Magnetic refrigeration material, method for manufacturing the same, and magnetic refrigeration apparatus

Abstract

La(Fe,Si) has high pulverizability and does not require a large load to be turned into a powder. 13 H α The present invention provides a magnetic refrigeration material, a method for producing the same, and a magnetic refrigeration apparatus equipped with the magnetic refrigeration material. [Solution] The magnetic refrigeration material of the present invention is based on the following general formula (1) TIFF2026066207000015.tif7170[In formula (1), M represents one or more elements selected from the group consisting of Mn and Co, and A represents the element Al. x, y, a, b, c, and z are 0≦x≦0.4, 1.0 respectively.

Description

Technical Field

[0001] The present invention relates to a magnetic refrigeration material, a method for producing the same, and a magnetic refrigeration device.

Background Art

[0002] Conventional gas compression type refrigeration and refrigeration equipment has a mechanism in which a gas refrigerant such as freon is compressed by a compressor, liquefied, heat is released, and then the object to be cooled is cooled by the heat of vaporization when it is vaporized again. However, the destruction of the ozone layer by freon discharged during the manufacture, operation, or disassembly of the refrigeration and refrigeration system has become a major problem. As a countermeasure to this problem, although the conversion to alternative freon refrigerants has been promoted, many of the alternative freon refrigerants have a high global warming potential, and this has become a new concern. In recent years, from the perspective of global warming suppression, there is a strong demand for refrigerants with a low global warming potential or a shift to a new refrigeration and refrigeration system.

[0003] As one of the new refrigeration and refrigeration systems, a magnetic refrigeration system can be mentioned. It is known that certain magnetic materials exhibit an exothermic reaction due to the generation of a magnetic field near the magnetic transition temperature (Curie temperature; T c ), and an endothermic reaction due to the removal of the magnetic field, which is called the magnetocaloric effect. The magnetic refrigeration system that utilizes this magnetocaloric effect is attracting attention as a system that does not require a gas refrigerant with a large environmental load and can be expected to have high efficiency without energy loss associated with gas compression and expansion.

[0004] As the magnetic refrigeration material used in the magnetic refrigeration system, a material having a Curie temperature (hereinafter sometimes referred to as T c ) near room temperature and a large magnetic entropy change amount is required. Various materials have been studied so far, and among them, as a material having a T c of around 320 K and a large magnetic entropy change amount, a hydride of La(Fe, Si) 13 alloy (La(Fe, Si) 13 H αMagnetic refrigeration materials) have attracted particular attention. For example, the materials shown in the following patent documents are known.

[0005] Patent Document 1 discloses La 1-a R a (Fe 1-x-y T y M x ) 13 H z , with a hydrogen content z of 90% or more of the hydrogen saturation value z sat , and values of a, x, and y selected to determine the Curie temperature T c . M is one or more elements from the group consisting of Al and Si, T is one or more elements from the group consisting of Co, Ni, Mn, Cr, Cu, Ti, and V, R is one or more elements from the group consisting of Ce, Nd, Y, and Pr, and T cmax is the Curie temperature of the La sat R 1-a R a (Fe 1-x-y T y M x ) 13 H z phase, and (T cmax - T c ) ≤ 20K. An operating component for magnetic heat exchange including a magnetic heat-active phase is disclosed.

[0006] Patent Document 2 discloses a magnetic refrigeration working substance represented by La 1-x Ce x (Fe 1-y-z Mn y Si z ) 13 H n , where n ≥ 1.5, and for each of La, Ce, Mn, and Si, 3σ indicating compositional non-uniformity is 1 at.% or less. A magnetic refrigeration working substance is disclosed.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

[0008] Various studies have been conducted regarding the shape of magnetic refrigeration materials when they are incorporated into magnetic refrigeration devices. For example, La(Fe,Si) 13 H α In the case of magnetic refrigeration materials, they are generally processed into powder form and used either as is or molded into various shapes according to the requirements of the magnetic refrigeration equipment to be installed. (La(Fe,Si)) 13 H α In the manufacturing process of magnetic refrigeration materials, La(Fe,Si) 13 When a hydrogenation treatment is applied to a alloy, hydrogen embrittlement of the material occurs, but this does not allow for sufficient powdering. Therefore, a final pulverization process is necessary to obtain a powder.

[0009] However, La(Fe,Si) 13 Because the hydrides of alloy systems have poor stability, the material changes when pulverization is applied, T c A discrepancy could occur. Therefore, La(Fe,Si) 13 H α In the manufacture of magnetic refrigeration materials, it is desirable to be able to produce a powder with as little load as possible from pulverization. From this perspective, La(Fe,Si) is a material that has high pulverability and does not require a large load to produce a powder. 13 H α Magnetic refrigeration materials were highly desired.

[0010] The present invention has been made in view of the above, and is made of La(Fe,Si) which has high pulverability and does not require a large load to be made into a powder. 13 H α The objective is to provide a magnetic refrigeration material, a method for manufacturing the same, and a magnetic refrigeration apparatus equipped with the magnetic refrigeration material.

Means for Solving the Problem

[0011] As a result of intensive studies to achieve the above object, the present inventor has found that the above object can be achieved by a hydrogenated alloy having a specific composition, and has completed the present invention. In particular, the present inventors have found that in a La(Fe,Si) 13 H α -based magnetic refrigeration material, when the amount of La relative to the amount of (Fe,Si) is present in excess of the stoichiometric ratio (i.e., La amount : (Fe,Si) amount = 1:13), the pulverizability of the material becomes high, and the present invention has been completed.

[0012] That is, the present invention includes, for example, the subject matters described in the following items. Item 1 The following general formula (1)

[0013]

Chemical formula

[0014] [In formula (1), M represents one or more elements selected from the group consisting of Mn and Co, A represents an Al element. x, y, a, b, c, and z are numbers satisfying 0≦x≦0.4, 1.0<y≦1.25, 0≦a≦0.04, 0.05≦b≦0.2, 0≦c≦0.01, and 0<z≦1.5, respectively.] A magnetic refrigeration material containing a hydrogenated alloy having a composition represented by the formula.

[0015] Item 2 The magnetic refrigeration material according to Item 1, wherein M is Mn or Co.

[0016] Item 3 A method for producing the magnetic refrigeration material according to Item 1 or 2, comprising The following general formula (2)

[0017]

Chemical formula

[0018] [In formula (2), M, A, x, y, a, b, and c are synonymous with M, A, x, y, a, b, and c in formula (1) respectively.] A process for obtaining the hydrogen storage alloy by hydrogenating a precursor having a composition represented by the following formula, wherein the precursor has an area ratio P calculated by the following measurement of the area ratio of the R-enriched phase of 0.4 to 3.0%, a method for producing a magnetic refrigeration material. <Measurement of the area ratio of the R-enriched phase> In the backscattered electron image obtained by observing the cross-section of the precursor with an EPMA at a magnification of 1000 times, the total area S of all the white regions present in the region surrounded by a rectangle with a short side of 85 μm and a long side of 120 μm R (μm 2 ) is measured, According to the following formula (A) P (%) = {S R / (85 × 120)} × 100 (A) the area ratio P of the precursor is calculated. Item 4 The hydrogenation has a first hydrogenation and a second hydrogenation, The first hydrogenation is performed by placing the precursor in a container under reduced pressure and introducing hydrogen into the container, The second hydrogenation is performed by placing the precursor treated by the first hydrogenation in a container under reduced pressure and introducing hydrogen into the container, After the first hydrogenation and before the second hydrogenation, the precursor treated by the first hydrogenation is heat-treated at 300 °C or higher under reduced pressure. The method for producing a magnetic refrigeration material according to item 3. Item 5 A magnetic refrigeration device comprising the magnetic refrigeration material according to claim 1 or 2.

Advantages of the Invention

[0019] The magnetic refrigeration material of the present invention has high pulverability and does not require a large load to be made into a powder. Furthermore, the method for producing the magnetic refrigeration material of the present invention is a suitable method for producing the magnetic refrigeration material, and the resulting magnetic refrigeration material has high pulverability and does not require a large load to be made into a powder. [Brief explanation of the drawing]

[0020] [Figure 1] This is an image analysis program for measuring the total area SR (μm2) of the white region visible in the backscattered electron composition image obtained by observing a precursor using EPMA. [Figure 2] (a) is a cross-sectional view of the backscattered electron composition of the precursor used in Example 1, and (b) is a cross-sectional view of the backscattered electron composition of the precursor used in Comparative Example 1. [Figure 3] This graph shows the results of the pulverization test for Examples 1 and 2, and Comparative Example 1. [Modes for carrying out the invention]

[0021] Embodiments of the present invention will be described in detail below. In this specification, the expressions "containing" and "including" include the concepts of "containing," "including," "substantially consisting of," and "consisting only of."

[0022] The magnetic refrigeration material of the present invention contains a hydrogenated alloy having a composition represented by the following general formula (1) as an essential component.

[0023] [ka]

[0024] Here, in equation (1) above, M represents one or more elements selected from the group consisting of Mn and Co. A represents the element Al.

[0025] Furthermore, in equation (1) above, x, y, a, b, c, and z are, respectively 0 ≤ x ≤ 0.4, 1.0 <y≦1.25、 0 ≤ a ≤ 0.04, 0.05 ≤ b ≤ 0.2, 0 ≤ c ≤ 0.01, and, 0 <z≦1.5 It is a number that satisfies the following condition.

[0026] The magnetic refrigeration material of the present invention contains the aforementioned hydrogenated alloy, and in particular, the amount of La relative to the amount of (Fe, Si) is present in excess of the stoichiometric ratio (i.e., La amount:(Fe,Si) amount = 1:13). This enhances the pulverizability of the magnetic refrigeration material of the present invention, and does not require a large load to produce a powder.

[0027] In equation (1), x, y, a, b, c, and z represent the molar ratios of each element, as detailed below. Hereafter, these ratios may also be referred to as "content" or "amount."

[0028] In equation (1) above, x represents the Ce content. When x=0, Ce is not present in the hydrogenated alloy, and when x>0, it has a structure in which part of La is replaced by Ce. The replacement of part of La with Ce results in a change in magnetic entropy (hereinafter, |ΔS M (represented by |) becomes larger.

[0029] In equation (1) above, if x exceeds 0.4, the equilibrium pressure with hydrogen becomes too high, which may prevent sufficient hydrogenation. It is preferable that x is 0 ≤ x ≤ 0.40, and more preferably 0 ≤ x ≤ 0.30.

[0030] In formula (1) above, y represents the total content of La and Ce. If y is 1.0 or less, La(Fe,Si) 13 H αThe amount of La with respect to the amount of (Fe, Si) in the magnetic refrigeration material will not be excessive compared to the stoichiometric ratio (i.e., the amount of La: the amount of (Fe, Si) = 1:13). Therefore, when y is 1.0 or less, the area ratio P of the R enrichment phase described later does not fall within the desired range, and as a result, the magnetic refrigeration material cannot obtain sufficient pulverizability. When y exceeds 1.25, |ΔS M | becomes small, which is not preferable as a magnetic refrigeration material. y is preferably 1.00 < y ≦ 1.25, more preferably 1.009 ≦ y ≦ 1.10, even more preferably 1.01 ≦ y ≦ 1.10, still more preferably 1.010 ≦ y ≦ 1.10, and particularly preferably 1.02 ≦ y ≦ 1.05.

[0031] In the above formula (1), 1 - a - b - c represents the content ratio of Fe. Fe affects the production efficiency of the 1 - 13 phase (La(Fe,Si) 13 phase having a NaZn 13 type crystal structure). Since a large Fe content may cause a decrease in the magnetocaloric effect, 0.840 ≦ 1 - a - b - c ≦ 0.900, preferably 0.845 ≦ 1 - a - b - c ≦ 0.895, and more preferably 0.850 ≦ 1 - a - b - c ≦ 0.890.

[0032] M in the formula (1) is one or more elements selected from the group consisting of Mn and Co. M is an element that contributes to the adjustment of the Curie temperature T c . By containing M in the hydrogenated alloy, it is possible to widen the adjustment temperature range of the magnetic transition temperature of the magnetic refrigeration material of the present invention.

[0033] In the above formula (1), a represents the content of M. a is preferably 0 ≦ a ≦ 0.040, more preferably 0 ≦ a ≦ 0.035, and even more preferably 0 ≦ a ≦ 0.03.

[0034] In formula (1), b represents the content of Si. Si is effective for stabilizing the 1-13 phase, and by including Si in the hydrogenated alloy, formation of the 1-13 phase by heat treatment becomes possible. It is preferable that 0.050 ≦ b ≦ 0.20, more preferably 0.08 ≦ b ≦ 0.18, and even more preferably 0.10 ≦ b ≦ 0.15.

[0035] A in formula (1) is an Al element and is an element that contributes to the adjustment of the Curie temperature T c and Al also makes it possible to widen the adjustment temperature range of the magnetic transition temperature of the magnetic refrigeration material of the present invention.

[0036] In formula (1), c represents the content of A, that is, Al. It is preferable that 0 ≦ c ≦ 0.010, more preferably 0 ≦ c ≦ 0.007, and even more preferably 0 ≦ c ≦ 0.005. c may be 0.

[0037] In formula (1), z represents the content of H (hydrogen). By introducing hydrogen into the La(Fe, Si) 13 series alloy, the Curie temperature T of the magnetic refrigeration material c can be adjusted to an appropriate range, for example, it can be adjusted near room temperature. It is preferable that 0 < z ≦ 1.50.

[0038] The magnetic refrigeration material of the present invention includes the hydrogenated alloy, has high pulverizability, and does not require a large load to be made into a powder form.

[0039] The magnetic refrigeration material of the present invention may consist only of the hydrogenated alloy represented by formula (1), or may contain other elements and components as long as the effects of the present invention are not inhibited. For example, the magnetic refrigeration material of the present invention may contain other elements and components that can be mixed in during the production of the hydrogenated alloy. For example, the magnetic refrigeration material of the present invention may substantially contain inevitable impurities such as oxygen, nitrogen, and those derived from raw materials, and it is preferable that their contents are small, but they may be contained in trace amounts.

[0040] In the magnetic refrigeration material of the present invention, the content of the hydrogenated alloy is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and particularly preferably 99.9% by mass or more.

[0041] The composition of the alloy before hydrogenation can be analyzed by known analytical methods; for example, the composition of the alloy before hydrogenation can be measured by ICP (Inductively Coupled Plasma) emission spectroscopy.

[0042] The method for producing the hydrogenated alloy is not particularly limited, and for example, known methods can be widely employed. For example, the hydrogenated alloy may be NaZn 13 La(Fe,Si) having a type crystal structure 13 It can be obtained by using a system alloy as a raw material (also called a precursor) and hydrogenating it. The hydrogenation method is not particularly limited, and for example, known hydrogenation methods can be broadly applied in this invention.

[0043] Here, the raw material (precursor) is La(Fe,Si) 13 The method for manufacturing the alloy is not particularly limited and can be selected from known methods, such as strip casting methods including the single-roll method, double-roll method, or disk method, and die casting methods.

[0044] In the present invention, the hydrogenated alloy is preferably manufactured by the following step 1. Step 1; The following general formula (2)

[0045] [ka]

[0046] [In formula (2), M, A, x, y, a, b, and c are the same as M, A, x, y, a, b, and c in formula (1), respectively.] A step of obtaining the hydrogenated alloy by hydrogenating a precursor having the composition represented by [formula].

[0047] The precursor (alloy) represented by formula (2) can also be obtained by using the strip casting methods such as the single-roll method, double-roll method, or disk method, and the die casting method. When the precursor is cast using this method, a peritectic structure is formed which has a grain boundary phase containing more rare earth elements than the main phase around the α-Fe main phase. From this peritectic structure, NaZn 13 Further heat treatment is necessary to create a microstructure where the type crystalline phase (phases 1-13) is the main phase.

[0048] Therefore, in order to heat-treat the precursor (alloy slab) obtained by casting, it is preferable to hold the precursor (alloy slab) in a vacuum or inert gas atmosphere at a temperature at which phases 1-13 are stable for an appropriate period of time. The holding time can be appropriately selected, for example, within the range of more than 0 seconds and 480 hours or less. The temperature at which phases 1-13 are stable varies depending on the alloy composition, so it is necessary to adjust it according to the composition, but for example, it is sufficient to hold it at a temperature of 900°C to 5°C lower than the melting point of the precursor. An example of a stable temperature is 900 to 1200°C.

[0049] As described above, the precursor obtained by heat-treating the alloy slab has an area fraction P of 0.4-3.0% (i.e., 0.4% or more and 3.0% or less) calculated by measuring the area fraction of the R-enriched phase. In this specification, the R-enriched phase refers to NaZn 13 This refers to a phase that forms around a primary phase and contains more rare earth elements than the primary phase.

[0050] The area fraction of the R-enriched phase described above is measured using the following procedure. First, a backscattered electron composition image is prepared by observing a cross-section of the heat-treated precursor at 1000x magnification using an EPMA (electron probe microanalyzer). In this backscattered electron composition image, a region enclosed by a rectangle with a short side of 85 μm and a long side of 120 μm (hereinafter referred to as region R) is randomly selected, and the total area S of all white regions present in region R is measured. R (μm 2) is measured. The total area S obtained is measured. R (μm 2 The area of ​​the region R in the above region (85 μm × 120 μm = 10200 μm) 2 The ratio to ) is defined as the "area ratio P of the R-enriched phase". That is, the area ratio P is The following formula (A) P(%)={S R / (85×120)}×100 (A) It is calculated by [this method].

[0051] In this case, numerous spotted white regions are observed in the aforementioned backscattered electron composition image. Such white regions are due to the uneven distribution of rare earth elements, namely NaZn. 13 The main phase of this type contains many rare earth elements, which are visible as white regions (e.g., white spots) in the backscattered electron composition image. Therefore, in the measurement of the area fraction P, the total area S of the white regions visible in the region R is measured. R (μm 2 ) should be measured. Total area S of the white region R (μm 2 This can be measured using an image analysis program.

[0052] Figure 1 shows the image analysis program. The program first arbitrarily determines a threshold (threshold1), and then binarizes the image (backscattered electron composition image) based on this threshold. From this binarized image, the contours of the white areas are extracted one by one, their areas are calculated, and the areas of the white areas are summed up to determine the total area S of the white region. R (μm 2 ) can be done as follows.

[0053] The image analysis program shown in Figure 1 can be created and executed using the following procedure. First, create a Python file based on the program shown in Figure 1 (for example, the file object is named "input_image.jpg"). Next, execute the Python file in the command prompt to perform the image analysis. This image analysis will determine the total area S mentioned above. R (μm2 ) can be derived.

[0054] In Figure 1, [1] is the code for loading the image, [2] is the code for applying thresholding to binarize the image (black and white), [3] is the code for detecting contours from the binarized image, [4] is the code for initializing the total area, [5] is the code for calculating the area for each contour, [6] is the code for displaying the total area percentage of the white areas, [7] is the code for displaying the original image, and [8] is the code for displaying the binarized image.

[0055] As mentioned above, the white region is due to the uneven distribution of rare earth elements, and therefore, in this specification, this white region is referred to as the "R-enriched phase."

[0056] In step 1, the precursor having the area ratio P of the R-enriched phase as described above is hydrogenated. This yields the hydrogenated alloy obtained by hydrogenating the precursor. Such a hydrogenated alloy has excellent pulverability. If the area ratio P of the R-enriched phase is less than 0.4%, sufficient pulverability cannot be obtained. Also, if the area ratio P of the R-enriched phase exceeds 3.0%, it does not exhibit sufficient magnetocaloric effect and is therefore undesirable as a magnetic refrigeration material. The area ratio P of the R-enriched phase is preferably 0.8% or more, and preferably 2.6% or less.

[0057] The hydrogenation method is not particularly limited, and for example, known hydrogenation treatment methods can be widely adopted in the present invention. For example, the hydrogenation can be carried out using a device (hydrogenation device) capable of introducing hydrogen to the heat-treated precursor.

[0058] In step 1, during hydrogenation, the precursor may be activated if necessary. This activation involves introducing hydrogen and evacuating the system beforehand to enhance the reactivity between the precursor and hydrogen.

[0059] More specifically, the hydrogenation in step 1 may consist of the following first hydrogenation and second hydrogenation. First hydrogenation: This is carried out by placing the precursor in a container under reduced pressure and introducing hydrogen into the container. Second hydrogenation: This is carried out by placing the precursor treated by the first hydrogenation in a container under reduced pressure and introducing hydrogen into the container.

[0060] The first hydrogenation process described above serves the role of the activation treatment. In other words, the first hydrogenation process increases the reactivity between the precursor and hydrogen in the subsequent second hydrogenation process, allowing for the efficient acquisition of the hydrogenated alloy.

[0061] In the first hydrogenation process described above, the precursor is placed (contained) in a container under reduced pressure. The type of container is not particularly limited; for example, containers used for the hydrogenation of alloys can be widely used in this invention.

[0062] In the first hydrogenation process described above, the method for reducing the pressure inside the container is not particularly limited, and the pressure can be reduced by known means. The degree of pressure reduction is also not particularly limited, and in terms of facilitating the activation treatment, the pressure inside the container can be reduced to 50 Pa or less when absolute vacuum is 0, preferably to 10 Pa or less. The temperature during pressure reduction is also not particularly limited, and can be, for example, around room temperature, specifically -10 to 40°C.

[0063] In the first hydrogenation process described above, hydrogen is introduced into a container under reduced pressure as described above. The method of introducing hydrogen is not particularly limited, and for example, a wide range of known hydrogen introduction methods can be employed. Hydrogen can be introduced into the container until the pressure inside the container (hydrogen pressure) reaches a desired pressure, for example, until it reaches a pressurized state of 0.3 MPa (meaning absolute pressure; 0.2 MPa if using gauge pressure). The pressure inside the container after hydrogen introduction is preferably 0.3 ± 0.05 MPa. The hydrogen introduction rate is also not particularly limited.

[0064] In the first hydrogenation process described above, after introducing hydrogen as described above until a predetermined pressurized state is reached, the temperature inside the container can be increased. This activates the precursor. In this temperature increase process, the temperature inside the container can be set to, for example, a range of 100 to 500°C. After reaching the desired temperature, it can be maintained at that temperature for an appropriate period of time, for example, 0.1 to 10 hours.

[0065] The precursor treated by the first hydrogenation described above can be subjected to an additional heating treatment. Specifically, the precursor can be subjected to an additional heating treatment while the container containing the precursor treated by the first hydrogenation described above is evacuated to create a reduced pressure state. This can further activate the precursor in the container. In this additional heating treatment, the temperature can be raised to a higher temperature than that of the heating treatment in the first hydrogenation, for example, 300°C or higher, preferably in the range of 400 to 800°C. After reaching the desired temperature, it can be held at that temperature for an appropriate time, for example, 0.1 to 10 hours. In the vacuuming during the additional heating treatment, the pressure inside the container can be set to, for example, 50 Pa or less, preferably 10 Pa or less, with absolute vacuum being 0.

[0066] After the additional heating process, the contents can be cooled by an appropriate method. For example, the contents of the container can be cooled to near room temperature by introducing an inert gas such as argon into the container.

[0067] In the second hydrogenation, the precursor treated in the first hydrogenation is placed in a container under reduced pressure, as described above, and hydrogen is introduced into the container. The precursor used in the second hydrogenation may be the precursor treated in the first hydrogenation and further subjected to the additional heating treatment described above. The same container used in the first hydrogenation can be used in the second hydrogenation.

[0068] In the second hydrogenation process, the inside of the container is also reduced in pressure, and hydrogen is introduced into the container. The method of reducing the pressure inside the container is not particularly limited and can be done by known means. The degree of pressure reduction is also not particularly limited and can be 50 Pa or less when absolute vacuum is considered as 0, preferably 10 Pa or less. The temperature during pressure reduction is also not particularly limited and can be, for example, around room temperature, specifically -10 to 40°C.

[0069] In the second hydrogenation stage, the method of introducing hydrogen is not particularly limited, and for example, a wide range of known hydrogen introduction methods can be employed. Hydrogen is introduced into the container, for example, until the pressure inside the container (hydrogen pressure) reaches a desired pressure, for example, 0.3 MPa (meaning absolute pressure; 0.2 MPa if using gauge pressure). In the second hydrogenation stage, the pressure inside the container after hydrogen introduction is preferably 0.3 ± 0.05 MPa. The hydrogen introduction rate is also not particularly limited.

[0070] In the second hydrogenation process, after introducing hydrogen as described above until a predetermined pressurized state is reached, the temperature inside the container can be increased. This allows the hydrogenation of the precursor to proceed sufficiently. In the heating process in the second hydrogenation process, the temperature inside the container can be increased to, for example, a range of 100 to 500°C. After reaching the desired temperature, it can be maintained at that temperature for an appropriate period of time, for example, 0.1 to 10 hours.

[0071] Subsequently, while maintaining the pressurized state inside the container, the container is cooled to room temperature or below. This cooling process makes it more difficult for hydrogen incorporated into the precursor to escape, thus lowering the Curie temperature T c This makes it possible to suppress deviations, and the resulting hydride alloy is stable even in the atmosphere and does not easily release hydrogen.

[0072] Following the cooling process, the inside of the container is replaced with an inert gas such as argon, and then the treated material inside the container is collected. This treated material is a precursor that has been sufficiently hydrogenated, that is, the target hydrogenated alloy.

[0073] As described above, the hydrogenation in step 1 preferably comprises a first hydrogenation and a second hydrogenation, and in one embodiment, it is preferable to heat-treat the precursor treated by the first hydrogenation to 300°C or higher under reduced pressure (the additional heating treatment described above) after the first hydrogenation and before the second hydrogenation. The first hydrogenation and the subsequent additional heating treatment may each be performed once before the second hydrogenation, or each may be performed two or more times.

[0074] The hydrogenated alloy obtained in step 1 above may be used as the magnetic refrigeration material of the present invention, or it may be combined with other components as needed to form the magnetic refrigeration material of the present invention. In other words, it is preferable that the magnetic refrigeration material of the present invention comprises step 1 for producing the hydrogenated alloy.

[0075] The hydride alloy obtained in step 1 undergoes some degree of pulverization due to hydrogen embrittlement, but it is desirable to adjust the particle size for use as a magnetic refrigeration material. If necessary, pulverization may be performed to adjust the particle size. Examples of pulverization methods include mechanical pulverization in the presence of an inert gas (e.g., hammer mill) and jet mill pulverization using an inert gas.

[0076] The powder obtained by grinding can be adjusted to a predetermined particle size by classifying it using a sieve with an appropriate mesh size. Methods for confirming particle size include dynamic light scattering, laser diffraction, gravity sedimentation, and image imaging. The average particle size D50 of the magnetic refrigeration material powder is not particularly limited and can be, for example, 25 μm or more and 300 μm or less. The average particle size D50 of the powder is preferably 50 μm or more, more preferably 80 μm or more, even more preferably 90 μm or more, particularly preferably 100 μm or more, and also preferably 250 μm or less, more preferably 220 μm or less, even more preferably 200 μm or less, and particularly preferably 180 μm or less. In this invention, the average particle size D50 of the powder is a value measured by laser diffraction / scattering and represents the particle size when it is 50% of the volume-based particle size distribution. A HORIBA Partica LA-960 can be used as the measuring device.

[0077] By adjusting the particle size as described above, foreign matter present in the hydrogenated material can be eliminated. This foreign matter is thought to be generated by the hydrogenation process in step 1 and does not contribute to the thermomagnetic properties, so it is preferable to eliminate it. Elimination of foreign matter results in a stable change in magnetic entropy |ΔS M It can be a magnetic refrigeration material having |.

[0078] Here, in the present invention, the change in magnetic entropy |ΔS M |(J / (kg·K)) can be measured using a SQUID magnetometer. |ΔS| represents the change in magnetic entropy. M | is determined by measuring the magnetization under a constant magnetic field of a specific temperature range and using Maxwell's relation shown in equation (B) below from the magnetization-temperature curve.

[0079]

number

[0080] In equation (B), M represents magnetization, T represents temperature, and H represents the applied magnetic field.

[0081] The form of the magnetic refrigeration material of the present invention is not particularly limited. For example, it may be a powder, a molded body sintered by a sintering method, or a composite formed by molding a mixture of a hydrogenated alloy and a resin into any shape. When the magnetic refrigeration material of the present invention is a powder, the average particle size D50 of such powder can be, for example, 25 μm or more and 300 μm or less. The average particle size D50 of the powder is preferably 50 μm or more, more preferably 80 μm or more, even more preferably 90 μm or more, particularly preferably 100 μm or more, and also preferably 250 μm or less, more preferably 220 μm or less, even more preferably 200 μm or less, and particularly preferably 180 μm or less. In the present invention, the average particle size D50 of the powder is a value measured by laser diffraction and scattering, and represents the particle size when it is 50% of the volume-based particle size distribution. A HORIBA Partica LA-960 can be used as the measuring device.

[0082] The magnetic refrigeration material of the present invention can be applied to various types of magnetic refrigeration devices. The magnetic refrigeration device of the present invention is not particularly limited as long as it is equipped with the magnetic refrigeration material of the present invention, and can, for example, have a configuration similar to that of known magnetic refrigeration chamber devices.

[0083] In specifying the inventions contained herein, the components (properties, structures, functions, etc.) described in each embodiment of this disclosure may be combined in any way. That is, this disclosure encompasses all subject matter consisting of any combination of the combinatable components described herein. [Examples]

[0084] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these. For the sake of clarity, in the description of these examples, both the hydrogenated alloys included in the present invention in the examples and the hydrogenated alloys not included in the present invention in the comparative examples will be referred to as "hydrogenated alloys." Furthermore, an alloy obtained in the form of a slab by the strip casting method will be referred to as an alloy slab, and a material obtained by heat-treating an alloy slab will be referred to as a precursor.

[0085] (Example 1) First, a precursor (alloy) with an elemental composition ratio as shown in Example 1 of Table 1 was synthesized by the following procedure. The raw materials were weighed to obtain the composition ratio shown in Example 1 of Table 1, and melted in an argon gas (Ar) atmosphere in a high-frequency induction melting furnace to obtain a molten material. Next, the pouring temperature of this molten material was set to 1550°C, and the alloy slab was rapidly cooled and solidified by a strip casting method using a single-roll casting apparatus with a copper water-cooled roll to obtain an alloy slab. The obtained alloy slab was heat-treated in an Ar atmosphere at 1100°C for 20 hours to produce NaZn 13 A precursor with a crystalline structure of the type was obtained. The area fraction P of the R-enriched phase of this precursor was 0.83%.

[0086] The above precursor was hydrogenated in a hydrogenation apparatus to obtain a hydrogenated alloy. The hydrogenation was carried out with the precursor placed (contained) in the processing chamber. Specifically, the hydrogenated alloy was obtained by performing the following operations 1 to 7 in that order. This hydrogenated alloy was used as a magnetic refrigeration material. Operation 1; The first hydrogenation process was performed by evacuating the processing chamber containing the alloy slab at room temperature (25°C), reducing the pressure to below 10 Pa (with absolute vacuum being 0), and then introducing hydrogen until the pressure (hydrogen pressure) inside the processing chamber reached 0.3 MPa in absolute pressure. Operation 2; The treatment chamber was heated to a temperature of 300°C while maintaining a hydrogen pressure of 0.3 MPa, and this temperature was maintained for one hour. Operation 3; Next, while evacuating the processing chamber until the pressure was below 10 Pa, an additional heating process was performed until the ambient temperature reached 500°C, and this was maintained for 1 hour while continuing to evacuate. Operation 4; After that, argon was introduced into the processing chamber and cooled to room temperature. Operation 5; Next, evacuation was performed to reduce the pressure to 10 Pa or less with an absolute vacuum of 0, and then hydrogen was introduced until the pressure (hydrogen pressure) in the processing chamber reached 0.3 MPa in absolute pressure to perform the second hydrogenation. Operation 6; The temperature was raised to 150 °C and held for 30 minutes in a state where the hydrogen pressure was 0.3 MPa. Operation 7; Finally, after cooling to room temperature in a state where the hydrogen pressure was 0.3 MPa, it was replaced with argon, and the hydrogenated alloy was taken out.

[0087] (Examples 2 to 9, Comparative Examples 1 to 5) A magnetic refrigeration material was obtained by the same operation as in Example 1, except that the raw materials were weighed so that the elemental composition of the obtained precursor (alloy) would be the composition ratios shown in each of the examples and comparative examples in Table 1.

[0088] (Measurement of the area ratio of the R-rich phase) In each of the examples and comparative examples, the area ratio of the R-rich phase of the precursor used to obtain the magnetic refrigeration material was measured. Specifically, the precursor was embedded in an epoxy resin and cured, and rough polishing and precision polishing were performed with a wet polishing machine, and finally finished until the polished surface became a mirror surface to form an alloy cross-section. The cross-section was observed under the conditions of magnification 1000 times, acceleration voltage 20 kV, current 2×10 -8 A, beam diameter 1 μm, contrast 2500, brightness 500, and the cross-section was analyzed. In the backscattered electron composition image obtained thereby, a region surrounded by a rectangle with a short side of 85 μm and a long side of 120 μm was randomly determined. The total area S 2 of all the white regions visible in the region (85 μm×120 μm = 10200 μm 2 R (μm 2 ) was measured by the image analysis program shown in FIG. 1. The total area S R (μm 2The ratio of the area of ​​the aforementioned region to the area of ​​the R-enriched phase P was defined as the area ratio P of the R-enriched phase. That is, the area ratio P was defined as The following formula (A) P(%)={S R / (85×120)}×100 (A) It was calculated using the method described below.

[0089] (Pulverization test) 600 g of the magnetic refrigeration material (hydrogenated alloy) obtained in each example and comparative example, and 30 g of φ10 mm zirconia balls were placed in a 100 mL container and placed on a ball mill rotating stand (Nittokagaku Co., Ltd., Benchtop Pot Mill Rotating Stand ANZ-51S). The container was rotated at 100 rpm to perform the grinding process. The grinding process started at T0. After 1 minute from T0, the rotation was stopped, all the processed material in the container was removed, and the processed material was passed through a sieve with a mesh size of 212 μm. The mass that passed through the sieve was measured, and the remaining processed material on the sieve was returned to the container, and grinding was continued. Subsequently, after 3 minutes from T0, the same process was repeated, passing the material through a sieve with a mesh size of 212 μm and measuring the mass that passed through the sieve (mass below sieve). The remaining processed material on the sieve was returned to the container, and grinding was continued. The same operation was performed after 5 minutes, 10 minutes, and 20 minutes from T0, and the grinding process was completed. The sieved mass after completion (after the aforementioned 20 minutes) was measured, and this mass was defined as the "sieved mass after grinding" to evaluate the grinding performance.

[0090] (Evaluation of magnetocaloric properties) The magnetic refrigeration material used in the measurement of the sieved mass after the completion of the aforementioned pulverizability confirmation test was collected, and the magnetic calorific value of this magnetic refrigeration material was measured. A SQUID magnetometer (PPMS VersaLab, manufactured by Quantum Design Japan) was used to measure the magnetic susceptibility at each temperature, thereby determining the maximum value of the change in magnetic entropy (|ΔS). max |) was sought.

[0091] (Measurement of D50 in powder) In the above pulverizability test, a sample of magnetic refrigeration material (20 minutes after T0) that passed through a sieve with a mesh size of 212 μm was taken for D50 measurement, and the average particle size D50 (50% volume average particle diameter) of the sample was measured. For this measurement, a HORIBA Partica LA-960 was used as the measuring device.

[0092] (Evaluation results) Figure 2 shows copies of the backscattered electron composition images used for measuring the area fraction of the R-enriched phase. (a) is the backscattered electron composition image of the cross-section of the precursor used in Example 1, and (b) is the backscattered electron composition image of the cross-section of the precursor used in Comparative Example 1. As can be seen from Figure 2, the precursor used in Example 1 shows more white spots compared to the precursor used in Comparative Example 1, indicating an R-enriched phase, i.e., NaZn 13 It can be seen that a large number of phases containing more rare earth elements than the main phase are formed around the main phase.

[0093] Tables 1 to 6 show the composition of the precursor used in each example, and the "weight after sieving after grinding," "area ratio P of the R-enriched phase," and "maximum value of the change in magnetic entropy (|ΔS)" of the magnetic refrigeration material obtained from that precursor. max The evaluation results for |) are shown. Note that the value of z in equation (1) is not shown in Tables 1 to 6, but when z was estimated from the weight change before and after hydrogenation for all magnetic refrigeration materials, z was found to be z = 1.5.

[0094] Figure 3 shows a graph illustrating the results of the pulverization test for the magnetic refrigeration materials obtained in Example 1, Example 2, and Comparative Example 1. From Table 1 and Figure 3, it is clear that the magnetic refrigeration materials obtained in Examples 1 and 2 have superior pulverization properties compared to Comparative Example 1.

[0095] Table 7 shows the measurement results of D50 for the magnetic refrigeration materials obtained in each example and comparative example. Comparisons between Examples 1 and 2 and Comparative Example 1, Examples 3 and 4 and Comparative Example 2, Examples 4 and 5 and Comparative Example 2, Examples 6 and 7 and Comparative Example 3, Example 8 and Comparative Example 4, and Example 9 and Comparative Example 5 show that the examples with superior pulverization properties tend to have lower D50 values ​​than the comparative examples. These results also support the superior pulverization properties of the magnetic refrigeration materials in the examples.

[0096] [Table 1]

[0097] [Table 2]

[0098] [Table 3]

[0099] [Table 4]

[0100] [Table 5]

[0101] [Table 6]

[0102] [Table 7]

Claims

1. The following general formula (1) 【Chemistry 1】 [In formula (1), M represents one or more elements selected from the group consisting of Mn and Co. A represents the element Al. x, y, a, b, c, and z are numbers that satisfy 0 ≤ x ≤ 0.4, 1.0 < y ≤ 1.25, 0 ≤ a ≤ 0.04, 0.05 ≤ b ≤ 0.2, 0 ≤ c ≤ 0.01, and 0 < z ≤ 1.5, respectively. A magnetic refrigeration material comprising a hydrogenated alloy having a composition represented by [the formula shown].

2. The magnetic refrigeration material according to claim 1, wherein M is Mn or Co.

3. A method for producing a magnetic refrigeration material according to claim 1 or 2, The following general formula (2) 【Chemistry 2】 [In formula (2), M, A, x, y, a, b, and c are the same as M, A, x, y, a, b, and c in formula (1), respectively.] A method for producing a magnetic refrigeration material, comprising the step of obtaining the hydrogenated alloy by hydrogenating a precursor having a composition represented by the following, wherein the precursor has an area ratio P of 0.4 to 3.0% as calculated by the area ratio measurement of the R-enriched phase described below. <Measurement of area ratio of R-enriched phase> In the backscattered electron composition image obtained by observing the cross-section of the precursor at 1000x magnification using EPMA, the total area S of all white regions present in the region enclosed by a rectangle with a short side of 85 μm and a long side of 120 μm. Ｒ (μm ２ ) Measure, The following formula (A) P(%)={S Ｒ / (85×120)}×100 (A) The area ratio P of the precursor is calculated accordingly.

4. The hydrogenation comprises a first hydrogenation and a second hydrogenation. The first hydrogenation described above is This is carried out by placing the precursor in a container under reduced pressure and introducing hydrogen into the container. The second hydrogenation described above is The process is carried out by placing the precursor treated by the first hydrogenation in a container under reduced pressure and introducing hydrogen into the container. A method for producing a magnetic refrigeration material according to claim 3, wherein, after the first hydrogenation and before the second hydrogenation, the precursor treated by the first hydrogenation is subjected to a heat treatment at 300°C or higher under reduced pressure.

5. A magnetic refrigeration apparatus comprising the magnetic refrigeration material described in claim 1 or 2.

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