JP2560566B2 - Method for producing hydrogen storage alloy - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hydrogen storage alloy.

[0002]

2. Description of the Related Art A technique has been developed in which hydrogen is occluded in a certain metal or alloy to be stored or transferred in the form of a metal hydride, and as its application, hydrogen refining, a heat pump, or a member of a heating and cooling system. There is. In this case, when the metal hydride absorbs and releases hydrogen, it always generates heat and absorbs heat. Therefore, it can be used for a heat exchange device or a heat pump by paying attention to this property. As a combination of alloys that have been announced as hydrogen storage alloys and have been partially put into practical use, Mg-Ni, Mg-Cu, Ca-Ni, Fe-
Ti, Ti-Mn, La-Ni, misch metal-Ni
A large number of alloys in which a part of this is replaced with another metal have been reported with the above as the main basic component. For example, Mg ₂
Ni _0.75 Cr _0.25 , Ca _0.7 Mn _0.3 Ni ₅ , LaNi
_4.7 Al _0.3 , TiFe _0.8 Mn _{0.2 and the} like are known. Generally speaking, one or more metals selected from a group formed of Mg, Ca, La, misch metal, Ti, etc. and Ni, Al, V, Cr, Fe, Co, Zn, C.
It is produced by alloying one or more metals selected from the group consisting of u and Mn. In order to produce a hydrogen storage alloy, different kinds of raw materials are melted in a high frequency induction furnace or an arc light type high temperature melting furnace. The high-frequency induction furnace is suitable for mass production, but among the raw material metals, Mg, Ca, A
Since many such as 1 have a large vapor pressure and a strong affinity with oxygen, the inside of the furnace must be adjusted to an inert atmosphere with Ar gas or the like to prevent metal oxidation. When the material metals are melted and mixed with each other, and the alloy reaction sufficiently proceeds at a high temperature so that all materials have a desired alloy composition, the material is cast into a mold in a non-oxidizing atmosphere to be ingot. The obtained ingot is heat-treated to complete the alloy and then crushed in a crusher in a non-oxidizing atmosphere to obtain a hydrogen storage alloy powder having a desired particle size.

On the other hand, the desired alloy composition remains as a solid without melting.
Recently, the technology to obtain the information has been in the spotlight. This is one
Generally called the mechanical alloying method, in the 1970s
By Benjamin of American Inco Company (INCO)
High energy ball mill (atlas
Give mechanical energy to metal powder by
Dispersing ultrafine particles by repeating cold pressing and fracture
Is the law. For the principles of mechanical alloying,
The powder is first forged by a high-impacting milling and biased.
Particles that are flattened and flaky and then work-hardened are destroyed or peeled.
Cold forging is repeated (kneading), then between alloy components
The lamella structure develops and the crystal grains suddenly become finer.
Are finely dispersed in the other particle, and finally the particle shape is equiaxed
It is said that the shape will be randomized. M Wai
Song and Ia Ivanov using a planetary ball mill
The Mg and Ni powders are combined by the mechanical alloying method.
The experimental results of monetization are shown in Hydrogen Energy magazine (Hydro
gen Energy vol10 No.3 P169-178, 1985).
You. In this report, the acceleration of the planetary ball mill is 6.1G.
And Ni is a carbon type and Ar gas atmosphere is used.
Various hydrogen was added to the sample obtained by mixing for 30 minutes in the atmosphere.
We have been comparing and comparing the products with oxidization treatment by X-ray diffraction.
You. As a result, the hydrogenation was repeated from 1 to 58 times.
Of the samples, the one with the least hydrogenation number is Mg₂ Ni, fine
Detects that a certain amount of MgO, Mg, Ni phases are mixed
Was subjected to heat treatment (annealing) and hydrogen
For those with a large number of chemicals, Mg and Ni are mostly Mg₂Ni
It was recognized that the heat treatment was more than the repeated hydrogenation.
The effect of the rationale is more strongly recognized, and it may be
For the first time, we have reported a method for producing hydrogen storage alloys.

[0004]

Among the conventional techniques, the production of hydrogen storage alloys by melting requires a considerably high level of technique and well-controlled equipment. For example, when producing Mg ₂ Ni, the vapor pressure of Ni is 2057 mmHg at 10 ° C,
It fluctuates at a high level of 2732 mmHg at 760 ° C, while M
Similarly, g also varies from 743 mmHg to 1107 mmHg. Ca also fluctuates from 983 mmHg to 1487 mmHg,
It is very difficult to raise the temperature in the furnace while maintaining the balance of these vapor pressures. On the other hand, in view of the general principle of melting, the degree of solid solubility of both components affects the difficulty of the alloy, but the most important problem is the difference between the density and the melting point of both components. That of Ni is 8.90 g / cm ³ , 1455 ° C.,
Mg is 1.74 g / cm ³ , 650 ℃, Ca is 1.55 g / c
m ³ , 850 ° C. Therefore, it is clear from this alone how difficult the alloying of Mg or Ca and Ni is. On the contrary, La has a density of 6.15 g / cm ³ and a melting point of 8
The temperature is 26 ° C., and the difficulty is reduced even if the density is close to that of Ni, but rare earth elements are generally valuable resources and expensive. A major problem when alloying Mg and Ni is that the vapor pressure of Mg reaches almost 25 atm near the melting point of Ni, and it is difficult to avoid evaporation of Mg from the molten metal due to this vapor pressure. Ni is excessive, and a part of the product becomes MgNi ₂ which does not form hydride. To prevent this, if Mg is excessively blended from the beginning, for example, the chemical formula is Mg _2.35.
Although expressed by Ni, the actual condition is a cause of including free Mg simple substance such as Mg ₂ Ni + Mg _0.35 .

How this is related to the characteristics of the hydrogen storage alloy will be described with reference to FIGS. 12 and 13. FIG. 12 is a pressure-composition isotherm diagram (hereinafter referred to as “PCT diagram”) of the hydrogen storage alloy Mg _2.35 Ni produced by the melting method, in which the hydrogen pressure P (unit is MPa) is taken on the vertical axis and the horizontal axis is taken. The atomic ratio H / M of hydrogen gas and metal is taken as a constant temperature (350
This is a diagram showing the behavior of the atomic ratio associated with the occlusion and release of hydrogen gas at (° C). In the figure, when the hydrogen pressure reaches near 0.5, the curve clearly divides into a range A that moves to the right following a gentle slope for both storage and release, and a range B that moves to the right almost horizontally. The storage and release of hydrogen by Mg alone is shown, and the range B shows the storage and release of hydrogen by Mg ₂ Ni. In other words, the fact that the range A is recognized indicates that there is Mg that binds to hydrogen gas, and the affinity for hydrogen is far inferior to Mg ₂ Ni.
Indicates that it is contained in the alloy and deteriorates the function required as a hydrogen storage alloy.

FIG. 13 is a high-pressure thermal differential analysis diagram (hereinafter referred to as “DTA diagram”) of the same sample, in which the vertical axis represents temperature, the horizontal axis represents time, and hydrogen at a constant pressure (1.1 MPa) is shown. Curve C shown by measuring the temperature of Mg _2.35 Ni enclosed in the container when the container was enclosed in a closed container and heated from the outside to a maximum temperature of 500 ° C or cooled from 500 ° C, and this sample was compared. Therefore, the curve D showing the temperature difference between the standard sample (alumina) sealed in the container and the temperature difference is shown. Since the hydrogen storage alloy generates heat when storing hydrogen gas and absorbs it when releasing hydrogen gas, curve D also has a downward peak associated with release during heating and an upward peak associated with storage during cooling. However the point P, Q, that this peak as clearly seen in R double peak及至not only sharp point is abnormal refraction point near the peak Mg ₂ Ni and M
In addition to the phase change of g ₂ NiH ₄ , there is also a phase change of Mg and MgH ₂ . This is M under the same hydrogen pressure
It occurs when g is dissociated on the higher temperature side than Mg ₂ Ni. In any case, there is a problem in that it is unavoidable that the hydrogen storage alloy produced by the melting method is not only difficult to produce, but also contains a component that causes a decline in function.

On the other hand, it has been suggested that an attempt to obtain Mg ₂ Ni by a so-called mechanical alloying method without using melting is technically possible. However, it was found by repeating the hydrogenation and dehydrogenation of the alloy of the sample while maintaining the temperature at 300 ° C. under the condition of hydrogen pressure of 0.7 MPa. The existence cannot be extinguished, and a heat treatment is carried out at a hydrogen pressure of 0.25 to 0.85 MPa for a temperature of 270 to 300 ° C. for 2 months,
Only after the hydrogenation treatment was repeated 58 times, it was confirmed that almost all the amount became Mg ₂ Ni. I think that the mechanical alloying method is now translated into Japanese as a mechanical alloying method, but at the current technological level, it has not been confirmed that the alloying of single dissimilar metals has been reached, and it has It is appropriate to evaluate that the oxides of the same system are dispersed ultrafinely or the intermetallic compound is changed to a different phase from the starting material (for example, an amorphous phase). An object of the present invention is to provide a method and an apparatus for producing a hydrogen storage alloy having a high alloying ratio without melting two or more kinds of metals selected to solve the above problems.

[0008]

According to the method for producing a hydrogen storage alloy of the present invention, a crushing ball having a diameter of 3 to 5 mm is filled in a mill pot of a high speed ball mill and alloyed to form a hydrogen storage alloy. After adding powder of different metal of the above and sealing it and adjusting the inside of the mill pot to a non-oxidizing atmosphere, an acceleration of more than 30 times the acceleration of gravity is added to the inside of the mill pot, and after mixing, pulverizing and dispersing, the alloying rate is high. The above problems were solved by forming a hydrogen storage alloy. Specifically, the non-oxidizing atmosphere is Ar gas, He gas, N
Filling the mill pot with either of the _two gases, and the two or more different metals are one or more metals selected from the group of Mg, Ca, Al, La, Misch metal, and Ti.
Ni, Al, V, Cr, Fe, Co, Zr, Cu, Mn
Clarified that it consists of one or more metals selected from the group. The most preferred high-speed ball mill in order to further implement the present invention, it has a mill pot for removably connected with the adjusting means of a non-oxidizing atmosphere, batch which rotates about its own axis of rotation while revolving by rotation of the spindle formula
Planetary ball mills are the best choice, in this case

[Equation 2] The composite crushing acceleration ratio G applied to the inside of the mill pot represented by the above formula is at least 30 or more, and the rotation / revolution angular velocity ratio R can be operated only under the operating conditions of 1.9 or less.
This is the best practice.

[0009]

The manufacturing method according to the present invention is an application of the mechanical alloying method because it is an alloy of two or more metals capable of forming a hydrogen storage alloy without melting in a furnace. An alloy having a much higher alloying ratio than that of the conventional one was obtained by applying an acceleration in the mill pot that was extremely different from the well-known conventional high-speed ball mill. It is needless to say that this acceleration is required to be 30 times or more of the gravitational acceleration, so that a device that can obtain this acceleration is the largest premise for implementing the manufacturing method. Although the process of mechanical alloying is still in the process of study and it is not known to be accurate, it is said that it is important that the mutual diffusion of atoms occurs sufficiently and that the enthalpy ΔHm of mixing is negative and large. ing. It is natural that the progress of the mutual diffusion of atoms at low temperature accelerates as the effective energy provided increases. Whereas conventional mechanical alloying was made finer and homogenized in the course of particle flattening, flaking, cold forging (kneading), lamellar organization, dispersion and randomization,
In the case of the present invention, it is considered that the alloying should be considered to be completed up to the stage of stronger atomic bond.

It can be easily inferred that the larger the synthetic crushing acceleration ratio G, the shorter the time required to complete the mechanical alloying, but even if the same acceleration is applied, the crushing balls of the crushing balls charged into the mill pot will be shortened. It was confirmed that the time required for completion was different for different diameters.
When the high-speed ball mill is operated under the same conditions except that the diameter of the crushed ball is changed, and the progress of alloying is checked after the operation is stopped in a relatively short time, a clear causal relationship with the diameter of the crushed ball is established. The theoretical elucidation is left for future research, but it was confirmed that the alloying progressed most actively when the ball diameter was selected in the range of 3 to 5 mm.

[0011]

EXAMPLE A batch type planetary ball mill 1 used for carrying out the manufacturing method of the present invention is shown in FIGS. 1 and 2. A general structure will be described with reference to the drawing. In response to rotation of a main shaft 22 driven by a motor 6, a plurality of mill pots 21 that revolve are evenly distributed around the main shaft 22 (if two, symmetrically, if three or more are present). For example, the mill pots 21 are arranged equidistantly from the main shaft 22, and the mill pot 21 itself rotates about its own rotation axis. Specifically, a planetary gear 8 is provided around the outer periphery of a mill pot 21 that rotates together with the main shaft 22, and the sun gear 7 that meshes with the planetary gear 8 is separately rotated or stopped (stopped in the figure) to revolve the mill pot 21. While rotating. The sun gear 7 is fitted onto the main shaft 22. A grinding ball B as a grinding medium and a metal powder M are housed inside the mill pot 21, and the internal atmosphere is replaced with an inert gas such as Ar gas in order to prevent the metal powder M from being oxidized during processing. . As shown in FIG. 1, a pipe 31 is provided on the lid of the mill pot 21 and a pair of one-touch couplers 32 are attached to the tip of the mill pot 21 as shown in FIG.
Attached to the vacuum pump 41 via the pipe 33 and the valve 11, to the pressure gauge 61 via the valve 13 and the pipe 34,
It is connected to an Ar gas filled cylinder 51 via a pipe 35 and a valve 12. With the valve 12 fully closed and the valves 11 and 13 fully opened, the vacuum pump 41 performs vacuuming.
The air in the mill pot 21 is removed. After confirming that a predetermined degree of vacuum has been reached with the pressure gauge 61, the valve 11 is fully closed and the valve 12 is opened.
The mill pot 21 is filled with gas. After confirming that the pressure of the filled Ar gas reaches a predetermined pressure equal to or higher than the atmospheric pressure by the pressure gauge 61, the valve 12 is also fully closed and the pipe 31 and the pipe 33 are separated by the one-touch coupler 32 part. The Ar gas in the mill pot 21 is held by one of the one-touch couplers 32. This Ar gas filling operation is performed once or more.
As described above, the powder M of the crushed ball B and the metal M are charged into the mill pot 21 and filled with Ar gas, and then the planetary ball mill is operated, whereby the centrifugal force and the Coriolis force due to the revolution and rotation are synergistically combined with the crushed ball B. Acts on the processed material M,
The metal powder M is processed.

FIG. 2 is a schematic diagram of the motion of the mill pot of the planetary ball mill, in which the revolution angular velocity ω ₁ and the revolution diameter K are 0.52.
m, the inner diameter N of the mill pot is 0.075 m, R = ω ₂ /
ω ₁ and ω ₂ are relative angular velocities of rotation with respect to the revolution, and ω ₁ is 43.4 (1 / s) and ω ₂ is 59 so that the composite crushing angular velocity ratio G is calculated to be 90. It was set to 0.0 (1 / s). In this case, ω ₂ / ω ₁ (= R) is 1.36, but this point is based on the following consideration. 3 (a), (b) and (c) show the relationship between the motion state of the ball B in the mill pot and the relative ratio of the angular velocity of the revolution and rotation of the mill. Figure (a) where the revolution angular velocity is ω ₁ , the relative angular velocity of rotation is ω ₂ , and the ratio of the two is R = ω ₂ / ω ₁ .
Indicates the state in the mill pot where R is 0.5. Here, the balls are integrally and collectively surging along the inner peripheral surface of the mill pot, and effective compressive force and shearing force are applied to the inner peripheral surface, the balls, and the metal charged between the balls, so that mechanical It has an effective effect on Ing. Figure
(B) shows the behavior of the ball when R = 1.0 and (C) shows R = 1.22. As the rotation angular velocity becomes relatively large, a part of the ball moves from the inner peripheral surface. They start to fly away in the space inside the mill pot, and some of the energy is wasted by the collision of the balls, and they start to recede for the purpose of mechanical alloying. This tendency becomes larger as R becomes larger, and when R exceeds 1.9, a hydrogen storage alloy having a high alloying ratio cannot be obtained no matter how the synthetic crushing acceleration ratio G is 30 or more. This time, taking this point into consideration, R was set to 1.36, but R is preferably 1.
A range of 5 to 0.5 is considered good. In this embodiment, Mg ₂ Ni is selected from the hydrogen storage alloys, and as its raw material, Ni powder having an average particle size of 9 μ and Mg powder having an average particle size of 85 μ are weighed in proportions of alloy composition and charged into a mill pot to obtain a high carbon content. The diameter of the crushed balls made of Cr bearing steel was variously changed over the range of 1 mm to 6.35 mm, and the crushed balls were charged in an amount corresponding to 30% of the space volume of the mill pot. Metal powder M
0.25 to 1.0% of stearic acid was added as an auxiliary agent, and the operation time was set to 30 minutes for the treatment.
Each sample was examined by DTA analysis to see if the metal powder was all alloyed or if the unreacted Mg remained in single phase form. Sample number and grinding ball diameter (m
Table 1 shows the relationship with m).

[0013]

[Table 1]

Here, the free powder refers to a proportion of the processed product which is immediately collected without adhering to the balls or the inner surface of the mill pot when the mill pot lid is opened and the processed product is taken out after the crushing process. That is, the ratio of 100% means that almost all the treated products were recovered without any modification.

What appears most clearly in the DTA analysis is the temperature dependence of the dissociation pressure of the metal hydride, which differs from component to component. In FIG. 4, when the temperature at which the hydrogen dissociation pressure becomes 1 MPa is obtained, the temperature T _{1 at} which Mg intersects with 1 MPa is M
It is shown that the temperature is always higher than the temperature T _{2 at} which g ₂ Ni intersects with 1 MPa. Therefore, whether the metal forming the hydride is a single phase or a composite phase in which two or more kinds coexist is determined by whether the temperature at which hydrogen dissociation or bonding is present is single or plural. You can

Each sample was collected from the mill pot and the DTA line
The results of creating the diagrams are shown in FIGS. (1) Sample 1 (FIG. 5) In the curve D representing the differential heat, Mg₂NiH_FourIs Mg₂N
i and H₂In addition to the peak point E which dissociates into₂Is Mg and H
₂There is a peak point F at which₂Ni is H₂ And join
In addition to the peak point I₂There is a peak point J
Indicates that a large amount of single-phase Mg is present. (2) Sample 2 (Fig. 6) Mg₂Ni and H₂Of a single peak point where and bind or dissociate
Other MgH₂ There is a peak point (refraction point) L where
Of Mg remains. (3) Sample 3 and Sample 4 (Figs. 7 and 8)

(Equation 3) Only the phase change indicated by is observed, indicating the presence of single-phase Mg. There are no double peaks and refraction points. (4) Sample 5 (FIG. 9) the peak point S again the dissociation from MgH ₂ of H ₂ wherein peak appears point T similarly showing the binding, little remains Mg single phase in a state close to the sample 1 Revealed that.

Samples 1 to 5 were mechanically alloyed under exactly the same conditions except that the starting materials were the same and the diameters of the crushed balls were different, but there was a large difference in the proportion of free powder, and this difference and alloying It is interesting to interpret that there is a correlation with the progression of, but its theoretical elucidation will be given elsewhere. When the synthetic crushing acceleration ratio G is set to 90, it has been confirmed from another experimental data that alloying is completely completed and single-phase Mg does not exist after operation for at least 4 hours. However, if the diameter of the crushed balls is 3 to 5 mm, alloying will be completed in about 30 minutes of operation. FIG. 10 is a PCT diagram of a hydrogen storage alloy obtained by operating a mill pot for 12 hours with a synthetic crushing acceleration ratio G of 30, and FIG. 11 is a DTA diagram of the same. Even in this case, it can be easily analogized that the desired time of 12 hours can be greatly shortened if the diameter of the crushed balls is unified to 3.9 mm and the operation is performed with G of 90 and R of 1.9 or less.

[0018]

As described above, the present invention produces a hydrogen storage alloy without melting, and contains only an alloy capable of effectively and rapidly changing its phase to a hydride as compared with the conventional one, and does not contain other single-phase metals. It is possible to obtain an alloy body having an extremely high alloying rate. Therefore, the reaction rate with hydrogen is fast, and its occluding and desorbing capacity is strengthened to near the theoretical value. Therefore, when it is attached to various applications which have been conventionally applied, it is expected that the result will be far superior to the conventional one. Moreover, among the manufacturing methods by non-melting method, focusing on the alloying speed, we found one of the best conditions and identified one of the most efficient manufacturing methods. I was able to improve significantly. It should be noted that the manufacturing cost is much lower than that of the melting method which is a conventional technique, and an alloy without using expensive La can be freely manufactured. In that respect, needless to say, a great economic effect can be obtained together with the improvement of quality. .

[Brief description of drawings]

FIG. 1 is a planetary ball bearing used for carrying out the manufacturing method of the present invention.
It is a vertical sectional front view of Le.

FIG. 2 is a schematic diagram of movement of the planetary ball mill .

3 (a), (b), and (c) show the relationship between the operating state of the ball and the relative angular velocity ratio of the rotation and revolution of the mill.

FIG. 4 is a relationship diagram between hydrogen dissociation pressure of Mg and Mg ₂ Ni and temperature.

FIG. 5 is a DTA diagram of a comparative example of the present invention.

FIG. 6 is a DTA diagram of a comparative example of the present invention.

FIG. 7 is a DTA diagram of an example of the present invention.

FIG. 8 is a DTA diagram of the embodiment of the present invention.

FIG. 9 is a DTA diagram of a comparative example of the present invention.

FIG. 10 is a PCT diagram of a reference example of the present invention.

FIG. 11 is a DTA diagram of a reference example of the present invention.

FIG. 12 is a prior art PCT diagram.

FIG. 13 is a prior art DTA diagram.

[Explanation of symbols]

 1 Planetary ball mill 2 Atmosphere adjusting means 7 Sun gear 8 Planetary gear 21 Mill pot 22 Spindle 41 Vacuum pump 51 Ar gas filled cylinder B Grinding ball

Claims (4)

(57) [Claims] 1. A diameter of 3 mm into a mill pot of a high-speed ball mill.
Filling a crushed ball of ~ 5mm, adding two or more different metal powders that can alloy to form a hydrogen storage alloy, and seal,
After adjusting the inside of the mill pot to a non-oxidizing atmosphere, an acceleration of 30 times or more of the acceleration of gravity is applied to the inside of the mill pot to form a hydrogen storage alloy having a high alloying rate through mixing, pulverization and dispersion. Manufacturing method of hydrogen storage alloy. 2. The non-oxidizing atmosphere according to claim 1, wherein A
A method for producing a hydrogen storage alloy, characterized in that a mill pot is filled with any one of r gas, He gas, and N ₂ gas. 3. The method according to claim 1, wherein the two or more different metals are one or more metals selected from the group consisting of Mg, Ca, La, Misch metal, and Ti, Ni, Al, V, Cr,
A method for producing a hydrogen storage alloy, comprising at least one metal selected from the group consisting of Fe, Co, Zr, Cu and Mn. 4. A high speed ball mill according to claim 1.
In addition , a batch type planetary ball mill that has a mill pot that is detachably connected to a non-oxidizing atmosphere adjusting means and that revolves around the rotation of the main spindle and that rotates about its own rotation axis.
Used, and The method for producing a hydrogen storage alloy , characterized in that the synthetic crushing acceleration ratio G applied to the inside of the mill pot is at least 30 or more and the rotation and revolution angular velocity ratio R is limited to the condition of 1.9 or less .