JP2585240B2 - Manufacturing method of cold storage material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a method for producing a cold storage material.

(Prior Art) In recent years, the development of superconducting technology has been remarkable, and as its application field has expanded, the development of a small, high-performance refrigerator has become indispensable. Such small refrigerators are required to be lightweight, small and have high thermal efficiency.

Therefore, a new refrigeration system (magnetic refrigeration) using the Ericsson cycle using the magnetocaloric effect instead of the gas refrigeration, and research on improving the performance of the gas refrigerator using the Stirling cycle have been actively conducted (Proceedings of ICEC 9 (198)).
2), pp. 26-29, Advances in Cryogenics Engineering,
1984, vol. 29, pp. 581-587 Proceedings of ICEC 10 (19
84), 3rd Cryo-cooler Conference (1984)).

The magnetic refrigeration method basically uses the heat absorption and heat release reactions due to the change in entropy (ΔS _M ) between the spin arrangement state when a magnetic field is applied to the magnetic material and the disordered spin state when the magnetic field is released. It is the principle. Thus, the greater the the [Delta] S _M is greater, it is possible to correspondingly exert a significant cooling effect, various magnetic material is studied.

In addition, the configuration of the regenerator, the compression unit, and the expansion unit is important for improving the performance of the gas refrigerator by the Stirling cycle. In particular, the performance of the regenerator material constituting the regenerator affects the performance (Proceedings of ICEC 10 (1984)). )). As such a cold storage material, a material having a high specific heat even at 20K at which the specific heat of copper or lead is drastically reduced is demanded, and various magnetic materials are also being studied.

The magnetic material as described above is required to exhibit a large magnetocaloric effect even in a very low temperature region. The efficiency of a refrigerator depends greatly on the magnetic material. That is, high entropy and good thermal conductivity are required.

As this magnetic substance, for example, Gd ₃ Ga ₅ O ₁₂ (GG
G), Carnet-based oxide single crystals containing rare earth elements typified by Dy ₃ Al ₅ O ₁₂ (DAG), and RAl ₂ Laves-type intermetallic compounds (R Is a rare earth element) (Proceedings of ICE)
C (1982, May); 30-33, etc.).

This magnetic material is required to have a large entropy change (ΔS) in the freezing temperature range. For example, when considering a magnetic working material for magnetic refrigeration from liquid nitrogen temperature covering a wide temperature range of 77 K to 15 K, a large entropy change over a wide temperature range and a change in this temperature change in a material system having the same crystal structure are considered. It is necessary to have successively different magnetic transition temperatures within the range. Examples of such a magnetic material include the aforementioned RAl ₂ Laves type intermetallic compound.

Here, in consideration of the practicality of the magnetic working material, in addition to the above characteristics, a high degree of freedom of workability is required. Therefore, it will be very effective if a high-density sintered body satisfying the above characteristics can be obtained.

The RAl ₂ Laves-type result of research on sintered intermetallic compound, sinterability of the intermetallic compound of the melting point of RAl ₂ are both 1500 ° C. or more as high for the stoichiometric composition is extremely poor, dense sintered It was found that it was difficult to obtain union. (Japanese Patent Application No. 60-20030) Considering sintering at a high temperature of 1500 ° C or higher, there are cost problems, oxidation problems due to the large amount of R components, and low thermal conductivity. It becomes a problem. Therefore, at present, a high-density magnetic sintered body that is effective as a magnetic working material for magnetic refrigeration or a cold storage material for gas refrigeration has not been obtained.

In magnetic refrigeration in the temperature range of about 77 K to 15 K, a regenerative cycle such as an Ericsson cycle is desirable because the contribution of lattice entropy is large. In such a cold storage refrigerator, heat transfer between the magnetic work material and the cold storage material is indispensable, and this greatly affects the cooling efficiency. At extremely low temperatures of 77 K or less, there is only a solid-state regenerator such as lead, for example, and it is necessary to make solid contact between the magnetic work material and the regenerator, or to form a narrow gap such as a He gas film to perform heat exchange. is there. Therefore, high-precision processing such as mirror finishing and processing of complex shapes is required for both magnetic working materials and cold storage materials (Cryogenic Engineering Society, November 1984). As described above, the appearance of a magnetic working material having particularly good workability has been desired for a regenerative refrigerator.

(Problems to be Solved by the Invention) The present invention has been made in order to solve the above-mentioned problems, and a regenerative material using a magnetic intermetallic compound having a stoichiometric composition has a high density comparable to the theoretical density. An object of the present invention is to provide a method for producing a regenerative material that can obtain a density molded body and has excellent thermal conductivity.

[Configuration of the invention]

(Means and Actions for Solving the Problems) The present invention is based on an ultrahigh-pressure press or an impact press method of 100,000 atmospheres or more, and is obtained by Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd. , Tb, D
at least one element selected from y, Ho, Er, Tm, Yb and
B, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Cu, Ag, Au, Be, Mg, Zn, Cd, Hg,
Ru, Rh, Pd, Os, Ir, Pt, Fe, Co, Ni, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo,
A high-pressure compact of microcrystalline particles of a magnetic intermetallic compound comprising at least one element selected from Re
× T _M Kelvin (T _M : melting temperature of microcrystalline particles (absolute temperature))
This is a method for producing a cold storage material, wherein the heat treatment is performed at a temperature of T _M or less.

According to such a manufacturing method, even in the case of an intermetallic compound having a stoichiometric composition in which it has conventionally been difficult to obtain a high-density sintered body, the high-density sintered body having a porosity comparable to the theoretical density and having almost no porosity Can be obtained. And the filling rate is
Since the content reaches 98% to 100%, the thermal conductivity is high, and since no sintering aid is contained, the magnetocaloric effect can be effectively exerted and the mechanical strength increases.

As described above, the heat treatment temperature after molding is set to 0.6 × T _M Kelvin (T
_M: it was not more than the melting temperature (absolute temperature) or T _M of the microcrystalline particles, at temperatures below 0.6 × T _M, improving the filling rate of the molded body is not remarkable, strength, thermal conductivity both insufficient The reason is that if the temperature exceeds T _M , the molded body is melted, the material is changed, and the workability is significantly deteriorated.

In the present invention, the microcrystalline particles of the magnetic intermetallic compound are at least one selected from Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb. Elements and B, Al, Ga, In, Tl, Si, G
e, Sn, Pb, Cu, Ag, Au, Be, Mg, Zn, Cd, Hg, Ru, Rh, Pd, Os, Ir, Pt,
The magnetic alloy is made of at least one selected from the group consisting of Fe, Co, Ni, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, and Re. Metal), rare earth- (Group IV metal),
A rare earth- (Ia group metal), a rare earth- (IIa group metal), a rare earth- (4d or 5d transition metal) intermetallic compound or a solid solution thereof, and more specifically, if the rare earth element is R _{, RAl 2, RAl 3, RNi} 2, RCo 2, RRh, RRh 2 Si 2, intermetallic compounds as represented by RCu ₂ Si ₂ or a solid solution thereof, the magnetic transition temperature, the crystal phase transformation point, Jahn-Teller The transformation point or spin rearrangement temperature resulting from the effect covers a wide temperature range of 4K to 300K, and particularly has an excellent magnetocaloric effect in a low temperature region of 77K (liquid nitrogen temperature) or lower.

The high-pressure molding in the present invention is desirably performed by an ultra-high pressure press of 100,000 atmospheres or more or an impact pressure molding method. That is, a molded article having a filling factor of 90% or more is obtained only by such high-pressure molding. Further, it is desirable that the filling rate of the molded body before the heat treatment is 90% or more. When the filling rate is less than 90%, the density after the heat treatment is not significantly improved, and the thermal conductivity is not significantly improved.

In the present invention, it is desirable that the particle diameter of the microcrystalline particles of each magnetic alloy is 0.1 to 1000 μm. This is because if the particle size is less than 0.1 μm, the surface of the microcrystalline particles increases, and the thermal conductivity decreases significantly due to oxidation of the powder surface, while the particle size decreases.
If the thickness exceeds 1000 μm, the high-pressure formability deteriorates.
A more preferable range of the particle size is 1 to 100 μm.

In the method of the present invention, the intermetallic compound having the above stoichiometric composition is prepared using, for example, an arc melting furnace. Next, the intermetallic compound is pulverized using, for example, a ball mill to obtain a fine powder of the intermetallic compound. The particle size of the fine powder of the intermetallic compound is preferably 0.1 to 1000 μm, more preferably 1 to 100 μm, for the above-mentioned reason. Thereafter, preforming is performed as necessary. Next, the compound powder or the preform thereof is surrounded by a ductile material, and the compound powder or the preform thereof is contained in a closed container via a pressure medium, and the explosive is exploded at a high speed to explode the compound powder or the preform thereof. After pressing and densification, the melting temperature (T _M ) of the intermetallic compound is 0.6
× T _M Heat treatment at a temperature of Kelvin or more and T _M or less.

The field of application of these high-density intermetallic compound magnetic polycrystalline body, a working magnetic refrigeration materials, other cold accumulating material gas refrigeration, hydrogen storage _{alloy, (RNi 5, RNi 2,} RCo 2), super magnetostrictive alloy ( RFe ₂ ) There are intermetallic compounds more suitable for each application field, such as RFe ₂ ). For example, as a working material for magnetic refrigeration, the magnetic transition point is lower than room temperature, preferably lower than liquid nitrogen temperature, according to the refrigeration principle. A Laves-type (MgCu ₂ ) compound of a heavy rare earth element having a large magnetic moment of a rare earth element and a nonmagnetic metal or Co or Ni is suitable. In addition, heavy rare earth MgCu ₂ (Laves type), a size factor compound that can be expected to have high density and large magnetocaloric value per unit volume as a cold storage material
In addition to compounds, cubic RAl ₃ (Cu ₃ An type), RCu ₂ , RRh, RRh ₂
Si ₂ and RCu ₂ Si ₂ compounds are suitable.

(Examples of the Invention) Hereinafter, examples of the present invention will be described.

First, an ErAl ₂ intermetallic compound (stoichiometric composition) consisting of Er 75.6% by weight and the balance Al was prepared using an arc melting furnace. Curie point (ferromagnetic transition temperature) of this compound is 13K
Met. Next, this compound was ground into a fine powder having a particle size of about 3 μm using a jet mill. The obtained fine powder was filled in a mild steel cylindrical container, preformed at a press pressure of 1 ton / cm ² , and then vacuum sealed. The vacuum-sealed cylindrical container was placed in an explosive and ignited from the upper portion of the cylinder to generate an explosive shock wave, and subjected to impact pressure molding. The propagation speed of the shock wave during molding was 5000 m / sec. The dimensions of the obtained molded body were 15 mm in diameter and 30 mm in height. The theoretical density is 10
When the value was set to 0, the filling rate was 95%. This compact was heat-treated at 1200 ° C. for 2 hours in an argon atmosphere. As a result of measuring the filling factor after the heat treatment, it was a high-density molded body of 99.9% or more. Next, FIGS. 1 and 2 show the results of various measurements performed on the molded body. FIG. 1 shows the results of examining the temperature dependence of the specific heat (Cp) in the absence of a magnetic field. FIG. 2 shows the results obtained by calculating the temperature dependence of the magnetic entropy change (ΔS _M ) from the temperature dependence of the specific heat (Cp) measured under a magnetic field of 5 Tesla and in the absence of a magnetic field.

For comparison, an ErAl ₂ compound having the same composition as in the example was pulverized in the same manner as in Example 1 and then press-molded at a pressure of 1 ton / cm ² , and the obtained compact was heated in an argon atmosphere. 12
Sintering was performed at 00 ° C. for 2 hours to obtain a normal sintered body. The packing ratio of the sintered body of this comparative example was as low as 70%. The results of various measurements performed on the sintered body (comparative example) are shown in FIGS. 1 and 2 together with the examples.

Example 2 17.45% by weight of Tb, 41.66% by weight of Dy, the balance being Fe (Tb
0.3Dy0.7) Fe ₂ intermetallic compound (stoichiometric composition) was adjusted in an arc melting furnace. Next, this compound was pulverized with a jet mill to obtain a fine powder of about 3 μm. The obtained fine powder was subjected to impact pressure molding under the same conditions as in Example 1 and then heat-treated at 950 ° C. for 2 hours in an argon atmosphere. The filling ratio after impact molding was 93%, and the filling ratio after heat treatment was 99% or more.

Next, the result of measuring the magnetostriction of this molded product is shown in FIG.
Shown in the figure. Magnetostriction was measured with a strain gauge and expressed as a rate of change in elongation in the magnetic field direction (δl / l).

After the same composition as Example for comparison (Tb0.3Dy0.7) Fe ₂ compound was micronized in the same manner as in Example 2, 1 ton / c
Press molding was performed at a pressure of m ² , and the obtained green compact was sintered at 950 ° C. for 2 hours in an argon atmosphere to obtain a normal sintered body. The filling rate of the sintered body of this comparative example was as low as 72%. FIG. 3 shows the results of magnetostriction measurement of the sintered body (comparative example) together with the example.

Example 3 Er58.75% wt%, was ErNi the balance Ni ₂ intermetallic compound (stoichiometric composition) adjusted by an arc melting furnace. The Curie point (ferromagnetic transition temperature) of this compound was 6K. Next, this compound was pulverized with a jet mill to obtain a fine powder of about 3 μm. The resulting fine powder was subjected to impact pressure molding under the same conditions as in Example 1 and then heated at 900 ° C. in an argon atmosphere.
Heat treated for hours. The filling ratio after impact molding was 92%, and the filling ratio after heat treatment was 99% or more.

Next, the results of specific heat (Cp) measurement performed on the molded product are shown in FIG.

For comparison, an ErNi ₂ compound having the same composition as in the example was pulverized in the same manner as in Example 3 and then press-molded at a pressure of 1 ton / cm ² , and the obtained compact was heated in an argon atmosphere. 90
Sintering was performed at 0 ° C. for 2 hours to obtain a normal sintered body. The filling rate of the sintered body of this comparative example was as low as 75%. FIG. 4 shows the result of specific heat measurement of the sintered body (comparative example) together with the example.

Example 4 HoCu ₂ intermetallic compound (stoichiometric composition) composed of 56.48% by weight of Ho and the balance of Cu was prepared using an arc melting furnace. The Neel point (antiferromagnetic transition temperature) of this compound was 9K.
Next, this compound was pulverized with a jet mill to obtain a fine powder of about 3 μm. The obtained fine powder was subjected to impact pressure molding under the same conditions as in Example 1 and then 850 ° C. in an argon atmosphere.
For 2 hours. The filling ratio after impact molding was 95%, and the filling ratio after heat treatment was 99.5% or more.

Next, the results of specific heat (Cp) measurement of this molded product are shown in FIG.

For comparison, a HoCu ₂ compound having the same composition as in the example was pulverized in the same manner as in Example 4, and then press-molded at a pressure of 1 ton / cm ² , and the obtained compact was heated in an argon atmosphere. 85
Sintering was performed at 0 ° C. for 2 hours to obtain a normal sintered body. The packing ratio of the sintered body of this comparative example was as low as 70%. FIG. 5 shows the result of specific heat measurement of the sintered body (comparative example) together with the example.

〔The invention's effect〕

As described in detail above, according to the present invention, it is possible to obtain a high-density molded product of an intermetallic compound having a stoichiometric composition, without impairing the magnetocaloric effect inherent to the compound, and having excellent strength and workability. It is possible to provide a method for obtaining a molded article, exhibiting excellent properties in terms of heat conduction properties, and particularly for producing a magnetic polycrystal having a high magnetocaloric effect in a low temperature range of 77 K or lower, such as an Ericsson cycle. As a result, excellent performance can be obtained as a magnetic material of a magnetic refrigerator or a cold storage material of a gas refrigerator by a Stirling cycle or the like.

[Brief description of the drawings]

 1 to 5 are characteristic curve diagrams.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichiro Inomata 1 Toshiba-cho, Komukai, Koyuki-ku, Kawasaki-shi Toshiba Research Institute, Inc. (56) References JP-A-61-183436 (JP, A) JP-A-62- 30840 (JP, A)

Claims (4)

(57) [Claims] 1. Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Y, La, Ce, Pr, Nd,
At least one element selected from Ho, Er, Tm, Yb and B, A
l, Ga, In, Tl, Si, Ge, Sn, Pb, Cu, Ag, Au, Be, Mg, Zn, Cd, Hg, Ru,
Rh, Pd, Os, Ir, Pt, Fe, Co, Ni, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, Re
A high pressure compact of microcrystalline particles of a magnetic intermetallic compound consisting of at least one element selected from the group consisting of 0.6 × T
_M Kelvin (T _M: melting temperature of the fine crystal particles (absolute temperature)) or more
A method for producing a cold storage material, comprising heat-treating at a temperature of T _M or less. 2. The method for producing a cold storage material according to claim 1, wherein the filling rate of the compact before the heat treatment is 90% or more. 3. The microcrystalline particles of the intermetallic compound having a particle size of 0.
2. The method according to claim 1, wherein the thickness is 1 to 1000 [mu] m. 4. A fine powder of a magnetic intermetallic compound or a preform thereof is surrounded by a ductile material, which is housed in a closed container via a pressure medium, and explosives are exploded at a high speed.
The method for producing a regenerative material according to claim 1, wherein after the fine powder or its preform is densified by explosion compression, the ductile material is removed to obtain a compact.