JP2008266781A - METHOD FOR MANUFACTURING Mg-Al BASED HYDROGEN STORAGE ALLOY POWDER AND Mg-Al BASED HYDROGEN STORAGE ALLOY POWDER OBTAINED BY THE MANUFACTURING METHOD - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing Mg-Al based hydrogen storage alloy powder capable of manufacturing the Mg-Al based hydrogen storage alloy powder which allows the existence of a composition ratio of Mg in a wide range, is stable as an alloy and is excellent in hydrogen storage ability as well at a high yield and low cost, and the Mg-Al based hydrogen storage alloy powder obtained by the manufacturing method. <P>SOLUTION: The method for manufacturing the Mg-Al based hydrogen storage alloy powder includes a pulverization treatment step of subjecting metal raw material powder containing desired ratio of Mg and Al and an appropriate amount of rare metal oxide to pulverization treatment by ball milling until crystal grains of a nano-level can be yielded, and a heat treatment step of subjecting the pulverized product of the metal raw material powder obtained by the pulverization treatment to heat treatment. The Mg-Al based hydrogen storage alloy powder in which the Mg can be made to exist in a composition ratio as wide as 47.5 to 70.0 and the hydrogen storage ability is excellent is provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing an Mg—Al-based hydrogen storage alloy powder and an Mg—Al-based hydrogen storage alloy powder obtained by the production method. More specifically, since it is stable as an alloy and has excellent hydrogen storage capacity, it is obtained by, for example, a manufacturing method of Mg—Al-based hydrogen storage alloy powder that is optimal for applications such as fuel cells, and the manufacturing method. In addition, the present invention relates to a Mg—Al-based hydrogen storage alloy powder.

  Hydrogen gas releases a large amount of energy by reacting with oxygen gas, but it reacts only to produce water, without producing carbon dioxide or sulfur compounds like fossil fuels, and even nuclear fuel. Thus, it is not necessary to worry about environmental pollution caused by fission materials, and is attracting attention as a clean energy alternative to fossil fuels such as oil and coal. On the other hand, since there is a problem of how to store and transport hydrogen as an energy source, in recent years, adoption of a hydrogen storage alloy has been studied for storing and transporting hydrogen.

  Such a hydrogen storage alloy can reversibly store or release hydrogen gas at around room temperature, and can store or transport a large amount of hydrogen gas, which is an alternative energy, in a lightweight and safe manner. Further, this hydrogen storage alloy has a wide function of being able to convert hydrogen gas, which is an energy medium, into heat, chemical, mechanical and electrical energy when necessary using a reversible reaction.

  Among hydrogen storage alloys, magnesium (Mg) -based hydrogen storage alloys can be expected to have a high capacity of hydrogen storage per mass, and show a large storage capacity about 3 to 5 times that of other hydrogen storage alloys. Therefore, development is expected. Various methods have been studied for producing a hydrogen storage alloy, and a typical production method is to heat the raw metal into a melting furnace for melting and homogenization after cooling. There is known a melting method in which an alloy powder is produced by applying the above. Further, two or more kinds of metal powders are subjected to solid phase reaction by repeatedly mixing and grinding the metal powders using a high energy mixing and stirring device such as a ball mill to produce uniform alloy particles in a solid state. A mechanical alloying method is used, and various reports have been made as a method for producing a magnesium-based hydrogen storage alloy (see, for example, Patent Document 1 and Patent Document 2).

JP 2004-292838 A JP 2005-78879 A

By the way, among the Mg-based hydrogen storage alloys, the Mg-Al-based alloy is converted into MgH ₂ (magnesium hydride) and Al (aluminum) through a two-stage hydrogenation process, and the formation enthalpy of this MgH ₂ is a very large negative Although it is a value, since the enthalpy of hydrogenation in the previous two stages is smaller than the enthalpy of formation of MgH ₂ , each reaction can proceed easily. For these reasons, the Mg—Al-based hydrogen storage alloy as the Mg-based hydrogen storage alloy can enhance the hydrogen storage capability of magnesium. Further, in the case of an Mg-based hydrogen storage alloy, in order to increase the hydrogen storage capacity, it is desirable to increase the ratio of the γ phase and increase the composition ratio of the constituent magnesium.

However, since the Mg—Al-based alloy obtained by the conventional manufacturing method cannot control the existence region of the γ phase (Mg ₁₇ Al ₁₂ phase), the Mg—Al-based alloy in which the composition ratio of magnesium is limited ( Only an alloy made of Mg ₁₇ Al ₁₂ could be provided. In addition, as for the performance of the alloy, the hydrogen storage capacity (hydrogen storage capacity and hydrogen storage speed) of the obtained alloy may not be as expected, even though magnesium containing high capacity hydrogen storage capacity is included in the composition. Many improvements were desired.

  The present invention has been made in view of the above-mentioned problems, and it is possible to make the composition ratio of magnesium present in a wide range, and it is stable as an alloy and excellent in hydrogen storage capacity. Of Mg-Al hydrogen storage alloy powder capable of manufacturing a hydrogen-based hydrogen storage alloy at high yield and low cost by simple means, and a Mg-Al-based hydrogen storage alloy powder obtained by the manufacturing method There is to do.

In order to solve the above-described problems, the Mg—Al-based hydrogen storage alloy powder production method of the present invention is Mg—Al-based hydrogen storage that becomes Mg _x Al _100-x (x = 47.5 to 70.0). In producing alloy powder, a metal raw material powder containing a desired proportion of magnesium (Mg) and aluminum (Al) and an appropriate amount of rare metal oxide is pulverized by ball milling until it becomes nano-level crystal grains. And a heat treatment step of heat-treating a pulverized metal raw material powder obtained by the pulverization treatment.

  The method for producing a Mg—Al-based hydrogen storage alloy powder according to claim 2 of the present invention is the above-described method according to claim 1, wherein the rare metal oxide is niobium (Nb), zirconium (Zr), vanadium (V), tantalum. It is at least one selected from the group consisting of oxides of (Ta), titanium (Ti), and aluminum (Al).

  The method for producing an Mg—Al-based hydrogen storage alloy powder according to claim 3 of the present invention is characterized in that, in the above-described claim 1 or 2, the heating temperature in the heat treatment step is 100 to 300 ° C. To do.

  According to a fourth aspect of the present invention, there is provided a method for producing a Mg—Al-based hydrogen storage alloy powder according to any one of the first to third aspects, wherein the ball milling is any of a vibration ball mill, a rotating ball mill, and a planetary ball mill. It is characterized by.

  The Mg—Al-based hydrogen storage alloy powder according to claim 5 of the present invention is obtained by the manufacturing method according to any one of claims 1 to 4.

In the manufacturing method of the Mg—Al-based hydrogen storage alloy powder of the present invention, an appropriate amount of a rare metal oxide is added in addition to magnesium and aluminum as a constituent of the metal raw material powder as a raw material. The resulting hydrogen-absorbing alloy powder can be used as a catalyst to promote the alloying of magnesium and aluminum, increase the hydrogen storage capacity, and increase the rate of hydrogen storage / release (hydrogen storage rate). An Mg—Al-based hydrogen storage alloy powder excellent in hydrogen storage capacity can be provided. In addition, a configuration in which a metal raw material powder is pulverized by ball milling until it becomes nano-level crystal grains, and a heat treatment step of heat-treating the pulverized metal raw material powder obtained by the pulverization process is combined. By adopting, it is possible to control the existence region of the γ phase (Mg ₁₇ Al ₁₂ phase) in the Mg—Al based alloy, and the magnesium composition ratio can exist in a wide range of 47.5 to 70.0. An Mg—Al-based hydrogen storage alloy powder having a composition ratio of Mg _x Al _100-x (x = 47.5 to 70.0) can be provided simply and at low cost.

  The method for producing a Mg—Al-based hydrogen storage alloy powder according to claim 2 of the present invention includes niobium (Nb), zirconium (Zr), vanadium (V) as rare metal oxides added to magnesium and aluminum, Since oxides of tantalum (Ta), titanium (Ti), and aluminum (Al) are selected and employed, alloying can proceed easily and reliably, and the hydrogen storage capacity of the resulting hydrogen storage alloy powder Can be improved, and the hydrogen storage rate can be further increased.

  In the manufacturing method of the Mg—Al-based hydrogen storage alloy powder according to claim 3 of the present invention, the heating temperature in the heat treatment step is set to 100 to 300 ° C. In the production method of the present invention, since the metal raw material powder is pulverized until it becomes nano-level crystal grains by ball milling in the pulverization process of the previous process, only the heat treatment is performed at a relatively low temperature. Thus, alloying can be promoted.

  In the method for producing a Mg—Al-based hydrogen storage alloy powder according to claim 4 of the present invention, any of a vibrating ball mill, a rotating ball mill, and a planetary ball mill is employed as the ball milling, so that the milling is stably performed. As a result, a fine structure can be reliably formed on the metal raw material powder, and the above effects can be achieved more efficiently.

  Since the Mg—Al-based hydrogen storage alloy powder according to claim 5 of the present invention is obtained by the above-described method for producing an alloy of the present invention, the magnesium composition ratio is as wide as 47.5 to 70.0. The hydrogen storage alloy powder is excellent in hydrogen storage capacity such as a large amount of hydrogen storage and high hydrogen storage speed, and can be used for industrial machines such as in-vehicle fuel cells. It becomes possible to respond. In addition, it can be expected to have three major characteristics of amorphous structure (high corrosion resistance, high mechanical strength, and high magnetism), and hydrogen storage with desired performance such as high corrosion resistance / corrosion resistance as alloy and high mechanical strength. It becomes alloy powder.

Hereinafter, the manufacturing method of the alloy powder of this invention is demonstrated. The production method of the Mg—Al-based hydrogen storage alloy powder of the present invention (hereinafter sometimes simply referred to as “the production method of the present invention”) is Mg _x Al _100-x (x = 47.5 to 70.0). In the production of the Mg—Al-based hydrogen storage alloy powder, the metal raw material powder containing a desired proportion of magnesium (Mg) and aluminum (Al), and an appropriate amount of a rare metal oxide is nano-leveled by ball milling. It includes a pulverization process for pulverizing until crystal grains are formed, and a heat treatment process for heat-treating a pulverized metal raw material powder obtained by the pulverization process.

FIG. 1 is an equilibrium diagram of the Mg—Al system. Magnesium and aluminum have a magnesium composition ratio of 47.5 to 70.0 with the entire system being 100, and (1) Magnesium is in the range of 47.5 to 55 at% (atomic%) (Mg _{47. 5 to 55} Al _{52.5 to 45} ), the alloy is composed of two phases of β phase (Mg ₂ Al ₃ phase) and γ phase (Mg ₁₇ Al ₁₂ phase). (2) Magnesium is 55 to 62 In the range of 5 at% (Mg _55-62.5 Al _45-37.5 ), the alloy is composed only of γ phase, and (3) the range of 62.5-70.0 at% magnesium (Mg _{62 .5-70.0} Al _37.5-30.0 ), the alloy is composed of two phases of γ phase and magnesium.

On the other hand, according to the phase diagram of FIG. 1, when the γ phase is at room temperature, magnesium can exist only in 58.6 at% (Mg ₁₇ Al ₁₂ ), and the γ phase exists in other regions. It was difficult. On the other hand, in the production method of the present invention, since the raw material magnesium and aluminum are finely pulverized to the order of several tens of nm by ball milling, the ratio of the surface energy to the total volume energy becomes extremely large (for example, , And several kJ / mol.) Furthermore, even with mechanical energy input to the raw material during ball milling, energy of several tens of kJ / mol is input to the raw material. This time, magnesium and aluminum are alloyed and synthesized as a non-equilibrium γ phase, including heat treatment in the subsequent process, using the energy and thermal energy stored by ball milling, and the energy state is higher than the equilibrium state. It will be possible to produce an alloy of. As apparent from the equilibrium diagram of FIG. 1, the existence region of the γ phase is considerably widened at a high temperature, and this state is achieved in the room temperature region by using the production method of the present invention.

In the present invention, Mg-Al-based hydrogen storage alloy powder that becomes Mg _x Al _100-x (x = 47.5 to 70.0) is obtained, that is, Mg _47.5 Al _52.5 to Since the composition range is up to Mg _70.0 Al _30.0 , a desired ratio of magnesium (Mg) and aluminum (Al) may be selected for Mg _x Al _100-x. As the compounding ratio of aluminum, the compounding ratio should be selected so that the desired composition ratio is obtained between magnesium / aluminum = 47.5 / 52.5-70.0 / 30.0 as the atomic weight ratio. That's fine.

  As a raw material for the Mg—Al-based hydrogen storage alloy powder, a mixed powder obtained by mixing a powder of magnesium alone and a powder of aluminum alone can be used. The average particle size of the magnesium simple powder or aluminum simple powder used is preferably about 1 μm to 3 mm, and particularly preferably about 100 μm to 1 mm.

Moreover, as a raw material, in addition to the powder composed of the above-mentioned simple metal, a powder composed of a hydride of a simple metal can be used. For example, magnesium hydride as a hydride (magnesium hydride: MgH ₂ ), aluminum A hydride (aluminum hydride: AlH ₃ ) or the like may be used.

  In the production method of the present invention, a rare metal oxide is added in addition to the aforementioned magnesium and aluminum and used as a metal raw material powder. Such rare metal oxides act as a catalyst in alloying magnesium and aluminum, promote the alloying of magnesium and aluminum, improve the hydrogen storage capacity of the resulting hydrogen storage alloy powder, and in particular increase the hydrogen storage rate. It works to improve (make it faster).

Examples of rare metal oxides that can be used include oxides such as niobium (Nb), zirconium (Zr), vanadium (V), tantalum (Ta), titanium (Ti), and aluminum (Al). If these oxides are used, alloying proceeds easily and reliably, the hydrogen storage ability of the obtained hydrogen storage alloy powder can be improved, and the hydrogen storage rate can be further increased. Of these, niobium (Nb) is preferably used. Examples of niobium oxides include niobium pentoxide (niobium oxide (V)) (Nb ₂ O ₅ ), zirconium oxides such as zirconium oxide (ZrO ₂ ), and vanadium oxides such as vanadium pentoxide (V Examples of tantalum oxides such as ₂ O ₅ ) include tantalum pentoxide (tantalum oxide (V)) (Ta ₂ O ₅ ), and examples of aluminum oxides include aluminum oxide (Al ₂ O ₃ ). One of these rare metal oxides may be used alone, or a combination of these two types may be used.

The amount of the noble metal oxide, depending on the amount of magnesium and aluminum, as mol% relative to _Mg x _{Al 100-x} 1mol to be added interest, may be added generally over 0.1 mol% 0.1 to 5.0 mol% is preferable, and 1.0 to 5.0 mol% is particularly preferable. If the addition amount is less than 0.1 mol%, the effect of adding a rare metal oxide may not appear, whereas if the addition amount exceeds 5.0 mol%, the effect of improving the hydrogen storage capacity of the alloy is On the other hand, it may be present as impurities against magnesium and aluminum. In addition, these rare metal oxides are relatively expensive, leading to high costs. There is no restriction | limiting in particular as a form of a rare metal oxide, The thing of arbitrary forms, such as a granular form, a powder form, and a pellet form, can be used.

  When preparing a metal raw material powder using magnesium, aluminum and a rare metal oxide, the rare metal oxide may be added to the mixed powder obtained by mixing magnesium and aluminum, or magnesium, aluminum. And a rare metal oxide may be mixed at the same time to obtain a metal raw material powder.

  In addition, in the metal raw material powder used in the production method of the present invention, in addition to the simple substance constituting the target alloy and the rare metal oxide serving as a catalyst, in a range that does not affect the purpose and effect of the present invention, One or more metal powders selected from the group consisting of Pd, Mn, Co, V, Cr, Mo, Ni, Zr, Nb, and Be can be added.

  In the production method of the present invention, pretreatment such as heat treatment, surface treatment, and pickling treatment may be performed on the metal raw material powder as long as the object and effect of the present invention are not affected.

(1) Grinding process:
In the production method of the present invention, a metal raw material powder composed of magnesium, aluminum, and a rare metal oxide is processed by ball milling and pulverized until it becomes nano-level crystal grains. Here, the nano-level crystal grain in the present invention means a state in which the crystal grain size is approximately 1 μm or less (preferably about several tens of nm). In the production method of the present invention, the metal raw material powder is pulverized until it becomes nano-level crystal grains, so that when the heat treatment is performed in the subsequent heat treatment step, the mutual atoms are diffused to each other, so that the production is performed. The alloy composition to be more uniform throughout the powder. On the other hand, when the metal raw material powder is not pulverized until it becomes nano-level crystal grains, a part in which the atoms are not mixed well is generated and is not locally alloyed or has a non-uniform composition. It becomes alloy powder.

  Ball milling refers to a method of mixing and pulverizing metal raw material powder with a ball mill or the like. Generally, ball milling of metal raw material powder containing two or more kinds of metal elements, particularly mechanical alloying (MA ). This mechanical alloying method (hereinafter sometimes abbreviated as “MA method”) refers to a metal raw material powder containing two or more kinds of metal elements, using a high energy mixing and stirring device or the like. This is a method of producing solid alloy particles in a solid state in a solid state by repeatedly mixing and pulverizing the powder and ball milling to cause a solid phase reaction. The mechanical alloying method as a manufacturing method can alloy and powder two or more kinds of metal powders at a temperature lower than the melting point by utilizing mechanical energy.

  Examples of the ball milling method (ball mill method) include a rotating ball mill method, a vibrating ball mill method, a planetary ball mill method, and a stirring ball mill method (also referred to as an attritor). Method, vibration ball mill method, and planetary ball mill method are preferable, and rotation ball mill method and vibration ball mill method are particularly preferable.

  The milling time in the production of the Mg—Al-based hydrogen storage alloy powder of the present invention is as follows: the type of ball mill method used, the amount of metal raw material powder, the size and number of balls for mixing and grinding, the capacity of the container However, it is preferably about 1 hour or more, and more preferably about 1 to 10 hours. If ball milling is performed with the milling time in this range, the metal raw material powder can be pulverized until it becomes a nano-level crystal grain. On the other hand, if the milling time is shorter than 1 hour as described above, the metal raw material powder may not be pulverized to the nano level. On the other hand, if the milling time is longer than 10 hours, the metal raw material powder is not contained in the container. The recovery rate is poor because it adheres, and the impurities in the container are mixed in the metal raw material powder, so that the alloy characteristics may not be satisfactory. The milling time is more preferably 1 to 5 hours, and particularly preferably 1 to 3 hours.

  The rotating ball mill method, which is one of the types of ball mill methods, rotates a container containing metal raw material powder and a ball for mixing and grinding (hereinafter sometimes simply referred to as “ball”), and the raw material powder and the container are rotated. In addition, the metal raw material powder in the container is mechanically mixed and ground in a state of high energy to be alloyed or pulverized by collision with a ball.

  In addition, the vibration ball mill method means that a cylindrical container containing a metal raw material powder and a ball for mixing and grinding is subjected to high-speed circular vibration, and the simultaneous action of intense shock and friction between the raw material powder and the inner wall of the container and the raw material powder. This is a method of pulverizing in a short time, mixing and pulverizing the metal raw material powder in the container in a mechanically high energy state, and alloying or pulverizing. In the production method of the present invention, the vibration ball mill method can be used for both dry and wet processes.

  In the planetary ball mill method, a container containing metal raw material powder and a ball for mixing and grinding is placed on a gantry and the container is rotated (rotated), and the gantry on which the container is placed is rotated (revolved). ), And the metal raw material powder in the container is mechanically mixed and pulverized in a high energy state to be alloyed or pulverized by collision of the raw material powder with the container and the ball for mixing and pulverizing. Is the method.

  When using the ball mill method, the metal raw material powder, which is the raw material used, is mixed and ground in a container (pot) together with the ball for mixing and grinding, and the metal raw material powder is mixed and ground using means such as rotating the container. A hydrogen storage alloy powder is prepared by the following means. In the case of producing the hydrogen storage alloy powder of the present invention, the shape of the container used can be various shapes such as a cylindrical shape and a rectangular tube shape, but it is preferable to use a cylindrical shape. .

  Further, the capacity of the container is appropriately determined depending on the amount of the metal raw material powder used, the size and the number of balls for mixing and grinding, etc., but generally it may be about 50 to 10,000 ml. Further, the material of the container can be stainless steel, chromium, tungsten, alumina, zirconia, etc., and stainless steel is particularly preferable.

  Similarly, the material of the balls for mixing and grinding used for carrying out the ball mill method can be stainless steel, chromium, tungsten, alumina, zirconia, etc., and particularly preferably stainless steel.

  The size of the ball for mixing and pulverizing is appropriately determined depending on the capacity of the container used as described above. However, when the metal raw material powder is pulverized until it becomes nano-level crystal grains, generally the diameter is It is preferable to use one having a diameter of about φ1 mm to φ50 mm. In the ball mill method, a plurality of balls for mixing and grinding are usually used. However, when producing the hydrogen storage alloy powder of the present invention, the same size of the balls is used. Alternatively, different sizes may be used.

  The number of balls for mixing and grinding is preferably 10 to 2000. By setting the relationship between the capacity of the container and the size and quantity of the balls for mixing and grinding, the metal raw material powder can be efficiently pulverized to nano-level crystal grains.

  Furthermore, the weight ratio between the metal raw material powder and the total amount of the balls for mixing and grinding is preferably set so that the metal raw material powder and the balls for mixing and grinding = 1/10 to 1/500. By setting the weight ratio of the metal raw material powder and the total amount of the balls for mixing and pulverizing in such a range, the metal raw material powder can be efficiently pulverized until it becomes nano-level crystal grains. The weight ratio is particularly preferably set to metal raw material powder and mixing and grinding balls = 1/10 to 1/100.

  When the planetary ball mill method is used as the ball mill method in producing the hydrogen storage alloy powder of the present invention, the rotational speed of the container and the rotational speed of the mount on which the container is placed are the rotational speed of the container (rotational speed). Is preferably 200 to 700 rpm. Moreover, it is preferable that the rotation speed (revolution rotation speed) of the gantry is 200 to 350 rpm. When the rotational speed is within these ranges, the metal raw material powder can be pulverized efficiently and reliably until it becomes nano-level crystal grains. Furthermore, the revolution radius in the case of using the planetary ball mill method may be about 30 to 300 cm, and preferably about 50 to 100 cm.

  Further, when the vibration ball mill method is used as the ball mill method for producing the hydrogen storage alloy powder of the present invention, it is preferable that the rotation speed (vibration rotation speed) of the container is 100 to 1000 rpm. When the rotation speed (vibration rotation speed) is within these ranges, the metal raw material powder can be pulverized efficiently and reliably to nano-level crystal grains as in the planetary ball mill method described above. .

  Furthermore, when the rotating ball mill method is used as the ball mill method for producing the hydrogen storage alloy powder of the present invention, the rotational speed of the container is preferably 10 to 100 rpm. When the rotational speed is within these ranges, the metal raw material powder can be pulverized efficiently and reliably to nano-level crystal grains, as in the planetary ball mill method and the vibration ball mill method described above.

  In producing the hydrogen storage alloy powder of the present invention, the atmosphere in the container is preferably an inert gas atmosphere such as argon, nitrogen, helium, or a hydrogen gas atmosphere. By setting the atmosphere in the container to such a state, oxidation of the metal raw material powder can be prevented. The atmosphere in the container is particularly preferably an argon gas atmosphere or a hydrogen gas atmosphere.

  Further, the inside of the container in the pulverization process may be evacuated with a rotary pump or the like under a condition of 10 Pa or less, and this can also prevent oxidation of the metal powder as in an inert gas atmosphere. .

(2) Heat treatment process:
In the manufacturing method of the Mg-Al hydrogen storage alloy powder of the present invention, by heat-treating the pulverized metal raw material powder until it becomes nano-level crystal grains by the pulverization step, The metal raw material powder is reliably alloyed. Such heat treatment is not completely alloyed by the pulverization process of the previous step, but forms a fine structure of the metal raw material powder, and does not break the nanostructure with respect to the metal raw material powder formed with such a fine structure. Heat treatment to promote and achieve alloying by atomic diffusion.

  As the holding temperature (heat treatment temperature), since the melting point of the Mg—Al alloy is about 450 ° C., it may be about 100 ° C., which is about 20% of the temperature, and the heat treatment is carried out at about 100 to 300 ° C. It is preferable to do. In the production method of the present invention, since the metal raw material powder is pulverized until it becomes nano-level crystal grains by ball milling in the pulverization process of the previous process, only the heat treatment is performed at a relatively low temperature. Thus, alloying can be promoted. However, there is no problem even if heat treatment is performed at a temperature exceeding 300 ° C. However, for example, if the temperature is higher than 350 ° C., crystal grain growth becomes remarkable, and segregation or separation may occur.

  The heat treatment is preferably performed in a vacuum state. For example, the heat treatment may be performed in a state in which a container containing the pulverized metal raw material powder is evacuated with a rotary pump or the like under a condition of 10 Pa or less. .

  The heating time is preferably 1 to 5 hours, and particularly preferably 1 to 3 hours. The rate of temperature rise is preferably 10 to 100 ° C./min, and particularly preferably 50 to 100 ° C./min. Note that after the heat treatment for a predetermined time is completed, the heat treatment may be performed until the temperature reaches room temperature in the electric furnace.

  In the manufacturing method of the Mg—Al-based hydrogen storage alloy powder of the present invention, an appropriate amount of a rare metal oxide is added in addition to magnesium and aluminum as a constituent of the metal raw material powder as a raw material. Mg-Al-based hydrogen that improves the hydrogen storage capacity of the obtained hydrogen storage alloy powder, such as by promoting the alloying of magnesium and aluminum and increasing the hydrogen storage rate, and especially the high hydrogen storage rate It is possible to provide a storage alloy powder.

In addition, a configuration in which a metal raw material powder is pulverized by ball milling until it becomes nano-level crystal grains, and a heat treatment step of heat-treating the pulverized metal raw material powder obtained by the pulverization process is combined. By adopting, it is possible to control the existence region of the γ phase (Mg ₁₇ Al ₁₂ phase) in the Mg—Al based alloy, and the magnesium composition ratio can exist in a wide range of 47.5 to 70.0. _{mg x Al 100-x (x} = 47.5~70.0) to become mg-Al-based hydrogen storage alloy powder can be provided.

  Furthermore, the production method of the present invention forms a microstructure of a metal raw material powder that is not completely alloyed by a pulverization process until it becomes nano-level crystal grains that can be achieved by milling for several hours. It is possible to produce hydrogen storage alloy powder efficiently and stably in a short time and at low cost by a simple means of heat treatment at a low temperature so as not to break the structure and promoting and achieving alloying by the diffusion phenomenon of atoms. It becomes possible.

  And, the hydrogen storage alloy powder of the present invention obtained by the above-mentioned production method combining different processes such as a pulverization process and a heat treatment process has a homogeneous structure, and a high hydrogen storage capacity is obtained as a hydrogen storage alloy. In addition, a hydrogen storage alloy powder having desired performance such as high corrosion resistance / corrosion resistance and high mechanical strength as an alloy is obtained. In consideration of the fact that the hydrogen storage alloy powder obtained by the production method of the present invention has a lot of amorphous and nano-sized parts compared with the melting method, etc., the three major characteristics of the amorphous structure (high corrosion resistance, high mechanical strength) And high magnetism).

  As described above, the Mg—Al-based hydrogen storage alloy powder obtained by the production method of the present invention has a main composition of magnesium that can be expected to have a hydrogen storage capacity, and therefore has a large hydrogen storage capacity and a high hydrogen storage speed. Thus, it becomes a hydrogen storage alloy powder that can be used for industrial machinery such as an on-vehicle fuel cell.

  In general, Mg-based hydrogen storage alloys store hydrogen by applying hydrogen pressure (hydrogen activation) at a temperature of 300 ° C. (or higher) at about 0.5 to 3.0 MPa in a vacuum state. However, in the Mg—Al-based hydrogen storage alloy powder of the present invention, hydrogen can be stably stored and reversibly stored and released from the second time. On the other hand, the Mg-based hydrogen storage alloy manufactured by a conventional manufacturing method is difficult to release even if hydrogen is stored. Or even if it is in the said conditions, several days of five days or more are required for hydrogen storage.

  Further, the conventional Mg-based hydrogen storage alloy has been considered to have a drawback that the storage / release rate (hydrogen storage rate) in hydrogen storage is slow and the hydrogen storage amount does not match the theoretical value. This Mg—Al-based hydrogen storage alloy powder can store hydrogen without initial activation, and can reversibly store and release 4.0% by mass or more of hydrogen. Further, the reaction is further accelerated after the second time, and 4.0 mass% or more of hydrogen is reversibly occluded / released within a few hours.

  EXAMPLES Next, although an Example is given and this invention is demonstrated in more detail, this invention is not restrict | limited at all by these Examples.

[Example 1]
(Production of Mg-Al hydrogen storage alloy powder)
An Mg—Al-based hydrogen storage alloy powder made of Mg ₇₀ Al ₃₀ was produced by the following steps (1) and (2). The Mg powder used (manufactured by Kojundo Chemical Laboratory Co., Ltd.) has an average particle size of 53 to 106 μm and a purity of 99.9% or more. ) Has an average particle size of about 1 μm and a purity of 99.9% or more.

(1) Grinding process by ball milling:
The above-mentioned specifications of Mg powder and Al powder are mixed at 1.123 g (Mg: 0.761 g, Al: 0.362 g) with a compounding ratio of Mg / Al = 70/30 in an atomic weight ratio to obtain a raw material powder. 1 mol% (0.119 g) of granular niobium pentoxide (Nb ₂ O ₅ ) powder as a rare metal oxide was added to the raw material powder to obtain a metal raw material powder. Using this metal raw material powder as a test device, a vibration type ball mill (product name: mechanical alloying device: manufactured by Nisshin Giken Co., Ltd.) was used, and a weight ratio of about 1 to the weight of stainless steel balls for mixing and grinding in a container with a capacity of 80 mL. After being put in a sealed state so as to be / 80, the inside of the container was made a vacuum atmosphere of 10 Pa or less with a rotary pump. This container was placed on a stand of a vibration ball mill test apparatus, and ball milling was performed with a vibration rotational speed of 710 rpm and a milling time of 3 hours, to obtain a pulverized metal raw material powder.

(2) Heat treatment process:
An appropriate amount of the pulverized metal raw material powder obtained by the ball milling step (1) was enclosed in a stainless steel reaction tube attached to a hydrogen storage evaluation apparatus described later without exposing the raw material powder to the atmosphere. Next, heat treatment was performed for 1 hour in an electric furnace heated to 300 ° C. in a vacuum atmosphere of 1 Pa or less with the rotary pump together with the container. After 1 hour, the stainless steel container was gradually cooled to room temperature in an electric furnace to obtain an Mg—Al-based hydrogen storage alloy powder of the present invention having an average particle size of 1 to 50 μm.

FIG. 2 is an X-ray diffraction spectrum of the Mg—Al-based hydrogen storage alloy powder obtained in Example 1. As shown in FIG. 2, in the hydrogen storage alloy powder of the present invention obtained in Example 1, only the peaks of Mg ₁₇ Al ₁₂ (γ phase) and Mg phase constituting Mg ₇₀ Al ₃₀ can be confirmed, and Mg ₇₀ It was confirmed that an Mg—Al alloy composed of Al ₃₀ could be produced.

[Test Example 1]
(Evaluation of hydrogen storage performance)
The Mg—Al-based hydrogen storage alloy powder obtained in Example 1 was subjected to hydrogen activation treatment using the following method to evaluate the hydrogen storage capacity.

  About 1.0 g of the Mg—Al-based hydrogen storage alloy powder obtained in Example 1 was sealed in a stainless steel reaction tube (capacity: 18 mL) connected to a hydrogen storage measuring device (conforming to JIS H7201) and sealed. . Next, the inside of the measuring apparatus was evacuated with a vacuum pump until a vacuum of 1 Pa or less was reached. When the vacuum was reached, only the reaction tube in which the hydrogen storage alloy powder was sealed was heated to 300 ° C. in an electric furnace.

  After the temperature and the degree of vacuum were stabilized, 1.52 MPa (15 atm) of hydrogen was introduced into a measuring apparatus sealed from a high-pressure hydrogen cylinder. Thus, the change of the pressure in the reaction tube when hydrogen was introduced into the measuring apparatus was confirmed. The measuring device is equipped with a pressure gauge so that the pressure in the reaction tube can be measured.

  In this test, if the hydrogen storage alloy powder sealed in the reaction tube absorbs hydrogen after introducing high-pressure hydrogen into the measurement apparatus, the hydrogen pressure in the measurement apparatus gradually decreases. Therefore, if the initial hydrogen pressure introduced in the sealed pressure vessel is known, the amount of hydrogen occluded by the alloy can be known from the change in pressure (note that the volume of the gas changes with temperature, the reaction tube Since the temperature gradient is generated in the measuring device because the heating is performed only in the electric furnace, in the actual measurement, the above correction is made to the measured pressure, and the actual hydrogen storage amount is secondarily determined. To calculate.) In addition, if the hydrogen pressure drops quickly with respect to time, it means that the hydrogen occlusion speed is fast.

  In the first hydrogen activation treatment, the reactivity with hydrogen is poor, and it usually takes a long time to absorb and release by reacting with hydrogen. It took 60 hours to occlude 0% by mass of hydrogen.

  FIG. 3 is a graph showing the second measurement result (relationship between the hydrogen pressure in the reaction tube and the time in the activation process. The same applies to the third and fourth times). Since the Mg—Al-based hydrogen storage alloy powder in the reaction tube occludes hydrogen, the hydrogen pressure in the reaction tube decreases with time, and the required time is about 0.65 V (0.658 MPa: 6 in 3 hours (10800 s)). .5 atm) and became saturated. It was calculated from the pressure that occluded approximately 4.0% by mass of hydrogen.

  Next, the vacuum was evacuated by a vacuum pump in a state where the pressure was saturated and the hydrogen equilibrium pressure was reached as described above. Thereby, the inside of the container once became 0 V (0 Pa: 0 atm). After the evacuation, hydrogen was released from the sample (hydrogen storage alloy powder), whereby the pressure in the container was increased and saturated at 0.25 V (0.253 MPa: 2.5 atm). It was calculated that approximately 2.0% by mass of hydrogen was released from the pressure.

  FIG. 4 is a graph showing the results of the third measurement. The Mg—Al-based hydrogen storage alloy powder in the reaction tube occluded hydrogen again, and the hydrogen pressure in the reaction tube decreased with time. The required time was saturated at about 1.28 V (1.30 MPa: 12.8 atm) in 40 minutes (2400 s). It was calculated from the pressure that occluded approximately 2.8% by mass of hydrogen.

  FIG. 5 is a graph showing the fourth measurement result. The Mg—Al-based hydrogen storage alloy powder in the reaction tube occluded hydrogen three times, and the hydrogen pressure in the reaction tube decreased with time. Then, the saturation time was reached at about 0.145 V (0.147 MPa: 1.45 atm) in 120 minutes (7200 s) as the required time. From the pressure, it was calculated that approximately 0.9% by mass of hydrogen was occluded.

  FIG. 6 is a graph showing the results of a PCT measurement test at 300 ° C. (horizontal axis: hydrogen storage amount (mass%), vertical axis: equilibrium hydrogen pressure (MPa)). The PCT measurement test is a method for measuring the pressure-composition isotherm (PCT line) of the hydrogen storage alloy defined in JIS H7201. As shown in FIG. 6, it was confirmed that the maximum hydrogen storage amount of the Mg—Al-based hydrogen storage alloy powder of the present invention obtained in Example 1 was about 5.3 mass%.

  Further, FIG. 7 is a graph showing the results of PCT measurement tests at 250 ° C., 300 ° C. and 350 ° C. (horizontal axis: hydrogen storage amount (mass%), vertical axis: equilibrium hydrogen pressure (MPa). The occlusion and release in the graph are the same as in FIG. The PCT measurement test is a method for measuring the pressure-composition isotherm (PCT line) of the hydrogen storage alloy defined in JIS H7201. As shown in FIG. 7, it was confirmed that the Mg—Al-based hydrogen storage alloy powder of the present invention obtained in Example 1 can store about 4.8% by mass of hydrogen at any temperature. .

  The present invention can be advantageously used as, for example, a hydrogen storage alloy powder applied to an on-vehicle fuel cell.

It is an equilibrium state diagram of Mg-Al system. 2 is a diagram showing an X-ray diffraction spectrum of an Mg—Al-based hydrogen storage alloy powder obtained in Example 1. FIG. It is the figure which showed the graph of the measurement result in Experiment 1 (2nd time). It is the figure which showed the graph of the measurement result in Experiment 1 (the 3rd time). It is the figure which showed the graph of the measurement result in Experiment 1 (the 4th time). It is the graph which showed the result of the PCT measurement test in 300 degreeC in Test Example 1. 4 is a graph showing the results of a PCT measurement test at 250 ° C., 300 ° C., and 350 ° C. in Test Example 1. FIG.

Claims (5)

In producing an Mg—Al-based hydrogen storage alloy powder of Mg _x Al _100-x (x = 47.5 to 70.0), a desired ratio of magnesium (Mg) and aluminum (Al), and an appropriate amount of rare earth A pulverization treatment step of pulverizing a metal raw material powder containing a metal oxide until it becomes nano-level crystal grains by ball milling;
The manufacturing method of the Mg-Al type hydrogen storage alloy powder characterized by including the heat processing process which heat-processes the ground material powder obtained by the said grinding | pulverization process.   The rare metal oxide is at least one selected from the group consisting of oxides of niobium (Nb), zirconium (Zr), vanadium (V), tantalum (Ta), titanium (Ti), and aluminum (Al). The manufacturing method of Mg-Al type hydrogen storage alloy powder of Claim 1 characterized by these.   The method for producing an Mg-Al-based hydrogen storage alloy powder according to claim 1 or 2, wherein a heating temperature in the heat treatment step is 100 to 300 ° C.   The method for producing an Mg-Al-based hydrogen storage alloy powder according to any one of claims 1 to 3, wherein the ball milling is any one of a vibration ball mill, a rotating ball mill, and a planetary ball mill.   An Mg—Al-based hydrogen storage alloy powder obtained by the manufacturing method according to claim 1.