to 2 mm and an aspect ratio of 1.3 or less were obtained at a ratio of 80% or more based on the weight of the molten metal. Each of the obtained magnetic bodies had a shape close to a sphere, and the surface thereof was smooth like a mirror surface, and the average crystal grain size in this magnetic body was 50 μm.

The magnetic particles thus obtained were mixed with an oxygen concentration of 1
Heat treatment was performed at 200 ° C. for 60 minutes in an Ar atmosphere containing about ppm. As a result, the surface pressure of the magnetic particles is 0.0
It was covered with an oxide film of 7 to 0.15 μm (FIG. 1). The regenerator material consisting of the granules thus obtained was filled in a GM refrigerator and the refrigerating capacity was measured. As a result, the same performance as that of Nd alone was obtained. The cold storage material was very stable with no change even when installed in the atmosphere. (Example 2)

First, using an arc melting furnace, Er75 atom
%, And the balance Ni was prepared, and this alloy was subjected to a uniform heat treatment for 100 hours in a vacuum of about 750 ° C. and 10 ⁻³ torr. According to an X-ray diffraction experiment of the obtained substance, an intermetallic compound portion Er ₃ Ni having an orthorhombic crystal structure was obtained.
It was found that a single phase was formed. The magnetic material thus obtained was further heat-treated at 300 ° C. for 30 minutes in an Ar atmosphere containing an oxygen concentration of about 1 ppm.
The surface of the magnetic material is Er oxide Er having an average film thickness of about 700 A.
It was covered with a ₂ O ₃ film. The substance of Example 2 covered with such an oxide coating, after 12 months in air,
Almost no change was seen in the chemical structure or the film thickness of the oxide film,
It was found to be chemically very stable. Further, when the low-temperature specific heat in the bulk state of the above example was measured,
A large low-temperature specific heat almost equal to the specific heat characteristic of Er ₃ Ni having a magnetic phase transition temperature T _N = ∼7K was obtained. (Example 3)

First, using an arc melting furnace, Er75 atom
%, Ni 12.5 atom%, and the balance Co, an intermetallic compound was prepared, and this alloy was subjected to a homogenizing heat treatment in a vacuum at about 700 ° C. and about 10 ⁻³ torr for 100 hours to remove Er ₃ Ni and Er ₃ Co. I got a pseudo binary system. According to the X-ray diffraction experiment of the obtained pseudo-binary substance, a single phase of an intermetallic compound having the same crystal structure as Er ₃ Ni and Er ₃ Co and an intermediate lattice constant is formed. I knew that. The magnetic material thus obtained was further heat-treated at 300 ° C. for 30 minutes in an Ar atmosphere containing an oxygen concentration of about 1 ppm. As a result, the surface of the magnetic material was Er oxide Er ₂ having an average film thickness of about 700 A. It was covered with an O ₃ film. The substance of Example 3 covered with such an oxide film showed very little change in the chemical composition and the film thickness of the oxide film even after 8 months in the air, and thus was very chemically chemically. It turned out to be stable. Also,
The low-temperature specific heat characteristics in the bulk state of the above-described examples also showed low-temperature specific heat having a size comparable to that of Er ₃ Ni _0.5 Co _0.5 having a magnetic phase transition temperature T _N = ˜6K. (Example 4)

First, using an arc melting furnace, Er 37.5 was used.
An intermetallic compound consisting of atom%, Ho37.5 atom% and the balance Co was prepared, and this alloy was subjected to homogenizing heat treatment in a vacuum of 700 ° C. and 10 ⁻³ torr for 100 hours to obtain Er ₃ C.
A quasi-binary system of o and Ho ₃ Co was obtained. According to the X-ray diffraction experiment of the obtained pseudo-binary substance, a single phase of an intermetallic compound having the same crystal structure as Er ₃ Co and Ho ₃ Co and an intermediate lattice constant is formed. I knew that. The magnetic material obtained in this way was further added with A containing an oxygen concentration of about 1 ppm.
When heat treatment was performed at 300 ° C. for 30 minutes in an r atmosphere, the surface of the magnetic material was covered with a rare earth oxide film having an average film thickness of about 750A. The substance of Example 4 covered with such an oxide film showed very little change in the chemical composition and the film thickness of the oxide film even after 6 months in the air, and thus was very chemically chemically. It turned out to be stable. Further, the magnetic phase transition temperature of the above example was T _N = ∼15K, and relatively low specific heat characteristics in the bulk state were obtained. (Example 5)

A Gd thin film was grown around the Nd simple substance sample by the vapor phase thin film growth method. The film thickness at this time is about 1
000A to 10000A. Furthermore, oxygen concentration 1pp
When heat treatment was performed at 200 ° C. for 60 minutes in an Ar atmosphere containing about m, the sample surface had an average film thickness of about 700.
It was covered with the Gd oxide coating of A (Figure 2). This sample is chemically stable and has a very low temperature range (2K-1
The specific heat at 0K) is very large. This large low temperature specific heat is associated with the magnetic phase transition of Nd, that is, T _N = ˜1.
9 K and T _N = ˜8 K, and due to the large magnetic entropy emission at T _N = ˜3.8 K associated with the magnetic phase transition of the Gd oxide, Example 5 prepared by the method described above.
With the addition of an oxide film, the substance (1) exhibits more excellent properties in terms of chemical stability and low-temperature specific heat characteristics.

[0025]

As described above, according to the present invention, in the rare earth regenerator material using a large specific heat at a low temperature (20 K or less), the main phase is covered with the oxide of the rare earth to lower the specific heat characteristic. It is possible to provide a regenerator material having improved chemical stability without having to do so.

[Brief description of drawings]

FIG. 1 is a sectional view of a cold storage material of the present invention.

FIG. 2 is a sectional view of the cold storage material of the present invention.

Claims (2)

[Claims] 1. A rare earth element alone or Ni, Co and C
The grain surface composed of a rare earth element compound of at least one metal selected from u has a small Nd, Ho, Gd and Er content.
A cool storage material characterized by being coated with at least one kind of oxide. 2. A regenerator characterized by being filled with the regenerator material according to claim 1.