JPS6296632A - Metallic alloy for hydrogen storage - Google Patents

Abstract

PURPOSE:To obtain an inexpensive metallic alloy for hydrogen storage occluding a large amount of hydrogen and easily releasing hydrogen in a wide temp. range by preparing an alloy by blending specific percentage of Zr, Fe and Cr. CONSTITUTION:The metallic alloy for hydrogen storage is prepared by providing a composition represented by a general expression, Zr(Fe1-xCrx)2, blending Zr, Fe and Cr so that 0.15<=x<=0.8 is satisfied, and carrying out melting in an inert gas atmosphere, such as Ar, etc., by an arc melting method and the like. In this way, a practical metallic alloy for hydrogen storage, having high rate of reaction with hydrogen by slight changes in pressure at a hydrogen equilibrium pressure (dissociation pressure) of about 10atm or below, occluding a large amount of hydrogen at a hydrogen equilibrium pressure of about 10atm or below, and causing no heat deterioration to a vessel in which the alloy is to be held because above-mentioned characteristics are obtained at low temp., can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a hydrogen storage alloy, and particularly to a Zr, Fc, and Cr-based hydrogen storage alloy that stores hydrogen as a metal hydride compound.

(Prior art) Hydrogen reacts explosively with oxygen, producing only water, and is attracting attention as a clean energy source that does not cause pollution.

When hydrogen is used as an energy source, it has conventionally been stored in a gaseous or liquid state, but recently hydrogen storage alloys that store it in a solid state have been provided.

This type of hydrogen-absorbing alloy stores hydrogen as a metal hydride compound, and by controlling the temperature or pressure, hydrogen storage and release, as well as exothermic and endothermic reactions, can proceed reversibly. .

By the way, the characteristics required for a practical hydrogen storage alloy are:
It is desirable that the material be inexpensive, easy to activate, have a large hydrogen storage capacity per unit weight, react quickly with hydrogen, and keep the pressure and temperature as low as possible during the reaction.

For example, as an energy source installed in an automobile, it is desirable that the energy source can be used at a temperature of 170° C. or less at 10 atmospheres or less.

Currently available hydrogen storage alloys include rare earth alloys, MO alloys, and Ti alloys.

(Problems to be Solved by the Invention) The hydrogen storage alloys produced in each prefecture described above have the following problems, making it difficult to put them into practical use.

That is, rare earth alloys such as 1aNi5 are expensive, and Ma alloys such as Mo2N1 have the disadvantage of slow reaction speed at low temperatures.

Furthermore, Ti-based alloys such as TiFe are difficult to activate and require heating to a temperature of several hundred degrees or more to absorb hydrogen.

This invention was made in view of this background, and its purpose is to have a large amount of hydrogen storage as a metal hydride compound, and to change the number of atoms in the alloy composition so that it can be used from low to high temperatures. An object of the present invention is to provide an inexpensive hydrogen storage alloy that easily releases hydrogen over a wide temperature range and reacts quickly with hydrogen.

(Means and effects for solving the problems) In order to achieve the above object, the present invention provides a hydrogen storage alloy having a composition represented by the general formula Zr(Fe Crx)2-x, × is 0.15
It is characterized by consisting of a number within the range of ≦x≦0.8.

The hydrogen-absorbing alloy having the above structure is produced by mixing single-phase raw material metals of Zr, Fe, and -Cr in a predetermined blending ratio by a normal alloy manufacturing method, such as an arc melting method, in an atmosphere of an inert gas such as argon. It can be easily manufactured by melting it as

Therefore, the hydrogen storage alloy of the present invention is made of relatively inexpensive Zr.
, Fe, and Cr, so it is not expensive like rare earth alloys.

The hydrogen storage alloy of the present invention obtained by the above manufacturing method has a single phase over the entire composition range, and the crystal structure does not change due to hydrogen storage.

In addition, many alloys generally require annealing treatment to make the alloy structure uniform after melting, but the hydrogen storage alloy of this invention can be made into a single-phase alloy by simply melting as described above. is obtained, no annealing treatment is required,
Therefore, there is an advantage that manufacturing time can be significantly shortened.

To activate the obtained hydrogen storage alloy, place the sample cell in a sealed container, use a vacuum pump to degas the container for about 30 minutes, and then introduce hydrogen at about 30 atm at room temperature into the container. The alloy is then left to stand for about 30 minutes to absorb hydrogen into the alloy and perform the initial introduction of hydrogen.

Thereafter, the procedure of performing vacuum degassing again and then introducing hydrogen is repeated several times, but activation can be performed in a shorter time than, for example, with ZrMn2.

By the way, the hydrogen storage alloy represented by the formula zr (F el-x Crx ) 2 satisfies 0.15≦x≦0.8
Within the range of C14 type tlexagonal La
It becomes a ves phase and absorbs hydrogen well, but 0≦×≦0.
Within the range of 1, it becomes a C15 type cubic laves phase and does not absorb hydrogen.

According to experiments conducted by the present inventors, the hydrogen storage capacity is 4.5 hydrogen atoms per unit cell when x=1, as shown in FIG.
2g, it gradually decreases as X decreases until x=0.
15 has 3.111 hydrogen atoms! J, and when X further decreases beyond this, the hydrogen storage capacity decreases rapidly, and x
=0.05, almost no hydrogen absorption was observed.

As is clear from the results in the same figure, when considering the amount of hydrogen storage per unit ff1ffi, Zr(Fe1-xCr
In the alloy represented by x)2, if the lower limit of

On the other hand, Figures 2 to 7 show zr (Fe1-xCrx)2 manufactured by changing the value of X stepwise from 0.2 to 1°0.
It shows the measurement results of the hydrogen equilibrium pressure and temperature of each alloy, and the number of hydrogen atoms for the alloys of 1 and Hol.According to these results, if the value of A hydrogen storage alloy is obtained.

Among them, those with X=0.4.0.6 have a temperature of 100
C. to 200.degree. C., it has good characteristics that can be used as a heat pump, and is useful in the intermediate temperature range of conventional rare earth alloys (120.degree. C. or lower) and ZrMn2 (200.degree. C. or higher).

In addition, in the hydrogen storage alloy with The equilibrium pressure of the alloy is on the order of several atmospheres, and the effective amount of hydrogen is as large as 2 or more hydrogen atoms per mole of alloy, indicating good properties for hydrogen storage.

Incidentally, the above-mentioned plateau pressure or plateau characteristic is an indicator that the hydrogen absorption capacity changes greatly with a small pressure change and the reaction rate is fast, and an alloy having this characteristic in as wide a range as possible at a low temperature is desirable.

From this point of view, the alloy with X=1.0 shown in FIG.
This is recognized in the relatively low temperature range of 130°C in the case of the alloy of No. is set to 0°8.

(Example) Hereinafter, preferred embodiments of the present invention will be described.

(Example 1) Zr with a purity of 99.7%, Fe with a purity of 99.9%.

Zr (Fe Cr) with 99.9% C
The composition ratio of 0.8 0.2 2, that is, Zr (F el-x Cr
x), , 2 were mixed so that X = 0.2, and melted with a plasma torch in an argon atmosphere for 4 hours.
An alloy having the composition was produced by repeating the process several times.

After crushing this alloy into soybean-sized pieces, it was placed in a pressure container.
This was activated by immersing it in an oil bath at 0.degree. C. and repeating vacuum degassing and hydrogen pressurization at 30 atmospheres three times.

Thereafter, the amount of hydrogen occluded as a metal hydride in 1 mole of the alloy obtained by a known method was measured, and the hydrogen equilibrium pressure, etc. 8! Figure 2 shows what was determined as a line.

The curves shown in the figure are for temperatures of 0°C, 30°C, and 75°C, the vertical axis is the equilibrium pressure of hydrogen (atmospheric pressure), and the horizontal axis is the amount of metal hydride (number of hydrogen atoms/mol of alloy). ) is shown,
Each exhibited good plateau characteristics at a relatively low equilibrium pressure of about 1 to 20 atm.

(Example 2) Z'(Fe
An alloy of Cr) was produced, and the same
The hydrogen equilibrium pressure isotherm of the obtained alloy after activation treatment at 0.32° C. is shown in FIG.

The curves shown in the figure are for temperatures of 30°C, 75°C, and 135°C, and good plateau characteristics are obtained at approximately the same hydrogen equilibrium pressure as in Example 1, and at about 10 atm below 100"C. Since the equilibrium pressure is , it is suitable for hydrogen storage along with Example 1.

(Example 3) Using the same method as in Example 1, Z'(Fe
An alloy of Cr) was produced, and the same
The hydrogen equilibrium pressure isotherm of the obtained alloy after activation treatment at 0.42° C. is shown in FIG.

The curves shown in the figure are for 75°C, 121°C, and 172°C, and in particular, the hysteresis phenomenon disappears in the curve at 172°C, and hydrogen absorption and desorption are completely reversible under these conditions. .

(Example 4.5) Using the same method as in Example 1, x=0.6, 0.8[Zr(F
eCr), Zr(FeO,40
, 62 Cr)] were manufactured, and the properties measured after activation treatment are shown in FIGS. 5 and 6.

Even in these composition ratios, the temperature is below 220°C or 130°C.
It exhibits a plateau characteristic at ℃, and the hydrogen equilibrium pressure is also 10 atmospheres or less, and can be applied to the same applications as in the above embodiments.

(Comparative Example 1) x-1,0 (Zr C “2)” in the same manner as in Example 1 above.
Figure 7 shows the hydrogen equilibrium pressure wAIliI measured after manufacturing the alloy and activating it.

As is clear from the figure, in the alloy with this composition ratio, either I! No plateau is observed even at 100°C, and the amount of occlusion cannot be increased unless the pressure is significantly increased, and the temperature is also quite high, which poses a practical problem.

Note that the hydrogen equilibrium pressure isotherm shown in FIG. 8 is for a conventional hydrogen storage alloy (ZrMn2), and the temperature at which plateau characteristics are observed is higher than that of the alloy of the present invention. Presented for comparison.

Moreover, FIG. 9 shows the change over time in the storage characteristics when hydrogen storage is performed at 30 atmospheres, and the vertical axis is .

Hydrogen atoms/number of alloy moles, horizontal axis is time (seconds), x
=1. In all the O, 0, 6, 0, and 4 alloys, occlusion occurs quickly, reaching 95% or more of the saturated occlusion amount in about 3 minutes.

Furthermore, FIG. 10 shows Zr(FeCr)-XX
2 Formation enthalpy change ΔH for alloy X with respect to
FIG. 6 is a diagram showing that as X increases, Δto1 also increases.

(Effects of the Invention) As explained in detail in the examples above, according to the hydrogen storage alloy according to the present invention, at a hydrogen equilibrium pressure (dissociation pressure) of 10 atmospheres or less, the reaction rate with hydrogen can be increased with a small pressure change. is fast, has a large amount of hydrogen storage at a hydrogen equilibrium pressure of 10 atmospheres or less, and the temperature at which these properties are obtained is low, so the container containing the alloy does not suffer from thermal deterioration, making it extremely practical.

Furthermore, since Zr, Fe, and Cr are used as raw materials, it is cheaper than rare earth alloys.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between X of the hydrogen storage alloy of the present invention and the hydrogen storage amount (number of hydrogen atoms) per unit cell, and FIGS. The relationship between the hydrogen equilibrium pressure and the number of hydrogen atoms per mole of alloy up to the example is shown in the respective characteristic diagrams measured at a constant temperature. Figures 7 and 8 are the respective characteristic diagrams of the comparative example and the conventional example. , Figure 9 shows the hydrogen absorption of the present invention alloy and the comparative example alloy! fi
FIG. 10 is a diagram showing the change in t over time, and FIG. 10 is a diagram showing the relationship between X and enthalpy change. Patent applicant Mazda Co., Ltd. Agent Patent attorney - Color Ken Shaft circumference Same Masatoshi Matsumoto Figure 1; υ
1.1. /χ Figure 2 Figure 3 Figure 4 /6 Lutaso's story No. 5112 [(87M) Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] It has a composition represented by the general formula Zr(Fe_1_-_xCr_x)_2, where x in the general formula is 0.15≦x≦0.
A hydrogen storage alloy characterized by comprising a number within the range of 8.