Raw material alloy for magnetic refrigeration material and method for manufacturing the same, and magnetic refrigeration material and method for manufacturing the same

Abstract

To provide a raw material alloy for a magnetic refrigeration material, which makes it possible to control the hydrogen storage amount and to homogenize the hydrogen concentration distribution under a wider range of hydrogenation conditions than in the conventional art; a method for producing the raw material alloy for the magnetic refrigeration material; a magnetic refrigeration material having a high ΔS and a controlled transition temperature; and a method for producing the magnetic refrigeration material.SOLUTION: A raw material alloy for a magnetic refrigeration material according to the present invention is expressed by a composition formula of La(1-a)Ra(Fe(1-b-c-d)TMbSicAd)z, and contains, as a sub-phase containing R, a total amount of 0.3 vol.% or less of at least one phase selected from (La,R)MSi phase, (La,R)5M3 phase, (La,R)6M11Si3 phase, and (La,R)2M17 phase, contains 0.1 vol.% or more and 2.2 vol.% or less of an α-Fe phase, and contains, as the remainder, a (La,R)(Fe,TM,Si,A) phase as the main phase. The magnetic refrigeration material according to the present invention is obtained by hydrogenation heat treatment of the raw material alloy for the magnetic refrigeration material according to the present invention.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a raw material alloy for a magnetic refrigeration material having a controlled transition temperature and a high magnetic entropy change, a method for producing the same, and a magnetic refrigeration material and a method for producing the same. [Background technology]

[0002] Because fluorocarbons are ozone depleting substances and global warming gases, new refrigeration and air conditioning systems that do not use fluorocarbons are attracting attention for environmental conservation. Although refrigerants that can replace fluorocarbons have been actively developed, no new refrigerants that are satisfactory in terms of performance, cost, and safety have yet been put to practical use.

[0003] On the other hand, unlike conventional refrigeration and air conditioning systems, magnetic refrigeration systems that utilize the change in entropy (magneto-caloric effect, ΔS) that accompanies an increase in the magnetic field have been attracting attention. Materials with a large absolute value of ΔS include Mn(As 1-x Sb x ) (Patent Document 1) and La(Fe 1-x S x ) 13 H z (Patent Document 2) and others are cited. In particular, the former has a very large ΔS of -30 J / kgK and can be an excellent magnetic refrigeration material. However, Mn(As 1-x Sb x ) is difficult to apply in practice because of the toxicity of As. 1-x S x ) 13 H z ΔS is -25J / kgK and Mn(As 1-x Sb x ), and its constituent elements are non-toxic and not rare metals, making it the most promising material. The change in ΔS is also proportional to the magnetic transition temperature (T c ) and one type of material can only operate at a certain temperature, so a refrigeration system that needs to create a wide temperature difference cannot be realized. Therefore, methods such as replacing some of the components with other elements are used to change the operating temperature.

[0004] A requirement for these materials is that they must operate near room temperature (approximately -70 to +70°C). However, unlike conventional magnetic refrigeration, which has been used as a means of generating extremely low temperatures that are difficult to achieve using gas refrigeration, magnetic refrigeration at the above operating temperatures has the problem that the magnetocaloric effect decreases because lattice vibrations cannot be ignored. This problem can be solved by using these lattice vibrations as a heat storage effect. The AMR (Active Magnetic Regenerative) cycle, which uses these lattice vibrations as a heat storage effect, has been developed, and refrigeration and air conditioning systems that operate near room temperature using the magnetocaloric effect are now becoming a reality.

[0005] In the AMR cycle, the magnetic refrigeration material is filled with a gap that allows a heat transfer medium such as water to pass through (called the bed section). The heat transfer medium can move to the high-temperature end and low-temperature end through the gap. With the heat transfer medium on the low-temperature end side, a magnetic field is applied to the bed section using a permanent magnet or the like to reduce the entropy of the magnetic refrigeration material and increase its temperature. The heat transfer medium is moved from the low-temperature end to the high-temperature end. At this time, the heat transfer medium receives heat from the magnetic refrigeration material and moves to the high-temperature end, where it is discharged using a heat exchanger. Next, the magnetic field of the permanent magnet is removed, increasing the entropy of the magnetic refrigeration material and decreasing its temperature. The heat transfer medium is moved from the high-temperature end to the low-temperature end. At this time, the heat transfer medium is cooled by the magnetic refrigeration material. The cooled heat transfer medium absorbs heat in the heat exchanger. By repeating this cycle, a temperature difference is generated between the high-temperature end and the low-temperature end, creating a refrigeration cycle.

[0006] In the AMR cycle, the temperature difference that can be generated with a single-composition material is about 2 to 10 K, depending on the material. In order to generate a large temperature difference required for applications such as refrigerators and air conditioners, it is necessary to use materials with different magnetic transition temperatures (T c ) from the high temperature end to the low temperature end of the magnetic refrigeration material. c By filling the materials in order from high to low (cascade filling) and exchanging heat between adjacent magnetic refrigeration materials, a large temperature difference can be generated. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2003-28532 A [Patent Document 2] JP 2006-89839 A Summary of the Invention [Problem to be solved by the invention]

[0008] For heat exchange to occur between the cascade-packed magnetic refrigeration materials, the operating temperatures of the adjacent magnetic refrigeration materials must overlap. 1-x S x ) 13 In the case of , the half-width is narrow at 3 to 5 K, so it has become clear that controlling the operating temperature (transition temperature) with high precision is preferable for good heat exchange.

[0009] However, La(Fe 1-x S x ) 13 The operating temperature of varies depending on the composition of the material as well as on manufacturing conditions such as the alloy homogenization conditions and hydrogenation conditions during manufacturing, and ΔS is similarly significantly affected by the manufacturing conditions (for example, the hydrogen concentration distribution within the material). Therefore, it was difficult to precisely control the transition temperature and achieve a high ΔS value on a manufacturing scale of kg or more, rather than in research-based experiments on a few gram scale.

[0010] Hydrogenation heat treatment is a particular problem. It is generally known that the degree of hydrogen absorption changes depending on the pretreatment (activation treatment) conditions, but it is also known that the degree of hydrogen absorption changes depending on the temperature and time of hydrogenation heat treatment, the atmosphere during cooling, and the cooling rate. 1-x S x ) 13Because the hydrogen storage capacity of the material and the hydrogen concentration distribution within the material change, it is not easy to control the hydrogen storage capacity (control of the transition temperature) and homogenize the hydrogen concentration distribution (high ΔS) on a manufacturing scale.

[0011] The present invention has been made in view of the above circumstances, and aims to provide a raw material alloy for a magnetic refrigeration material and a manufacturing method thereof, and a magnetic refrigeration material and a manufacturing method thereof, which are capable of precisely controlling the transition temperature in response to changes in hydrogenation conditions and obtaining a high ΔS. [Means for solving the problem]

[0012] As a result of extensive research into achieving the above-mentioned object, the inventors have discovered that by adjusting the composition of the raw material alloy to a predetermined range and performing a homogenization treatment on the produced raw material alloy so that the precipitation amounts of the subphase containing a rare earth element and α-Fe are in a predetermined ratio, it is possible to control the amount of hydrogen absorption over a wide range of hydrogenation conditions, thereby adjusting the transition temperature, and to homogenize the hydrogen concentration distribution, thereby achieving a high ΔS, and have completed the present invention.

[0013] Therefore, the present invention provides the following raw alloy for a magnetic refrigeration material and a method for producing the same, as well as a magnetic refrigeration material and a method for producing the same. 1.La (1-a) R a (Fe (1-b-c-d) TM b S c A d ) z (R is one or more rare earth elements selected from Ce, Pr, and Nd; TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and the following conditions are satisfied: 0≦a≦0.5, 0≦b≦0.03, 0.09≦c≦0.14, 0≦d≦0.05, and 13.0≦z≦13.4.) 5 M 3 Phase, (La,R) 6 M 11 S 3 phase, and (La,R)2 M 17 contains at least one phase (M is one or more elements selected from Fe and TM) in a total amount of 0.3% by volume or less as a sub-phase containing R, contains an α-Fe phase in an amount of 0.1% by volume or more and 2.2% by volume or less, and the balance contains a (La, R)(Fe, TM, Si, A) phase as a main phase, which is a raw material alloy for a magnetic refrigeration material. 2. The raw material alloy for a magnetic refrigeration material according to 1, wherein the average circular approximation diameter of the α-Fe phase is 6 μm or less. 3. La (1-a) R a (Fe (1-b-c-d) TM b Si c A d ) z (R is one or more rare earth elements selected from Ce, Pr, and Nd, TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag, A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and 0 ≦ a ≦ 0.5, 0 ≦ b ≦ 0.03, 0.09 ≦ c ≦ 0.14, 0 ≦ d ≦ 0.05, 13.0 ≦ z ≦ 13.4), and the alloy represented by the composition formula is heat-treated at 1000 to 1300 °C for 10 to 100 hours in a vacuum atmosphere or an inert gas atmosphere, which is a method for producing a raw material alloy for a magnetic refrigeration material according to 1 or 2. 4. La (1-a) R a (Fe (1-b-c-d) TM b Si c A d ) z H e (R is one or more rare earth elements selected from Ce, Pr, and Nd, TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag, A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and 0 ≦ a ≦ 0.5, 0 ≦ b ≦ 0.03, 0.09 ≦ c ≦ 0.14, 0 ≦ d ≦ 0.05, 0 < e ≦ 1.5, 13.0 ≦ z ≦ 13.4), and is represented by the composition formula, and (La, R)MSi phase, (La, R) 5 M 3 phase, (La, R) 6 M 11 Si 3Phase, (La,R) 2 M 17 phase and at least one of the hydride phases thereof (M is one or more elements selected from Fe and TM) in a total amount of 0.3 vol% or less as a subphase containing R, α-Fe phase in an amount of 0.1 vol% to 2.2 vol%, and the balance being (La, R)(Fe, TM, Si, A). 13 H e A magnetic refrigeration material containing the phase as a main phase. 5. The magnetic refrigeration material according to 4, wherein the α-Fe phase has an average circular approximation diameter of 6 μm or less. 6. La (1-a) R a (Fe (1-b-c-d) TM b S c A d ) z (R is one or more rare earth elements selected from Ce, Pr, and Nd; TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and the following conditions are satisfied: 0≦a≦0.5, 0≦b≦0.03, 0.09≦c≦0.14, 0≦d≦0.05, and 13.0≦z≦13.4.) 5 M 3 Phase, (La,R) 6 M 11 S 3 phase, and (La,R) 2 M 17 6. A method for producing a magnetic refrigeration material according to claim 4 or 5, wherein the alloy contains at least one of the phases (M is one or more elements selected from Fe and TM) as a subphase containing R in a total amount of 0.3 volume % or less, the α-Fe phase in an amount of 0.1 volume % or more and 2.2 volume % or less, and the remainder is the (La, R)(Fe, TM, Si, A) phase as a main phase, and the cooling rate during hydrogenation heat treatment is 0.1°C / min or more and 50°C / min or less. Effect of the Invention

[0014] According to the present invention, it is possible to provide a raw material alloy for a magnetic refrigeration material that is capable of controlling the amount of hydrogen absorption and homogenizing the hydrogen concentration distribution over a wider range of hydrogenation conditions than conventional methods, and a method for manufacturing the same, as well as a magnetic refrigeration material with a high ΔS and a controlled transition temperature and a method for manufacturing the same. [Brief description of the drawings]

[0015] [Figure 1] 3 is a photograph of the structure of the alloy for magnetic refrigeration material obtained in Comparative Example 1. [Diagram 2] 4 is a photograph of the structure of the alloy for magnetic refrigeration material obtained in Example 3. [Diagram 3] 1 shows the results of measuring the mT characteristics of the alloys for magnetic refrigeration materials obtained in Examples 1 to 3 and Comparative Examples 1 to 4. [Figure 4] 1 shows the results of measuring the mT characteristics of the magnetic refrigeration materials obtained in Examples 1 to 3 and Comparative Examples 1 to 4. [Diagram 5] 11 is a photograph of the structure of the alloy for magnetic refrigeration material obtained in Comparative Example 5. [Figure 6] 1 is a photograph of the structure of the alloy for magnetic refrigeration material obtained in Example 4. [Figure 7] 1 is a photograph of the structure of the alloy for magnetic refrigeration material obtained in Example 5. [Figure 8] 1 shows the results of measuring the mT characteristics of the magnetic refrigeration materials obtained in Examples 4 to 5 and Comparative Example 5. [Figure 9] 1 shows the results of measuring the mT characteristics of the alloys for magnetic refrigeration materials obtained in Examples 4 to 5 and Comparative Example 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The raw alloy for magnetic refrigeration material of the present invention is La (1-a) R a (Fe (1-b-c-d) TM b S c A d ) z(R is one or more rare earth elements selected from Ce, Pr, and Nd; TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and the following conditions are satisfied: 0≦a≦0.5, 0≦b≦0.03, 0.09≦c≦0.14, 0≦d≦0.05, and 13.0≦z≦13.4.) 5 M 3 Phase, (La,R) 6 M 11 S 3 phase, and (La,R) 2 M 17 The alloy contains at least one of the phases (wherein M is one or more elements selected from Fe and TM) in a total amount of 0.3 vol% or less as a subphase containing R, and contains α-Fe phase in an amount of 0.1 vol% to 2.2 vol%, with the balance being (La, R)(Fe, TM, Si, A). 13 The raw material alloy for magnetic refrigeration contains the phase as a main phase.

[0017] In the above composition formula, R is one or more rare earth elements selected from Ce, Pr, and Nd, and a is 0 to 0.5, preferably 0.2 to 0.4. A method is known in which ΔS and transition temperature are changed by substituting a part of La with other rare earth elements, and high properties can be obtained by substituting a part of La with one or more rare earth elements selected from Ce, Pr, and Nd, in particular, so it is desirable to substitute an appropriate amount according to the required magnetic properties. However, if the substitution ratio is large, the RM may be deteriorated when the raw alloy for magnetic refrigeration material is obtained by performing homogenization treatment. 13 Since a different phase other than the Fe phase is stably formed and the magnetic properties including a decrease in ΔS are deteriorated, the substitution ratio is 0.5 or less.

[0018] In the above composition formula, TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag, and b is 0 to 0.03, preferably 0.005 to 0.025. The transition temperature of the magnetic refrigeration material obtained by subjecting the raw alloy for magnetic refrigeration material to a hydrogenation heat treatment, which will be described later, is controlled by controlling the amount of hydrogen storage or the amount of TM added. However, since it is difficult to control the transition temperature of about 1 to 3°C required for AMR by controlling the amount of hydrogen storage alone, the TM element is added to control it. However, when b exceeds 0.03, TM becomes a cause of RM after homogenization treatment. 13 Phases are less likely to form.

[0019] The Si content c in the above composition formula is 0.09 to 0.14, and preferably 0.095 to 0.11. The smaller c is, the greater the magnetization change due to phase transition. 13 The phase becomes unstable, making it difficult to obtain a raw alloy for magnetic refrigeration material by homogenization. On the other hand, if c is greater than 0.14, the phase transition approaches a second-order phase transition, and the ΔS of the raw alloy for magnetic refrigeration material obtained after homogenization decreases. If c is 0.095 or more, an alloy in which 95% or more is the main phase can be easily obtained by general homogenization, for example, treatment at 1100°C for 50 hours. On the other hand, the smaller c is, the larger ΔS is, so c is preferably 0.11 or less. ΔS is the jump in entropy (S) that appears at the phase transition temperature.

[0020] In the above composition formula, A is one or more elements selected from Al, Ga, P, Ge, Sn and In, and d is 0 to 0.05, preferably 0.03 or less. Since these substitution elements A are substitution elements for Si, if the addition ratio exceeds 0.05, RM 13 As the phase transition approaches a second-order phase transition, ΔS decreases significantly.

[0021] In the above composition formula, z is 13.0 or more and 13.4 or less, and preferably 13.0 or more and 13.2 or less. As described later, in order to appropriately control the hydrogen storage amount and hydrogen concentration distribution in the present invention, the (La,R)MSi phase and the (La,R) 5 M 3 Phase, (La,R) 6 M 11 S 3 Phase, (La,R) 2 M 17 Since the volume ratio of the RM phase and its hydride phase (M is one or more elements selected from Fe and TM) must be equal to or less than a certain value, z must be 13.0 or more. In addition, if z exceeds 13.4, the RM phase responsible for the magnetocaloric effect may not be able to be fully depleted. 13 H x Since the amount of phase is reduced, the volumetric output of the magnetic refrigeration material is reduced.

[0022] Incidentally, Fe is the balance of TM, Si, and A. In addition to the above elements, the inclusion of unavoidable impurities such as oxygen, nitrogen, and carbon is permitted, but the content thereof is preferably as low as possible.

[0023] The raw alloy for magnetic refrigeration of the present invention is NaZn 13 (La,R)(Fe,TM,Si,A) type crystal structure 13 The volume ratio of the main phase is the remainder of the subphase, which will be described later.

[0024] The raw alloy for magnetic refrigeration material of the present invention has a subphase containing R, which is a (La, R) MSi phase and a (La, R) 5 M 3 Phase, (La,R) 6 M 11 S 3 phase, and (La,R) 2 M 17The magnetic refrigeration material contains at least one of the subphases, and the total amount of the subphases is 0.3 volume % or less. Here, M is one or more elements selected from Fe and TM. If the magnetic refrigeration material contains more than this amount of subphases, microcracks will occur starting from the subphases during the hydrogenation heat treatment described below, causing the magnetic refrigeration material to be crushed. This increases the hydrogen absorption and hydrogen release capabilities of the magnetic refrigeration material, making it easier to absorb hydrogen in a hydrogen atmosphere and easier to release hydrogen in a non-hydrogen atmosphere during the cooling process during the hydrogenation heat treatment. This makes it difficult to appropriately control hydrogen absorption and hydrogen concentration distribution during the hydrogenation heat treatment.

[0025] The volume ratio of the α-Fe phase is 0.1% or more and 2.2% or less. The α-Fe phase does not absorb hydrogen and has high toughness, so it is considered to suppress microcracks caused by the subphase containing R described above. For this reason, it is preferable to include the α-Fe phase in the magnetic refrigeration material, but if the volume ratio of the α-Fe phase exceeds 2.2%, the amount of the main phase responsible for the magnetocaloric effect decreases, and the volumetric output of the obtained magnetic refrigeration material decreases, which is not appropriate.

[0026] The average circular approximation diameter of the α-Fe phase is 6 μm or less. The average circular approximation diameter is obtained by binarizing 20 photographs taken by SEM using the difference in contrast due to the composition, calculating the number and area of ​​the α-Fe phase, and calculating the average diameter assuming that the α-Fe phase is circular. The α-Fe phase contributes to improving the toughness of the material, but in order to do so, it must be properly dispersed in the raw alloy for the magnetic refrigeration material. If the average circular approximation diameter of the α-Fe phase exceeds 6 μm, the α-Fe phase is not properly dispersed and the toughness of the material is not improved, so that microcracks are generated in the magnetic refrigeration material, making it difficult to appropriately control the amount of hydrogen absorption and the hydrogen concentration distribution during hydrogenation heat treatment. The lower limit of the range of the average circular approximation diameter of the α-Fe phase is not particularly limited, but is, for example, 0.1 μm.

[0027] The compositional analysis and calculation of the volume fraction of the above-mentioned main phase, secondary phase, and α-Fe can be performed using SEM. Specifically, using 20 photos obtained by SEM, binarization is performed by utilizing the contrast difference due to the composition, and the area of each phase is calculated for each photo. Then, the area fraction of each phase is calculated for each photo, and the average value of the area fractions of each phase in the 20 photos is taken as the volume fraction of each phase.

[0028] Note that, as described later, a magnetic refrigeration material can be obtained by hydrogenating the magnetic refrigeration material alloy of the present invention. However, if it is not necessary to increase the magnetic transition temperature, the magnetic refrigeration material alloy of the present invention can be directly used for a desired application.

[0029] The magnetic refrigeration material of the present invention can be obtained by subjecting the above-mentioned raw material alloy for magnetic refrigeration material to a hydrogenation heat treatment described later, and La (1-a) R a (Fe (1-b-c-d) TM b Si c A d ) z H e (R is one or more rare earth elements selected from Ce, Pr, and Nd, TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag, A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and 0 ≦ a ≦ 0.5, 0 ≦ b ≦ 0.03, 0.09 ≦ c ≦ 0.14, 0 ≦ d ≦ 0.05, 0 < e ≦ 1.5, 13.0 ≦ z ≦ 13.4 are satisfied), and is represented by the compositional formula, and at least one of the (La,R)MSi phase, (La,R) 5 M 3 phase, (La,R) 6 M 11 Si 3 phase, (La,R) 2 M 17 phase, and their hydride phases (M is one or more elements selected from Fe and TM) is contained as a secondary phase containing R with a total amount of 0.3% by volume or less, the α-Fe phase is contained at 0.1% by volume or more and 2.2% by volume or less, and the balance is (La,R)(Fe,TM,Si,A) 13 He The magnetic refrigeration material contains the phase as a main phase.

[0030] The magnetic refrigeration material of the present invention is used in a hydrogenated state in order to increase the transition temperature. When hydrogenated, the above-mentioned magnetic refrigeration material as a whole can theoretically occlude up to 3.0 atomic % of hydrogen, but under atmospheric pressure, it can usually occlude approximately 1.5 atomic % or less of hydrogen. When the magnetic refrigeration material is intended to be used at room temperature, it is generally used in a hydrogenated state in order to increase the transition temperature.

[0031] In the above composition formula, e is greater than 0 and is equal to or less than 1.5. As mentioned above, it is necessary to change e together with b depending on the transition temperature required for the magnetic refrigeration material. However, if e exceeds 1.5, it is difficult to obtain RM in the air. 13 H X This is not practical because the phase becomes unstable and hydrogen is released from the material over time.

[0032] The amount of hydrogen contained in the magnetic refrigeration material can be determined by the following method. The hydrogen concentration contained in the magnetic refrigeration material of the present invention is about 1000 to 2000 ppm, but it is generally difficult to measure a hydrogen concentration difference of about tens of ppm for a material with a hydrogen concentration of several thousand ppm. Therefore, the amount of hydrogen can be estimated by the following method and used as the amount of hydrogen in the magnetic refrigeration material. Specifically, an alloy with the same composition and homogenization conditions is subjected to activation treatment in which heat is treated in a vacuum, and then hydrogen is introduced and hydrogen is treated under predetermined heat treatment conditions. After that, the alloy is cooled to room temperature while maintaining the hydrogen atmosphere to prepare a comparative sample. This sample is regarded as a sample containing saturated hydrogen at room temperature, and the hydrogen equivalent is set to 1.5. The transition temperatures T before and after hydrogenation of this sample are peak The change in T p_max is measured using the method described below, and then the transition temperature T peak After measuring, T p_max The hydrogen equivalent can be estimated from the ratio of

[0033] The above-mentioned T peakThe mT characteristic of the sample is measured using, for example, the VSM unit of a small cryogen-free physical property measuring device (manufactured by Quantum Design Co., Ltd., product name "VersaLab"), and the transition temperature is calculated by temperature differentiation of the mT characteristic to obtain the dm / dT-T characteristic, and the temperature at which the peak is obtained is called the T peak It can be calculated as:

[0034] Next, a method for producing the raw alloy for a magnetic refrigeration material and the magnetic refrigeration material of the present invention will be described. The raw alloy for a magnetic refrigeration material and the method for producing a magnetic refrigeration material of the present invention are used to produce the above-mentioned magnetic refrigeration material, and include a melting step in which a raw material is melted to obtain a raw alloy containing La, Fe, and Si, a homogenization step in which the obtained raw alloy is heat-treated to obtain a raw alloy for a magnetic refrigeration material with a predetermined structure, and a hydrogenation heat treatment step in which hydrogen is absorbed into the alloy as necessary to increase the magnetic transition temperature.

[0035] In the melting step, the metal or alloy that is the raw material of each element is weighed so as to obtain the composition of the raw alloy for magnetic refrigeration material of the present invention described above, and the raw material is heated to 1500°C by high-frequency melting in an Ar atmosphere, for example, to melt, and then cooled as quickly as possible at a cooling rate of 300 to 1000°C / sec to obtain an alloy. Although there is no particular limitation, the casting of this alloy can be performed by strip casting or liquid quenching. With the strip casting method, rapid cooling can be performed, making it easy to obtain a fine and good structure. With the liquid quenching method, cooling can be performed more quickly, making it easy to obtain a fine and good structure. In this way, a raw alloy having a predetermined composition can be obtained.

[0036] In the homogenization process, the raw alloy obtained in the melting process is subjected to a heat treatment for homogenizing the structure. This homogenization process is not particularly limited because it depends on the alloy structure and composition, but can be performed in a vacuum atmosphere or an inert gas atmosphere at a temperature range of 1100°C to 1300°C. In particular, when a part of La is replaced with a rare earth element as described above, the optimal heat treatment temperature in the homogenization process changes. For example, when a part of La is replaced with Ce, the temperature tends to vary by about -10 to -20°C compared to the case of no replacement, and when replaced with Pr or Nd, the temperature tends to vary by about +10 to +30°C. In addition, the temperature varies by several tens of degrees depending on the amount of Si and the element type and the amount of replacement that replaces a part of the Fe element. For example, when the amount of Si is small, the decomposition temperature decreases, so the optimal heat treatment temperature tends to decrease. Therefore, the optimal heat treatment temperature is not limited to the above range. The optimal heat treatment temperature means the temperature at which the magnetocaloric effect is highest, that is, the peak value of the dm / dT-T characteristic is maximum, and can be experimentally confirmed taking the above factors into consideration. The homogenization time can be appropriately adjusted depending on the state of the alloy obtained in the melting step, and can be, for example, in the range of 1 hour to 100 hours, and more preferably 25 hours to 75 hours. In this range, the amount of the subphase containing the rare earth element (R), especially R 5 A 3 The amount of the α-Fe phase and the amount of α-Fe can be controlled within an optimal range. In addition, the homogenization treatment is preferably performed in an Ar atmosphere so that deviation from the composition of the raw material alloy caused by evaporation of certain elements from the raw material alloy can be suppressed. By such a homogenization treatment process, the raw material alloy for magnetic refrigeration material of the present invention can be obtained.

[0037] In the hydrogenation heat treatment step, when the magnetic transition temperature of the obtained raw alloy for magnetic refrigeration material is increased, hydrogen is absorbed in the raw alloy for magnetic refrigeration material under a hydrogen atmosphere, thereby obtaining the magnetic refrigeration material of the present invention. The specific conditions are not particularly limited, but the hydrogen atmosphere can be, for example, 0.1 to 0.25 MPa. The temperature during hydrogenation can be, for example, 200°C or higher and 500°C or lower. In this range, the hydrogen saturation concentration at the treatment temperature can be reached in a relatively short time. The hydrogenation treatment time can be, for example, 1 hour or higher and 200 hours or lower, and more preferably 3 hours or higher and 10 hours or lower. After hydrogen introduction, a cooling treatment is performed to room temperature, and the hydrogen absorption amount and hydrogen concentration distribution can be controlled by cooling at a rate of 50°C / min or lower in an inactive and non-hydrogen atmosphere such as a hydrogen atmosphere or an Ar atmosphere. Specifically, it is preferable to cool at a rate of 0.1°C / min or higher and 50°C / min or lower after the hydrogenation heat treatment. It is known that the faster the cooling rate after hydrogenation, the more precisely the amount of hydrogen absorbed can be controlled, but in consideration of productivity, the cooling rate must be 50°C / min or less. If the cooling rate is slower than 0.1°C / min, hydrogen absorption or release during cooling may become impossible to ignore. EXAMPLES

[0038] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0039] [Examples 1 to 3, Comparative Examples 1 to 4] La metal, Ce metal, Mn metal, Si metal, and electrolytic iron were weighed out to obtain the desired composition, and the mixture was melted by heating to 1500°C in an Ar gas atmosphere in a high-frequency melting furnace, and then cooled at a rate of 300-1000°C / sec by strip casting to produce an alloy ribbon with an average thickness of approximately 300 μm. The composition of the obtained raw alloy for magnetic refrigeration material is shown in Table 1. The composition of the alloy was analyzed using a high-resolution ICP optical emission spectrometer (manufactured by Hitachi High-Tech Corporation, product name "SPS3500DD").

[0040] [Table 1]

[0041] The alloys of Examples 1 to 3 and Comparative Examples 1 to 4 were homogenized under the optimal homogenization conditions of 1115°C for 50 hours in an Ar atmosphere to obtain alloys for magnetic refrigeration materials. The volume ratios of the subphases and α-Fe contained in the alloys for magnetic refrigeration materials, the main phase composition, and the subphase composition were then analyzed using a scanning electron microscope (SEM) (manufactured by JEOL Corporation, product name "JSM-IT300LV"). The volume ratios were obtained by performing image analysis on 20 SEM images. The main phase and subphase compositions were analyzed using EDS. The amounts of the subphases, the amount of the α-Fe phase, and the average circular approximation diameter of the α-Fe phase for each alloy are shown in Table 2. In addition, Comparative Example 1 and Example 3 are shown in Fig. 1 and Fig. 2, respectively, as examples of structural photographs.

[0042] [Table 2]

[0043] The obtained alloy for magnetic refrigeration material was subjected to the following hydrogenation heat treatment. First, activation treatment was performed in a vacuum at 500°C for 2 hours, and then hydrogen at 0.15 MPa was introduced and hydrogenation heat treatment was performed at 200°C for 24 hours. After hydrogenation heat treatment, the alloy was cooled to room temperature at a cooling rate of 0.1°C / min while maintaining the hydrogen atmosphere, and a magnetic refrigeration material was obtained. The composition after hydrogenation is shown in Table 3. The amount of hydrogen in the alloy was determined by the following method. The hydrogen concentration of this material is about 1000 to 2000 ppm, but since it is generally difficult to measure the hydrogen concentration difference of about tens of ppm for a substance with a hydrogen concentration of several thousand ppm, the amount of hydrogen was estimated by the following method. First, as a comparison sample, an alloy with the same composition and homogenization conditions was subjected to activation treatment in a vacuum at 500°C for 2 hours, then hydrogen at 0.15 MPa was introduced, hydrogenation heat treatment was performed at 500°C for 2 hours, and then cooled to room temperature for 60 hours while maintaining the hydrogen atmosphere. This sample was considered to be saturated with hydrogen at room temperature, and the hydrogen equivalent was set to 1.5. The transition temperature T peak The change in T p_max was measured using the method described below. Next, the transition temperature T peak After measuring, T p_max The hydrogen equivalent was estimated from the ratio of

[0044] The mT characteristics of the obtained magnetic refrigeration material were then measured using the VSM unit of a small cryogen-free physical property measuring device (manufactured by Quantum Design Co., Ltd., product name "VersaLab"). The transition temperature was calculated by temperature differentiation of the mT characteristics to obtain the dm / dT-T characteristics, and the temperature at which the peak was obtained was defined as T peak The mT characteristic measurement results are shown in Figure 3 and Table 4.

[0045] [Table 3]

[0046] [Table 4]

[0047] In Comparative Examples 1 and 2, the transition temperature is high at around 306 K, and the amount of hydrogen absorption cannot be appropriately controlled. This is thought to be because the amount of subphases is large, which causes frequent microcracks, which cause the magnetic refrigeration material to be crushed, resulting in hydrogen absorption during cooling. Comparative Example 3 has a transition temperature of 294 K, but as shown in Figure 3, it has multiple transition points with multiple stages. This is because there is an uneven distribution of hydrogen concentration within the material, and the RM has multiple hydrogen concentrations. 13 H x This is due to the presence of the α-Fe phase. This is thought to be because the amount of subphases caused partial microcracks, which led to the alloy being crushed into various particle sizes and non-uniform hydrogen absorption. In addition, in Comparative Example 4, the transition temperature was well controlled, but the dm / dT was low. This is because the amount of α-Fe phase in the material was large, and the RM 13 H x This is believed to be because the total amount of phases decreased, resulting in a decrease in the total amount of magnetocaloric effect. In Examples 1 to 3, the transition temperature was about 291 K, and dm / dT was good at 0.02 or more, and it can be judged that the control of the hydrogen absorption amount and the homogenization of the hydrogen concentration distribution were performed well.

[0048] Separately from the above, the obtained alloy for magnetic refrigeration material was subjected to the following hydrogenation heat treatment. First, activation treatment was performed in a vacuum at 500°C for 2 hours, and then hydrogen at 0.15 MPa was introduced and hydrogenation heat treatment was performed at 200°C for 24 hours. After the hydrogenation heat treatment, the hydrogen was evacuated and the alloy was cooled to room temperature in a non-hydrogen atmosphere (Ar atmosphere) at a cooling rate of 50°C / min. The composition at this time is shown in Table 5. The mT characteristics of the obtained magnetic refrigeration material were then evaluated using the same method. The results of the mT characteristic measurements are shown in Figure 4 and Table 6.

[0049] [Table 5]

[0050] [Table 6]

[0051] In Comparative Examples 1 and 2, the transition temperature of the mT curve is unclear and the maximum value of dm / dT is low. This is thought to be due to the non-uniform hydrogen concentration distribution in the material, but the cause is the RM due to the crushing of the alloy caused by the generation of microcracks during hydrogenation. 13 H x This is believed to be because the reactivity of the phase was improved, which resulted in increased release of hydrogen in a non-hydrogen atmosphere. Examples 1 to 3 and Comparative Examples 3 and 4 showed good results.

[0052] [Examples 4 and 5, Comparative Example 5] La metal, Ce metal, Si metal, and electrolytic iron were weighed to obtain the desired composition, and the materials were melted in an Ar gas atmosphere in a high-frequency melting furnace by heating to 1500°C. The materials were then cooled at a rate of 300-1000°C / sec by strip casting to produce an alloy ribbon with an average thickness of about 300 μm. The composition of the obtained raw alloy for magnetic refrigeration material was (La 0.7 Ce 0.3 )(Fe 0.895 S 0.105 ) 13.0 The composition of the alloy was analyzed using a high-resolution ICP optical emission spectrometer (manufactured by Hitachi High-Tech Corporation, product name "SPS3500DD").

[0053] The obtained raw alloy for magnetic refrigeration material was subjected to homogenization treatment at 1130℃, 1140℃, and 1150℃ for 50 hours in an Ar atmosphere to obtain an alloy for magnetic refrigeration material. The volume ratio of the subphase and α-Fe contained in the alloy for magnetic refrigeration material, the main phase composition, and the subphase composition were analyzed using a scanning electron microscope (SEM) (manufactured by JEOL Corporation, product name "JSM-IT300LV"). The volume ratio was obtained by performing image analysis on 20 SEM images. The main phase and subphase composition were analyzed using EDS. The amount of the subphase, the amount of the α-Fe phase, and the average circular approximation diameter of the α-Fe phase for each alloy are shown in Table 7. In addition, as examples of structural photographs, Comparative Example 5 is shown in FIG. 5, Example 4 is shown in FIG. 6, and Example 5 is shown in FIG. 7.

[0054] [Table 7]

[0055] The obtained alloy for magnetic refrigeration was subjected to the following hydrogenation heat treatment. First, activation treatment was performed in a vacuum at 500°C for 2 hours, and then hydrogen was introduced at 0.15 MPa and hydrogenation treatment was performed at 250°C for 24 hours. After the hydrogenation heat treatment, the hydrogen was evacuated and the alloy was cooled to room temperature at a cooling rate of 50°C / min in a non-hydrogen atmosphere (Ar atmosphere). The composition obtained at this time was (La 0.7 Ce 0.3 )(Fe 0.895 S 0.105 ) 13.0 H 1.23 The mT characteristics of the obtained magnetic refrigeration material were then evaluated using the same method. The results of the mT characteristic measurements are shown in Figure 8 and Table 8. For reference, the mT measurement results of the alloy before hydrogenation are shown in Figure 9.

[0056] [Table 8]

[0057] The mT curves before hydrogenation are almost the same, but the dm / dT after hydrogenation is higher in Example 4 than in Comparative Example 5. This is believed to be because the amounts of the subphase and the α-Fe phase are controlled within appropriate ranges, suppressing crushing caused by microcracks and achieving a uniform hydrogen concentration distribution. In Example 5, the amounts of the subphase and the α-Fe phase satisfy the prescribed ranges, but the average circular approximation diameter of the α-Fe phase is large at 15.3 μm, so appropriate dispersion of the α-Fe phase cannot be achieved, resulting in a non-uniform hydrogen concentration distribution and a lower dm / dT than in Example 4.

Claims

1. La （１－ａ） R ａ (Fe （１－ｂ－ｃ－ｄ） T.M. ｂ S ｃ A ｄ ) ｚ (R is one or more rare earth elements selected from Ce, Pr, and Nd; TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and satisfies 0≦a≦0.5, 0≦b≦0.03, 0.09≦c≦0.14, 0≦d≦0.05, and 13.0≦z≦13.4), and is represented by the composition formula of (La,R)MSi phase, (La,R) ５ M ３ Phase, (La, R) ６ M １１ S ３ phase, and (La, R) ２ M １７ The alloy contains at least one of the phases (wherein M is one or more elements selected from Fe and TM) in a total amount of 0.3 vol% or less as a subphase containing R, 0.1 vol% to 2.2 vol% of the α-Fe phase, and the remainder contains the (La, R)(Fe, TM, Si, A) phase as a main phase.

2. 2. The raw alloy for a magnetic refrigeration material according to claim 1, wherein the average circular approximation diameter of the α-Fe phase is 6 μm or less.

3. La （１－ａ） R ａ (Fe （１－ｂ－ｃ－ｄ） T.M. ｂ S ｃ A ｄ ) ｚ 3. A method for producing a raw alloy for a magnetic refrigeration material according to claim 1 or 2, comprising heat treating an alloy represented by a composition formula of: (R is one or more rare earth elements selected from Ce, Pr, and Nd; TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; and A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and satisfying 0≦a≦0.5, 0≦b≦0.03, 0.09≦c≦0.14, 0≦d≦0.05, and 13.0≦z≦13.4) at 1000 to 1300° C. for 10 to 100 hours in a vacuum atmosphere or an inert gas atmosphere.

4. La （１－ａ） R ａ (Fe （１－ｂ－ｃ－ｄ） T.M. ｂ S ｃ A ｄ ) ｚ H ｅ (R is one or more rare earth elements selected from Ce, Pr, and Nd; TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and satisfies 0≦a≦0.5, 0≦b≦0.03, 0.09≦c≦0.14, 0≦d≦0.05, 0<e≦1.5, and 13.0≦z≦13.4), and is represented by the composition formula of (La,R)MSi phase, (La,R) ５ M ３ Phase, (La, R) ６ M １１ S ３ Phase, (La, R) ２ M １７ phase, and at least one of the hydride phases thereof (M is one or more elements selected from Fe and TM) in a total amount of 0.3 vol% or less as a subphase containing R, α-Fe phase in an amount of 0.1 vol% to 2.2 vol%, and the balance being (La, R)(Fe, TM, Si, A). １３ H ｅ A magnetic refrigeration material containing the phase as a main phase.

5. 5. The magnetic refrigeration material according to claim 4, wherein the average circular approximation diameter of the α-Fe phase is 6 μm or less.

6. La （１－ａ） R ａ (Fe （１－ｂ－ｃ－ｄ） T.M. ｂ S ｃ A ｄ ) ｚ (R is one or more rare earth elements selected from Ce, Pr, and Nd; TM is one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; A is one or more elements selected from Al, Ga, P, Ge, Sn, and In, and satisfies 0≦a≦0.5, 0≦b≦0.03, 0.09≦c≦0.14, 0≦d≦0.05, and 13.0≦z≦13.4), and is represented by the composition formula of (La,R)MSi phase, (La,R) ５ M ３ Phase, (La, R) ６ M １１ S ３ phase, and (La, R) ２ M １７ 6. The method for producing a magnetic refrigeration material according to claim 4 or 5, wherein the alloy contains at least one of the phases (wherein M is one or more elements selected from Fe and TM) in a total amount of 0.3 vol% or less as a subphase containing R, 0.1 vol% to 2.2 vol% of the α-Fe phase, and the remainder is the (La, R)(Fe, TM, Si, A) phase as a main phase, and the cooling rate during hydrogenation heat treatment is 0.1°C / min to 50°C / min.

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