JPH06116665A - Hydrogen storage alloy and its production - Google Patents

Abstract

PURPOSE:To provide a hydrogen storage alloy low in plateau flatness parameter sigma. CONSTITUTION:This hydrogen storage alloy is expressed by R1-xAx(Ni5-yBy)z, where R is a misch metal or La A is at least one kind selected from a group consisting of Ce, Nd, Pr, Sm and Y, B is at least one kind selected from a group consisting of Al, Sn, V, Cr, Mn, Fe, Co and Cu, 0<=x<=0.5, 0<y<=1.0 and 0.8<=z<=1.2. When the plateau region is expressed by the normal cumulative frequency distribution function with hydrogen absorption as the frequency and the logarithm of the equilibrium hydrogen pressure as the random variable, the standard deviation sigma is controlled to 0.04-0.10 when the hydrogen storage alloy is heat-treated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy suitable as a functional material used in a heat utilization system such as a heat pump and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a heat utilization system utilizing the hydrogen storage function of a hydrogen storage alloy has been developed. Especially, the equilibrium hydrogen pressure which is excellent in hydrogen absorption and desorption cycle life and is easy to handle in normal temperature range. A rare earth element-Ni-based alloy is known as a hydrogen storage alloy having.

By the way, the equilibrium reaction between a hydrogen storage alloy and hydrogen is evaluated by a hydrogen pressure-composition (hydrogen absorption amount) isotherm curve. As shown in FIG. 1, the hydrogen pressure-composition isotherm (P-C-T characteristic curve) has a steeply sloped hydrogen solid solution region (α phase) and a metal hydride compound region (β phase), and It has a flat plateau region sandwiched between.

Here, the inclination of the plateau region is a very important factor for improving the performance such as the thermal efficiency of the heat utilization system, and it is required that the plateau region is flat and the pressure change with respect to the hydrogen absorption amount is as small as possible. .

Therefore, the present inventors have proposed a new method for quantitatively evaluating the flatness of the plateau region in a rare earth element-nickel based hydrogen storage alloy (Japanese Patent Application No. 3-103).
251381, The Japan Institute of Metals, Vol. 56, No. 8 (1992)
965-972). In the method, when the plateau region of the hydrogen storage alloy is represented by a normal cumulative frequency distribution function having a hydrogen absorption amount as a frequency and a logarithm of the equilibrium hydrogen pressure as a random variable, the standard deviation of the normal type cumulative frequency distribution function ( This is based on the finding that σ, which is hereinafter referred to as the plateau flatness parameter, accurately represents the slope of the plateau region due to the metallurgical inhomogeneity of the alloy phase.

In the above evaluation method, the equilibrium hydrogen pressure P
Logarithm of ratio of unit pressure to P ₀ (= 0.1 MPa): ln
The plateau region is formulated by a normal type cumulative frequency distribution function (ncdf) ψ in which (P / P ₀ ) is a random variable and the hydrogen absorption amount X is a frequency. That is, the distribution of ln (P / P ₀ ) is calculated by
As described above, it is considered as a normal type probability density function φ with standard deviation σ and average m = ln (P _m / P ₀ ).

[0007]

[Equation 2] here,

[Equation 3]

Therefore, the normal type cumulative frequency distribution function ψ obtained by integrating the normal type probability density function φ is expressed by the following equation 4.

[Equation 4]

The normal cumulative frequency distribution function ψ scaled by the plateau region width (Xβ-Xα) is given by
The hydrogen absorption amount component X _{P in the} plateau region was set as in Equation 5.

[Equation 5]

In the above-mentioned evaluation method, the chemical potential of hydrogen in the alloy corresponding to the plateau pressure P is such as grain boundary existing in the alloy, structural or compositional heterogeneity such as segregation, dislocation, stacking fault, etc. It is assumed to be statistically distributed due to crystallographic heterogeneity. Therefore, the standard deviation σ can be an objective indicator of the inhomogeneity of the alloy as well as the plateau slope.

On the other hand, it has been proposed to subject a hydrogen storage alloy to a heat treatment within 10 hours for the purpose of flattening the plateau region (Japanese Patent Publication Nos. 59-28624 and 59-28625).
No. 59-28626).

[0012]

In a heat utilization system using a hydrogen storage alloy as a functional material, the influence of the plateau flatness parameter σ on the system was examined, and in order to obtain practical performance, the plateau flatness was obtained. It was concluded that the sex parameter σ needs to be suppressed to at least 0.10 or less.

However, using the above evaluation method,
As a result of examining the plateau flatness parameter σ of the hydrogen storage alloy used in the conventional heat utilization system, the following Table 1 is shown.
As shown in a part thereof, all the values are large values exceeding 0.1, and it was found that the characteristics of the hydrogen storage alloy are insufficient.

Further, in the known heat treatment for flattening the plateau, the plateau flatness parameter σ could not be suppressed to 0.10 or less. This is because, in the known heat treatment method, the alloy is heated at a temperature equal to or higher than the melting point of the substituting element segregated during melting and casting, and thus the segregating substitutional element reacts with the component of the mother phase that substantially controls hydrogen absorption / desorption to form a compound It is considered that the reason is that the heat treatment time is insufficient.

Therefore, an object of the present invention is to provide a hydrogen storage alloy having a plateau flatness parameter σ of 0.10 or less and a method for producing the same.

[0016]

The hydrogen storage alloy according to the present invention has a CaCu ₅ type hexagonal structure and has the general formula: R _{1 -X} AX (N
i _5-y B _y ) _z . Where R is Mm
(Misch metal) or La, A is Ce, Nd, P
at least one selected from the group consisting of r, Sm and Y
The seed, B, is at least one selected from the group consisting of Al, Sn, V, Cr, Mn, Fe, Co and Cu.
Further, x, y, and z in the above general formula are respectively 0 ≦ x ≦ 0.5,
The values are in the range of 0 <y ≦ 1.0 and 0.8 ≦ z ≦ 1.2.
Further, the hydrogen storage alloy has a plateau flatness parameter σ
Is 0.04 or more and 0.10 or less.

Further, in the method for producing a hydrogen storage alloy according to the present invention, the plateau flatness parameter σ is 0.04 in the heat treatment of heating the hydrogen storage alloy having the above composition and then cooling it.
As described above, the heating temperature and the heating time are determined so that the values are 0.10 or less.

As an industrial method for realizing the plateau flatness parameter σ having the above value, a method of calculating the heating temperature T (K) and the heating time t based on the following equation 6 can be adopted.

Lnσ = ab−t · exp [−c / T] where a, b and c are constants determined by the composition of the alloy.

In this case, the heating temperature T can be set below the melting point of B, and the heating time t can be set within the range of 15 hours to 100 hours.

[0020]

[Function] In the above hydrogen storage alloy, a large amount of hydrogen absorption /
Hydrogen absorption / desorption by forming an intermetallic compound with Ni or substituting an element that forms a solid solution with respect to Ni of the CaCu ₅ type RNi ₅ alloy having a releasing capacity. It is possible to prevent the deterioration of the alloy due to the liberation of Ni as a simple substance that occurs when the above step is repeated and to improve the durability.

On the other hand, the equilibrium hydrogen pressure is greatly reduced by substituting the above elements for Ni. Therefore, R
In contrast, Ce, Nd, Pr, S, which can increase the equilibrium hydrogen pressure greatly and still maintain a large amount of hydrogen absorption / desorption capacity
By further substituting at least one of m and Y, a high equilibrium hydrogen pressure (5 to 10 atm near room temperature) required for heat-mechanical energy conversion in a heat pump or the like is obtained.
And the above), a large hydrogen storage capacity, and an excellent hydrogen storage alloy having both excellent durability against repeated absorption and release of hydrogen.

In order to maintain a large amount of hydrogen absorbing / releasing ability, the substitution amount x of Ce, Nd, Pr, Sm, and Y for R is set in the range of 0 to 0.5, and the substitution amount for Ni is also set. The amount y is in the range of 0 to 1.0, R and A (Ce, Nd, P
The stoichiometric ratio z of the total amount of Ni and its substituting element B to the total amount of r, Sm, Y) is set in the range of 0.8 to 1.2.

In the hydrogen storage alloy having the above composition,
By setting the plateau flatness parameter σ to a value of 0.04 or more and 0.10 or less, the structural, compositional, or crystallographic homogeneity of the alloy is enhanced, and as a result, P-C-T
The plateau region of the characteristic curve is almost horizontal.

The hydrogen storage alloy according to the present invention can be produced by subjecting the alloy having the above composition to a heat treatment under specific conditions (heating temperature T (° C.), heating time t).
This is for the following reason. That is, after the melting and casting, segregation of the substituting element represented by B is observed in the alloy which is not heat treated, which causes the plateau inclination. Therefore, as a result of analyzing the unsteady diffusion model of the alloy in which segregation occurs, the present inventors have found that the heat treatment conditions (temperature T ° C.,
It is clarified that the quantitative relationship shown in the above-mentioned equation 6 is established between the heat treatment time t) and the plateau flatness parameter σ. This relationship was also confirmed experimentally.

The solid line shown in FIG. 2 is a graph of the equation (6). As is clear from this graph,
To achieve a plateau flatness parameter σ of 1 or less,
A heat treatment for a certain period of time or more is required. However, in the conventional case, since the heat treatment time was less than 10 hours in all cases, the plateau flatness parameter σ exceeded 0.1.

As described above, the desired plateau flatness parameter σ (0.04) is obtained based on the mathematical analysis result (6) or the experimentally found relationship between the heat treatment condition and the plateau flatness parameter σ. It is possible to determine the heating temperature T and the heating time t required to obtain (~ 0.10).

When heat treatment time is 10 hours or more, 0.0
As a result of examining the manufacturability of an alloy having a plateau flatness parameter σ of 4 to 0.10, as a result of heating any alloy within 100 hours industrially, a heating temperature equal to or lower than the melting point of the B component, It has been found that the required plateau flatness parameter σ can be achieved.

It should be noted that 0 ≦ x ≦ 0.5, 0 <y ≦ 1.0, 0.0.
When it exceeds the range of 8 ≦ z ≦ 1.2, segregation of component elements or compounds other than the B component becomes remarkable, and a hydrogen storage alloy having a plateau flatness parameter σ of 0.100 or less cannot be obtained.

Further, the plateau flatness parameter σ is set to 0.0.
In order to obtain a value of 40 or less, heat treatment for 100 hours or more is required, which is not suitable as an industrial alloy manufacturing method.

[0030]

In the hydrogen storage alloy according to the present invention,
Since the plateau flatness parameter σ is a value of 0.10 or less, the system performance can be raised to a practical level even when used as a functional material of a heat utilization system. Further, according to the method for producing a hydrogen storage alloy of the present invention, a hydrogen storage alloy having a plateau flatness parameter σ of 0.10 or less can be easily produced by a heat treatment industrially realizable.

[0031]

EXAMPLES First, La in which a part of Ni was replaced by the element M
For Ni _5-y M _y alloys, an alloy in which segregation occurs is represented by an unsteady diffusion model, and the model is analyzed to derive the relationship between heat treatment conditions and the plateau flatness parameter σ.

In general, the change of the concentration y along the x-axis with time t can be represented by the non-stationary diffusion model of Eq.

[0033]

[Equation 7]

Here, if the concentration distribution of the substituting element M in the alloy where segregation occurs is represented by a cosine curve as shown by the broken line in FIG. 3 and the array pitch of the substituting element M is represented by 2 × 1, the boundary condition is several. 8 and the initial condition is defined by Eq.

[0035]

[Equation 8]

[Equation 9]

Under these boundary conditions and initial conditions,
By solving, the following formula 10 is obtained.

[Equation 10]

The fluctuation width Δy of the concentration y which causes the plateau inclination is Δy (0) after t hours as shown by the solid line in FIG.
To Δy (t). This Δy (t) is derived from the above equation 10 as the following equation 11.

[Equation 11]

The concentration distribution of M in the alloy is shown by the solid line after the time t from the state where the width of the initial distribution (t = 0) shown by the broken line, that is, the standard deviation σ is large as shown in FIG. Standard deviation σ
Changes to a small state.

Here, it is known that the logarithm of the equilibrium hydrogen pressure P of the LaNi _5-y M _y alloy changes in proportion to the substitution amount y as shown in Expression 12.

[Equation 12]

Therefore, the fluctuation width Δy of the density y and the standard deviation σ
And the relations shown in the following Expressions 13 and 14 are obtained.

[Equation 13]

[Equation 14]

Here, k is a coefficient for converting the density fluctuation width Δy into the standard deviation σ _y of the density distribution. In the case of the Gaussian distribution, the density fluctuation width Δy is approximately 6σ _y , so k is about 6 Becomes

Therefore, the following Expression 15 is derived from the above Expressions 11, 13, and 14.

[Equation 15]

Further, by substituting the constants in Expression 15 with a, b, and c, the above-mentioned Expression 6 lnσ = ab−t · exp [−c / T] can be obtained.

Next, examples of the present invention will be specifically described. <Example 1> Predetermined amount of massive Mm, Ni, Al, Mn,
Alloys No. 1, No. 3 and No. 5 shown in Table 1 were manufactured by using Co as a raw material and melting a mixture of these with high frequency. or,
For the alloy, the constants a, b, and
Based on c, the heat treatment time t at which the plateau flatness parameter σ becomes 0.1 or less was determined, and the alloy was heat treated.

The heat treatment is carried out in a vacuum atmosphere, and the heating temperature takes into consideration the melting points and vapor pressures of Al, Mn, and Co, which are the compositions of B, and for Al, 650 ° C. and Mn just below the melting point for Al.
Was 950 ° C. and Co was 1000 ° C. The composition of Mm is La: 25 wt%, Ce: 51 wt%
%, Nd: 17 wt%, other: 7 wt%.

Any known method such as an arc melting method can be used for melting the alloy. Further, the heat treatment may be performed in an atmosphere of an inert gas such as argon gas.

Table 1 shows the heat treatment conditions of the hydrogen storage alloys according to the present invention for alloys No. 1, No. 3 and No. 5 and the plateau flatness of the hydrogen storage alloys produced under the heat treatment conditions. Indicates the parameter σ. On the other hand, alloy N
No. 2, No. 4 and No. 6 are hydrogen storage alloys manufactured under conventional heat treatment conditions, and Table 1 shows the heat treatment conditions and plateau flatness parameter σ of each alloy. The plateau flatness parameter σ in the table is obtained by measuring the P-C-T characteristic curve at 40 ° C., and further by the above-mentioned evaluation method (Journal of the Japan Institute of Metals, Vol. 56, No. 8 (1992), 965-972). Page) is applied. This parameter σ represents the plateau flatness and at the same time represents the homogeneity of the alloy phase, and is an index that directly indicates the difference between the alloys themselves.

[0048]

[Table 1]

As is apparent from the comparison of Table 1, the plateau flatness parameter σ of each of the hydrogen storage alloys No. 1, No. 3 and No. 5 of the present invention is suppressed to a value of 0.100 or less. On the other hand, conventional hydrogen storage alloys No. 2, No. 4, No.
In all of 6, the plateau flatness parameter σ is 0.100.
Is over.

FIG. 1 shows the hydrogen storage alloy of the present invention in Example 1 (solid line) and the conventional hydrogen storage alloy (broken line) of 40.
The P-C-T characteristic curve in ° C is shown. As is clear from this figure, the hydrogen storage alloy of the present invention has a smaller plateau region slope than the conventional hydrogen storage alloy.

FIG. 2 shows the hydrogen storage alloy No. 1 in Table 1 above.
Regarding the heat treatment temperature is 650 ° C., which is lower than the melting point of Al, the relation between the plateau flatness parameter σ of the equation 6 and the heat treatment time t is shown. The broken line in the figure is
The plateau flatness parameter σ shows a level of 0.100. As is clear from this figure, the heat treatment temperature is Al
At 650 ° C, which is lower than the melting point of, the heat treatment time t is 10
The plateau flatness parameter σ shows a value larger than 0.1 over time, but after t = 30 hours, the plateau flatness parameter σ becomes a value of 0.1 or less. For the hydrogen storage alloy No. 1, the three constants in the above-mentioned equation 6 are a = -0.616 and b = 1.74 × 10.
^{It was 8} / sec and c = 20.13 × 10 ³ cal / mol.

As described above, in the heat treatment below the melting point of the B component, the heat treatment conditions which were difficult to predict in the past can be reasonably predicted according to the present invention. As a result, the plateau flatness parameter It is possible to produce a hydrogen storage alloy having excellent characteristics of σ of 0.100 or less.

Example 2 Massive La, Ce, Nd, P
r, Sm, Y, Mm, LRM (lanthanum rich misch metal), Al, Sn, V, Cr, Mn, Fe, Co,
Based on the present invention, the hydrogen storage alloys No. 7 to No. 26 shown in Table 2 were manufactured using Cu as a raw material in the same manner as in Example 1 above. Mm has the same composition as in Example 1, LRM is L
a: 41 wt%, Ce: 7 wt%, Nd: 39 wt%, and others: 13 wt% were used.

However, the heat treatment time was determined so that the plateau flatness parameter σ was 0.050 using the constants a, b, and c in the equation 6 obtained in the preliminary experiment. Furthermore, the P-C-T characteristic curve was measured about each hydrogen storage alloy manufactured through heat treatment, and the actual plateau flatness parameter σ was calculated based on the above evaluation method.

[0055]

[Table 2]

As a result, as shown in Table 2, it was clarified that the plateau flatness parameter σ was 0.10 or less in all cases, and most of them showed values around the predicted value of 0.050.

As is clear from the above Examples 1 and 2,
According to the present invention, the plateau flatness parameter σ is 0.1
A hydrogen storage alloy having the following excellent characteristics can be industrially easily manufactured, and a heat utilization system such as a heat pump that exhibits practical performance can be realized only by using the hydrogen storage alloy as a functional material.

The above description of the embodiments is for explaining the present invention, and should not be construed as limiting the invention described in the claims or reducing the scope. The configuration of each part of the present invention is not limited to the above-mentioned embodiment, and it goes without saying that various modifications can be made within the technical scope described in the claims.

For example, in the above embodiment, the plateau area is set to 1
Although it is represented by the normal cumulative frequency distribution function of the term, it can also be represented by the sum of the normal cumulative frequency distribution function of the two terms (Journal of the Institute of Metals, Vol. 56, No. 8 (1992), 967). In this case, either _one of the standard deviations σ ₁ and σ ₂ of the two normal type cumulative frequency distribution functions can be treated as the representative value.

Further, the method for producing a hydrogen storage alloy based on the equation 6 of the present invention is not limited to an alloy mainly containing CaCu ₅ type rare earth and Ni, and a plateau inclination caused by segregation of constituent elements As long as it has alloy system, it can be applied as it is.

[Brief description of drawings]

FIG. 1 is a graph showing a P-C-T characteristic curve.

FIG. 2 is a graph showing a relationship between a plateau flatness parameter σ and a heating time t.

FIG. 3 is a diagram illustrating an unsteady diffusion model of an alloy with segregation.

FIG. 4 is a graph showing changes in concentration distribution in the model.

[Explanation of symbols]

 σ Plateau flatness parameter T Heating temperature t Heating time

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[Procedure amendment]

[Submission date] August 12, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0005

[Correction method] Change

[Correction content]

Therefore, the present inventors have proposed a novel method for quantitatively evaluating the flatness of the plateau region in a rare earth element- Ni system hydrogen storage alloy (Japanese Patent Application No. 3-25).
1381, The Japan Institute of Metals, Vol. 56, No. 8 (1992) No. 96
5 to 972). In the method, when the plateau region of the hydrogen storage alloy is represented by a normal cumulative frequency distribution function having a hydrogen absorption amount as a frequency and a logarithm of the equilibrium hydrogen pressure as a random variable, the standard deviation of the normal type cumulative frequency distribution function ( This is based on the finding that σ, which is hereinafter referred to as a plateau flatness parameter), accurately represents the slope of the plateau region due to the metallurgical inhomogeneity of the alloy phase.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction content]

On the other hand, the equilibrium hydrogen pressure is greatly reduced by substituting the above elements for Ni. Therefore, R
In contrast, Ce, Nd, Pr, S, which can increase the equilibrium hydrogen pressure greatly and still maintain a large amount of hydrogen absorption / desorption capacity
By substituting at least one of m and Y, the high equilibrium hydrogen pressure required for heat energy conversion in a heat pump, etc. (5-10 atm or more near room temperature)
And a hydrogen storage alloy having both a large hydrogen storage capacity and excellent durability against repeated hydrogen absorption / desorption.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction content]

It should be noted that 0 ≦ x ≦ 0.5, 0 <y ≦ 1.0, 0.0.
When it exceeds the range of 8 ≦ z ≦ 1.2, segregation of component elements or compounds other than the B component becomes remarkable, and a hydrogen storage alloy having a plateau flatness parameter σ of 0.10 or less cannot be obtained.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0051

[Correction method] Change

[Correction content]

FIG. 2 shows the hydrogen storage alloy No. 1 in Table 1 above.
Regarding the heat treatment temperature is 650 ° C., which is lower than the melting point of Al, the relation between the plateau flatness parameter σ of the equation 6 and the heat treatment time t is shown. The broken line in the figure is
The plateau flatness parameter σ shows a level of 0.100. As is clear from this figure, the heat treatment temperature is Al
At 650 ° C, which is lower than the melting point of, the heat treatment time t is 10
The plateau flatness parameter σ shows a value larger than 0.1 over time, but after t = 30 hours, the plateau flatness parameter σ becomes a value of 0.1 or less. For the hydrogen storage alloy No. 1, the three constants in the above-mentioned equation 6 are a = -0.616 and b = 1.74 × 10.
It was ^{8 /} sec and c = 20.13 × 10 ³ K.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Name of item to be corrected] 0057

[Correction method] Change

[Correction content]

As is clear from the above Examples 1 and 2,
According to the present invention, the plateau flatness parameter σ is 0.1
A hydrogen storage alloy having excellent characteristics of 0 or less can be industrially easily manufactured, and a heat utilization system such as a heat pump exhibiting practical performance can be realized only by using the hydrogen storage alloy as a functional material. .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ikuro Ikuro 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (72) Toshihiko Saito 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Within the corporation

Claims (5)

[Claims] _1. A compound represented by the general formula: R _1-X A _X (Ni _5-y B _y ) _z , R is Mm (Misch metal) or La, and A is C.
at least one selected from the group consisting of e, Nd, Pr, Sm and Y, B is Al, Sn, V, Cr, Mn, F
at least one selected from the group consisting of e, Co and Cu, and 0 ≦ x ≦ 0.5, 0 <y ≦ 1.0,
In a hydrogen storage alloy with 0.8 ≦ z ≦ 1.2, a plateau region sandwiched between a hydrogen solid solution region (α phase region) and a metal hydride compound region (β phase region) is used for hydrogen absorption amount. Is a frequency and the logarithm of the equilibrium hydrogen pressure is a random variable, and the standard cumulative frequency distribution function has a standard deviation σ of 0.04 or more and 0.10 or less. Storage alloy. 2. The content of Ce having a composition of Mm is 10 w.
The hydrogen storage alloy according to claim 1, wherein the hydrogen storage alloy is t% or less. 3. A compound represented by the general formula: R _1-X A _X (Ni _5-y B _y ) _z , R is Mm (Misch metal) or La, and A is C.
at least one selected from the group consisting of e, Nd, Pr, Sm and Y, B is Al, Sn, V, Cr, Mn, F
at least one selected from the group consisting of e, Co and Cu, and 0 ≦ x ≦ 0.5, 0 <y ≦ 1.0,
A method for producing a hydrogen storage alloy, comprising heating an alloy satisfying 0.8 ≦ z ≦ 1.2 and then cooling the alloy, wherein a hydrogen solid solution region (α phase region) and a metal hydrogen compound region (β When the plateau region sandwiched between the (phase regions) is represented by a normal cumulative frequency distribution function having a hydrogen absorption amount as a frequency and a logarithm of the equilibrium hydrogen pressure as a random variable, the standard deviation of the normal type cumulative frequency distribution function A method for producing a hydrogen storage alloy, wherein the heating temperature and time are determined so that σ becomes a value of 0.04 or more and 0.10 or less. 4. The heating temperature T (K) and the heating time t are expressed by
The method for producing a hydrogen storage alloy according to claim 3, wherein the hydrogen storage alloy is defined as a value satisfying the above condition. Lnσ = ab−t · exp [−c / T] where a, b and c are constants determined by the composition of the alloy. 5. The heating temperature T is not higher than the melting point of B, and the heating time t is in the range of 15 hours to 100 hours.
The method for producing the hydrogen storage alloy according to 1.