JPH01140701A - Magnetic polycrystalline substance and its manufacture - Google Patents

Abstract

PURPOSE:To make a magnetic thermal-value effect and a thermal-conductive characteristic at a low temperature excellent by a method wherein a fine crystal particle of a magnetic alloy where a specific coating layer has been formed on its surface is molded under a high pressure. CONSTITUTION:A coating layer composed of a metal simple substance or an alloy which has a face-centered cubic structure and whose coefficient of thermal expansion at 400-700K is 8-14X10<-6>/ deg.C is formed on the surface of a fine crystal particle of a magnetic alloy by a plating method or a vapor growth method; an obtained powder is molded under a high pressure. Because the metal simple substance or the alloy which has the face-centered cubic structure displaying impact ductility is coated on the surface of the fine crystal particle of the magnetic alloy, it is possible to obtain a magnetic polycrystalline substance which enhances resistance to an impact during a high-pressure molding operation, whose density is high and which displays an excellent thermal- conductive characteristic. By this setup, it is possible to achieve a high magnetic thermal-value effect over a wide temperature range in a low-temperature region and, at the same time, the excellent thermal-conductive characteristic.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to a magnetic polycrystalline material and a method for producing the same, and particularly to a magnetic polycrystalline material and a method for producing the same, and particularly to a magnetic polycrystalline material having an excellent magnetocaloric effect over a wide temperature range at extremely low temperatures below liquid nitrogen temperature. and a magnetic polycrystalline body exhibiting thermal conductivity and a method for producing the same.

(Prior Art) In recent years, superconducting technology has made remarkable progress, and as its application fields expand, the development of compact, high-performance refrigerators has become essential. Such small refrigerators are required to be lightweight, compact, and have high thermal efficiency.

Therefore, research is actively being conducted on a new refrigeration method (magnetic refrigeration) using the Ericsson cycle that uses the magnetocaloric effect to replace gas refrigeration, and on improving the performance of gas refrigerators using the Stirling cycle.
of' I CE C9 (1982).

pp, 26-29, Advances in C
ryogenicsEnglneerlnL 1
984. vol, 29. pp, 581-587
, Proceedings of I CE Ct.
o (1984), 3rd Cryo-cooler
Conf'erence (1984)).

The basic principle of the magnetic refrigeration method is to utilize heat absorption and heat release reactions due to entropy changes (68M) between the state in which the spins are aligned when a magnetic field is applied to a magnetic material and the state in which the spins are disordered when the magnetic field is removed. That is. Therefore, the larger 68M is, the greater the cooling effect can be exerted, and therefore various magnetic materials are being considered.

In addition, in order to improve the performance of a gas refrigerator using the Stirling cycle, the configuration of the regenerator, compression section, and expansion section is important, and the regenerator material that makes up the regenerator particularly affects its performance.
C10(1,984)). As such a cold storage material, there is a demand for a material that has a high specific heat even at 20 K, where the specific heat of copper and lead is drastically reduced, and various magnetic materials are being considered for this as well.

Furthermore, since the magnetic working material is required to efficiently dissipate absorbed heat to the outside, it must also have excellent thermal conductivity.

Under the above requirements, for example, Japanese Patent Application Laid-Open No. 60-204
No. 852 describes a porous magnetic material obtained by mixing and sintering three or more types of magnetic powders having different Curie temperatures. In such magnetic materials, the range of large entropy changes near the Curie temperature, which differs depending on the type of magnetic material powder, is continuous, and the large entropy change is almost constant over a wide temperature range, so the performance of the magnetic refrigerator is We can expect it to improve.

However, since the magnetic material described in the above-mentioned publication is a porous sintered body, it has poor thermal conductivity, making it difficult to effectively exhibit the excellent magnetocaloric effect described above. On the other hand, if compression molding and sintering is performed at high pressure in an attempt to obtain a magnetic material with a high filling rate of magnetic powder, a uniform solid solution is formed, making it impossible to obtain a large entropy change that is almost constant over a wide temperature range.

Therefore, as a result of intensive research to achieve the above object, the present inventors have discovered a magnetic polycrystalline material obtained by molding a coated powder in which a magnetic alloy powder having a magnetocaloric effect at extremely low temperatures is coated with a metal binder. It has excellent thermal conductivity, and when it is made of a mixture of multiple types of magnetic alloy powders, mutual diffusion between different types of magnetic alloy powders is suppressed, and therefore it has multiple different magnetic transition points. After discovering the facts, a patent application was filed as Japanese Patent Application No. BO-214817.

However, with this technique, a new problem has arisen in that the metal binder diffuses into the magnetic alloy powder during sintering, reducing the magnetocaloric effect of the magnetic alloy powder. For this reason,
Although the above-mentioned magnetic polycrystalline material has high thermal conductivity, there is a problem in that the effect cannot be fully utilized.

(Problems to be Solved by the Invention) The present invention has been made in consideration of the above points, and provides a magnetic polycrystalline body having excellent magnetocaloric effect at low temperatures and excellent thermal conductivity, and a method for producing the same. The purpose is to provide

[Structure of the invention] (Means and effects for solving the problems) The magnetic polycrystalline body of the present invention is a magnetic polycrystalline body formed by high-pressure molding of microcrystalline particles of a magnetic alloy having a coating layer formed on the surface. The coating layer has a face-centered cubic structure and is made of a metal element or alloy having a coefficient of thermal expansion of 8 to 14×10″6/°C at 400 to 700 K, and the coating layer has an abundance ratio of 10
~40% by volume.

Further, in the method for producing a magnetic polycrystalline body of the present invention, the surface of the microcrystalline particles of the magnetic alloy has a face-centered cubic structure, and
Thermal expansion coefficient at 00 K is 8 to 14 x 1.0-6/
It is characterized in that a coating layer made of a simple metal or an alloy of 'C is formed by a plating method or a vapor phase growth method, and the obtained powder is molded under high pressure.

Hereinafter, the magnetic polycrystalline body of the present invention will be explained in more detail.

In the present invention, the microcrystalline particles of the magnetic alloy include Y,
La, CesPr, Nd, Pm, Sm5Eu, Gd
, Tb5Dy, HoSErSTm.

At least one rare earth element selected from yb (hereinafter referred to as
R), BSA, f', Cu, Fe.

It is desirable to use at least one magnetic element selected from Co and Ni (hereinafter referred to as M).

It is desirable that the content ft of R (in the case of two or more types of R, the total content of both) in such a magnetic alloy is 20 to 99%. That is, when the R content is less than 20% by weight, 68M does not increase at any temperature below room temperature, and a sufficient magnetocaloric effect is achieved. I can't. on the other hand,
When the content of R exceeds 99% by weight, the content of M decreases and the alloy grinding properties are significantly deteriorated, making it difficult to produce fine powder and making it virtually impossible to obtain powder. An alloy powder that satisfies the above content conditions is a ferromagnetic alloy powder.

In addition, in order to obtain a good magnetocaloric effect, Gd5Tb
, Dy, Ho, and Er (R3) is preferably essential, and R1/R is preferably 50% or more.

In addition, excellent thermal conductivity can be obtained when there is only one type of microcrystalline grain of a magnetic alloy, but if two or more types of microcrystalline grains of a magnetic alloy are formed, multiple different magnetic transition points can be obtained at the grain level. A mixed magnetic polycrystalline body having the following properties is obtained. Here, R
When using two or more magnetic alloy powders with different elements,
The remaining metals in each magnetic alloy powder may be of the same type or different types.

Therefore, the powder used (e.g. DyNi2, E
Combination of rNi2, HoNi2, DyHoNi2;
The result is a combination of DyNi2 and DyCo2. By mixing and molding two or more kinds of magnetic alloy powders in this manner, a magnetic polycrystalline body having two or more magnetic transition points can be obtained, and a magnetocaloric effect can be obtained over a wide temperature range.

In the present invention, the coating layer formed on the surface of the magnetic alloy has the effect of improving thermal conductivity in the final molded body (magnetic polycrystalline body), and the effect of improving the thermal conductivity of the microcrystalline particles of two or more types of magnetic alloys. It has the effect of binding the mixed powders in a separate and independent state.

As this coating layer, a single metal or an alloy having a face-centered cubic structure is used. This is because single metals or alloys with a face-centered cubic structure exhibit impact ductility, so during impact forming described later, the microcrystalline particles of the magnetic alloy inside are subject to adverse effects such as distortion and changes in lattice constant. This is to prevent this and improve moldability to obtain a high-density molded product.

400~ for metals or alloys constituting the coating layer
Thermal expansion coefficient at 700K is 8~14X 10″6/
℃ was chosen for the following reasons. That is, if it is out of the above range, the difference in coefficient of thermal expansion between the microcrystalline particles of the magnetic alloy and the coating layer becomes large, and there is a risk that the adhesion between the two may deteriorate due to temperature changes before and after impact pressure forming.

The abundance ratio of the coating layer in the magnetic polycrystalline body is 10 to 40.
The reason why it is defined as volume % is as follows. That is, when the proportion of the coating layer is less than 10% by volume, the bonding ability of the coating layer is small and molding is difficult, and the thermal conductivity cannot be improved.

On the other hand, when the proportion of the coating layer exceeds 40% by volume, the formability improves, but the proportion of microcrystalline particles in the magnetic alloy decreases, the magnetocaloric effect per unit volume decreases, and the The cooling effect is significantly reduced due to heat generation caused by eddy current loss.

In addition, this coating layer is required to have high thermal conductivity;
．． A metal tIt body or alloy having a thermal conductivity at 2K of I W / cm K or higher is preferred. Also, the coating' layer is 8g/cZ! A single metal or an alloy having a density of 13 or higher is preferred. Therefore, as a single metal or an alloy constituting the coating layer, P d having the above-mentioned physical properties is used.
-P t SRh % N t ST h less (
It is desirable that the material consists of only one type.

Next, the method for manufacturing the magnetic polycrystalline body of the present invention will be explained in more detail.

The microcrystalline particles of the magnetic alloy are manufactured as follows. First, for example, RA)2. RN i 2, RC02, RF
The e2 alloy is melted in an arc melting furnace. The resulting alloy is then ground into a fine powder. The particle size of this powder is 0.
It is desirable that it is 05-1000u.

The surface of the magnetic alloy fine powder obtained as described above is coated with a metal element or alloy having a face-centered cubic structure. As a method for forming it, a plating method such as electroless plating, or a vapor growth method such as sputtering or vapor deposition, which can form a thin and uniform coating layer, is used. In addition, when employing the plating method, it is desirable to perform pre-treatments such as degreasing, activation, and cleaning.

Next, the metal-coated magnetic alloy fine powder is subjected to impact pressure molding to obtain a desired molded body.

This impact pressing method is a method in which metal-coated magnetic alloy fine powder is inserted into a capsule and subjected to impact pressing to obtain a molded body.

For example, impact pressurization using a rail gun at 1 million or 10 million atmospheres, impact pressurization using a rifle gun, explosive molding using gunpowder, etc. are effective. Further, high-pressure molding using an ultra-high pressure press of 100,000 mL or more is also effective.

The structure of the compact obtained by this impact pressure forming is such that microcrystalline particles of the magnetic alloy are bonded with the coating layer as a binder. At this time, since the metal element or alloy constituting the coating layer has a face-centered cubic structure exhibiting impact ductility, formability is improved and a high-density magnetic polycrystalline body can be obtained.

Furthermore, due to improved formability, it is expected that the adhesion between the microcrystalline particles of the magnetic alloy and the coating layer will improve, and that thermal resistance can also be prevented.

As described above, the magnetic polycrystalline body according to the present invention is obtained by high-pressure molding, and the temperature during molding is 5.
00, and is molded instantly at high speed, it is possible to prevent diffusion between the coating layer and the microcrystalline particles of the magnetic alloy, thereby preventing deterioration of the magnetic properties of the magnetic alloy. Can be done. Moreover, since the surface of the microcrystalline particles of the magnetic alloy is coated with a single metal or alloy having a face-centered cubic structure that exhibits impact ductility, impact resistance during high-pressure forming is improved, and high density and excellent thermal properties are achieved. A magnetic polycrystalline body exhibiting conductivity is obtained. Therefore, a high magnetocaloric effect over a wide low temperature range and excellent thermal conductivity can be achieved at the same time.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

First, E r 75.8% by weight, balance AI! An alloy (A) consisting of 75% by weight of Ho, the balance CB) consisting of 75.1% by weight of DY, the balance A, and an alloy (C) consisting of 75.1% by weight of DY, the balance A were prepared using an arc melting furnace.

Next, each of these alloys was ground into fine powder with a particle size of 3p using a jet mill. The three types of fine powders obtained were mixed for about 5 hours in an argon atmosphere using a mixer to obtain a mixed powder. The weight ratio of the AlB and C alloy fine powders was 3:1:4.

Subsequently, the obtained mixed powder was degreased using 1.1.1-)lichloroethane, activated with an activation solution of pH 10 to 11, washed with ethanol, and then electroless palladium (
(manufactured by Nippon Engelhard Co., Ltd.) was subjected to electroless plating under conditions of pH 4 to 10.90° C. and strong stirring to prepare Pd-coated powder. Furthermore, this powder was washed with ethanol and dried. Through this plating process, the surface of the alloy powder has a 0.
A Pd coating layer having a thickness of 11JJR was formed. Moreover, the existence ratio of the Pd coating layer in the mixed powder was 20% by volume.

Next, the plated mixed powder was filled into a cylindrical container made of mild steel, preformed under a press pressure of 1 ton/cm2, and then vacuum sealed. This vacuum-sealed cylindrical container was placed in gunpowder, and by igniting it from the top of the cylinder, an explosive shock wave was generated and impact pressure molding was performed. The propagation velocity of the shock wave during molding was 5000 m/s.

The dimensions of the obtained molded body are 15 mm in diameter and 30 m in height.
It was m. Further, assuming the theoretical density to be 100, the compact was a high-density molded product with a filling rate of 99.9%.

The results of SEM-EDX analysis of the obtained molded body are shown in FIGS. 1 and 2 (a) to (e). As schematically shown in Figure 1, each microcrystalline particle has become dense while maintaining its initial particle size (average 3uJR), and P
With the d coating layer 1 as a boundary, the microcrystalline particles 2 of the He alloy, the microcrystalline particles 3 of the B alloy, and the microcrystalline particles 4 of the C alloy were uniformly mixed in an independent state in each crystal grain unit. Furthermore, from the results of EDX elemental analysis shown in Figures 2(a) to (e),
It was confirmed that no diffusion occurred between the Pd coating layer and the microcrystalline particles of each magnetic alloy.

Furthermore, the results of various measurements performed on this magnetic polycrystal are shown in FIGS. 3 to 6. Figure 3 shows the results of investigating the temperature dependence of magnetization in a 2 Tesla magnetic field. Fourth
The figure shows the results of investigating the temperature dependence of specific heat (Cp) in the absence of a magnetic field. Figure 5 shows the magnetic entropy change tEt (6
These are the results of determining the temperature dependence of 3M). FIG. 6 shows the results of investigating the temperature dependence of thermal conductivity.

As is clear from Figure 3, the temperature range in which significant magnetization can be obtained in this magnetic polycrystal is as wide as 28°C, and the magnetization decreases as the temperature rises, but two inflection points are observed in the curve. be done.

Moreover, as is clear from FIG. 4, the specific heat curve of this magnetic polycrystalline body shows three peaks at 8, IIIK, and 27.

Furthermore, as is clear from FIG. 5, in this magnetic polycrystalline material, the curve of entropy change is almost constant over a relatively wide range of 3 to 28.

Furthermore, as is clear from FIG. 6, this magnetic polycrystalline material has a high thermal conductivity of 15 W/cm.

[Effects of the Invention] As detailed above, according to the present invention, a magnetic polycrystalline body exhibiting a high magnetocaloric effect over a wide temperature range in a low temperature range of 77 or below and having excellent thermal conductivity, and such a magnetic polycrystalline body A method for easily producing a polycrystalline body can be provided, and excellent performance can be obtained as a magnetic material for a magnetic refrigerator using an Ericsson cycle or as a cold storage material for a gas refrigerator using a Stirling cycle.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the surface state of a magnetic polycrystalline body according to an example of the present invention, as observed by SEM, and Fig. 2 (a
) to (e) are spectrum diagrams obtained by EDX elemental analysis of the same magnetic polycrystalline body, Figure 3 is a diagram showing the temperature dependence of magnetization of the same magnetic polycrystalline body in a 2 Tesla magnetic field, and Figure 4 is a diagram showing the temperature dependence of magnetization of the same magnetic polycrystalline body in a 2 Tesla magnetic field. A diagram showing the temperature dependence of the specific heat of a magnetic polycrystal in the absence of a magnetic field. Figure 5 is a diagram showing the temperature dependence of magnetic entropy change in the same magnetic polycrystal. Figure 6 is a diagram showing the temperature dependence of the magnetic entropy change in the same magnetic polycrystal. FIG. 2 is a diagram showing the temperature dependence of thermal conductivity of a body. DESCRIPTION OF SYMBOLS 1... Pd coating layer, 2... Microcrystalline particles of A alloy, 3
... Microcrystalline particles of B alloy, 4... Microcrystalline particles of C alloy. Applicant's representative Patent attorney Takehiko Suzue ■(ni) Figure 3 (ni) Figure 4 0 5 10
05t. (a) Total Area (b
)5potl(c) 5pot2(d
) 5po+ 3 (e) 5pot 4Figure 2Figure 5'' Continued from page 1

Claims (16)

[Claims] (1) In a magnetic polycrystalline body formed by high-pressure molding of microcrystalline particles of a magnetic alloy having a coating layer formed on its surface, the coating layer has a face-centered cubic structure and a thermal expansion coefficient at 400 to 700K. Made of a single metal or alloy with a temperature of 8 to 14 x 10^-^6/°C, and the abundance ratio of the coating layer is 10 to 10.
A magnetic polycrystalline material having a content of 40% by volume. (2) The magnetic polycrystalline body according to claim 1, wherein the coating layer is made of a single metal or an alloy having a density of 8 g/cm^3 or more. (3) The thermal conductivity of the coating layer at 4.2K is 1W/cm
The magnetic polycrystalline body according to claim 1, characterized in that the magnetic polycrystalline body is made of a single metal or an alloy of K or more. (4) The magnetic polycrystalline material according to claim 1, wherein the coating layer is made of at least one of Pd, Pt, Rh, Ni, and Th. (5) The microcrystalline particles of the magnetic alloy are Y, La, Ce, Pr.
, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,
Claim 1 comprising at least one rare earth element selected from Er, Tm, and Yb and at least one magnetic element selected from B, Al, Cu, Fe, Co, and Ni. Magnetic polycrystalline body described in . (6) The magnetic polycrystalline body according to claim 1, characterized in that the microcrystalline particles of the magnetic alloy are a mixed powder of two or more types. (7) The grain size of the microcrystalline particles of the magnetic alloy is 0.05 to 100.
The magnetic polycrystalline body according to claim 1, wherein the magnetic polycrystalline body has a diameter of 0 μm. (8) The surface of the magnetic alloy microcrystalline particles has a face-centered cubic structure and has a thermal expansion coefficient of 8 to 14 at 400 to 700K.
A method for manufacturing a magnetic polycrystalline body, characterized by forming a coating layer made of a single metal or an alloy with a temperature of . (9) The method for manufacturing a magnetic polycrystalline body according to claim 8, wherein the coating layer is made of a single metal or an alloy having a density of 8 g/cm^3 or more. (10) The thermal conductivity of the coating layer at 4.2K is 1W/c
9. The method for manufacturing a magnetic polycrystalline body according to claim 8, characterized in that the magnetic polycrystalline body is made of a single metal or an alloy having a magnetic conductivity of mK or more. (11) The method for producing a magnetic polycrystalline body according to claim 8, wherein the coating layer is made of at least one of Pd, Pt, Rh, Ni, and Th. (12) The microcrystalline particles of the magnetic alloy are Y, La, Ce, Pr
, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,
Claim No. 1, characterized in that it consists of at least one rare earth element selected from Er, Tm, and Yb, and at least one magnetic element selected from B, Al, Cu, Fe, Co, and Ni. The method for producing a magnetic polycrystalline body according to item 8. (13) The method for producing a magnetic polycrystalline body according to claim 8, wherein the microcrystalline particles of the magnetic alloy are a mixed powder of two or more types. (14) The particle size of the microcrystalline particles of the magnetic alloy is 0.05 to 10
9. The method for producing a magnetic polycrystalline material according to claim 8, wherein the magnetic polycrystalline material has a diameter of 00 μm. (15) The method for producing a magnetic polycrystalline body according to claim 8, wherein the high-pressure molding is performed using an ultra-high pressure press of 100,000 atmospheres or more. (16) The method for producing a magnetic polycrystalline body according to claim 8, wherein the high-pressure molding is performed by impact pressure molding.