JPH03240933A - Hydrogen storage alloy and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture a hydrogen storage alloy improved in pulverizing resistance and hydrogen occluding speed hy adding and dispersing a specified amt. of Mg into the powder of hydrogen occluding material such as Zr(Fe1-xCrx)2 having specified grain size and subjecting it to heat treatment in a specified temp. range. CONSTITUTION:By weight, 10 to 45% Mg is added and dispersed into hydrogen occluding material powder constituted of <=20mu, powder selected from Zr(Fe1-xCrx)2, TiMnx, TiFex and LaNi5, and this mixed powder is heat-treated in a temp. range of 200 to 650 deg.C. In this way, the hydrogen storage alloy in which the generation of cracks is remarkably suppressed in the case of repeating the occluding and discharging of hydrogen and exceedingly improved in hydrogen occluding capacity can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a hydrogen storage alloy and a method for producing the same.

(Prior Art) In recent years, global warming and other issues have been taken up as environmental issues, and hydrogen is attracting attention as an energy source to replace fossil fuels. Hydrogen is extremely useful as an alternative energy source because it has no resource constraints, is clean, can be transported and stored, does not disturb the natural circulation system, and has legal uses. For this reason, hydrogen has traditionally been used as gaseous or liquid hydrogen, but recently hydrogen storage alloys that store hydrogen as metal hydrides have been developed.
It is beginning to attract particular interest.

The hydrogen storage alloy stores, transports, and converts energy of hydrogen by applying the phenomenon of hydrogenation and dissociation of metals, and hydrides of transition metals such as Zr and Ti are known (
For example, see Japanese Patent Publication No. 59-50-744).

(Problems to be Solved by the Invention) At present, the above-mentioned hydrogen storage alloys have the following problems: (1) initial activation is not easy;

(2) Problems of hydrogen storage amount and hydrogen storage speed.

(3) Problems with alloy durability, poisoning, and pulverization.

(4) Thermal conductivity issues (5) There are cost issues, but among these, pulverization resistance and occlusion speed are
This is considered an important issue in the practical application of hydrogen storage alloys.

In other words, hydrogen storage alloys repeatedly expand and contract when storing and desorbing hydrogen, but cracks occur due to the strain energy generated at this time. A pulverization phenomenon occurred in which the powder became a fine powder of about 15 μm. If the hydrogen storage alloy becomes pulverized in this way, in severe cases, the alloy powder may scatter through the filter after several cycles of occlusion and desorption, or thermal conductivity may deteriorate, resulting in poor occlusion efficiency. be. In addition, the hydrogen absorption rate has a large practical impact on the storage and release of hydrogen during filling and use.

Therefore, how to suppress the pulverization of hydrogen storage alloys and how to increase the hydrogen storage rate have become important technical issues for practical use.

The present invention has been made in view of the above points, and an object of the present invention is to improve the pulverization resistance and hydrogen storage rate of a hydrogen storage alloy.

(Means for solving the problem) In the invention of claim 1, as a means for solving the above problem, Zr(Fe+-xCrx)t, TiMnx,
10 to 45 wt% of Mg is dispersed and added to a hydrogen storage material selected from TiFex and LaNi5. The reason for using Mg is that it is lightweight, inexpensive, has a low softening point and is highly malleable, and is considered to have excellent properties as a binder.

In the invention of claim 2, as a means for solving the above problem, in the hydrogen storage alloy according to claim 1, the hydrogen storage material is in a powder state of 20 μm or less.

In the invention of claim 3, as a means for solving the above problem, Zr(Fe+-xCrx)t, TiMnx,
A heat treatment at 200 to 650° C. is applied to a hydrogen storage material powder made of a selected one of TiF exSL aN is and 10 to 45 wt % of Mg added thereto. Note that Mg does not absorb hydrogen in the temperature range from room temperature to 300° C., and only serves as a binder.

(Function) In the invention of claim 1, the following effects can be obtained by the above means.

In other words, hydrogen storage materials that can store and release hydrogen near room temperature and have a large hydrogen storage capacity [for example, Z r (F elxCr
x), TiMnx, TiFex, LaNi 1 in 5
By dispersing and adding 0 to 45 wt% Mg,
When the hydrogen storage material expands during hydrogen storage, Mg acts to absorb and relax the stress caused by the expansion.

Note that if the amount of Mg added is too small (i.e., 10 wt%
If the hydrogen absorbing material is less than 10%), Mg cannot be uniformly dispersed around the hydrogen storage material, and therefore a sufficient effect of absorbing and relaxing stress due to expansion cannot be obtained. Furthermore, if the amount of Mg added is too large (that is, exceeding 45 wt%), hydrogen storage and release by the hydrogen storage material becomes slow. Therefore, M
The amount of g added is preferably 10 to 451 L%.

In the invention of claim 2, the following effects can be obtained by the above means.

That is, the hydrogen storage material in the hydrogen storage alloy [for example, Z
r(Fe+-xc rx)t, T iMnxlT
By adjusting the particle size of [iF ex, LaNi1] to 20 μm or less, the contact area is increased, which facilitates the diffusion of the hydrogen storage material and improves the mutual bonding strength.

Note that if the particle size of the hydrogen storage V exceeds 20 μm, the contact area may decrease and the mutual bonding force may decrease slightly, so it is desirable that the particle size of the hydrogen storage material is 20 μm or less.

In the invention of claim 3, the following effects can be obtained by the above means.

In other words, a hydrogen storage gas that can store and release hydrogen at around room temperature and has a large amount of absorbed Ia [for example, Zr(Fe+-xc
rx)t, T iMnx, T iF ex, L
After adding 10 to 45 wt% of Mg as a binder to aN i5J, heat treatment was performed at 200 to 650°C.
Effective diffusion occurs between the hydrogen storage material and the hydrogen storage material, which improves the bonding strength between the two.In addition, in the heat treatment process, the hydrogen storage material is reduced by removing 1g of nitrogen or oxygen from the hydrogen storage material. Hydrogen storage capacity will be improved.

Note that if the heat treatment temperature is less than 200°C, sufficient diffusion will not occur between the hydrogen storage material and Mg as a binder, and the above-mentioned effect cannot be expected. In addition, the heat treatment temperature is 65
If the temperature exceeds 0° C., the melting point of N1g will be exceeded, making it difficult to maintain the shape and being impractical. Therefore, it is desirable that the heat treatment temperature be in the range of 200 to 650°C.

(Effect of the invention) According to the invention of claim 1, Z r(Fe, -xCrx
)t, T iMnx, T iF ex%L aN i
In the hydrogen storage material selected from s, 10
~45wt% of Mg is added dispersedly so that when a hydrogen storage material that can store and release hydrogen near room temperature and has a large storage capacity expands during hydrogen storage, Mg absorbs and relieves the stress caused by the expansion. As a result, the occurrence of cracks when hydrogen is repeatedly absorbed and released is significantly suppressed, and the pulverization resistance is significantly improved (i.e., compared to the conventional 1
This has an excellent effect of improving the performance (by 0 to 100 times).

According to the invention of claim 2, in the hydrogen storage alloy according to claim 1, the hydrogen storage material is in a powder state of 20 μm or less, and the hydrogen storage material is capable of storing and desorbing hydrogen at around room temperature and has a large hydrogen storage amount. By adjusting the particle size of the material to 20 μm or less, we increased the contact area, which facilitates the diffusion of the hydrogen storage material and improves the mutual bonding strength, which reduces the storage and release of hydrogen. This has the excellent effect of further suppressing the occurrence of cracks when repeated, and further improving the pulverization resistance (that is, about 100 times that of the conventional method).

According to the invention of claim 3, Z r(Fe, -xCrx
)t, T iMnx, T iF ex, L aN
20 to 45 wt% of Mg is added to the hydrogen storage material powder made of selected is.
By applying heat treatment at 0 to 650°C, effective diffusion occurs between the hydrogen storage material, which is capable of absorbing and desorbing hydrogen at around room temperature and has a large hydrogen storage capacity, and Mg, which is a binder. As the bonding strength of
This has the excellent effect of significantly suppressing the occurrence of cracks in the case of repeated discharge, and significantly improving the pulverization resistance (that is, 10 to 100 times that of the conventional method). In addition, in the heat treatment step, Mg deprives the hydrogen storage material of oxygen and reduces the hydrogen storage material, which has the effect of significantly improving the hydrogen storage capacity of the obtained hydrogen storage material.

(Example) The present invention will be described below based on specific examples.

Example 1 Hydrogen storage material powder represented by the chemical formula of 2r(Peo, tcro, s>x and adjusted to a particle size of 2゜μm or less,
23.1wL% of Mg powder was mixed with Ar in a non-oxidizing atmosphere.
The mixture was mixed in gas and compacted at a pressure of 8.5 t/cm', and the obtained powder compact was heated at 500°C for 20 hours at 2 to 3 atm in a non-oxidizing atmosphere such as Ar. When the heat treatment was performed, an Mg composite hydrogen storage alloy was obtained in which 23.1 wt % of Mg was dispersed and added to the hydrogen storage material represented by the chemical formula Z r (F eo7c ro, .)t.

In the Mg composite hydrogen storage alloy obtained as described above, as shown in the microstructure photograph in Figure 1, Mg (black part in the photograph) is present between hydrogen storage materials (gray part in the photograph).
It can be seen that Mg is dispersed and added, and that the Mg acts as a binder.

In the case of a hydrogen storage alloy with such a configuration, when the hydrogen storage material expands during hydrogen storage, Mg, which acts as a binder, acts to absorb and relax the stress caused by the expansion, and hydrogen storage and release occur. The occurrence of cracks when the process is repeated is significantly suppressed, and the resistance to pulverization is significantly improved. Incidentally, in the case of a material to which Mg is not added, it becomes pulverized after absorbing and desorbing hydrogen about 10 times, whereas in the case of the hydrogen storage alloy of this example,
No pulverization occurred even after absorbing and releasing hydrogen 1000 times.

Now, in order to investigate the influence of changes in the amount of Mg added to the hydrogen storage material on pulverization and the amount of hydrogen transfer, tests were conducted with various amounts of Mg added, and the characteristics shown in FIG. 2 were obtained.

In Figure 2, the changes in pulverization resistance (i.e., the number of times of hydrogen absorption and release leading to pulverization) and the amount of hydrogen transfer (H/m) with respect to the amount of Mg added (wt%) are shown by solid lines and dotted lines, respectively. ing. Here, H/m represents the number of hydrogen atoms per mole of hydrogen storage alloy.

According to this, it can be seen that when the amount of Mg added is less than 10 wt%, the pulverization resistance decreases rapidly, and when the amount of Mg added exceeds 45 wt%, the amount of hydrogen transfer decreases. This indicates that the action of Mg as a binder decreases as the amount added decreases, and conversely, the hydrogen storage capacity decreases due to the presence of a large amount of Mg. Therefore, it is desirable that the amount of Mg added is in the range of 10 to 45 wt%.

In addition, Mg due to changes in the particle size of the raw hydrogen storage material powder expressed by the chemical formula
In order to investigate the pulverization resistance of a composite hydrogen storage alloy (for example, a 23.1 wt% Mg-added hydrogen storage alloy), tests were conducted with various particle sizes (μl 11) of the raw hydrogen storage material, and the characteristics shown in Figure 3 were obtained. It was done.

According to this, regardless of the particle size of the hydrogen storage material,
It exhibits 10 times higher durability (i.e., pulverization resistance) than conventional materials, but when the particle size of the hydrogen storage material is adjusted to 20 μm or less, it exhibits remarkable pulverization resistance (i.e., 10 times higher than conventional pulverization resistance).
0 times or more). This is believed to be due to the fact that by reducing the particle size of the hydrogen storage material, the contact area is increased, which facilitates the diffusion of the hydrogen storage material and improves the mutual bonding force. Seem.

In addition, when the particle size of the hydrogen storage material exceeds 20 μl, the contact area decreases and the mutual bonding force slightly decreases, which seems to lead to a decrease in pulverization resistance. Therefore, it is desirable that the particle size of the hydrogen storage material be 20 μm or less.

Furthermore, in order to investigate the effects of heat treatment on the durability (i.e., pulverization resistance) and hydrogen storage depth during the manufacturing process of the hydrogen storage alloy, tests were conducted under various heat treatment conditions, as shown in Figures 4 and 5. The properties shown were obtained.

According to this, those without heat treatment or 150
It can be seen that the sample subjected to the heat treatment at <500° C. for 20 hours in this example exhibits extremely superior pulverization resistance and hydrogen storage rate, compared to the sample subjected to the heat treatment at 500° C. for 20 hours. This means that the heat treatment causes effective diffusion between the hydrogen storage material and Mg as a binder, improving the bonding strength between the two, and that Mg absorbs oxygen in the hydrogen storage material during the heat treatment process. This seems to be due to the fact that the hydrogen storage capacity of the hydrogen storage material is improved by removing and reducing the hydrogen.

In addition, when the heat treatment temperature is less than 200°C, sufficient diffusion does not occur between the hydrogen storage material and the binder Mg,
The aforementioned effects cannot be expected. In addition, the heat treatment temperature is 650
If the temperature exceeds .degree. C., the melting point of Mg will be exceeded, making it difficult to maintain the shape and being impractical. Therefore, it is desirable that the heat treatment temperature be in the range of 200 to 650°C.

Example 2 Mg was added to the hydrogen storage materials represented by the chemical formulas of TiMn+, s, TiFe, and LaNi in the same manner as in Example 1, and heat treatment was performed to obtain TiMn, s, respectively. , TideSLaNi, were manufactured, and these Mg composite hydrogen storage alloys also exhibited characteristics similar to those of Example 1. That is, it exhibits high pulverization resistance and high hydrogen storage rate.

In addition, in the above example, Z r (Fe, -xCrx)
X=0.3 at t, x=1 at TiMnx
．． 5. Although x=1 in TiFex, the present invention is also applicable to other numerical values.

[Brief explanation of drawings]

Fig. 1 is a micrograph showing the internal structure of the hydrogen storage alloy according to Example I of the present invention, and Fig. 2 shows the change in pulverization resistance (times) with respect to the amount of Mg added (wt%) in the hydrogen storage alloy. Characteristic diagram, Figure 3 is a characteristic diagram showing changes in pulverization resistance (times) with respect to changes in particle size (μm) of hydrogen storage material, Figure 4
The figure is a characteristic diagram showing changes in pulverization resistance (times) with changes in heat treatment conditions, and FIG. 5 is a characteristic diagram showing changes in hydrogen storage rate due to changes in heat treatment conditions. Figure 1 Figure 2 Main chapter Particle size of storage material powder (tm) Figure 3

Claims (1)

[Claims] 1, Zr(Fe_1_-_XCr_X)_2, TiMn
A hydrogen storage alloy characterized in that 10 to 45 wt% of Mg is dispersed and added to a hydrogen storage material made of a hydrogen storage material selected from _X, TiFe_X, and LaNi_5. 2. The hydrogen storage alloy according to claim 1, wherein the hydrogen storage material is made of powder of 20 μm or less. 3, Zr(Fe_1_−_XCr_X)_2, TiMn
10 to 45 wt% of Mg in the hydrogen storage material powder consisting of one selected from _X, TiFe_X, and LaNi_5
1. A method for producing a hydrogen storage alloy, which comprises subjecting a hydrogen storage alloy to heat treatment at 200 to 650°C.