Magnetocaloric Materials

Abstract

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

Description

[Technical field]

[0001] The present disclosure relates to a magnetocaloric material for use in magnetic cooling. To the fee This is related to. [Background technology]

[0002] Cooling technology is essential in our daily lives and industries. Currently, alternative fluorocarbons are used in vapor compression heat pumps used in air conditioners and refrigerators. In recent years, it has been discovered that these alternative fluorocarbons are substances that cause the destruction of the ozone layer 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 are likely to destroy the ozone layer were identified, and the Montreal Protocol was amended with the aim of regulating the production, consumption, and trade of these substances globally. Against this background, next-generation cooling is needed.

[0003] In recent years, magnetic cooling technology, which is a technology for freezing or cooling by magnetism, has been attracting attention as a cooling technology with a small environmental load and high cooling efficiency. Magnetic cooling technology is used in extremely low temperature ranges where vapor compression cooling technology cannot be used or has low cooling efficiency. As a specific example, it is used to generate liquid helium. In addition to use in extremely low temperature ranges, the use of magnetic cooling technology in high temperature ranges has also been studied in recent years, and for example, magnetic cooling technology is being considered for hydrogen liquefaction or room temperature cooling.

[0004] Magnetic cooling technology utilizes the magnetic entropy of magnetic materials to cool them. Its greatest feature is that it contains a spin system, which is a magnetic component, and a lattice system, which is a non-magnetic component, and uses the non-magnetic lattice system component, which would normally be a thermal load, to store cold air, in a solid system whose entropy can be controlled by a magnetic field.

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

[0006] The major advantage of magnetic cooling 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 the conventional vapor compression method, and is therefore expected to achieve highly efficient heat exchange.

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

[0008] The most promising compound for magnetic cooling in the high temperature range of about 200 K is the La(Fe,Si)-based compound with a NaZn13-type crystal structure, which is 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, which is a phase having the NaZn13-type crystal structure, and elements such as La are substituted for the Na site.

[0009] La(Fe,Si) based compounds with NaZn13 type crystal structure can change the nature of phase transition by substituting elements at each site or by introducing light elements between the lattices. For example, it has been confirmed that by substituting rare earth elements such as La at the Na site, the first-order phase transition property is strengthened and the magnetocaloric effect is increased, but the hysteresis loss also increases. On the other hand, by substituting an element at the Zn site, for example, Fe with Co, the Curie temperature is increased while the nature of the phase transition is switched from a first-order phase transition to a second-order phase transition. In addition, the hysteresis loss can be reduced. In addition, the Curie temperature can be increased by introducing light elements such as H between the lattices. The introduction of H is essential, especially when using La(Fe,Si) based compounds at room temperature.

[0010] In addition, 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 out to areas where the magnetic field is not applied, significantly reducing the efficiency of magnetic refrigeration and the life of the device.

[0011] Therefore, some method of molding is necessary. It has been confirmed that hydrogen in La(Fe,Si)H-based compounds undergoes hydrogen desorption at temperatures higher than 150°C, changing the magnetic properties. Therefore, molding at temperatures below 150°C is required. Molding with resin is generally proposed, but the thermal conductivity of a compact of La(Fe,Si)H-based compounds depends on the thermal conductivity of the powder itself and the thermal conduction between the powders, and molding with resin, which has extremely low thermal conductivity, significantly reduces the thermal conductivity. In addition, improving the thermal conductivity by ultra-high pressure powder molding, as used for other materials, is not realistic due to the brittleness of La(Fe,Si)H-based compounds.

[0012] In order to solve this problem of a large decrease in thermal conductivity, Patent Document 1 discloses a method of increasing the thermal conductivity by adding metal powder, fluorinated polymers, or the like. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] JP 2018-107203 A Summary of the Invention [Problem to be solved by the invention]

[0014] However, the above-mentioned method requires the addition of a large amount of metal powder or fluorinated polymer to obtain 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 problems, and provides a magnetocaloric material that includes a La(Fe,Si)H-based compound and has improved thermal conductivity while maintaining or improving cooling efficiency per volume. Fee The purpose is to provide. [Means for solving the problem]

[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 on La(Fe,Si)13 is coated with a coating, and a resin, the coating having a higher thermal conductivity and a lower hardness than the material powder, the coating of the coating powder adjacent to each other forms a mesh structure, and the resin is included between the mesh structure. 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 placed between the gaps between the coating powders. It is something. Effect of the Invention

[0018] Magnetocaloric materials according to the present disclosure To the fee According to this, the mesh structure obtained from the coating having low hardness provides high thermal conductivity, and the high density La(Fe,Si)H based compound in the magnetocaloric material 1 maintains or improves the cooling efficiency. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a plan view showing a schematic diagram of a magnetocaloric material according to an embodiment; [Diagram 2] 1 is a flowchart showing a method for manufacturing a magnetocaloric material according to an embodiment. [Diagram 3] FIG. 1 includes a first table showing evaluation results of the thermal conductivity of magnetocaloric materials according to examples and magnetocaloric materials according to comparative examples. [Figure 4] FIG. 11 includes a second table showing the evaluation results of the thermal conductivity of the magnetocaloric materials according to the examples and the magnetocaloric materials according to the comparative examples. [Diagram 5] FIG. 13 includes a third table showing the evaluation results of the thermal conductivity of the magnetocaloric materials according to the examples and the magnetocaloric materials according to the comparative examples. [Figure 6] FIG. 4 includes a fourth table showing the evaluation results of the thermal conductivity of the magnetocaloric materials according to the examples and the magnetocaloric materials according to the comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 dimensional relationships between the components in the drawings may differ from the actual ones.

[0021] Embodiment Fig. 1 is a plan view showing a magnetocaloric material 1 according to an embodiment. The magnetocaloric material 1 is a compact obtained by kneading a coating powder 4 and 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 the method for producing the material powder 2 include a die 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 a La(Fe,Si)H-based compound, but 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. In the embodiment, the material powder 2 such as a La(Fe,Si)H-based compound has a NaZn13-type crystal structure, and the NaZn13-type crystal structure phase refers to a phase having a NaZn13-type crystal structure. In addition, 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. Moreover, the material powder 2 may contain elements B, C, N, O, or F instead of or together with H. Moreover, the material powder 2 does not need to be a single compound phase of NaZn13 type crystal, and other phases such as α-Fe phase may be mixed. In the following, 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 viewpoint of deterioration of magnetic properties due to oxidation or uniformity of the magnetocaloric material 1.

[0024] The coating 3 has higher thermal conductivity and lower hardness than the La(Fe,Si)H-based compound. The material of the coating 3 is not particularly limited, but from the viewpoint of thermal conductivity and hardness, Cu or an alloy containing Cu is particularly preferable. In addition, as long as the material has higher thermal conductivity and lower hardness than the material powder 2, the material may be an alloy containing one or more elements selected from Zn, Si, Al, Mo, Cu, Ag, Au, Fe, Co, and Ni. By making the coating 3 have higher thermal conductivity and lower hardness than the La(Fe,Si)H-based compound, the thermal conductivity of the magnetocaloric material 1 is increased. The thickness of the coating 3 is preferably 0.5% or more and 13% or less of the particle size of the material powder 2 or the coating powder 4, based on the viewpoint of 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. The resin binder 5 is preferably an epoxy resin, but may be a thermosetting resin other than epoxy resin. The resin binder 5 may be a thermoplastic resin. In the embodiment, at least one of epoxy resin, melamine resin, phenol 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 made by kneading the resin binder 5 and the coating powder 4, pressure is applied to the mold to push the resin component out of the mold while molding. This causes adjacent coating powder particles 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, a 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 higher thermal conductivity than 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 a powder may be referred to as an 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 more.

[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) In addition, 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 a 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 equations (1) and (2) are satisfied, the following equation (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 in the manufacturing process of the magnetocaloric material 1 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. The respective volumes or cross-sectional areas of the material portion and the coating portion can be obtained based on the pixel number ratio of an optical microscope image or an electron microscope image, etc.

[0029] In the embodiment, the thermal conductivity of the coating 3 is 10 W / m·K or more. If the thermal conductivity of the coating 3 is less than 10 W / m·K, the thermal conductivity of the coating 3 is lower than that of the La(Fe,Si)H-based compound, and the thermal conductivity of the La(Fe,Si)H-based compound to which the coating 3 is applied is reduced. In the embodiment, the hardness of the coating 3 is 800 HV or less, that is, the hardness of the material powder 2 or less. If the hardness of the coating 3 is 800 HV or less, the coating 3 is deformed preferentially over the La(Fe,Si)H-based compound, and a mesh-like structure is easily formed. As a result, fine heat conduction paths are formed, and high thermal conductivity can be obtained with a large ratio of the material powder 2 in the magnetocaloric material 1.

[0030] 2 is a flow chart 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 for coating the material powder 2 with the coating 3, a kneading step S2 for kneading the coating powder 4 obtained by coating with a resin binder 5, a forming step S3 for applying pressure to the kneaded coating powder 4 and resin binder 5 to form them, a structure forming step S4 for forming a mesh structure by the coating 3 by pressure, and a molding and solidification step S5 for molding the kneaded coating powder 4 and resin binder 5 at 150° C. or less to solidify 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 having a NaZn13-type crystal structure and hydrogen is introduced into the La(Fe,Si)-based compound. The coating method of the film 3 in the coating step S1 is preferably electroless plating from the viewpoint of uniformity of the film 3 and film formation cost, but may be sputtering or vapor deposition.

[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 at a temperature of 150° C. or less for the coated powder 4. This is because at temperatures higher than 150° C., hydrogen introduced into the La(Fe,Si)-based compound is released.

[0033] The clearance of the mold 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 a 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, and orientation control may be performed. 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 processing of the structure generating step S4 is performed in parallel with the processing of the molding step S3. In the molding step S3, molding is performed while pushing the resin binder 5 out of the mold to increase the density of the coated powder 4. In the process of increasing the density of the coated powder 4, the coated powder particles 4 come into contact with each other, and a mesh structure made of a high thermal conductivity material is formed by the coating 3 applied to the material powder 2. The pressure during the generation of the mesh 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. EXAMPLES

[0036] The magnetocaloric material 1 according to the embodiment and its manufacturing method will be described in more detail below with reference to examples and comparative examples. In the following, 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 300μm x 300μm. 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 coating 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 300μm×300μm area in a 300x field of view of the electron microscope to the number of pixels in the part of the material powder 2 of the magnetocaloric material 1 in the measurement area.

[0039] The third item is the thermal conductivity evaluation. The thermal conductivity evaluation was performed using the laser flash method on a 10 mm x 10 mm x 1.5 mm t The measurements were performed using samples that had been processed as follows. The surfaces of the samples were finished with waterproof paper of No. 2000 and then blackened with carbon spray. The number of measurements was determined by the average value of measurements taken at three points per sample.

[0040] [Example 1] In Example 1, the material powder 2 of the La(Fe,Si)H-based compound is La(Fe 0.88 S 0.12 ) 13 H 1.25 The composition was adjusted as follows. This composition is publicly known. First, La(Fe 0.88 S 0.12 ) 13 The alloy was prepared by arc melting in an Ar atmosphere to have the composition. 0.88 S 0.12 ) 13is an example of the La(Fe,Si)13 system. After the alloy was prepared, the test piece was homogenized 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, and the La(Fe 0.88 S 0.12 ) 13 H 1.25 The La(Fe 0.88 S 0.12 ) 13 H 1.25 is an example of a La(Fe,Si)H compound. La(Fe 0.88 S 0.12 ) 13 H 1.25 After the preparation of La(Fe 0.88 S 0.12 ) 13 H 1.25 The mixture was crushed in a mortar and sieved through a 120 mesh sieve to obtain powder having an average particle size of 100 μm. The powder was then classified to obtain material powder 2 having an average particle size of 100 μm.

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

[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 applied to 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 applied to 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] A 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. The powder was then classified to obtain a material powder 2 with an average particle size of 30 μm. A Cu coating 3 with a film thickness of 1 μm was then applied to the material powder 2 in the same manner as in Example 1. A magnetocaloric material 1 was then prepared in the same manner as in Example 1.

[0045] [Example 5] A 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 20-40 mesh sieve to obtain powder with an average particle size of 500 μm. The powder was then classified to obtain a material powder 2 with an average particle size of 500 μm. A Cu coating 3 with a film thickness of 1 μm was then applied to the material powder 2 in the same manner as in Example 1. A magnetocaloric material 1 was then 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 in the same manner as in Example 1. Then, a Cu coating 3 having a thickness of 1 μm was applied to the material powder 2 in the same manner as in Example 1 to obtain a coated powder 4. Furthermore, a Cu powder having a weight of 1 / 5 of the total weight of the coated powder 4 for producing the magnetocaloric material 1 was mixed with the coated powder 4. The average particle size of the Cu powder was 10 μm, which is 1 / 3 or less of the average particle size of the coated powder 4. Then, the powder obtained by mixing the coated powder 4 and the Cu powder was kneaded with a resin binder 5 and molded in a square mold having an inner diameter of 30 mm×30 mm. The pressure during molding was 50 MPa. Then, molding was performed 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 was kneaded with a resin binder 5 and molded 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 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 20-40 mesh sieve to obtain a powder with an average particle size of 500 μm, which 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 providing a coating 3 on the material powder 2, 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 with an average particle size of 100 μm was obtained in the same manner as in Example 1. Then, a Cu coating 3 with a thickness of 1 μm was applied to the material powder 2 in the same manner as in Example 1. Thereafter, the obtained coating powder 4 was kneaded with a resin binder 5, placed in a square mold with an inner dimension of 30 mm×30 mm, and solidified at room temperature without applying pressure to produce a magnetocaloric material without a 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 applied to 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 was kneaded with a resin binder 5, placed in a square mold having an inner dimension of 30 mm×30 mm, and solidified at room temperature without applying pressure to produce a magnetocaloric material having no mesh structure.

[0051] [Comparative Example 5] A material powder 2 of a La(Fe,Si)H-based compound with 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 was kneaded with a resin binder 5, placed in a square mold with an inner dimension of 30 mm×30 mm, and solidified at room temperature without applying pressure to produce a magnetocaloric material without a mesh-like 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 in the same manner as in Example 1. Then, a Cu coating 3 having a thickness of 1 μm was applied to the material powder 2 in the same manner as in Example 1 to obtain a coated powder 4. Furthermore, a Cu powder having a weight of 1 / 5 of the total weight of the coated powder 4 for producing the magnetocaloric material 1 was mixed with the coated powder 4. 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. Then, the powder obtained by mixing the coated powder 4 and the Cu powder was kneaded with a resin binder 5 and molded in a square mold having an inner diameter of 30 mm×30 mm. The pressure during molding was 50 MPa. Then, molding was performed 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 in the same manner as in Example 1. Then, a Cu coating 3 having a thickness of 1 μm was applied to the material powder 2 in the same manner as in Example 1 to obtain a coated powder 4. Furthermore, a Cu powder having a weight of 1 / 5 of the total weight of the coated powder 4 for producing the magnetocaloric material 1 was mixed with the coated powder 4. 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. Then, the powder obtained by mixing the coated powder 4 and the Cu powder was kneaded with a resin binder 5 and molded in a square mold having an inner diameter of 30 mm×30 mm. The pressure during molding was 50 MPa. Then, molding was performed 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 coating 3 of Cu 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 20 μm. In this case, there was a difference of 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 film 3, the obtained coated powder was kneaded with a resin binder 5 to prepare a magnetocaloric material in the same manner as in Example 1. 3 <2r 3 does not hold, the volume ratio of 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 coating 3 of Cu 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 to prepare a magnetocaloric material in the same manner as in Example 1. In Comparative Example 9, as in Comparative Example 8, R 3 <2r 3 does not hold, the volume ratio of 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 coating 3 of Cu 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 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 element, i.e., tungsten, was applied to the material powder 2 by a sputtering method. 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 to produce a magnetocaloric material in the same manner as in Example 1.

[0058] [Comparative Example 12] A material powder 2 of a La(Fe,Si)H-based compound with an average particle size of 100 μm was obtained in the same manner as in Example 1. Then, a coating of aluminum oxide with the chemical formula Al2O3 was applied to the material powder 2 by sputtering. The coating had a thickness of 0.5 μm. The coated powder obtained by forming an Al2O3 coating on the material powder 2 was mixed with a resin binder 5 to produce a magnetocaloric material in the same manner as in Example 1.

[0059] [Comparative Example 13] A material powder 2 of a La(Fe,Si)H-based compound with an average particle size of 100 μm was obtained in the same manner as in Example 1. Then, a coating of silicon oxide with the chemical formula SiO2 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 SiO2 coating on the material powder 2 was mixed with a resin binder 5 to produce a magnetocaloric material in the same manner as in Example 1.

[0060] The evaluation results of the examples and the 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 conductivity of the magnetocaloric material 1 according to the examples and the magnetocaloric material according to the comparative examples. Fig. 4 is a diagram including a second table showing the evaluation results of the thermal conductivity of the magnetocaloric material 1 according to the examples and the magnetocaloric material according to the comparative examples. Fig. 5 is a diagram including a third table showing the evaluation results of the thermal conductivity of the magnetocaloric material 1 according to the examples and the magnetocaloric material according to the comparative examples. Fig. 6 is a diagram including a fourth table showing the evaluation results of the thermal conductivity of the magnetocaloric material 1 according to the examples and the magnetocaloric material according to the comparative examples.

[0061] FIG. 3 shows the presence or absence of a mesh-like structure, the powder density, and the thermal conductivity of the magnetocaloric materials 1 of Examples 1 to 5 and the magnetocaloric materials of Comparative Examples 1 to 5. As shown in FIG. 3, a mesh-like structure was formed in Examples 1 to 5. On the other hand, in Comparative Examples 1 to 2 in which no coating was formed, and Comparative Examples 3 to 5 in which no pressure was applied, no mesh-like structure was formed. Also, as shown in FIG. 3, in Examples 1 to 5, the density of the material powder 2 was 65% or more, and a large amount of the material powder 2 for obtaining the magnetocaloric effect was contained in the magnetocaloric material 1. On the other hand, in Comparative Examples 3 to 5, the density of the material powder 2 was 60% or less. As shown in FIG. 3, in Examples 1 to 5, magnetocaloric materials 1 having a thermal conductivity 10 times or more that of the magnetocaloric material of Comparative Example 1 were obtained. In particular, in Example 2, magnetocaloric materials 1 having a thermal conductivity 210 times that of the magnetocaloric material of Comparative Example 1 were obtained. On the other hand, in Comparative Examples 2 to 5, no magnetocaloric materials having thermal conductivity greater than 7.5 times that of the magnetocaloric material of Comparative Example 1 were obtained. 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%, and the magnetocaloric material 1 contained a large amount of the 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 having a thermal conductivity 60 times that of the magnetocaloric material of Comparative Example 1 was obtained. 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 portion of the magnetocaloric material due to Cu powder was large.

[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%, and the magnetocaloric material 1 contained a large amount of the material powder 2 for obtaining the magnetocaloric effect. On the other hand, in Comparative Examples 8 to 9, in which a Cu coating having a greater thickness relative to the average radius of the material powder 2 was applied, the density of the material powder 2 was below 50%. As shown in FIG. 5, in Example 1, a magnetocaloric material 1 having a thermal conductivity 45 times that of the magnetocaloric material of Comparative Example 1 was obtained. On the other hand, in Comparative Examples 8 to 9, a magnetocaloric material having a thermal conductivity 200 times or more that of the magnetocaloric material of Comparative Example 1 was obtained because the Cu coating having a high thermal conductivity was thick. Note that, as shown in FIG. 5, in Comparative Example 10, molding was not possible due to the 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 the material powder 2 for obtaining the magnetocaloric effect. On the other hand, in Comparative Examples 11 to 13, in which the material powder 2 was coated with a film made of 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 film coating the material powder 2 was low, and therefore only half or less of the thermal conductivity in Example 3 was obtained.

[0065] The magnetocaloric material 1 according to the embodiment and the effects of 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 a material powder 2 of a La(Fe,Si)H-based compound in which hydrogen is adsorbed to La(Fe,Si)13-based, coated 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 the coating powders 4 adjacent to each other form a mesh structure.

[0066] According to the above configuration, the coating 3 has a lower hardness than the material powder 2, so it deforms preferentially over the material powder 2, and the mesh-like structure is easily formed. The coating 3 has a higher thermal conductivity than the material powder 2, so the mesh-like structure provides a high thermal conductivity. In addition, the heat conduction path of the mesh-like structure is fine, so the magnetocaloric material 1 contains the material powder 2 of the La(Fe,Si)H-based compound at a high density. This allows the cooling efficiency to be maintained or improved. Therefore, according to the magnetocaloric material 1 according to the embodiment, it is possible to maintain or improve the cooling efficiency, that is, to achieve both a high magnetocaloric effect and an improvement in thermal conductivity. In addition, the magnetocaloric material 1 contains a resin with high electrical resistance instead of a low melting point metal, which suppresses the generation of eddy currents, thereby suppressing 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 1 / 3 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.

[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 material powder 2 for obtaining the magnetocaloric effect in the magnetocaloric material 1 to have a high density, and the cooling efficiency is maintained or improved.

[0069] The coating 3 in the 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. Since the hardness is 800 HV or less, it becomes easy to form a mesh structure by the coating 3 having high thermal conductivity. Furthermore, the mesh structure improves the thermal conductivity.

[0070] The manufacturing method of the magnetocaloric material 1 in the 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 in La(Fe,Si)13 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 coating powder 4 obtained by coating the material powder 2 with the coating 3 with a resin. The molding step S3 is a step of applying pressure to the kneaded coating powder 4 and resin to perform molding. The structure generation step S4 is a step of generating a mesh-like structure by the coating 3 by pressure. The molding and solidification step S5 is a step of molding the kneaded coating powder 4 and resin at 150°C or less to solidify them. This manufacturing method can obtain a magnetocaloric effect that achieves both a high magnetocaloric effect and an improvement in thermal conductivity.

[0071] Although the embodiments have been described above, the contents of the present disclosure are not limited to the embodiments and include possible 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. [Explanation of symbols]

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

Claims

1. A coated 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 film; Resin and Including, The coating has a higher thermal conductivity and a lower hardness than the material powder, The coating of the adjacent coating powders forms a mesh structure, The resin is contained between the network structures, A magnetocaloric material, comprising powder of a high thermal conductivity material having a particle size 1 / 3 or less of the particle size of the coating powder, disposed between the gaps between the coating powder particles.

2. The magnetocaloric material of claim 1, wherein the powder of high thermal conductivity material is Cu powder.

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. 3. The magnetocaloric material according to claim 1 or 2, 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.