Hydrogen alloys

Abstract

This invention provides a hydrogenated alloy in which the magnetic phase transition temperature (Tc) is controlled by the amount of hydrogen while maintaining performance, thereby suppressing splitting. [Solution] This invention relates to RE(M 1-x A x ) y X z H w A hydrogenated alloy represented by the compositional formula, where x, y, z, and w are 0.08 ≤ x ≤ 0.13, 12.3 ≤ y ≤ 13.2, 0.005 ≤ z ≤ 0.25, 0 <w<H sat (H sat The following conditions must be met: (the amount of saturated hydrogen at room temperature); RE is one or more elements selected from rare earth elements and Zr, and La is required; M is one or more elements selected from Fe, Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti, and Fe is required; A is one or more elements selected from Si, Al, Ga, P, Ge, Sn, and In, and Si is required; and X is one or more elements selected from B, C, and N, and B is required.

Description

Technical Field

[0001] The present invention relates to a hydrogenated alloy for magnetic refrigeration in which split progression is suppressed.

Background Art

[0002] In conventional gas compression / expansion type heat pumps, the use of CFC, which is an ozone layer depleting substance, has been prohibited, and currently HFC is mainly used. However, HFC has a problem in that its global warming potential is high. Although the development of refrigerants with a low global warming potential has been actively carried out, no new refrigerant that satisfies in terms of performance, cost, and safety has been put into practical use. Under such circumstances, magnetic refrigeration systems using the magnetocaloric effect without using greenhouse gases have attracted attention.

[0003] Magnetic refrigeration systems utilize the change in magnetic entropy (magnetocaloric effect, ΔS). As materials with a large absolute value of ΔS, Mn(As Z , 13 Sb x )(Patent Document 1) and La(Fe 1-x Si x ) 13 H Z (Patent Document 2) etc. can be mentioned. In particular, the former has a very large ΔS of -30 J / kgK and can be an excellent magnetic refrigeration material. However, since As in the components of Mn(As 1-x Sb x ) shows toxicity, it is substantially difficult to apply. La(Fe 1-x Si x ) 13 H Z has a ΔS of ~25 J / kgK, which is large next to Mn(As 1-x Sb x ), and the constituent elements do not show toxicity and are not rare metals, so it is the most promising substance.

[0004] These materials are required to operate near room temperature (around -70 to +70°C). However, unlike conventional magnetic refrigeration, which has been used as a means to generate extremely low temperatures that are difficult to achieve with gas refrigeration, there was a problem that the magnetocaloric effect decreased at the above operating temperature because lattice vibrations could not be ignored. With the development of AMR (Active Magnetic Regenerator), which utilizes these lattice vibrations as a heat storage effect, refrigeration and air conditioning systems that utilize the magnetocaloric effect at near room temperature have become a reality.

[0005] When applying magnetic refrigeration materials to AMR systems operating near room temperature, it is necessary to adjust the magnetic phase transition temperature (Tc) to be near room temperature. (La(Fe) 1-x Si x ) 13 H Z In this case, by absorbing hydrogen, the Tc can be raised from around -80°C to around 60°C with almost no decrease in ΔS. Furthermore, as reported in Non-Patent Literature 1, by adjusting the amount of hydrogen absorbed, the Tc can be controlled to any temperature within the above temperature range, making it possible to produce a material with a Tc adjusted to near room temperature.

[0006] On the other hand, as described in Non-Patent Literature 2, it is known that when an alloy with reduced hydrogen content is kept near the magnetic phase transition temperature for a long period of time, a phenomenon called split occurs, in which transitions occur at multiple temperatures. This split is thought to occur because, near the magnetic phase transition temperature, the paramagnetic and ferromagnetic phases coexist, causing hydrogen to diffuse from the paramagnetic phase to the more stable ferromagnetic phase as a hydride. In AMR, the magnetic refrigeration material is constantly kept near its Tc, and is therefore constantly exposed to an environment where split is likely to occur.

[0007] As a method to suppress splitting, Patent Document 3 proposes a method of using hydrogen absorbed to a saturation point. This method is said to be able to stop the progression of splitting. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2003-28532 [Patent Document 2] Japanese Patent Publication No. 2006-89839 [Patent Document 3] Japanese Patent Publication No. 2012-41631 [Non-patent literature]

[0009] [Non-Patent Document 1] PHYSICAL REVIEW B 67, 104416 (2003) [Non-Patent Document 2] IEEE Transactions on Magnetics (Volume:47,Issue:10, October 2011) [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] However, the method described in Patent Document 3 involves adsorbing hydrogen to a saturation level, so the adjustment of Tc in the magnetic refrigeration material is mainly done by adding Mn, which presents the problem of a decrease in ΔS simultaneously with a decrease in Tc.

[0011] Furthermore, when magnetic refrigeration materials that have absorbed hydrogen in a hydrogen atmosphere are removed from the hydrogen atmosphere to the atmosphere, the partial pressure of hydrogen decreases, and ultimately, it is thought that the absorbed hydrogen will gradually escape. Therefore, magnetic refrigeration materials that have absorbed hydrogen to a saturation level may, during long-term storage in the atmosphere, gradually lose hydrogen, exceeding a certain threshold for the amount of hydrogen at which a split occurs, and thus risk suddenly initiating a split.

[0012] On the other hand, methods for controlling Tc by controlling the amount of hydrogen through hydrogenation conditions, such as Non-Patent Document 1, have the advantage of being able to adjust Tc while maintaining ΔS. However, because the amount of hydrogen is reduced from the saturation level, splits tend to occur as described above, making long-term use in AMR systems difficult.

[0013] The present invention has been made in view of the above circumstances, and aims to provide a hydrogenated alloy in which Tc is controlled by reducing the amount of hydrogen from the saturation amount, thereby suppressing splitting due to changes over time and enabling long-term use. [Means for solving the problem]

[0014] As a result of diligent research to achieve the above objective, the inventors of the present invention have discovered that a hydrogenated alloy having a predetermined composition can be used for a long period of time without splitting even when the hydrogen content is reduced from the saturation amount to control Tc, thereby obtaining a highly durable hydrogenated alloy that can be used for a long period of time, and thus the present invention has been completed.

[0015] Therefore, the present invention provides the following hydrogenated alloys. [1] RE(M 1-x A x ) y X z H w A hydrogenated alloy represented by the compositional formula, where x, y, z, and w are 0.08 ≤ x ≤ 0.13, 12.3 ≤ y ≤ 13.2, 0.005 ≤ z ≤ 0.25, 0 <w<H sat (H sat A hydrogenated alloy that satisfies the amount of saturated hydrogen at room temperature, wherein RE is one or more elements selected from rare earth elements and Zr, and La is required, M is one or more elements selected from Fe, Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag and Ti, and Fe is required, A is one or more elements selected from Si, Al, Ga, P, Ge, Sn and In, and Si is required, and X is one or more elements selected from B, C and N, and B is required. [2]H sat Ratio of absorbed hydrogen P H(=w / H sat The hydrogenated alloy described in [1] above, wherein the ratio is 0.95 or less. [3] Keeping the composition the same except for the value of w, w = H sat A hydrogenated alloy according to [1] or [2] above, having a magnetic phase transition temperature that is 2K or more lower than the magnetic phase transition temperature when [the other method is used]. [4] The amount of B contained in X is z B , the amount of C is z C , the amount of N is z N Let z = z B +z C +z N When z B A hydrogenated alloy described in any one of the above [1] to [3], wherein the ratio is 0.005 or greater. [5]z B While keeping the composition the same except for the value of z B Let c0 be the lattice constant when z = 0. B While keeping the composition the same except for the value of z B When the lattice constant is >0, c B In that case, c B The hydrogenated alloy described in [4] above, wherein c0 ≤ c0. [6] Compared to a hydrogenated alloy where z=0 while keeping the composition other than the value of z the same, the change in which the magnetic phase transition temperature separates into multiple parts when held at the magnetic phase transition temperature for 300 hours is suppressed, as described in any one of [1] to [6] above. [7] A hydrogenated alloy according to any one of [1] to [6] above, wherein the hydrogen is absorbed at 300°C and 0.10 MPaH2 until the saturated hydrogen content is reached, held at the magnetic phase transition temperature for 300 hours, and the difference in magnetic phase transition temperature between the temperature at which the split is allowed to proceed and the magnetic phase transition temperature is 3.0 K or less. [8]H sat Ratio of absorbed hydrogen (w / H) sat ) to P H Let t be the time when the difference between the magnetic phase transition temperatures during the split widens to a certain temperature, and plot P on the x-axis. H , log on the y-axis 10Plot (t) and perform linear approximation. The slope of the approximate line for the hydride alloy at z=0 is a0, the intercept is b0, and the slope of the approximate line for the sample at z>0 is a. Z , the intercept is b Z When a0 > a Z Or, b0 Z A hydrogenated alloy as described in any one of the following [1] to [7]. [9] A hydrogenated alloy as described in any one of the following [1] to [8], wherein the α-Fe phase content is 6 volume% or less.

[10] NaZn 13 The main phase has a type crystal structure, and RE2Fe 14 A hydrogenated alloy as described in any one of the following [1] to [9], comprising an X-phase and a sub-phase.

[11] RE2Fe 14 A hydrogenated alloy as described in

[10] , wherein the volume fraction of the X phase is 0.01% or more and 6% or less.

[12] The Si concentration in the main phase is Si 1-13 The RE2Fe 14 The Si concentration in the X phase is Si 2-14-1 When that happens, Si 1-13 / Si 2-14-1 The hydrogenated alloys described in

[10] or

[11] above, wherein the ratio is ≤ 1.2. [Effects of the Invention]

[0016] According to the present invention, the magnetic phase transition temperature (Tc) can be controlled by the amount of hydrogen while maintaining performance, and a hydrogenated alloy with suppressed splitting can be provided. [Brief explanation of the drawing]

[0017] [Figure 1] Figure 1 is a graph showing the progress of the split when Examples 1-4 and Comparative Example 1 were held in a constant temperature bath set to the magnetic phase transition temperature of each sample. [Figure 2] Figure 2 is a graph showing the progress of the split when Examples 5 and 6 and Comparative Examples 2 and 3 were held in a constant temperature bath set to the magnetic phase transition temperature of each sample. [Figure 3] ​Figure 3 is a graph showing the amount of B added and the latent heat of the FP magnetic phase transition for Examples 1-4 and Comparative Examples 1 and 4. [Figure 4] Figure 4 is a graph showing the temperature difference between each magnetic phase transition temperature when an alloy of composition 7 is homogenized under the homogenization conditions shown in Table 4, then hydrogenated at 300°C for 7 hours in a hydrogen atmosphere of 0.10 MPaH2, and held in a constant temperature bath set to the magnetic phase transition temperature for 100 hours to allow the split to proceed. [Figure 5] Figure 5 is a graph showing the change in the amount of B added and the lattice constant of the main phase for Examples 1-4 and Comparative Example 1. [Figure 6] Figure 6 is a graph showing the changes in Si concentration in the RE(Fe,Si)13 phase and RE2Fe14X phase when composition 3 is subjected to homogenization treatment at different temperatures for 45 hours. [Figure 7] Figure 7 is a graph showing the changes in Si concentration in the RE(Fe,Si)13 phase and RE2Fe14X phase when composition 3 is subjected to homogenization treatment at different temperatures for 45 hours. [Figure 8] Figure 8 is a graph showing the dm / dT-T characteristics when composition 3 was homogenized at 1130°C and 1150°C for 45 hours, followed by hydrogen storage at 300°C and 0.10 MPa. [Modes for carrying out the invention]

[0018] The hydrogenated alloy of the present invention is RE(M 1-x A x ) y X z H w A hydrogenated alloy represented by the compositional formula, where x, y, z, and w are 0.08 ≤ x ≤ 0.13, 12.3 ≤ y ≤ 13.2, 0.005 ≤ z ≤ 0.25, 0 <w<H sat (H sat The hydrogenated alloy of the present invention satisfies the saturation hydrogen content at room temperature. 13 RE(Fe,Si) with a type crystal structure 13 It is preferable that the phase contains a hydride as the main phase.

[0019] RE is one or more elements selected from rare earth elements and Zr, with La being essential, and may also contain one or more elements selected from Nd, Ce, and Pr. This allows for control of the magnetic phase transition temperature and other parameters.

[0020] When elements other than La are present in RE, homogenization becomes more difficult as the amount of substitution increases. Ce can be contained in up to 40 atomic percent or less of the total RE, Pr in up to 60 atomic percent or less of the total RE, and Nd in up to 40 atomic percent or less of the total RE. This lowers the magnetic phase transition temperature, increases ΔS, and increases hysteresis. The maximum content of RE elements other than La is also affected by the values ​​of x and z; the smaller x and the larger z, the smaller the maximum content. When a portion of RE is replaced with Zr, the replacement can be limited to less than 10 atomic percent of the total RE. Within this range, the magnetic phase transition temperature can be increased. Furthermore, some of the RE in the subphase can be substituted with one or more elements selected from rare earth elements and Zr.

[0021] M is one or more elements selected from the group consisting of Fe, Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti, with Fe being essential. If M contains elements other than Fe, the magnetic phase transition temperature, full width at half maximum, hysteresis, etc. of the magnetic refrigeration material can be controlled in the same way as above. If M contains Mn, it can be included in a range of 4 atomic percent or less of the total M. By including it within this range, the magnetic phase transition temperature can be lowered. Furthermore, some of the Fe in the subphase can be replaced with one or more elements selected from the group consisting of Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti.

[0022] A is one or more elements selected from the group consisting of Si, Al, Ga, P, Ge, Sn, and In, with Si being essential. Even if A contains elements other than Si, the magnetic phase transition temperature, full width at half maximum, hysteresis, etc., can be controlled. If A contains Al, it can be substituted for the essential element Si in an amount of 0 to 50 atomic percent. Within this range, the magnetic phase transition temperature can be lowered, and the hysteresis can be further reduced. The larger x is, and the higher the Si concentration in A, the larger the maximum content of RE elements other than La and the maximum content of X can be. Furthermore, some of the Si in the subphase can be replaced with one or more elements selected from the group consisting of Al, Ga, P, Ge, Sn, and In.

[0023] In the above composition, X is one or more elements selected from the group consisting of B, C, and N, with B being essential. X may also contain at least one element of C and N. C and N are inevitably present due to raw material origins or adsorption and reactions during the manufacturing process, but they may be intentionally added within the range of z described later.

[0024] In the above composition, x is between 0.08 and 0.13. If x is less than 0.08, the stability of the main phase decreases, making homogenization difficult, and the formation of heterogeneous phases degrades the properties. As x increases, the stability of the main phase increases, but the first-order phase transition tends to weaken, causing ΔS to decrease. Therefore, if x is greater than 0.13, the performance degradation becomes too great.

[0025] In the above composition, y is between 12.3 and 13.2. By changing y from the symmetric ratio of the main phase (13.0) to produce alloys, the hydrogen storage behavior can be controlled. However, if y is less than 12.3 or greater than 13.2, the proportion of the main phase decreases, resulting in a decrease in properties. For this reason, y is preferably 12.7 or higher. Furthermore, y is preferably 13.1 or lower.

[0026] The z value in the above composition is between 0.005 and 0.25. If z is less than 0.005 or greater than 0.25, the split progression cannot be effectively suppressed. From this viewpoint, the z value in the above composition is preferably 0.04 or higher, preferably 0.13 or lower, and more preferably 0.08 or lower.

[0027] The amount of B contained in the above X is z B , the amount of C is z C , the amount of N is z N Let z = z B +z C +z N When expressed as, z B A value of 0.005 or higher is preferred, and 0.01 or higher is more preferred. Furthermore, a value of 0.25 or lower is preferred, and 0.05 or lower is more preferred. Within this range, split progression is more effectively suppressed while maintaining performance.

[0028] The hydrogenated alloy of the present invention is 0 <w<H sat This is a hydrogenated alloy that absorbs hydrogen within a certain range. This hydrogen content range indicates that while hydrogen is absorbed, the hydrogen content is less than the saturation point at room temperature, and it is a region where splitting can occur. sat While it varies depending on the composition, it is generally considered to be around w = 1.4 to 1.7. H sat H is the amount of saturated hydrogen at room temperature in each alloy composition. In this invention, H is the amount of hydrogen at which Tc does not rise any further when hydrogen is absorbed at a temperature of 30°C and in a hydrogen atmosphere of 0.10 to 0.25 MPa for at least 5 hours. sat Prior to hydrogen storage treatment, an activation treatment is generally performed, for example, by heat treatment at 300-500°C for 1-2 hours in a vacuum or hydrogen atmosphere.

[0029] In this type of hydrogenated alloy, w <H sat In other words, P H (=w / H sat A split occurs when ) is less than 1, P H The smaller the value, the faster the split progresses. P of the hydrogenated alloy of the present invention His preferably 0.95 or less, more preferably 0.90 or less, and even more preferably 0.85 or less. The P of the hydrogen storage alloy of the present invention H The lower limit of the range is not particularly limited, but the P of the hydrogen storage alloy of the present invention H is usually 0.01 or more, preferably 0.10 or more, more preferably 0.50 or more, still more preferably 0.55 or more, even more preferably 0.60 or more, and even more preferably 0.65 or more. The above is the hydrogen concentration range in which splitting can proceed. The hydrogen storage alloy of the present invention can effectively suppress splitting even in such a range. Incidentally, P H represents the ratio of the amount of hydrogen occluded to H sat and is represented by P H = w / H sat . Although not particularly limited, the amount of hydrogen w contained in the hydrogen storage alloy can be measured, for example, by an inert fusion conduction method using an oxygen, nitrogen, and hydrogen analyzer ONH836 manufactured by LECO.

[0030] The hydrogen storage alloy of the present invention preferably has a Tc that is 2 K or more lower than Tc when w = H sat while keeping the composition other than the value of w the same. Thereby, it is possible to obtain a hydrogen storage alloy in which splitting is suppressed while sufficiently reducing Tc. From such a viewpoint, the hydrogen storage alloy of the present invention has a Tc that is 5 K or more lower than Tc when w = H sat while keeping the composition other than the value of w the same, more preferably 10 K or more lower, still more preferably 20 K or more lower.

[0031] The hydrogen storage alloy of the present invention has a lattice constant c0 when z B is set to 0 while keeping the composition other than the value of z the same, and a lattice constant c B when z B is set to be greater than 0 while keeping the composition other than the value of z the same. In the case where B is c B , c B ​It is preferable that c ≤ c0. This suppresses splitting and allows for the acquisition of a magnetic refrigeration material with high properties. From this viewpoint, the lattice constant when the lattice constant takes its minimum value is c min When that happens, c min ≤c B It is more preferable that c0 ≤ c0.

[0032] Normally, it is generally assumed that light elements such as B, C, and N penetrate the lattice in interstitial solid solution mode, expanding the crystal lattice and increasing the lattice constant monotonically. However, when a small amount of B is added and the amount is increased, the lattice constant initially decreases, reaches a minimum value at a certain point, then reverses and begins to increase. Simultaneously, Tc also decreases once, reaches a minimum value, and then increases. The reason for this is not entirely clear, but it is speculated that in the case of small amounts of B added, the lattice constant decreases because B substitutes, for example, at Fe sites in a substitutional solid solution mode, whereas when a certain amount or more of B is added, substitutional solid solution becomes difficult, and B begins to dissolve in the lattice in an interstitial solid solution mode, causing the lattice constant to increase.

[0033] Under the above assumptions, the stability of the main phase hydride in paramagnetic and ferromagnetic states was evaluated for three cases: no B solid solution, B substitution type solid solution, and B interstitial type solid solution. In the case of substitution type solid solution, the difference in stability between paramagnetic and ferromagnetic states became smaller in the total hydrogen content region, showing a tendency for splitting to be further suppressed. In the case of interstitial type solid solution, H sat In the low hydrogen concentration region below / 2, the difference in stability between paramagnetism and ferromagnetism was small, and a tendency for splitting to be suppressed was observed. Therefore, it is thought that adding B further suppresses splitting in regions where the lattice tends to shrink, and even more so in regions where the lattice tends to expand. However, while increasing the amount of B added can suppress the progression of splitting, increasing it too much increases the amount of heterogeneous phase formation and degrades the properties. Therefore, it is preferable that the lattice constant when B is added is c0 or less.

[0034] The hydrogenated alloy of the present invention is NaZn 13 The main phase has a type crystal structure, and RE2Fe14 It is preferable to include a subphase containing the X phase. For example, by adding B as the element X, RE2Fe can be used as the subphase. 14 The X phase can be formed in the hydrogenated alloy. The hydrogenated alloy of the present invention is RE2Fe 14 It is preferable that the X phase is present in a volume of 0.01% or more. This allows for more effective suppression of splitting. Furthermore, the hydrogenated alloy of the present invention is RE2Fe 14 It is preferable that the X phase be present in a volume percentage of 6% or less. This helps to suppress the deterioration of properties due to a decrease in the proportion of the main phase. The method for measuring the volume fraction is not particularly limited, but the volume fraction can be calculated by, for example, using a JSM-IT300LV (manufactured by JEOL Corporation), binarizing the SEM image obtained using the difference in contrast due to composition, calculating the area of ​​each phase, and considering the area fraction as the volume fraction. RE2Fe 14 The reason why the X phase can suppress the progression of the split is not entirely clear, but it can be thought of as follows: When the sample is hydrogenated, not only the main phase but also RE2Fe 14 The X phase can also form hydrides, but when the sample is held directly above Tc where the split is progressing, ferromagnetic and paramagnetic phases RE(Fe,Si) with different hydride stabilities are formed. 13 In addition, there is a third RE2Fe with a different hydride stability. 14 It is presumed that the presence of the hydride in phase X causes the third phase to act as a hydrogen buffer, making it difficult for differences in hydrogen concentration to occur between the ferromagnetic and paramagnetic phases.

[0035] In the field of permanent magnets, RE2Fe 14 It is known that the B phase can have some of its B sites replaced with carbon. In the present invention, carbon, whether due to impurities or intentionally added, is also found in RE2Fe 14 It is thought that the B site of the B phase is being replaced. Therefore, it is inevitably included as an impurity, but even if C is intentionally added as X, RE2Fe 14 It is presumed that the formation of (B,C) is promoted, enhancing the split-suppressing effect.

[0036] As described above, although the reason why the inclusion of X suppresses the progression of splitting is not entirely clear, it is presumed that two factors contribute. The first is the reduction of the difference in stability between the paramagnetic and ferromagnetic phase hydrides due to the solid solution of B in the main phase. The second is the formation of RE2Fe by adding X. 14 The X phase acts as a hydrogen buffer, making it difficult for the hydrogen concentration to differ between the ferromagnetic and paramagnetic phases of the main system. It is presumed that these combined effects suppress the progression of the split.

[0037] In the hydrogenated alloy of the present invention, the α-Fe content is preferably 6% by volume or less, and more preferably 4% by volume or less. By controlling homogenization to fall within this range, a high-performance alloy can be obtained.

[0038] The hydrogenated alloy of the present invention preferably exhibits suppressed splitting when held at the magnetic phase transition temperature, compared to a hydrogenated alloy with the same composition except for the z value, but with z=0. Specifically, the hydrogenated alloy of the present invention preferably exhibits suppressed separation of the magnetic phase transition temperature into multiple parts when held at the magnetic phase transition temperature for 300 hours, compared to a hydrogenated alloy with the same composition except for the z value, but with z=0. The evaluation of split progression involves changing the hydrogen concentration to H sat For hydrogenated alloys controlled to a certain temperature, the hydrogenated alloy is held above its Tc for a sufficiently long period of time. Measurements used to detect the magnetic phase transition of magnetic refrigerants, such as DSC-T characteristics by DSC measurement and dm / dT-T characteristics by VSM measurement, can be evaluated by the temperature difference between each of the multiple magnetic phase transition temperatures that occur. A smaller temperature difference indicates a smaller difference in hydrogen concentration in each region and suppressed splitting. The vicinity of the peak value in each measurement is fitted with a quadratic function, and the temperature at which the maximum value is obtained is defined as the magnetic phase transition temperature.

[0039] To evaluate the split progression, it is necessary to maintain the state directly above Tc where paramagnetism and ferromagnetism coexist, but RE(Fe,Si) 13The magnetic phase transition of a phase is fundamentally a first-order phase transition and therefore exhibits temperature hysteresis. The temperature (Tc) changes when the temperature is lowered (a transformation from paramagnetic to ferromagnetic, called the PF transformation) and when the temperature is raised (a transformation from ferromagnetic to paramagnetic, called the FP transformation). It is necessary to pay attention to the direction of the transition when determining the holding temperature. For example, a constant temperature bath is used to control the temperature of a sample. If the sample's Tc is lower than room temperature, when lowering the temperature by placing it in the constant temperature bath from room temperature, a transformation from paramagnetic to ferromagnetic occurs, so it is necessary to hold the sample just above the Tc of the PF transformation. If the Tc is too far away, splitting is less likely to occur, making it difficult to determine how the peaks separate. Furthermore, since there are usually differences between the temperature of measuring devices such as DSC measuring instruments and the temperature of the constant temperature bath, it is necessary to maintain the temperature while taking into account the differences between each device.

[0040] Regarding retention time, depending on the sample composition and hydrogen content, split progression may not be observed for several months, so it is necessary to use a sufficiently long retention period. Since split progression tends to accelerate as the hydrogen content decreases, it is also possible to accelerate and evaluate the split using samples with reduced hydrogen content.

[0041] It is preferable that the magnetic phase transition temperature difference between the magnetic phase transition temperature (Tc) of the hydrogenated alloy of the present invention and the magnetic phase transition temperature obtained when the hydrogenated alloy of the present invention is subjected to hydrogen absorption treatment at 300°C and 0.10 MPaH2 until it reaches a saturated hydrogen amount, held at the magnetic phase transition temperature for 300 hours to allow splitting to proceed is 3.0 K or less. Hydrogenated alloys within this range have sufficiently suppressed splitting and can be said to be suitable for use as magnetic refrigeration materials. From this viewpoint, the above magnetic phase transition temperature difference is more preferably 2.8 K or less, even more preferably 2.0 K or less, and even more preferably 1.5 K or less.

[0042] To quantify the split progression, the saturated hydrogen amount H sat Ratio of absorbed hydrogen to (w / H sat ) to P H Let t be the time when the temperature between peaks is separated by more than a certain temperature, and plot P on the x-axis. H log 10Plot (t). While 2K is often used as the threshold for the temperature difference between peaks that determines t, it is not limited to 2K and can be set to any value, as long as it is consistent within the test being evaluated. In this case, P H vs log 10 (t) can be approximated by a straight line, and a small slope a and a large intercept b indicate that the split is less likely to progress. This method can also be used for predicting lifespan through accelerated split testing.

[0043] In the linear approximation above, let a0 be the slope and b0 be the intercept when z is 0, and let a be the slope when z is 0.005 or greater. Z , the intercept is b Z When a0 > a z Or, b0 z When this occurs, splits are suppressed, allowing the AMR system to maintain performance for a longer period of time.

[0044] The hydrogenated alloy of the present invention is NaZn 13 The main phase has a type crystal structure, and RE2Fe 14 When the main phase includes a subphase containing the X phase, the Si concentration in the main phase is Si 1-13 RE2Fe 14 The Si concentration in X is Si 2-14-1 When that happens, Si 1-13 / Si 2-14-1 It is preferable that the value be ≤1.2. Good magnetic properties can be obtained within this range. The main phase is RE(Fe,Si) 13 It is known that as the Si concentration of the phase hydride increases, the magnetic phase transition approaches a second-order transition from a first-order transition, causing ΔS and dm / dT to decrease. However, since it is within the above range, B is added to RE2Fe 14 Even in the environment where the X phase is formed, the amount of Si in the main phase can be controlled without becoming unnecessarily high, and it is believed that a high-performance material can be obtained. Subphase is RE2Fe 14 If the X phase is present, changing the homogenization temperature (temperature, time, etc.) will produce RE(Fe,Si). 13 Phase hydrides and RE2Fe 14 ​The amount of Si in the X phase changes, which is due to RE2Fe 14 The X phase decomposes, resulting in RE2Fe 14 RE(Fe,Si) from phase X 13 This is presumed to be because Si migrates to the hydride phase. While not particularly limited, the Si concentration in each phase can be measured, for example, by point analysis using EDS with JSM-IT300LV (manufactured by JEOL Corporation).

[0045] Next, the method for producing the hydrogenated alloy for magnetic refrigeration according to the present invention will be described. The present invention provides a method for producing a hydrogenated alloy, comprising: a melting step of dissolving raw materials to obtain a raw material alloy containing RE, M, A, and X; a homogenization step of performing heat treatment on the obtained raw material alloy to obtain a predetermined structure; and a hydrogenation step of performing hydrogen storage in the alloy.

[0046] In the melting process, the raw materials metals or alloys of each element are weighed to obtain the alloy composition of the present invention described above. The raw materials are heated to 1600°C and melted by, for example, high-frequency induction melting in an Ar atmosphere, and the alloy is obtained by cooling as rapidly as possible at a cooling rate of 500°C / sec or more. There are no particular limitations on the casting of this alloy, but methods such as strip casting, liquid quenching, and atomization can be applied. With the strip casting method, cooling can be performed quickly, making it easier to obtain a fine and good microstructure. Using the liquid quenching method allows for even faster cooling, making it easier to obtain an even finer and better microstructure.

[0047] In the homogenization process, the alloy obtained in the melting process is heat-treated to create a homogeneous RE(Fe,Si) alloy. 13A heat treatment is performed to form the phase. This homogenization treatment is not particularly limited as it depends on the alloy structure and composition, but can be performed in a temperature range of, for example, 1000°C to 1300°C. In particular, as mentioned above, when rare earth elements other than La are included as RE, the optimal heat treatment temperature range for the homogenization treatment becomes narrower. For example, compared to the case with La alone, the temperature tends to fluctuate by about +10 to +20°C when Ce is included, and by about +10 to +50°C when Pr and Nd are included. In addition, the temperature can fluctuate by several tens of degrees depending on the amount of element A and the type of element M and its substitution amount. For example, when the amount of Si as element A is small, the decomposition temperature decreases, so the optimal heat treatment temperature tends to decrease. Therefore, the optimal heat treatment conditions are not limited to the above range, but are the state in which the amount of Fe deposition is minimized or the latent heat obtained from DSC is maximized, and can be experimentally confirmed considering the above factors. Furthermore, the homogenization time can be appropriately adjusted depending on the state of the alloy obtained in the melting process, and can be carried out in a range of, for example, 1 hour to 200 hours, with a range of 25 hours to 75 hours being more preferable. Within this range, a sufficiently homogenized alloy can be obtained while maintaining mass productivity. In addition, it is preferable to carry out the homogenization treatment in an Ar atmosphere in order to suppress compositional deviations caused by the evaporation of specific elements from the raw alloy.

[0048] In the hydrogenation process, to raise the magnetic phase transition temperature of the obtained magnetic refrigeration material, hydrogen can be absorbed into the magnetic refrigeration material under a hydrogen atmosphere to obtain a hydride. While there are no particular restrictions on specific conditions, activation treatment is generally performed before hydrogenation, for example, by heat treatment at 300-500°C for 1-2 hours in a vacuum or hydrogen atmosphere. For the hydrogen atmosphere during the hydrogenation treatment, conditions of 0.1-0.35 MPa can be used. The hydrogenation temperature can be, for example, between 50°C and 500°C. Within this range, the hydrogen saturation concentration can be reached in a relatively short time. The hydrogenation treatment time can be, for example, between 1 hour and 1000 hours, but considering mass productivity and the attainment of hydrogen saturation concentration, a time of 3 hours to 50 hours is more preferable. [Examples]

[0049] The present invention will be described more specifically below with reference to examples, but the present invention is not limited to these examples.

[0050] La metal, Ce metal, Mn metal, Si metal, electrolytic iron, and metal B were weighed to achieve the desired composition. These were then heated to 1500°C in an Ar gas atmosphere in a high-frequency induction melting furnace to melt them, and then cooled at a rate of 300-1000°C / sec by strip casting to produce alloy strips with an average film thickness of approximately 300 μm. The obtained alloys were heat-treated under an Ar atmosphere for 45 hours, with the homogenization temperature varied between 1000°C and 1250°C. The composition of the prepared samples and the optimal homogenization temperature are shown in Table 1. The alloy composition was analyzed using an SPS3500DD (manufactured by Hitachi High-Tech Corporation). The optimal homogenization temperature was determined by performing a DSC (NETZSCH DSC3500Sirius) measurement after the hydrogenation treatment described later, and the temperature at which the latent heat was greatest was considered the optimal homogenization condition.

[0051] [Table 1]

[0052] The subsequent hydrogenation treatment involved activation in a vacuum at 500°C, followed by hydrogen absorption in a 0.10 MPa hydrogen atmosphere at 250-300°C for 1-200 hours, and then rapid cooling. 13 The main phase of the type crystal structure has less hydrogen storage capacity at higher temperatures, so hydrogenation storage at 50°C or higher, preferably 100°C or higher, is required to achieve a saturated hydrogen content (H sat The following materials are produced. The method for adjusting the amount of hydrogen is not limited to temperature; it can also be controlled by controlling the hydrogen partial pressure and time.

[0053] Subsequent split experiments were conducted using ESPEC constant temperature baths (SH-642, LU-114) to measure the T of each hydride alloy. cThe samples were kept at a temperature, removed after a certain period of time, and their mT characteristics were measured using a VersaLab VSM unit (manufactured by QuantumDesign Inc.). The evaluation was performed by calculating the temperature difference between peaks from the peak values ​​of the dm / dT-T curve.

[0054] [Examples 1-4, Comparative Examples 1, 4] After homogenizing alloys of compositions 1 to 6 at the optimal homogenization temperature for 45 hours, hydrogen was absorbed under a hydrogen atmosphere of 0.10 MPaH2 at 300°C for 15 hours, followed by rapid cooling and extraction to obtain hydride alloys. Comparative Example 1 is obtained by performing the above treatment on composition 1, Examples 1 to 4 are obtained by performing the treatment on compositions 2 to 5, and Comparative Example 4 is obtained by performing the treatment on composition 6.

[0055] Figure 1 shows the progression of splitting when Examples 1-2 and Comparative Example 1 were held in a constant temperature bath set to the magnetic phase transition temperature of each sample. The vertical axis represents the temperature difference between each magnetic phase transition temperature at the time of splitting, and the horizontal axis represents the holding time. It can be seen that as the amount of B added increases, it takes longer for the temperature difference between peaks to widen, and the progression of splitting is suppressed.

[0056] [Examples 5 and 6, Comparative Examples 2 and 3] Compositions 1 and 3 were homogenized under optimal homogenization conditions, then hydrogen was absorbed under a hydrogen atmosphere of 0.10 MPaH2 at 275°C for 148 hours, followed by rapid cooling to obtain the hydrogenated alloys. Comparative Example 2 is the result of the above treatment on composition 1, and Example 5 is the result of the above treatment on composition 3. Compositions 1 and 3 were homogenized under optimal homogenization conditions, then hydrogen was absorbed under a hydrogen atmosphere of 0.10 MPaH2 at 250°C for 166 hours, followed by rapid cooling to obtain the hydrogenated alloys. Comparative Example 3 is the result of the above treatment on composition 1, and Example 6 is the result of the above treatment on composition 3.

[0057] Figure 2 shows the progress of splitting when Examples 5 and 6 and Comparative Examples 2 and 3 were held in a constant temperature bath set to the magnetic phase transition temperature of each sample. The vertical axis represents the temperature difference between each magnetic phase transition temperature at the time of splitting, and the horizontal axis represents the holding time.H In the sample with a high amount of B added, it takes longer for the interpeak temperature difference to widen, indicating that the splitting is suppressed. From this, it can be concluded that, regardless of the hydrogen concentration, if B is an alloy with a predetermined concentration, the splitting will be suppressed.

[0058] [Examples 7-9, Comparative Example 5] Compositions 8 to 11 were homogenized under optimal homogenization conditions, then hydrogen was absorbed under a hydrogen atmosphere of 0.10 MPaH2 at 275°C for 148 hours, followed by rapid cooling and extraction to obtain the hydrogenated alloys. Comparative Example 5 is the result of the above treatment applied to composition 8, and Examples 7 to 9 are the results of the above treatment applied to compositions 9 to 11.

[0059] Figure 3 shows the progress of splitting when Examples 7-9 and Comparative Example 5 were held in a constant temperature bath set to the magnetic phase transition temperature of each sample. The vertical axis represents the temperature difference between each magnetic phase transition temperature at the time of splitting, and the horizontal axis represents the holding time. H In the sample with a high amount of B added, it takes longer for the interpeak temperature difference to widen, indicating that the splitting is suppressed.

[0060] Figure 4 shows the amount of B added and the latent heat of the FP magnetic phase transition for Examples 1-4 and Comparative Examples 1 and 4. B As z increases, the latent heat decreases, B At =0.3 (Comparative Example 4), the latent heat is less than half. Table 3 shows the optimal homogenization conditions for α-Fe and RE2Fe in Examples 1-4 and Comparative Examples 1 and 4. 14 This shows the volume fraction of X. Increasing the addition of B results in α-Fe and RE2Fe. 14 It is presumed that the increase in the amount of X formed reduces the proportion of the main phase and thus lowers the latent heat. Therefore, α-Fe is 6% by volume or less, and RE2Fe 14 It is desirable that X is 6% or less by volume.

[0061] Composition of the hydride alloys in Examples 1-9 and Comparative Examples 1-5, and Hsat, P H The values ​​are shown in Table 2. [Table 2]

[0062] [Table 3]

[0063] [Examples 10-14] Figure 5 shows the temperature difference between each transition temperature when an alloy of composition 7 was homogenized under the homogenization conditions shown in Table 4, then hydrogenated at 300°C for 7 hours in a hydrogen atmosphere of 0.10 MPaH2, and held in a constant temperature bath set to the magnetic phase transition temperature for 100 hours to allow the split to proceed. Table 4 also shows the volume fraction of α-Fe at that time. It can be seen that the degree of splitting progresses changes depending on the homogenization conditions. This may be because the precipitation of α-Fe itself affects the splitting, but it is also thought that other changes in the subphase, or the resulting changes in the composition of the main phase, are having an effect. Therefore, in order to suppress splitting, it is preferable to appropriately control the homogenization conditions so that the amount of α-Fe is at least 6% by volume or less.

[0064] [Table 4]

[0065] Figure 6 shows the change in the amount of B added and the lattice constant of the main phase for Examples 1-4 and Comparative Example 1. B As the value increased, the lattice constant initially decreased, then reversed and increased. This is thought to reflect the difference in the solid solution form of B, as mentioned above.

[0066] [Example 12] RE(Fe,Si) when homogenization treatment was performed on composition 3 at different temperatures for 45 hours. 13 Phase and RE2Fe 14 Figure 7 shows the change in Si concentration in the X phase. RE(Fe,Si) is obtained when the homogenization temperature is 1140°C or higher.13 The Si concentration in the phase increases, RE2Fe 14 The Si concentration in the X phase is decreasing. The Si concentration in each phase was measured by point analysis using EDS with JSM-IT300LV (manufactured by JEOL Corporation). Figure 8 shows the dm / dT-T characteristics when composition 3 was homogenized at 1130°C and 1150°C for 45 hours, followed by hydrogen storage at 300°C and 0.10 MPa. Therefore, Si 1-13 / Si 2-14-1 By adjusting the homogenization temperature to the region where the coefficient is ≤1.2, it is possible to obtain a magnetic refrigeration material with even higher properties in a material where splitting is suppressed.

Claims

1. RE(M １－ｘ A ｘ ) ｙ X ｚ H ｗ A hydrogenated alloy represented by the following compositional formula, where x, y, z, and w satisfy the following conditions: 0.08 ≤ x ≤ 0.13, 12.3 ≤ y ≤ 13.2, 0.005 ≤ z ≤ 0.25, and 0 < w < H ｓａｔ (H ｓａｔ A hydrogenated alloy that satisfies the amount of saturated hydrogen at room temperature, wherein RE is one or more elements selected from rare earth elements and Zr and La is required, M is one or more elements selected from Fe, Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag and Ti and Fe is required, A is one or more elements selected from Si, Al, Ga, P, Ge, Sn and In and Si is required, and X is one or more elements selected from B, C and N and B is required.

2. H ｓａｔ The hydrogen storage ratio P Ｈ (= w / H ｓａｔ ) is 0.95 or less, and the hydrogen storage alloy according to claim 1.

3. While keeping the composition the same except for the value of w, w = H ｓａｔ The hydrogenated alloy according to claim 1, having a magnetic phase transition temperature that is 2K or more lower than the magnetic phase transition temperature when the conditions are met.

4. The amount of B contained in X is z Ｂ , the amount of C is z Ｃ , the amount of N is z Ｎ Let z = z Ｂ +z Ｃ +z Ｎ When z Ｂ The hydrogenated alloy according to claim 1, wherein the ratio is 0.005 or more.

5. z Ｂ While keeping the composition the same except for the value of z Ｂ When c is set to = 0, the lattice constant is c. ０ to, z Ｂ While keeping the composition the same except for the value of z Ｂ When the lattice constant is set to >0, c Ｂ In that case, c Ｂ ≤ c ０ The hydrogenated alloy according to claim 4.

6. The hydrogenated alloy according to claim 1, characterized in that, compared to a hydrogenated alloy where z=0 while keeping the composition other than the value of z the same, the change in which the magnetic phase transition temperature separates into multiple parts when held at the magnetic phase transition temperature for 300 hours is suppressed.

7. 300℃, 0.10MPaH ２ The hydrogenated alloy according to claim 1, wherein hydrogen absorption treatment is performed until the saturated hydrogen amount is reached, the material is held at the magnetic phase transition temperature for 300 hours, and the difference in magnetic phase transition temperature between the magnetic phase transition temperature at which the split is carried out and the magnetic phase transition temperature at which the split is carried out is 3.0 K or less.

8. H ｓａｔ Ratio of absorbed hydrogen (w / H) ｓａｔ ) to P Ｈ Let t be the time when the difference between the magnetic phase transition temperatures during the split expands to a certain temperature, and plot P on the x-axis. Ｈ log on the y-axis １０ Plot (t) and perform a linear approximation, and the slope of the approximate line for the hydride alloy at z=0 is a ０ , the intercept is b ０ The slope of the approximation line for the sample z > 0 is a Ｚ , the intercept is b Ｚ When this is the case, a ０ > a Ｚ Or, b ０ <b Ｚ The hydrogenated alloy according to claim 1.

9. The hydrogenated alloy according to claim 1, wherein the α-Fe phase content is 6 volume percent or less.

10. NaZn １３ The main phase has a type crystal structure, and RE ２ Fe １４ The hydrogenated alloy according to claim 1, comprising a subphase containing phase X.

11. The aforementioned RE ２ Fe １４ The hydrogenated alloy according to claim 10, wherein the volume fraction of phase X is 0.01% or more and 6% or less.

12. The Si concentration in the main phase is Si １－１３ The RE ２ Fe １４ The Si concentration in the X phase is Si ２－１４－１ When that happens, Si １－１３ / Si ２－１４－１ The hydrogenated alloy according to claim 10, wherein the ratio is ≤ 1.2.

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