Hydrogenated alloy

Abstract

The present invention is a hydrogenated alloy represented by the compositional formula RE(M1-xAx)yXzHw, wherein x, y, z, and w respectively satisfy 0.08≤x≤0.13, 12.3≤y≤13.2, 0.005≤z≤0.25, and 0<w<Hsat (where Hsat represents the amount of saturated hydrogen at ordinary temperature), RE is one or more elements selected from rare earth elements and Zr and must include La, M is one or more elements selected from Fe, Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag, and Ti and must include Fe, A is one or more elements selected from Si, Al, Ga, P, Ge, Sn, and In and must include Si, and X is one or more elements selected from B, C, and N and must include B. According to the present invention, a hydrogenated alloy with suppressed splitting can be provided in which the magnetic phase transition temperature (Tc) is controlled by the amount of hydrogen while maintaining performance.

Description

Hydrogenated alloy

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

[0002] In a conventional gas compression / expansion type heat pump, the use of CFC, which is an ozone layer-depleting substance, is 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 is being actively carried out, the practical application of a new refrigerant that is satisfactory in terms of performance, cost, and safety has not been achieved. In such a situation, a magnetic refrigeration system using the magnetocaloric effect without using greenhouse gases has attracted attention.

[0003] A magnetic refrigeration system utilizes a change in magnetic entropy (magnetocaloric effect, ΔS). As materials having a large absolute value of ΔS, there are Mn(As １３ , Ｚ Sb ｘ )(Patent Document 1) and La(Fe １－ｘ Si ｘ )(Patent Document 2), etc. 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 component 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 about 25 J / kgK, which is large next to Mn(As １－ｘ Sb ｘ ), and its 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 at or 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 with gas refrigeration, there was a problem that the magnetocaloric effect decreased at the above operating temperatures 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 or 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 approximately -80°C to approximately 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 Document 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.

[0008] Japanese Patent Publication No. 2003-28532, Japanese Patent Publication No. 2006-89839, Japanese Patent Publication No. 2012-41631

[0009] PHYSICAL REVIEW B 67, 104416 (2003) IEEE Transactions on Magnetics (Volume: 47, Issue: 10, October 2011)

[0010] However, in the method described in Patent Document 3, since hydrogen is absorbed up to a saturation level, the adjustment of Tc in the magnetic refrigeration material is mainly performed by adding Mn, which presents a problem in that ΔS decreases simultaneously with the 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.

[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 completed the present invention.

[0015] Therefore, the present invention provides the following hydrogenated alloys: [1] RE(M １－ｘ A ｘ ) ｙ Xｚ 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 essential, M is one or more elements selected from Fe, Co, Mn, Ni, Nb, W, Ta, Cr, Cu, Ag and Ti and Fe is essential, A is one or more elements selected from Si, Al, Ga, P, Ge, Sn and In and Si is essential, and X is one or more elements selected from B, C and N and B is essential. [2] H ｓａｔ Ratio of absorbed hydrogen P Ｈ (= w / H ｓａｔ The hydrogenated alloy described in [1] above, wherein w = H ｓａｔ The 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 [2] 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 according to any one of the above [1] to [3], wherein z is 0.005 or greater. [5] 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 ０The hydrogenated alloy described in [4] above. [6] The hydrogenated alloy described in any one of [1] to [6] above, characterized in that, compared to the hydrogenated alloy when 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 A hydrogenated alloy according to any one of [1] to [6] above, 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 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 A hydrogenated alloy as described in any one of [1] to [7]. [9] A hydrogenated alloy as described in any one of [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 RE ２ Fe １４ A hydrogenated alloy according to any one of [1] to [9], including an X-phase and a subphase.

[11] The RE ２ Fe 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 RE ２ Fe １４ The Si concentration in the X phase is Si ２－１４－１ When that happens, Si １－１３ / Si ２－１４－１The hydrogenated alloy described in

[10] or

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

[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.

[0017] Figure 1 is a graph showing the progress of splitting when Examples 1 and 2 and Comparative Example 1 were held in a constant temperature bath set to the magnetic phase transition temperature of each sample. Figure 2 is a graph showing 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. Figure 3 is a graph showing the progress of splitting when Examples 7 to 9 and Comparative Example 5 were held in a constant temperature bath set to the magnetic phase transition temperature of each sample. Figure 4 is a graph showing the amount of B added and the latent heat of the FP magnetic phase transition for Examples 1 to 4 and Comparative Examples 1 and 4. Figure 5 shows the alloy of composition 7 after homogenization under the homogenization conditions shown in Table 4, at 0.10 MPaH ２ Figure 6 is a graph showing the temperature difference between each magnetic phase transition temperature when hydrogenation treatment is performed at 300°C for 7 hours in a hydrogen atmosphere, and then the mixture is held in a constant temperature bath set to the magnetic phase transition temperature for 100 hours to allow the split to proceed. Figure 7 shows the change in the amount of B added and the lattice constant of the main phase for Examples 1 to 4 and Comparative Example 1. Figure 7 shows the RE(Fe,Si)13 phase and RE when homogenization treatment is performed at different temperatures for 45 hours for composition 3. ２ Fe １４ This graph shows the change in Si concentration in the X phase. 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.

[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 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 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 RE contains elements other than La, homogenization becomes more difficult as the substitution amount increases. The maximum amount of Ce that can be contained is 40 atomic percent or less of the total RE, Pr 60 atomic percent or less, and Nd 40 atomic percent or less. This lowers the magnetic phase transition temperature, increases ΔS, and increases hysteresis. The maximum content of elements other than La in RE 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 substituted with Zr, the substitution can be limited to 10 atomic percent or less of the total RE. Within this range, the magnetic phase transition temperature can be increased. Furthermore, a portion of the RE in the subphase can also 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. In addition, a portion 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. In addition, a portion of the Si in the subphase can also be substituted 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 further contain at least one element from C and N. C and N are inevitably included 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 in the above composition from the symmetric chemical ratio of the main phase of 13.0 to produce the alloy, the hydrogen storage behavior can be controlled. However, if y in the above composition 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 greater. Furthermore, y is preferably 13.1 or less.

[0026] For the above composition, z is 0.005 or more and 0.25 or less. If z is less than 0.005 or greater than 0.25, the split progress cannot be effectively suppressed. From such a viewpoint, z of the above composition is preferably 0.04 or more, preferably 0.13 or less, and more preferably 0.08 or less.

[0027] Let the amount of B contained in the above X be z Ｂ and the amount of C be z Ｃ and the amount of N be z Ｎ When z is expressed as z = z Ｂ + z Ｃ + z Ｎ when, z Ｂ is preferably 0.005 or more, and more preferably 0.01 or more. Also, it is preferably 0.25 or less, and more preferably 0.05 or less. When it is within such a range, the split progress is more effectively suppressed while maintaining the performance.

[0028] The hydrogen storage alloy of the present invention is a hydrogen storage alloy that stores hydrogen within the range of 0 < w < H ｓａｔ . This hydrogen amount range stores hydrogen, but is a range where the hydrogen amount is less than the saturation amount at room temperature and is a region where split can occur. H ｓａｔ varies depending on the composition and the like, but is generally said to be about w = 1.4 to 1.7. H ｓａｔ is the saturation hydrogen amount at room temperature in the alloy of each composition. In the present invention, when hydrogen is stored for at least 5 hours or more at a temperature of 30 ° C and in a hydrogen atmosphere of 0.10 to 0.25 MPa, when the Tc does not increase any more, the hydrogen amount at that time is defined as H ｓａｔ . Before the hydrogen storage treatment, an activation treatment is generally performed, for example, a heat treatment at 300 to 500 ° C for 1 to 2 hours in a vacuum or a hydrogen atmosphere.

[0029] In this type of hydrogen storage alloy, w < H ｓａｔ that is, when P Ｈ (= w / H ｓａｔ ) is less than 1, split occurs, and the smaller P Ｈ is, the faster the split progresses. P of the hydrogen storage alloy of the present invention ＨThe P of the hydrogenated alloy of the present invention is preferably 0.95 or less, more preferably 0.90 or less, and more preferably 0.85 or less. Ｈ The lower limit of the range is not particularly limited, but the P of the hydrogenated alloy of the present invention Ｈ The hydrogen concentration is typically 0.01 or higher, preferably 0.10 or higher, more preferably 0.50 or higher, even more preferably 0.55 or higher, even more preferably 0.60 or higher, and even more preferably 0.65 or higher. The above is the hydrogen concentration range in which splitting can occur. The hydrogenated alloy of the present invention can effectively suppress splitting even within this range. Note that P Ｈ H ｓａｔ This represents the ratio of the amount of absorbed hydrogen to P. Ｈ = w / H ｓａｔ It is expressed as follows. However, although not particularly limited, the amount of hydrogen w contained in the hydride alloy can be measured, for example, by the inert fusion conduction method using the LECO ONH836 oxygen, nitrogen, and hydrogen analyzer.

[0030] The hydrogenated alloy of the present invention has the same composition except for the value of w, while w = H ｓａｔ It is preferable to have a Tc that is 2K or more lower than the Tc in the case of [the above]. This makes it possible to obtain a hydrogenated alloy in which the split is suppressed while sufficiently lowering the Tc. From this viewpoint, the hydrogenated alloy of the present invention has the same composition except for the value of w, while w = H ｓａｔ Compared to the Tc in the case of [the above], it is more preferable to have a Tc that is 5K or more lower, even more preferable to have a Tc that is 10K or more lower, and even more preferable to have a Tc that is 20K or more lower.

[0031] The hydrogenated alloy of the present invention is 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 ０It is preferable that this is the case. 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 ≤ c ０ It would be more preferable if this were the case.

[0032] Normally, it is generally assumed that light elements such as B, C, and N penetrate the lattice in a solid solution form, 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 presumed 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 form, whereas when a certain amount or more of B is added, substitutional solid solution becomes difficult, and B begins to solid dissolve in the lattice in an interstitial solid solution form, 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 / 2 In the low hydrogen concentration region shown below, 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 splitting is further suppressed in the region where the lattice tends to contract when B is added, and even more so in the region 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, so the lattice constant when B is added is c ０ It is preferable that it be within the following range.

[0034] The hydrogenated alloy of the present invention is NaZn １３ The main phase has a type crystal structure, and RE ２ Fe １４It is preferable to include a subphase containing the X phase. For example, by adding B as the element X, RE can be used as the subphase. ２ Fe １４ The X phase can be formed in the hydrogenated alloy. The hydrogenated alloy of the present invention is RE ２ Fe １４ It is preferable that the X phase is present in a volume of 0.01% or more. This makes it possible to more effectively suppress splitting. Furthermore, the hydrogenated alloy of the present invention is RE ２ Fe １４ It is preferable that the X phase be present in a volume percentage of 6% or less. This suppresses 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, for example, by binarizing an SEM image acquired using JSM-IT300LV (manufactured by JEOL Corporation) using the difference in contrast due to composition, calculating the area of ​​each phase, and considering the area fraction as the volume fraction. ２ Fe １４ The reason why the X phase can suppress the progression of the split is not entirely clear, but it is thought to be as follows: When the sample is hydrogenated, not only the main phase but also RE ２ Fe １４ Although the X phase can also form hydrides, 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 observed. １３ In addition, a third RE with different hydride stabilities ２ Fe 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, RE ２ Fe １４ It is known that the B-phase can have some of its B-sites replaced with C. In the present invention, C caused by impurities or intentionally added is RE ２ Fe １４ It is thought that the B site of phase B is being replaced. Therefore, it is inevitably included as an impurity, but even if C is intentionally added as X, RE ２ Fe １４It is presumed that the formation of (B, C) is promoted, enhancing the split-suppressing effect.

[0036] As shown 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 RE formed by the addition of X. ２ Fe 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 be 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 the splitting progression is performed by setting 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. Also, there is usually a difference between the temperature of the measuring device such as DSC measurement and the temperature of the constant temperature bath, so it is necessary to hold the sample at a temperature that takes 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] The magnetic phase transition temperature (Tc) of the hydrogenated alloy of the present invention, and the hydrogenated alloy of the present invention at 300°C and 0.10 MPaH ２ It is preferable that the magnetic phase transition temperature difference between the temperature at which the hydrogen absorption treatment is performed up to the saturation hydrogen amount, the temperature at which the split is allowed to progress (held at the magnetic phase transition temperature for 300 hours), and the magnetic phase transition temperature at which the split is allowed to progress 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 (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 on the vertical axis 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. At this time, 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 the lifespan of a split through accelerated testing.

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

[0044] The hydrogenated alloy of the present invention is NaZn １３ The main phase has a type crystal structure, and RE ２ Fe １４ When a subphase containing phase X is included, the Si concentration in the main phase is Si １－１３ RE ２ Fe 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, within the above range, adding B and RE ２ Fe 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 thought that a high-performance material can be obtained. The secondary phase is RE ２ Fe １４When the X phase is present, changing the homogenization temperature (temperature, time, etc.) results in RE(Fe,Si) １３ Phase hydrides and RE ２ Fe １４ The amount of Si in the X phase changes, which is due to RE ２ Fe １４ The X phase decomposes, resulting in RE ２ Fe １４ RE (Fe, Si) from phase X １３ This is presumed to be due to the migration of Si 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 a JSM-IT300LV (manufactured by JEOL Corporation).

[0045] Next, the method for producing the hydrogenated alloy for magnetic refrigeration of the present invention will be described. The method for producing the hydrogenated alloy of the present invention comprises a dissolution 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 higher. 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 structure. Using the liquid quenching method allows for even faster cooling, making it easier to obtain an even finer and better structure.

[0047] In the homogenization process, the alloy obtained in the melting process is subjected to heat treatment to create a homogeneous RE(Fe,Si) １３A heat treatment is performed to form a 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 of 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, and more preferably between 3 hours and 50 hours, considering mass productivity and the attainment of hydrogen saturation concentration.

[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 melted in a high-frequency induction furnace in an Ar gas atmosphere at 1500°C, and then cooled at a rate of 300–1000°C / sec using the strip casting method to produce alloy strips with an average thickness of approximately 300 μm. The resulting alloys were then heat-treated in an Ar atmosphere for 45 hours, varying the homogenization temperature between 1000°C and 1250°C. Table 1 shows the composition of the prepared samples and the optimal homogenization temperature. The alloy composition was analyzed using an SPS3500DD (Hitachi High-Tech Corporation). The optimal homogenization temperature was determined by DSC (NETZSCH DSC3500Sirius) measurement after the hydrogenation treatment described later, with the point at which the latent heat was greatest being considered the optimal homogenization condition.

[0051]

[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; therefore, by storing hydrogen at 50°C or higher, preferably 100°C or higher, the saturated hydrogen amount (H) can be increased. 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. ｃ The samples were kept at a constant temperature, removed after a certain period of time, and their m-T characteristics were measured using a VersaLab VSM unit (manufactured by Quantum Design Co., Ltd.). 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] Alloys of composition 1-6 were homogenized at the optimal homogenization temperature for 45 hours, followed by heating to 0.10 MPaH ２ Hydrogen alloys were obtained by absorbing hydrogen under a hydrogen atmosphere at 300°C for 15 hours, followed by rapid cooling and extraction. Comparative Example 1 was obtained by performing the above treatment on composition 1, Examples 1 to 4 were obtained by performing the treatment on compositions 2 to 5, and Comparative Example 4 was 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, 6, Comparative Examples 2, 3] Compositions 1 and 3 were homogenized under optimal homogenization conditions, and then heated to 0.10 MPaH ２ Hydrogenated alloys were obtained by absorbing hydrogen under a hydrogen atmosphere at 275°C for 148 hours, followed by rapid cooling and extraction. Comparative Example 2 is obtained by performing the above treatment on composition 1, and Example 5 is obtained by performing the above treatment on composition 3. After homogenization of compositions 1 and 3 under optimal homogenization conditions, 0.10 MPaH ２ Hydrogen alloys were obtained by absorbing hydrogen under a hydrogen atmosphere at 250°C for 166 hours, followed by rapid cooling and extraction. Comparative Example 3 is obtained by performing the above treatment on composition 1, and Example 6 is obtained by performing 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 temperature difference between peaks to widen, indicating that the progression of splitting is suppressed. From this, it can be concluded that, regardless of the hydrogen concentration, if B is present at a predetermined concentration in the alloy, the progression of splitting is suppressed.

[0058] [Examples 7-9, Comparative Example 5] Compositions 8-11 were homogenized under optimal homogenization conditions, and then heated to 0.10 MPaH ２ Hydrogen alloys were obtained by absorbing hydrogen under a hydrogen atmosphere at 275°C for 148 hours, followed by rapid cooling and extraction. Comparative Example 5 is obtained by performing the above treatment on composition 8, and Examples 7 to 9 are obtained by performing the above treatment on 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 temperature difference between peaks to widen, indicating that the progression of 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 = 0.3 (Comparative Example 4) results in less than half the latent heat. Table 3 shows the α-Fe and RE under the optimal homogenization conditions for Examples 1-4 and Comparative Examples 1 and 4. ２ Fe １４ This shows the volume fraction of X. Increasing the addition of B increases the amount of α-Fe and RE. ２ Fe １４ It is presumed that the amount of X formed increases, which reduces the proportion of the main phase and thus lowers the latent heat. Therefore, α-Fe is 6 volume% or less, RE ２ Fe １４ It is desirable that X is 6% by volume or less.

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

[0062]

[0063] [Examples 10-14] Figure 5 shows an alloy of composition 7 that was homogenized under the homogenization conditions shown in Table 4, and then subjected to 0.10 MPaH ２Table 4 shows the temperature difference between each transition temperature when hydrogenation treatment is performed at 300°C for 7 hours under a hydrogen atmosphere, and then the sample is held in a constant temperature bath set to the magnetic phase transition temperature for 100 hours to allow splitting to proceed. The volume fraction of α-Fe at that time is shown in Table 4. It can be seen that the degree of splitting progress 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 changes in other subphases, or the resulting changes in the main phase composition, also have 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 volume% or less.

[0064]

[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 coefficient of the lattice constant increased, it was observed that it initially decreased, then reversed and increased. As mentioned above, this is thought to reflect the difference in the solid solution form of B.

[0066] [Example 12] RE(Fe,Si) when composition 3 was subjected to homogenization treatment at different temperatures for 45 hours. １３ A and RE ２ Fe 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, RE ２ Fe １４ The Si concentration in phase X 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. From the above, Si １－１３ / Si ２－１４－１ By adjusting the homogenization temperature to the region where ≤ 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. Hydrogen storage ratio P ｓａｔ with respect to H Ｈ (= w / H ｓａｔ ) is 0.95 or less, 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. Compared to a hydrogenated alloy where z=0 while keeping the composition other than the value of z the same, the hydrogenated alloy is characterized in that the separation of the magnetic phase transition temperature into multiple values ​​that occurs 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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