JPS5839218B2 - Rare earth metal quaternary hydrogen storage alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a quaternary hydrogen storage alloy containing a rare earth metal. The present invention relates to a novel and practically extremely useful quaternary rare earth metal hydrogen storage alloy that can rapidly release hydrogen and has an extremely small difference between the hydrogen storage pressure and the release pressure, that is, hysteresis.

Hydrogen has no resource limitations and is clean, transportable,
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 desorption equilibrium pressure near room temperature, and that it has an appropriate hydrogen storage and desorption equilibrium pressure. The hysteresis of hydrogen is small, the hydrogen absorption and release reaction is reversible, and its speed is high.

By the way, typical known hydrogen storage materials include, for example, LaNi5 and FeTi.

However, although these alloys have reversible hydrogen storage and release reactions and a large hydrogen storage capacity, the hydrogen storage and release reactions are slow, activation is not easy, and they have large hysteresis. There were drawbacks and major practical problems.

Therefore, the present inventors conducted intensive studies to solve these conventional problems, and found that rare earth metals, nickel, manganese,
The inventor discovered that a quaternary alloy composed of a metal element selected from the group consisting of titanium, zirconium, vanadium, and niobium satisfies the above conditions and is extremely useful compared to conventional alloys. I have come to give two commandments.

That is, the present invention is a rare earth metal quaternary hydrogen storage alloy represented by the general formula RNi5xMnyMtz.

However, in the formula, R represents a rare earth metal atom, Mt is a metal atom selected from the group consisting of titanium, zirconium, vanadium, and niobium, and X is 0.01 to 2
．． A number in the range of 0, y is a number in the range of 0.01 to 2.0, 2
is a number less than or equal to 0.2, and 5.0≦5−x+y+z≦5
．． Two relationships are established.

Here, the rare earth metal atom R is not only a single metal, but also
Also includes mixed metal Mitsushimetal Mm.

Mitsushmetal generally weighs 25 to 35 lanterns (weight,
(hereinafter referred to as 1), cerium 40-50%, praseodymium 1-15φ, neodymium 4-15 east samarium + cadrinium 1-7, iron 0.1-5, silicon 0.1-1 width,
It is made of magnesium 0.1-2φ, aluminum 0.1-1mm, etc., and is already commercially available in Japan.

The composition of the hydrogen storage alloy of the present invention is explained as follows.

That is, the alloy of the present invention is basically an RNi5-αMnCt alloy in which a part of the nickel in the alloy RNi5 of rare earth metal R and nickel is replaced with manganese.
A part of the metal Mt is substituted with a metal Mt selected from the group consisting of titanium, zirconium, vanadium and niobium, or a metal Mt selected from the group consisting of titanium, zirconium, vanadium and niobium is substituted in the RN i 5-αMnα alloy. The metal Mt is added.

It is generally known that the rare earth metal R and nickel form a CaCu5-type hexagonal crystal and become a metal compound called RN i 5, but materials other than LaNi5 have a high hydrogen absorption and release pressure near room temperature.

For example, MmNi5 has a pressure of 20 to 40 atm, CeNi5 and S
For mNi5, the pressure is 40 to 80 atmospheres.

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

That is, in alloy RNi5 of rare earth metal and nickel, an alloy in which part of nickel is replaced with manganese is RNi5.
When expressed as -αMnα, when α is adjusted in the range of 0.01 to 2.0, the hydrogen storage and desorption pressure decreases significantly.

Preferably α is in the range of 0.1 to 1.0.

Since this α corresponds to X and y in the alloy RNi5 xMnyMtz of the present invention, the range of α is the range of X and y.

When X and y are larger than 2.0, it becomes difficult to release the stored hydrogen, resulting in the problem that high temperature heating and sometimes depressurization must be combined.

Moreover, if X and y are smaller than 0.01, the amount of Mn substitution will be too small, making it difficult to lower the hydrogen storage and release pressure.

However, in the alloy RNi5-αMnα, the difference between the hydrogen storage pressure and the hydrogen release pressure, that is, the hysteresis, increases due to the introduction of Mn.

For example, in an alloy with a composition of MmNi4.5Mno,5,
The hydrogen storage pressure is about 8 atm at 50°C, the hydrogen release pressure is about 4 atm, and the hysteresis is about 4 atm.

If the hysteresis is large, the hydrogen storage alloy or its metal hydride must be heated and cooled with a larger temperature difference, or the hydrogen must be pressurized or depressurized with a larger pressure difference in order to perform hydrogen storage and release operations. Therefore, hydrogen storage capacity and hydrogenation reaction heat cannot be used effectively.

This hysteresis problem is caused by the alloy RNi5+ ctMn
A part of Mn in α is further replaced with a kind of metal Mt selected from the group consisting of titanium, zirconium, vanadium and niobium.
or by adding a metal Mt selected from the group consisting of titanium, zirconium, vanadium, and niobium to RN i 5-αMnα.

A part of the Mn of the alloy RN i 5-αMnα is added to the metal M
In the t-substituted form, the alloy of the invention RNi5 xM
In nyMtz, x = y + z, and y≧Z
The following relationship is established, Z is 0.2 or less, 5x+y+z-5
It is.

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 Mt is added to the alloy RNi5-αMn (1), the relationship x=y and y≧2 holds true in the alloy RNi5 xMnyMtz of the present invention, where 2 is 0.2 or less, preferably o, i or less. Yes, 5.0<5-x+
y + z≦5.2.

Although the structure of the alloy of the present invention when metal Mt is added is not clear, it is basically an RNi5 type metal compound.

When 2 is larger than 0.2, the hydrogen storage capacity of the alloy decreases, and the plateau region of the hydrogen storage and release pressure curve tends to become two-stage, which is not preferable.

In addition to the above two typical examples of substitution or addition, there is naturally a range that spans both the case where metal Mt is substituted for a part of RN i 5-αMnα and the case where it is added. do.

Due to the presence of metal Mt, the difference in hydrogen absorption and release pressure and hysteresis at 50°C, for example, are reduced by MmN i4.5Mno, 45T
iO,05 is about 1.4 atm, MmNi4.5Mn□,
5T io , about 1.4 atm in 05, Mm N i4
, r, M nQ , about 1.2 for 45vo, o5
Atmospheric pressure, MmNi4,5 Mn0A5Nb□, 05 is about 1.3 atm, and the conventional alloy MmNi4 without titanium, vanadium and niobium substitution and addition
．． Hysteresis was reduced to less than half compared to 5Mno.5.

Moreover, the presence of metal Mt has little effect on the hydrogen release pressure, and instead reduces only the hydrogen storage pressure, thereby reducing the hysteresis.

This is beneficial in the design of metal hydride reactors.

Although the details of the function of the metal Mt are unknown, it is certain that it gives a subtle change to the crystal structure of the RN i 5 type metal compound, judging from the above-mentioned effect on hysteresis.

In producing the rare earth metal quaternary hydrogen storage alloy of the present invention, various known methods can be employed, but the strong light melting method is preferably employed.

That is, rare earth metals, nickel, manganese and metal Mt
It can be easily produced by separating and mixing each component, press-molding it into an arbitrary shape, charging the molded product into an arc-light melting furnace, heating and melting it in an inert atmosphere, and allowing it to cool.

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

The rare earth metal quaternary hydrogen storage alloy of the present invention can be activated extremely easily, and after activation can easily and rapidly store and release a large amount of hydrogen.

Activation is carried out by heating the alloy to 80° C. under vacuum 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 hydride 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 2 ok/ca or less.

As described above, with the rare earth metal quaternary hydrogen storage alloy of the present invention, hydrogen can be applied at a low pressure of 20 kg/air or less and in an extremely short time, within several minutes, at room temperature.

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

However, if the metal hydride is heated below room temperature,
By reducing the pressure, hydrogen can be released more efficiently and in a shorter time.

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

As described above, the rare earth metal quaternary hydrogen storage alloy of the present invention is a novel alloy developed for the first time and has all the properties required as a hydrogen storage material, especially in terms of hydrogen storage and release pressure. The hysteresis is greatly improved compared to conventional hydrogen storage alloys, and the hydrogen storage capacity of the hydrogen storage alloy and the reaction heat accompanying the hydrogen storage and release reaction can be effectively utilized.

Moreover, the rare earth metal quaternary hydrogen storage alloy of the present invention is extremely easy to activate the hydrogen storage/release reaction, and can store a large amount of hydrogen with high density, and can store and release hydrogen at a temperature near room temperature. No matter how many times hydrogen storage/release is repeated, there is virtually no deterioration in the performance of the hydrogen storage alloy, so it can be used for a long period of time. It can be said to be an extremely useful hydrogen storage material in practice, with almost no effects from impurities inside.

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 desorption reactions.

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

Example 1 The atomic ratio of commercially available Mitsushi metal, nickel, manganese, and metal Mt (Ti, Zr, V, or Nb) is Mm:Ni:Mn:Mt=1:4.5:
0.45:0.05, this was charged into a copper crucible of a high vacuum arc melting furnace, and after creating a high purity argon atmosphere in the furnace, it was heated to about 2000°C and melted and left to stand. Cool and MmN i4.5Mn□,45T iO,05
MmN i4 , 5Mn6.45zrO, )5MmN
i4.5Mn□, 45VO005 and MmN i4
．． Alloys having compositions of 5 Mn□, 45 Nbg, and 05 were obtained, respectively.

The obtained alloy was pulverized into 120 meshes, 50 g of which was collected in a stainless steel hydrogen storage and release reactor, and the reactor was connected to an exhaust system and heated to a temperature of 80°C under reduced pressure to degas it. went.

Next, hydrogen with a purity of 99.999% was introduced, and when the hydrogen pressure inside the vessel was maintained at 10 kg/aa or less, hydrogen absorption was immediately observed, and after the hydrogen absorption was completed, exhaust was performed again to release the hydrogen. Completed.

Activation of these alloys was completed in this operation.

introducing hydrogen with a purity of 99.999% into the activated alloy in a reactor at a hydrogen pressure of less than 10/9/cut 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 above method, the relationship between pressure and temperature on hydrogen storage and release of each rare earth metal quaternary hydrogen storage alloy was determined.

One example is MmN i 4 , 5 Mn□ , 45
FIG. 1 shows the relationship between the logarithm of pressure and the reciprocal of absolute temperature for the Tio, 05-H system.

In FIG. 1, the straight line A represents the hydrogen storage pressure, the straight line B represents the hydrogen release pressure, and the dotted lines C and D represent a ternary hydrogen storage system having a composition of MmN i 4 , 5 Mn 6.5 as a comparative example. 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, Table 1 below shows the hydrogen storage capacity of the Tani alloy obtained above and 50
It shows the ratio of hydrogen absorption pressure to hydrogen release pressure at °C, that is, the hysteresis index, and it shows the ratio of hydrogen absorption pressure to hydrogen release pressure at °C, that is, the hysteresis index,
Compared to the conventional alloy MmNi4,3Mno, sample Arashi 5), the hysteresis index was smaller and the hydrogen storage capacity was almost the same.

Example 2 MmN'14.5Mn0.5 in the same manner as Example 1
Mto, o5 (also as metal Mt, as in Example 1, T
i,zr.

(using V and Nb) were produced and activated, hydrogen storage and desorption experiments were conducted, and the relationship between pressure and temperature on hydrogen storage and desorption was determined for each alloy.

One example is MmNi4.5Mn0,5Ti□,05
FIG. 2 shows the -H system expressed as logarithm of pressure-reciprocal of absolute temperature.

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 as a comparative example as in Example 1.
, 5 M nQ , 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.

Furthermore, when comparing the alloy of the present invention and the alloy of the comparative example, there is almost no difference in the hydrogen release pressure, and only the hydrogen storage pressure decreases.
Since the pressure characteristics do not deviate significantly from those of conventional alloys, they are extremely advantageous in the design of metal hydride reactors.

Table 2 below shows the hydrogen storage capacity of each alloy obtained above and the ratio of hydrogen storage pressure to hydrogen release pressure at 50°C, that is, the hysteresis index.
Mno, 5: Compared to sample &10), the hysteresis index was smaller and the hydrogen storage amount was almost the same.

Example 3 MmN i4.5 Mno,
5 Mt□, 1 (as in Example 1 as metal Mt, '
l'i, Zr.

(using V and Nb) were produced and activated, and hydrogen storage and release experiments were conducted to determine the relationship between pressure and temperature on hydrogen storage and release for Tani alloy.

One example is MmNi4.5Mn□, 5V□, 1-H
FIG. 3 shows the relationship between the logarithm of pressure and the reciprocal of absolute temperature for the system.

In FIG. 3, straight lines J and L represent hydrogen storage pressure, and straight line M represents hydrogen release pressure, and straight lines shown by dotted lines and M represent MmN i 4 , 5Mn□, 5 as in Example 1.
It is a pressure-temperature diagram of .

As is clear from FIG. 3, the alloy of the present invention has significantly improved hysteresis compared to the conventional alloy (MmN i4 , 5 Mno, 5 ) of the comparative example.

Further, as in Example 2, the alloy of the present invention shows less change in hydrogen release pressure than conventional alloys, and only the hydrogen storage pressure decreases, so that the metal hydride reactor can be easily designed.

The hysteresis index of these alloys is 1.20 to 1.4.
5, smaller than conventional alloys, and hydrogen storage capacity of 1.5~
It was confirmed that the weight width was 1.6%, which was almost the same as the conventional alloy (1.5% by weight).

[Brief explanation of drawings]

FIGS. 1, 2, and 3 show examples of rare earth metal quaternary hydrogen storage alloys according to the present invention and conventional ternary alloys.
FIG. 3 is a diagram showing the relationship between pressure and temperature on hydrogen absorption and desorption.

Claims (1)

[Claims] 1. A rare earth metal quaternary hydrogen storage alloy represented by the general formula RNi5-xMnyMtz. However, in the formula, R represents a rare earth metal atom, Mt is a metal atom selected from the group consisting of titanium, zirconium, vanadium, and niobium, and X is 0.01 to 2
．． A number in the range of 0, y is a number in the range of 0.01 to 2.0, 2
is a number less than or equal to 0.2, and 5.0≦5−x+y+z≦5
．． Two relationships are established. 2. The rare earth metal quaternary hydrogen storage alloy according to claim 1, wherein x=y+z and y≧2. 3. The rare earth metal quaternary hydrogen storage alloy according to claim 1, wherein x=y, y≧2, and 2 is a number of 0.1 or less.