JPS626739B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a ternary hydrogen storage alloy containing a rare earth metal, and more specifically, it can store a large amount of hydrogen in the form of a metal hydride, and can easily and quickly release hydrogen with a small amount of heating. The present invention relates to a new rare earth metal ternary hydrogen storage alloy which is extremely useful in practice and has an extremely small difference between hydrogen storage pressure and hydrogen release pressure, that is, steresis. Hydrogen is attracting attention as a new energy source to replace fossil fuels because it is clean, has no resource limitations, and is easy to transport and store. 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 and release reaction between metals and hydrogen is reversible, and a considerable amount of reaction heat is generated and absorbed during the reaction, and the hydrogen absorption and release 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, LaNi ₅ and FeTi. However, although these alloys have reversible hydrogen storage and release reactions and can store a large amount of hydrogen, they have drawbacks such as slow hydrogen storage and release reactions, difficulty in activation, and large hysteresis. There was a big practical problem. In view of the above-mentioned situation, the present inventors have carried out various studies in order to develop a hydrogen storage alloy having the above-mentioned properties. As a result, rare earth metals,
We have discovered that a specific ternary alloy composed of nickel and Mt, which will be described later, has all of the above properties and is novel and extremely useful as a hydrogen storage alloy, and hereby the present invention has been made. I was able to complete it. That is, the present invention relates to a rare earth metal ternary hydrogen storage alloy represented by the general formula RxNiyMtz. Here, in the formula, R represents a rare earth metal atom, Mt is a metal atom selected from the group consisting of niobium, tin, and molybdenum, and x is 1.0 to 2.0.
, y is a positive number from 3.0 to 9.0, z is a positive number from 0.01 to 1.0, and y+z/x>5 or y+z/x<5. Here, the rare earth metal atom R includes not only a single metal but also a mixed metal (Mm). By the way, rare earth metal alloys such as LaNi ₅ and MmNi ₅ are also used for hydrogen storage and transportation, and as heat pumps for waste heat recovery. It was necessary to adjust the dissociation pressure of the compound. Therefore LaNi ₅
Techniques have been developed to adjust the dissociation pressure by substituting a part of Ni, La, or Mm in MmNi and MmNi ₅ -based alloys with a third element such as Al, Mn, Cr, Si, or Co. For example, with Al, the dissociation pressure can be greatly changed even by slightly changing the amount of substitution. However, alloys containing Al as the third element (LaNi ₅ −
xALx, La _1-x Ni ₅ Alx, MmNi _5-x ALx,
For Mn _1-x Ni ₅ Alx), the dissociation pressure, hydrogen storage capacity, and hysteresis are all determined by the amount of Al, so
The degree of freedom when putting it into practical use is small. Particularly when used for heat pumps, the pressure difference in the hydrogen storage and release curves, that is, hysteresis, is extremely important.If this is large, the storage alloy or hydride will have to be heated or heated with a larger temperature difference during hydrogen storage or release operations. The hydrogen must be cooled or pressurized or depressurized with a larger pressure difference, reducing the efficiency of the device. Therefore, in order to effectively utilize the hydrogen storage capacity and hydrogenation reaction heat on a practical scale, it is necessary to reduce the hysteresis. Furthermore, it has been confirmed that in the case of an alloy with a composition in which the amount of Al substitution is relatively large, the amount of hydrogen storage decreases. Under these circumstances, the present invention aims to develop rare earth metal-nickel alloys, such as RNi ₅ (R represents a rare earth metal atom), which have properties suitable for hydrogen storage (especially low dissociation pressure and hydrogen storage capacity). The aim is to improve practicality by reducing the hysteresis while maintaining the characteristic of large
Basically, a specific amount of a metal (Mt) selected from the group consisting of niobium, tin, and molybdenum is blended as a third element with the above rare earth metals and nickel, and the alloy component ratio is adjusted to meet the requirements of the general formula RxNiyMtz. The purpose can be achieved by adjusting. The reason why x, y, and z are determined as described above in the general formula RxNiyMtz of the hydrogen storage alloy of the present invention is as follows. x: 1.0 to 2.0 If x is less than 1.0, the effect of reducing the amount of hydrogen storage and reducing hysteresis will not appear. On the other hand, when x exceeds 2.0, it becomes difficult to release the stored hydrogen, and it becomes impossible to release the stored hydrogen unless high temperature or a combination of low pressure is used. y: 3.0 to 9.0 If y is less than 3.0, the dissociation pressure and hydrogen storage capacity will be extremely reduced, while if y exceeds 9.0, the dissociation pressure will tend to increase, making it suitable for hydrogen storage and waste heat recovery. will no longer be shown. z: 0.01 to 1.0 If z is less than 0.01, the absolute amount of the added metal Mt is insufficient, so the dissociation pressure cannot be lowered sufficiently, and furthermore, the effect of reducing hysteresis is not achieved. On the other hand, if it exceeds 1.0, the amount of stored hydrogen decreases, it becomes difficult to release the stored hydrogen, or the plateau region of the hydrogen storage/release curve tends to become two-stage, and it is not possible to reduce the hysteresis. . Mt is an essential component for maintaining dissociation pressure suitable for hydrogen storage and reducing hysteresis. y+z/x>5 or y+z/x<5: y+z/x=
5, the amount of hydrogen storage decreases and the hysteresis increases. Activation is also somewhat difficult. When the composition of the alloy is in the above range, it has the advantage that the hydrogen storage pressure and release pressure of the alloy can be varied over a wide range suitable for hydrogen storage, and has excellent characteristics such as small hysteresis. Although the basic structure of the rare earth metal ternary hydrogen storage alloy according to the present invention is not clear, for example,
RxNi ₅ Mtz alloy is considered to be a hexagonal intermetallic compound similar to LaNi ₅ , MmNi ₅ , etc.
In any case, compared to LaNi ₅ , MmNi ₅ , and LaNi _5-x Mtx alloys, they retain properties for hydrogen storage and have smaller hysteresis during hydrogen storage and release, so they are suitable for hydrogen storage as hydrogen storage alloys. It is possible to effectively utilize the capacity and the heat generation and endotherm associated with hydrogen storage and release. Moreover, this alloy is extremely easy to activate, can store large amounts of hydrogen at high density, and the hydrogen storage and desorption reactions are completely reversible. There is virtually no deterioration, and it can withstand long-term use.
Furthermore, it has many features such as being almost unaffected by impurities contained in storage gases such as oxygen, nitrogen, argon, carbon dioxide, and carbon monoxide. By the way, when compared with conventional ternary alloys regarding hysteresis, which is the greatest feature of the alloy of the present invention,
For example, the hysteresis of _the conventional LaNi _4.4 Al _0.6 alloy at 120°C is about 1.0 atm, while that of _the present alloy at the same temperature is about 1.0 atm for LaNi ₅ Sn _{0.6 .}
It showed 0.3 atm, which is less than half that of conventional alloys. Similar trends are observed in other metals, Mt.
The same was true when Nb, Sn and Mo were used. In producing the rare earth metal ternary hydrogen storage alloy of the present invention, various known methods can be employed, but it is preferable to employ the arc light melting method. That is, after separating and mixing the components of rare earth metals, nickel, and metal Mt, they are press-molded into an arbitrary shape, and then this molded product is charged into an arc light melting furnace and heated and melted in an inert atmosphere. It can be easily manufactured by allowing it to cool. The obtained hydrogen storage alloy is 800 to 1100
C. for 8 to 25 hours, and the resulting alloy is conventionally used in powder form to increase its surface area. The rare earth metal ternary hydrogen storage alloy of the present invention is
It can be activated extremely easily, and after activation, it can easily and rapidly absorb and release a large amount of hydrogen. Activation is carried out by pumping the alloy under reduced pressure with a rotary pump, e.g.
It is carried out by heating to 80° C. to degas, then occluding and desorbing hydrogen in a single operation. To absorb and release hydrogen after activation and to form metal hydrides, fill the alloy powder into a suitable container, degas it, fill it with hydrogen at room temperature, and apply a hydrogen pressure of 20 kg/cm ² or less. This is done by As described above, with the rare earth metal ternary hydrogen storage alloy of the present invention, hydrogen can be applied at a low pressure of 20 kg/cm ² or less and in an extremely short time, within several minutes, at room temperature. On the other hand, in the case of general-purpose Ti-Fe alloys, hydrogen absorption hardly occurs when a hydrogen pressure of about 50 kg/cm ² is applied at room temperature, and therefore activation is impossible under these conditions. . Therefore, approximately 400~
High-temperature treatment of around 500°C is required, and such severe occlusion operations must be repeated several times for activation.Such problems are common with Ti-Ni alloys and Mg-Ni alloys. The case is also substantially the same. 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 above room temperature or 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 ternary hydrogen storage alloy of the present invention is a novel alloy developed for the first time.
It has all the properties required as a hydrogen storage material, and in particular, the hysteresis of hydrogen storage and release pressure has been greatly improved compared to conventional hydrogen storage alloys, and the hydrogen storage ability as a hydrogen storage alloy has been improved. This makes it possible to effectively utilize the reaction heat accompanying the hydrogen storage and release reaction. Moreover, the rare earth metal ternary hydrogen storage alloy of the present invention is extremely easy to activate the hydrogen storage and release reaction, and can store a large amount of hydrogen with high density.
It is possible to absorb and release hydrogen at a temperature near room temperature, and no matter how many times hydrogen storage and desorption 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. Further, it can be said to be a practically extremely useful hydrogen storage material, with almost no influence from impurities in storage gases such as oxygen, nitrogen, argon, and carbon dioxide gas. Therefore, it exhibits outstanding effects not only in its original use as a hydrogen storage material but also in other uses that utilize the reaction heat accompanying the hydrogen absorption and release reaction. Hereinafter, the present invention will be specifically explained based on Examples. Example 1 Commercially available lanthanum, nickel and Mt (Nb, Sn,
A type of Mo) with an atomic ratio of La:Nh:Mt=1.0:
5.0:0.6, 1:4:0.5, 1:5.5:0.5, 1:1.5:
0.5 and 1:8.5:0.5 and charged into a copper crucible in a high vacuum arc melting furnace. After creating a high-purity argon atmosphere in the furnace, it was heated to about 2000°C to melt it, and then _allowed to cool to produce LaNi ₅ Nb _0.6 ,
_{LaNi5Sn0.6 , LaNi5Mo0.6 , LaNi4Nb0.5 , _ _ _
LaNi4Sn0.5 , LaNi4Mo0.5 , LaNi5.5Nb0.5 , _ _ _ _}
LaNi _5.5 Sn _{0.5 , LaNi 5.5} Mo _{0.5 , LaNi 1.5 Nb 0.5 ,}
LaNi _1.5 Sn _{0.5 , LaNi 1.5 Mo 0.5} , _{LaNi 8.5 Nb 0.5 ,}
A ternary alloy having the compositions _{LaNi 8.5 Sn 0.5} and _{LaNi 8.5 Mo 0.5} was obtained. Each of these alloys was annealed at 1100°C for 8 hours. The resulting alloy was ground to 120 mesh, and its 5.0
g 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. Then purity
Introducing 99.99% hydrogen and increasing the hydrogen pressure inside the vessel to 20Kg/
When the temperature was maintained below cm ² , hydrogen storage was immediately observed, and after hydrogen storage was completed, exhaust was performed again to complete hydrogen release. Activation of these alloys was completed by this operation. Hydrogen with a purity of 99.99% was introduced into the activated alloy in a reactor at a hydrogen pressure of 20 Kg/cm ² or less and at a temperature above room temperature to absorb 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 composition isotherms in hydrogen storage and desorption of each rare earth metal ternary hydrogen storage alloy was determined. One example is _{LaNi 5} Sn _0.6 −
The figure (solid line) shows the pressure-composition isotherm at 120°C for the H system. In the figure, curve A is a hydrogen absorption line, and curve B is a hydrogen release line. In addition, the chain line in the figure is the comparative alloy.
This is a hydrogen absorption/dissociation pressure-composition isotherm diagram _of LaNi _4.4 Al _0.6 at 120°C, where curve C is _the hydrogen absorption line and curve D is the hydrogen desorption line. As is clear from this figure, the alloy of the present invention has improved hysteresis compared to the conventional hydrogen storage alloy shown in the comparative example. In addition, the table below shows the hydrogen storage capacity of each of the above alloys, 25
℃, 40℃ and 120℃ hydride storage pressure and dissociation pressure and the ratio of hydrogen storage pressure (Pa) to hydrogen release pressure (Pd) at 25℃, 40℃ and 120℃,
In other words, it shows the hysteresis index (Pa/Pd) all at once, and the alloys of the present invention (Nos. 1 to 9 and Nos. 15 to 20) have lower hysteresis than the comparative alloys (Nos. 10 to 14). is small and has a large hydrogen storage capacity.

【table】

【table】 [Brief explanation of the drawing]

The figure shows a hydrogen storage/dissociation pressure-composition isotherm curve of the alloy of the present invention in comparison with that of a conventional alloy.

Claims (1)

[Scope of Claims] 1. A rare earth metal ternary hydrogen storage alloy characterized by being represented by the following general formula (). RxNiyMtz...() In the formula, R represents a rare earth metal atom, Mt is a metal atom selected from the group consisting of niobium, tin, and molybdenum, x is a positive number from 1.0 to 2.0, and y is
A positive number between 3.0 and 9.0, z is a positive number between 0.01 and 1.0,
y+z/x>5 or y+z/x<5.