JPS5922783B2 - Alloy for hydrogen storage - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an industrial hydrogen storage alloy that can store and release hydrogen at relatively low temperatures and can repeatedly perform this storage and release.

Conventionally, hydrogen storage alloys include alloys of good and poor hydrogen absorbers, such as J, aNi5, Mg2Ni.
, TiFe, etc. are known.

These alloys not only absorb hydrogen, but these hydrides have the advantage of releasing hydrogen at lower temperatures than hydrides of simple metals such as La, Mg, and Ti.

Further, the dissociation pressure of hydrogen in the hydrides of these alloys is constant at a certain temperature when the hydrogen content in the alloy is within a certain range, and a so-called plateau exists.

Regarding the TiFe alloy, there is a first stage plateau in the region where the α phase, in which a small amount of hydrogen is solidly dissolved in TiFe, and the β phase, which is a hydride phase called TiFeH, coexist, and the β phase and TiFe
There is a second plateau in the region where the r-phase of hydride H2 coexists, and the second plateau is at a higher pressure than the first plateau.

And the highest hydrogen content of TiFe corresponds to TiFeH2, which is 1.89 wt%, 216 m1/g alloy.

This TiFe alloy hydride has a high equilibrium dissociation pressure;
It is said to be a promising alloy for practical use due to its high hydrogen content and low price, and is being studied in various ways.

However, since the TiFe alloy phase is generated by a peritectic reaction, it is difficult to produce an intermetallic compound of this phase as a pure phase, and phases such as TiFe2 and βTi are often mixed.

In addition, TiFe may lose its r phase due to repeated use, and Fe
Problems have been pointed out, such as the separation of oxygen, the influence of trace amounts of oxygen, and the difficulty of activation, and there are many problems that need to be resolved for practical use.

According to the present invention, it is made of zirconium, titanium, and iron, and the total number of atomic moles of zirconium and titanium is equal to the number of atomic moles of iron, and zirconium contains the same number of atomic moles as titanium or more. A hydrogen storage alloy is provided.

This alloy is manufactured in an atmosphere of an inert gas such as argon by a conventional alloy manufacturing method, such as a method using a high frequency furnace or an arc melt method.

The composition of the hydrogen storage alloy according to the present invention is expressed by the following formula.

TilZrmFe.

In the formula, 1. m and n represent real numbers, the sum of l and m is substantially equal to n (1+m=n), and m is substantially equal to 1 or more than l (m≧l).

When m is smaller than 1, problems such as a decrease in the amount of saturated hydrogen per metal atom occur, and when l+m becomes smaller or larger than n, a metal phase that does not absorb hydrogen appears. Problems arise, such as the appearance of a phase that absorbs hydrogen but does not release it at an appropriate temperature.

In the present invention, the relationship between l and m is preferably l≦m
/1≦9.

Alloys within this range can store 230 ml or more of hydrogen per gram and have high stability in repeated use.

When m/1 exceeds 9 and there is an excess of Zr, the hydrogen storage performance of the sample starts to show variations depending on the alloy production lot, and m becomes significantly larger than 1 and substantially equal to n, and the composition of ZrFe When the amount of absorbed hydrogen is reached, the amount of absorbed hydrogen sharply decreases to one-third or less of the amount of absorbed hydrogen.

The most preferable composition for a hydrogen storage alloy is substantially an atomic ratio of Ti:Zr:Fe=1:1:2.

Alloys with such compositions contain hydrogen (
For example, it has the advantage that it does not generate foreign phases even if it is repeatedly used in hydrogen that has remained in a hydrogen line for several days.

Although the crystal structure of this alloy has not yet been clearly elucidated, it shows an X-ray diffraction pattern different from alloy phases such as TiFe, TiFe2, and ZrFe2 and metallic phases such as Ti, Zr, and Fe, and is similar to a single-phase intermetallic compound. Conceivable.

In terms of composition, it is thought that 1/2 atoms of Ti in TiFe are replaced with Zr, but the X-ray diffraction pattern is different from that of TiFe.

This alloy exhibits excellent hydrogen storage and desorption properties at room temperature.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Sponge Ti with a purity of 99.8%, sponge Zr with a purity of 99.6%, and electrolytic Fe with a purity of 99.9% were mixed in an atomic molar ratio of 1:1:2, and arc melting was repeated 6 times to obtain a uniform TiZr.
An alloy having a composition of Fe2 was produced.

This alloy is easy to crush.

This alloy, roughly crushed into soybean-sized pieces, is placed in a pressure-resistant container, evacuated at room temperature, and then hydrogen is introduced at a rate of 5 to 40 kg/crrt at room temperature, which absorbs hydrogen immediately and rapidly.
The alloy was finely ground.

That is, in the case of the alloy of the present invention, hydrogen can be occluded without requiring troublesome operations such as activation by repeating high-temperature exhaust and hydrogen introduction, as is the case with TiFe.

The hydride of this alloy produced by absorbing hydrogen releases hydrogen even at room temperature.

The hydrogen storage capacity is 5.2 or more in atomic molar ratio of H/alloy.

When this value is converted into the standard amount of hydrogen bound per alloy 11, it becomes 232 ml or more.

The figure shows the hydrogen dissociation pressure isotherm of the hydride of this alloy measured after hydrogen absorption and desorption was repeated several times.

In this figure, the vertical axis indicates hydrogen dissociation pressure (atm),
The horizontal axis is the composition of TiZrFe2 hydride (H/TiZr
Fe2).

Curve 1 is 77℃, curve 2 is 137℃, curve 3 is 270℃
, and curve 4 show the relationship between hydrogen dissociation pressure and composition at 340°C.

As can be seen from the figure, the hydrogen dissociation pressure of the hydride in this alloy changes greatly with small changes in the amount of hydrogen in the alloy, and there is no so-called plateau.

Since the alloy of the present invention does not show a plateau in its hydrogen dissociation pressure isotherm, for example, if a container containing the hydride of the alloy of the present invention is placed under reduced pressure and hydrogen is constantly released at 1 atm. Then, by increasing the temperature of the container, 1 atm of hydrogen can be constantly released.

As can be seen from the figure, when the temperature is increased from 77°C to 340°C, the H/TiZrFe2 ratio changes from 4.6 to 1.
Up to 2 hydrogen can be used, and this value is 152
m1/? Corresponds to an alloy.

In the case of a hydride with a plateau, there is no change in pressure even if hydrogen is released, so it is difficult to accurately know the amount of residual hydrogen, but in the case of the hydride of the alloy of the present invention, there is no plateau. Therefore, if you know the temperature and pressure, you can know the amount of remaining hydrogen.

According to X-ray diffraction, expansion of the crystal lattice is observed due to hydrogen absorption in the alloy according to the present invention, but the diffraction lines of the alloy phase do not disappear or new diffraction lines appear due to hydrogen absorption.

Furthermore, no Ti-H system or Zr-H system diffraction lines are observed.

The X-ray diffraction pattern of the alloy after complete hydrogen release is the same as that of the original alloy.

In other words, it was confirmed that this alloy could withstand repeated use without causing structural changes even after repeated hydrogen absorption and release.

Example 2 Using the metal raw material described in Example 1, the following atomic molar ratio (a) Zr (0,5) Ti (0,5) Fe (1
)(b) Zr (0,6) Ti (0,4) F
e (1) (c) Zr (0,7) Ti (0,3
) Fe(1)(d) Zr(0,8) Ti(
0,2)Fe(1)(e)Zr(0,9)Ti
A metal particle mixture of (0,1)Fe(1) was produced and arc melted six times each in an argon stream to produce an alloy ingot.

These alloys crushed into soybean-sized pieces were placed in a pressure-resistant container and evacuated at room temperature. When 5 to 40 kg/crA of hydrogen was introduced at room temperature, hydrogen absorption occurred immediately.

These alloy hydrides were decomposed by evacuation while heating the pressure container to 300° C., and after cooling to room temperature, hydrogen was introduced again at 40 kg/crA.

Table 1 shows the amount of hydrogen occluded in each alloy sample after repeating this operation five times.

It can be seen that the amount of absorbed hydrogen per unit weight of the alloys within the scope of the present invention does not vary greatly depending on the alloy composition, and only increases slightly as the amount of ZrO increases.

None of the metallurgies (a) to (e) has a plateau in the hydrogen dissociation pressure isotherm.

The equilibrium pressure showed a tendency to decrease with increasing amount of Zr.

According to X-ray diffraction, both (a) to (e metallurgy) showed expansion of the crystal lattice due to hydrogen absorption.

The diffraction lines of the original alloy phase do not disappear and new diffraction lines do not appear.

Furthermore, no Ti-H system or Zr-H system diffraction lines are observed.

Moreover, the X-ray diffraction pattern of the alloy after complete hydrogen release was the same as that of the original alloy.

However, if you proceed with the procedure of this example using hydrogen that has been stagnant in the hydrogen line for several days without using cylinder hydrogen immediately, 1. Diffraction lines of unknown origin appeared after several hydrogen occlusions and desorptions, and this tendency was more pronounced in alloys with a high Zr content.

For comparison, when an alloy with the composition ZrFe was manufactured using the same procedure and hydrogenated in the same manner, the hydrogen storage capacity was 76 m1/f.
Furthermore, hydrogen was not reversibly released upon heating up to 350°C.

[Brief explanation of the drawing]

The drawing shows the dissociation isotherm of TiZrFe2 hydride.

Claims (1)

[Claims] 1 formula % formula % (where l, m and n represent real numbers, the sum of 1 and m is substantially equal to n, and m is substantially equal to 1 or l
A hydrogen storage alloy consisting of an alloy having a composition represented by: 2. The hydrogen storage alloy according to claim 1, comprising an alloy having a composition represented by 2TiZrFe2.