JP4240380B2 - Manufacturing method of magnetic material - Google Patents

Description

  The present invention relates to a magnetic material used for a refrigerator that does not use Freon gas, and relates to a method for producing a magnetic material used in a highly efficient refrigeration system that realizes an environmentally friendly refrigerator and air conditioner that uses the magnetocaloric effect.

A refrigeration technique using the magnetocaloric effect of a magnetic material has been known for a long time. As a magnetic material used in this refrigeration technology, R-Ni (rare earth element-Ni alloy) has been studied mainly for cryogenic use. However, in recent years, as described in Non-Patent Document 1, Ames Laboratories has verified that the magnetocaloric effect at room temperature can be used as a refrigeration technology. Attention has been gathered. Gd particles have been common as magnetic materials that exhibit a large magnetocaloric effect near room temperature, but in recent years, La has a Curie temperature near room temperature and a large change in magnetic entropy due to adiabatic demagnetization. Magnetic materials such as (Fe, Si) ₁₃ , La (Fe, Si) ₁₃ Hz, Mn-As-Sb, Gd ₅ Si ₂ Ge ₂ were discovered. It has come to the attention of the world. The main reason for this is that the conventional refrigeration method using chlorofluorocarbon gas and alternative chlorofluorocarbon gas has a large environmental burden such as destruction of the ozone layer due to disposal of working gas, and an environmentally friendly alternative cooling technology has been desired. It is. Refrigerators made by this refrigeration technology have not yet been able to replace conventional large refrigerators and air conditioners, but new products that use magnetic refrigeration technology may be created due to their high efficiency. Among these materials having a magnetocaloric effect, the La (Fe, Si) _{13 Hz-} based material described in Patent Document 1 has an excellent Curie temperature near room temperature and the Curie temperature can be adjusted by the hydrogen storage amount. Therefore, it is promising as a magnetocaloric effect material at room temperature because its magnetic entropy change is larger than other materials.
When the magnetocaloric effect material is applied to an actual refrigeration system, it is necessary to produce a unit packed with magnetic particles. The refrigeration method considered to be the most promising at present is called an AMR (Active Magnetic Regenerator) method as described in Patent Document 2, and the magnetocaloric effect material also serves as a regenerator.
JP 2003-96547 A (2nd page, 24th line) U.S. Pat. No. 4,332,135 (column 6, lines 16-35, FIG. 8) Ames Laboratory News Release, December 7, 2001 (page 2, line 12)

However, when applied to an actual refrigeration system, a magnetic material exhibiting a magnetocaloric effect needs to have a magnetic particle in a bulk shape such as a flat plate shape called an AMR bed, an arc shape, a cylindrical shape, and a cylindrical shape. In the La (Fe, Si) _{13 Hz} material, a method for producing a porous bulk material advantageous for heat exchange used in an actual refrigeration system has not yet been sufficiently studied. In particular, when producing a sintered body, it was found that if the present material in which hydrogen atoms entered between crystal lattices was heated and sintered at a high temperature, hydrogen was desorbed and the Curie temperature was lowered. In addition, it is understood that it is not possible to achieve a bulk body having a porosity of 20 to 35% necessary for enhancing heat exchange by simply sintering La (Fe, Si) ₁₃ H _z magnetic particles. It was. Therefore, the present invention provides a manufacturing method for making a magnetic body using La (Fe, Si) _{13 Hz} magnetic particles into a bulk body having a predetermined porosity so that it can be applied to an actual refrigeration system. .

The present inventors diligently studied a manufacturing method for providing a porous body of La (Fe, Si) ₁₃ Hz material, which is promising as a material that exhibits a magnetocaloric effect at room temperature, by a method that is industrially inexpensive and capable of mass production. did. When bulking this system powder material, it is necessary to sinter the hydrogen-absorbed La (Fe, Si) ₁₃ Hz powder alone, but a sintering temperature of 1000 ° C. or higher is required, but the temperature is 1000 ° C. In the above, hydrogen is desorbed by heating, and the magnetocaloric effect at room temperature is reduced. Therefore, a method for forming a bulk body having appropriate voids by using a binder at a lower temperature was found.
In other words, the present invention has the following composition formula: La _A Si _B H _C Fe _bal (atomic%, 6.4 ≦ A ≦ 7.8%, 9 ≦ B ≦ 10.2%, 6 ≦ C ≦ 9%, balance Fe And Sn or Sn alloy-based metal film is coated around the magnetic particles represented by (inevitable impurities), and then subjected to heat treatment at 100 ° C. to 300 ° C. in an inert gas atmosphere to bond the magnetic particles to each other. A bulk body having a porosity of 20% to 35% is characterized. As the metal film, Sn-Ag, Sn-Cu, Sn-Bi, or the like can be selected as appropriate. A Sn—Ag—Cu-based alloy is particularly preferable because it is advantageous in terms of adhesion at low temperatures and cost.

These metal coatings are preferably multilayer coatings composed of at least one metal coating composed of an Sn metal coating and an element other than Sn. As an element other than Sn, at least one metal selected from Ag, Cu, and Bi can be used. Since this alloy has a melting point near 220 ° C., low temperature sintering and particle bonding using this alloy are possible.
As will be described later, the La (Fe, Si) ₁₃ Hz magnetic particles used are those pulverized to have an average particle size of 30 to 200 μm. With the current plating technology, it is possible to produce a binary alloy such as Sn—Ag and Sn—Cu by plating, but it is difficult to directly plate a Sn—Ag—Cu ternary alloy having excellent reliability as a solder alloy. . In addition to plating, PVD coating such as ion plating and sputtering can be applied, but the PVD method is not suitable for mass production and leads to increased costs. It is also difficult to control the composition. The spot plating method is advantageous in terms of cost, and the film thickness of each element can be easily controlled by adjusting the plating time. For this reason, the method of plating each element separately, forming a solder alloy in the heating process, and using it for the coupling | bonding of each magnetic material particle is the most preferable. Thus, a method was considered in which a solder alloy having a melting point lower than that of Sn is formed in the sintering process by a heating reaction and used for bonding magnetic particles exhibiting a magnetocaloric effect. This made it possible to produce a porous sintered body excellent in heat exchange without reducing the magnetocaloric effect of this material. Similarly to the above, it is preferable to use three layers of Sn, Ag, and Cu (regardless of the order of the layers) because it is the easiest and excellent in reliability.

As a method for producing magnetic particles used in the present invention, a LaSiFe-based alloy was melted in a vacuum melting furnace, and then the LaSiFe-based alloy was rapidly cooled after heat treatment at 900 ° C. to 1300 ° C. in a vacuum and pressurized to 1013 hPa or more. Heat treatment is performed at 250 ° C. to 350 ° C. in a hydrogen-containing gas, and then the LaSiFe alloy in which the hydrogen is occluded is pulverized in an inert (nitrogen) gas whose oxygen concentration is controlled to 3 to 100 ppm, and then the average particle size is It is preferable to grind so that it may become 30-180 micrometers.
The characteristics required for the AMR bed are that the heat of the refrigeration system is taken into the magnetic body, and the heat is dissipated to the heat exchange fluid, so the AMR bed has excellent heat conduction and heat transfer, or good thermal diffusivity. Things are required. However, if the porosity is excessively porous, the thermal conductivity decreases, so that the AMR bed is required to have an appropriate density, that is, a porosity and a high thermal conductivity. For this reason, it can be said that the particle size of the magnetic particles utilizing the magnetocaloric effect is an important factor that affects the density and thermal conductivity of the sintered body. For this reason, a porous sintered body (magnetic material) with a porosity of 20% to 35% is obtained by adjusting the magnetic particle powder to an average particle size of 30 μm to 200 μm and producing a sintered body. When the porosity exceeds 35%, the volume ratio of the magnetic particles in the magnetic particle unit becomes small, and the refrigeration performance decreases. If it is less than 20%, the cooling medium hardly moves in the magnetic material, and the refrigeration performance is also lowered.
When the La-Si-Fe-based alloy is heated in vacuum and homogenized, α-Fe remains without being diffused below 900 ° C. If the temperature exceeds 1300 ° C., the alloy will be in a molten state, and it will be easily oxidized and the properties of the magnetic particles will deteriorate. Moreover, when this La-Si-Fe-type alloy is crushed as needed, it is preferable to make it an average particle diameter of about 10 mm-50 mm. Easy to set in a hydrogen storage container and easy to handle. Thereafter, heat treatment is performed at 250 to 350 ° C. in a hydrogen-containing gas. When the heat treatment temperature in the hydrogen-containing gas is less than 250 ° C., hydrogen is not occluded in a necessary amount. When it exceeds 350 ° C., La hydride is formed and the NaZn ₁₃ type crystal structure is broken. Here, the hydrogen-containing gas may be hydrogen + Ar, ammonia, hydrogen + ammonia, etc., in addition to hydrogen alone gas. And after hydrogen storage treatment, it is made into powder of magnetic particles.
In addition, control of the oxygen concentration in the pulverization process of this material is important. If excessive oxygen and nitrogen are contained in the material, a ferromagnetic material that adversely affects itinerant electron metamagnetism is formed in the material. Therefore, it is important to control the oxygen concentration in the pulverizer at the final stage to an appropriate value. For this reason, it is preferable to control the oxygen concentration in a grinder to 100 ppm or less. On the other hand, if the oxygen concentration in the pulverizer is less than 3 ppm, the magnetic particles tend to react with nitrogen in the atmosphere, and the nitrogen content may exceed 9000 ppm. Therefore, it is preferable that the lower limit of the oxygen concentration in the pulverizer is 3 ppm or more.

In the magnetic material of the present invention, the composition of each element has an important influence on the performance of magnetic refrigeration. First, La is an essential element for forming the NaZn ₁₃ type structure which is the crystal structure of this compound. If the amount of La is less than A = 6.4 at%, α-Fe is excessively formed in the molten alloy, and even if homogenization is performed, it is impossible to eliminate α-Fe. On the other hand, if A exceeds 7.8 at%, a Th ₂ Zn ₁₇ type crystal structure is formed and the magnetization curve is changed, which is not preferable as a magnetocaloric effect material. On the other hand, Si is an element essential for forming a NaZn ₁₃ type structure. When the amount of Si is less than B = 9.0 at%, it becomes difficult to sufficiently form a NaZn ₁₃ type crystal structure. On the other hand, if it exceeds B = 10.2 at%, it becomes difficult to form a NaZn ₁₃ type crystal structure, and Fe ₂ Si unnecessary for the magnetocaloric effect is formed. Al is an element that can replace Si, but it is desirable that impurities such as Al be small, but it is allowed as long as the magnetic refrigeration performance is not deteriorated. Furthermore, the hydrogen content C is an essential element for improving the Curie temperature. When the hydrogen content C is less than 6 at%, the Curie temperature is lower than room temperature, and when it exceeds 9 at%, the crystal lattice expands excessively, and NaZn ₁₃ type. This results in breaking the crystal structure.

The performance of this material as a magnetocaloric effect material depends on the amount of La (Fe, Si) ₁₃ Hz compound formed by La, Fe, Si, and H. The nitrogen amount is desirably 5,000 ppm or less (excluding 0 ppm or less) and 50 ppm to 9,000 ppm, respectively. Ideally, it is preferable that there is no oxygen content, but a powder with a low oxygen content has high reactivity, and it is necessary to pay attention to ignition in handling, which makes handling difficult. The nitrogen content is also an unnecessary impurity like oxygen, but it is difficult to completely eliminate it. When the nitrogen content is less than 50 ppm, the reactivity is high and handling is difficult. If the nitrogen content exceeds 9000 ppm, excess α-Fe is formed as a reaction product, which is not preferable.

In this material, hydrogen (H) enters the La (Fe, Si) ₁₃ crystal lattice in an interstitial manner, thereby expanding the crystal lattice and increasing the Curie temperature. Since this La (Fe, Si) ₁₃ Hz material contains metals such as La and Fe that are easily oxidized, when the oxygen content and the nitrogen content increase, α-Fe and iron oxide are formed as reaction products. Since these are ferromagnets, the properties of La (Fe, Si) ₁₃ Hz, a magnetocaloric effect material, which is a metamagnet with the property of transition from paramagnetism to ferromagnetism just above the Curie temperature, will be reduced. . That is, when the amount of oxygen in the grinding atmosphere increases, La oxide is formed, while Fe becomes α-Fe or iron oxide. On the other hand, when the amount of nitrogen in the grinding atmosphere increases, La nitride is formed, while Fe becomes α-Fe. alpha-Fe because of a ferromagnetic material, a meta-magnetic La (Fe, Si) reduces the magnetocaloric effect of ₁₃ H _z, that is, it reduces the magnetic entropy change. It is preferable to reduce α-Fe and iron oxide as much as possible.

As described above, by laminating magnetic particles having a composition of La (Fe, Si) ₁₃ Hz to a predetermined particle size and applying a film of Sn or Sn alloy, and molding and sintering, the magnetic properties are excellent. A porous sintered body having a porosity of 20% to 35% is obtained.
In addition, by controlling the oxygen content and nitrogen content of the La (Fe, Si) ₁₃ Hz-based material, the generation of α-Fe and iron oxide unnecessary for the magnetocaloric effect is suppressed, and a corrosion-resistant coating by plating is provided. By forming a porous sintered body that is advantageous for heat exchange, it is possible to provide a magnetic material that exhibits a magnetocaloric effect at room temperature and has excellent characteristics.

EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited by these Examples.
Example 1
Taking into account the weight loss during dissolution of La metal having a purity of 99.9% or more, electrolytic iron and ferrosilicon so that the final composition after dissolution is La _7.14 Si _10.22 Fe _82.64 (at%), the total weight is 10 kg. The sample was weighed and dissolved in a vacuum melting furnace. For melting, set the Fe and Si raw materials in an alumina crucible, melt the Fe and Si raw materials by high-frequency heating in vacuum, then stop the high frequency, introduce argon gas into the melting furnace, and then apply the high frequency again Then, after putting La metal into the molten metal, the molten metal temperature was maintained at 1500 ° C. and cast into a water-cooled iron mold. The obtained alloy lump was heat-treated in a vacuum of 0.001 Pa under conditions of 1150 ° C. × 10 h and rapidly cooled. Next, the alloy was crushed to 10 mm square or less by a jaw crusher, and the alloy lump which became the NaZn ₁₃ type crystal single phase was heated and maintained in high-pressure hydrogen gas at a pressure of 2030 hPa at 300 ° C. for 6 hours to remove hydrogen atoms between crystal lattices. Invaded. Next, the powder was pulverized to a particle size of 500 μm or less with a jaw crusher and a brown mill, and further a powder with an average particle size of 50 μm was obtained with a bantam mill in a nitrogen atmosphere in which the atmospheric oxygen content was controlled to 5 ppm. Thereafter, fine particles having a particle size of 10 μm or less were removed using a classifier to obtain a powder having a uniform particle size distribution (average particle size 82.8 μm). A Hosokawa micron micron separator was used as the classifier. When the amount of each element of the obtained powder was analyzed, the final composition was La _6.67 Si _9.53 Fe _77.13 H _6.67 (at%). A Rigaku X-ray fluorescence analyzer was used for the analysis of La, Fe, and Si, and a LECO gas analyzer was used for the analysis of the amount of hydrogen. Moreover, when the oxygen content and nitrogen content of this pulverized powder were analyzed, they were 80 ppm and 4500 ppm, respectively. Next, three-layer plating of Sn—Ag—Cu was performed on the powder particles. First, the pulverized powder is pretreated in 0.5% nitric acid in ethyl alcohol to remove the oxide scale, and after washing with water, the particle surface is activated using an activation treatment solution manufactured by Uemura Kogyo. Then, a Cu film having a film thickness of 2 μm was formed by the electroless copper plating solution sulcup ELC-SP manufactured by Uemura Kogyo. Next, silver plating was performed continuously after washing with water. An electroless silver plating solution manufactured by Uemura Kogyo Co., Ltd. was used as the plating solution to obtain a silver plating film having a thickness of 15 μm. Subsequently, it was continuously washed with water, subjected to electrolytic tin plating, washed with water and dried. A matte electrolytic tin plating solution manufactured by Uemura Kogyo was used as the plating solution. Thereby, an Sn plating film having a tin film thickness of 10 μm was obtained. 3% of EVA (ethyl vinyl alcohol) was added to the La-Fe-Si-H-based particles on which the Sn-Ag-Cu trilayer film thus obtained was formed, and kneaded. This is molded into a flat plate of 40 x 50 x 5 mm and a cylindrical shape of outer diameter 60 mm x inner diameter 50 x length 30 mm at a molding pressure of 3 t / cm ² with a hydraulic molding machine, and heated in a hydrogen stream at 180 ° C x 5 h. Then, after performing the binder removal treatment, it was further heated to 240 ° C. in Ar gas and soldered. The density of the flat plate was 5.3 Mg / m ³ when measured by weight instead of underwater substitution method and then divided by volume. Moreover, it was 250 W / mK when the thermal conductivity in 24 degreeC was measured using the Kyoto electronic industry laser flash method thermophysical property measuring apparatus.

(Comparative Example 1)
In consideration of the weight loss during dissolution of La metal having a purity of 99.9% or more, electrolytic iron and ferrosilicon so that the final composition after dissolution is La _7.17 Si _11.14 Fe _81.69 (at%), the total weight is 10 kg. The sample was weighed and dissolved in a vacuum melting furnace. For melting, set the Fe and Si raw materials in an alumina crucible, melt the Fe and Si raw materials by high-frequency heating in vacuum, then stop the high frequency, introduce argon gas into the melting furnace, and then apply the high frequency again Then, after putting La metal into the molten metal, the molten metal temperature was maintained at 1500 ° C. and cast into a water-cooled iron mold. The obtained molten alloy was heat-treated in a vacuum of 0.001 Pa under conditions of 1150 ° C. × 10 h and rapidly cooled. Next, the alloy was crushed to a size of 15 mm square or less by a jaw crusher, and the alloy lump which became a NaZn ₁₃ type crystal single phase was heated and held in high-pressure hydrogen gas at a pressure of 2030 hPa at 300 ° C. for 6 hours to allow hydrogen atoms to be interstitial. Invaded. Next, the powder was pulverized to a particle size of 500 μm or less with a jaw crusher and a brown mill, and further a powder with an average particle size of 50 μm was obtained with a bantam mill in a nitrogen atmosphere in which the atmospheric oxygen content was controlled to 5 ppm. Thereafter, fine particles having a particle size of 10 μm or less were removed using a classifier to obtain a powder having a uniform particle size distribution. A Hosokawa micron micron separator was used as the classifier. When the composition of the obtained magnetic particles was analyzed, it was La _6.62 Si _10.33 Fe _75.76 H _7.29 (at%). For the analysis, a fluorescent X-ray analyzer manufactured by Rigaku and a gas analyzer manufactured by LECO were used. The magnetic particles were made into a sintered body regardless of solder bonding. First, a 40 × 50 × 5 mm flat plate was formed with a forming pressure of 3 t / cm ² using a hydraulic molding machine, and sintered under a condition of 1,170 ° C. × 3 h in a vacuum of 0.001 Pa. When this sintered body was crushed and the composition was analyzed again, it was La _7.17 Si _11.14 Fe _75.76 H _0.01 (at%). Thus, when this magnetic powder in which hydrogen was occluded was heated at a high temperature, hydrogen atoms were almost eliminated. Further, the Curie temperature of the sintered body was measured using a SQUID magnetometer manufactured by Quantum Design. The change in temperature of the AC susceptibility was measured in the range of 0 to 350 K, and the inflection point of the AC susceptibility was taken as the Curie temperature. It was found that Tc = 189K, and clearly that the magnetocaloric effect cannot be exhibited at room temperature at this Curie temperature.

(Example 2, comparative example 2)
10 kg of an alloy having the same composition as in Example 1 was melted in a vacuum melting furnace, and homogenization was performed under the same production conditions as in Example 1. The obtained alloy lump was crushed to 10 mm square or less with a jaw crusher, and then heated and maintained at 290 ° C. for 8 h in high-pressure hydrogen at a pressure of 2026 hPa, and cooled. As a result, La _6.67 Si _9.53 Fe _77.13 H _6.67 (at%) was obtained as the final composition. Next, the alloy lump is pulverized to a particle size of 500 μm or less by a jaw crusher and a brown mill, and further pulverized by a bantam mill in which the amount of oxygen in the pulverizer is controlled to various values so that the average particle size becomes almost the same. It grind | pulverized according to grinding | pulverization conditions. As a result, various powders having different amounts of oxygen and nitrogen were obtained. For these powders, first, the Curie temperature was measured. For the measurement, the temperature change of the AC susceptibility was measured with a SQUID magnetometer (MQMS5S) manufactured by Quantum Design, and the Curie temperature was obtained. Next, the magnetization curve when the applied magnetic field is −5 to 5 T just above the Curie temperature (1 to 5 ° C.) is also measured using the SQUID magnetometer (MQMS5S) manufactured by Quantum Design, and the equation shown in Equation 1 is obtained. Was used to calculate the magnetic entropy difference. The results are shown in Table 1. As is clear from Table 1, the oxygen content in the material can be reduced by reducing the oxygen content in the grinder, but conversely, the nitrogen content increases, and as a result, α-Fe increases and magnetic entropy increases. As a result, the difference is reduced. In Table 1, Examples 2-1 to 2-3 are within the scope of the claims, and the magnetic entropy difference exceeds -20 J / kgK. Comparative Example 2-1 was the result of an experiment conducted with the oxygen concentration in the pulverizer as low as possible. However, since the oxygen content was small, the magnetic particles easily occluded nitrogen, and the magnetic entropy difference was low. In Comparative Examples 2-2 and 2-3, the experiment was conducted with the oxygen concentration in the crusher as high as possible, but it was found that useful magnetic properties were not obtained. From this, it is necessary to control not only the oxygen content in the material but also the nitrogen content to an appropriate value, and it can be said that control of the atmospheric oxygen content during pulverization is important.

(Example 2)
_Weigh metal La, electrolytic iron, and metal Si with a purity of 99.9% or more so that the total composition is 10 kg so that the composition after dissolution is La _7.14 S _11.14 Fe _81.71 (at%). It melt | dissolved, the homogenization process was performed on the same manufacturing conditions as Example 1, it pulverized to 20 mm or less, and the hydrogen storage process was performed. The hydrogen storage treatment was performed by heating and maintaining at 290 ° C. for 8 hours in high-pressure hydrogen at a pressure of 3039 hPa to allow hydrogen atoms to enter between crystal lattices. Subsequently, it was pulverized by a jaw crusher and a brown mill to a particle size of 500 μm or less, and further pulverized by a bantam mill in nitrogen gas in which the atmospheric oxygen amount was controlled to 5 ppm to obtain magnetic particles having an average particle size of 48 μm. A surface coating of Sn—Ag—Cu ternary alloy was formed on the magnetic particles by ion plating. The composition of the mother alloy before film formation was Sn ₂₂ Ag ₆₇ Cu ₁₁ (Sn-3Ag-0.5Cu), but when the composition of the surface film was analyzed by SEM-EDX, it was Sn ₄₂ Ag ₃₁ Cu ₂₇ and the amount of Cu Is higher than the target value. As a result, the melting point of the solder film also increased, so that the magnetic particles were formed into a predetermined shape and sintered in an Ar atmosphere at 240 ° C. × 3 h to obtain a porous sintered body. Comparing the strength with the magnetic material of Example 1, it was found that the strength of the magnetic material made of Sn—Ag—Cu alloy using the ion plating in Example 2 was low. When a ternary alloy is produced by ion plating, it is presumed that compositional deviation tends to occur and a desired strength may not be obtained. It was found that the manufacturing method of plating each layer as in Example 1 was more stable and a magnetic material having a predetermined strength was obtained.

(Example 3)
_Weigh metal La, electrolytic iron, and metal Si with a purity of 99.9% or more so that the total composition is 10 kg so that the composition after dissolution is La _7.14 S _11.14 Fe _81.71 (at%). Dissolved and homogenized under the same production conditions as in Example 1. The obtained alloy lump was crushed to 20 mm or less with a jaw crusher, then heated and held at 290 ° C. × 8 h in high-pressure hydrogen at a pressure of 3039 hPa, Hydrogen atoms were allowed to penetrate between the crystal lattices. The alloy lump that has been subjected to hydrogen storage treatment is roughly pulverized to a particle size of 500 μm or less with a jaw crusher and a brown mill, and further pulverized with a bantam mill in nitrogen gas in which the amount of atmospheric oxygen is controlled to 5 ppm. Of powder was obtained. These powders are classified according to particle size, under the same conditions as in Example 1, formation of Sn-Ag-Cu tri-layer plating film, formation of 20 × 20 × 2 mm plate, debinding treatment for solder bonding, and soldering Heat treatment was performed. When the thermal conductivity of the obtained magnetic particle unit was measured with a laser thermal flash thermal property measuring apparatus manufactured by Kyoto Electronics Industry, the results shown in Table 2 were obtained. Examining the relationship between the porosity and the pulverized particle size, it was found that a magnetic material having an optimal porosity of 20 to 35% can be obtained by setting it to 30 to 200 μm.

(Example 4)
La _7.14 Si _11.14 Fe _81.71 (at%) La, Fe, Si metal with a purity of 99.9% or more was weighed so as to have a composition after dissolution, and three button ingots with a total weight of 100 g were obtained by arc melting. Produced. In order to prevent oxidation, these were wrapped with Nb foil and SUS foil, and homogenized under a condition of 1150 ° C. × 10 h in a vacuum of 0.0013 Pa using a vacuum heat treatment furnace. Subsequently, the three button ingots were crushed with an iron mortar, and each was sieving with a sieve to a size of 5 mm square, 1 mm square, and 0.5 mm square. Next, each coarse powder was heat-treated in high-pressure hydrogen at a pressure of 2026 hPa at 290 ° C. × 5 h, cooled, pulverized by a disk mill, and crushed powder having a particle size of 100 μm to 150 μm was obtained using a sieve. . When these magnetic entropy differences were measured with a SQUID magnetometer manufactured by Quantum Design at 24 ° C. in the same manner as in the comparative example, and the magnetic entropy difference was calculated, the results shown in Table 3 were obtained.
Obviously, the hydrogen storage mode is affected by the grain size of the alloy lump before hydrogen storage, resulting in a difference in Curie temperature. For this reason, uniform hydrogen occlusion was achieved by reducing the particle size within a range not excessively increasing the oxygen content.

  It is particularly preferred as a magnetic refrigeration material for a highly efficient and environmentally friendly cooling device that replaces conventional refrigerators and air conditioners.

Claims (5)

Composition formula: La _A Si _B H _C Fe _bal (atomic%, 6.4 ≦ A ≦ 7.8%, 9 ≦ B ≦ 10.2%, 6 ≦ C ≦ 9%, balance Fe and inevitable impurities) A magnetic coating of Sn or Sn alloy is coated around the magnetic particles represented, and then heat treatment is performed at 100 ° C. to 300 ° C. in an inert gas atmosphere to bond the magnetic particles to each other, and the porosity is 20% to A method for producing a magnetic material, wherein the bulk material is 35%. 2. The method for producing a magnetic material according to claim 1, wherein the metal film has a multilayer film composed of an Sn metal film and at least one metal film composed of an element other than Sn. The method for producing a magnetic material according to claim 1, wherein the element other than Sn is at least one metal selected from Ag, Cu, and Bi. The magnetic particles melt LaSiFe alloy in a vacuum melting furnace, and then heat-treat the LaSiFe alloy at 900 ° C. to 1300 ° C. in a vacuum and then rapidly cool it to 250 ° C. in a hydrogen-containing gas pressurized to 1013 hPa or more. Heat treatment at ˜350 ° C., then pulverize the LaSiFe alloy in which the hydrogen is occluded in an inert gas whose oxygen concentration is controlled to 3 to 100 ppm, and then pulverize so that the average particle size becomes 30 to 200 μm. The method for producing a magnetic material according to claim 1, wherein the magnetic material is produced. 5. The method for producing a magnetic material according to claim 1, wherein the magnetic particles have an oxygen content of 5000 ppm or less (excluding 0 ppm) and a nitrogen content of 50 ppm to 9000 ppm.