JPS5947019B2 - Rare earth metal hydrogen storage alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydrogen storage alloy, and more particularly to a quaternary hydrogen storage alloy containing a rare earth metal.

Hydrogen has no resource limitations (cleanliness, transportation,
Because it is easy to store, it is attracting attention as a new energy source to replace fossil fuels.

However, since hydrogen is a gas at room temperature and its liquefaction temperature is extremely low, it is important to develop storage technology for hydrogen.

A storage method that has attracted attention in recent years is a method in which hydrogen is absorbed into a metal and stored as a metal hydride.

In addition, the absorption/desorption reaction between metals and hydrogen is reversible, and a considerable amount of reaction heat is generated and absorbed during the reaction, and hydrogen absorption/desorption pressure depends on temperature. Research is being conducted to apply it to pressure (mechanical) energy conversion devices.

The properties required for such a hydrogen storage material are that it is inexpensive and abundant in terms of resources, that it is easy to activate and has a large hydrogen storage capacity, that it has an appropriate hydrogen storage and release equilibrium pressure near room noise, and that it has a suitable hydrogen storage and release equilibrium pressure. The release hysteresis is small, the hydrogen storage and release reaction is reversible, and its speed is high;
Examples include less pulverization.

By the way, as a typical known hydrogen storage material, for example, LaN i5t FeT i * Mg2N1 is known.

However, although these alloys have reversible hydrogen absorption and release reactions and a large amount of hydrogen storage, the hydrogen storage and release reactions are slow (and cannot be easily activated, and their hysteresis is large). However, there were drawbacks such as absorption and release of hydrogen (repeated pulverization, etc.), which was a major problem in practical use.

Therefore, the present invention has been made to eliminate such conventional drawbacks, and is capable of storing a large amount of hydrogen in the form of a metal hydride, easily and quickly releasing hydrogen, and increasing the hydrogen storage pressure and release pressure. It has the characteristics of an extremely small difference in hysteresis, and less pulverization.

That is, the rare earth metal-based hydrogen storage alloy of the present invention is characterized by being represented by the general formula RNi5-xAyBz.

However, in the formula, R is a rare earth metal atom, A is iron or copper,
B is titanium, zirconium, vanadium or niobium, X is a number in the range of 0.01 to 2.0, and y is 0.01
A number in the range of ~2.0, where 2 is a number less than or equal to 0.2, and 5.
The relationship 0≦5−x+y+z≦5.2 holds true.

Here, the rare earth metal atom R in the present invention includes not only a single metal but also a mixed metal Mm.

Mitsushmetal generally has 25-35% of lanterns (1 scene,
(same below), cerium 40-50%, praseodymium 1
-15 parts, neodymium 4-15 parts, samarium + gadolinium 1-7 parts, iron 0.1-5 parts, silicon 0.1-1 parts,
It consists of 0.1 to 2 parts of magnesium, 0.1 to 1 part of aluminum, etc., and is already commercially available in Japan.

The composition of the rare earth metal-based hydrogen storage alloy of the present invention is explained as follows.

That is, the alloy of the present invention is basically an alloy RNi5 of rare earth metal R and nickel, in which part of the nickel is replaced with iron or copper. Substituting one or more metals selected from the group consisting of zirconium, vanadium and niobium, or replacing the RN i 5-αAα alloy with one or more metals selected from the group consisting of titanium, zirconium, vanadium and niobium. It was added.

It is generally known that the rare earth metal R and nickel form a hexagonal crystal of CaCu3W and become a metal compound called RNts, but metals other than LaNi5 have a high hydrogen absorption and release pressure near room temperature.

For example, the pressure is 20 to 40 atmospheres for MmNi5, and 40 to 80 atmospheres for CeNi5 and SmNi5.

Therefore, if part of the nickel is replaced with iron or copper, the hydrogen absorption and release pressure can be reduced.

In other words, in alloy RNi5 of rare earth metal and nickel, an alloy in which part of the nickel is replaced with iron or copper is called RNi5.
When expressed as i5-αAα, when α is adjusted in the range of 0.01 to 2.0, the hydrogen storage and release pressures are significantly reduced.

Preferably α is in the range of 0.1 to 1.0.

This α is X in the alloy RNi5-xAyBzK of the present invention.
and y, the range of α is the range of X and y, and X and y are each in the range of 0.01 to 2.0.

If X and y are larger than 2.0, it becomes difficult to release the occluded hydrogen, creating the problem that high-temperature heating and sometimes depressurization must be combined.

Furthermore, if X and y are smaller than 0.01, the amount of iron or copper substitution is too small, making it difficult to lower the hydrogen absorption and release pressures.

However, due to the introduction of iron or copper, the alloy RNi5-αAα exhibits a difference in hydrogen storage pressure and hydrogen release pressure.
In other words, as the hysteresis becomes thicker, the alloy becomes noticeably finer due to repeated absorption and release of hydrogen.

For example, in an alloy having a composition of ■Δ'4.5F80.5, the hydrogen storage pressure is about 9 atm at 10°C, the hydrogen release pressure is about 3 atm, and the hysteresis is about 6 atm.

In addition, in an alloy with a composition of MmN i4.5 Cuo, 5, the hydrogen storage pressure is about 15 atm at 10°C, and the hydrogen release pressure is about 6
It has a hysteresis of about 9 atmospheres.

If the hysteresis is large, the hydrogen storage alloy or its metal hydride must be heated with a larger temperature difference, or the hydrogen must be pressurized or depressurized with a larger pressure difference, which reduces the hydrogen storage capacity and hydrogenation reaction. Heat cannot be used effectively.

On the other hand, the alloy repeatedly expands and contracts by absorbing and desorbing hydrogen, becoming a fine powder (.

This phenomenon increases the packing density of the alloy in the container and reduces its volume. If hydrogenation is continued in this state, the expansion of the alloy will apply local stress to the container, resulting in strain. This causes hydrogen leakage.

Furthermore, the heat transfer efficiency of the packed bed is reduced.

Finely divided metal hydrides and alloys can mix into the emitted hydrogen gas and cause clogging of pipes and pulp.

For example, in an alloy with a composition of MmN i4.5 FeO05, it has been revealed that most of the particles become smaller than 10 μm after 500 hydrogen absorption and desorption cycles, and that pulverization progresses significantly.

Since the problem of pulverization is an essential problem of metal hydrides, although there are differences in degree, it is desirable that some kind of countermeasure be taken for practical use.

The present invention solves the problem of hysteresis and pulverization by further substituting a part of iron or copper in alloy RNi5-αAα with titanium, zirconium, vanadium, or niobium, or by replacing RNi5-αAα with titanium, zirconium, This problem was solved by adding vanadium or niobium.

In the form in which part of the iron or copper of the alloy RNi5-αAα is replaced with the metal B, the alloy RNi5-xAy of the present invention
In Bz, the relationship X=y+z1 and y≧Z is established, 2 is 0.2 or less, and 5−X+y+z ”5.

Moreover, the alloy of the present invention in this case becomes an RNi5-type hexagonal metal compound.

In the form in which the above metal B is added to the alloy RNi5-αAα, the alloy RNi5-xAyBz of the present invention is
=y1 and y≧2 holds true, where 2 is less than or equal to 0.2,
Preferably it is 0.1 or less, and 5.0 < 5-x
y+z≦5.2.

Although the structure of the alloy of the present invention when metal B is added is not clear,
Basically, it is a metal compound of the RNiB type.

Z! J: thicker than 0.2 (if this happens, the hydrogen storage capacity of the alloy will decrease, and the plateau region of the hydrogen storage and release pressure curve will become 2.
This is not preferable because it tends to become step-like.

In addition to the above two typical examples of substitution or addition, there is naturally a range that spans both the case where a part of the metal BIJ''-RNi5-αAα is substituted and the case where it is added. .

In producing the hydrogen storage alloy of the present invention, various known methods can be employed, but it is preferable to employ the arc light melting method.

In other words, rare earth metals, nickel, iron or copper, and metal B are separated and mixed together. L is press-molded into an arbitrary shape, and then this molded product is charged into an arc light melting furnace and heated under an inert atmosphere. It can be easily manufactured by melting and cooling.

The hydrogen storage alloy obtained is conventionally used in powder form in order to increase its surface area.

The hydrogen storage alloy of the present invention can be activated extremely easily,
After activation, large amounts of hydrogen can be stored and released easily and rapidly.

Activation is carried out by heating the alloy to 80° C. under reduced pressure with a rotary pump to degas it, followed by a single hydrogen storage and desorption operation.

This hydrogen absorption/desorption operation and the formation of metal hydrides are carried out by filling a suitable container with alloy powder, degassing the container, then filling the container with hydrogen at room temperature and applying a hydrogen pressure of 20 kg/Cl or less.

In this way, the hydrogen storage alloy of the present invention has hydrogen application of 20
It can be carried out at a low pressure of less than kg/d and at room temperature in an extremely short time, within several minutes.

The release of hydrogen from the metal hydride can be accomplished simply by opening the container at room temperature.

However, by heating the metal hydride slightly above room temperature or reducing the pressure, hydrogen can be released more quickly and efficiently.

That is, the hydrogen storage alloy of the present invention can be activated much more easily than conventional alloys, and after activation, hydrogen can be stored and released at high speed.

Further, in the present invention, due to the presence of metal B, for example,
Hydrogen storage, release pressure difference, and hysteresis are MmN i4,
5 F eo, 5 Z ro, o 5 and MmN i
For 4,5 cuO,5Z rO105, it is about 3 to 4 atm, and for MmN i4,5 Fe□,5 TiO,0
5t MmN i4.5 FC (1,45Vo, 05
5MmNi4.5FeO045NbO605#MmNi
4.5CuO05TiO005゜MmN i4,5 c
ub, 45 Vo, o 51 and MmNt 4.5
CuO045Nb □ and o5 each have a pressure of 2 to 3 atm.

Conventional alloy MmN without substitution and addition of metal B
i4. s Feo, s and ■Rain t4.5 Cu6
．． , the hysteresis was reduced to about half compared to .

On the other hand, due to the presence of metal B, for example, MmN i,,5 Fe6.5 Z r□, o5s
In the case of MmN i,, 5 F eo, 5 Z rO,1 and MmN it, 5 F eo, 5 Z ro, 2, 500 hydrogen absorption and desorption cycles (repeatedly 4
0 μm, 60 μm and 170 μm, and the pulverization of the alloy was significantly suppressed compared to the conventional alloy MmNi4,5FeO,5, which did not contain Zr.

As described above, the hydrogen storage alloy of the present invention is a new alloy developed for the first time and has all the properties required as a hydrogen storage material, especially hydrogen storage, release pressure hysteresis, and pulverization. This has been greatly improved compared to conventional hydrogen storage alloys, and it is possible to effectively utilize the hydrogen storage capacity as a hydrogen storage alloy and the reaction heat associated with hydrogen storage and release reactions.

Moreover, the rare earth metal-based hydrogen storage alloy of the present invention is extremely easy to activate hydrogen storage and release reactions, can store large amounts of hydrogen at high density, and can store and release hydrogen at temperatures around room temperature. No matter how many times hydrogen storage and release are repeated, there is virtually no deterioration in the performance of the hydrogen storage alloy, and there is little pulverization (therefore, long-term use is possible. It can be said that it is a practically extremely useful hydrogen storage material, as it is hardly affected by impurities in storage gases such as nitrogen, argon, and carbon dioxide.

Therefore, in addition to its original use as a hydrogen storage material,
It also exhibits outstanding effects in other applications that utilize the reaction heat associated with hydrogen absorption and release reactions.

Hereinafter, the present invention will be specifically explained based on Examples.

Example 1 Commercially available Mitshu metal, nickel, gold MA (Fe or Cu) and metal B (Tts Zrs V and N
b) atomic ratio Mm:Ni:A:B''=1:4.
5: 0.5: 0.05, this was charged into a copper crucible in a high vacuum arc melting furnace, the furnace was made into a high purity argon atmosphere, and then heated and melted at approximately 2000°C. Leave to cool and MmN i4.5 F eo, 5 T 5
.

5 *IVhnNi4.5 FeO,5zro,051
MmN i4,5 Feo, 5%, o! 5.

MrnN14.5 F eo, s N b o, o 5
* MrTIN14.5 Cu o, s T IQ,
05 *MmNi4.5Cu□, 5 zrO, 05t
MmN i4,5 cuO,5vO,05 and MmN
Alloys having the compositions i4.5 Cu □ and 5 Nb Olo 5 were obtained.

The obtained alloy was crushed into 120 meshes, and
was collected in a stainless steel hydrogen storage/release reactor, the reactor was connected to an exhaust system, and degassed by heating to a temperature of 80° C. under reduced pressure.

Next, hydrogen with a purity of 99.999% is introduced, and when the hydrogen pressure inside the vessel is maintained at 10 to 9/clt or less, hydrogen absorption is immediately observed. After the hydrogen absorption is completed, exhaust is performed again to remove the hydrogen. The release has been completed.

Activation of these alloys was completed by this operation.

10 kq/c of activated alloy in the reactor! Introducing hydrogen with a purity of 99.999% at a hydrogen pressure of less than i and at room temperature,
It absorbed hydrogen.

On the other hand, hydrogen release can be carried out at room temperature, but is more efficiently carried out by heating the reactor and/or under reduced pressure.

Using the method described above, the relationship between pressure and temperature in hydrogen storage and release for each hydrogen storage alloy was determined.

For example, MmNi4.5Feo, 5Zro, os
FIG. 1 shows the H system expressed as the logarithm of pressure - the reciprocal of absolute temperature.

In FIG. 1, straight line A represents hydrogen storage pressure, straight line B represents hydrogen release pressure, and dotted lines C and D represent a ternary hydrogen storage system having a composition of MmN i4.5 Feo, 5 as a comparative example. The case where an alloy is used is shown, where the straight line C represents the hydrogen storage pressure and the straight line represents the hydrogen release pressure.

As is clear from FIG. 1, the alloy of the present invention has significantly improved hysteresis compared to the conventional hydrogen storage alloy shown in the comparative example.

In addition, the hydrogen storage capacity of each alloy obtained above, the logarithm of the ratio of hydrogen storage pressure to hydrogen release pressure, that is, the hysteresis factor, and the average particle size of the alloy after 500 hydrogen storage and release cycles (repeated) The results of the calculated t are shown in Table 1 below.

From this Table 1, it can be seen that the alloy AI""A8 of the present invention is different from the conventional alloys (MmN i4,5 F eo,s and MmNi4
．． 5Cug, 5=Sample A8. It is clear that the hysteresis factor is smaller than that of 9), and the amount of hydrogen storage is almost the same even though it is finely pulverized.

Example 2 MmNi, 5Ao, 45B was prepared in the same manner as in Example 1.
o and o5 (as in Example 1, metal A was Fe) Cu metal B was T1$ Zr) V) Nb) were produced and activated, and hydrogen absorption and release experiments were conducted. The relationship between pressure and temperature on occlusion and desorption was determined.

An example is MmNi4.5Feo, 4sZro, o
Figure 2 shows the logarithm of pressure←reciprocal of absolute temperature for the sH system.

In FIG. 2, straight lines E and G represent hydrogen storage pressure, straight lines F and H represent hydrogen release pressure, and dotted lines G and H represent MmN i4,
5 is a pressure-temperature diagram when a ternary hydrogen storage alloy having a composition of 5 is used.

As is clear from FIG. 2, the alloy of the present invention has significantly improved hysteresis compared to the alloy of the comparative example.

In addition, the hysteresis factor is 0.30 to 0.50, and the average particle size of the alloy after 500 hydrogen absorption and desorption cycles is 30 to 40 μm, which exhibits better properties than conventional alloys. Hydrogen storage capacity is also 1.5-1.6% by weight
It was confirmed that this was almost the same as the conventional alloy (1.5% by weight).

Example 3 MmNi4.5 F eo, 5Z rO, 05t Mm was prepared in the same manner as in Example 1.
N i, 5F eQ, 5 ZrO, 11MmN i4.
s F eo, s Z To, zp MmN 14,
5 Cu o, 5 Zro, os jMmN i4.5
Cu O,, Z ro,t and MmN i4,5
Cuo, s Z ro, 2 are respectively produced and activated, 9
500% hydrogen storage and release operation using 9.5% hydrogen
The test was repeated several times, and the average grain size of the alloy was then measured.

Table 2 below shows the average grain size of the alloy of the present invention after hydrogen absorption and desorption was repeated 500 times.
CuO,5: The average grain size of the alloy was larger than that of samples A7 and 8), and it was confirmed that the addition of Zr significantly suppressed the pulverization of the alloy.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams showing the relationship between pressure and temperature on hydrogen storage and release of an embodiment of the hydrogen storage alloy according to the present invention and a conventional ternary alloy.

Claims (1)

[Scope of Claims] 1. A rare earth metal-based hydrogen storage alloy characterized by being represented by the general formula RNi5 xAyBz. However, in the formula, R is a rare earth metal atom, A is iron or copper,
B is titanium, zirconium, vanadium or niobium, X is a number in the range of 0.01 to 2.0, and y is 0.01
a number in the range of ~2.0, Z is a number less than or equal to 0.2, and 5.
The relationship 0≦5−x+y+z≦5.2 holds true. 2. The rare earth metal-based hydrogen storage alloy according to claim 1, wherein x = y + z, and y≧Z. 3. The rare earth metal-based hydrogen storage alloy according to claim 1, wherein X2y1y≧2 and 2≦0.1.