Method for manufacturing magnetic refrigeration material, and magnetic refrigeration material

Abstract

This method for manufacturing a magnetic refrigeration material according to the present invention includes a step for heat treating a magnetic refrigeration material in the atmosphere. The magnetic refrigeration material is an La-Fe-Si-H-based material containing at least La, Fe, Si, and H. The magnetic refrigeration material according to the present invention comprises: 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. According to the present invention, the method for manufacturing a magnetic refrigeration material by which a magnetic refrigeration material having a large change in magnetic entropy can be manufactured with a suppression in deterioration over time due to hydrogen desorption over a long period of time can be provided. In addition, the magnetic refrigeration material manufactured by the manufacturing method thereof can also be provided.

Description

Magnetic refrigeration material manufacturing method and magnetic refrigeration material

[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.

[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 (magneto-caloric effect, ΔS) that accompanies an increase in magnetic field have attracted 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 the like. In particular, the former has a very large ΔS of -30 J / kgK, making it an excellent magnetic refrigeration material. However, Mn(As １－ｘ Sb ｘ ) is difficult to apply because of its toxicity. １－ｘ Si ｘ ) １３ H ｚ ΔS is -25 J / 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 a single material can only operate at a certain temperature, so it is not possible to create a refrigeration system that requires a wide temperature difference. Therefore, a method of substituting some of the components with other elements to change the operating temperature has been adopted (Patent Document 3).

[0004] These substances 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 of a reduced magnetocaloric effect due to non-negligible lattice vibrations. This problem can be solved by utilizing these lattice vibrations as a heat storage effect. The AMR (Active Magnetic Regenerative) cycle, which utilizes 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 have become a reality.

[0005] In the AMR cycle, the magnetic refrigeration material is filled with a gap (called the bed section) through which a heat transfer medium such as water can pass. The heat transfer medium can move between the high-temperature and low-temperature ends through the gap. With the heat transfer medium at the low-temperature end, a magnetic field is applied to the bed section using a permanent magnet or other device to reduce the entropy of the magnetic refrigeration material and raise its temperature. The heat transfer medium is then moved from the low-temperature end to the high-temperature end. 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. The heat transfer medium is then cooled by the magnetic refrigeration material. The cooled heat transfer medium absorbs heat in the heat exchanger. Repeating this cycle creates a temperature difference 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, different magnetic transition temperatures (T ｃ ) from the high temperature end to the low temperature end. ｃ By filling the materials in order from high to low (cascade filling), and by performing 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 Tｙ 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 the characteristics by preventing hydrogen splitting.

[0008] JP 2003-28532 A JP 2006-089839 A JP 2006-089840 A JP 2012-041631 A

[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 the hydrogen content be made as high as possible to achieve a 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 hydrogen desorption by heating to 150°C or higher in relation to changes in magnetic properties over time due to hydrogen desorption from materials, 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 above-mentioned materials (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 environments other than high temperatures. 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 periphery 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 ｃIt 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 significantly. 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 preferable 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.

[0013] As a result of intensive 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 manufacturing method of a magnetic refrigeration material and the magnetic refrigeration material. [1] A manufacturing method of a magnetic refrigeration material, comprising a step of heat-treating a magnetic refrigeration material in an air atmosphere, wherein the magnetic refrigeration material is a La-Fe-Si-H-based material containing at least La, Fe, Si, and H. [2] A manufacturing method of 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] A manufacturing method of a magnetic refrigeration material according to the above [1], wherein 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, 12.0≦Z≦13.4). [4] A method for producing a magnetic refrigeration material according to the above [1] or [2], wherein the La—Fe—Si—H system material contains 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), １ ５ Fe ３ H ｘ% or less of the α-Fe phase, and when 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 the α-Fe in an amount of 0.5 volume % or less of the total La-Fe-Si-H system material. [5] A magnetic refrigeration material having 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] The magnetic refrigeration material according to [5], wherein the hydrogen concentration distribution within the La-Fe-Si-H system material is uniform.

[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.

[0016] 1 shows the change in ΔTc when an accelerated test for evaluating hydrogen desorption properties was performed at 80°C for the magnetic refrigeration materials of Example 1 and Comparative Example 1. 1 shows the change in ΔTc when an accelerated test for evaluating hydrogen desorption properties was performed at 100°C for the magnetic refrigeration materials of Example 1 and Comparative Example 1. 1 shows the change in maximum magnetic entropy for the magnetic refrigeration materials of Examples 2 to 31 when the thermal aging treatment conditions were changed. 1 shows the change in transition temperature for the magnetic refrigeration materials of Examples 2 to 31 when the thermal aging treatment conditions were changed. 1 shows the change in maximum magnetic entropy for the magnetic refrigeration materials of Example 32 and Comparative Examples 2 and 3 when the atmosphere during the thermal aging treatment was changed.

[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.) 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 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 entire 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 ｘ When 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 ) １３is sometimes called the 1-13 phase. １ ５ Fe ３ H ｘ The ratio of the phase is preferably 20% by volume or more. Furthermore, the La—Fe—Si—H system material does not contain α-Fe, or, if the La—Fe—Si—H system material contains α-Fe, the La—Fe—Si—H system material preferably contains α-Fe in an amount of 0.5% by volume or less of the total La—Fe—Si—H system 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 0 to 0.5, preferably 0 to 0.3. A method of changing ΔS and transition temperature by substituting a portion of La with another rare earth element is known, and high properties can be obtained by substituting a portion of La with one or more rare earth elements selected from Ce, Pr, and Nd, so it is desirable to substitute 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, and when homogenization treatment is performed, phases other than the main phase 1-13 phase are stably formed, resulting in deterioration of magnetic properties including a decrease in ΔS. For these reasons, 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 about 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 or more and 0.14 or less, preferably 0.095 or more and 0.11 or less. 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 more, an alloy in which 95% or more is the main phase can be easily obtained through general homogenization, for example, treatment at 1100°C for 50 hours. On the other hand, since ΔS increases as c is smaller, c is preferably 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 substitution elements for Si, 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 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. Depending 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 described 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. When e is small, the influence of hydrogen splitting becomes greater, which tends to cause greater deterioration of the magnetic properties over time, and when e is less than 1.3, this influence becomes significantly greater. On the other hand, when e is large, the material excessively occludes hydrogen, which results in greater hydrogen desorption in the air atmosphere, and the transition temperature of the material changes over time.

[0026] As described above, the La—Fe—Si—H-based material is NaZn １３ R having a 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 La—Fe—Si—H-based material is R １ By containing a subphase containing rare earth elements, hydrogenation can proceed easily, and hydrogen can be absorbed up to a saturated hydrogen amount under a wide range of hydrogenation conditions. 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 It is preferable to contain at least one selected from the group consisting of R １ ５ Fe ３ H ｘMore preferably, it contains a phase.

[0028] The above-mentioned R １ The amount of the subphase containing R varies depending not only on the composition of the La—Fe—Si—H system material but also on the homogenization treatment. １ It is preferable that the La—Fe—Si—H system material contains a subphase containing the above-mentioned R in an amount of 2% by volume or less of the entire La—Fe—Si—H system material. 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 as a whole. 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 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 ５ Fe ３ H ｘ When a phase is formed, R in the subphase １ ５ Fe ３ H ｘ The 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 the subphase containing the element １ ５ Fe ３ H 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 above-mentioned main phase and subphase. In this case, the proportion of α-Fe is preferably 0.5 vol% or less of the total La—Fe—Si—H-based material, and more preferably 0.3 vol% or less. Within this range, appropriate homogenization is achieved, resulting in a large amount of main phase, and therefore a large calorific value can be obtained. The lower limit of the range of the α-Fe proportion is not particularly limited, but since it is preferable to contain as little α-Fe as possible, it is 0.001 vol%.

[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 taken 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 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 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 the 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 the magnetic properties, when the magnetic refrigeration material is particulate, it is desirable for the thickness to 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 made of an oxide of a La--Fe--Si--H-based material obtained by oxidizing a 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 a magnetic refrigeration material 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 a 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 air atmosphere, and 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 air atmosphere.

[0034] In the melting process, the metals or alloys that serve as raw materials for each element are weighed so as 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, to melt, and then cooled as rapidly as possible at a cooling rate of 300 to 1000°C / sec to obtain an alloy. 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 easy to obtain a fine and good structure. Liquid quenching allows for faster cooling, making it easy to obtain an even finer and better 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 because it depends on the alloy structure and composition, but can be performed, 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 approximately −10 to −20°C compared to the unsubstituted case, and when substituted with Pr or Nd, the temperature tends to fluctuate by approximately +10 to +30°C. In addition, the temperature also 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 low, the decomposition temperature decreases, and 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 is defined as the temperature at which the amount of Fe precipitates is minimized and R is maintained. １ ５ Fe ３ This means that the amount of precipitated subphases containing R elements, particularly R elements, is maximized and the peak value of the dm / dT-T characteristic is maximized, and this can be confirmed experimentally by 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. Within this range, the amount of subphases containing R elements, particularly R elements, is maximized. １ ５ Fe ３ The amount of the α-Fe phase and the amount of α-Fe can be controlled within an optimum range. In addition, the homogenization treatment is preferably performed in an Ar atmosphere so as 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, a hydrogen atmosphere of 0.1 to 0.25 MPa can be used, for example. 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.

[0037] In the heat aging process, the obtained hydrogenated material (La-Fe-Si-H material) is subjected to heat treatment 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 treatment. Specific conditions are not particularly limited, but the heat treatment temperature is preferably 60°C or higher, more preferably 70°C or higher. Also, 100°C or lower is preferable, and 90°C or lower is more preferable. At a heat treatment temperature of 60°C or lower, it is difficult to form an oxide film within an industrial time frame. At temperatures above 100°C, intense hydrogen desorption occurs, resulting in non-uniform hydrogen concentrations within the material, thereby reducing the magnetic entropy change of the material. The heat treatment time is preferably 10 hours or longer, more preferably 12 hours or longer. Also, 400 hours or shorter is preferable, and 200 hours or shorter is more preferable. 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 value equivalent 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 surface of the material, the higher the surface area ratio of the material, the greater the proportion of contact with a non-hydrogen atmosphere, i.e., the air, resulting in greater hydrogen migration 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, and are not particularly limited. However, as an example of hydrogen desorption evaluation, it is possible to perform evaluation using a 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.

[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 a predetermined 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 strip-cast to produce alloy ribbons with an average thickness of approximately 300 μm by cooling 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]

[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 material. Then, the following hydrogenation heat treatment was performed. First, activation treatment was performed in vacuum at 500°C for 2 hours, and then hydrogen of 0.15 MPa was introduced 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 １．５０The volume ratio of the contained subphases and α-Fe, the main phase composition, and the subphase composition of this La—Fe—Si—H-based material 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 acquired SEM images. The main phase and subphase compositions were analyzed using EDS. The amounts of subphases and α-Fe phases in the alloy are shown in Table 2.

[0043]

[0044] The obtained hydrogenated alloy 1 was crushed 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 an air atmosphere at 80° C. for 24 hours, which was designated Example 1, and a 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 measuring device (manufactured by Quantum Design Co., Ltd., 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 the temperature peaked was determined as T c ΔT after the accelerated test ｃ The measurement results for the applied magnetic field of 1 T are shown in Figure 1 for the accelerated test results at 80°C and in Figure 2 for the accelerated test results at 100°C. 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 can suppress the decrease in transition temperature, i.e., suppress hydrogen desorption. This is thought to be due to the following reasons. It is thought that hydrogen desorption can be suppressed by preliminarily releasing hydrogen through the thermal aging treatment 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 in the amount of hydrogen of about 10 to 20 ppm within this range changes the transition temperature by about 1°C. Since it is difficult to directly detect minute changes in the amount of hydrogen in such high concentrations of hydrogen with high precision, changes in the amount of hydrogen content are estimated from the highly precise "change in transition temperature."

[0048] Examples 2 to 31 La metal, Si metal, and electrolytic iron were weighed to obtain a predetermined composition, and the materials were melted by heating to 1500°C in an Ar gas atmosphere in a high-frequency melting furnace. The materials were then strip-cast to produce alloy ribbons with an average thickness of approximately 300 μm. The compositions of the resulting raw alloys are shown in Table 3. The resulting raw alloys were homogenized at 1170°C for 50 hours in an Ar atmosphere to obtain alloys for magnetic refrigeration. The alloys were then 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, followed by hydrogenation treatment at 300°C for 6 hours. After the hydrogenation heat treatment, the alloys were cooled to room temperature in a hydrogen atmosphere at a cooling rate of 4°C / sec to obtain La—Fe—Si—H-based materials. The resulting composition was La(Fe) ０．８９０ Si ０．１１ ) １２．３ H １．５０The La—Fe—Si—H-based material was analyzed for the volume ratio of the subphases and α-Fe contained therein, the main phase composition, and the subphase composition. The amounts of the subphases and α-Fe phase in the alloy are shown in Table 4.

[0049]

[0050]

[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 a 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. The results showed that the maximum magnetic entropy change (|ΔS| ｍａｘ ) results are shown in Figure 3. ｃ The results are shown in Figure 4.

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

[0053]

[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 after hydrogenation to heat treatment, the non-uniform hydrogen concentration distribution within the material is homogenized (the "decrease rate of magnetic entropy change (|ΔS|max) before and after hydrogenation" is 5-10%), resulting in an improvement in |ΔS|max. However, if the heating temperature is too high or the heating time is too long, the homogenized hydrogen gradually desorbs (the "decrease rate of magnetic entropy change (|ΔS|max) before and after hydrogenation" is 10-15%), resulting in the same or slightly decreased |ΔS|max.

[0055] [Example 32, Comparative Examples 2 and 3] For hydrogenated alloy 2, a sample without heat aging treatment (Comparative Example 2), a sample that was heat-treated at 100°C for 3 hours in an air atmosphere after hydrogenation (Example 32), and a sample 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) were prepared, and 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 not stable, and in some cases, it has been found to decrease by more than 20%. From this point of view, it is desirable to carry out the 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. A method for producing a magnetic refrigeration material, comprising a step of heat-treating a magnetic refrigeration material in an air atmosphere, wherein 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 claim 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 3. The 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 contains R as the 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), １ ５ Fe ３ H ｘ 4. The method for producing a magnetic refrigeration material according to claim 3, wherein the ratio of the La-Fe-Si-H phase is 20% by volume or more, and when 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 α-Fe in an amount of 0.5% by volume or less of 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. The magnetic refrigeration material according to claim 5, wherein the hydrogen concentration distribution within the La-Fe-Si-H system material is uniform.

Images