JPS5911652B2 - Alloy for hydrogen storage - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to hydrogen storage alloys, and more particularly to hydrogen storage alloys.
The present invention relates to a hydrogen storage alloy that can easily store and release hydrogen at temperatures of 50° C. or higher, and whose storage and release characteristics do not change over a long period of time and can be used on an industrial scale.

Conventionally, hydrogen storage alloys include Mg, rare earth metals, and Ti.
Those based on the above are known.

For example, Mg2Ni, LaNi5. TiFe, etc., and these are made of metals (Mg, La, Ti, etc.) that occlude or release hydrogen even in a single metal, and metals (Ni, Fe, etc.) that have a catalytic ability to activate hydrogen.

In recent years, research has been progressing with the goal of industrializing and putting metal hydrides into practical use.

As a result, M absorbs and releases hydrogen at relatively high temperatures.
For alloys based on g, the working temperature (approximately 250-400
°C) is the melting temperature of the alloy itself (for example, Mg-23,
It was found that the reaction rate between the alloy and hydrogen decreases when used as a hydrogen storage material for a long period of time (approximately 503°C) for a 3 wt% Ni alloy.

Although this phenomenon is not completely understood, it is thought that the working temperature is close to the melting temperature, which causes the alloy particles to sinter, reducing the contact area with hydrogen, and also as active sites for the reaction. This is thought to be due to the effect that the structurally disordered parts of the alloy surface gradually return to a regular surface, or the synergistic effect of both.

The present invention was made in view of the above-mentioned circumstances, and
The object of the present invention is to provide a hydrogen storage alloy that uses Mg as a basic metal and can maintain reaction activity with hydrogen for a long time even at working temperatures in a relatively high temperature range.

Therefore, the hydrogen storage alloy of the present invention has the general formula Mg-A
-Th, where A represents a Group II transition metal, the amount of A is 1 to 55% by weight based on the total, and the amount of Th is 1 to 40% by weight based on the total. It is characterized by a range.

Hereinafter, the configuration of the present invention will be explained in detail.

Among the metals constituting the alloy of the present invention, the A component is Fe
It is a transition metal of group Ⅰ of the long period periodic table, such as y Co t N I.

This component A is added as a catalyst that acts to speed up the reaction in the reaction process of decomposing hydrogen gas molecules (H2) and adsorbing them to the alloy surface as H atoms (H).

The amount is 1 to 55% by weight based on the total amount of the alloy.
It is preferably in the range of 3 to 30% by weight.

When the amount of component A is less than 1%, the effect as a catalyst is poor.

On the other hand, if the amount exceeds 55% by weight, the A component metal will be isolated or exist as a phase unrelated to the reaction.
It is necessary that the content be 55% by weight.

Further, Th (Th) is a metal that forms a stable hydride at the temperature at which Mg absorbs and releases hydrogen.

This Th forms an intermetallic compound with Mg.

Therefore, since Th is not mechanically dispersed in the alloy but exists in the form of an intermetallic compound, its dispersion is extremely good.

The amount of Th is in the range of 1 to 40% by weight, preferably in the range of 5 to 40% by weight, based on the total amount of the alloy.

If the amount of Th is less than 1%, the effect will not be exhibited due to the small amount; on the other hand, if it exceeds 40% by weight, only the intermetallic compound consisting of Mg and Th will occupy the entire alloy. Therefore, it must be between 1 and 40% by weight.

The alloy of the present invention melts Mg metal in a crucible,
It can be produced very easily by adding calculated amounts of both A and Th acid component metals, completely melting them, and then pouring them into a mold.

The metals used in this case may be of industrial grade containing about 1% of impurities, but in consideration of increasing the amount of absorbed hydrogen in the resulting alloy, it is preferable that the metals have a purity of 99% or more.

The alloy obtained in this way is roughly crushed to an appropriate size, placed in a container, and after being evacuated at working temperature, it is 0.1 to 4 M
By repeating the introduction of hydrogen at a pressure of about Pa several times into the container, hydrogen can be reversibly and quickly absorbed and absorbed.
It starts to emit.

Note that if the introduction of hydrogen is repeated several times as described above, Th
The alloy phase of Mg and Mg reacts with hydrogen to form Mg hydride and T.
Since the phase is separated into Th hydride and Th hydride, a very fine stable phase of Th hydride is dispersed and prevents the growth of Mg particles.

Even if hydrogen pressure application and evacuation are repeated, the Th hydride does not decompose and remains in the alloy as a fine metal hydride.

Therefore, even at operating temperatures close to the melting temperature of the alloy, the Mg fine particles do not sinter, so that the reaction activity is maintained for a long period of time.

As described above, the hydrogen storage alloy of the present invention is inexpensive because it can be easily manufactured by a known alloy manufacturing method, and can absorb and absorb hydrogen reversibly and over a long period of time in a relatively high temperature range. It is possible to repeat the release.

Therefore, the hydrogen storage alloy of the present invention can be preferably used as a hydrogen transport material, a heat storage material using a hydrogenation reaction, and the like.

Hereinafter, the present invention will be explained in detail based on examples.

Example By a crucible melting method, 5% by weight of Ni and 5% of Th were added to Mg.
An alloy containing % by weight was prepared.

After the alloy was crushed, it was placed in a pressure container, and evacuation at 330° C. and introduction of hydrogen at 0.1 to 40 MPa were repeated several times.

As a result, the alloy quickly absorbed and released hydrogen, and was pulverized.

Next, we calculated the reaction rate with hydrogen at 330°C for a conventionally known alloy consisting of Mg and 23.3 wt% Ni obtained by thermogravimetric analysis in a hydrogen atmosphere and the above alloy of the present invention. It was measured using a thermobalance in an atmosphere.

The results are shown in the table below.

As is clear from the above table, there is no difference between the two immediately after repeated application of exhaust gas and hydrogen pressure for activation, but on the other hand, when left at working temperature for 138 hours, the alloy of the present invention It can be seen that although no deterioration in activity is observed in the alloys, clear deterioration is observed in the conventionally known alloys.

Therefore, the alloy of the present invention does not suffer from deterioration of reaction activity over time, which was a drawback of conventional hydrogen storage alloys using Mg as the basic metal, and therefore can be used repeatedly over a long period of time. is possible.

Claims (1)

[Claims] 1. A hydrogen storage alloy represented by the general formula Mg-A-Th. However, in the formula, A represents a Group Ⅰ transition metal, the amount of A is 1 to 55% by weight based on the total, and the amount of Th is in the range of 1 to 40% by weight based on the total.