JPH0242893B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a hydrogen storage alloy, and particularly the present invention relates to a zirconium hydrogen storage alloy. (Conventional technology) Hydrogen is an abundant element in terms of resources, and burning it only produces water, so the balance of the ecosystem is not disrupted, and it is easy to store and transport. For these reasons, it is expected to become the main source of secondary energy in future clean energy systems. However, since hydrogen is a gas at room temperature and its liquefaction temperature is extremely low, developing technology to store it has become a major issue. As one method for solving the above problems, a method of storing hydrogen in the form of metal hydride is attracting attention. This method not only allows the same weight of hydrogen to be stored in less than 20% of the volume of commercially available 150-atm hydrogen cylinders, or 80% of the volume of liquid hydrogen, but also improves safety and ease of handling. This is because it is extremely superior in this respect. Now, a material suitable for absorbing hydrogen in the form of metal hydride and then releasing it is a hydrogen storage alloy.
Hydrogen is stored in such alloys, and then the generation or absorption of reaction heat accompanying the generation or decomposition reaction of metal hydrides when hydrogen is released from these alloys can be used to generate heat storage devices, heat pumps, thermal energy, and mechanical energy. The development of a wide range of application systems such as conversion devices is expected. The properties required of a hydrogen storage material are: 1) It should be inexpensive and abundant in terms of resources. 2) It should have a large hydrogen storage capacity. 3) It should have a suitable hydrogen storage/release equilibrium pressure at the operating temperature, and the hydrogen storage pressure should be equal to the storage pressure. The hysteresis, which is the difference with the release pressure, is small. 4) The hydrogen storage and release reaction is reversible and its speed is high. By the way, binary hydrogen storage alloys, especially
ZrV ₂ has a high hydrogen storage capacity, is easy to activate, that is, removes substances that inhibit hydrogenation such as oxide films, adsorbed gas, and attached moisture on the surface of the alloy, and has small hysteresis. It is known as an alloy that has a fast reaction rate and strong resistance to gaseous impurities. However, this alloy produces an extremely stable hydrogen compound, ZrV ₂ H _4.8 , with an equilibrium hydrogen dissociation pressure of 10 ^-8 atm at room temperature, and the hydrogen release requires a temperature of several hundred degrees or more and a pressure of 10 ^-5 atm. It requires a high degree of vacuum and is also as expensive as LaNi ₅ . The Journal of Less-Common Metals was created with the aim of increasing the hydrogen equilibrium pressure and reducing costs while maintaining the above advantages.
73 ( _{1980 ) 329-338} . (Problem to be solved by the invention) Among the above compounds, Zr (Fe _0.75
V _0.25 ) ₂ has an equilibrium hydrogen dissociation pressure of 0.1 atm at 40°C, and a plateau region (a diagram showing the relationship between equilibrium hydrogen pressure and the ratio of the number of hydrogen atoms/number of alloy atoms at various temperatures, that is, P - In the CT diagram, there is no relatively flat part where the equilibrium hydrogen pressure does not change much even if the ratio changes, which is called a plateau region. Therefore, it was an alloy system that could not be used efficiently for system applications such as actual hydrogen storage or heat storage. The purpose of the present invention is to overcome the drawbacks of the alloy system Zr(Fe _1-k V _k ) ₂ . That is, to provide an alloy that has a low equilibrium hydrogen dissociation pressure without a plateau region and has a plateau region and becomes about 1 atm or more in the range of room temperature to 100° C., improves other properties, and is inexpensive. It is in. (Means for Solving the Problems) The alloy of the present invention has an atomic composition with a characteristic formula of Zr _x
A zirconium multi-component hydrogen storage alloy characterized by the formula Ay(Fe _1-k V _k ) ₂ , where A is
At least one element selected from Ti, Nb, and Mo, 0.4≦x≦1.0, 0<y
≦0.6, 0.2≦k≦0.3. (Function) The present inventors investigated the above-mentioned known alloy Zr(Fe _1-k V _k ) ₂ .
When we studied the changes in the properties of hydrogen storage alloys by replacing or adding a portion of Zr with one or more of Ti, Nb, and Mo, we found that, completely unexpectedly, a plateau region was realized, and the plateau pressure increased. The pressure is approximately 1 to 20 atm at room temperature to 100℃, the effective hydrogen release amount is large, the hydrogen storage and release rate is even higher, and the maximum hydrogen storage amount, hysteresis, and ease of activation are better than conventional values. The present invention was completed based on the new findings that it can be maintained and inexpensive. In the alloy of the invention, x is less than 0.4, or
When y is larger than 0.6, the hydrogen storage capacity decreases and P
- In the CT diagram, the intermetallic compound phase (β phase) disappears, the plateau region disappears, and the hysteresis increases. Furthermore, when x increases beyond 1.0, the stoichiometric composition of the Rava phase binary compound collapses, and the amount of hydrogen absorption and release becomes small. Therefore, x
must be 0.4 or more and 1.0 or less, and y must be 0.6 or less. Regarding the value of k, as the value of k becomes smaller than 0.2, the hydrogen storage capacity decreases extremely, and as it becomes larger than 0.3, the plateau region disappears, and the equilibrium hydrogen dissociation pressure decreases extremely, so 0.2≦k≦0.3. There is a need to. Next, a method for manufacturing the alloy of the present invention will be described. Although the alloy of the present invention can be produced by conventionally known methods for producing zirconium-based hydrogen storage alloys, it is most preferable to use the arc melting method. Therefore, a method for manufacturing the alloy of the present invention using an arc melting method will be described below. First, Zr, Fe,
After weighing and mixing the elements V and metal A, they are press-formed into an arbitrary shape, the molded body is charged into an arc melting furnace, heated and melted in an inert atmosphere, and solidified in the furnace. After cooling to room temperature, take it out of the furnace. In order to make this extracted alloy homogeneous, it was charged into a container that can be evacuated, and heated at 1000°C in a high vacuum atmosphere of 10 ^-2 Torr or less.
After being kept in the furnace at ~1100°C for 8 hours or more, it is cooled by putting it into water, or the vacuum container is taken out of the furnace and left to cool. The alloy is then crushed into granules to increase its surface area and increase its hydrogen storage capacity. Example 1 Commercially available Zr, Fe, Ti, Nb, Mo, Ni (all purity 99.9% or higher), V (purity 99.7%), Al (99.4%),
Weigh the appropriate amount of Mm (Mitsuyu Metal: 98.7% rare earth elements), charge it into a copper crucible of a high vacuum arc melting furnace, create an atmosphere of 99.99% Ar in the furnace, and then heat and melt at approximately 2000℃. About 40g, 1st
Samples No. 1 to 9 (alloy materials of the present invention) and No. 1 shown in the table.
Eleven types of alloys (excluding Nos. 10 and 13) of Nos. 11 and 12 (comparative gold materials) were manufactured, respectively. In addition, Mm is La
28.2%, Ce 50.2%, Nd 15.4%, Pr 4.8%, Sm
The composition is 0.1%, Fe 0.8%, Mg 0.3%, and Al 0.2%.

【table】

[Table] Insert each button-shaped sample into a quartz tube,
After holding the sample at 1100°C for 8 hours in a heating furnace under a vacuum of 10 ^-2 Torr using a rotary vacuum pump, the sample was put into water at room temperature and rapidly cooled to perform homogeneous heat treatment. It was then ground to -100 mesh. The method for measuring the activation of the alloy and the amount of hydrogen absorbed and released will be explained with reference to the principle diagram shown in FIG. A hydrogen storage/release reactor 10 made of stainless steel contains 15 g of the pulverized hydrogen storage alloy sample 12, and the reactor 10 is connected to a reservoir 16 via a valve 14. reservoir 1
6 is connected to a hydrogen cylinder 20 via a valve 18 and to a rotary vacuum pump 24 via a valve 22. A pressure transducer 26 and a digital pressure indicator 28 are arranged between the valve 14 and the reservoir 16. Connect the reactor 10 to the vacuum pump 24
Degassed at 40° C. under a vacuum of 10 ⁻² Torr. Next, while cooling the reactor 10 with water at room temperature, the purity was maintained at 99.999% and the pressure was increased.
Hydrogen at 40 atmospheres was introduced into the reactor 10 to start hydrogen storage. After hydrogen storage is almost completed,
After vacuum degassing at 40°C, the operation of pressurizing hydrogen while cooling with room temperature water was repeated until activation was completed. Next, the amount of hydrogen absorption and release was measured as follows. After maintaining the reactor 10 at 40°C, the vacuum pump 24
After operating the valves 14 and 22 to create a vacuum in the reservoir 16 and the reactor 10, open the valves 14 and 22.
Close 22. Open valve 18 and open reservoir 1
Several atmospheres of hydrogen is introduced into the tank 6, the valve 18 is closed, and the pressure P _t1 and the ambient temperature T ₁ K are measured. Next, the valve 14 is opened, hydrogen in the reservoir 16 is introduced into the reactor 10, and the pressure P _e1 when the sample absorbs hydrogen and reaches an equilibrium pressure is measured. Valve 14
is closed, the valve 18 is opened, the hydrogen pressure in the reservoir 16 is increased by several atmospheres, the valve 18 is closed, and the pressure P _t2 and the ambient temperature T ₂ are measured. Open the valve 14 and introduce new hydrogen into the reactor 10, and the pressure when the sample absorbs more hydrogen and reaches equilibrium pressure.
Measure P _e2 . P _to (n is the number of repetitions)
Repeat until the pressure reaches approximately 40 atm. The n-th hydrogen storage amount is calculated as follows. Assuming pressure P, volume V, absolute temperature T of hydrogen gas, number of moles of hydrogen gas M, gas constant R, and correction coefficient Z from ideal gas to real hydrogen gas (function of pressure and temperature), the relationship PV = MZRT. There is. Using this, the n-th reservoir hydrogen pressure P _to , P _eo and the reactor hydrogen pressure (P _e(o-1) ,
P _eo and the ambient temperature T _o at the time of each measurement,
The amount of hydrogen stored for the nth time can be determined from T _(o+1) and the reactor temperature T _r (313K). With the pressure of P _to introduced into the reservoir 16, the reactor 10 (internal space volume V ₁ ) and the reservoir 1
6 (inner volume V ₂ ) is expressed by the _formula
(1) becomes. Mn=1/R ・(P _e(o-1)・V ₁ /Z(P _e(o-1) , T _r )・T _r +P _to・V ₂ /Z(P _to , T _o )・T _o ) ...(1) Next, open the valve 14, and the alloy sample 12 newly absorbs ΔMn moles of hydrogen (in terms of ₂ molecules of H), and the equilibrium pressure
When P _eo is reached, the amount of hydrogen in the above Mn mole is present in the reactor 10 and reservoir 16 as shown in equation (2). Mn=P _eo /R ・(V ₁ /Z (P _eo , T _r )・T _r +V ₂ /Z (P _eo , T _(o+1) )・T _(o+1) ) +ΔMn …(2) Therefore, the amount ΔMn moles of hydrogen occluded in the alloy sample for the nth time is calculated according to equation (3), assuming equations (1) and (2) to be equal. ΔMn=1/R・{(P _to /Z(P _to , T _o )・T _o
−P _eo /Z (P _eo , T _(o+1) )・T _(o+1) )・V ₂ −(P _eo /Z (P _eo , T _r )−P _e(o-1) /Z
(P _e(o-1) , T _r ))・V ₁ /T _r }...(3) Calculate the amount of hydrogen storage each time using equation (3), and calculate the hydrogen storage amount between the hydrogen equilibrium pressure and the hydrogen storage amount of the alloy. relationship can be obtained. Measurement of hydrogen release begins when reservoir 16 and reactor 10 reach an equilibrium hydrogen pressure of approximately 40 atmospheres. The valve 14 is closed, the valve 22 is opened, the hydrogen pressure in the reservoir 16 is reduced by several atmospheres, and the valve 22 is closed. Measure pressure and ambient temperature. Next, the valve 14 is opened, and the hydrogen in the reactor 10 is introduced into the reservoir 16, and some of the hydrogen occluded in the alloy sample 12 is released, and the pressure at equilibrium is measured. This operation is repeated until the reactor 10 is evacuated. The amount of hydrogen released is calculated in accordance with the calculation method for occlusion described above. The relationship between the equilibrium hydrogen pressure during hydrogen release and the hydrogen release amount of the alloy can be obtained. In this way, the relationship between equilibrium hydrogen pressure and composition at isothermal conditions was determined, and the results were used for sample No. 1 in Table 1.
~9 and 11 and 12. Shown in samples No. 11 and 12 in the same table. Samples Nos. 5 and 6 in the same table are materials with known compositions. Sample No. 11 of known composition material for comparison shown in Table 4
Although it has a large maximum hydrogen storage capacity, there is no plateau region and the equilibrium hydrogen dissociation pressure is very low at less than 1 atmosphere. Therefore, the hydrogen release amount, that is, the effective hydrogen release amount between 1 and 30 atmospheres is extremely small, and the material is not suitable as a hydrogen storage alloy. For this reason, the Mitsushi metal alloy (sample No. 12), which is widely known and currently used in system applications such as hydrogen storage devices and heat pumps, was used as a comparison material. As can be seen from Table 1, the invention alloy samples No. 1~
A comparison of No. 9 with known material No. 12 is as follows. 1) All of the alloy samples of the present invention have a plateau region, and the equilibrium hydrogen dissociation pressure is in the range of 0.5 to 6 atm. 2) The maximum hydrogen storage capacity is approximately equal to or higher than that of known materials. 3) The hydrogen absorption rate of all samples is much higher than that of known materials. 4) The hysteresis index is gradually smaller than known materials, except for No. 3, which is close to the limit of the claimed range of composition. 5) Activation of any sample can be completed in one operation and is easier than known materials. Example 2 Sample No. 10 of the alloy material of the present invention and No. 13 of the known comparative alloy material shown in Table 1 are the objects of this example. These samples were prepared using the same raw materials as described in Example 1,
A button-shaped sample was prepared in the same manner, subjected to the same homogeneous heat treatment, and ground into -100 mesh. In this example, the vacuum degassing temperature during activation was 80°C, and the sample storage reactor used to measure the amount of hydrogen absorption and release was maintained at 80°C for samples No. 10 and No. 13. Other activation methods and methods for measuring the amount of hydrogen absorption and release are the same as in Example 1. Although the equilibrium hydrogen dissociation pressure of known comparative material sample No. 13 shown in Table 1 was higher than that of sample No. 11 of the same composition due to the increase in measurement temperature of 80° C., it was still below 1 atm. Hysteresis index, hydrogen absorption rate,
Although the maximum hydrogen storage amount is relatively good, the plateau slope is large and the effective hydrogen release amount is small, so it is not a suitable material as a hydrogen storage alloy. From Table 1, it was found that sample No. 10, which is an alloy material of the present invention measured at a temperature of 80° C., has the following characteristics compared to No. 13, which is a comparative alloy material. 1) The equilibrium hydrogen dissociation pressure is as high as 1.7 atm. 2) It has a plateau region, the slope of the plateau is smaller than the comparative material, and the hysteresis is also smaller. 3) The maximum hydrogen storage capacity is the same, and the effective hydrogen release capacity is large. 4) The hydrogen absorption rate is equally fast. 5) Activation is equally or even easier. (Effects of the invention) Since the alloy of the present invention has the above-mentioned properties,
By using the alloy of the present invention, the following effects can be achieved. 1) All the alloys of the present invention have a plateau region of equilibrium hydrogen pressure, and the dissociation pressure is 0.5 to 6 at 40°C.
Atmospheric pressure is 1.7 atm at 80°C. It is an easy-to-use alloy because the equilibrium hydrogen pressure can be changed from 1 to several atmospheres by changing the alloy composition. 2) Activation can be easily completed with just one operation of vacuum degassing at room temperature and pressurization of hydrogen at 30 atm at room temperature. 3) The maximum hydrogen storage capacity and effective hydrogen release capacity are equal to or higher than those of conventional alloys. 4) The hydrogen absorption and release rate is higher than that of conventional alloys. This allows for quick and repeated use.
Even if the effective amount of hydrogen storage and release is small, the alloy can be used with good overall efficiency. 5) Since the hysteresis is the same or lower than that of conventional alloys, it can be used efficiently with little energy loss even when used repeatedly. 6) Zirconium alloys are originally Mg-based and Ti-based.
The alloy of the present invention has a stronger resistance to gaseous impurities than other rare earth alloys, but the alloy of the present invention is also almost unaffected by impurities such as oxygen, nitrogen, argon, and carbon dioxide. 7) No matter how many times hydrogen absorption and release are repeated, there is virtually no deterioration of the alloy itself. As mentioned above, the zirconium-based hydrogen storage alloy of the present invention has all the performances required as a hydrogen storage material, and in particular, the maximum hydrogen storage capacity, hydrogen storage/release rate, and hysteresis are superior to those of conventional hydrogen storage alloys. has been improved compared to. This alloy is extremely easy to activate, can store large amounts of hydrogen at high density, has completely reversible hydrogen storage and desorption reactions, and has strong resistance to gaseous impurities. It has many advantages compared to alloys. Therefore, the alloy of the present invention exhibits excellent effects not only in heat storage devices and temperature sensors used at room temperature to 100°C, but also particularly in applications such as hydrogen storage/transport and hydrogen separation/purification systems.

[Brief explanation of the drawing]

Figure 1 shows the activation and hydrogen storage of the alloy of the present invention.
FIG. 3 is an explanatory diagram of a method for measuring a release amount. 10...Reactor, 12...Hydrogen storage alloy sample, 1
4...Valve, 16...Reservoir, 18...Valve,
20...Hydrogen cylinder, 22...Valve, 24...Rotary vacuum pump, 26...Pressure transducer, 28...Digital pressure indicator.

Claims (1)

[Scope of Claims] 1. A zirconium-based hydrogen storage alloy characterized in that its atomic composition is represented by the formula Zr _x Ay (Fe _1-k V _k ) ₂ [However, in the formula, A is titanium, Indicates at least one element selected from niobium and molybdenum, 0.4≦x≦1.0, 0<y≦0.6, 0.2
≦k≦0.3].