Raw material alloy for magnetic refrigeration material and magnetic refrigeration material

Abstract

A raw material alloy for a magnetic refrigeration material according to the present invention is expressed by compositional formula R1(M1 1-xA1 x)y. The magnetic refrigeration material of the present invention contains as a main phase a La(Fe,Si)13 compound that is expressed by the compositional formula R1(M1 1-xA1 x)y and has a NaZn13 crystal structure, and further contains a sub-phase containing a rare earth element (R2). The percentage of the sub-phase containing the rare earth element (R2) in the raw material alloy for the magnetic refrigeration material is 0.1 vol% or more, and the percentage of alpha-Fe is 0.5 vol% or less when alpha-Fe is not included or when alpha-Fe is included. The present invention makes it possible to provide a raw material alloy for a magnetic refrigeration material in which the amount of change in the transition temperature due to the homogenization temperature is small, and in which hydrogen is absorbed to a saturation amount of hydrogen and the transition temperature is stable under a wide range of hydrogenation conditions.

Description

Raw alloys for magnetic refrigeration materials and magnetic refrigeration materials

[0001] The present invention relates to a raw material alloy for a magnetic refrigeration material whose transition temperature changes little with the homogenization temperature, a magnetic refrigeration material that absorbs hydrogen up to the saturated hydrogen amount over a wide range of hydrogenation conditions and has a stable transition temperature, and an alloy for a magnetic refrigeration material used in producing 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. ｃ ) and a single material can only operate at a certain temperature, so refrigeration systems that require a wide temperature difference cannot be created. Therefore, methods such as replacing some of the components with other elements are used to change the operating temperature.

[0004] These materials 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, there is a problem in that the magnetocaloric effect decreases at the above operating temperatures because lattice vibrations cannot be ignored. 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 at 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] JP 2003-28532 A JP 2006-89839 A

[0008] In order 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 Si ｘ ) １３ In the case of , the half-width is narrow at 3 to 5 K, so it has been found that controlling the operating temperature (transition temperature) with high precision is preferable for good heat exchange.

[0009] However, La(Fe １－ｘ Si ｘ ) １３ The operating temperature of a material varies depending on manufacturing conditions, such as the heat treatment (homogenization) and hydrogenation conditions, making it difficult to control accurately. During homogenization, the transition temperature changes as the degree of progress changes depending on factors such as the homogenization temperature and time. It is known that hydrogenation is performed to raise the transition temperature to room temperature, but the change in transition temperature due to homogenization persists even after hydrogenation. Additionally, the hydrogenation conditions also affect the hydrogen concentration in the material, which in turn affects the transition temperature. If the transition temperature is not well controlled, the amount of overlap between each material when assembling a cascade will change, resulting in poor heat exchange.

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an alloy for a magnetic refrigeration material and a magnetic refrigeration material in which the transition temperature can be controlled with high precision in response to changes in the homogenization temperature and hydrogenation conditions.

[0011] As a result of extensive research conducted by the inventors to achieve the above object, they discovered that by adjusting the composition of the raw material alloy to a predetermined range, the amount of change in the transition temperature due to the homogenization temperature is small, and further, by subjecting the prepared raw material alloy to a homogenization treatment so that the amounts of precipitated subphases containing rare earth elements and α-Fe are in a predetermined ratio, hydrogen can be absorbed up to the saturated hydrogen amount under a wide range of hydrogenation conditions, and the transition temperature can be stabilized, thereby completing the present invention.

[0012] Therefore, the present invention provides the following raw alloy for a magnetic refrigeration material and the magnetic refrigeration material: [1] R １ (M １ １－ｘ A １ｘ ) ｙ (R １ is at least one element selected from the group consisting of La, La, rare earth elements other than La, and Zr, and M １ is Fe, or Fe and at least one element selected from the group consisting of Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti, and A １ is Si, or Si and at least one element selected from the group consisting of Al, Ga, P, Ge, Sn, and In, and x and y satisfy 0.09≦x≦0.14 and 12.4≦y<13.0, respectively. [2] A raw material alloy for a magnetic refrigeration material according to [1] above, wherein y in the composition formula satisfies 12.5≦y≦12.9. [3] R １ (M １ １－ｘ A １ ｘ ) ｙ (R １ is at least one element selected from the group consisting of La, La, rare earth elements other than La, and Zr, and M １ is Fe, or Fe and at least one element selected from the group consisting of Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti, and A １ is Si, or Si and at least one element selected from the group consisting of Al, Ga, P, Ge, Sn, and In, and x and y satisfy 0.09≦x≦0.14 and 12.4≦y<13.0, respectively, and NaZn １３ La(Fe,Si) having a type crystal structure １３ The main phase of the alloy is a rare earth element (R ２ (R ２ is at least one element selected from the group consisting of La, La, rare earth elements other than La, and Zr), ２ [4] A magnetic refrigeration material in which the ratio of a subphase containing the rare earth element (R) is 0.1% by volume or more, and the material does not contain α-Fe, or if it contains α-Fe, the ratio of the α-Fe is 0.5% by volume or less. ２ ) is a subphase containing R ２ M２ A ２ , R ２ ５ A ２ ３ , R ２ ６ M ２ １１ A ２ ３ and R ２ ２ M ２ １７ , R ２ (M ２ is Fe, or Fe and at least one element selected from the group consisting of Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti, and A ２ is Si, or Si and at least one element selected from the group consisting of Al, Ga, P, Ge, Sn, and In. １ [6] The magnetic refrigeration material according to the above [3] or [4], wherein the rare earth element (R ２ ) is a subphase containing R ２ ５ A ２ ３ [7] The magnetic refrigeration material according to any one of the above [3] to [5], containing the rare earth element (R ２ ) in the subphase containing ２ ５ A ２ ３ [8] The magnetic refrigeration material according to the above [6], wherein the ratio of the rare earth element (R ２ [9] The magnetic refrigeration material according to any one of [3] to [8] above, wherein the ratio of the subphase containing hydrogen is 2.00 volume % or less.

[10] The magnetic refrigeration material according to any one of [3] to [8] above, wherein the ratio of the subphase containing hydrogen is 2.00 volume % or less.

[0013] According to the present invention, it is possible to provide a raw alloy for a magnetic refrigeration material in which the transition temperature changes little with the homogenization temperature, and a magnetic refrigeration material in which hydrogen is absorbed up to the saturated hydrogen amount under a wide range of hydrogenation conditions and the transition temperature is stable.

[0014] FIG. 1 shows the T ｐｅａｋ 2 is a graph plotting the change in the rare earth element (R ２ ) is a diagram showing the results of structural observation of a subphase containing α-Fe. FIG. 3 shows the change in the Si content in the main phase at various homogenization temperatures for the magnetic refrigeration material of Comparative Example 1. FIG. 4 shows the α-Fe content of the raw material alloys for magnetic refrigeration materials of Examples 1 to 3 and Comparative Examples 1 to 3 when heat-treated at 1105°C for 50 hours. FIG. 5 shows the m-T characteristics of the raw material alloys for magnetic refrigeration materials of Examples 1 to 3 and Comparative Examples 1 to 3 when heat-treated at 1105°C for 50 hours. FIG. 6 shows the m-T characteristics of the magnetic refrigeration materials of Example 4 and Comparative Example 5 when hydrogenation was performed at 200°C for 3 hours in a 0.1 MPa hydrogen atmosphere. FIG. 7 shows the m-T characteristics of the magnetic refrigeration materials of Example 4 and Comparative Example 7 when hydrogenation was performed at 500°C, 0.1 MPa, and 1 hour.

[0015] The raw alloy for the magnetic refrigeration material of the present invention is R １ (M １ １－ｘ A １ ｘ ) ｙ (R １ is at least one element selected from the group consisting of La, La, rare earth elements other than La, and Zr, and M １ is Fe, or Fe and at least one element selected from the group consisting of Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti, and A １ is Si, or Si and at least one element selected from the group consisting of Al, Ga, P, Ge, Sn, and In, and x and y satisfy 0.09≦x≦0.14 and 12.4≦y<13.0, respectively.

[0016] As described above, the raw material alloy for the magnetic refrigeration material of the present invention is R １ (M １ １－ｘ A １ ｘ ) ｙIn the composition formula, x is 0.09 or more and 0.14 or less, and preferably 0.095 or more and 0.105 or less. The smaller x is, the larger the amount of magnetization change due to phase transition. However, if x is smaller than 0.09, R １ (M １ １－ｘ A １ ｘ ) ｙ is unstable, making homogenization difficult. On the other hand, as x increases, the phase transition approaches a second-order phase transition, resulting in a decrease in ΔS of the magnetic refrigeration material obtained after homogenization; therefore, x is set to 0.14 or less. If x 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 x is, the larger ΔS becomes, so x is preferably set to 0.105 or less. ΔS is the jump in entropy (S) that appears at the phase transition temperature.

[0017] In the above composition, y is 12.4 or more and less than 13.0, and preferably 12.5 or more and 12.9 or less. If y is less than 12.4, 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 y is 13.0 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, when y 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. For these reasons, y is 12.4 or more and less than 13.0, and preferably 12.5 or more and 12.9 or less.

[0018] In the raw alloy for magnetic refrigeration material of the present invention, R １ may be La, or may be at least one element selected from the group consisting of La, rare earth elements other than La, and Zr. １ may be Fe, or may be Fe and at least one element selected from the group consisting of Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti. １may be Si, or may be Si and at least one element selected from the group consisting of Al, Ga, P, Ge, Sn, and In.

[0019] R １ The proportion of La in the above range is preferably 50 to 100 atomic %, more preferably 65 to 100 atomic %, even more preferably 70 to 100 atomic %, and still more preferably 90 to 100 atomic %.

[0020] M １ The proportion of Fe in the above range is preferably 97 to 100 atomic %.

[0021] A １ The proportion of Si in the above is preferably 50 to 100 atomic %.

[0022] The raw alloy for magnetic refrigeration material having the above composition is subjected to a homogenization treatment, which will be described later, to form a main phase and a rare earth element (R ２ (R ２ is at least one element selected from the group consisting of La, or La, a rare earth element other than La, and Zr), and a subphase containing La.

[0023] The magnetic refrigeration material of the present invention is R １ (M １ １－ｘ A １ ｘ ) ｙ (R １ is at least one element selected from the group consisting of La, La, rare earth elements other than La, and Zr, and M １ is Fe, or Fe and at least one element selected from the group consisting of Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti, and A １ is Si, or Si and at least one element selected from the group consisting of Al, Ga, P, Ge, Sn, and In, and x and y satisfy 0.09≦x≦0.14 and 12.4≦y<13.0, respectively, and NaZn １３ La(Fe,Si) having a type crystal structure １３ The main phase contains a rare earth element (R ２ (R ２is at least one element selected from the group consisting of La, or La, a rare earth element other than La, and Zr), and α-Fe precipitated from the raw material alloy for magnetic refrigeration material, ２ The proportion of the subphase containing α-Fe is 0.1% by volume or more, and the amount of α-Fe precipitated in the raw alloy for the magnetic refrigeration material is 0.5% by volume or less.

[0024] In the main phase contained in the magnetic refrigeration material of the present invention, R １ may be La, or may be La partially substituted with at least one element selected from the group consisting of rare earth elements other than La and Zr. １ may be Fe, or may be Fe partially substituted with at least one element selected from the group consisting of Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti. １ may be Si, or may be Si partially substituted with at least one element selected from the group consisting of Al, Ga, P, Ge, Sn, and In.

[0025] R １ By substituting a part of La with at least one element selected from the group consisting of rare earth elements other than La and Zr, it is possible to control the transition temperature, half width, hysteresis, etc. of the magnetic refrigeration material. Among the rare earth elements, substituting a part of La with at least one rare earth element selected from the group consisting of Ce, Nd, and Pr is particularly preferable from the viewpoint of the above control. １ When a part of La is replaced with Ce in R １ 30% or less of the total atoms, when substituted with Nd, R １ 35% or less of the total atoms, when substituted with Pr, R １ The substitution can be made at 50 atomic % or less of the total. Within this range, the increase in the transition temperature due to the magnetic field is small, and the half-width becomes small, which increases ΔS and increases the hysteresis. Ce has the greatest effect of increasing ΔS. When a part of La is substituted with Zr, R １The substitution can be made at 10 atomic % or less of the total. If the substitution is made within this range, the transition temperature can be increased by several K. The lower limit of the range of the substitution amount is not particularly limited, but for example, R １ The ratio of R in the subphase is 1 atomic % of the total. ２ However, a portion of La may be substituted with at least one element selected from the group consisting of rare earth elements other than La and Zr.

[0026] R １ and R ２ The proportion of La in the above range is preferably 50 to 100 atomic %, more preferably 65 to 100 atomic %, even more preferably 70 to 100 atomic %, and still more preferably 90 to 100 atomic %.

[0027] M １ By substituting at least one element selected from the group consisting of Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti for part of the Fe, it is possible to control the transition temperature, half width, hysteresis, etc. of the magnetic refrigeration material in the same manner as above. １ The substitution amount can be 0 atomic % or more and 3 atomic % or less of the total. If it is within this range, it can be added without decomposing the structure, and the transition temperature can be lowered. The lower limit of this range of substitution amount is not particularly limited, but for example, M １ The subphase is 1 atomic % of the total. ２ (M ２ is Fe, or Fe and at least one element selected from the group consisting of Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti), M in the subphase ２ Alternatively, a portion of the Fe may be substituted with at least one element selected from the group consisting of Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti.

[0028] M １ and M ２ The proportion of Fe in the above range is preferably 97 to 100 atomic %.

[0029] Furthermore, A １By substituting a part of Si with at least one element selected from the group consisting of Al, Ga, P, Ge, Sn, and In, the transition temperature, half width, hysteresis, etc. can be controlled. １ The substitution amount can be 50 atomic % or less of the total. Within this range, the transition temperature can be lowered and the hysteresis can be further reduced. The lower limit of this range of substitution amount is not particularly limited, but for example, A １ The subphase is 1 atomic % of the total. ２ If it includes (A ２ is Si, or Si and at least one element selected from the group consisting of Al, Ga, P, Ge, Sn, and In), A in the subphase ２ Alternatively, a portion of Si may be substituted with at least one element selected from the group consisting of Al, Ga, P, Ge, Sn, and In.

[0030] A １ and A ２ The proportion of Si in the above is preferably 50 to 100 atomic %.

[0031] The magnetic refrigeration material of the present invention can be obtained by subjecting the above-mentioned raw alloy for the magnetic refrigeration material to a homogenization treatment. ２ By containing a subphase containing rare earth elements (R), hydrogenation can proceed more easily, and hydrogen can be absorbed up to the saturated hydrogen amount under a wide range of hydrogenation conditions. ２ The subphase containing R ２ M ２ A ２ , R ２ ５ A ２ ３ , R ２ ６ M ２ １１ A ２ ３ and R ２ ２ M ２ １７ , R ２ It is preferable to contain at least one selected from the following, among which R２ ５ A ２ ３ It is more preferred that the compound contains:

[0032] The above-mentioned rare earth elements (R ２ The amount of the subphase containing rare earth elements (R) formed varies depending on not only the composition of the magnetic refrigeration material but also the homogenization treatment, but the content is 0.1% by volume or more of the entire magnetic refrigeration material, preferably 0.1% by volume to 2.0% by volume, and more preferably 0.1% by volume to 0.5% by volume. 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 the rare earth elements (R ２ This is thought to be because the inclusion of a subphase containing R causes microcracks to be introduced due to volume expansion during hydrogenation, making it easier for hydrogenation to proceed. ２ ５ A ２ ３ When the rare earth element (R ２ It is preferable that the content of the rare earth element (R) is 20% by volume or more of the subphase containing the rare earth element (R). When the content 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 in the main phase becomes more uniform. ２ ) in the subphase containing R ２ ５ A ２ ３ The upper limit of the range of the content is not particularly limited, but is, for example, 100% by volume.

[0033] The magnetic refrigeration material of the present invention preferably does not contain α-Fe. However, the magnetic refrigeration material of the present invention 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 entire magnetic refrigeration material, and more preferably 0.3 vol% or less. Within this range, the material is appropriately homogenized, resulting in a large amount of main phase, and therefore a large calorific value. The lower limit of the range of the α-Fe proportion is not particularly limited, but is 0 vol%, since it is preferable to contain as little α-Fe as possible.

[0034] 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.

[0035] The magnetic refrigeration material of the present invention can also be hydrogenated to increase the transition temperature. When hydrogenated, the above-mentioned magnetic refrigeration material can theoretically store up to 3.0 atomic % of hydrogen, but typically stores approximately 1.7 atomic % or less of hydrogen under atmospheric pressure. When using the magnetic refrigeration material at room temperature, it is generally hydrogenated to increase the transition temperature. In this case, the hydrogen concentration after hydrogenation is approximately 1.5 to 1.6. Therefore, the present invention can store hydrogen at 1.7 atomic % or less. The magnetic refrigeration material of the present invention can store hydrogen up to the saturated hydrogen amount under a wide range of hydrogenation conditions, stabilizing the transition temperature. The lower limit of the range of hydrogen storage capacity is not particularly limited, but is, for example, 1 atomic %.

[0036] Next, a raw material alloy for a magnetic refrigeration material and a method for manufacturing the magnetic refrigeration material of the present invention will be described. The raw material alloy for a magnetic refrigeration material and a method for manufacturing the magnetic refrigeration material of the present invention are used to manufacture the above-mentioned magnetic refrigeration material, and include a melting step in which raw materials are melted to obtain a raw material alloy containing La, Fe, and Si, a homogenization step in which the obtained raw material alloy is heat-treated to obtain a predetermined structure, and a hydrogenation step in which hydrogen is absorbed into the alloy as needed to raise the magnetic transition temperature.

[0037] In the melting process, the metals or alloys that will serve as the raw materials for each element are weighed so as to obtain the composition of the raw alloy for a magnetic refrigeration material of the present invention described above. 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 to obtain the 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 easier to obtain a fine and favorable structure. Liquid quenching allows for even faster cooling, making it easier to obtain an even finer and favorable structure. In this way, the raw alloy for a magnetic refrigeration material of the present invention can be obtained.

[0038] In the homogenization process, the raw alloy for magnetic refrigeration 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 a rare earth element, 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 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, 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. ２ ５ A ２ ３ This means that the amount of precipitation of the phase reaches a maximum and the peak value of the dm / dT-T characteristic reaches a maximum, 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 step, and can be carried out for example in the range of 1 hour to 100 hours, and more preferably in the range of 25 hours to 75 hours. Within this range, the amount of rare earth elements (R ２ ), the amount of the subphase containing R ２ ５ A２ 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.

[0039] In the hydrogenation process, when the magnetic transition temperature of the obtained magnetic refrigeration material is increased, hydrogen is absorbed into the magnetic refrigeration 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.

[0040] [Examples 1 to 3, Comparative Examples 1 to 3] La metal, Ce 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 300 to 1000°C / sec. The compositions of the obtained raw alloys for magnetic refrigeration materials are shown in Table 1. The alloy compositions were analyzed using a high-resolution ICP optical emission spectrometer (manufactured by Hitachi High-Tech Corporation, product name "SPS3500DD").

[0041]

[0042] The alloys of Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to heat treatment for 50 hours in an Ar atmosphere at homogenization temperatures of 1070°C, 1080°C, 1090°C, 1095°C, 1100°C, 1105°C, 1110°C, 1115°C, and 1120°C. The m-T characteristics of the resulting magnetic refrigeration materials were then measured using the VSM unit of a compact cryogen-free physical property measuring device (manufactured by Quantum Design, Inc., product name "VersaLab"). The transition temperature was determined by temperature differentiation of the m-T characteristics to determine the dm / dT-T characteristics, and the temperature at which the dm / dT-T characteristics peaked was determined as T. ｐｅａｋ The T ｐｅａｋ The graph plotting the change in

[0043] The rare earth elements (R ２ The volume ratio of the subphase containing α-Fe and the main phase composition, subphase 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 acquired SEM images. The main phase and subphase compositions were analyzed using EDS.

[0044] As shown in FIG. 1, in the case of y=12.3 in Comparative Example 1, a specific T ｐｅａｋ On the other hand, when y is 12.5 or more in Examples 1 to 3 and Comparative Examples 2 and 3, the specific T ｐｅａｋ No increase in temperature is observed, making it easier to control the transition temperature.

[0045] The magnetic refrigeration material of Comparative Example 1 was subjected to the homogenization temperature test. ２ The results of the structural observation of the subphase containing Cr are shown in FIG. 2, and the change in the Si content in the main phase at different homogenization temperatures is shown in FIG.

[0046] From the results of the structure observation in FIG. 2, it can be seen that the rare earth elements (R ２ It was found that the composition of the subphase containing rare earth elements (R) changes. In addition, it was found that the Si concentration in the main phase also changes accordingly, as shown in Figure 3. ２It was suggested that the Mn concentration and the rare earth element concentration in the main phase were also changed from the composition of the subphase containing such rare earth elements (R ２ ) due to the change in the composition of the subphase containing M １ Concentration of elements other than Fe in A １ It is considered that the concentration of elements other than Si changes in the transition temperature as homogenization progresses. ２ It is considered that the amount of the subphase containing the sintered ... ２ M ２ A ２ is LaFeSi, and R ２ ５ A ２ ３ Is La ５ Si ３ and R ２ ６ M ２ １１ A ２ ３ Is La ６ Fe １１ Si ３ It was.

[0047] The α-Fe content of the raw material alloys for magnetic refrigeration materials of Examples 1 to 3 and Comparative Examples 1 to 3 after heat treatment at 1105°C for 50 hours is shown in Figure 4, and the mT characteristics are shown in Figure 5. As Figure 4 shows, the α-Fe remains in the raw material alloys of Comparative Examples 2 and 3 even when optimally homogenized, and as a result, as shown in Figure 5, the magnetization in the paramagnetic state above the transition temperature becomes high, which is undesirable because it reduces the magnetization change due to the transition.

[0048] [Examples 4 to 6, Comparative Examples 4 to 7] In Examples 4 to 6 and Comparative Examples 4 to 6, the raw alloys for magnetic refrigeration materials of Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to an optimal homogenization treatment at 1105°C for 50 hours to obtain magnetic refrigeration materials. In Comparative Example 7, the raw alloy for magnetic refrigeration material of Example 2 was subjected to a homogenization treatment at 1080°C for 50 hours to obtain a magnetic refrigeration material.

[0049] Table 2 shows the rare earth elements (R ２ ) for Examples 4 to 6 and Comparative Examples 4 to 7. ２ The volume ratio of the subphase containing rare earth elements (R ２ ) among the subphases including R ２ ５ A ２ ３ The ratio of each phase is shown.

[0050]

[0051]

[0052] 6 shows the mT characteristics of the magnetic refrigeration materials of Example 4 and Comparative Example 5 when hydrogenation treatment was carried out at 200° C. for 3 hours in a hydrogen atmosphere of 0.1 MPa. ２ ), hydrogenation proceeds quickly and hydrogen is absorbed up to the saturated hydrogen amount, resulting in a steep mT characteristic. ２ ) content is low, α-Fe is precipitated, and rare earth elements (R ２ There are few subphases containing rare earth elements (R ２ Since there are few subphases containing rare earth elements (R), hydrogenation does not proceed sufficiently, and the mT characteristic indicates a broad and multi-stage transition, making it difficult to control the transition temperature. ２ ), the volume expansion caused by hydrogen absorption leads to the introduction of microcracks, which rapidly progresses hydrogenation, resulting in the appearance of a single, sharp transition.

[0053] 7 shows the mT characteristics when the magnetic refrigeration materials of Example 4 and Comparative Example 7 were subjected to hydrogenation treatment at 500°C and 0.1 MPa for 1 hour. In Comparative Example 7, the amount of α-Fe precipitated was large, resulting in large magnetization in the paramagnetic state, which is undesirable because the magnetization change is small when used as a magnetic refrigeration material, reducing the amount of heat that can be extracted.

Claims

1. R １ (M １ １－ｘ A １ ｘ ) ｙ (R １ is at least one element selected from the group consisting of La, La, rare earth elements other than La, and Zr, and M １ is Fe, or Fe and at least one element selected from the group consisting of Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti, and A １ is Si, or Si and at least one element selected from the group consisting of Al, Ga, P, Ge, Sn, and In, and x and y satisfy 0.09≦x≦0.14 and 12.4≦y<13.0, respectively.

2. A raw alloy for a magnetic refrigeration material according to claim 1, wherein y in said composition formula satisfies 12.5≦y≦12.

9.

3. R １ (M １ １－ｘ A １ ｘ ) ｙ (R １ is at least one element selected from the group consisting of La, La, rare earth elements other than La, and Zr, and M １ is Fe, or Fe and at least one element selected from the group consisting of Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti, and A １ is Si, or Si and at least one element selected from the group consisting of Al, Ga, P, Ge, Sn, and In, and x and y satisfy 0.09≦x≦0.14 and 12.4≦y<13.0, respectively. １３ La(Fe,Si) having a La-type crystal structure １３ The main phase of the alloy is a rare earth element (R ２ (R ２ is at least one element selected from the group consisting of La, La, rare earth elements other than La, and Zr), ２ % or more of a subphase containing α-Fe; and if α-Fe is contained, the proportion of said α-Fe is 0.5 vol % or less.

4. The rare earth element (R ２ ) is a subphase containing R ２ M ２ A ２ , R ２ ５ A ２ ３ , R ２ ６ M ２ １１ A ２ ３ and R ２ ２ M ２ １７ , R ２ (M ２ is Fe, or Fe and at least one element selected from the group consisting of Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti, and A ２ is Si, or Si and at least one element selected from the group consisting of Al, Ga, P, Ge, Sn, and In.

5. The above R １ 5. The magnetic refrigeration material according to claim 3, wherein the content of Ce is 30 atomic % or less.

6. The rare earth element (R ２ ) is a subphase containing R ２ ５ A ２ ３ The magnetic refrigeration material according to claim 3 or 4, comprising:

7. The rare earth element (R ２ The R ２ ５ A ２ ３ The magnetic refrigeration material according to claim 6, wherein the ratio of 8. The rare earth element (R ２ 5. The magnetic refrigeration material according to claim 3, wherein the ratio of the subphase containing the above-mentioned CrNbO2 is 2.00% by volume or less.

9. A magnetic refrigeration material according to claim 3 or 4, containing 1.7 atomic % or less of hydrogen.