JP2003064435A - Hydrogen storage alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means for improving the hyderogen storage content of a Ti-Cr based hydrogen storage alloy. SOLUTION: This hydrogen storage alloy consists of a phase (BCC phase) with a body-centered cubic structure as the main phase, and can occlude and release hydrogen. The alloy has a composition expressed by the general formula of Ti(100-a-b-c-d-e) Cra Xb X'c Td Le ; wherein, 20<=a (at%)<=80, 0<b (at%)<=10, 0<c (at%)<=30, 0<d (at%)<=30, and 0<e (at%)<=10, and containing at least one group selected from X, X', T and L (X denotes at least one kind of element selected from Ru, Rh, Os, Ir, Pd, Pt and Re; X' is at least one kind of element selected from Mo, W and Al; T is at least one kind of element selected from Mn, Fe, Co, Ni, Cu, Nb, Ta, B and C; and L is at least one kind of element selected from Y and lanthanoide elements), and the content of oxygen is <=3,000 ppm.

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 capable of storing and releasing hydrogen, and in particular, to a body-centered cubic (BCC) crystal structure type hydrogen storage alloy having a theoretically high capacity. Is.

[0002]

2. Description of the Related Art At present, there is a concern about acid rain caused by NOx (nitrogen oxide), which is increased by the use of fossil fuels, and global warming due to CO _2. These environmental destructions are serious problems. Is coming. Among them, the practical application of hydrogen energy as clean energy has been attracting worldwide attention. Hydrogen is an inexhaustible constituent element of water on the earth, and not only can it be created using various primary energies, but it is also a by-product of water, so there is no concern of environmental damage. Further, it has excellent characteristics such as being relatively easy to store as compared with electric power.

Therefore, in recent years, research and development and practical application of hydrogen storage alloys as storage and transport media for these hydrogens have been actively carried out. With these hydrogen storage alloys,
An alloy that can absorb and release hydrogen under appropriate conditions. By using this alloy, it becomes possible to store hydrogen at a low pressure and at a high density as compared with a conventional hydrogen gas cylinder. The volume density thereof is almost equal to or higher than that of liquid hydrogen or solid hydrogen, and the handling safety is remarkably excellent.

LaNi is one of these hydrogen storage alloys._Five
AB such as_FiveType alloy or TiMn ₂AB such as₂Pattern
Gold has been put to practical use. However, its hydrogen storage capacity is at most
It is around 1.4 mass%, for example, WE-NET (country
Water such as fuel cells advocated by the International Energy Network)
The target performance of the hydrogen storage alloy used for elementary storage is 100.
The value of 3 mass% has not been reached below ℃
Yes. In recent years, for example, Japanese Patent Laid-Open No. 10-110225
Report, JP-A-11-106859, JP-A-10-1
21180 and Japanese Patent Laid-Open No. 2000-345273.
As suggested in, the number of hydrogen storage sites is large,
The theoretical amount of hydrogen that can be stored per unit weight of alloy is about 4 ma
ss%, (H / M = 2, H: stored hydrogen atom, M: alloy structure
And the extremely large body-centered cubic structure (hereinafter “BCC”)
Phase "," BCC type "or" BCC ")
The Ti-Cr alloys that have been paid attention to, aiming for practical use
Many studies are under way.

In this Ti-Cr binary alloy, the mixing ratio is 40≤Cr (at%) ≤60 which allows hydrogen to be stored and released at a practical temperature and pressure. However, the alloy of 40 ≦ Cr (at%) ≦ 60 is
As can be seen from the Ti-Cr binary system phase diagram of FIG. 2, the melting point of the alloy and the temperature at which the C14 type crystal structure (βTiCr ₂ / Laves phase) or the C15 type crystal structure (αTiCr ₂ / Laves phase) is generated. The width of the temperature region generated by the BCC phase between them becomes extremely small. Therefore, another C14 type or C15 type different from the BCC phase in the alloy
A considerable amount of type Laves phase is formed, and it is difficult to obtain an alloy having a BCC phase as a main phase. Therefore, for example, JP-A-10-110225 and JP-A-10-121180.
In JP-A No. 11-106859 or JP-A No. 2000-345273, M is used as an element having a high ability to form a BCC phase with respect to both Ti and Cr.
It has been proposed to make the BCC phase the main phase more stably and at a low temperature by further adding o, W, Al and the like. Further, in Japanese Patent Laid-Open No. 11-106859, 1
It proposes a treatment for converting the BCC phase to a single phase by heating at 000 to 1400 ° C and then rapidly cooling.

[0006]

With the above proposals and improvements, the hydrogen storage capacity of the Ti-Cr system hydrogen storage alloy is
Although it approaches the theoretical hydrogen storage amount described above, it goes without saying that it is desirable to approach the theoretical hydrogen storage amount. On the other hand, elements such as Mo, W and Al are 10 at
% Or more is recommended, which means that the hydrogen storage amount per unit weight is reduced. Therefore, it goes without saying that it is desirable to use the BCC phase as the main phase without adding a large amount. Further, conventional alloys require heating at a high temperature and subsequent rapid quenching treatment in order to convert the BCC phase into a single phase, but it is desirable to omit such treatment in industrial production. Nor. Therefore, the first object of the present invention is to provide a method of improving the hydrogen storage amount of various improved Ti-Cr-based hydrogen storage alloys. Furthermore, the present invention provides Mo, W that causes a decrease in the hydrogen storage amount per unit weight.
A second object is to obtain a hydrogen storage alloy containing the BCC phase as the main phase by a simple heat treatment with a minimal or minimal content of Al and the like.

[0007]

In order to solve the first problem, the present inventor has paid attention to impurities contained in a Ti--Cr based hydrogen storage alloy. As a result, the hydrogen storage capacity depends on the amount of oxygen contained in the alloy. It was found that the amount fluctuates. At the same time, when the additive elements to the Ti-Cr binary alloy were examined, Ru, Rh, Os, Ir, Pd, Pt and Re suppressed the generation of the Laves phase in the Ti-Cr binary alloy. As a result, it has been found that it is a unique element that is effective for making the BCC phase into a single phase, and also has the effect of increasing the hydrogen storage amount and the effect of increasing the plateau pressure. In addition, these effects can be achieved with a predetermined effect only by containing a small amount as compared with the conventionally proposed Mo, W and Al. That is, in order to solve the second problem, R
It is proposed that one or more of u, Rh, Os, Ir, Pd, Pt and Re be contained in the Ti—Cr based hydrogen storage alloy.

The present invention has been made based on the above findings, and is a hydrogen storage alloy having a body-centered cubic structure (BCC phase) capable of storing and releasing hydrogen as a main phase, and having a composition. formula _{Ti (100-abcde) Cr a} X b X 'c T d
L _e However, 20 ≦ a (at%) ≦ 80, 0 <b (at%) ≦ 10,0
<C (at%) ≦ 30, 0 <d (at%) ≦ 30, 0 <e (at%) ≦
And includes at least one group of X, X ′, T and L, wherein X is Ru, Rh, Os, Ir, Pd, Pt, R
at least one element of e, X ′ is at least one element of Mo, W and Al, T is Mn, Fe, Co and N
At least one element of i, Cu, Nb, Ta, B and C, L is at least one element of Y and a lanthanoid element, and the oxygen content is 3000 ppm or less. In the hydrogen storage alloy of the present invention, the oxygen content is 2000 ppm or less, further 1000 p
It is preferably pm or less.

In the hydrogen storage alloy of the present invention, X,
It is sufficient to include at least one group of X ′, T, and L, but as described above, X suppresses the generation of Laves phase in the Ti—Cr binary alloy and is effective for making the BCC phase single phase. In addition, since it is an element that has both the effect of increasing the hydrogen storage amount and the effect of increasing the plateau pressure, it is desirable to make it an essential element. With this alloy, it is possible to obtain a BCC phase single phase alloy without special heat treatment. Ru is most desirable as X, and has a BCC stabilizing effect and C14.
The effect of suppressing the appearance of the Laves phase of the C type, C15 type, etc. is the largest, and a remarkably excellent hydrogen storage performance can be realized.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The hydrogen storage alloy of the present invention can improve the hydrogen storage amount because the oxygen content is limited to 3000 ppm or less. Oxygen content of 300
There are several approaches to limit below 0 ppm. For example, a raw material having a low oxygen concentration is used, the atmosphere during melting is controlled, and a deoxidation process is performed during melting. However, this method does not matter in the present invention.
As a result, the amount of oxygen in the alloy should be 3000 ppm or less.

The reasons for limiting the components in the present invention will be described below. The atomic radius of Ti (0.146 nm) is Cr
Is larger than the atomic radius (0.125 nm), the lattice constant of the BCC phase increases and the plateau pressure decreases if the Ti content in the alloy is increased and the Cr content is decreased. That is,
The Ti-Cr alloy can control the plateau pressure by controlling the composition ratio of Ti and Cr. Therefore, the plateau pressure of the hydrogen storage alloy changes depending on the alloy operating temperature, but Cr /
The Ti ratio may be selected. However, the Cr content a is 80
When it exceeds at%, the plateau pressure rises remarkably and conversely 20 at
If it is less than%, the plateau pressure is remarkably lowered and it becomes poor in practical use. Therefore, the range is 20 ≦ a (at%) ≦ 80. It is preferable to select a Cr / Ti ratio that matches the target operating temperature within the range of 30 ≦ a (at%) ≦ 70, and more preferably within the range of 45 ≦ a (at%) ≦ 65. Considering some practicality, 20 ° C (293K) to 40 ° C (313
It is desirable to have an appropriate plateau pressure in K), in which case it is recommended that the Cr / Ti ratio be in the range of 1.0 to 1.7. Specifically, it has a composition of Ti _{37 to 50} Cr _{63 to 50} . However, the present invention is not limited to this composition.

In the present invention, X, X ', T and L include at least one group. Hereinafter, these elements will be described in order. X element (Ru, Rh, Os, Ir, Pd, Pt, R
One or two or more of e) has a high BCC phase forming ability only by containing a trace amount in the Ti-Cr alloy, and is harmful if the heat treatment and simple cooling are performed in the state of casting or after casting. A BCC single-phase alloy containing almost no Laves phase such as C14 type and C15 type can be obtained.

Like the X element of the present invention, B can be added in a small amount.
No element has been found so far that has a strong stabilizing effect on the CC phase and a strong effect of increasing the plateau pressure. This effect is due to the conventionally known BCC such as Mo, W and Al.
It surpasses stabilizing elements. This means that depending on the conventionally known BCC stabilizing elements such as Mo, W, and Al, BCC in the state after casting (hereinafter referred to as “as cast”)
Even if the phase is a main phase or a composition in which the BCC single phase cannot be achieved, it becomes apparent from the examples described later that the B element single phase can be achieved by the element X of the present invention. Similarly, according to the X element of the present invention, according to the examples described later,
It has the effect that the plateau pressure can be improved with a smaller content compared to the conventional BCC stabilizing element. The content of the X element in the present invention may be appropriately selected depending on the target operating temperature and operating pressure. But,
If it exceeds 10 at%, the hydrogen storage amount per unit weight decreases, and the cost becomes industrially too high. Therefore, the content is set to 10 at% or less. Preferably 7 at% or less,
More preferably, it may be selected in the range of 5 at% or less,
Even at 3 at% or less, a useful hydrogen storage alloy can be obtained.

As described above, the X element of the present invention is
Combines the stabilizing effect and the plateau pressure increasing effect at a high level.
The reason for preparing is not clear. About stabilization of BCC phase
The atomic radius is Ti (atomic radius: 0.146 nm)
Element showing an intermediate value of Cr (atomic radius: 0.125 nm)
It is effective to contain the element. Laves phase is AB
₂It is represented by the composition of the molds, and in these compositions the ideal
The atomic radius of both A and B atoms is required to obtain a logical structure.
(R_A: R_B) Should be about 1.225: 1
On the other hand, the atomic radius of Ti: the atomic radius of Cr is 1.17:
Since it is 1, it is far from the ideal geometric structure.
In other words, the Ti-Cr binary alloy has an ideal Laves phase structure.
It is not suitable for forming structures. And Ti-Cr
By increasing the amount of Ti in the binary alloy,
Apparently, more Ti penetrates into the B site.
The atomic radius ratio of A site and B site is reduced,
Can be further separated from the ideal geometry of the phase
It The atomic radius is smaller than that of the A site, and the B
Element with a larger atomic radius than Ti
If it is contained in gold, this element is either A or B site
Even if you enter_A: R_BBecomes even smaller, Laves phase
Speculation that it inhibits growth, that is, promotes the formation of BCC phase
To be done. The X element of the present invention is, as shown below,
Its atomic radius is Ti (atomic radius: 0.146 nm)
Show intermediate value of Cr (atomic radius: 0.125 nm)
There is. Therefore, the BCC phase is reduced by the X element of the present invention.
Although the standardization effect is based on the above-mentioned assumption,
The conventional BCC phase stabilizing element has an atomic radius of Ti.
Since the intermediate value of Cr is shown, the conventional BC
Notable from the stabilizing element of phase C
Has an effect. Ru: 0.133 nm, Rh: 0.134 nm, Os:
0.134 nm, Ir: 0.135 nm, Pd: 0.13
8 nm, Pt: 0.138 nm, Re: 0.137 nm

The reason for the plateau pressure increasing effect is not clear. However, regarding the X element of the present invention,
Focusing on the physical properties, especially electronegativity,
As shown below, all X elements are Ti (electronegativity:
1.5), Cr (electronegativity: 1.6), and larger than hydrogen (electronegativity: 2.1), or close to it. The electronegativity referred to here is the electronegativity by Pauling. Ru: 2.2, Rh: 2.2, Os: 2.2, Ir: 2.2 Pd: 2.2, Pt: 2.2, Re: 1.9 In addition, the electronegativity of the X element is Conventional BC shown below
It is higher than the electronegativity of the stabilizing element of the C phase. Mo: 1.8, W: 1.7, Al: 1.5 Therefore, the effect of increasing the plateau pressure by the X element of the present invention is that the average electronegativity of the metal element in the alloy is close to that of hydrogen. In the sense that it makes the hydrogen atom more unstable, it can be sorted by electronegativity. However, as is clear from the examples described below, even if the electronegativity is the same, there is a difference in the effect of increasing the plateau pressure, and as described above, the reason cannot be clearly explained. .

The alloy of the action of the X element described above is a concrete alloy.
An explanation will be given based on an example. Alloys with composition (at%) shown below
Melting, stirring, and solidification using the arc melting device described above.
An alloy (ingot) was obtained by repeating. Na
The solidification is done by naturally cooling the molten alloy on a copper hearth.
It The result of X-ray diffraction of the obtained alloy is shown in FIG.
2 and FIG. Ti₅₅Cr₄₅, Ti₅₅Cr₄₀Ru_Five, Ti₅₅Cr₄₀R
h_Five, Ti₅₅Cr₄₀Os_Five, Ti₅₅Cr₄₀Ir_Five, Ti₅₅
Cr₄₀Pd_Five, Ti₅₅Cr₄₀Pt_Five, Ti₅₅Cr₄₀Re_Five As shown in FIGS. 12 and 13, Ti₅₅Cr₄₅Is la
-Although X phase is present, it contains X element
All the alloys are BCC single-phase alloys. This result
, Ru, Rh, Os, Ir, Pd, Pt, Re
The element has a strong BCC forming ability and a Laves phase appearance suppressing effect.
Has been demonstrated. Note that Ti ₅₅Cr₄₅BC
When the ratio of the C phase was calculated by the above-mentioned formula, it was 66%.
It was. Ru, Rh, Os, Ir, Pd, Pt, R
As can be seen from FIG. 2, the composition of the alloy containing e has a Laves phase.
Although it is a composition that does not easily precipitate,
BC in the as cast state without heat treatment consisting of cold treatment
It is very noticeable that the C single phase has been achieved.

The following alloys were prepared in the same manner as the above alloy examples and subjected to X-ray diffraction in the as cast state. The result is shown in Figure 1.
4 shows. The Ti / Cr ratio of these alloys was adjusted so that the plateau pressure was in the practical range of 0.1 to 0.2 MPa. Ti ₄₀ Cr ₅₇ Mo ₃ Ti ₄₄ Cr ₅₃ Ru ₃ Ti ₄₀ Cr ₅₆ Mo ₃ Ru _{1 As} can be seen from FIG. 14, Ti ₄₀ Cr ₅₇ Mo ₃ has many Laves phases, while Ti ₄₀ Cr ₅₇ Mo ₃ has ₄₄ Cr ₅₃ Ru ₃
Is a BCC single phase alloy. Also, Ti ₄₀ Cr _{5 6} Mo ₃
In Ru ₁ , a Laves phase was observed, but Ti ₄₀ Cr ₅₇ M
o ₃ has a BCC phase ratio of 5%, whereas
It was confirmed that the phase was 90% and the BCC phase was the main phase. As described above, it was demonstrated that the X element of the present invention has a BCC-forming ability and a Laves phase appearance suppressing effect which are significantly superior to those of Mo, which is an element having a BCC-forming ability known in the related art.

After subjecting the above alloy (as cast) to the activation treatment, the pressure-composition isotherm (PCT line) at 40 ° C. was measured by the vacuum origin method. The measurement is JIS H
7201 (and so on). The result is shown in FIG. From Fig.15, T where Laves phase appears
It can be seen that i ₄₀ Cr ₅₇ Mo ₃ does not show a plateau (flat motion part). On the other hand, Ti ₄₀ Cr ₅₆ Ru ₁ Mo _{3 which} is a BCC single phase or an alloy having a BCC phase as a main phase in which a small amount of Ru is contained alone or in a complex manner is 0.07 each.
With a practical plateau pressure of MPa and 0.20 MPa,
It was revealed that it has an excellent hydrogen storage / release performance. The plateau pressure is the median value of the plateau region when hydrogen is released. Next, Ti ₄₅ Cr ₅₃ M ₂ (however,
M = Cr, Ru, Rh, Os, Ir, Pd, Pt, R
(e, Mo) was prepared in the same manner as described above, and then held in an Ar atmosphere of 0.1 MPa (the atmosphere is the same in the following examples) at 1400 ° C. for 10 minutes and then in ice water. A sample was obtained by charging and quenching. When phase identification was performed by X-ray diffraction, all samples had a BCC single-phase structure. After subjecting this sample to the activation treatment, the pressure-composition isotherm (PCT
Line) was measured. The results are shown in FIGS. M
The alloy of = Cr is substantially a Ti-Cr binary alloy, but this binary alloy has a low plateau pressure. On the other hand, it is understood that the plateau pressures of the alloys containing the element X show higher values than those of the Ti-Cr binary alloy. Further, the alloy of M = Mo has a lower plateau pressure than the alloy of the present invention containing the X element. That is, it is understood that the element X of the present invention is an extremely effective element for increasing the plateau pressure.

The hydrogen storage alloy of the present invention may contain at least one element of Mo, W and Al as the X'element. By containing this X'element at the same time as the X element, the content of the X element is further reduced, and
Since the content of the X ′ element can be reduced to a small amount, the decrease in the hydrogen storage amount per unit weight can be suppressed to a slight level. As a result, it is possible to obtain a hydrogen storage alloy that is highly practical and has a good balance between these costs and the hydrogen storage amount per unit weight. In the present invention, although the X'element can exhibit a predetermined effect with a small amount, it does not deny that the X'element is contained in the same amount as the conventional one. Therefore, the content of 30 at% or less (not including 0%; the same applies hereinafter) is allowed. But,
It is desirable that the content is as small as possible in the range where a predetermined effect is obtained. Therefore, in the present invention, the content of 20 at% or less, further 10 at% or less is recommended. Since the present invention contains the X element, depending on the combination with the X element, a predetermined effect can be exhibited even with an extremely small content of 5 at% or less.

The hydrogen-absorbing alloy of the present invention contains M as the T element.
n, Fe, Co, Ni, Cu, Nb, Ta, B and C
At least one element of 30 at% or less, preferably 2
It can be appropriately contained in a range of 0 at% or less, more preferably 10 at% or less. By containing this T element, the plateau pressure is arbitrarily controlled, the plateau pressure is flatly controlled, the melting temperature is controlled in the manufacturing process, the heat treatment temperature is controlled, the corrosion resistance of the alloy is improved, and the alloy as a secondary battery electrode material is collected. It is possible to control electric characteristics and the like.

Further, in the hydrogen storage alloy of the present invention, as the L element, Y and lanthanoid series elements (La, Ce, P) are used.
r, Nd, Pm, Sm, Eu, Gd, Tb, Dy, H
at least one of O, Er, Tm, Yb, Lu)
at% or less, preferably 5 at% or less, more preferably 3
It can be contained within the range of at% or less. L element is
Since it has a strong affinity with oxygen, it exerts an effect of removing oxygen existing in the alloy as an L element oxide. As a result, it becomes possible to stabilize the hydrogen storage amount and to effectively use industrially a raw material having a relatively large amount of oxygen.

The hydrogen storage alloy of the present invention contains at least one group of X element, X'element, T element and L element. Therefore, the hydrogen storage alloy of the present invention includes the following aspects. _{Ti (100-ab) Cr a} X b Ti (100-abc) Cr a X b X 'c Ti (100-abd) Cr a X b T d Ti (100-abe) Cr a X b L e Ti (100 _{-abde) Cr a X b T d} L e Ti (100-abcd) Cr a X b X 'c T d Ti (100-abce) Cr a X b X' c L e Ti (100-abcde) Cr a X _{b X 'c T d L e} Ti (100-ac) Cr a X' c Ti (100-acd) Cr a X 'c T d Ti (100-ace) Cr a X' c L e Ti (100-acde _{) Cr a X 'c T d} L e Ti (100-ad) Cr a T d Ti (100-ae) Cr a L e Ti (100-ade) Cr a T d L e

The hydrogen storage alloy of the present invention has the BCC phase as the main phase. Whether or not the alloy has the BCC phase as the main phase can be determined by X-ray diffraction. Also in the present invention, whether or not the BCC phase is the main phase is determined by X-ray diffraction. More specifically, an alloy having a BCC phase as a main phase is defined as an alloy having a ratio (%) of 50% or more according to the following formula based on the integrated intensity of diffraction lines. In the hydrogen storage alloy of the present invention, the higher the proportion of the BCC phase is, the more desirable it is.
It is desirable that it consists of CC phase. Needless to say, the present invention includes the case where the BCC phase is 100%, that is, the BCC phase is a single phase, and is the most desirable form for hydrogen storage capacity and other characteristics. bcc (110) / [bcc (110) + {C14Laves (201) + C15Laves (31
1)} × 2] In the present invention, a phase that can exist in addition to the BCC phase is a Laves phase. As I mentioned earlier, the Laves phase is
C14 type crystal structure (βTiCr ₂ / Laves phase) and C15 type crystal structure (αTiCr ₂ / Laves phase), and C36 type crystal structure (γTiCr) which is not usually observed.
₂ / Laves phase), and one of the Laves phases is mixed with the BCC phase.

The hydrogen storage alloy of the present invention can achieve BCC single-phase formation in the as cast state when it contains X element. In view of the fact that the alloys proposed so far are heated to a predetermined temperature for a predetermined time as described in the section of the prior art, and a BCC single phase alloy cannot be obtained unless heat treatment of quenching after holding is performed, It can be seen that the usefulness of element X is outstanding. That is, from the viewpoint of hydrogen storage characteristics, it is desirable that the alloy be a BCC single phase, but this BCC single phase alloy can be obtained by a simple heat treatment without the heat treatment as described above, or even if the heat treatment is performed. Therefore, the alloy of the present invention containing the element X is desirable for industrial productivity.

Next, a desirable manufacturing method for obtaining the hydrogen storage alloy of the present invention will be described. FIG. 1 is a flow chart showing a typical form of a method for producing a hydrogen storage alloy according to the present invention. The manufacturing method shown in FIG. 1 includes steps of weighing of alloying elements, arc melting, heat treatment in Ar gas, and rapid cooling (hereinafter, quenching). This method for producing a hydrogen storage alloy is as follows. First, when it is desired to produce each metal constituting the hydrogen storage alloy desired to be obtained, for example, Ti-Cr-Ru alloy,
And Cr and Ru are weighed in amounts corresponding to the composition ratio. In the examples described below, the ingot obtained was weighed so as to weigh 12 g.

Each weighed metal is put into an arc melting apparatus (not shown) and melted, stirred and solidified in an argon atmosphere of about 50 kPa for a predetermined number of times (in the embodiment, it depends on the number of constituent elements, Only about 3 to 5 times). The reason for repeating melting, stirring and solidifying is to enhance the homogeneity of the alloy. As described above, the hydrogen storage alloy of the present invention can be made into a BCC single phase in the as cast state after solidification.

The obtained ingot is held in the temperature region just below its melting point for a predetermined time. As shown in the state diagram of FIG. 2, the heating temperature at this time is a BCC type melting point because there is a BCC type temperature range immediately below the melting temperature of the alloy having the composition to be obtained. It may be appropriately selected within the temperature range immediately below the temperature. For example, Cr is about 60
In the case of a composition containing at%, the temperature may be maintained at about 1400 ° C. However, if the temperature is low (about 1000 ° C. or less) even within the temperature range immediately below the melting temperature for BCC type, it is necessary to lengthen the heat treatment time. When the heating temperature is high, the heat treatment time is short, but the heating cost is increased. Therefore, the heating temperature may be selected in consideration of these points.

If the heating and holding time is too short, sufficient formation of the BCC phase cannot be obtained, and conversely, if it is too long, not only the heat treatment cost rises, but also a different phase precipitates to deteriorate the hydrogen storage characteristics. There may be side effects. Therefore, it may be appropriately selected in consideration of the heating temperature,
INDUSTRIAL APPLICABILITY The hydrogen storage alloy of the present invention has an excellent ability to form BCC phase in X
Since the element is contained, heating in the range of 1 minute to 1 hour is sufficient. However, it does not prevent the heating and holding for more than 1 hour. Hold by heating with an inert gas such as Ar
It is preferably carried out in gas or vacuum. This is to prevent oxidation of the alloy.

The alloy which has been heated and held is subjected to a quenching treatment. This rapid cooling treatment is for holding the BCC phase formed by heating and holding to room temperature. As a specific means for the rapid cooling treatment, charging into ice water or spraying with an inert gas can be mentioned. However, charging into ice water or spraying with an inert gas is a desirable mode of the present invention, but other cooling methods are not excluded. Here, the volume ratio of the BCC phase in the alloy changes depending on the cooling rate in the quenching process. That is, since the volume ratio of the BCC phase decreases when the cooling rate is slow, it is desirable to perform rapid cooling at a cooling rate of 100 K / sec or more.

In the above embodiment, melting, stirring,
After solidification to obtain an ingot, the ingot was subjected to heat treatment of heating and holding-quenching. However, the hydrogen storage alloy of the present invention can also be manufactured by a rapid solidification process in which solidification and rapid cooling are performed simultaneously. For example, it is a process of obtaining a plate-shaped, ribbon-shaped, or powder-shaped alloy from a molten alloy by a method such as a strip casting method, a single roll method, or an atomizing method. By using this rapid solidification process, it is possible to efficiently obtain the hydrogen storage alloy of the present invention having the BCC phase as the main phase, without performing the above-described heat treatment of holding and quenching. Even in the case of an alloy obtained by rapid solidification, when the BCC phase is not the main phase (Laves phase (main phase) + BCC phase or Laves phase), the above-mentioned heat holding-quenching heat treatment may be performed. it can. Of course, depending on the alloy composition, BCC may be applied even if the molten alloy is not rapidly heat-treated after being rapidly solidified.
The phase may become the main phase (including single phase).

The characteristics of the obtained hydrogen storage alloy can be known by measuring the pressure-composition isotherms (PCT). PCT
The measuring method of the line is specified in JIS H7201, and the most common method is the vacuum origin method (JIS H7003 30
03). The hydrogen storage amount of a hydrogen storage alloy is generally obtained by this vacuum origin method.

[0032]

EXAMPLES The hydrogen storage alloy of the present invention will be described below based on specific examples. (Example 1) An alloy (ingot) was obtained by repeating melting, stirring, and solidifying an alloy having the following composition (at%, the same below) using the above-described arc melting apparatus. By controlling the starting material and the melting atmosphere,
Alloys with different oxygen contents were obtained. The solidification is performed by naturally cooling the molten alloy on a copper hearth. After holding the obtained alloy in an Ar atmosphere of 0.1 MPa (the atmosphere is the same in the following examples) at 1400 ° C. for 10 minutes,
A sample was obtained by pouring into ice water and quenching. After the rapid cooling in ice water, the surface oxide was mechanically removed. This oxide removal treatment may be carried out by pickling. The results of X-ray diffraction of the obtained alloy are shown in FIG. 3 (alloy A) and FIG. 4 (alloy B). Ti ₄₀ Cr ₅₈ Mo ₂ (alloy A) Ti ₄₀ Cr ₅₄ Mo ₆ (alloy B)

The oxygen content shown in FIGS. 3 and 4 is 300.
It was confirmed that the BCC phase was the main phase of the alloy in the sample of 0 ppm or less. Especially, oxygen content is 1000p
In the case of pm or less, both alloy A and alloy B were confirmed to be BCC single phase alloys. The results of the ratio of the BCC phase in Alloy A and Alloy B obtained by the above-mentioned formula are described in FIGS. 3 and 4. After subjecting the alloy A having different oxygen contents to the activation treatment, the pressure-composition isotherm (PCT line) at 40 ° C. by the vacuum origin method was measured. The measurement is based on JIS
Performed according to H7201. Results are shown in FIG. Figure 5
From this, it can be seen that the hydrogen storage amount increases as the oxygen content decreases. On the contrary, it can be seen that the plateau pressure increases as the oxygen content increases. That is, in order to have a practical plateau pressure and increase the hydrogen storage amount with the same alloy composition, it is desirable to reduce the oxygen content in the alloy.

FIG. 6 is a graph showing the relationship between the oxygen content in alloys A and B and the maximum hydrogen storage amount by the vacuum origin method after activation treatment. As shown in FIG. 6, it can be seen that in both alloy A and alloy B, the hydrogen storage amount increases as the oxygen content decreases. Especially when the oxygen content is around 3000 ppm,
If it exceeds 000 ppm, the hydrogen storage amount is significantly reduced. In order to improve the hydrogen storage capacity, the oxygen content should be 20%.
It is desirable to set it to 00 ppm or less, and further 1000 ppm or less.

(Example 2) The following alloy C was prepared in the same manner as in Example 1, and was set to 1400 in an Ar atmosphere of 0.1 MPa.
After holding at 10 ° C. for 10 minutes, it was put into ice water and rapidly cooled to obtain a sample. By controlling the starting material and the melting atmosphere, alloys with various oxygen contents were obtained. The result of X-ray diffraction of the obtained sample is shown in FIG. 7. Ti ₄₁ Cr ₅₇ Ru ₂ (alloy C) Sample with oxygen content of 3000 ppm or less (O
₂ = 834 ppm) was confirmed to be a BCC single phase alloy.

For alloy C having different oxygen contents, pressure-composition isotherm (PCT line) was measured in the same manner as in Example 1. The results are shown in Fig. 8. It can be seen that the sample having the lowest oxygen content of 834 ppm has the largest hydrogen storage amount. Figure 9
The relationship between the oxygen content in alloy C and the maximum hydrogen storage amount by the vacuum origin method after the activation treatment is shown in Fig. 7. In alloy C, the hydrogen storage amount increases as the oxygen content decreases. It became clear. It was also found from FIG. 8 that the plateau pressure increased as the oxygen content increased.

(Example 3) In the same manner as in Example 1, an ingot made of alloy D having the following composition was obtained. After holding this ingot at 1420 ° C. for 5 minutes, it was put into ice water and subjected to a heat treatment of quenching to prepare a sample. By controlling the starting material and the melting atmosphere,
Two types of samples having oxygen contents of 400 ppm and 2000 ppm were obtained. Ti ₄₀ Cr ₅₆ Mo ₃ La ₁ (Alloy D) As a result of X-ray diffraction of the obtained sample, it was confirmed that the BCC phase was the main phase in both two types of samples. The sample having an oxygen content of 400 ppm was a single-phase alloy of BCC phase.

With respect to the two alloys D having different oxygen contents, the pressure-composition isotherm (PCT line) was obtained as in Example 1.
Was measured. The results are shown in Fig. 10. Oxygen content is 400
It can be seen that the hydrogen storage amount is higher in the sample as low as ppm. It was also found from FIG. 10 that the plateau pressure increased as the oxygen content increased.

(Example 4) In the same manner as in Example 1, an ingot made of alloy E and alloy F having the following compositions was obtained. After holding this ingot at 1420 ° C. for 5 minutes,
A sample was prepared by performing a heat treatment in which it was put into ice water and rapidly cooled. When phase identification was performed by X-ray diffraction, all samples had a BCC single-phase structure. For this sample,
After removing the oxide layer on the surface of the alloy, the amount of oxygen was measured, and further the pressure-composition isotherm (PCT line) was measured by the vacuum origin method at 40 ° C. The result is shown in FIG. In order to remove the oxide layer on the surface of the alloy, a method of mechanically removing it with a grinder or a chemical method such as pickling can be used. Ti ₄₀ Cr _58.5-X Ru _0.5 Mo ₁ La _X (X = 0 (alloy E), 1 (alloy F)) First, focusing on the amount of residual oxygen, while the alloy D containing no La is 2200 ppm, Alloy E containing La has a residual oxygen content of 400 ppm, which is reduced to about 1/4. This is because oxygen in the BCC phase and La form oxides to remove residual oxygen. It has been clarified that the BCC main phase is more stable and the hydrogen storage performance is improved in the alloy having a smaller residual oxygen content. Further, in the alloy E having a large amount of residual oxygen, oxygen is likely to form a solid solution, the lattice constant becomes small, the hydrogen storage performance deteriorates, and the plateau pressure rises. Industrially, it is unavoidable that impurity oxygen is mixed from raw materials and manufacturing processes, but the residual oxygen content in the final alloy is 300
0 ppm or less, preferably 2000 ppm or less, more preferably 1000 ppm or less.

Example 5 Samples made of alloys having various compositions shown in Table 1 were prepared in the same manner as in Example 1, and then, similarly to Example 1, the pressure-composition isotherm (PCT line) was obtained.
Was measured to determine the maximum hydrogen storage amount. In addition, the oxygen content of each sample was measured, and the phase was identified by X-ray diffraction. The above measurement results are also shown in Table 1.

[0041]

[Table 1]

[0042]

As described above, the oxygen content is 30%.
The hydrogen storage alloy of the present invention regulated to 00 ppm or less,
Excellent hydrogen storage characteristics. In particular, the alloy of the present invention containing the element X is an excellent alloy that can facilitate BCC single-phase formation.

[Brief description of drawings]

FIG. 1 is a flowchart showing a method for producing a hydrogen storage alloy of the present invention.

FIG. 2 is a phase diagram of a Ti—Cr binary alloy.

FIG. 3 is an X-ray diffraction diagram of Ti ₄₀ Cr ₅₈ Mo ₂ (alloy A).

FIG. 4 is an X-ray diffraction diagram of Ti ₄₀ Cr ₅₄ Mo ₆ (alloy B).

FIG. 5 is a pressure-composition isotherm (PCT line) of Ti ₄₀ Cr ₅₈ Mo ₂ (alloy A) according to a vacuum origin method at 40 ° C.

FIG. 6 Ti ₄₀ Cr ₅₈ Mo ₂ (alloy A) and Ti ₄₀
3 is a graph showing the relationship between the oxygen content of Cr ₅₄ Mo ₆ (alloy B) and the maximum hydrogen storage amount.

FIG. 7 is an X-ray diffraction diagram of Ti ₄₁ Cr ₅₇ Ru ₂ (alloy C).

FIG. 8 is a pressure-composition isotherm (PCT line) of Ti ₄₁ Cr ₅₇ Ru ₂ (alloy C) at 40 ° C. measured by a vacuum origin method.

FIG. 9 is a graph showing the relationship between the oxygen content and the maximum hydrogen storage amount of Ti ₄₁ Cr ₅₇ Ru ₂ (alloy C).

FIG. 10: _{40 of} Ti ₄₀ Cr ₅₆ Mo ₃ La ₁ (alloy D)
Pressure-composition isotherm (PCT
Line).

FIG. 11 Ti ₄₀ Cr _58.5-X Ru _0.5 Mo ₁ La _X (X
= 0 (alloy E), 1 (alloy F)) at 40 ° C. according to the vacuum origin method, pressure-composition isotherm (PCT line).

FIG. 12 Ti₅₅Cr₄₅, Ti₅₅Cr₄₀Ru_Five, Ti
₅₅Cr₄₀Rh_Five, Ti ₅₅Cr₄₀Os_FiveAfter arc melting (as
 It is an X-ray diffraction diagram in a cast state).

FIG. 13 Ti ₅₅ Cr ₄₀ Ir ₅ , Ti ₅₅ Cr ₄₀ Pd ₅ ,
It is an X-ray diffraction diagram after arc melting of Ti ₅₅ Cr ₄₀ Pt ₅ and Ti ₅₅ Cr ₄₀ Re ₅ (as cast state).

FIG. 14 Ti ₄₀ Cr ₅₇ Mo ₃ , Ti ₄₄ Cr ₅₃ Ru ₃ ,
It is an X-ray diffraction diagram after arc melting of Ti ₄₀ Cr ₅₆ Mo ₃ Ru ₁ (as cast state).

FIG. 15: Ti ₄₀ Cr ₅₇ Mo ₃ , Ti ₄₄ Cr ₅₃ Ru ₃ ,
It is a pressure-composition isotherm (PCT line) by the vacuum origin method at 40 ° C. after arc melting of Ti ₄₀ Cr ₅₆ Ru ₁ Mo ₃ (as cast state).

FIG. 16: Ti ₄₅ Cr ₅₃ M ₂ (where M = Cr, R
(u, Rh, Os) is a pressure-composition isotherm (PCT line) by a vacuum origin method at 40 ° C. after heat treatment (holding at 1400 ° C. for 10 minutes, rapid cooling in ice water).

FIG. 17: Ti ₄₅ Cr ₅₃ M ₂ (where M = Ir, P
(d, Pt, Re) is a pressure-composition isotherm (PCT line) by a vacuum origin method at 40 ° C. after heat treatment (holding at 1400 ° C. for 10 minutes, rapid cooling in ice water).

FIG. 18: Ti ₄₅ Cr ₅₃ M ₂ (where M = Cr, M
o) Pressure-composition isotherm (PCT line) by the vacuum origin method at 40 ° C. after heat treatment (holding at 1400 ° C. for 10 minutes, rapid cooling in ice water) on the alloy.

Continued front page    (72) Inventor Tatsuji Sano             1-13-1, Nihonbashi, Chuo-ku, Tokyo             -In DC Inc. (72) Inventor chief duty             1-13-1, Nihonbashi, Chuo-ku, Tokyo             -In DC Inc. (72) Inventor Masuo Okada             Miyagi Prefecture Sendai City Taihaku Ward Yagiyama Minami 3-9 6 F-term (reference) 4G040 AA36 AA44 AA45

Claims (3)

[Claims] 1. A hydrogen storage alloy having a main phase of a body-centered cubic structure (BCC phase) capable of storing and releasing hydrogen, the composition of which is represented by the general formula Ti _(100-abcde) Cr _a X. _{b X'c} T
_d L _e However, 20 ≦ a (at%) ≦ 80, 0 <b (at%) ≦ 10,0
<C (at%) ≦ 30, 0 <d (at%) ≦ 30, 0 <e (at%) ≦
Represented by 10, including at least one group of the X, X ', T and L, the X is at least one element of Ru, Rh, Os, Ir, Pd, Pt, Re, X'is Mo, W , At least one element of Al, the T is Mn, Fe, Co, Ni, Cu, Nb, Ta,
At least one element of B and C, said L is at least one element of Y and a lanthanoid element, and the content of oxygen is 3000 ppm or less. 2. The hydrogen storage alloy according to claim 1, wherein the oxygen content is 2000 ppm or less. 3. The hydrogen storage alloy according to claim 1, wherein the oxygen content is 1000 ppm or less.