JPH04323334A - Method and device for producing hydrogen storage alloy - Google Patents

Abstract

PURPOSE:To economically produce a hydrogen storage alloy enhanced in alloying rate. CONSTITUTION:This hydrogen storage alloy is produced by the following steps. Namely, (1) the powders M of >=2 different kinds of metals, e.g. Mg and Ni, giving a hydrogen storage alloy on alloying and the crushing ball B having 3-5mm diameter are charged into the mill pot 21 of a high-speed ball mill. (2) The mill pot is filled in with a nonoxidizing atmosphere. (3) The mill is operated under conditions where the resultant crushing acceleration ratio G expressed by the following equation is controlled to >=30 and the ratio R of the rotating to revolving angular speeds to <=1.9 to exert an effective alloying action. The equation is expressed by G=amax/g=(omega1)<2>/2g(K+NX(1+R)<2> wherein G is the resultant crushing acceleration ratio, amax is the resultant crushing acceleration (m/S<2>), g m/S<2> is the gravitational acceleration, omega1 is the revolving angular speed (1/S), K is the diameter (m) of revolution, N is the inner diameter (m) of the mill pot, omega2 is the relative angular speed (1/S) of the rotation to revolution, and R=omega2/omega1.

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 hydrogen storage alloys.

0002

[Prior Art] Technology has been developed to absorb hydrogen in certain metals or alloys, store or transport it in the form of metal hydrides, and use the hydrogen as a component in hydrogen purification, heat pumps, and heating and cooling systems. There is. In this case, when a metal hydride absorbs or releases hydrogen, it always generates heat or absorbs heat, so this property can be used for heat exchange devices and heat pumps. The alloy combinations that have been announced and partially put into practical use as hydrogen storage alloys to date include Mg-Ni, Mg-Cu, Ca-Ni, Fe-T.
Many alloys have been reported in which the main basic components are i, Ti-Mn, La-Ni, Mischmetal-Ni, etc., and some of these are replaced with other metals. For example, Mg2
Ni0.75Cr0.25, Ca0.7Mn0.3N
i5, LaNi4.7Al0.3, TiFe0
．． 8Mn0.2 and the like are known. Generally speaking, one or more metals selected from the group consisting of Mg, Ca, La, misch metal, Ti, etc. and Ni, Al,
It is manufactured by alloying one or more metals selected from the group consisting of V, Cr, Fe, Co, Zn, Cu, and Mn. To manufacture hydrogen storage alloys, raw materials of different metals are melted in a high-frequency induction furnace or arc-type high-temperature melting furnace. High-frequency induction furnaces are suitable for mass production, but many of the raw metals, especially Mg, Ca, and Al, have high vapor pressures and strong affinity for oxygen, so the inside of the furnace must be kept in an inert atmosphere with Ar gas, etc. must be adjusted to prevent metal oxidation. When the material metals are melted and mixed with each other and the alloy reaction progresses sufficiently at high temperatures to reach the desired alloy composition, the material is cast into a mold in a non-oxidizing atmosphere to form an 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 with a desired particle size.

On the other hand, a technique for obtaining a desired alloy composition while remaining solid without melting has recently been in the spotlight. This is generally called the mechanical alloying method, and was first developed by Benjamin of INCO in the United States in the 1970s. It involves applying mechanical energy to metal powder using a high-energy ball mill (attritor), etc. to achieve cold compression and fracture. In this method, ultrafine particles are dispersed by repeating the above steps. The principle of mechanical alloying is that the powder is first forged by milling with a high impact force to flatten and flake, then the work-hardened particles are broken or exfoliated and cold forge welding is repeated (kneading), and then the alloy components are The theory is that a lamellar structure develops during this period, the crystal grains rapidly become finer, one grain becomes finely dispersed within the other, and finally the grain shape becomes equiaxed and becomes random. M Y
Song and Yi Ivanov published their experimental results in Hydrozen Energy magazine (H
Hydrogen Energy vol10 No. 3
P169-178, 1985). In this report, the acceleration of the planetary ball mill is 6.1G, and N
i compares and examines samples obtained by mixing for 30 minutes in an Ar gas atmosphere using a carbonyl type and subjected to various hydrogenation treatments by X-ray diffraction. As a result, among the samples that were hydrogenated from 1 to 58 times, the one with the lowest hydrogenation number was Mg2Ni, with a trace amount of M.
It was detected that gO, Mg, and Ni phases coexisted, but it was recognized that most of the Mg and Ni became Mg2Ni in those that were heat-treated (annealed) and had a large number of hydrogenations. The effect of heat treatment was recognized to be stronger than that of repeated steps, and this was the first report on a method for producing a hydrogen storage alloy without melting, although it was incomplete.

0004

Among the conventional techniques, manufacturing hydrogen storage alloys by melting requires considerably sophisticated technology and well-managed equipment. For example, Mg2Ni
When manufacturing Ni, the vapor pressure of Ni is 2057 mm at 10°C.
Hg, fluctuates at a high level of 2732 mmHg at 760°C, while Mg also varies from 743 mmHg to 11
It fluctuates at 0.07 mmHg. Ca also fluctuates from 983 mmHg to 1487 mmHg, and it is extremely difficult to raise the temperature inside the furnace while maintaining the balance of these vapor pressures. On the other hand, from the general principle of melting, the degree of solid solubility of both components influences the difficulty of forming an alloy, but the most problematic one is the difference in density and melting point of both components. That of Ni is 8.90g
/cm3, 1455℃, Mg is 1.74g/c
m3, 650℃, Ca is 1.55g/cm3, 850℃
It is. Therefore, it is clear from this fact alone how difficult it is to alloy Mg or Ca with Ni. On the other hand, La has a density of 6.15 g/cm3 and a melting point of 826°C.
However, in general, rare earth elements are valuable resources and are expensive. A major problem when alloying Mg and Ni is that the vapor pressure of Mg reaches approximately 25 atmospheres 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 in excess, and part of the product becomes MgNi2, which does not form hydrides. To prevent this, if Mg is added in excess from the beginning, for example, the chemical formula can be changed to Mg2.35N.
Although it is expressed as i, the actual situation is that it contains free Mg alone, such as Mg2Ni+Mg0.35.

How this relates to the characteristics of the hydrogen storage alloy will be explained with reference to FIGS. 12 and 13. Figure 12 shows the hydrogen storage alloy Mg2.35Ni produced by the melting method.
pressure-composition isotherm diagram (hereinafter referred to as "PCT diagram")
The vertical axis shows the hydrogen pressure P (unit: MPa), the horizontal axis shows the atomic ratio H/M of hydrogen gas and metal, and the constant temperature (3
This is a graphical representation of the behavior of the atomic ratio associated with the absorption and desorption of hydrogen gas at a temperature of 50°C. In the figure, when the hydrogen pressure reaches nearly 0.5, both the absorption and desorption trace a gentle slope to the right in range A, and the range B shifts almost horizontally to the right.
Range A is hydrogen absorption by Mg alone,
release, and range B indicates hydrogen absorption by Mg2Ni,
showing release. In other words, the fact that range A is observed indicates the presence of Mg that binds to hydrogen gas, and Mg, which has a far inferior affinity for hydrogen than Mg2Ni, is contained in the alloy, reducing the functionality required as a hydrogen storage alloy. Indicates that the

FIG. 13 is a high-pressure differential thermal analysis diagram (hereinafter referred to as "DTA diagram") of the same sample, with temperature on the vertical axis and time on the horizontal axis, with hydrogen at a constant pressure (1.1 MPa) Curve C shown by measuring the temperature of Mg2.35Ni sealed in the container when the container was heated to a maximum of 500°C from the outside or cooled from 500°C, and compared with this sample. Therefore, curve D shows the temperature difference generated between the sample and the standard sample (alumina) sealed in the container. Since a hydrogen storage alloy generates heat when storing hydrogen gas and absorbs heat when releasing hydrogen gas, curve D also shows a downward peak due to release during heating, and an upward peak due to occlusion during cooling. However, as clearly seen at points P, Q, and R, there is not only one point where the peak is sharp, but also a double peak or an abnormal refraction point close to the peak.In addition to the phase change between Mg2Ni and Mg2NiH4, This shows that there is also a phase change between Mg and MgH2. This occurs because Mg dissociates at a higher temperature than Mg2Ni under the same hydrogen pressure. In any case, hydrogen storage alloys manufactured by the melting method have the problem that, in addition to manufacturing difficulties, it is difficult to avoid the presence of components that cause functional deterioration.

On the other hand, it has been suggested that an attempt to obtain Mg2Ni by a so-called mechanical alloying method without dissolution is technically possible. However, by repeatedly hydrogenating and dehydrogenating the sample alloy at a hydrogen pressure of 0.7 MPa and at a temperature of 300°C, it was found that single-phase Mg and Ni The presence of Mg2Ni could not be eliminated, and it was not until a heat treatment was performed at a temperature of 270 to 300°C for two months under a hydrogen pressure of 0.25 to 0.85 MPa, and the hydrogenation treatment was repeated 58 times, that almost the entire amount became Mg2Ni. Not too much. I believe that the mechanical alloying method is now translated into Japanese as a mechanical alloying method, but at the current technological level, it is not recognized that complete alloying of single dissimilar metals has been achieved, and there are It is appropriate to evaluate that the same type of oxide is dispersed in ultrafine particles or that the intermetallic compound is used as a starting material and changes to a different phase (for example, an amorphous phase). In order to solve the above problems, the present invention aims to provide a method and an apparatus for producing a hydrogen storage alloy with a high alloying ratio without melting two or more selected metals.

[0008]

[Means for Solving the Problems] A method for producing a hydrogen storage alloy according to the present invention is to fill a mill pot of a high-speed ball mill with crushed balls having a diameter of 3 to 5 mm, and to alloy two or more balls that can form a hydrogen storage alloy. After adding dissimilar metal powder 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 applied to the inside of the mill pot, and through mixing, crushing, and dispersion, a high alloying rate is achieved. The above problem was solved by forming a hydrogen storage alloy. Specifically, the non-oxidizing atmosphere is Ar gas, He gas, N2
The mill pot is filled with one of the gases, and the two or more dissimilar metals are one or more metals selected from the group consisting of Mg, Ca, Al, La, misch metal, and Ti.
Ni, Al, V, Cr, Fe, Co, Zr, Cu, Mn
It was clearly stated that the material consists of one or more metals selected from a group of. Furthermore, the high-speed ball mill essential to carrying out the present invention has a non-oxidizing atmosphere adjustment means and a mill pot that is detachably connected, and it revolves around the rotation of the main shaft and rotates around its own rotation axis. and

[Number 2
] It was shown that this is a batch type planetary ball mill in which the synthetic grinding acceleration ratio G applied to the inside of the mill pot is at least 30 or more, and the rotation-revolution angular velocity ratio R is 1.9 or less.

[0009]

[Function] The manufacturing method according to the present invention alloys two or more metals that can form a hydrogen storage alloy without melting them in a furnace, so it can be said to be a type of mechanical alloying method. By applying an extraordinary acceleration inside the mill pot compared to the well-known and conventional high-speed ball mill, we were able to obtain an alloy with a much higher alloying rate than the conventional method. Since this acceleration is required to be at least 30 times the gravitational acceleration, it goes without saying that an apparatus capable of obtaining this acceleration is the greatest prerequisite for implementing the manufacturing method. The mechanical alloying process is still under research and the exact details are not known, but it is said that the important conditions are that sufficient interdiffusion of atoms occurs and that the enthalpy of mixing ΔHm is large and negative. ing. It is natural that the interdiffusion of atoms at low temperatures accelerates as the effective energy provided increases. While conventional mechanical alloying is refined and homogenized through the process of flattening, flaking, cold forging (kneading), lamellar structure, dispersion, and randomization of particles, in the case of the present invention, considers that alloying should be considered to have been completed to the stage of stronger atomic bonds.

It can be easily inferred that the larger the synthetic grinding acceleration ratio G is, the shorter the time required to complete mechanical alloying is. However, even when the same acceleration is applied, the grinding balls charged into the mill pot are It was confirmed that there was a difference in the time required to complete the process when the diameter was different. When a high-speed ball mill is operated with the diameter of the grinding balls changed and all other conditions kept the same, and the progress of alloying is examined after the operation is stopped in a relatively short period of time, a clear causal relationship is established between the diameter of the grinding balls and the progress of alloying. Although we will leave the theoretical elucidation to future research, we have confirmed that alloying progresses most actively when the diameter of the ball is in the range of 3 to 5 mm.

[0011]

[Embodiment] An embodiment of a batch-type planetary ball mill 1, which is the premise of the manufacturing method, is shown in FIGS. 1 and 2. To explain the general structure in the figure, a main shaft 22 driven by a motor 6
A plurality of mill pots 21 are arranged evenly around the main shaft 22 (symmetrically if there are two mill pots, radially equidistant from the main shaft 22 if there are three or more mill pots 21), which revolve in response to the rotation of the mill pots 21 themselves. also rotates around its own axis of rotation. Specifically, a planetary gear 8 is provided around the outer periphery of the 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).
, rotates the mill pot 21 while revolving around it. The sun gear 7 is externally fitted onto the main shaft 22. The mill pot 21 houses grinding balls B as grinding media and metal powder M, and the internal atmosphere is replaced with an inert gas such as Ar gas to prevent oxidation of the metal powder M during processing. . In order to replace the atmosphere with Ar gas as an example of the atmosphere adjustment means 2, as shown in FIG.
A pair of one-touch couplers 32 are attached to the tip, and a vacuum pump 41 is connected via a tube 33 and a valve 11, a pressure gauge 61 is connected via a valve 13 and a tube 34, and an Ar gas cylinder is connected via a tube 35 and a valve 12. Connect to 51. With the valve 12 fully closed and the valves 11 and 13 fully open, the vacuum pump 41 is used to evacuate the air inside the mill pot 21. After confirming that the predetermined degree of vacuum has been reached with the pressure gauge 61, fully close the valve 11 and close the valve 1.
2 is opened, and the mill pot 21 is filled with Ar gas from the Ar gas filling cylinder 51. After confirming by the pressure gauge 61 that the filled Ar gas pressure has reached a predetermined pressure equal to or higher than atmospheric pressure, the valve 12 is also fully closed, and the one-touch coupler 32 separates the pipes 31 and 33. Ar gas in the mill pot 21 is held by one side of the one-touch coupler 32. This Ar gas filling operation is performed at least once. As described above, put the powder M of the grinding ball B metal into the mill pot 21.
After filling with r gas, by operating the planetary ball mill, the centrifugal force and Coriolis force due to the revolution and rotation motion act synergistically on the grinding balls B and the processed material M, and the metal powder M
is processed.

FIG. 2 is a schematic diagram of the motion of the mill pot of a planetary ball mill, where the revolution angular velocity ω1 and the revolution diameter K are 0.5.
2m, Mill pot inner diameter N is 0.075m, R=ω2
/ω1, ω2 are the relative angular velocities of rotation with respect to revolution,
ω1 is 43.4 (1/s) and ω2 is 59.0 so that the synthetic crushing angular velocity ratio G is calculated using the formula listed above and becomes 90.
(1/s). Note that ω2/ω1 (=R) is 1.36 in this case, but this point is based on the following considerations. Figures 3(a), (b), and (c) show the relationship between the motion state of ball B in the mill pot and the relative ratio of the angular velocities of revolution and rotation of the mill. Assuming that the angular velocity of revolution is ω1, the relative angular velocity of rotation is ω2, and the ratio of the two is R=ω2/ω1, Figure (a) shows the state inside the mill pot where R is 0.5. Here, the balls collectively and collectively surge along the inner circumferential surface of the mill pot, applying effective compressive force and shearing force to the inner circumferential surface, the balls, and the metal charged between the balls. It has an effective effect on ing. Figure (b) shows R=1.
0. Figure (c) shows the behavior of the ball when R = 1.22, and as the rotational angular velocity becomes relatively large, a part of the ball separates from the inner peripheral surface and flies in the space inside the mill pot. As the balls collide with each other, some of the energy is wasted, and the purpose of mechanical alloying begins to fall behind. This tendency increases as R increases, and when R exceeds 1.9, a hydrogen storage alloy with a high alloying ratio cannot be obtained no matter how high the synthetic crushing acceleration ratio G is 30 or more. This time, taking this point into consideration, R
was selected to be 1.36, but it is considered that R is desirably in the range of 1.5 to 0.5. In this example, Mg2Ni was selected from among the hydrogen storage alloys, and the average particle size was 9μ as its raw material.
Ni powder and Mg powder with an average particle size of 85μ are weighed in the proportion of the alloy composition and charged into a mill pot, and the diameter of the grinding ball made of high carbon Cr bearing steel is 1 mm to 6.35 m.
The spatial volume of the mill pot is varied over a range of 30 m.
% was charged. In addition, 0.2 of metal powder M
Stearic acid corresponding to 5 to 1.0% was added as an auxiliary agent, and the operation time was set to 30 minutes. For each sample, it was examined by DTA analysis whether all the metal powders were alloyed or whether unreacted Mg remained in the form of a single phase. Sample number and diameter of grinding ball (m
m) is shown in Table 1.

[0013]

[Table 1]

[0014] Here, free powder refers to the proportion of the processed material that is immediately collected without adhering to the balls or the inner surface of the mill pot when the lid of the mill pot is opened and the processed material inside is taken out after the grinding process is completed. In other words, a percentage of 100% indicates that almost the entire amount of treated material was recovered without any modification.

What is most clearly revealed in DTA analysis is the temperature dependence of the dissociation pressure of metal hydrides, which differs from component to component. In Figure 4, if we now find the temperature at which the dissociation pressure of hydrogen is 1 MPa, the temperature T1 at which Mg crosses 1 MPa is M
It is shown that g2Ni is always on the higher temperature side than the temperature T2 which crosses 1 MPa. Therefore, whether the metal forming the hydride is a single phase or a complex phase in which two or more types coexist can be determined by whether the temperature at which hydrogen dissociates or bonds is single or multiple. Can be done.

FIGS. 5 to 9 show the results of DTA diagrams prepared by collecting each sample from the mill pot. (1) Sample 1 (Figure 5) In curve D representing differential heating, Mg2NiH4 is
In addition to the peak point E where MgH2 dissociates into Ni and H2, MgH2
There is a peak point F where Mg2Ni dissociates into H2 and H2.
In addition to the peak point I where MgH2 is combined, there is a peak point J where MgH2 is generated, indicating that a considerable amount of single-phase Mg exists. (2) Sample 2 (Figure 6) In addition to the single peak point where Mg2Ni and H2 bond or dissociate, there is a peak point (refraction point) L where MgH2 is generated, indicating that traces of Mg remain. There is. (3) Both sample 3 and sample 4 (Figures 7 and 8)

Only the phase change shown by Equation 3 was observed, indicating the presence of single-phase Mg. No double peaks or inflection points are observed. (4) Sample 5 (Figure 9) Here again, peak point S indicating dissociation of H2 from MgH2 and peak point T indicating bonding appear, and the state is similar to sample 1, with a small amount of single-phase Mg remaining. It revealed that.

Samples 1 to 5 were mechanically alloyed under exactly the same conditions except for the same starting materials and different diameters of the grinding balls, but there was a large difference in the proportion of free powder, and this difference and alloying It is interesting that there seems to be a correlation between the progress of When the synthetic crushing acceleration ratio G is 90, other experimental data confirms that alloying is completely completed and no single phase Mg exists after at least 4 hours of operation. However, if the diameter of the grinding balls is 3 to 5 mm, alloying can be completed in approximately 30 minutes of operation. FIG. 10 is a PCT diagram of a hydrogen storage alloy obtained by operating the mill pot for 12 hours with a synthetic crushing acceleration ratio G of 30, and FIG. 11 is a DTA diagram. Even in this case, it can be easily inferred that if the diameter of the grinding balls is unified to 3.9 mm and the operation is performed with G of 90 and R of 1.9 or less, the desired time of 12 hours can be significantly shortened.

[0018]

[Effects of the Invention] As described above, the present invention produces a hydrogen storage alloy without melting, and contains only an alloy that undergoes a phase change to a hydride more effectively and quickly than in the past, and does not contain other single-phase metals. It is possible to obtain an alloy body with an extremely high alloying rate. Therefore, the reaction rate with hydrogen is fast, and its absorption and desorption capabilities are enhanced to near theoretical values. Therefore, it is expected that when installed in various applications that have been applied in the past, it will produce results far superior to those of the past. Moreover, among non-melting manufacturing methods, we focused on the speed of alloying and found one of the best conditions, and found one of the most efficient manufacturing methods, surpassing the conventional level in terms of mass production and economy. We were able to improve significantly. Furthermore, the manufacturing cost is much lower than the conventional melting method, and alloys that do not use expensive La can also be manufactured freely, so it goes without saying that in this respect, as well as improving quality, a large economic effect can be obtained. .

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional front view of an apparatus used to implement the present invention.

FIG. 2 is a schematic diagram of the movement of the device.

[Fig. 3] (A), (B), and (C) show the relationship between the operating state of the ball and the relative ratio of angular velocities of rotation and revolution of the mill.

FIG. 4 is a diagram showing the relationship between hydrogen dissociation pressure and temperature for Mg, Mg2Ni, etc.

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 embodiment of the present invention.

FIG. 8 is a DTA diagram of an 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 PCT diagram of the prior art.

FIG. 13 is a DTA diagram of the prior art.

[Explanation of symbols]

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

Claims (4)

[Claims] Claim 1: Grinding balls with a diameter of 3 to 5 mm are filled into the mill pot of a high-speed ball mill, powders of two or more dissimilar metals that can be alloyed to form a hydrogen storage alloy are added and sealed, and the inside of the mill pot is non-oxidized. Production of a hydrogen storage alloy characterized by forming a hydrogen storage alloy with a high alloying rate through mixing, pulverization, and dispersion by applying an acceleration of 30 times or more of gravitational acceleration in a mill pot after adjusting the atmosphere to a neutral atmosphere. Method. 2. In claim 1, the non-oxidizing atmosphere is
A method for producing a hydrogen storage alloy, characterized in that a mill pot is filled with any one of Ar gas, He gas, and N2 gas. 3. In claim 1 or 2, the two or more dissimilar metals are one or more metals selected from the group of Mg, Ca, La, misch metal, Ti, and Ni, Al, V, Cr.
, Fe, Co, Zr, Cu, and Mn. [Claim 4] The high-speed ball mill according to Claim 1 comprises:
It has a mill pot that is removably connected to a non-oxidizing atmosphere adjustment means, revolves around the rotation of the main shaft and rotates around its own rotation axis, and has a synthetic pulverization acceleration applied to the inside of the mill pot expressed by [Equation 1] An apparatus for producing a hydrogen storage alloy, characterized in that it is a batch planetary ball mill having a ratio G of at least 30 and a revolution-revolution angular velocity ratio R of 1.9 or less.