JPS6280247A - Magnetic working substance for magnetic refrigeration - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a magnetic working material for magnetic refrigeration that performs cooling using the magnetocaloric effect.

[Technical background of the invention and its problems]

With the remarkable development of superconducting technology in recent years, applications of industrial electronics are being considered in a wide range of fields such as the information industry and medical equipment. In order to use superconducting technology, it is essential to develop a refrigerator that can create an extremely low temperature environment. Gas refrigeration is a well-known refrigeration method, but its efficiency is extremely low and the equipment is large.As a new refrigeration method, we are researching a magnetic refrigeration method that uses the magnetocaloric effect of magnetic materials. is actively practiced (pro
ceedings of ICEC9 (1982,
MaY): 26-29, Advances
inCryogenic Engineering
*1984 e Vo7 +29.581-587)
o To put it simply, there is a great advantage in multiplying the heat absorption and heat release reactions due to entropy changes between the spin alignment state when a magnetic field is applied to a magnetic material and the spin disordered state when the magnetic field is released. This is a promising method. The efficiency of magnetic refrigeration is greatly influenced by the magnetic working material. That is,
It is required to have large entropy and good thermal conductivity.

As this magnetic working material, for example, Gd s Ga50u (
GGG), Dy 3A-41012 (DA
C) Garnet-based oxide single crystals containing rare earth elements represented by RA t, Laves type intermetallic compounds (R
is a rare earth element) Gin is being researched (Proceed
ings of ICEC (1982, May)
;30-33 etc.).

This magnetic working material is required to have an end-low change (ΔS) of W in the freezing temperature range. For example 77 to 15
When considering a magnetic working material for magnetic refrigeration from liquid nitrogen temperature, which targets a wide temperature range, there is a large entroneau change in a material system with the same crystal structure over a wide temperature range, and within this temperature range. It is necessary to have continuously different magnetic transition temperatures. Examples of such magnetic materials include the aforementioned RAt and Laves type intermetallic compounds.

When considering the practicality of magnetic working materials, in addition to the above characteristics, flexibility in workability and high precision are required. Therefore, it would be very effective if a sintered body satisfying the above characteristics could be obtained.

Although there are no reports on the above RAG and Laves-type metallic intermetallic compounds, the melting points of both RAG and RAt are 1500
Since the temperature is as high as ℃ or higher, it is expected that sinterability will be poor. Furthermore, considering sintering at a high temperature of 1500° C. or higher, cost problems arise, and furthermore, cost problems due to the large amount of R component contained, low thermal conductivity, etc. arise. Therefore, at present, a magnetic sintered body that is effective as a magnetic working material for magnetic refrigeration has not been obtained.

In addition, in magnetic refrigeration that targets a temperature range of about 77 to 15 degrees, in a lattice entro♂- contributing refrigerator,
Heat transfer between the magnetic working material and the regenerator material is essential. Here, in the extremely low temperature range described below in 77, there is only a solid regenerator material such as lead, and the magnetic working material and the regenerator material are brought into solid contact, but a narrow gap of He gas film thickness is formed to facilitate heat exchange. It is necessary to do it. Therefore, high-precision processing such as mirror finishing and processing of complex shapes is required for both magnetic working materials and regenerator materials (Cryogenic Society of Japan, November 1984). As described above, there has been a desire for a magnetic working material with particularly good processability for regenerator refrigerators.

[Purpose of the invention]

The present invention has been made in consideration of the above points, and an object of the present invention is to provide a magnetic working material having a large entroneau change, high thermal conductivity, and excellent workability.

[Summary of the invention]

It has been found that a sintered body can be obtained. Furthermore, it was discovered that the obtained sintered body has good thermomagnetic properties and thermal conductivity, leading to the creation of the present invention.

That is, the present invention is a material containing rare earth elements from La to Yb in the periodic table and Y (hereinafter referred to as R). Such a sintered body has a high density with a filling rate exceeding 80%, and obtains a large magnetic entroneau change near the magnetic transition point (Kiely temperature) in the range of 77 to 15 degrees.

Regarding the amount of rare earth elements from La to Yb and Y, if the amount is too large, the thermomagnetic effect, that is, the magnetic nitro♂-change will be small, and if it is too small, the magnetic refrigeration efficiency will be lower than that of sintering, so 55% by weight or more, It was set to be 65 fftts or less. In addition, among rare earth elements, heavy rare earth elements such as Gd - Yb have a large magnetic moment per rare earth element ion, so they are effective elements in improving the thermomagnetic effect and magnetic refrigeration efficiency, and are effective in increasing the magnetic refrigeration efficiency when the content is 35% by weight or more. is preferred. The density of the sintered body changes depending on the sintering conditions and has a large effect on heat transfer characteristics, but when considered as a magnetic working material for magnetic refrigeration, it is desirable that the density is 7 f/cd or more. If it is too small, the heat transfer characteristics will deteriorate significantly.

The particle size of such magnetic working material influences the sintered density, and is preferably in the range of 1 to 10 μm. If it is too large, the sintered density will decrease, and if it is too small, it will be easily oxidized, the thermomagnetic effect will decrease, and the sintered density will also decrease.

O These n-"cJ alloy fine particles are press-formed into a desired shape and sintered. Sintering is performed in a non-oxidizing atmosphere such as an inert gas such as Ar gas. There is a sintering temperature, which is preferably 500 to 1100° C. If it is too low, a high degree of sintering cannot be obtained, and if it is high, it becomes difficult to obtain a good sintered body due to oxidation, evaporation, etc.

They discovered that by utilizing the solid-liquid phase reaction line around 600 to 1000°C, it is possible to obtain properties with a filling rate exceeding 80% and a density comparable to that of the Ichibes type intermetallic compound.

Amounts of Nl, Fe, Mn, St, Mg
, Ca, Cu, Zn.

Impurities such as Ti, C, N, and O, or other impurities that do not impair the effects of the present invention, may be contained.

Further, the thermal conductivity can be further improved by performing heat treatment after sintering. This is 500-800℃
The degree is favorable, and it is thought that grain growth is the cause.

[Effect of light]

As explained above, according to the present invention, it is possible to obtain a magnetic working material for magnetic refrigeration that has excellent thermomagnetic properties and thermal conductivity, and is highly workable.

In addition, the magnetic working material of the present invention has a large degree of processing freedom and can be processed with complex and high precision, so it is suitable for liquids such as the Ericsson cycle, which has a large contribution from lattice entropy and requires the use of a cold storage method. It is particularly effective when used as a magnetic working material for magnetic refrigeration from nitrogen temperatures, since good heat transfer can be obtained.

[Embodiments of the invention]

The present invention will be described in detail below.

A rare earth/cobalt alloy with a predetermined composition is produced in an arc melting furnace, and a particle size of 3μF is produced using a ball mill method. After pulverizing the powder into a fine powder of about i, the powder was press-molded to obtain a green compact. This green compact was sintered in an Ar gas atmosphere.

The density (ρ) of the obtained sintered body, the effective bore magneton number (μeH) determined by measuring the magnetic susceptibility, the Kiley point (Te), and the thermal conductivity (value at Te) were measured. These measured values are shown in Table 1 together with the alloy composition and sintering conditions. (iI
/, Ding Wu Bai) Examples 1 to 8 are related to the present invention, and it can be seen that all of them are excellent in both the effective bore magneton number and thermal conductivity. Examples 1 to 6 contain 35 wt% or more of heavy rare earth elements, and as is clear from comparison with Example 7, the effective bore magneton number is large and the thermomagnetic effect is excellent.

Comparative Examples 1 and 2 are both examples with a small amount of rare earth elements, but it can be seen that the density is low and the sinterability is poor. Therefore, it has very poor thermal conductivity and is difficult to use as a magnetic working material.

Further, Example 1 was subjected to heat treatment at 700° C. x 150 I. As a result, it was confirmed that the thermal conductivity was improved to 650 mW/c1n-.

The same was true for other items.

As described above, the present invention has made it possible to use a magnetic sintered body as a magnetic working material, and has significant advantages for improving the performance of magnetic refrigerators and for practical application of regenerator type magnetic refrigerators. .

Claims (3)

[Claims] (1) Contains 55 to 65% by weight of at least one of rare earth elements from La to Yb in the periodic table of elements and Y,
1. A magnetic working material for magnetic refrigeration, characterized in that a sintered body whose remainder is substantially composed of Co is used. (2) The magnetic working material for magnetic refrigeration according to claim 1, which contains 35 to 65% by weight of at least one of the heavy rare earth elements from Gd to Yb in the periodic table of elements. (3) The magnetic working material for magnetic refrigeration according to claim 1, wherein the sintered body has a sintered density of 7 g/cm^3 or more.