JPH11209842A - Hydrogen storage alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a hydrogen storage alloy where the necessity of initil activation is obviated or relieved and which has excellent hydrogen absorbing and releasing properties. SOLUTION: Respective contents of Nb, Ti, and Fe are regulated so that they are within the region enclosed with straight lines AB, BC, CD, and DA connecting points A(96, 0, 4), B(30, 60, 10), C(20, 40, 40), and D(60, 0, 40) on the triangular coordinate in the figure. By this method, the hydrogen storage alloy, where initial activation is unnecessary or a treatment under remarkably relaxed conditions is applied and, further, hydrogen occlusion at ordinary temp. at one atmospheric pressure and has excellent hydrogen absorbing and releasing properties can be manufactured at a low cost and used.

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 used as a hydrogen storage material or a catalyst material.

[0002]

2. Description of the Related Art In 1964, the discovery of a magnesium-nickel alloy (Mg ₂ Ni) at Brookhaven National Laboratory in the United States was started in 1964, and in 1974 TiF was used.
e, L at Philips Research Institute in the Netherlands in 1968
aNi and ₅ is found, by further subsequent study, the rare earth-nickel alloy, a magnesium - nickel alloy, a zirconium - hydrogen storage alloy, such as manganese-based alloys have come to be developed.

[0003] Generally, properties required for a hydrogen storage alloy include easy initial activation, a large amount of hydrogen storage and release, a high absorption and release rate, and excellent durability. However, conventional alloys all have advantages and disadvantages. However, there is agreement that any alloy requires initial activation. This is because a hydrogen storage alloy has an oxide film or moisture attached to its surface and cannot absorb hydrogen as it is, so that an activation treatment as a pretreatment is required. In this activation treatment, usually, the hydrogen storage alloy is heated to a high temperature under reduced pressure to degas the hydrogen storage alloy, and then the hydrogen storage alloy is held in a high-pressure hydrogen gas atmosphere at a low temperature, and hydrogen is added to the alloy. Is performed by repeating a series of steps of causing occlusion. The number of repetitions will be repeated until hydrogen is absorbed.

[0004] The difficulty of the activation varies depending on the type of the alloy. For example, TiFe is known as an alloy that is difficult to activate. In the activation, a TiFe alloy is pulverized in advance into a powder form, which is degassed under vacuum at 400 to 450 ° C., and then cooled to about 65 atm at room temperature. Hydrogen is absorbed only by repeating the process of pressurizing hydrogen. On the other hand, among the conventional hydrogen storage alloys, the alloy which is most easily activated is a rare earth-nickel alloy (LaNi ₅ , MmNi ₅ ).
The nickel-based alloy lump hardly absorbs hydrogen at room temperature and 1 atm, but the activation process is more relaxed than TiFe (for example, high temperature (500 ° C.) and high pressure (1
Hydrogen absorption becomes possible by repeating (zero pressure) the operation (processing twice).

[0005]

As described above, in order for the alloy to absorb hydrogen, initial activation is indispensable, and high-temperature, high-pressure processing is repeated even for an alloy that is relatively easily activated. There is a need to do. For this reason, it is a big problem that the burden of the activation treatment is large in the hydrogen storage alloy, and even recently, the treatment temperature, pressure,
Research has been conducted to further reduce the number of repetitions, but sufficient results have not been obtained, and activation treatment raises the production cost (pretreatment cost) of hydrogen storage alloys. .

The present invention has been made in view of the above circumstances, and it is possible to occlude hydrogen without specially performing an initial activation or by a very simple activation treatment. It is an object of the present invention to provide a hydrogen storage alloy having good characteristics.

[0007]

Means for Solving the Problems To solve the above problems, the hydrogen storage alloy according to the present invention comprises Nb, Fe or Nb, T
In the triangular coordinates of (Nb wt%, Ti wt%, Fe wt%) with i and Fe as constituents, the content of each component is represented by points A (96, 0, 4) and B (30, 60, 1
0), C (20, 40, 40), D (60, 0, 40)
Are located in a region surrounded by straight lines AB, BC, CD, and DA connecting.

[0008] The present invention relates to Nb, Fe or Nb, Ti,
It can be said that it is an Nb-Ti-Fe alloy containing Fe as a constituent. However, Nb-Fe not containing Ti as a constituent component
System alloys are also included. By adjusting the contents of these components so as to be included in the quadrangular region having the vertices of the points A, B, C, and D, the initial activation becomes unnecessary or the condition is greatly eased. be able to. Note that this area includes each point and components on a straight line connecting each point. Further, the hydrogen storage alloy in the above region can absorb hydrogen at a high speed at room temperature and 1 atm, and can absorb and release hydrogen at a higher temperature and a lower equilibrium pressure. Excellent characteristics. on the other hand,
If the ratio is out of this range, the effect of reducing the activation cannot be sufficiently obtained, and the intended purpose cannot be achieved.

In order to obtain a more reliable effect within the above range, the weight ratio of Ti and Fe (Ti / Fe) is desirably set to 1, and the Nb concentration is set to 40% by weight or more. Is more desirable.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The hydrogen storage alloy of the present invention can be produced by a conventional method, and the production method is not particularly limited in the present invention. For example, an alloy lump prepared at a predetermined component ratio is melted by arc melting or the like to obtain a hydrogen storage alloy.

The hydrogen storage alloy obtained by the above method or the like is used in the form of a powder or in the form of a lump, but the form of use is not particularly limited. Further, the hydrogen storage alloy of the present invention has excellent hydrogen absorption / desorption characteristics, although it greatly reduces the load of the activation treatment, and can be used for various applications. For example, it can be used as a material for transporting and storing hydrogen, and can be used as a material for energy conversion, a catalyst material involving a hydrogen reaction, and the like.

[0012]

The present invention will be described below in detail with reference to examples. After weighing the Nb-Fe binary alloy or the Nb-Ti-Fe ternary alloy of the present invention as a working sample to the composition ratio (weight percent) shown in Table 1 below, arc melting was performed in an argon atmosphere containing several percent of hydrogen. Redissolved by the method. After the inside of the apparatus was evacuated (about 10 Pa) using a rotary pump, the surface-clean alloy lump produced in this manner was introduced into the apparatus with 100% hydrogen gas to a pressure of 1 atm. As a standard comparative sample (conventional material), a LaNi ₅ alloy was used, and a comparative material having Nb, Ti, and Fe contents outside the range of the present invention was prepared. A treatment and a hydrogen storage test were performed.

As a result of the above hydrogen storage test, any of the hydrogen storage alloys of the present invention rapidly absorbs hydrogen gas after introducing hydrogen gas into the apparatus as described above, and at the same time, the alloy lumps turn into fine powder, It became an alloy fine powder that absorbed a lot of hydrogen. On the other hand, in the case of the LaNi ₅ hydrogen storage alloy, the hydrogen storage amount measurement result at the room temperature and the hydrogen pressure of 1 atm is 0.1% by weight or less as shown in Table 1. That is, LaNi
_{Since the} alloy No. ₅ had not been activated, hydrogen absorption hardly occurred. Also, in the comparative materials outside the scope of the present invention, the hydrogen storage amount at room temperature and 1 atm of hydrogen pressure is zero as shown in Table 1. From the above points, Nb, Ti, Fe
It is evident that hydrogen is rapidly absorbed as produced without activation treatment only when the content of is within an appropriate range. In addition, it is possible to perform a significantly relaxed activation treatment on these materials, and in such a case, it is expected that hydrogen is sufficiently absorbed.

In the hydrogen storage alloy of the present invention, the hydrogen storage amount was measured by a Sievert type gas absorption / desorption measuring device. As shown in Table 1, the results fluctuate within the range of 0.3 to 1.6% by weight depending on the alloy composition and the hydrogen pressure in the atmosphere, but the Ti / Fe ratio is set to 1 and the Nb concentration is set to 40% by weight.
It is also apparent that the amount of hydrogen storage is significantly increased by the above. In addition, the standard comparison sample (conventional material) L
aNi ₅ alloy and the above alloy sample no. 2 (NTF62
2), No. FIG. 2 (PCT diagram) shows the measurement results of the relationship between the hydrogen concentration in the alloy and the equilibrium hydrogen pressure for hydrogen absorption and desorption at room temperature (303 K) of No. 8 (NTF 811). From the figure,
The hydrogen concentration in the alloy at an equilibrium hydrogen pressure of 100 KPa (about 1 atm) was about 0.1% by weight or less for the standard comparative sample (conventional material) LaNi ₅ alloy, and the alloy sample No. 2 (NTF62
In the case of alloy sample No. 2), about 1% by weight at the time of absorption, about 1.17% by weight at the time of release, and 8 (NTF811) is about 1% by weight at the time of absorption and about 1.6% by weight at the time of release.
It is clear that the alloy of the present invention absorbs a larger amount of hydrogen than the standard comparative sample (conventional material) LaNi ₅ alloy. The hydrogen storage capacity of the alloy of the present invention at room temperature varies depending on the alloy composition. 8 (NTF811) is 1.6% by weight at an equilibrium hydrogen pressure of 400 KPa (about 4 atm),
This is a very large value. Then, high temperature (500K-10
00K). FIG. 3 (PCT diagram) shows the measurement results of the relationship between the hydrogen concentration in the alloy for absorbing and releasing hydrogen of No. 8 (NTF811) and the equilibrium hydrogen pressure. From the figure, it can be seen that there is a history difference between the hydrogen concentration of the alloy sample at the time of hydrogen absorption and the history of hydrogen release, and the equilibrium hydrogen pressure giving the same hydrogen concentration is lower at the time of absorption, but becomes smaller as the temperature rises. Also, 57
Even at a high temperature of 3K, it absorbs a large amount of hydrogen,
It is 0.9% by weight in Pa, and it is clear that hydrogen is easily absorbed even at high temperatures.

Further, the hydrogen storage alloy of the present invention has the advantage that it reliably stores a large amount of hydrogen at normal temperature to high temperature and 1 atm and has a high storage rate. The alloy sample no. 2 (NTF622) and the standard comparative sample were subjected to the following hydrogen absorption test separately from the above. That is, 10.17 g of each alloy was put into a reaction vessel (capacity: 15900 ml) of a Geebelt type pressure measuring device, and an initial hydrogen pressure of 92 KPa was used to investigate the situation where hydrogen was absorbed into the alloy over time and the hydrogen pressure decreased. Figure 4
It was shown to. As is clear from the figure, the hydrogen storage rate is slow until immediately after the introduction of hydrogen (0 to 120 seconds), but the hydrogen storage rate increases rapidly after about 300 seconds and the maximum is about 5 ml / s.
G, indicating that it has a large occlusion rate. In the case of LaNi ₅ as a standard comparative sample, no change in hydrogen pressure was observed even after a long time.

[0016]

[Table 1]

[0017]

As described above, according to the hydrogen storage alloy of the present invention, Nb, Fe or Nb, Fe, Ti is used as a component and is composed of (Nb wt%, Ti wt%, Fe wt%). On the triangular coordinates, the content of each component is represented by points A (96, 0, 4), B (30, 60, 10), C (2
0, 40, 40) and D (60, 0, 40) are in the region surrounded by straight lines AB, BC, CD, and DA.
In addition to enabling the treatment under conditions where the activation treatment is unnecessary or more relaxed, it can absorb and release hydrogen gas at room temperature to high temperature and 1 atm. The effect is obtained at a cost.

If the Fe content of the above alloy is 3% by weight or more and the weight ratio of Ti and Fe (Ti / Fe) is 0.3 or more and 1.2 or less, the above-mentioned effect is further ensured. .
In the above alloy, the weight ratio of Ti and Fe (Ti /
When Fe) is set to 1 and the Nb concentration is set to 40% by weight or more, in addition to the above effects, there is an effect that the amount of absorbed and released hydrogen can be further increased.

[Brief description of the drawings]

FIG. 1 is a diagram showing (Nb, Ti, Fe) triangular coordinates plotting points A, B, C, and D of the present invention and Nb—Ti—Fe-based test alloys in Examples based on their contents.

FIG. 2 is a graph showing a relationship between an equilibrium hydrogen pressure and a hydrogen storage amount at the time of hydrogen absorption / release at various temperatures of a test alloy.

FIG. 3 is a graph showing the relationship between the equilibrium hydrogen pressure and the amount of hydrogen occlusion at the time of hydrogen absorption / release at room temperature of a test alloy.

FIG. 4 is a graph showing the relationship between the hydrogen storage amount (change in hydrogen pressure) of a test alloy and elapsed time.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuhiro Kawasaki 5983 Tamura, Hiratsuka-shi, Kanagawa Prefecture High-frequency refining Co., Ltd.

Claims (1)

[Claims] 1. On a triangular coordinate system composed of (Nb wt%, Ti wt%, Fe wt%) containing Nb, Fe or Nb, Ti, Fe as constituents, the content of each component is represented by a point A (96%). , 0, 4), B (30, 60, 10), C (2
0, 40, 40) and D (60, 0, 40), in a region surrounded by straight lines AB, BC, CD, and DA.