JPS6372851A - Zirconium-type alloy for hydrogen occlusion - Google Patents

Abstract

PURPOSE:To improve the maximum amount of hydrogen occlusion and hydrogen occluding and releasing velocities of the titled alloy to be obtained and also to improve hysteresis, by specifying a composition of a Zr alloy containing Fe, V, and metal A (at least one element among Ti, Nb, and Mo). CONSTITUTION:The titled alloy has a composition represented by a rational formula ZrXAy(Fe1-kVk)2 by atomic composition ratio, where A is mentioned above and the symbols (x), (y), and (k) stand for 0.4-1.0, >0-0.6, and 0.2-0.3, respectively. Owing to this composition, this alloy is easily activated and is capable of occluding large amounts of hydrogen in high density and also capable of exerting hydrogen releasing and occluding reactions perfectly reversibly and, moreover, it has high gaseous impurity-resisting property. Accordingly, this alloy is suitable for use in hydrogen storage and transportation system, hydrogen separation and purification system, etc., in particular as well as in heat accumulation devices, temperature sensors, etc., used at a temp. between ordinary temp. and about 100 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a hydrogen storage alloy, and particularly the present invention relates to a zirconium-based 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 been a major challenge. As one method for solving the above problems, a method of storing hydrogen in the form of metal hydride is attracting attention. According to this method, it is not only possible to store the same weight of hydrogen in less than 20% of the volume of a commercially available 150-atm hydrogen cylinder, or 80% of the volume of liquid hydrogen.
This is because it is extremely superior in terms of safety and ease of handling.

Now, materials suitable for absorbing hydrogen in the form of metal hydrides and then releasing it are hydrogen storage alloys. Heat storage devices, heat pumps,
The development of a wide range of application systems such as thermal energy/mechanical energy 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 4) The hydrogen absorption/release reaction is reversible and its speed is high.

By the way, binary hydrogen storage alloys, especially ZrV.

has a high hydrogen storage capacity, is easy to activate, that is, removes substances that inhibit hydrogenation such as oxide films on the surface of the alloy, adsorbed gas, and attached moisture, has low hysteresis, and has a high hydrogen reaction rate. It is known as an alloy that has high speed and strong resistance to gaseous impurities. However, this alloy has an extremely low equilibrium hydrogen dissociation pressure of 10-e atm at room temperature.
producing a constant hydrogen compound ZrVJ4.1 at room temperature,
Its hydrogen release requires a temperature of several hundred degrees or more and a vacuum of 10-S atmosphere, and it is also characterized by being as expensive as LaNi. J was created by increasing the hydrogen equilibrium pressure and reducing costs while maintaining the above advantages.
Our own of 1ess-Common Met
als, 73 (1980) 329-338.
Vm)t.

(Problems to be solved by the invention) Among the above compounds, Zr (Fee, '
FsVo, ts)z is still 0 when the equilibrium hydrogen dissociation pressure is 40℃
．． 1 atm, and in the 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, the P-C-T diagram, even if the ratio changes) There is no relatively flat area in which the equilibrium hydrogen pressure does not change much (this is called the plateau region), so this alloy system cannot be used efficiently for actual system applications such as hydrogen storage or heat storage.

The object of the present invention is to improve the alloy system Zr (Fet-i+Vm)
The purpose is to overcome the shortcomings of z. In other words, a low equilibrium hydrogen dissociation pressure with no plateau region can be maintained at room temperature to
The object of the present invention is to provide an alloy that can maintain a pressure of about 1 atm or more in a temperature range of 100° C., improve other mechanical properties, and be inexpensive.

(Means for Solving the Problems) The alloy of the present invention has an atomic composition with a specific formula of Zrx Ay (
It is a zirconium multi-component hydrogen storage alloy characterized by being represented by Fe, -+, Vb)z, where A is Ti
, Nb, and No, and 0.4≦x≦1.0, 0<y≦0
．． 6, 0.2≦k≦0.3.

(Function) The present inventors used the above-mentioned known alloy Zr(Fet-mVm)z
When we studied the changes in the properties of hydrogen storage alloys by replacing or adding a part of Zr with one or more of Ti, Nb, and No, we found that, completely unexpectedly, a plateau region was realized, and the plateau pressure increased. is approximately 1 to 20 atm at room temperature to 100°C, the effective amount of hydrogen released is large, the hydrogen storage and release rate is even higher, and the maximum hydrogen storage amount, hysteresis, and ease of activation are the same as conventional values. The present invention was completed based on the new findings that it is possible to maintain the quality of the product and to reduce the cost.

In the alloy of the present invention, X is less than 0.4 or y is 0.
．． When it is larger than 6, the hydrogen storage capacity decreases, the intermetallic compound phase (β phase) disappears in the PCT diagram, the plateau region disappears, and the hysteresis becomes large. Furthermore, when X increases beyond 1.0, the stoichiometric composition of the Rava phase pseudo binary compound collapses, and the amount of hydrogen absorption and release becomes small. Therefore, X needs to be 0.4 or more and 1.0 or less, and y needs to be 0.6 or less. In addition, as the value of k becomes smaller than 0.2, hydrogen absorption Ml decreases extremely, and 0.3
As it becomes larger, the plateau region disappears and the equilibrium hydrogen dissociation pressure decreases extremely, so it is necessary to satisfy 0.2≦k≦0.3.

Next, a method for producing the alloy of the present invention will be described.

The alloy of the present invention can be produced by conventionally known methods for producing zirconium-based hydrogen storage alloys, but
The most preferred method is arc melting. Therefore, a method for producing the alloy of the present invention using an arc melting method will be described below. First, the elements Zr, Fe, V, and metal A are weighed and mixed, and then press-formed into an arbitrary shape.
This compact is charged into an arc melting furnace, heated and melted in an inert atmosphere, solidified in the furnace, cooled to room temperature, and then taken out of the furnace. The alloy is charged into a container that can be evacuated, and 10-
”1000 to 110 in a high vacuum atmosphere below Torr.
After being kept in the furnace at 0° 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 expand its surface area and increase its hydrogen storage capacity.

Example 1 Commercially available Zr, Fe, Ti, Nb, Mo, Ni
(all purity 99.9% or more), ■ (purity 99.7
%), AI (99,4%).

An appropriate amount of M+s (Misos metal: 98.7% of rare earth elements) was weighed during the process, and it was charged into a copper crucible of a high vacuum arc melting furnace, and after making the inside of the furnace an atmosphere of 99.99% Ar, it was heated to about 2000°C. By heating and melting, approximately 40 g of five types of alloys, samples 1 to 3 and Arashi 5 and 6 shown in the table, were produced.

In addition, Mat, La 2B, 2%, Ce 50.2
%.

Nd 15.4%, Pr 4.8%, Sm 0.1
%, FeO,8%, MgO03%, Aj! 0
．． It has a composition of 2%.

Each button-shaped sample was placed in a quartz tube and kept at 1100°C for 8 hours in a heating furnace under a vacuum of 10-” Torr using a rotary vacuum pump, and then placed in water at room temperature. Homogeneous heat treatment with rapid cooling was applied.After that-
It was crushed into 100 pieces.

The method of activating the alloy and measuring the amount of hydrogen absorbed and released will be explained with reference to the principle diagram shown in FIG. 1.

A hydrogen storage/release reactor 10 made of stainless steel contains 15 g of the pulverized hydrogen storage alloy sample 12,
The reactor 10 is connected to a reservoir 16 via a valve 14. The reservoir 16 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 between valve 14 and reservoir 16. Digital pressure indicator 28
is installed.

The reactor 10 is connected to a vacuum pump 24 to provide a 10-” Tor
Next, the reactor 10 was degassed at 40° C. under a vacuum of R, and hydrogen with a purity of 99.999% and a pressure of 40 atm was introduced into the reactor 10 while cooling it with water at room temperature to start occluding hydrogen. .

After hydrogen occlusion was almost completed, vacuum degassing was performed again at 40° C., and 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 the reactor 10 is maintained at 40° C., the vacuum pump 24 is operated, and the valve 14.22 is opened to evacuate the reservoir 16 and the reactor 10, and then the valve 14.22 is closed. Open the valve 18 to supply hydrogen at a diffused pressure to the reservoir 16, then close the valve 1B and set the pressure Ptl and the ambient temperature TIK.
Measure 0 then open valve 14 and drain reservoir 16.
The hydrogen in the sample is introduced into the reactor 10, and the pressure pe1 when the sample absorbs hydrogen and reaches an equilibrium pressure is measured. Valve 1
4 and open the valve 18 to increase the hydrogen pressure in the reservoir 16 to a diffused pressure, close the valve 18, and measure the pressure Pt2 and the ambient temperature T2.

opening valve 14 to introduce new hydrogen into reactor 10;
The pressure pez when the sample further absorbs hydrogen and reaches an equilibrium pressure is measured. This operation is repeated until Ptn (n is the number of repetitions) reaches approximately 40 atm, and the n-th hydrogen storage amount is calculated as follows.

Assuming pressure P1 volume V, absolute temperature T of hydrogen gas, number of moles of hydrogen gas M, gas constant R1 correction coefficient Z (function of pressure and temperature) from ideal gas to real hydrogen gas, there is the relationship PV-MZRT. . Using this, the n-th reservoir hydrogen pressure PEn, Pen and the reactor hydrogen pressure P6(n-1)+
pen and the ambient temperature Tn at the time of each measurement.

The amount of stored hydrogen at the nth time can be determined from T (n+x) and the reactor temperature Tr (313K).

With the pressure of Ptn introduced into the reservoir 16, the reactor 10 (internal space volume V1) is taken into the reservoir 16 (internal volume V1).
The hydrogen gas Mn mole in 2) is expressed by formula (1).

Next, the valve 14 is opened, and the alloy sample 12 is newly charged with hydrogen ΔM.
When n moles (K in terms of OX molecules) are absorbed and the equilibrium pressure Pen is reached, the amount of Mn moles of hydrogen is present in the reactor 10 and the reservoir 16 as shown in equation (2).

Therefore, the amount ΔMn moles of hydrogen occluded in the alloy sample for the nth time is calculated according to equation (3), with equations (11 and (2) being equal).

The hydrogen storage amount for each time is calculated using equation (3), and the relationship between the hydrogen equilibrium pressure and the hydrogen storage amount of the alloy can be obtained.

Measurement of the amount of hydrogen released begins when the equilibrium hydrogen pressure in the reservoir 16 and reactor 10 is approximately 40 atmospheres. The valve 14 is closed, the valve 22 is opened, the hydrogen pressure in the reservoir 16 is reduced to a diffused pressure, and the valve 22 is closed. Measure the pressure and ambient temperature. Then open the valve 14 and open the reactor 10.
The hydrogen contained in the alloy sample 12 is introduced into the reservoir 16, a portion 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 becomes vacuum, and the amount of hydrogen released is calculated in accordance with the calculation method for the storage case 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 the equilibrium hydrogen pressure car composition at isothermal conditions was determined, and the results were used for samples &1 to 3 and 5.6 in Table 1.
Sample floors 5 and 6 shown in the same table are materials with known compositions.

Sample No. 5, which is a material with a known composition for comparison shown in Table 1, has a large maximum hydrogen storage capacity, but has no plateau region and has a very low equilibrium hydrogen dissociation pressure of less than 1 atm. The amount of hydrogen released, that is, the effective amount of hydrogen released, becomes extremely small.
It is not a suitable material as a hydrogen storage alloy.

For this reason, as a comparative material, Mitsushi metal alloy (sample 1lkL6), which is widely known and is currently being used for system applications such as hydrogen storage devices and heat pumps, was used.

As can be seen from Table 1, the alloy samples 1 to 3 of the present invention are compared with the known material No. 6 as follows.

1) All of the alloy samples of the present invention have a plateau region,
Equilibrium hydrogen dissociation pressures range from 1 to 3 atmospheres.

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 much smaller than known materials, except for positive 3, which is close to the claimed limits of composition.

5) Activation of any sample can be completed in one operation and is easier than known materials.

Example 2 Sample No. 4 of the alloy material of the present invention and known comparative material No. 7 shown in Table 1 are used as objects of this example.

These samples are the same raw materials as described in Example 1.

A button-shaped sample was melted in the same manner, subjected to the same homogeneous heat treatment, and ground to -100 mesh.

In this example, the vacuum degassing temperature during activation was set to 80°C, and the sample storage reactor used to measure the amount of hydrogen absorption and release was maintained at 80°C for samples 11h4 and N117. Other activation methods and hydrogen storage/release amount measurement methods are the same as in Example 1.

Although the equilibrium hydrogen dissociation pressure of material No. 7 of the known composition shown in Table 1 was higher than that of sample No. 5 of the same composition due to an increase in the measurement temperature of 80° C., it was still less than 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. 4, which was an alloy of the present invention measured at a temperature of 80° C., had the following characteristics compared to comparative material No. 7.

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) 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 characteristics, the following effects can be achieved by using the alloy of the present invention.

1) All the alloys of the present invention have a plateau region of equilibrium hydrogen pressure, and the dissociation pressure is 1 to 3 atm at 40°C and 1 atm at 80°C.
．． The equilibrium hydrogen pressure is 1 by changing the alloy composition, which is 7 atm.
It is an easy-to-use alloy because it can change the pressure to several atmospheres.

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/release rate is higher than that of conventional alloys. This means that it can be used repeatedly and quickly, and even if the effective hydrogen absorption/release amount is small, the alloy has good usage efficiency as a whole.

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 inherently more resistant to gas-like impurities than shaft-based, Ti-based, and rare earth-based alloys, but the alloy of the present invention also resists oxygen, nitrogen, and argon.

There is almost no effect from impurities such as carbon dioxide gas.

7) No matter how many times hydrogen absorption and release are repeated, there is virtually no deterioration of the alloy itself.

The zirconium-based hydrogen storage alloy of the present invention has all the performances required as a hydrogen storage material as described above, 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 can be used not only for heat storage devices and temperature sensors used at room temperature to 100°C, but also for hydrogen storage and transportation.
Demonstrates outstanding effects in applications such as hydrogen separation and purification systems.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a method for activating the alloy of the present invention and measuring the amount of hydrogen absorption and release. 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.

Claims (1)

[Claims] 1. In terms of atomic composition, the specific formula is Zr_kAy(Fe_1_-
_kV_k)_2 [However, in the formula, A represents at least one element selected from titanium, niobium, and molybdenum, and 0.4≦x≦1 .0, 0<y≦0.6
, 0.2≦k≦0.3].