Magnetocaloric material, and method for producing magnetocaloric material

Abstract

This magnetocaloric material includes a coating powder and a resin. The coating powder is obtained by coating, with a coating film, a material powder of a La(Fe, Si)H-based compound in which hydrogen is adsorbed onto a La(Fe, Si)13-based compound. The coating film has a higher thermal conductivity and a lower hardness than the material powder. The coating films of the coating powders adjacent to each other form a mesh-like structure.

Description

Magnetocaloric material and method for manufacturing the same

[0001] The present disclosure relates to magnetocaloric materials for use in magnetic refrigeration and methods for making magnetocaloric materials.

[0002] Cooling technology is essential in daily life and industry. Currently, vapor compression heat pumps used in air conditioners, refrigerators, and other appliances use alternative fluorocarbons. In recent years, it has been discovered that these alternative fluorocarbons are substances that cause ozone layer depletion and contribute to global warming. In response to this, at the 28th Meeting of the Parties to the Montreal Protocol held in Gikali, Rwanda in 2016, substances such as fluorocarbons that pose a risk of ozone layer depletion were identified, and the Montreal Protocol was amended to globally regulate the production, consumption, and trade of these substances. Against this backdrop, next-generation cooling is needed.

[0003] In recent years, magnetic refrigeration technology, which uses magnetism to freeze or cool, has been attracting attention as a cooling technology with low environmental impact and high cooling efficiency. Magnetic refrigeration technology is used in extremely low temperature ranges where vapor compression refrigeration technology cannot be used or has low cooling efficiency. A specific example is its use in the production of liquid helium. In addition to its use in extremely low temperature ranges, the use of magnetic refrigeration technology in high temperature ranges has also been studied in recent years, and for example, magnetic refrigeration technology is being considered for hydrogen liquefaction or room temperature cooling.

[0004] Magnetic refrigeration technology utilizes the magnetic entropy of magnetic materials to cool them. Its greatest feature is that it uses the non-magnetic lattice component, which would normally be a heat load, to store cold air, while containing a spin system, which is a magnetic component, and a lattice system, which is a non-magnetic component, and can control entropy with a magnetic field.

[0005] When a magnetic material is adiabatically excited, magnetic entropy is converted into lattice entropy. The converted lattice entropy is converted into heat, raising the temperature of the magnetic material. By removing this heat and performing adiabatic demagnetization, the temperature of the magnetic material decreases. Magnetic cooling technology cools the material by repeating this series of Brayton cycles.

[0006] The major advantage of magnetic refrigeration technology is that it uses micro-Brayton coupling, which continuously arranges Brayton cycles in accordance with the temperature gradient between the low and high temperature ends in the basic S (entropy)-T (temperature) cycle. This method realizes a cycle that is closer to a thermodynamically ideal system than conventional vapor compression methods, and is therefore expected to achieve highly efficient heat exchange.

[0007] The phenomenon in which the temperature of a magnetic material increases when a magnetic field is applied to it is known as the magnetocaloric effect, and known magnetocaloric materials with a large magnetocaloric effect include Gd-Si-Ge, Ni-Mn-Ga, and La(Fe,Si)-based compounds. Common characteristics of these compounds include a larger change in magnetic entropy than that of Gd, a traditional room-temperature magnetic refrigeration material, and the occurrence of a first-order phase transition due to a transition in crystalline structure, rather than just a typical second-order magnetic phase transition. This results in a large magnetocaloric effect due not only to the magnetic specific heat but also to the latent heat.

[0008] The most promising materials for magnetic cooling in the high-temperature region of approximately 200 K are La(Fe,Si)-based compounds with a NaZn13-type crystal structure, which are known to exhibit a magnetocaloric effect at room temperature. In such materials, Fe is substituted for the Zn site of the NaZn13-type crystal structure phase, and elements such as La are substituted for the Na site.

[0009] The phase transition properties of La(Fe,Si)-based compounds having an NaZn13-type crystal structure can be changed by substituting elements at each site or by introducing light elements into the interstitial spaces. For example, substituting rare earth elements such as La at the Na site has been confirmed to strengthen the first-order phase transition properties and increase the magnetocaloric effect, but also increase hysteresis loss. On the other hand, substituting elements at the Zn site, such as Fe with Co, increases the Curie temperature while switching the phase transition properties from a first-order phase transition to a second-order phase transition. It also reduces hysteresis loss. Furthermore, the Curie temperature can be increased by introducing light elements such as H into the interstitial spaces. The introduction of H is essential, especially when using La(Fe,Si)-based compounds at room temperature.

[0010] Furthermore, La(Fe,Si)-based compounds have insufficient pressure resistance due to magnetostriction caused by strong magnetic coupling. In particular, La(Fe,Si)-based compounds containing H spontaneously pulverize due to hydrogen embrittlement. The pulverized magnetocaloric material clogs the flow path of the heat exchange medium in the magnetic refrigeration cycle or flows into areas where a magnetic field is not applied, significantly reducing the efficiency of magnetic refrigeration and the lifespan of the device.

[0011] Therefore, some molding method is necessary. It has been confirmed that hydrogen in La(Fe,Si)H-based compounds undergoes hydrogen desorption at temperatures above 150°C, changing their magnetic properties. Therefore, molding at temperatures below 150°C is required. While molding using resins is generally proposed, the thermal conductivity of La(Fe,Si)H-based compound compacts depends on the thermal conductivity of the powder itself and the thermal conduction between the powders. Molding using resins with extremely low thermal conductivity significantly reduces the thermal conductivity. Furthermore, improving the thermal conductivity through ultra-high-pressure powder compaction, as used with other materials, is not practical due to the brittleness of La(Fe,Si)H-based compounds.

[0012] In order to solve this significant decrease in thermal conductivity, Patent Document 1 discloses a method for increasing the thermal conductivity by adding metal powder, fluorinated polymer, or the like.

[0013] Japanese Patent Application Laid-Open No. 2018-107203

[0014] However, the above-mentioned method requires the addition of a large amount of metal powder or fluorinated polymer to achieve the desired thermal conductivity, which significantly reduces the volume fraction of the magnetic material in the compact, thereby reducing the cooling efficiency per volume.

[0015] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a magnetocaloric material that contains a La(Fe, Si)H-based compound and has improved thermal conductivity while maintaining or improving cooling efficiency per volume, and a method for manufacturing the magnetocaloric material.

[0016] The magnetocaloric material according to the present disclosure includes a coating powder in which a material powder of a La(Fe,Si)H-based compound in which hydrogen is adsorbed to a La(Fe,Si)13-based compound is coated with a film, and a resin, wherein the film has a higher thermal conductivity and a lower hardness than the material powder, and the films of adjacent coating powders form a mesh structure.

[0017] The method for producing a magnetocaloric material according to the present disclosure includes a coating step of coating a material powder of a La(Fe,Si)H-based compound in which hydrogen is adsorbed into a La(Fe,Si)13-based compound with a film having a higher thermal conductivity and a lower hardness than the material powder; a kneading step of kneading the coated powder obtained by coating the material powder with the film with a resin; a forming step of applying pressure to the kneaded coated powder and the resin to form a structure; a structure forming step of forming a network structure by the film using the pressure; and a forming and solidifying step of forming the kneaded coated powder and the resin at 150°C or less and solidifying them.

[0018] The magnetocaloric material and method of manufacturing the magnetocaloric material according to the present disclosure provide a high thermal conductivity due to the mesh structure obtained from the low hardness coating, while the high density La(Fe,Si)H based compound in the magnetocaloric material 1 maintains or improves the cooling efficiency.

[0019] FIG. 1 is a plan view schematically showing a magnetocaloric material according to an embodiment; FIG. 2 is a flowchart showing a method for manufacturing a magnetocaloric material according to an embodiment; FIG. 3 is a diagram including a first table showing evaluation results of the thermal conductivity of the magnetocaloric material according to an example and a magnetocaloric material according to a comparative example; FIG. 4 is a diagram including a third table showing evaluation results of the thermal conductivity of the magnetocaloric material according to an example and a magnetocaloric material according to a comparative example; and FIG. 5 is a diagram including a fourth table showing evaluation results of the thermal conductivity of the magnetocaloric material according to an example and a magnetocaloric material according to a comparative example.

[0020] Hereinafter, a magnetocaloric material 1 according to an embodiment and a method for manufacturing the same will be described in detail with reference to the drawings. Note that the size relationships between the components in the drawings may differ from the actual size relationships.

[0021] 1 is a plan view schematically showing a magnetocaloric material 1 according to an embodiment. The magnetocaloric material 1 is a compact obtained by kneading a coating powder 4 with a resin binder 5. The coating powder 4 is obtained by coating a material powder 2 with a coating 3. The material powder 2 in the embodiment is a powder of a La(Fe, Si)H-based compound. The coating 3 has higher thermal conductivity and lower hardness than the material powder 2.

[0022] The method for producing the material powder 2 of the embodiment is not particularly limited, and the material powder 2 may be produced by an existing method. Examples of methods for producing the material powder 2 include a mold casting method, an arc melting method, a roll quenching method, and an atomization method. The produced material powder 2 may be subjected to a heat treatment for homogenization.

[0023] In the embodiment, the material powder 2 is an La(Fe, Si)H-based compound; however, the material powder 2 is not limited to a composition consisting of the elements La, Fe, Si, and H. For example, the Na site of the NaZn13-type crystal structure phase of the material powder 2 contains at least one element selected from rare earth elements such as Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb. Note that in the embodiment, the material powder 2, such as an La(Fe, Si)H-based compound, has an NaZn13-type crystal structure, and the NaZn13-type crystal structure phase refers to a phase having an NaZn13-type crystal structure. Furthermore, the Zn site of the NaZn13-type crystal structure phase of the material powder 2 contains at least one element selected from Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Si, Ga, Ge, In, and Sn. Furthermore, the material powder 2 may contain elements such as B, C, N, O, or F instead of or together with H. Furthermore, the material powder 2 does not need to be a single compound phase of NaZn13-type crystal, and other phases such as an α-Fe phase may be mixed in. Below, La(Fe, Si)H-based compounds are described as materials in which element substitution is possible as described above. The particle size of the material powder 2 of the magnetocaloric material 1 is preferably 1 μm or more and 1000 μm or less, based on the viewpoints of deterioration of magnetic properties due to oxidation and uniformity of the magnetocaloric material 1.

[0024] The coating 3 has higher thermal conductivity and lower hardness than La(Fe, Si)H-based compounds. While the constituent material of the coating 3 is not particularly limited, from the viewpoints of thermal conductivity and hardness, Cu or an alloy containing Cu is particularly desirable. Note that, as long as the material has higher thermal conductivity and lower hardness than the material powder 2, an alloy containing one or more of Zn, Si, Al, Mo, Cu, Ag, Au, Fe, Co, and Ni may be used. By making the coating 3 higher thermal conductivity and lower hardness than La(Fe, Si)H-based compounds, the thermal conductivity of the magnetocaloric material 1 can be increased. The thickness of the coating 3 is preferably 0.5% to 13% of the particle size of the material powder 2 or the coating powder 4, based on the continuity of the coating 3 or the volume of the magnetocaloric material 1.

[0025] The resin binder 5 aggregates and holds the coating powder 4. Epoxy resin is preferable as the resin binder 5, but a thermosetting resin other than epoxy resin may also be used. The resin binder 5 may also be a thermoplastic resin. In the embodiment, at least one of epoxy resin, melamine resin, phenolic resin, fluororesin, polyethylene resin, and polypropylene resin is used as the resin binder 5. The magnetocaloric material 1 is formed by kneading the resin binder 5 and the coating powder 4.

[0026] When molding the material obtained by kneading the resin binder 5 and the coating powder 4, pressure is applied to the mold to extrude the resin component to the outside of the mold, causing adjacent particles of coating powder 4 to come into contact with each other, and a mesh-like heat conduction path is formed by the coating 3.

[0027] When obtaining the magnetocaloric material 1, powder having an average particle size of 1 / 3 or less of the average particle size of the coating powder 4 and made of a material having a thermal conductivity higher than that of the La(Fe, Si)H-based compound may be introduced into the gaps between the coating powders 4. This can further improve the thermal conductivity of the magnetocaloric material 1. Hereinafter, such powder may also be referred to as auxiliary powder. The composition of the auxiliary powder is not particularly limited, but it is desirable that the thermal conductivity be 10 W / mK or higher.

[0028] Here, when the volume of the coating 3 of the coating powder 4 is smaller than the volume of the material powder 2, the following formula (1) holds: {(4 / 3)πR ３ -(4 / 3)πr ３} < (4 / 3) πr ３ ... (1) The left side of formula (1) is the volume of the coating 3, and the right side is the volume of the material powder 2. In formula (1), r is the average radius of the material powder 2, and R is the average radius of the coating powder 4. Furthermore, assuming that the center of the coating powder 4 and the center of the material powder 2 contained in the coating powder 4 coincide with each other, if the area of ​​the coating 3 in the cross section including the center of the coating powder 4 is smaller than the area of ​​the cross section of the material powder 2, the following formula (2) holds. (πR ２ -πr ２ ) <πr ２...(2) When the formulas (1) and (2) are satisfied, the following formula (3) is satisfied: R ３ <2r ３ ...(3) In the magnetocaloric material 1 according to the embodiment, R ３ <2r ３ holds. This improves the volume ratio of the La(Fe, Si)H-based compound in the magnetocaloric material 1. The average radius r of the material powder 2 and the average radius R of the coating powder 4 are obtained by measuring the volume or cross-sectional area of ​​the material portion, which is the La(Fe, Si)H-based compound portion in the magnetocaloric material 1, and the volume or cross-sectional area of ​​the coating portion, which is the coating powder 4 portion in the magnetocaloric material 1, in the manufacturing process of the magnetocaloric material 1. The respective volumes or cross-sectional areas of the material portion and the coating portion can be obtained based on the pixel count ratio of an optical microscope image or an electron microscope image, etc.

[0029] In this embodiment, the thermal conductivity of the coating 3 is 10 W / m·K or higher. If the thermal conductivity of the coating 3 is less than 10 W / m·K, the thermal conductivity of the La(Fe, Si)H-based compound decreases because the thermal conductivity of the coating 3 is lower than that of the La(Fe, Si)H-based compound. In this embodiment, the hardness of the coating 3 is 800 HV or lower, i.e., the hardness of the material powder 2 or lower. When the hardness of the coating 3 is 800 HV or lower, the coating 3 deforms preferentially over the La(Fe, Si)H-based compound, and a mesh-like structure is easily formed. This allows fine heat conduction paths to be formed, and high thermal conductivity can be achieved even when the ratio of the material powder 2 in the magnetocaloric material 1 is increased.

[0030] 2 is a flowchart showing a method for manufacturing the magnetocaloric material 1 according to the embodiment. The method for manufacturing the magnetocaloric material 1 includes a coating step S1 of coating the material powder 2 with the coating 3, a kneading step S2 of kneading the coated powder 4 obtained by coating with a resin binder 5, a molding step S3 of molding the kneaded coated powder 4 and resin binder 5 by applying pressure, a structure forming step S4 of forming a network structure by the coating 3 using pressure, and a molding and solidification step S5 of molding the kneaded coated powder 4 and resin binder 5 at a temperature of 150° C. or less and solidifying them.

[0031] The material powder 2 in the coating step S1 is not limited as long as it is a La(Fe,Si)H-based compound in which hydrogen has been introduced into a La(Fe,Si)-based compound having a NaZn13-type crystal structure. Electroless plating is desirable as a coating method for the coating 3 in the coating step S1 from the viewpoints of uniformity of the coating 3 and film formation cost, but techniques such as sputtering or vapor deposition may also be used.

[0032] The kneading method in the kneading step S2 is not particularly limited as long as it sufficiently mixes the coated powder 4 and the resin binder 5. The treatment in the kneading step S2 is performed so that the temperature of the coated powder 4 and the like is 150° C. or less. This is because at temperatures higher than 150° C., the hydrogen introduced into the La(Fe, Si)-based compound is released.

[0033] The clearance of the molding die used in the molding step S3 is desirably smaller than the particle size of the coating powder 4. In the molding step S3, the magnetocaloric material 1 may be near-net molded into a shape required by the magnetic cooling system. In addition, in the molding step S3, in order to reduce loss during the cooling cycle of the La(Fe, Si)H-based compound in the magnetocaloric material 1, molding may be performed while applying a magnetic field to control the orientation. Furthermore, in order to increase the density of the coating powder 4 and the material powder 2, molding may be performed while applying vibration.

[0034] The structure generating step S4 is performed in parallel with the molding step S3. In the molding step S3, molding is performed while the resin binder 5 is being pushed out of the mold, thereby increasing the density of the coated powder 4. As the density of the coated powder 4 increases, the coated powder particles 4 come into contact with each other, and a network structure made of a high thermal conductivity material is formed by the coating 3 applied to the material powder 2. The pressure used to generate the network structure is preferably 10 MPa or more and 100 MPa or less.

[0035] In the molding and solidification step S5, in order to achieve both solidification of the resin binder 5 and improvement of the fluidity of the resin binder 5, it is desirable to solidify the resin binder 5 at as high a temperature as possible within the range of 70°C to 150°C at which hydrogen is not desorbed.

[0036] The magnetocaloric material 1 according to the embodiment and the manufacturing method thereof will be described in more detail below with reference to examples and comparative examples. The magnetocaloric material 1 according to each of the examples and comparative examples will be evaluated based on the following items.

[0037] The first item is cross-sectional structure observation. Here, cross-sectional structure observation was performed using an electron microscope. The field of view was 300x magnification, which allows sufficient observation of the structure, and the measurement area was 300 μm x 300 μm. Then, the mesh-like structure of the coating 3 applied to the material powder 2 was confirmed. In addition, the distribution of elements in the coating 3 was measured using EDS (Energy-dispersive X-ray spectroscopy). Note that the mesh-like structure refers to a structure in which the images of the coating 3 of adjacent coated powders 4 are continuous at each magnification.

[0038] The second item is powder density evaluation. The powder density evaluation was performed based on the brightness of the cross section of the magnetocaloric material 1 in a 300x field of view of the electron microscope. More specifically, the powder density evaluation was performed based on the ratio of the number of pixels in a 300 μm×300 μm area in a 300x field of view of the electron microscope to the number of pixels in the portion of the material powder 2 of the magnetocaloric material 1 in that measurement area.

[0039] The third item is the thermal conductivity evaluation. The thermal conductivity evaluation was carried out using the laser flash method on a 10 mm x 10 mm x 1.5 mm ｔ Measurements were carried out using samples processed as follows. Before the measurements, the surfaces of the samples were finished with waterproof sandpaper of No. 2000, and then subjected to a surface blackening treatment using carbon spray. Measurements were taken at three points per sample, and the average value was used for evaluation.

[0040] [Example 1] In Example 1, the material powder 2 of the La(Fe, Si)H-based compound is La(Fe 0.88 Si 0.12 ) 13 H 1.25 The composition was adjusted by the following method. This composition is publicly known. First, La(Fe 0.88 Si 0.12 ) 13 The alloy was prepared by arc melting in an Ar atmosphere so as to have the composition.0.88 Si 0.12 ) 13 is an example of a La(Fe,Si)13 alloy. After the alloy was prepared, the test piece was subjected to homogenization treatment in a quartz tube at 1323K for 10 days. After that, the test piece was heated and held in high-pressure hydrogen gas to introduce hydrogen. 0.88 Si 0.12 ) 13 H 1.25 The La(Fe 0.88 Si 0.12 ) 13 H 1.25 is an example of a La(Fe,Si)H-based compound. 0.88 Si 0.12 ) 13 H 1.25 After the preparation of the La(Fe 0.88 Si 0.12 ) 13 H 1.25 was pulverized in a mortar, and passed through a 120 mesh sieve to collect powder having an average particle size of 100 μm, which was then classified to obtain material powder 2 having an average particle size of 100 μm.

[0041] The obtained La(Fe 0.88 Si 0.12 ) 13 H 1.25 A coating 3 with high thermal conductivity and low hardness was applied to the material powder 2. In Example 1, Cu was coated as the coating 3 by electroless plating. For the coating, water was used as the solvent, and Cu, a reducing agent, and a chelating agent were used as the solutes. The Cu concentration in the solution was adjusted to 5.0 g / L and the pH of the solution was adjusted to 13.0. While maintaining the solution at 50°C, 10 g of material powder 2 was added and plating was performed while stirring. The resulting plating film thickness was 1 μm. The resulting coated powder 4 and resin binder 5 were then kneaded and molded into a square mold with an inner diameter of 30 mm x 30 mm. The molding pressure was 50 MPa. The mixture was then heated at 80°C for 5 hours while being molded.

[0042] [Example 2] A material powder 2 of a La(Fe, Si)H-based compound having an average particle size of 100 μm was obtained in the same manner as in Example 1. Then, a Cu coating 3 was formed on the material powder 2 in the same manner as in Example 1. However, in Example 2, the thickness of the coating 3 was set to 10 μm. Thereafter, a magnetocaloric material 1 was produced in the same manner as in Example 1.

[0043] [Example 3] A material powder 2 of a La(Fe, Si)H-based compound having an average particle size of 100 μm was obtained in the same manner as in Example 1. Then, a Cu coating 3 was formed on the material powder 2 in the same manner as in Example 1. However, in Example 3, the thickness of the coating 3 was set to 0.5 μm. Thereafter, a magnetocaloric material 1 was produced in the same manner as in Example 1. However, in Example 3, the molding pressure was set to 60 MPa.

[0044] [Example 4] An La(Fe, Si)H-based compound was prepared in the same manner as in Example 1. The La(Fe, Si)H-based compound was then pulverized in a mortar and sieved through a 270-500 mesh sieve to obtain powder with an average particle size of 30 μm. This was then classified to obtain material powder 2 with an average particle size of 30 μm. Then, in the same manner as in Example 1, a Cu coating 3 with a film thickness of 1 μm was applied to the material powder 2. Thereafter, in the same manner as in Example 1, a magnetocaloric material 1 was prepared.

[0045] [Example 5] An La(Fe, Si)H-based compound was prepared in the same manner as in Example 1. The La(Fe, Si)H-based compound was then pulverized in a mortar and sieved through a 20-mesh to 40-mesh sieve to obtain powder with an average particle size of 500 μm. This was then classified to obtain material powder 2 with an average particle size of 500 μm. Then, in the same manner as in Example 1, a Cu coating 3 with a film thickness of 1 μm was applied to the material powder 2. Thereafter, a magnetocaloric material 1 was prepared in the same manner as in Example 1.

[0046] Example 6: A material powder 2 of a La(Fe, Si)H-based compound having an average particle size of 100 μm was obtained using the same method as in Example 1. Then, a Cu coating 3 having a thickness of 1 μm was applied to the material powder 2 using the same method as in Example 1 to obtain a coated powder 4. Furthermore, Cu powder was mixed with the coated powder 4 in an amount of 1 / 5 of the total weight of the coated powder 4 used to prepare the magnetocaloric material 1. The average particle size of the Cu powder was 10 μm, which is less than 1 / 3 of the average particle size of the coated powder 4. The powder obtained by mixing the coated powder 4 and the Cu powder was then kneaded with a resin binder 5 and molded in a square mold with an inner diameter of 30 mm x 30 mm. The molding pressure was 50 MPa. The mixture was then molded while heating at 80°C for 5 hours.

[0047] [Comparative Example 1] A material powder 2 of a La(Fe, Si)H-based compound having an average particle size of 100 μm was obtained in the same manner as in Example 1. Thereafter, without providing a coating 3 on the material powder 2, the material powder 2 and a resin binder 5 were kneaded together, and molding was carried out in the same manner as in Example 1 to produce a magnetocaloric material.

[0048] [Comparative Example 2] A La(Fe, Si)H-based compound was produced in the same manner as in Example 1. The La(Fe, Si)H-based compound was then pulverized in a mortar and sieved through a 20-mesh to 40-mesh sieve to obtain a powder with an average particle size of 500 μm. This was then classified to obtain a material powder 2 with an average particle size of 500 μm. The material powder 2 was then kneaded with a resin binder 5 without being coated with a coating 3, and molded in the same manner as in Example 1 to produce a magnetocaloric material.

[0049] Comparative Example 3 A material powder 2 of a La(Fe, Si)H-based compound having an average particle size of 100 μm was obtained in the same manner as in Example 1. Then, a Cu coating 3 having a film thickness of 1 μm was applied to the material powder 2 in the same manner as in Example 1. Thereafter, the obtained coated powder 4 and a resin binder 5 were kneaded together, placed in a square mold having an inner diameter of 30 mm × 30 mm, and solidified at room temperature without applying pressure to produce a magnetocaloric material having no mesh structure.

[0050] Comparative Example 4 A material powder 2 of a La(Fe, Si)H-based compound having an average particle size of 100 μm was obtained in the same manner as in Example 1. Then, a Cu coating 3 was formed on the material powder 2 in the same manner as in Example 1. However, in Comparative Example 4, the thickness of the coating 3 was set to 10 μm. Thereafter, the obtained coated powder 4 and a resin binder 5 were kneaded together, placed in a square mold with an inner diameter of 30 mm × 30 mm, and solidified at room temperature without applying pressure, to produce a magnetocaloric material without a mesh-like structure.

[0051] Comparative Example 5 A material powder 2 of a La(Fe, Si)H-based compound having an average particle size of 100 μm was obtained in the same manner as in Example 1. Thereafter, without providing a coating 3 on the material powder 2, the material powder 2 and a resin binder 5 were kneaded together, placed in a square mold with an inner diameter of 30 mm×30 mm, and solidified at room temperature without applying pressure to produce a magnetocaloric material having no mesh structure.

[0052] Comparative Example 6: A material powder 2 of a La(Fe,Si)H-based compound having an average particle size of 100 μm was obtained using the same method as in Example 1. Then, a Cu coating 3 with a thickness of 1 μm was applied to the material powder 2 using the same method as in Example 1 to obtain a coated powder 4. Furthermore, Cu powder was mixed with the coated powder 4 in an amount of 1 / 5 of the total weight of the coated powder 4 used to prepare the magnetocaloric material 1. The average particle size of the Cu powder was 100 μm, which is longer than 1 / 3 of the average particle size of the coated powder 4. The powder obtained by mixing the coated powder 4 and the Cu powder was then kneaded with a resin binder 5 and molded in a square mold with an inner diameter of 30 mm x 30 mm. The molding pressure was 50 MPa. The mixture was then molded while heating at 80°C for 5 hours.

[0053] Comparative Example 7: A material powder 2 of a La(Fe, Si)H-based compound having an average particle size of 100 μm was obtained using the same method as in Example 1. Then, a Cu coating 3 with a thickness of 1 μm was applied to the material powder 2 using the same method as in Example 1 to obtain a coated powder 4. Furthermore, Cu powder was mixed with the coated powder 4 in an amount equal to 1 / 5 of the total weight of the coated powder 4 used to prepare the magnetocaloric material 1. The average particle size of the Cu powder was 50 μm, which is longer than 1 / 3 of the average particle size of the coated powder 4. The powder obtained by mixing the coated powder 4 and the Cu powder was then kneaded with a resin binder 5 and molded in a square mold with an inner diameter of 30 mm x 30 mm. The molding pressure was 50 MPa. The mixture was then molded while heating at 80°C for 5 hours.

[0054] Comparative Example 8 A material powder 2 of a La(Fe, Si)H-based compound having an average particle size of 100 μm was obtained in the same manner as in Example 1. Then, a Cu coating 3 was formed on the material powder 2 in the same manner as in Example 1. However, in Comparative Example 8, the thickness of the coating 3 was set to 20 μm. In this case, there was a difference R between the average radius r of the material powder 2 and the average radius R of the coated powder. ３ <2r ３ does not hold. In Examples 1 to 6, R ３ <2r ３ After the formation of the coating 3, the obtained coated powder was kneaded with a resin binder 5, and a magnetocaloric material was produced in the same manner as in Example 1. In Comparative Example 8, R ３ <2r ３ does not hold, the volume ratio of the material powder 2 for obtaining the magnetocaloric effect in the magnetocaloric material is lower than in Examples 1 to 6.

[0055] [Comparative Example 9] A material powder 2 of a La(Fe, Si)H-based compound having an average particle size of 100 μm was obtained in the same manner as in Example 1. Then, a Cu coating 3 was applied to the material powder 2 in the same manner as in Example 1. However, in Comparative Example 8, the thickness of the coating 3 was set to 30 μm. After the coating 3 was formed, the coated powder obtained was kneaded with a resin binder 5, and a magnetocaloric material was produced in the same manner as in Example 1. In Comparative Example 9, as in Comparative Example 8, R ３ <2r ３does not hold, the volume ratio of the material powder 2 for obtaining the magnetocaloric effect in the magnetocaloric material is lower than in Examples 1 to 6.

[0056] [Comparative Example 10] A material powder 2 of a La(Fe, Si)H-based compound having an average particle size of 100 μm was obtained in the same manner as in Example 1. Then, a Cu coating 3 was applied to the material powder 2 in the same manner as in Example 1. However, in Comparative Example 10, the thickness of the coating 3 was set to 50 μm. After the coating 3 was formed, the coated powder obtained was kneaded with a resin binder 5. Then, an attempt was made to manufacture a magnetocaloric material in the same manner as in Example 1. In Comparative Example 10, as in Comparative Example 8, R ３ <2r ３ does not hold, the volume ratio of the material powder 2 for obtaining the magnetocaloric effect in the magnetocaloric material is lower than in Examples 1 to 6.

[0057] Comparative Example 11 A material powder 2 of a La(Fe, Si)H-based compound having an average particle size of 100 μm was obtained in the same manner as in Example 1. Then, a coating of W, i.e., tungsten, was applied to the material powder 2 by sputtering. The coating had a thickness of 0.5 μm. The coated powder obtained by forming a W coating on the material powder 2 was kneaded with a resin binder 5, and a magnetocaloric material was produced in the same manner as in Example 1.

[0058] Comparative Example 12 A material powder 2 of a La(Fe, Si)H-based compound having an average particle size of 100 μm was obtained in the same manner as in Example 1. Then, a compound having the chemical formula Al was added to the material powder 2 by a sputtering method. ２ O ３ The material powder 2 was coated with an aluminum oxide film having a thickness of 0.5 μm. ２ O ３ The coated powder obtained by forming the coating film of the above was kneaded with a resin binder 5, and a magnetocaloric material was produced in the same manner as in Example 1.

[0059] Comparative Example 13 A material powder 2 of a La(Fe, Si)H-based compound having an average particle size of 100 μm was obtained in the same manner as in Example 1. Then, a compound having the chemical formula SiO was added to the material powder 2 by a sputtering method. ２The material powder 2 was coated with a silicon oxide film having a thickness of 0.5 μm. ２ The coated powder obtained by forming the coating film of the above was kneaded with a resin binder 5, and a magnetocaloric material was produced in the same manner as in Example 1.

[0060] The evaluation results of the examples and comparative examples will be described below with reference to FIGS. 3 to 6. FIG. 3 is a diagram including a first table showing the evaluation results of the thermal conductivities of the magnetocaloric material 1 according to the example and the magnetocaloric material according to the comparative example. FIG. 4 is a diagram including a second table showing the evaluation results of the thermal conductivities of the magnetocaloric material 1 according to the example and the magnetocaloric material according to the comparative example. FIG. 5 is a diagram including a third table showing the evaluation results of the thermal conductivities of the magnetocaloric material 1 according to the example and the magnetocaloric material according to the comparative example. FIG. 6 is a diagram including a fourth table showing the evaluation results of the thermal conductivities of the magnetocaloric material 1 according to the example and the magnetocaloric material according to the comparative example.

[0061] FIG. 3 shows the presence or absence of a network structure, powder density, and thermal conductivity for magnetocaloric materials 1 of Examples 1 to 5 and magnetocaloric materials of Comparative Examples 1 to 5. As shown in FIG. 3, a network structure was formed in Examples 1 to 5. On the other hand, a network structure was not formed in Comparative Examples 1 and 2, in which no coating was formed, and in Comparative Examples 3 to 5, in which no pressure was applied. Also, as shown in FIG. 3, in Examples 1 to 5, the density of material powder 2 was 65% or more, and a large amount of material powder 2 for obtaining the magnetocaloric effect was contained in magnetocaloric material 1. On the other hand, in Comparative Examples 3 to 5, the density of material powder 2 was 60% or less. As shown in FIG. 3, magnetocaloric materials 1 obtained in Examples 1 to 5 had thermal conductivities 10 times or more that of the magnetocaloric material of Comparative Example 1. In particular, magnetocaloric material 1 obtained in Example 2 had a thermal conductivity 210 times that of the magnetocaloric material of Comparative Example 1. On the other hand, in Comparative Examples 2 to 5, no magnetocaloric materials were obtained that had thermal conductivity greater than 7.5 times that of the magnetocaloric material of Comparative Example 1. In addition, the thermal conductivity of the magnetocaloric material of Comparative Example 5 was lower than that of the magnetocaloric material of Comparative Example 1.

[0062] FIG. 4 shows the density and thermal conductivity of the material powder 2 in the magnetocaloric material 1 of Example 6 and the magnetocaloric materials of Comparative Examples 6 to 7. As shown in FIG. 4, in Example 6, the density of the material powder 2 was as high as 68%, meaning that the magnetocaloric material 1 contained a large amount of material powder 2 for obtaining the magnetocaloric effect. On the other hand, in Comparative Examples 6 to 7, in which Cu powder with a large particle size was added, the density of the material powder 2 was below 50%. As shown in FIG. 4, in Example 6, a magnetocaloric material 1 was obtained having a thermal conductivity 60 times that of the magnetocaloric material of Comparative Example 1. On the other hand, in Comparative Examples 6 to 7, a magnetocaloric material having a thermal conductivity 72 times or more that of the magnetocaloric material of Comparative Example 1 was obtained because the Cu powder accounted for a large portion of the magnetocaloric material.

[0063] FIG. 5 shows the density of the material powder 2 in the magnetocaloric material 1 of Example 1 and the magnetocaloric materials of Comparative Examples 8 to 10. As shown in FIG. 5 , in Example 1, the density of the material powder 2 was as high as 74%, indicating that the magnetocaloric material 1 contained a large amount of material powder 2 for achieving the magnetocaloric effect. On the other hand, in Comparative Examples 8 to 9, in which a Cu coating thicker than the average radius of the material powder 2 was applied, the density of the material powder 2 was less than 50%. As shown in FIG. 5 , in Example 1, a magnetocaloric material 1 was obtained having a thermal conductivity 45 times that of the magnetocaloric material of Comparative Example 1. Meanwhile, in Comparative Examples 8 to 9, the thick Cu coating with high thermal conductivity resulted in magnetocaloric materials having a thermal conductivity 200 times or more that of the magnetocaloric material of Comparative Example 1. Note that, as shown in FIG. 5 , in Comparative Example 10, molding was not possible due to aggregation of the coating powder, and a magnetocaloric material could not be produced.

[0064] Fig. 6 shows the powder density and thermal conductivity of the material powder 2 in the magnetocaloric material 1 of Example 3 and the magnetocaloric materials of Comparative Examples 11 to 13. As shown in Fig. 6, in Example 3, the density of the material powder 2 was as high as 75%, and the magnetocaloric material 1 contained a large amount of material powder 2 for obtaining the magnetocaloric effect. On the other hand, even in Comparative Examples 11 to 13, in which the material powder 2 was coated with a material having a low thermal conductivity, the density of the material powder 2 was 50% or more. As shown in Fig. 6, in Comparative Examples 11 to 13, the thermal conductivity of the coating covering the material powder 2 was low, and therefore only half or less of the thermal conductivity of Example 3 was obtained.

[0065] The effects of the magnetocaloric material 1 according to the embodiment and the manufacturing method of the magnetocaloric material 1 will be described below. The magnetocaloric material 1 according to the embodiment includes a coating powder 4 and a resin. The coating powder 4 is obtained by coating a material powder 2 of a La(Fe, Si)H-based compound in which hydrogen is adsorbed to a La(Fe, Si)13-based compound with a coating 3. The coating 3 has a higher thermal conductivity and a lower hardness than the material powder 2. The coatings 3 of adjacent coating powders 4 form a network structure.

[0066] According to the above configuration, the coating 3 has a lower hardness than the material powder 2, and therefore deforms preferentially over the material powder 2, easily forming a mesh-like structure. The coating 3 has a higher thermal conductivity than the material powder 2, and therefore the mesh-like structure provides high thermal conductivity. Furthermore, because the heat conduction paths of the mesh-like structure are fine, the magnetocaloric material 1 contains the La(Fe, Si)H-based compound material powder 2 at a high density. This maintains or improves cooling efficiency. Therefore, the magnetocaloric material 1 according to the embodiment can maintain or improve cooling efficiency, i.e., achieve both a high magnetocaloric effect and improved thermal conductivity. Furthermore, the magnetocaloric material 1 contains a resin with high electrical resistance rather than a low-melting-point metal, which suppresses the generation of eddy currents and thereby reduces losses.

[0067] The magnetocaloric material 1 according to the embodiment is such that powder of a high thermal conductivity material having a particle size of one-third or less of the particle size of the coating powder 4 is disposed in the gaps between the coating powders 4. This improves the thermal conductivity while maintaining a high density of the material powder 2. Therefore, the magnetocaloric material 1 according to the embodiment can maintain or improve the cooling efficiency while improving the thermal conductivity at the same time.

[0068] In the embodiment, the average radius r of the material powder 2 and the average radius R of the coating powder 4 are R ３ <2r ３ This allows the density of the material powder 2 for obtaining the magnetocaloric effect to be increased in the magnetocaloric material 1, thereby maintaining or improving the cooling efficiency.

[0069] The coating 3 in this embodiment is an alloy containing at least one element selected from the group consisting of Zn, Si, Al, Mo, Cu, Ag, Au, Fe, Co, and Ni, and has a thermal conductivity of 10 W / mK or more and a hardness of 800 HV or less. Having a hardness of 800 HV or less facilitates the formation of a mesh-like structure using the coating 3, which has high thermal conductivity. Furthermore, this mesh-like structure improves the thermal conductivity.

[0070] The manufacturing method of the magnetocaloric material 1 in this embodiment includes a coating step S1, a kneading step S2, a molding step S3, a structure generation step S4, and a molding and solidification step S5. The coating step S1 is a step of coating a material powder 2 of a La(Fe,Si)H-based compound in which hydrogen is adsorbed to a La(Fe,Si)H-based compound with a coating 3 having a higher thermal conductivity and a lower hardness than the material powder 2. The kneading step S2 is a step of kneading a resin with the resulting coated powder 4 obtained by coating the material powder 2 with the coating 3. The molding step S3 is a step of applying pressure to the kneaded coated powder 4 and resin to form a shape. The structure generation step S4 is a step of forming a network structure by the coating 3 using pressure. The molding and solidification step S5 is a step of molding the kneaded coated powder 4 and resin at 150°C or less and solidifying the material powder 2. This manufacturing method achieves a magnetocaloric effect that achieves both a high magnetocaloric effect and improved thermal conductivity.

[0071] Although the embodiments have been described above, the contents of the present disclosure are not limited to the embodiments and include conceivable equivalents. Furthermore, the configurations described in the embodiments and their modifications can be combined with each other as long as the functions and operations are not impaired.

[0072] 1 magnetocaloric material, 2 material powder, 3 coating, 4 coating powder, 5 resin binder, R, r average radius.

Claims

1. A magnetocaloric material comprising: a coating powder in which a material powder of a La(Fe,Si)H-based compound in which hydrogen is adsorbed on La(Fe,Si)13 is coated with a coating; and a resin, wherein the coating has a higher thermal conductivity and a lower hardness than the material powder, and the coatings of adjacent coating powders form a mesh structure.

2. The magnetocaloric material according to claim 1, wherein a powder of a high thermal conductivity material having a particle size of 1 / 3 or less of the particle size of the coating powder is disposed in the gaps between the coating powder particles.

3. The radius r of the material powder and the radius R of the coating powder are R ３ <2r ３ The magnetocaloric material according to claim 1 or 2, which satisfies the above.

4. The magnetocaloric material according to any one of claims 1 to 3, wherein the coating is an alloy containing at least one element selected from the group consisting of Zn, Si, Al, Mo, Cu, Ag, Au, Fe, Co, and Ni, and has a thermal conductivity of 10 W / mK or more and a hardness of 800 HV or less.

5. A method for producing a magnetocaloric material, comprising: a coating step of coating a material powder of a La(Fe,Si)H-based compound in which hydrogen is adsorbed in La(Fe,Si)13-based with a coating having a higher thermal conductivity and lower hardness than the material powder; a kneading step of kneading the coated powder obtained by coating the material powder with the coating with a resin; a forming step of applying pressure to the kneaded coated powder and resin to form them; a structure forming step of forming a mesh-like structure by the coating using the pressure; and a molding and solidification step of molding the kneaded coated powder and resin at 150°C or less and solidifying them.

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