JP2010236084A - Hydrogen storage alloy, method of preparing the same and hydrogen storage device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen storage alloy having a high initial effective hydrogen amount and excellent cycle durability, and to provide a method of preparing the same, and a hydrogen storage device using such a hydrogen storage alloy. <P>SOLUTION: There are disclosed the hydrogen storage alloy having, as a main phase thereof, a bcc structure phase having a composition represented by Ti<SB>x</SB>Cr<SB>y</SB>V<SB>z</SB>X<SB>w</SB>, and a hydrogen generator using the alloy. The method of preparing the hydrogen storage alloy includes: a melting/casting process of melting/casting raw materials mixed to be the composition represented by Ti<SB>x</SB>Cr<SB>y</SB>V<SB>z</SB>X<SB>w</SB>; a heat treatment process of heat-treating an ingot obtained in the melting/casting process; and an activation process of executing the treatment of storing/releasing hydrogen to the heat-treated ingot at least once, wherein 3/2≤y/x≤3/1, 50≤z≤75 mol%, 0≤x≤5 mol%, (x+y+z+w) is 100 mol%, and X is at least one selected from Al, Si and Fe. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a hydrogen storage alloy capable of reversibly storing and releasing hydrogen, a method for producing the same, and a hydrogen storage device using such a hydrogen storage alloy.

  In recent years, hydrogen energy has attracted attention as a clean alternative energy due to environmental problems such as global warming caused by carbon dioxide emissions and energy problems such as exhaustion of petroleum resources. For the practical application of hydrogen energy, it will be important to develop technology for safely storing and transporting hydrogen. There are several candidates for hydrogen storage methods. Among them, methods using hydrogen storage materials that can store and release hydrogen reversibly are considered the safest means of storing and transporting hydrogen. It is expected as a hydrogen storage medium mounted on fuel cell vehicles.

Known hydrogen storage materials include carbon materials such as activated carbon, fullerene, and nanotubes, and hydrogen storage alloys such as LaNi ₅ and TiFe. Among these, hydrogen storage alloys are promising as hydrogen storage materials for storing and transporting hydrogen because they have a higher hydrogen density per unit volume than carbon materials.
As practical hydrogen storage alloys that can be stored and released near room temperature, which are easy to control, LaNi ₅ , TiFe alloys, V—Ti—Cr alloys, and the like are known. Among these, LaNi ₅ and TiFe alloys have a problem that the hydrogen storage amount per weight is small. On the other hand, the V—Ti—Cr alloy has a feature that the hydrogen storage amount per weight is larger than these.

Various proposals have been made regarding V-Ti-Cr alloys.
For example, Patent Document 1, Ti _x Cr _y V _z alloy having a regular periodical structure formed by spinodal decomposition (x = 5~70, y = 20~70 , z = 10~30) and Ti ₂₅ A Cr ₃₅ V ₄₀ alloy is disclosed.
In the same document,
(1) spinodal lattice constant of two phases apparent formed by decomposition when in the vicinity of 0.3040nm, Ti _x Cr _y V _z hydrogen absorbing volume is the maximum value of the alloy (1.4H / M) that takes a ,as well as,
(2) The hydrogen storage amount (maximum hydrogen storage amount) of the heat-treated Ti ₂₅ Cr ₃₅ V ₄₀ alloy is about 3.7 wt%,
Is described.

Patent Document 2 _discloses Ti _28.3 Cr _50.3 V _19.2 Fe _1.7 Al _0.5 alloy, Ti ₃₀ Cr ₅₀ V ₂₀ alloy, Ti ₃₀ Cr ₅₀ V ₁₉ Cu ₁ alloy, Ti ₂₅ Cr ₅₀ V ₂₀ Fe ₄ Ni ₁ alloy, And Ti ₂₅ Cr ₅₅ V ₅ Mo ₁₀ Fe ₅ alloy.
In the same document,
(1) When the temperature is lowered to the mixed phase region of the BCC structure phase and the C15 Loves phase at a cooling rate of 10 to 200 ° C./hour after the homogenization heat treatment, the precipitation of acicular α-Ti in the crystal grains is suppressed, and the complete crystal structure of the BCC structure Improving the efficiency and increasing the amount of effective hydrogen transfer, and
(2) When water quenching is performed after the homogenization heat treatment, the effective hydrogen amount is 235 to 262 cc / g, whereas when it is gradually cooled at a predetermined cooling rate after the homogenization heat treatment, the effective hydrogen amount is 261 to 281 cc / g. The point that becomes
Is described.

Patent Document 3 discloses a V ₇₀ Ti ₁₂ Cr ₁₈ alloy, a V ₄₀ Ti ₂₄ Cr ₃₆ alloy, and a V ₆₀ Ti ₁₆ Cr ₂₄ alloy.
This document describes that when the alloy composition is optimized, the stored hydrogen in the alloy becomes unstable in the low-pressure plateau region or the lower plateau region of the inclined plateau, and hydrogen can be taken out from these regions.

Patent Document 4 discloses a Ti _15.0 Cr _34.7 V _49.8 Al _0.5 alloy.
This document describes that when Al is added to a Ti—Cr—V alloy, the plateau flatness is improved.
Patent Document 5 discloses a hydrogen storage alloy obtained by mechanically milling a V-10% Ti-20% Cr alloy in a hydrogen atmosphere.
This document describes that hysteresis can be reduced because the composition can be made uniform at the same time as pulverization by milling.

Further, Patent Document 6 includes Ti ₂₀ Cr ₄₅ V ₃₀ Mo ₅ alloy, Ti ₂₅ Cr ₅₀ V ₂₀ Mo ₅ alloy, Ti ₂₅ Cr ₄₀ V ₂₅ Mo ₁₀ alloy, and Ti ₂₅ Cr ₄₀ V ₂₀ Mo ₁₅ alloy. It is disclosed.
This document describes that when the chemical composition, the crystal structure of the main phase, and the lattice constant are optimized, the hydrogen release characteristics in the low temperature region are improved.

  In order to put the hydrogen storage alloy into practical use, the initial value of the hydrogen amount (effective hydrogen amount) that can be stored and released reversibly is high, and the deterioration of the effective hydrogen amount over time is small (that is, the cycle). It must be highly resistant. However, the conventional alloy is excellent only in either the initial effective hydrogen amount or the cycle resistance, and there has never been an example in which an alloy excellent in both is developed.

JP-A-10-110225 JP 2004-169102 A JP 2000-345273 A Japanese Patent Application Laid-Open No. 11-106859 JP 2001-11560 A JP 2006-188737 A

The problem to be solved by the present invention is to provide a hydrogen storage alloy having a high initial effective hydrogen amount and excellent cycle resistance and a method for producing the same.
Another object of the present invention is to provide a hydrogen storage device using a hydrogen storage alloy having a high initial effective hydrogen amount and excellent cycle resistance.

In order to solve the above problems, the gist of the hydrogen storage alloy according to the present invention is that the main phase is a bcc structure phase having a composition represented by the following formula (1).
_{Ti x Cr y V z X w} ··· (1)
However, 3/2 ≦ y / x ≦ 3/1, 40 ≦ z ≦ 75 mol%, 0 ≦ w ≦ 5 mol%, x + y + z + w = 100 mol%.
X = any one or more selected from Al, Si and Fe.

The method for producing a hydrogen storage alloy according to the present invention includes:
(1) a melting / casting step of melting / casting a raw material blended to have a composition represented by the formula;
A heat treatment step for heat-treating the ingot obtained in the melting and casting step;
And an activation step of performing at least one treatment for occluding and releasing hydrogen in the heat-treated ingot.
_{Ti x Cr y V z X w} ··· (1)
However, 3/2 ≦ y / x ≦ 3/1, 40 ≦ z ≦ 75 mol%, 0 ≦ w ≦ 5 mol%, x + y + z + w = 100 mol%.
X = any one or more selected from Al, Si and Fe.

Furthermore, the hydrogen storage device according to the present invention is:
A hydrogen storage alloy according to the present invention;
A container for containing the hydrogen storage alloy;
The gist of the invention is that it comprises a heat exchanger for controlling the temperature of the hydrogen storage alloy housed in the container.

  When the Cr / Ti ratio (y / x) is optimized in the Ti—Cr—V alloy, the initial effective hydrogen amount can be increased while maintaining the plateau pressure in a practically sufficient range. In addition, when the amount of V is optimized, cycle durability can be improved while maintaining the initial effective hydrogen amount high. Furthermore, when a predetermined amount of Al, Si and / or Fe is contained, the plateau pressure can be increased and the cycle resistance can be improved without greatly reducing the maximum hydrogen amount.

It is an X-ray-diffraction pattern of the alloy after the heat processing obtained in Examples 1-4. 2 is a pressure-composition isotherm of an initial hydrogen release process at room temperature of the alloy obtained in Example 1. FIG. It is a figure which shows the cycle tolerance of the alloys obtained in Examples 1 and 4 and Comparative Examples 1 and 3 at room temperature (Example 1 and Comparative Example 3) or 0 ° C. (Example 4 and Comparative Example 1). , ◆, Δ, ■ are measured values, and each curve is an approximate curve of measured values). Is a diagram showing a relationship between Ti _x Cr _y V _z alloy (z = 75) of the y / x ratio and initial effective hydrogen amount and cycle durability. Is a diagram showing a relationship between Ti _x Cr _y V _z alloy (z = 65) of the y / x ratio and initial effective hydrogen amount and cycle durability. Is a diagram showing a relationship between Ti _x Cr _y V _z alloy (z = 50) of the y / x ratio and initial effective hydrogen amount and cycle durability. Is a diagram showing a relationship between Ti _x Cr _y V _z alloy (z = 40) of the y / x ratio and initial effective hydrogen amount and cycle durability. Is a diagram showing a relationship between Ti _x Cr _y V _{z z} and initial effective hydrogen amount and cycle durability of the alloy (y / x = 1.5). Is a diagram showing a relationship between Ti _x Cr _y V _{z z} and initial effective hydrogen amount and cycle durability of the alloy (y / x = 2.0). Is a diagram showing a relationship between Ti _x Cr _y V _z alloy (y / x = 2.5) of z and initial effective hydrogen amount and cycle durability.

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Hydrogen storage alloy]
The hydrogen storage alloy according to the present invention has a bcc structural phase having a composition represented by the following formula (1) as a main phase.
_{Ti x Cr y V z X w} ··· (1)
However, 3/2 ≦ y / x ≦ 3/1, 40 ≦ z ≦ 75 mol%, 0 ≦ w ≦ 5 mol%, x + y + z + w = 100 mol%.
X = any one or more selected from Al, Si and Fe.

[1.1. Alloy composition]
[1.1.1. y / x]
In the present invention, the “maximum hydrogen amount” refers to the maximum value of the hydrogen amount that can be theoretically extracted. In the present invention, the “effective hydrogen amount” refers to an amount of hydrogen that can be reversibly occluded and released within a range of 0.01 to 10 MPa.

x represents the amount of Ti (mol%) contained in the alloy. y represents the amount of Cr (mol%) contained in the alloy. Furthermore, y / x represents the molar ratio (Cr / Ti) of the Cr amount to the Ti amount in the alloy.
The smaller the y / x ratio (that is, the greater the Ti content), the greater the maximum hydrogen content. However, if y / x becomes too small, the plateau pressure decreases. When the plateau pressure is excessively reduced, the amount of effective hydrogen is reduced because a reduced pressure is required to extract hydrogen. Therefore, y / x needs to be 3/2 or more. y / x is more preferably 3 / 1.65 or more.

  On the other hand, as y / x increases (that is, the amount of Cr increases), the plateau pressure increases and it becomes easier to extract hydrogen. However, if the plateau pressure becomes too high, a high pressure is required to occlude hydrogen. Moreover, when y / x becomes too large, the maximum amount of hydrogen also decreases. Therefore, y / x needs to be 3/1 or less. y / x is more preferably 3 / 1.2 or less, and further preferably 3 / 1.35 or less.

[1.1.2. z]
z represents the amount of V (mol%) contained in the alloy. As z decreases (that is, the amount of V decreases), the cycle resistance decreases. In order to obtain high cycle resistance, z needs to be 40 mol% or more. z is more preferably 50 mol% or more, further preferably 55 mol% or more, more preferably 57.5 mol% or more, and further preferably 60 mol% or more.
On the other hand, when V becomes excessive, the initial value of the effective hydrogen amount (initial effective hydrogen amount) decreases. Therefore, z needs to be 75 mol% or less.
In order to obtain a hydrogen storage alloy that is particularly excellent in the initial effective hydrogen amount, z is preferably less than 70 mol%. z is more preferably 68 mol% or less.
On the other hand, in order to obtain a hydrogen storage alloy particularly excellent in cycle resistance, z is preferably more than 70 mol% and 75 mol% or less. z is more preferably 71 mol% or more, and still more preferably 72 mol% or more.

[1.1.3. w]
w represents the amount (mol%) of the element X contained in the alloy. X represents one or more elements selected from Al, Si, and Fe.
The element X is not necessarily a necessary element, but when these elements are added, the plateau pressure can be increased and the cycle resistance can be improved without greatly reducing the maximum hydrogen amount.
On the other hand, if w is too large, the effective hydrogen amount is extremely reduced. Therefore, w needs to be 5 mol% or less. w is more preferably 3 mol% or less, and still more preferably 2 mol% or less.

[1.2. Specific examples of alloy composition]
The hydrogen storage alloy represented by the formula (1) has a relatively high initial effective hydrogen amount and relatively high cycle resistance. By further optimizing the components of this hydrogen storage alloy, the initial effective hydrogen amount and / or cycle resistance can be further improved. Specific examples of such alloys include the following.

[1.2.1. First specific example]
The first specific example of the hydrogen storage alloy has a bcc structure phase having a composition represented by the following formula (2) as a main phase. The hydrogen storage alloy represented by the formula (2) has moderate cycle resistance and a high initial effective hydrogen amount.
_{Ti x Cr y V z X w} ··· (2)
However, 3/2 ≦ y / x ≦ 3/1, 50 ≦ z ≦ 70 mol%, 0 ≦ w ≦ 5 mol%, x + y + z + w = 100 mol%.
X = any one or more selected from Al, Si and Fe.

In the equation (2), the initial effective hydrogen amount increases as z increases. However, if z becomes too large, the initial effective hydrogen amount may decrease. Moreover, in Formula (2), cycle tolerance improves, so that z becomes large.
In order to achieve both a high initial effective hydrogen amount and high cycle resistance, z is preferably 55 mol% or more. z is more preferably 57.5 mol% or more, and still more preferably 60 mol% or more.
Similarly, in order to achieve both a high initial effective hydrogen amount and high cycle resistance, z is preferably 68 mol% or less.

In the equation (2), the initial effective hydrogen amount increases as y / x increases. However, if y / x becomes too large, the initial effective hydrogen amount is reduced. Similarly, in the formula (2), the cycle tolerance improves as y / x increases. However, if y / x becomes too large, the cycle resistance may decrease.
In order to achieve both a high initial effective hydrogen amount and high cycle resistance, y / x is preferably 3 / 1.65 or more.
Similarly, in order to achieve both a high initial effective hydrogen amount and high cycle resistance, y / x is preferably 3 / 1.2 or less, and more preferably 3 / 1.35 or less.

Furthermore, in the formula (2), when y / x and z are simultaneously optimized, a high initial effective hydrogen amount and a high cycle resistance can be achieved at a high level. Preferred ranges of y / x and z are as follows.
(A) 3/2 <y / x ≦ 3 / 1.2, 55 ≦ z <70 mol%.
(B) 3/2 <y / x ≦ 3 / 1.2, 57.5 ≦ z <70 mol%.
(C) 3/2 <y / x ≦ 3 / 1.35, 57.5 ≦ z <70 mol%.
(D) 3 / 1.65 ≦ y / x ≦ 3 / 1.35, 57.5 ≦ z <70 mol%.
(E) 3/2 <y / x ≦ 3 / 1.2, 60 ≦ z ≦ 68 mol%.
(F) 3/2 <y / x ≦ 3 / 1.35, 60 ≦ z ≦ 68 mol%.
(G) 3 / 1.65 ≦ y / x ≦ 3 / 1.35, 60 ≦ z ≦ 68 mol%.

[1.2.2. Second specific example]
The second specific example of the hydrogen storage alloy has a bcc structure phase having a composition represented by the following formula (3) as a main phase. The hydrogen storage alloy represented by the formula (3) has an appropriate initial effective hydrogen amount and high cycle resistance.
_{Ti x Cr y V z X w} ··· (3)
However, 3/2 ≦ y / x ≦ 3/1, 70 ≦ z ≦ 75 mol%, 0 ≦ w ≦ 5 mol%, x + y + z + w = 100 mol%.
X = any one or more selected from Al, Si and Fe.

In the formula (3), cycle resistance improves as z increases. However, if z becomes too large, the initial effective hydrogen amount decreases.
In order to achieve both a high initial effective hydrogen amount and high cycle resistance, z is preferably 71 mol% or more. z is more preferably 72 mol% or more.
Similarly, z is preferably 74 mol% or less in order to achieve both a high initial effective hydrogen amount and high cycle resistance.

In the equation (3), the initial effective hydrogen amount increases as y / x increases. However, if y / x becomes too large, the initial effective hydrogen amount is reduced. Moreover, in Formula (3), cycle tolerance improves, so that y / x becomes large. However, if y / x becomes too large, the cycle resistance may decrease.
In order to achieve both a high initial effective hydrogen amount and high cycle resistance, y / x is preferably 3 / 1.65 or more.
Similarly, in order to achieve both a high initial effective hydrogen amount and high cycle resistance, y / x is preferably 3 / 1.2 or less, and more preferably 3 / 1.35 or less.

Further, in the formula (3), when y / x and z are simultaneously optimized, a high initial effective hydrogen amount and a high cycle resistance can be achieved at a high level.
When emphasizing the initial effective hydrogen amount, preferred ranges of y / x and z are as follows.
(A) 3/2 ≦ y / x ≦ 3 / 1.2, 70 <z ≦ 75 mol%.
(B) 3 / 1.65 ≦ y / x ≦ 3 / 1.35, 71 ≦ z ≦ 75 mol%.
Moreover, when importance is attached to cycle resistance, preferred ranges of z and y / x are as follows.
(A) 3 / 1.35 ≦ y / x ≦ 3/1, 70 ≦ z ≦ 75 mol%.
(B) 3 / 1.2 ≦ y / x ≦ 3/1, 71 ≦ z ≦ 75 mol%.

[1.3. bcc structure phase]
When the raw materials are blended so as to obtain the composition described above and melt cast, a hydrogen storage alloy having a bcc structure phase represented by the formula (1) as a main phase is obtained. The hydrogen storage alloy preferably comprises only the bcc structure phase, but may contain inevitable impurities. Inevitable impurities include, for example, pure Ti and TiCr ₂ (Laves phase). The smaller the inevitable impurities that adversely affect the hydrogen storage / release characteristics, the better.
In the present invention, “having the bcc structure phase as the main phase” means that the volume ratio of the bcc structure phase contained in the hydrogen storage alloy is 80 vol% or more. The volume ratio of the bcc structural phase is more preferably 90 vol% or more.

[1.4. Particle size]
The particle size of the hydrogen storage alloy affects the hydrogen storage / release characteristics. Generally, when the particle size becomes too small, the surface area increases. As a result, the oxide layer on the surface increases and the hydrogen storage amount decreases. In addition, when a long pulverization process is performed to reduce the particle size, strain is introduced into the hydrogen storage alloy. As a result, the hydrogen storage amount is reduced or the plateau flatness is lowered. Therefore, the particle size of the hydrogen storage alloy is preferably 0.1 mm or more before the activation treatment.
On the other hand, when the particle size of the hydrogen storage alloy becomes too large, the surface area becomes small. Therefore, high temperature and / or high pressure are required for the activation process for a long time. In addition, the number of activation processes increases. Therefore, the particle size of the hydrogen storage alloy is preferably 10 mm or less before the activation treatment.
Here, the “particle size of the hydrogen storage alloy” refers to the size of a sieve used in a classification test using a sieve (mesh).

[2. Method for producing hydrogen storage alloy]
The method for producing a hydrogen storage alloy according to the present invention includes a melting / casting step, a heat treatment step, and an activation step.

[2.1 Melting / Casting Process]
The melting / casting step is a step of melting / casting the raw materials blended so as to have the composition represented by the formula (1). Since the details of the expression (1) are as described above, the description thereof is omitted.
_{Ti x Cr y V z X w} ··· (1)
However, 3/2 ≦ y / x ≦ 3/1, 40 ≦ z ≦ 75 mol%, 0 ≦ w ≦ 5 mol%, x + y + z + w = 100 mol%.
X = any one or more selected from Al, Si and Fe.

The raw material melting / casting method is not particularly limited, and various methods such as an arc melting method and a high-frequency induction melting method can be used.
In order to prevent deterioration of the alloy characteristics due to mixing of a large amount of oxygen, the melting and casting of the raw materials are performed under an inert gas atmosphere, a reducing atmosphere, and under vacuum (1 × 10 ⁻¹ to 1 × 10 ⁻⁶ Torr (13.3 to 1. It is preferable to carry out in a non-oxidizing atmosphere such as 33 × 10 ⁻⁴ Pa)). The melting temperature and the melting time are not particularly limited, but may be any temperature and time at which a uniform molten metal can be obtained.

[2.2 Heat treatment process]
The heat treatment step is a step of heat-treating the ingot obtained in the melting / casting step.
In general, the bcc structural phase of a TiCrV alloy is a high temperature equilibrium phase. In order to eliminate and solidify the solidification segregation of each component (particularly the dendritic solidification segregation of Ti and V components) formed during melting and casting, heat treatment in a stable high temperature region of the bcc structure phase ( Homogenization heat treatment) is required. In addition, when the homogenization heat treatment is performed, the flatness of the plateau increases, and the hydrogen storage / release characteristics can be improved.

In order to diffuse the constituent elements in a short time and to homogenize the components, the heat treatment temperature is preferably 1200 ° C. or higher.
On the other hand, in order to suppress partial melting of the alloy, the heat treatment temperature is preferably equal to or lower than the melting point of the alloy. The heat treatment temperature is more preferably 20 to 100 ° C. lower than the melting point.

In order to obtain a sufficient homogenizing effect, the longer the heat treatment time, the better. Specifically, the heat treatment time is preferably 1 hour or longer.
On the other hand, the heat treatment more than necessary has no practical effect because the effect is saturated. Therefore, the heat treatment time is preferably 24 hours or less.

The heat treatment is performed in an inert gas atmosphere, a reducing atmosphere, or under vacuum (1 × 10 ⁻¹ to 1 × 10 ⁻⁶ Torr (13.3 to 1.33 × 10 ⁻⁴ Pa)) to prevent oxidation of the alloy. It is preferably performed in a non-oxidizing atmosphere.

[2.3 Activation process]
The activation process is a process of performing at least one process of occluding and releasing hydrogen in the heat-treated ingot.
The activation treatment is performed by reducing the pressure while the ingot is heated to a predetermined temperature, and then bringing the ingot into contact with pressurized hydrogen.
If the temperature of the activation process is too low, it becomes difficult to occlude hydrogen. Accordingly, the temperature for the activation treatment is preferably 300 ° C. or higher.
On the other hand, if the temperature of the activation process becomes too high, the homogenized structure may become non-uniform. Therefore, the temperature for the activation treatment is preferably 450 ° C. or lower.

The pressure at the time of depressurization and the hydrogen pressure at the time of storing hydrogen are not particularly limited, and any pressure can be used as long as it can be sufficiently activated. The pressure at the time of depressurization is usually about 1 × 10 ⁻⁴ Torr (1.33 × 10 ⁻² Pa. Further, the hydrogen pressure when hydrogen is occluded is usually about 50 atm (5.07 MPa).

  In the hydrogen storage alloy according to the present invention, the activation process needs to be performed at least once. In general, the activation treatment of the hydrogen storage alloy needs to be repeated several times, but the hydrogen storage alloy according to the present invention can be sufficiently activated even by a single treatment.

[3. Hydrogen storage device]
The hydrogen storage device according to the present invention includes the hydrogen storage alloy according to the present invention, a container, and a heat exchanger.
Since the details of the hydrogen storage alloy according to the present invention are as described above, the description thereof is omitted.
The container is for containing a hydrogen storage alloy. The container may be any container that can maintain the inside at a predetermined temperature and pressure when storing and releasing hydrogen.
A heat exchanger is for controlling the temperature of the hydrogen storage alloy accommodated in the container. Generally, at the time of storage / release of hydrogen, heat absorption or heat generation is accompanied. Therefore, in order to stably store and release hydrogen, it is necessary to maintain the temperature of the hydrogen storage alloy within a predetermined range. The structure of the heat exchanger is not particularly limited, and heat exchangers having various structures can be used.

[4. Hydrogen storage alloy, method for producing the same, and operation of hydrogen storage device]
When the Cr / Ti ratio (y / x) is optimized in the Ti—Cr—V alloy, the initial effective hydrogen amount can be increased while maintaining the plateau pressure in a practically sufficient range.
In addition, when the amount of V is optimized, cycle durability can be improved while maintaining the initial effective hydrogen amount high. Moreover, a relatively large amount of hydrogen can be occluded and released by one activation process.
Further, when any one or more selected from Al, Si and Fe is added to the Ti—Cr—V alloy, the plateau pressure is increased and the cycle resistance is increased without greatly reducing the maximum hydrogen content. Can be improved. As a result, the effective hydrogen amount can be increased.

(Examples 1-6, Comparative Examples 1-3)
[1. Preparation of sample]
The raw materials blended at a predetermined ratio were arc-melted to obtain an ingot. The obtained ingot was heat-treated at 1300 to 1350 ° C. under Ar. Furthermore, activation treatment at 300 to 450 ° C. was performed once on the heat-treated alloy.
[2. Test method]
[2.1 X-ray diffraction]
X-ray diffraction measurement was performed on the heat-treated alloy. The lattice constant was calculated from the obtained X-ray diffraction pattern.
[2.2 Hydrogen storage / release characteristics]
Ten cycles of pressure-composition isotherm measurement were performed on the alloy after the activation treatment at −20 ° C. to room temperature. Using the obtained initial effective hydrogen amount and the effective hydrogen amount at the 10th cycle, the maintenance ratio (= effective hydrogen amount at the 10th cycle × 100 / initial effective hydrogen amount (%)) was calculated.
Furthermore, the pressure-composition isotherm measurement was performed for 50 to 100 cycles at room temperature or 0 ° C., and the change in the effective hydrogen amount was examined.

[3. result]
Table 1 summarizes the evaluation results. Table 1 also shows the composition of each sample and the heat treatment conditions.
From Table 1,
(1) The alloys obtained in Comparative Examples 1 and 2 have a relatively large initial effective hydrogen amount, but the maintenance rate (cycle resistance) of the effective hydrogen amount at the 10th cycle is low.
(2) The alloy obtained in Comparative Example 3 has high cycle resistance, but the initial effective hydrogen amount is small.
(3) All the alloys obtained in Examples 1 to 6 have a large initial effective hydrogen amount and high cycle resistance.
I understand that.

In FIG. 1, the X-ray-diffraction pattern of the alloy obtained in Examples 1-4 is shown. From FIG. 1, it was confirmed that the alloys obtained in Examples 1 to 4 are all bcc single phase.
FIG. 2 shows a pressure-composition isotherm in the initial hydrogen release process at room temperature of the alloy obtained in Example 1. The initial effective hydrogen amount of the alloy of Example 1 was 2.51 mass%.

FIG. 3 shows the cycle resistance of the alloys obtained in Examples 1 and 4 and Comparative Examples 1 and 3 at room temperature (Example 1 and Comparative Example 3) or 0 ° C. (Example 4 and Comparative Example 1).
From FIG. 3, the alloy obtained in Comparative Example 1 has a relatively large decrease in the effective hydrogen amount as the number of cycles increases, whereas the alloy obtained in Examples 1 and 4 has a cycle number of It can be seen that the decrease in the effective hydrogen amount accompanying the increase is relatively small.
On the other hand, it can be seen that the alloy obtained in Comparative Example 3 has a relatively small decrease in the effective hydrogen amount accompanying the cycle, but the initial effective hydrogen amount is smaller than the others.

(Example 7)
[1. Preparation of sample]
In the same manner as in Example 1 to prepare a different variety of Ti _x Cr _y V _z alloys of y / x ratio and z.
[2. Test method]
In the same manner as in Example 1, the initial effective hydrogen amount at 0 to 50 ° C. and the effective hydrogen amount at the 10th cycle were measured, and the maintenance ratio (cycle resistance) was calculated.

[3. result]
In FIGS. 4-10 are various Ti _x Cr _y V _z initial effective hydrogen amount and cycle durability of the alloys.
4 to 10 show the following.
(1) In the range of 3 / 1.65 ≦ y / x ≦ 3/1, the initial effective hydrogen amount takes a maximum value, and the cycle resistance improves as y / x increases.
(2) When 3/2 ≦ y / x ≦ 3/1 and 65 ≦ z ≦ 75, the initial effective hydrogen amount is 2.2 mass% or more, and the cycle resistance is 94% or more.
(3) When 3/2 ≦ y / x ≦ 3 / 1.2 and 50 ≦ z <65, the initial effective hydrogen amount is 2.2 mass% or more, and the cycle resistance is 91% or more.
(4) When 3/2 ≦ y / x ≦ 3/1 and 50 ≦ z ≦ 75, the initial effective hydrogen amount is 2.2 mass% or more, and the cycle resistance is 91% or more.
(5) When 3/2 ≦ y / x ≦ 3 / 1.2 and 40 ≦ z <50, the initial effective hydrogen amount is 1.8 mass% or more, and the cycle resistance is 90% or more.
(6) When 3/2 ≦ y / x ≦ 3 / 1.5 and 40 ≦ z <50, the initial effective hydrogen amount is 2.3 mass% or more, and the cycle resistance is 90% or more.
(7) When 3 / 1.5 ≦ y / x ≦ 3 / 1.2 and 65 ≦ z ≦ 75, the initial effective hydrogen amount is 2.3 mass% or more, and the cycle resistance is 95% or more.
(8) When 3 / 1.5 ≦ y / x ≦ 3 / 1.2 and 50 ≦ z ≦ 65, the initial effective hydrogen amount is 2.2 mass% or more, and the cycle resistance is 92% or more.
(9) When 3/2 ≦ y / x ≦ 3 / 1.2 and 65 ≦ z ≦ 75, the initial effective hydrogen amount is 2.3 mass% or more, and the cycle resistance is 94% or more.
(10) When 3/2 ≦ y / x ≦ 3 / 1.5 and 50 ≦ z ≦ 65, the initial effective hydrogen amount is 2.3 mass% or more, and the cycle resistance is 91% or more.

(11) When 3/2 <y / x ≦ 3/1 and 50 ≦ z <70 mol%, the hydrogen storage alloy has moderate cycle resistance and a high initial effective hydrogen amount.
In particular, when 3 / 1.65 ≦ y / x ≦ 3 / 1.35 and 60.0 mol% ≦ z ≦ 68 mol%, the hydrogen storage alloy has high cycle resistance and high initial effective hydrogen amount in a high dimension. Both can be achieved.
(12) When 3/2 ≦ y / x ≦ 3/1 and 70 <z ≦ 75 mol%, the hydrogen storage alloy has an appropriate initial effective hydrogen amount and high cycle resistance.
In particular, when 3 / 1.65 ≦ y / x ≦ 3 / 1.35 and 71 ≦ z ≦ 75 mol%, the hydrogen storage alloy has a high initial effective hydrogen amount.
Further, when 3 / 1.2 ≦ y / x ≦ 3/1 and 71 ≦ z ≦ 75 mol%, the hydrogen storage alloy has extremely high cycle resistance.

(Example 8)
V, Ti, and Cr were arc-melted. Thereafter, the ingot was heat-treated at 1300 ° C. under Ar to produce V ₄₀ Ti _18.4 Cr _41.6 . When the X-ray diffraction measurement of the obtained alloy was performed, it was confirmed that the BCC phase is the main phase. Ten cycles of pressure-composition isotherm measurement at 0 ° C. of the heat-treated alloy were performed. The initial effective hydrogen amount was 2.29 mass%. On the other hand, the effective hydrogen amount at the 10th cycle was 2.07 mass% (the initial 90%).

(Comparative Example 4)
V, Ti, and Cr were arc-melted. Thereafter, the ingot was heat-treated at 1260 ° C. under Ar to produce V ₄₀ Ti ₂₅ Cr ₃₅ . When the obtained alloy was subjected to X-ray diffraction measurement, it was confirmed to be a BCC phase single phase. Ten cycles of pressure-composition isotherm measurement at 50 ° C. of the heat-treated alloy were performed. The initial effective hydrogen amount was 2.26 mass%. On the other hand, the effective hydrogen amount at the 10th cycle was 2.00 mass% (88% of the initial).

(Comparative Example 5)
V, Ti, and Cr were arc-melted. Thereafter, the ingot was heat-treated at 1350 ° C. under Ar to produce V ₂₀ Ti ₃₅ Cr ₄₅ . When the X-ray diffraction measurement of the obtained alloy was performed, it was confirmed that the BCC phase is the main phase. Ten cycles of pressure-composition isotherm measurement at 50 ° C. of the heat-treated alloy were performed. The initial effective hydrogen amount was 2.17 mass%. On the other hand, the effective hydrogen amount at the 10th cycle was 1.81 mass% (the initial 84%).

(Comparative Example 6)
V, Ti, and Cr were arc-melted. Thereafter, the ingot was heat-treated at 1260 ° C. under Ar to produce V ₂₅ Ti ₄₂ Cr ₃₃ . When the X-ray diffraction measurement of the obtained alloy was performed, it was confirmed that the BCC phase is the main phase. Ten cycles of pressure-composition isotherm measurement at 50 ° C. of the heat-treated alloy were performed. The initial effective hydrogen amount was 0.34 mass%. On the other hand, the effective hydrogen amount at the 10th cycle was 0.28 mass% (the initial 83%).

(Comparative Example 7)
V, Ti, and Cr were arc-melted. Thereafter, the ingot was heat-treated at 1260 ° C. under Ar to produce V ₂₁ Ti ₅₀ Cr ₂₉ . When the X-ray diffraction measurement of the obtained alloy was performed, it was confirmed that the BCC phase is the main phase. Ten cycles of pressure-composition isotherm measurement at 50 ° C. of the heat-treated alloy were performed. The initial effective hydrogen amount was 0.26 mass%. On the other hand, the effective hydrogen amount at the 10th cycle was 0.23 mass% (88% of the initial).

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.

  The hydrogen storage alloy and the manufacturing method thereof according to the present invention are used as a hydrogen storage medium used in a hydrogen storage means for a fuel cell system, a chemical heat pump, an actuator, a hydrogen storage body for a metal-hydrogen storage battery, and the manufacturing method thereof. can do.

Claims (9)

A hydrogen storage alloy having a bcc structural phase having a composition represented by the following formula (1) as a main phase.
_{Ti x Cr y V z X w} ··· (1)
However, 3/2 ≦ y / x ≦ 3/1, 40 ≦ z ≦ 75 mol%, 0 ≦ w ≦ 5 mol%, x + y + z + w = 100 mol%.
X = any one or more selected from Al, Si and Fe.   2. The hydrogen storage alloy according to claim 1, wherein 3/2 <y / x ≦ 3/1 and 50 ≦ z <70 mol%.   The hydrogen storage alloy according to claim 2, wherein 55 ≦ z <70 mol%.   3. The hydrogen storage alloy according to claim 2, wherein 3/2 <y / x ≦ 3 / 1.2.   3. The hydrogen storage alloy according to claim 2, wherein 3/2 <y / x ≦ 3 / 1.2 and 55 ≦ z <70 mol%.   The hydrogen storage alloy according to claim 2, wherein 3 / 1.65 ≦ y / x ≦ 3 / 1.35 and 60 ≦ z ≦ 68 mol%.   The hydrogen storage alloy according to claim 1, wherein 3/2 ≦ y / x ≦ 3/1 and 70 <z ≦ 75 mol%. (1) a melting / casting step of melting / casting a raw material blended to have a composition represented by the formula;
A heat treatment step for heat-treating the ingot obtained in the melting and casting step;
A method for producing a hydrogen storage alloy, comprising an activation step of performing at least one process of storing and releasing hydrogen in the heat-treated ingot.
_{Ti x Cr y V z X w} ··· (1)
However, 3/2 ≦ y / x ≦ 3/1, 40 ≦ z ≦ 75 mol%, 0 ≦ w ≦ 5 mol%, x + y + z + w = 100 mol%.
X = any one or more selected from Al, Si and Fe. The hydrogen storage alloy according to any one of claims 1 to 7,
A container for containing the hydrogen storage alloy;
A hydrogen storage device comprising: a heat exchanger for controlling the temperature of the hydrogen storage alloy accommodated in the container.

Images