Magnetic refrigeration material manufacturing method and magnetic refrigeration material

Abstract

To provide a magnetic refrigeration material manufacturing method that can suppress deterioration over time due to hydrogen desorption over a long period of time and that can manufacture a magnetic refrigeration material with a large magnetic entropy change, and a magnetic refrigeration material manufactured by the method.SOLUTION: A magnetic refrigeration material manufacturing method according to the present invention includes a step of heat-treating a magnetic refrigeration material in an air atmosphere, and the magnetic refrigeration material is an La-Fe-Si-H-based material containing at least La, Fe, Si, and H. The magnetic refrigeration material of the present invention includes an La-Fe-Si-H-based material containing at least La, Fe, Si, and H, and an oxide film formed on the surface of the La-Fe-Si-H-based material.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a magnetic refrigeration material that suppresses hydrogen desorption over time and has a high magnetic entropy change, and the magnetic refrigeration material. [Background technology]

[0002] Because fluorocarbons are ozone-depleting substances and greenhouse gases, new refrigeration and air-conditioning systems that do not use fluorocarbons are attracting attention for environmental conservation. Although active development of refrigerants to replace fluorocarbons has been underway, no new refrigerants that are satisfactory in terms of performance, cost, and safety have yet been put into practical use.

[0003] On the other hand, unlike conventional refrigeration and air conditioning systems, magnetic refrigeration systems that utilize the change in entropy (magnetocaloric effect, ΔS) that accompanies an increase in magnetic field are 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 Si x ) 13 H z (Patent Document 2) and others are cited. In particular, the former has a very large ΔS of -30 J / kgK, making it a potential 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 Si 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 related to the magnetic transition temperature (T c ), and since a single type of material can only operate at a certain temperature, it is not possible to create a refrigeration system that requires a wide temperature difference. Therefore, a method is used in which some of the components are replaced with other elements to change the operating temperature (Patent Document 3).

[0004] These materials must be able to 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 of reducing the magnetocaloric effect 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 (called the bed section) that allows a heat transfer medium such as water to pass through. The heat transfer medium can move between the high-temperature and low-temperature ends through the gap. With the heat transfer medium on the low-temperature side, a magnetic field is applied to the bed section using a permanent magnet or other device, reducing the entropy of the magnetic refrigeration material and raising its temperature. The heat transfer medium is then 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 released using a heat exchanger. The magnetic field from the permanent magnet is then removed, increasing the entropy of the magnetic refrigeration material and lowering its temperature. The heat transfer medium is then 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 created between the high-temperature and low-temperature ends, 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. To generate a large temperature difference required for applications such as refrigerators and air conditioners, it is necessary to combine 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 allowing heat exchange between adjacent magnetic refrigeration materials, a large temperature difference can be generated.

[0007] Regarding the magnetic transition temperature, Patent Document 4 states that La(Fe 1-x-y T y M x ) 13 H z By adding elements such as Mn after ensuring a sufficient hydrogen concentration in the material, it is possible to control the magnetic transition temperature of the material and stabilize its characteristics by preventing hydrogen splitting. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-28532 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-089839 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-089840 [Patent Document 4] Japanese Patent Application Laid-Open No. 2012-041631 Summary of the Invention [Problem to be solved by the invention]

[0009] In Patent Document 4, measures are taken to stabilize characteristics by preventing hydrogen splitting by increasing the amount of hydrogen storage. It is known that destabilization of magnetic characteristics due to hydrogen splitting occurs when the hydrogen content of the material is low. Therefore, Patent Document 4 proposes that by increasing the hydrogen content as much as possible, it is possible to achieve the desired T that is stable over a longer operating time. c It has been reported that the material can be stabilized.

[0010] On the other hand, Patent Document 4 mentions the change in magnetic properties over time due to hydrogen desorption from the material when heated to 150°C or higher, but does not mention or consider hydrogen desorption at all in the operating temperature range of a magnetic refrigerator, which is 100°C or lower.

[0011] The materials described above (hereinafter referred to as La-Fe-Si-H-based materials) are hydrogen storage alloys, and hydrogen is not completely stabilized, so hydrogen desorption occurs over time in non-hydrogen atmospheres, even in non-high temperature environments. This is thought to be because when the material is left standing in a non-hydrogen atmosphere, hydrogen desorbs from the material due to the difference in hydrogen concentration between the inside and the surroundings of the material. Since hydrogen desorption occurs due to the difference in hydrogen concentration between the material and the atmosphere, the higher the hydrogen concentration of the material, the more hydrogen desorption tends to be promoted, and therefore the transition temperature (T c It has been found that there is a tendency for the decrease in the hydrogen content (deterioration over time) of the magnetic flux density (Hf) to increase. This deterioration over time cannot be ignored when implementing a magnetic refrigerator. From this perspective, simply increasing the hydrogen content in the material as in Patent Document 4 is not desirable because it will impair the magnetic stability of the material due to hydrogen desorption.

[0012] The present invention has been made in consideration of the above circumstances, and aims to provide a method for manufacturing a magnetic refrigeration material that can suppress hydrogen desorption, thereby suppressing deterioration of the material over time, and achieve a high magnetic entropy change, and the magnetic refrigeration material itself. [Means for solving the problem]

[0013] As a result of extensive research to achieve the above-mentioned objective, the inventors discovered that by subjecting a magnetic refrigeration material, which is a La-Fe-Si-H based material, to heat treatment in an air atmosphere, an oxide film is formed on the surface of the material, which results in the suppression of hydrogen desorption from the material and the achievement of a high magnetic entropy change due to the homogenization of the hydrogen concentration distribution, and thus completed the present invention.

[0014] Therefore, the present invention provides the following method for producing a magnetic refrigeration material and the magnetic refrigeration material. [1] A step of heat-treating a magnetic refrigeration material in an air atmosphere, The magnetic refrigeration material is a La-Fe-Si-H-based material containing at least La, Fe, Si, and H. [2] The method for producing a magnetic refrigeration material according to the above [1], wherein the heat treatment temperature is 60 to 100°C and the heat treatment time is 10 to 400 hours. [3] The composition of the La-Fe-Si-H-based material is La (1-a) R a (Fe (1-b-c-d) T b Si c A d ) Z X e (R is one or more rare earth elements selected from the group consisting of Ce, Pr, and Nd; T is one or more elements selected from the group consisting of Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; A is one or more elements selected from the group consisting of Al, Ga, P, Ge, Sn, and In; X is H or one or more elements selected from the group consisting of B and C and H; and 0≦a≦0.5, 0≦b≦0.03, 0.08≦c≦0.14, 0≦d≦0.1, 1.3≦e≦1.5, and 12.0≦Z≦13.4.) [4] The La-Fe-Si-H-based material contains R as the main phase. 1 (T (1-y) Si y ) 13 H x Contains R as a subphase 1 FeSiH x Phase, R 1 5Fe3H x Phase, R 1 5Fe 11 Si3H x Phase and R 1 2Fe 17 H x phase in an amount of 2% by volume or less of the total La-Fe-Si-H system material (R 1 is La, or La and one or more rare earth elements selected from the group consisting of Ce, Pr, and Nd, and 1.3≦x≦1.5, 0.09≦y≦0.14), The R in the subphase 1 5Fe3H x The proportion of the phase is 20% by volume or more, The method for producing a magnetic refrigeration material according to the above-mentioned [3], wherein the La-Fe-Si-H-based material does not contain α-Fe, or when the La-Fe-Si-H-based material contains α-Fe, the La-Fe-Si-H-based material contains 0.5% by volume or less of the α-Fe based on the total volume of the La-Fe-Si-H-based material. [5] A magnetic refrigeration material comprising a La-Fe-Si-H-based material containing at least La, Fe, Si, and H, and an oxide film formed on the surface of the La-Fe-Si-H-based material. [6] The magnetic refrigeration material according to the above [5], wherein the hydrogen concentration distribution within the La-Fe-Si-H-based material is uniform. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a method for producing a magnetic refrigeration material that can suppress deterioration over time due to hydrogen desorption over a long period of time and that can produce a magnetic refrigeration material with a large magnetic entropy change, and a magnetic refrigeration material produced by the method. [Brief explanation of the drawings]

[0016] [Figure 1] 1 shows the change in ΔTc when an accelerated test for evaluating hydrogen desorption properties was conducted at 80° C. for the magnetic refrigeration materials of Example 1 and Comparative Example 1. [Figure 2] 1 shows the change in ΔTc when an accelerated test for evaluating hydrogen desorption properties was conducted at 100° C. for the magnetic refrigeration materials of Example 1 and Comparative Example 1. [Figure 3] 1 shows the maximum magnetic entropy change for the magnetic refrigeration materials of Examples 2 to 31, in which the heat aging treatment conditions were changed. [Figure 4] 1 shows the amount of change in transition temperature for the magnetic refrigeration materials of Examples 2 to 31 when the heat aging treatment conditions were changed. [Figure 5] 10 shows the change in maximum magnetic entropy of the magnetic refrigeration materials of Example 32 and Comparative Examples 2 and 3 when the atmosphere during the heat aging treatment is changed. DETAILED DESCRIPTION OF THE INVENTION

[0017] The magnetic refrigeration material of the present invention comprises a La-Fe-Si-H-based material containing at least La, Fe, Si and H, and an oxide film formed on the surface of the La-Fe-Si-H-based material.

[0018] The composition of the La-Fe-Si-H based material is preferably La (1-a) R a (Fe (1-b-c-d) T b Si c A d ) Z X e (R is one or more rare earth elements selected from the group consisting of Ce, Pr, and Nd; T is one or more elements selected from the group consisting of Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; A is one or more elements selected from the group consisting of Al, Ga, P, Ge, Sn, and In; X is H or one or more elements selected from the group consisting of B and C and H; and 0≦a≦0.5, 0≦b≦0.03, 0.09≦c≦0.14, 0≦d≦0.05, 1.3≦e≦1.5, and 12.0≦Z≦13.4). In addition, the La-Fe-Si-H system material contains R as the main phase. 1 (T (1-y) Si y ) 13 H x Contains R as a subphase 1 FeSiH x Phase, R 1 5Fe3H x Phase, R 1 5Fe 11 Si3H x Phase and R 1 2Fe 17 H x It is preferable that the La-Fe-Si-H-based material contains the R phase in an amount of 2% by volume or less of the total volume of the La-Fe-Si-H-based material. 1 is La, or La and one or more rare earth elements selected from the group consisting of Ce, Pr, and Nd, and 1.3≦x≦1.5, 0.09≦y≦0.14. 1 (T (1-y) Si y ) 13 H xIf hydrogen is not absorbed, the composition of this phase is R 1 (T (1-y) Si y ) 13 Also, R 1 (T (1-y) Si y ) 13 H x and R 1 (T (1-y) Si y ) 13 This is sometimes called the 1-13 phase. Furthermore, R in the above subphase 1 5Fe3H x The proportion of this phase is preferably 20% by volume or more. Furthermore, it is preferable that the La-Fe-Si-H-based material does not contain α-Fe, or if the La-Fe-Si-H-based material contains α-Fe, the La-Fe-Si-H-based material contains α-Fe in an amount of 0.5% by volume or less of the total volume of the La-Fe-Si-H-based material.

[0019] In the above composition formula, R represents one or more rare earth elements selected from the group consisting of Ce, Pr, and Nd, and a is between 0 and 0.5, preferably between 0 and 0.3. A method for changing ΔS and the transition temperature by partially substituting La with other rare earth elements is known. In particular, substituting a portion of La with one or more rare earth elements selected from Ce, Pr, and Nd can achieve high performance. Therefore, it is desirable to perform the substitution in an appropriate amount depending on the required magnetic properties. However, as the substitution ratio increases, it becomes difficult to control the homogenization temperature and time. Furthermore, during homogenization, phases other than the main 1-13 phase are stably formed, resulting in degradation of magnetic properties, including a decrease in ΔS. Therefore, the substitution ratio is set to 0.5 or less.

[0020] In the above composition formula, T is one or more elements selected from the group consisting of Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag, and b is between 0 and 0.03, preferably between 0.005 and 0.025. The transition temperature of the magnetic refrigeration material obtained by hydrogenation heat treatment is controlled by controlling the amount of hydrogen storage or the amount of T element added. However, since it is difficult to control the transition temperature of approximately 1 to 3°C required for AMR by controlling the amount of hydrogen storage alone, the T element is added to control the temperature. However, if b exceeds 0.03, the T element makes it difficult to form the 1-13 phase after homogenization treatment.

[0021] The Si content c in the above composition formula is 0.09 to 0.14, preferably 0.095 to 0.11. The smaller c is, the greater the magnetization change due to the phase transition. However, if c is less than 0.09, the 1-13 phase becomes unstable, making it difficult to obtain a good material through homogenization. On the other hand, if c is greater than 0.14, the phase transition approaches a second-order phase transition, resulting in a decrease in ΔS of the magnetic refrigeration material obtained after homogenization. If c is 0.095 or greater, it is easy to obtain an alloy in which 95% or more of the main phase is obtained through conventional homogenization, for example, treatment at 1100°C for 50 hours. On the other hand, since ΔS increases with decreasing c, it is preferable that c be 0.11 or less. ΔS is the jump in entropy (S) that appears at the phase transition temperature.

[0022] In the above composition formula, A is one or more elements selected from the group consisting of 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 Si substitution elements, if the addition ratio exceeds 0.05, the phase transition of the 1-13 phase approaches a second-order phase transition, resulting in a significant decrease in ΔS.

[0023] In the above composition formula, z is 12.0 or more and 13.4 or less, preferably 12.3 or more and 13.0 or less. If z is less than 12.0, the transition temperature changes drastically depending on the homogenization temperature, resulting in a processing temperature at which the transition temperature rises sharply. On the other hand, if z is 13.4 or more, the stoichiometry is exceeded, and clear precipitation of α-Fe begins to be observed in the resulting magnetic refrigeration material. Although it depends on the conditions, for example, if z is 13.0 or more, the amount of α-Fe precipitation increases several times. As a result, magnetization increases above the transition temperature, and the amount of magnetization change due to the transition decreases.

[0024] Incidentally, Fe is the balance of T, Si, and A. In addition to the elements mentioned above, the inclusion of unavoidable impurities such as oxygen, nitrogen, and carbon is permitted, but the content thereof is preferably as low as possible.

[0025] In the above composition formula, X represents one or more elements selected from H, B, and C, with H being essential. Adjusting the content of this X element makes it possible to control the transition temperature of the magnetic refrigeration material. The content of X, e, is 1.3 or more and 1.5 or less, and preferably 1.4 or more and 1.5 or less. If e is small, the influence of hydrogen splitting tends to increase, resulting in significant deterioration of the magnetic properties over time. If e is less than 1.3, this influence becomes significantly greater. On the other hand, if e is large, the material will excessively occlude hydrogen, and hydrogen desorption will increase in the air atmosphere, causing the transition temperature of the material to change over time.

[0026] As described above, the La-Fe-Si-H-based material is composed of NaZn 13 R type crystal structure 1 (TM (1-y) Si y ) 13 H x phase as the main phase (R 1 is La, or La and one or more rare earth elements selected from the group consisting of Ce, Pr, and Nd, and 1.3≦x≦1.5, 0.09≦y≦0.14). The volume ratio of the main phase is the remainder of the subphases described below.

[0027] The above La-Fe-Si-H based materials are R 1 By containing a subphase containing rare earth elements, hydrogenation can proceed more easily, and hydrogen can be absorbed up to the saturated hydrogen amount under a wide range of hydrogenation conditions. 1 FeSiH x Phase, R 1 5Fe3H x Phase, R 1 5Fe 11 Si3H x Phase and R 1 2Fe 17 H x It is preferable that the compound contains at least one selected from the group consisting of R 1 5Fe3H x More preferably, it contains a phase.

[0028] The above-mentioned R 1 The amount of the subphase containing R changes depending not only on the composition of the La-Fe-Si-H system material but also on the homogenization treatment. 1 The La-Fe-Si-H system material preferably contains 2% by volume or less of the subphase containing the above-mentioned R 1 It is preferable that the La-Fe-Si-H system material contains 0.1% by volume or more of the subphase containing the above-mentioned R in the La-Fe-Si-H system material. 1 The amount of the subphase containing R is preferably 0.1% by volume or more and 2.0% by volume or less, and more preferably 0.1% by volume or more and 0.5% by volume or less. By being in such a range, it becomes possible to absorb up to the saturated amount of hydrogen under a wide range of hydrogenation conditions. This is because R 1 This is thought to be because the inclusion of a subphase containing an element introduces microcracks due to volume expansion during hydrogenation, making hydrogenation more likely to proceed. 1 5Fe3H x When a phase is formed, R in the subphase 1 5Fe3H xThe ratio of the R phase is preferably 20% by volume or more. When the ratio is in this range, the change in magnetization due to the transition becomes steep. This is thought to be because the distribution of the composition within the main phase becomes more uniform. 1 R in subphases containing elements 1 5Fe3H x The upper limit of the range of the content of the phase is not particularly limited, but is, for example, 100% by volume.

[0029] The La-Fe-Si-H-based material preferably does not contain α-Fe. However, the La-Fe-Si-H-based material may contain α-Fe in addition to the main phase and subphase described above. In this case, the proportion of α-Fe is preferably 0.5 vol% or less, more preferably 0.3 vol% or less, of the total La-Fe-Si-H-based material. Within this range, the material is appropriately homogenized, resulting in a large amount of main phase, allowing for a large calorific value. The lower limit of the range of the α-Fe proportion is not particularly limited, but is preferably 0.001 vol%, since it is preferable to contain as little α-Fe as possible.

[0030] The composition analysis and volume fraction calculation of the main phase, subphase, and α-Fe described above can be performed using an SEM. Specifically, 20 photographs taken with the SEM are binarized using the contrast difference due to the composition, and the area of ​​each phase is calculated for each photograph. The area fraction of each phase is then calculated for each photograph, and the average value of the area fractions of each phase for the 20 photographs is used as the volume fraction of each phase.

[0031] The magnetic refrigeration material of the present invention preferably has an oxide film formed on the surface of the La-Fe-Si-H-based material. That is, the magnetic refrigeration material of the present invention preferably includes a La-Fe-Si-H-based material containing at least La, Fe, Si, and H, and an oxide film formed on the surface of the material. The oxide film is formed to suppress hydrogen desorption. The thicker the oxide film, the more hydrogen desorption is suppressed. However, if the oxide film is too thick, the proportion of the 1-13 phase, the main phase in the material, decreases, resulting in deterioration of magnetic properties. Since the effect varies depending on the shape and particle size of the material, the optimal film thickness is not particularly limited. However, in order to mitigate adverse effects on magnetic properties, if the magnetic refrigeration material is particulate, the thickness should be 0.1 to 1% of the approximate radius of the circle of the magnetic refrigeration material. The thickness of the oxide film is preferably 0.3 to 3.0 μm, more preferably 0.5 to 1.5 μm. The oxide film is preferably composed of an oxide of the La-Fe-Si-H-based material obtained by oxidizing the La-Fe-Si-H-based material.

[0032] Furthermore, the magnetic refrigeration material of the present invention preferably has a uniform hydrogen concentration distribution within it. The uniformity of the hydrogen concentration distribution can be evaluated as follows. It is known that the magnetic entropy change of magnetic refrigeration materials decreases before and after hydrogenation, and it is also known that the magnetic entropy change after hydrogenation varies depending on the hydrogenation conditions, i.e., the amount of hydrogen absorption and the hydrogen concentration distribution. This is thought to be because when the hydrogen concentration distribution within the material is nonuniform, phases with different transition temperatures coexist, resulting in a broad magnetic entropy change with temperature. In other words, when the hydrogen concentration distribution is uniform, it can be considered that the decrease in magnetic entropy change before and after hydrogenation is appropriately suppressed. The decrease in magnetic entropy change before and after hydrogenation is preferably 20% or less, and more preferably 10% or less. The lower limit of the range of the decrease in magnetic entropy change before and after hydrogenation is not particularly limited, but is, for example, 0%.

[0033] Next, a method for producing the magnetic refrigeration material of the present invention will be described. The method for producing a magnetic refrigeration material of the present invention involves producing a material having a predetermined composition and heat-treating the resulting material in an atmospheric environment. The method includes the following steps: a melting step in which raw materials are melted to obtain a raw alloy containing La, Fe, and Si; a homogenization step in which the resulting raw alloy is heat-treated to obtain a predetermined structure; a hydrogenation step in which hydrogen is absorbed into the alloy to increase the magnetic transition temperature; and a heat-aging step in which the hydrogenated alloy is heat-treated in an atmospheric environment.

[0034] In the melting process, the metals or alloys that serve as raw materials for each element are weighed to obtain the above-mentioned composition, and the raw materials are heated to 1500°C by high-frequency melting in an Ar atmosphere, for example, and melted. The alloy is then cooled as rapidly as possible at a cooling rate of 300 to 1000°C / sec. Although there are no particular limitations on the casting of this alloy, strip casting or liquid quenching can be applied. Strip casting allows for rapid cooling, making it easier to obtain a fine, good structure. Liquid quenching allows for faster cooling, making it easier to obtain an even finer, good structure.

[0035] In the homogenization process, the raw alloy obtained in the melting process is subjected to heat treatment to homogenize the structure. This homogenization process is not particularly limited as it depends on the alloy structure and composition, but can be carried out, for example, at a temperature range of 1100°C to 1300°C. In particular, as described above, when a portion of La is substituted with one or more rare earth elements selected from the group consisting of Ce, Pr, and Nd, the optimal heat treatment temperature for the homogenization process changes. For example, when a portion of La is substituted with Ce, the temperature tends to fluctuate by about -10 to -20°C compared to the unsubstituted case, and when substituted with Pr or Nd, the temperature tends to fluctuate by about +10 to +30°C. In addition, the temperature fluctuates by several tens of degrees depending on the amount of Si and the type of element substituting a portion of the Fe element and its substitution amount. 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. Note that the optimal heat treatment temperature is the temperature at which the amount of Fe precipitates is minimized and R is maintained. 1This means that the amount of 5Fe3 phase precipitated is maximized and the peak value of the dm / dT-T characteristic is maximized, and this can be confirmed experimentally taking the above factors into consideration. The homogenization time can be appropriately adjusted depending on the state of the alloy obtained in the melting process, and can be, for example, in the range of 1 hour to 100 hours, and more preferably 25 hours to 75 hours. Within this range, the amount of subphases containing R elements, especially R 1 The amount of 5Fe3 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 to prevent deviation from the initial composition due to evaporation of specific elements from the raw alloy.

[0036] In the hydrogenation process, when the magnetic transition temperature of the material obtained by the homogenization treatment is increased, hydrogen is absorbed into the material in a hydrogen atmosphere to obtain a hydride. While the specific conditions are not particularly limited, the hydrogen atmosphere can be, for example, 0.1 to 0.25 MPa. Furthermore, the hydrogenation temperature can be, for example, 200°C or higher and 500°C or lower. Within this range, the hydrogen saturation concentration can be reached in a relatively short time. The hydrogenation treatment time can be, for example, 1 hour or higher and 100 hours or lower, and more preferably 3 hours or higher and 30 hours or lower. Within this range, a material saturated with hydrogen can be obtained satisfactorily.

[0037] In the heat aging process, the obtained hydrogenated material (La-Fe-Si-H material) is heat-treated in an air atmosphere to form an oxide film on the surface, promote uniformity of the hydrogen concentration distribution within the material, suppress hydrogen desorption from the magnetic refrigeration material, and maximize the maximum magnetic entropy change (ΔS max) can be produced. This heat treatment is sometimes called heat-aging. Specific conditions are not particularly limited, but the heat treatment temperature is preferably 60°C or higher, more preferably 70°C or higher. It is also preferably 100°C or lower, more preferably 90°C or lower. At a heat treatment temperature of 60°C or lower, it is difficult to form an oxide film within an industrial timeframe. At temperatures above 100°C, intense hydrogen desorption occurs, resulting in uneven hydrogen concentration within the material and a decrease in the magnetic entropy change of the material. The heat treatment time is preferably 10 hours or higher, more preferably 12 hours or higher. It is also preferably 400 hours or lower, more preferably 200 hours or lower. Under industrial conditions, if the heat treatment time is less than 10 hours, it is difficult to suppress variations in the heat treatment conditions within the material, while heat treatment for more than 400 hours significantly reduces productivity. Under these conditions, a ΔS that is equal to or higher than that before the heat-aging treatment can be obtained. max In the heat aging treatment, the material may be treated in the state after hydrogenation, or may be powdered and then treated.

[0038] When evaluating hydrogen desorption, it is desirable to standardize the shape and particle size of the target magnetic refrigeration material. This is for the following reason: Because hydrogen desorption occurs from the material's surface, the higher the surface area ratio of the material, the greater the proportion of contact with a non-hydrogen atmosphere, i.e., the air. This increases the transfer of hydrogen from the magnetic refrigeration material to the air, resulting in greater hydrogen desorption. The optimal shape and particle size of the magnetic refrigeration material are determined by the structure of the AMR bed, so there are no particular limitations. However, as an example of hydrogen desorption evaluation, it is possible to perform evaluations using magnetic refrigeration material with an average circular approximation diameter of approximately 300 μm, for example, by crushing the material in a mortar and pestle and classifying it using a sieve. [Example]

[0039] EXAMPLES The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0040] [Example 1, Comparative Example 1] La metal, Mn metal, Si metal, and electrolytic iron were weighed to obtain the desired composition, and the mixture was heated to 1500°C in an Ar gas atmosphere in a high-frequency melting furnace and melted. The mixture was then strip-cast to produce an alloy ribbon with an average thickness of approximately 300 μm, which was cooled at a rate of 500°C / sec. The composition of the resulting raw alloy is shown in Table 1. The alloy composition was analyzed using a high-resolution ICP optical emission spectrometer (manufactured by Hitachi High-Tech Corporation, product name "SPS3500DD").

[0041] [Table 1]

[0042] The obtained raw alloy was subjected to homogenization treatment at 1150°C for 50 hours in an Ar atmosphere to obtain an alloy for magnetic refrigeration. Then, the following hydrogenation heat treatment was performed. First, activation treatment was performed in vacuum at 500°C for 2 hours, and then hydrogen was introduced at 0.15 MPa and hydrogenation treatment was performed at 300°C for 6 hours. After the hydrogenation heat treatment, the alloy was cooled to room temperature in a hydrogen atmosphere at a cooling rate of 4°C / sec to obtain a La-Fe-Si-H-based material. The composition obtained at this time was La(Fe 0.870 Mn 0.020 Si 0.11 ) 12.3 H 1.50 The volume ratio of the subphases and α-Fe contained in this La-Fe-Si-H system material, as well as the main phase composition and subphase composition, were analyzed using a scanning electron microscope (SEM) (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 amounts of subphases and α-Fe phase in the alloy are shown in Table 2.

[0043] [Table 2]

[0044] The obtained hydrogenated alloy 1 was pulverized and classified in an Ar atmosphere using a mortar and a sieve (upper limit 500 μm, lower limit 150 μm) to produce a powder with an average circular diameter of 300 μm. This sample was heat-treated in air at 80°C for 24 hours, and the sample that was not heat-treated was designated Example 1, and the sample that was not heat-treated was designated Comparative Example 1.

[0045] In order to evaluate the hydrogen desorption properties under a heating environment in Example 1 and Comparative Example 1, the following accelerated test was carried out. Heat treatment was carried out for 1 to 600 hours in an air atmosphere at 80°C and 100°C, which are temperatures higher than the operating temperature of the magnetic refrigerator, and the amount of change in transition temperature (ΔT c The transition temperature was measured by measuring the mT characteristics of the obtained magnetic refrigeration material using the VSM unit of a small cryogen-free physical property measurement device (manufactured by Quantum Design, product name "VersaLab"). The transition temperature was determined by determining the temperature dependence of the magnetic entropy change from the mT characteristics for an applied magnetic field of 0 to 1 T, and the temperature at which this peak was reached was defined as T. c ΔT after the accelerated test c The measurement results for the accelerated test at 80°C and 100°C are shown in Figure 1 and Figure 2, respectively, for the applied magnetic field of 1 T. The magnetic entropy change (|ΔS| max The rate of decrease in the viscosity of the resin was 25 to 20% in Comparative Example 1 and 15 to 10% in Example 1.

[0046] The results in Figures 1 and 2 confirm that the thermal aging treatment suppresses the decrease in the transition temperature, i.e., it suppresses hydrogen desorption. This is thought to be due to the following reason. It is thought that hydrogen desorption can be suppressed by using the thermal aging treatment to release hydrogen in advance from areas within the material where hydrogen desorption is likely to occur, i.e., areas with a high hydrogen concentration. It was also confirmed that releasing hydrogen from areas with a high hydrogen concentration improves the uniformity of the hydrogen concentration distribution within the La-Fe-Si-H-based material.

[0047] The reason why hydrogen analysis results are not used in hydrogen content evaluation is due to a lack of precision. Generally, the hydrogen concentration in La-Fe-Si-H materials is about 1000 to 4000 ppm, and it has been found from analysis of the hydrogen content in the material and the relationship between the amount of transition temperature change due to hydrogen absorption that a change of about 10 to 20 ppm in the amount of hydrogen changes the transition temperature by about 1°C. Because it is difficult to directly detect minute changes in the amount of hydrogen in such high concentrations with high precision, changes in the amount of contained hydrogen are estimated from the highly accurate "change in transition temperature."

[0048] [Examples 2 to 31] La metal, Si metal, and electrolytic iron were weighed to obtain the desired composition. The materials were melted in an Ar gas atmosphere by heating to 1500°C in a high-frequency melting furnace. The materials were then strip-cast to produce an alloy ribbon with an average thickness of approximately 300 μm. The composition of the resulting raw alloy is shown in Table 3. The resulting raw alloy was homogenized in an Ar atmosphere at 1170°C for 50 hours to obtain an alloy for magnetic refrigeration. The alloy was then subjected to the following hydrogenation heat treatment: It was first activated in a vacuum at 500°C for 2 hours, and then hydrogen was introduced at 0.15 MPa, followed by hydrogenation at 300°C for 6 hours. After the hydrogenation heat treatment, the material was cooled to room temperature in a hydrogen atmosphere at a cooling rate of 4°C / sec to obtain a La-Fe-Si-H-based material. The resulting composition was La(Fe 0.890 Si 0.11 ) 12.3 H 1.50 The La-Fe-Si-H material was analyzed for the volume ratio of the subphases and α-Fe contained therein, as well as the main phase composition and subphase composition. The amounts of the subphases and α-Fe phase in the alloy are shown in Table 4.

[0049] [Table 3]

[0050] [Table 4]

[0051] The obtained hydrogenated alloy 2 was crushed and classified in an Ar atmosphere using a mortar and a sieve (upper limit 500 μm, lower limit 150 μm) to produce powder with an average circular approximation diameter of 300 μm. This sample was subjected to heat treatment (heat aging treatment) in an air atmosphere at 60 to 150 °C for 1 to 420 hours. As a result, the maximum magnetic entropy change (|ΔS| max ) results are shown in Figure 3, and ΔT c The results are shown in Figure 4.

[0052] To evaluate hydrogen desorption, the heat-aged samples were subjected to an accelerated test in air at 80°C for 24 hours. The results are shown in Table 5. Comparative Example 1 is also shown for comparison.

[0053] [Table 5]

[0054] From the results in Table 5, it was confirmed that the heat-seasoning treatment suppressed hydrogen desorption compared to the untreated material (Comparative Example 1). Furthermore, from the results in Figure 3, it can be seen that at heating temperatures of 60 to 100°C, |ΔS|max is improved compared to before heat-seasoning. Here, ΔT c Looking at the correlation with ΔT c It can be seen that an improvement in |ΔS|max is observed when the temperature is 1°C or less. This is because by subjecting the material to heat treatment after hydrogenation, the uneven hydrogen concentration distribution within the material becomes uniform (the "decrease rate of magnetic entropy change (|ΔS|max) before and after hydrogenation" is 5-10%), improving |ΔS|max. However, if the heating temperature is too high or the heating time is too long, the uniformly distributed hydrogen gradually desorbs (the "decrease rate of magnetic entropy change (|ΔS|max) before and after hydrogenation" is 10-15%), so |ΔS|max remains the same or slightly decreases.

[0055] [Example 32, Comparative Examples 2 and 3] For hydrogenated alloy 2, three samples were prepared: one without heat aging treatment (Comparative Example 2), one that was heat-treated at 100°C for 3 hours in an air atmosphere after hydrogenation (Example 32), and one that was heat-treated at 100°C for 3 hours in an inert gas (argon) atmosphere without being exposed to the air atmosphere after hydrogenation (Comparative Example 3).Their magnetic properties were evaluated.The results are shown in Figure 5.

[0056] The sample surface of Example 32, in which an oxide film is formed, has magnetic properties equivalent to those of Comparative Example 2 before heat treatment. However, the sample surface of Comparative Example 3, in which no exposure to the air atmosphere after hydrogenation, in which no oxide film is formed, has magnetic properties equivalent to those of Comparative Example 2 before heat treatment. c is about 5°C, |ΔS| max The value of |ΔS| decreases by approximately 10%. This is thought to be because the oxide film on the sample surface suppresses hydrogen desorption. For samples without an oxide film, the amount of hydrogen desorbed increases, which increases the non-uniformity of the hydrogen concentration distribution. max Therefore, it is desirable to perform the heat treatment in the atmosphere to form an oxide film. In Patent Document 4, the sample after hydrogenation is subjected to a heat treatment at 140°C for 30 minutes in an argon atmosphere (inert gas atmosphere) as a stabilization treatment. c ) decreases by about 3°C ​​and hydrogen desorption is large, so the maximum magnetic entropy change (ΔS max ) is unstable, and in some cases, it has decreased by more than 20%. For this reason, it is desirable to carry out heat treatment in an oxidizing atmosphere.

[0057] From the above, it was found that by performing heat treatment under certain conditions in an air atmosphere after hydrogenation, it is possible to suppress hydrogen desorption and improve magnetic properties.

Claims

1. heat-treating the magnetic refrigeration material in an air atmosphere; The magnetic refrigeration material is a La—Fe—Si—H-based material containing at least La, Fe, Si, and H.

2. 2. The method for producing a magnetic refrigeration material according to claim 1, wherein the heat treatment is carried out at a temperature of 60 to 100° C. for a period of 10 to 400 hours.

3. The composition of the La—Fe—Si—H-based material is La （１－ａ） R ａ (Fe （１－ｂ－ｃ－ｄ） T ｂ Si ｃ A ｄ ) Ｚ X ｅ 3. A method for producing a magnetic refrigeration material according to claim 1, wherein R is one or more rare earth elements selected from the group consisting of Ce, Pr, and Nd; T is one or more elements selected from the group consisting of Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag; A is one or more elements selected from the group consisting of Al, Ga, P, Ge, Sn, and In; X is H, or a combination of H and one or more elements selected from the group consisting of B and C, and 0≦a≦0.5, 0≦b≦0.03, 0.09≦c≦0.14, 0≦d≦0.05, 1.3≦e≦1.5, and 12.0≦Z≦13.

4.

4. The La—Fe—Si—H-based material has R as a main phase. １ (T （１－ｙ） Si ｙ ) １３ H ｘ and R as a subphase. １ FeSiH ｘ Phase, R １ ５ Fe ３ H ｘ Phase, R １ ５ Fe １１ Si ３ H ｘ Phase and R １ ２ Fe １７ H ｘ The La—Fe—Si—H-based material contains the phase in an amount of 2% by volume or less (R １ is La, or La and one or more rare earth elements selected from the group consisting of Ce, Pr, and Nd, and 1.3≦x≦1.5, 0.09≦y≦0.14; The R in the subphase １ ５ Fe ３ H ｘ The proportion of the phase is 20% by volume or more, 4. The method for producing a magnetic refrigeration material according to claim 3, wherein the La-Fe-Si-H system material does not contain α-Fe, or when the La-Fe-Si-H system material contains α-Fe, the La-Fe-Si-H system material contains 0.5% by volume or less of the α-Fe based on the total volume of the La-Fe-Si-H system material.

5. A magnetic refrigeration material comprising a La-Fe-Si-H system material containing at least La, Fe, Si and H, and an oxide film formed on the surface of the La-Fe-Si-H system material.

6. 6. The magnetic refrigeration material according to claim 5, wherein the La--Fe--Si--H-based material has a uniform hydrogen concentration distribution.

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