JPS6227534A - Zirconium alloy for hydrogen storage - Google Patents

Abstract

PURPOSE:To obtain the titled alloy capable of occluding and releasing a large quantity of hydrogen easily, by melting Zr, Mn, V, Fe at specified ratios and alloying them. CONSTITUTION:Zr, Mn V, Fe are weighed respectively and mixed, press formed to arbitrary shape, then the green compact is melted by arc electric furnace of inert gas atmosphere, to prepare Zr alloy having compsn. shown by the following formula. Compsn. of Zr alloy is shown by Zrx(Mn1-y-zVyFez)2 under quantity relation of 0.5<x<1.5, 0<y<1.0<z<1 further y+z<=1. The alloy is solidified in electric furnace of inert gas atmosphere, cooled as it is to room temp., then taken out therefrom, put into vacuum vessel to heat and hold it at 1,000-1,100 deg.C for >=8hr, then cooled and milled to increase surface area. The titled alloy capable of occluding and releasing a large quantity of hydrogen easily is obtd.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a zirconium-based hydrogen storage alloy, and more specifically, it can store a large amount of hydrogen in the form of a hydride, and can easily store hydrogen with a slight amount of heating or depressurization. , and can quickly release hydrogen, and the difference between the hydrogen storage pressure and release pressure,
That is, the present invention relates to a new zirconium-based hydrogen storage alloy that has extremely small hysteresis and is extremely useful in practice.

(Conventional technology) Hydrogen is an abundant raw material, water, and has no resource constraints; its combustion products are clean, such as water; and it is easy to store and transport. It is attracting attention as a new energy source.

However, since hydrogen is a gas at room temperature and has an extremely low liquefaction temperature, the development of technology to store it has long been a major challenge. One way to solve this problem is to store hydrogen in the form of metal hydrides. This system can store the same weight of hydrogen in less than 20% of the volume of a commercially available 150-atmosphere cylinder, or 80% or less of liquid hydrogen. Therefore, hydrogen storage methods using metal hydrides are extremely superior to conventional methods in terms of safety and ease of handling.

Now, the hydrogen absorption/desorption reaction between metals or alloys is reversible, and not only is it used to store hydrogen, but a considerable amount of reaction heat is generated or absorbed during the reaction, and the hydrogen storage/desorption pressure is Hydrogen storage devices and hydrogen transport devices utilize temperature dependence.

The development of a wide range of applied systems such as hydrogen purification equipment 1 heat storage devices, heat pumps, and thermal energy/mechanical energy conversion devices is expected.

The properties required for such a hydrogen storage material are as follows:
It is inexpensive and has abundant resources, is easy to activate, has a large hydrogen storage capacity, has a suitable hydrogen storage/release equilibrium pressure at the operating temperature, and has bisteresis, which is the difference between the storage pressure and release pressure. These include its small size, reversible hydrogen absorption and desorption reactions, and its high speed.

Typical known hydrogen storage materials include magnesium-nickel alloy, rare earth-nickel alloy, and titanium-nickel alloy.
Iron-based alloys, zirconium-manganese alloys, and the like are known. However, among these alloys, magnesium-nickel alloy 2, for example Mg2Ni, has a large hydrogen storage capacity per unit weight, but has a high hydrogen storage and release temperature, so even if this alloy is multi-component, it is still sufficient as a hydrogen storage material. A product with such performance has not yet been obtained. Rare earth-nickel alloys, such as LaNi5, have excellent hydrogen storage and desorption properties, but their biggest drawback is that lanthanum is expensive. Titanium-iron alloys, such as TiFe, are difficult to hydrogenate in the initial stage, requiring high temperatures and pressures (450°C, hydrogen pressure of 50 atm) for activation treatment, large hysteresis, and repeated hydrogen absorption and release. The disadvantage is that the hydrogen storage capacity decreases over time. TiFe, manganese, niobium and oxygen.

An alloy with improved initial activity by adding small amounts of sulfur and the like has been discovered, but it still does not have sufficient performance as a hydrogen storage material. ZrMn2 has high initial activity, but has the disadvantage of large hysteresis.

(Problems to be Solved by the Invention) Each of the above-mentioned alloys has unique characteristics, but they generally have problems such as a small amount of hydrogen storage and large hysteresis. At present, an alloy that satisfies all of the above-mentioned conditions required as a material has not yet been found.

(Means for Solving the Problems) The purpose of the present invention is to provide an alloy that solves the various drawbacks and problems of conventional hydrogen storage alloys, and provides the alloy described in the claims. The alloy of the present invention, which can achieve the above object by
A dik:I-based hydrogen storage alloy represented by e z ) 2, where x+y and 2 are each 0.5
< 1 < 1.5 y O < 7 < 1 + 0
(Z<1 and y+z≦1.

The present inventors conducted research to eliminate the drawbacks of the conventional hydrogen storage alloy and found that an alloy composed of Zr l Mn t V and Fe possesses all the properties required as a hydrogen storage material. The present inventors have discovered that the alloy is novel and extremely useful as a hydrogen storage alloy, and have now completed the present invention.

General formula Zrx of the zirconium hydrogen storage alloy of the present invention
The reason why X1F and 2 in (In 1-y-z Vy Fez ) 2 are determined as described above is as follows.

When X is larger than 1.5, disproportionation tends to occur thermodynamically, and ZrH2, which does not dissociate unless the temperature is high, is generated, resulting in a decrease in the amount of hydrogen storage and release. On the other hand, if X is smaller than 0.5, initial activation will be difficult and the hydrogen storage capacity will decrease.
Moreover, it becomes difficult to release the occluded hydrogen, and smooth release of hydrogen cannot be achieved unless the temperature is raised or heated under reduced pressure or vacuum.
(X (needs to be 1,5). When y is 1 or more, the hydrogen release condition is around room temperature and about 10-8 atm, making it difficult to handle as a hydrogen storage material; on the other hand, y = O
When the general formula is ZrX(Mn, -, Fe2)2, the dissociation pressure tends to increase and becomes a pressure that can be used as a hydrogen storage material. <I need to do it. For example, Zr
In a known alloy with a composition of Mn2, the hydrogen storage pressure is 150°C.
The hydrogen release pressure is about 0.56 atm, and the hysteresis is about 0.8 atm. The large hysteresis means that hydrogen storage and release operations are required.
The hydrogen storage alloy or its metal hydride must be heated and cooled with a large temperature difference, or the hydrogen must be pressurized or depressurized with a large pressure difference, to effectively improve the hydrogen storage capacity and hydrogenation reaction. Not available. When Z=1, the hydrogen storage capacity decreases and the hydrogen release conditions approach 10 −8 atm near room temperature, making it difficult to handle as a hydrogen storage material. When z=0, the general formula is Zr
(In, -yVy) 2 and has characteristics that can be used as a hydrogen storage material.

An alloy in which X, y and 2 are within the scope of the claims of the present invention, such as Zr(Kn, 8V,, Fe, 1) 2, has a hydrogen storage capacity of about 0.07 atm at 100°C and a hydrogen release pressure of about 0. ．．
05 atm, and the hysteresis is extremely small.

In this way, the zirconium-based hydrogen storage alloy of the present invention is
This is a new alloy developed for the first time, and it has all the properties required as a hydrogen storage material.In particular, the hysteresis of hydrogen storage and release pressure is significantly improved compared to conventional hydrogen storage alloys. and hydrogen storage capacity as a hydrogen storage alloy.

This makes it possible to effectively utilize the reaction heat associated with hydrogen storage and release. Moreover, the activation of the hydrogen storage/release reaction is easy, the reaction rate is extremely fast, and a large amount of hydrogen can be stored with high density, and the performance of the alloy does not deteriorate even after repeated hydrogen storage/release. This makes it an extremely useful hydrogen storage material.

Although the alloy of the present invention can be produced by conventionally known methods for producing hydrogen storage alloys, it is most preferable to use the arc melting method. Next, a method for manufacturing the alloy of the present invention using an arc melting method will be described.

After weighing and mixing Zr + Mn r V and Fe, they are press-molded into an arbitrary shape, and this molded body is charged into an arc melting furnace and heated and melted in an inert atmosphere.
After being solidified in the furnace and cooled to room temperature, it is taken out of the furnace. In order to make the extracted alloy homogeneous, it was charged into a container that can be evacuated and kept in a furnace at 1000-1100℃ for more than 8 hours under a high vacuum atmosphere of 10'l'orr or less. , the vacuum container is taken out of the furnace and left to cool, or the vacuum container is placed in water and cooled. After that, in order to increase the surface area of the alloy and increase its hydrogen storage capacity,
Crush into granules.

Next, the present invention will be explained with reference to examples.

Example 1 An appropriate amount of commercially available Zr*Mn, V + Fe was weighed,
This was charged into a copper crucible of a high vacuum arc melting furnace, and after creating a 99.99% argon atmosphere in the furnace, approximately 2000
Five types of button-shaped alloy ingots having the following atomic compositions of about 402 were produced by heating and melting at a temperature of about 402°C. That is, Zr(M
n, 8”0.I Feo,, ) 2 r Zr(M
n. ,4vO,i Feo,5) 2.

Zr (MnO,aVo,sFe0.5)
21 Zr (Mn0.a VO,5Fe O,j
) 2.

It is ZrMn2. Each button-shaped sample was placed in a quartz tube and heated to 10-2 TOrr using a rotary pump.
After being held at 1100°C for 8 hours in a heating furnace under a vacuum of
A homogeneous heat treatment was performed in which the sample was taken out of the quartz tube and quenched in water. It was then broken into three or fewer fins. 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.

The pulverized hydrogen storage alloy sample 12 of 15 gr is stored in the stainless steel hydrogen storage/release reactor 10, and the reactor IO is connected to the reservoir 16 through the valve 14.
is connected to. The reservoir 16 is connected to a hydrogen cylinder 20 via a pulp 18 and to a rotary vacuum pump 24 via a fuel valve 22. A pressure transducer 26 between the pulp 14 and the reservoir 16. A digital pressure indicator 28 is provided.

The reactor 10 is connected to the vacuum pump 24 and the pressure is increased to 10-2 Tor.
Degassed at 150° C. under vacuum of r. Next, while cooling the reactor 10 with water at room temperature, hydrogen with a purity of 99.999% and a pressure of 30 atmospheres was introduced into the reactor to start occlusion of hydrogen. After hydrogen occlusion was almost completed, the operation of vacuum degassing at 150° C. and then 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 the reactor 10 is maintained at 100° C., the vacuum pump 24 is operated, the valves 14.22 are opened to evacuate the reservoir 16 and the reactor 10, and the valves 14.22 are closed. The valve 18 is opened to introduce diffused pressure hydrogen into the reservoir 16, the pulp 18 is closed, and the pressure PH and the ambient temperature T1 are
Measure. Next, the valve 14 is opened, hydrogen in the reservoir is introduced into the reactor 10, and the pressure pe1 when the sample absorbs hydrogen and reaches an equilibrium pressure is measured. Close the valve 14 and open the valve 18 to increase the hydrogen pressure in the reservoir 16 by several atmospheres, close the valve 18, and measure the pressure Pt2 and the ambient temperature 2. Open valve 14 to turn reactor lO
new hydrogen is introduced into the sample, and the pressure P82 is measured when the sample absorbs more hydrogen and reaches an equilibrium pressure. This operation is repeated until Ptn (n is the number of repetitions) reaches approximately 40 atm. The n-th hydrogen storage amount is calculated as follows.

Assuming pressure P1 volume V, absolute temperature of hydrogen, number of moles of hydrogen gas M, gas constant R2 correction coefficient from ideal gas to real hydrogen gas 2 (function of pressure and temperature), PV = MZPT (1)
There is a relationship between Utilizing this, the hydrogen pressure Ptn·pen of the n-th oxidizer and the hydrogen pressure P of the reactor. (n-1)1
Pen and ambient temperature at the time of each measurement TB +T
The amount of hydrogen absorbed for the nth time can be determined from the temperature Tr of the n+1+ reactor.

With the pressure of Ptn introduced into the reservoir 16, the reactor 10 (internal space volume V+) is taken and the reservoir 16 (content fi
Hydrogen gas M in V2)! 1 mole is expressed by formula (2).

Next, the valve 14 is opened, and the alloy sample 12 is newly charged with hydrogen ΔM.
When n moles (in terms of H2 molecules) are absorbed and the equilibrium pressure pen is reached, the above M. The molar amounts of hydrogen are present in reactor 1° and reservoir 16 as follows:

+2M (3) Therefore, the amount of hydrogen occluded in alloy sample 12 at the nth time ΔM
11 moles is calculated as follows, assuming that (2> and equation (3) are equal).

The hydrogen storage amount for each time is calculated using equation (4), and the relationship between the hydrogen equilibrium pressure and the hydrogen storage amount of the alloy can be obtained. Measuring the amount of hydrogen released The reservoir 16 and reactor 10 are approximately 4
Start when the equilibrium hydrogen pressure reaches 0 atmospheres. Valve 1
4, open the valve 22, reduce the hydrogen pressure in the reservoir 16 by several atmospheres, and close the valve 22. Measure pressure and ambient temperature. Next, the valve 14 is opened to introduce the hydrogen in the reactor 10 into the reservoir 16, allowing a portion of the hydrogen occluded in the alloy sample to be 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 hydrogen equilibrium pressure in 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 are shown in Table 1. Sample 141 in the same table
, 2, 3.4 are alloys of the present invention, and sample Arashi 5 is a conventional alloy.

Table 1 Further, as an example, the equilibrium hydrogen pressure-composition crosstalk of sample %1 is shown in FIG. Curve 2 in the figure is the equilibrium hydrogen pressure-composition isotherm of a conventional alloy having a composition of zrMn2. As is clear from Table 1 and FIG. 2, the alloy of the present invention has a larger hydrogen storage capacity than the conventional alloy, and the hysteresis has been significantly improved.Example 2 Commercially available Zr + Mn + V An appropriate amount of +Fe was weighed out, and four types of alloys having the following atomic compositions were melted in the same manner as in Example 1. That is, zrO,9("0.8VO,I Fe,
,)2' zr(MnO,8VojFeo,j”21
Zr,2(Mn,,8V,,Feo,,)2 + Zr
It is Mn2. The button-shaped sample thus obtained was held at 1100°C for 8 hours under a vacuum of 10'' Torr using a rotary pump, and then subjected to homogeneous heat treatment by quenching it in water at room temperature, and then crushed into three or less pieces. Activation treatment was carried out. Next, in the same manner as in Example 1, the relationship between equilibrium hydrogen pressure and composition at isothermal conditions was determined.

These results are shown in Table 2.

In Table 2, samples 1', 6, 7, and 8 are alloys of the present invention, and sample 9 is a conventional alloy. As is clear from Table 2, the alloy of the present invention has a hydrogen storage capacity equal to or greater than that of the conventional alloy.

(Effects of the present invention) Since the alloy of the present invention has the above-mentioned characteristics, the following effects can be achieved by using the alloy of the present invention.

■Hydrogen storage capacity is greater than that of conventional alloys.

■ Difference between hydrogen storage pressure and release pressure! l] Since the hysteresis is extremely small compared to conventional alloys, hydrogen storage capacity and reaction heat can be used effectively.

■ Activation is easy, hydrogen storage and release rates are high, and are comparable to conventional alloys.

■ No matter how many times hydrogen is absorbed and released, there is virtually no deterioration of the alloy itself.

■ There is little influence from impurities such as acid binders, nitrogen, argon, and carbon dioxide gas.

As described above, the alloy of the present invention has all the various performances required as a hydrogen storage material, and in particular, the hydrogen storage capacity and hysteresis are significantly improved compared to conventional zirconium alloys. This alloy has many advantages over conventional alloys, such as being easy to activate, storing hydrogen at a high density, and hydrogen storage and desorption reactions being completely reversible. Therefore, it is more effective in applications such as hydrogen storage alloys, getter materials under reduced pressure, and system applications that utilize the reaction heat associated with hydrogen storage and release reactions.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the activation of the alloy of the present invention and the method for measuring the amount of hydrogen absorbed and released. Figure 2 is the equilibrium hydrogen pressure-composition diagram of the alloy of Example 1 and the conventional alloy for the alloy of the present invention. It is. 10...Reactor, 12...Hydrogen storage alloy sample, 1
4...Valve, 16...Reservoir, 18...Valve, 20...Hydrogen cylinder, 22...Valve, 24
...Rotary complete vacuum pump, 26...Pressure transducer, 28...Digital pressure indicator. Patent applicant: Nippon Yakin Kogyo Co., Ltd. Agent: Patent attorney Mura 1) Masaru Oil quantity
Patent attorney Takuya Hatano Figure 2

Claims (1)

[Claims] General formula Zr_x(Mn_1_-_y_-_zV_yFe
_z) A zirconium-based hydrogen storage alloy represented by _2. However, in the formula, x, y, z are each 0.5<x<1.5
, 0<y<1, 0<z<1 and y+z≦1.