JP2009155682A - Hydrogen storage alloy and method for producing the same - Google Patents

Abstract

A hydrogen storage alloy capable of improving durability and a method for producing the hydrogen storage alloy are provided.
SOLUTION: Hydrogen storage comprising, in mass%, Ti: 5 to 10%, Cr: 5 to 15%, V: 70 to 89%, and Mo: 1 to 10%, with the balance being inevitable impurities The alloy is a hydrogen storage alloy in which a needle-like or plate-like high Ti phase is precipitated in the parent phase, and in mass%, Ti: 5 to 10%, Cr: 5 to 15%, V: 70% to 89%, and Mo: 1% to 10%, a first step of producing a molten alloy consisting of inevitable impurities, and a time of 5 minutes to 15 minutes after the first step And a second step of cooling the mold poured in the molten metal to 860 ° C. and a third step of cooling the mold to 670 ° C. in a time of 5 minutes to 30 minutes after the second step. An alloy manufacturing method is used.
[Selection] Figure 1

Description

  The present invention relates to a hydrogen storage alloy used as a hydrogen storage material for a fuel cell, and a method for producing the hydrogen storage alloy.

  The fuel cell, which is being studied as a global warming countermeasure technology, is a device that extracts the electrical energy generated during the electrochemical reaction of reactants (hydrogen, air, etc.) to the outside, and is a clean device that does not generate harmful gases. Known as a powerful energy source. In a vehicle equipped with a fuel cell (hereinafter referred to as “fuel cell vehicle”), when hydrogen is used as a reactant, a means for storing the hydrogen to be used is required. As a hydrogen storage mode, gaseous hydrogen is used. In addition to the form of direct filling and liquid hydrogen, a form of using a hydrogen storage alloy has been proposed. Among these, from the viewpoint of being able to store a larger amount of hydrogen than liquid hydrogen and being excellent in safety, a form using a hydrogen storage alloy is attracting attention.

  A hydrogen storage alloy is an alloy that can store and release hydrogen by controlling temperature and pressure, and hydrogen stored in the hydrogen storage alloy enters voids in the crystal structure. Therefore, in order to increase the amount of stored hydrogen, it is effective to use a hydrogen storage alloy having a crystal structure with many voids. As a hydrogen storage alloy having a large amount of hydrogen storage, a body-centered cubic lattice system ( Hereinafter, a hydrogen storage alloy of “BCC type” is known.

  The hydrogen storage alloy mounted on the fuel cell vehicle is required to release hydrogen during operation of the fuel cell, and the hydrogen used during operation is stored in the hydrogen storage alloy when the fuel cell is stopped. In general, since the fuel cell vehicle is repeatedly operated and stopped, the hydrogen storage alloy mounted on the fuel cell vehicle repeatedly stores and releases hydrogen. However, the BCC-type hydrogen storage alloy with a large amount of hydrogen storage reduces the amount of hydrogen that can be stored in the hydrogen storage alloy when the storage and release of hydrogen is repeated, and the hydrogen storage / release performance decreases (in the following). It is sometimes referred to as “deterioration” or “durability reduction”). When the hydrogen storage / release performance deteriorates, the amount of hydrogen that can be stored at one time is reduced, so the cruising distance of the fuel cell vehicle is reduced. Therefore, in order to maintain the cruising distance of the fuel cell vehicle for a long period of time, a hydrogen storage alloy that does not easily deteriorate even if hydrogen is repeatedly stored and released is required.

  As a technique related to such a BCC-based hydrogen storage alloy, for example, Patent Document 1 contains 5 to 40 atomic% Ti, 10 to 56 atomic% Cr, and 15 to 82 atomic% V. The total content of Ti, Cr and V is 90 atomic% or more, the oxygen content is WO (mass%), the nitrogen content is WN (mass%), and the carbon content is WC (mass%). A hydrogen storage alloy is disclosed in which the oxygen equivalent is 0.1% by mass or less when the oxygen equivalent is expressed as WO + 2.97WN + 1.13WC. Patent Document 2 discloses that a melted BCC single-phase hydrogen storage alloy is subjected to a solution treatment in a non-oxidizing atmosphere, and thereafter, at a cooling rate of 300 ° C./hour or less in the non-oxidizing atmosphere. A technique relating to a heat treatment method for a hydrogen storage alloy, characterized in that the temperature is lowered to 350 ° C. or lower is disclosed. Patent Document 3 discloses a technique relating to a method for producing a hydrogen storage alloy, characterized in that a molten hydrogen storage alloy is solidified while being gradually cooled at a cooling rate of 5 ° C./min or less.

JP 2004-27247 A JP 2006-28621 A JP 2003-277847 A

  The cause of the decrease in the durability of the hydrogen storage alloy has not been fully elucidated at this time, but the strain caused by repeated storage and release of hydrogen is considered to be a cause of the decrease in the durability of the hydrogen storage alloy. Yes. Therefore, in order to improve the durability of the hydrogen storage alloy, it is considered effective to use a hydrogen storage alloy in a form in which the strain is easily reduced. However, the technique disclosed in Patent Document 1 has a problem that it is difficult to obtain a hydrogen storage alloy in a form in which distortion is easily reduced, and durability cannot be sufficiently improved. Further, even if a hydrogen storage alloy is manufactured by the methods disclosed in Patent Document 2 and Patent Document 3, it is difficult to manufacture a hydrogen storage alloy in a form in which distortion is easily reduced. There was a problem that the durability of the storage alloy could not be improved sufficiently.

  Then, this invention makes it a subject to provide the hydrogen storage alloy which can improve durability, and the manufacturing method of the said hydrogen storage alloy.

In order to solve the above problems, the present invention takes the following means. That is,
The first aspect of the present invention contains at%, Ti: 5 to 10%, Cr: 5 to 15%, V: 70 to 89%, and Mo: 1 to 10%, and the balance is inevitable The hydrogen storage alloy is characterized in that a needle-like or plate-like high Ti phase is precipitated in the matrix phase.

  Here, the crystal structure of the hydrogen storage alloy according to the first aspect of the present invention is a body-centered cubic lattice structure (BCC structure). Therefore, in the first aspect of the present invention, the “parent phase” means a phase that is V-rich. Furthermore, in the first aspect of the present invention, the “high Ti phase” means a precipitated phase containing more Ti than the parent phase. The amount of Ti contained in the high Ti phase is not particularly limited as long as it is larger than the amount of Ti contained in the matrix phase. For example, it contains 21.6 to 93.6% Ti at at%. The phase to be made can be the high Ti phase in the first aspect of the present invention. Furthermore, “the needle-like or plate-like high Ti phase is precipitated in the matrix phase” means that the needle-like or plate-like high Ti phase is precipitated in the crystal grains constituting the matrix phase. Means that.

  The hydrogen storage alloy according to the first aspect of the present invention contains at%, Ti: 5 to 10%, Cr: 5 to 15%, V: 70 to 89%, and Mo: 1 to 10%. A first step of casting a molten metal whose remainder is an inevitable impurity, a second step of cooling the mold into which the molten metal has been poured to 860 ° C. in a time period of 5 minutes to 15 minutes after the first step; After the second step, it is preferably manufactured through a third step of cooling the mold to 670 ° C. in a time of 5 minutes to 30 minutes.

  Here, in the first aspect of the present invention and the present invention described below, “the second step of cooling the mold into which the molten metal has been poured to 860 ° C. in a period of 5 minutes to 15 minutes after the first step” In the first step, a molten metal in which Ti, Cr, V, and Mo (hereinafter referred to as “each component”) are uniformly mixed is cast by being heated to a temperature of about 1650 ° C., for example. It means that the step of lowering the temperature of the mold into which the molten metal has been poured to 860 ° C. for 5 to 15 minutes from the time is the second step. Furthermore, “the third step in which the mold is cooled to 670 ° C. in a time period of 5 minutes to 30 minutes after the second step” means that at least 5 minutes from the time when the temperature dropped to 860 ° C. in the second step. It means that the step of further lowering the temperature of the mold to 670 ° C. in 30 minutes or less is the third step.

  In the first aspect of the present invention manufactured through the first step to the third step, a fourth step of cooling the mold to 200 ° C. in a time of 50 minutes or less after the third step may be provided. preferable.

  Here, “it is preferable that the fourth step is provided” means that the hydrogen storage alloy according to the first aspect of the present invention is preferably manufactured through the first step to the fourth step.

  In the first aspect of the present invention (including modifications), when the cross-sectional area of the parent phase at an arbitrary cut surface is A and the cross-sectional area of the high Ti phase at the cut surface is B, 0.05 ≦ It is preferable that B / (A + B) ≦ 0.2.

  Here, “A” and “B” in “0.05 ≦ B / (A + B) ≦ 0.2” are more specifically, the cut surface of the hydrogen storage alloy according to the first aspect of the present invention is examined with a microscope ( For example, when observed with a transmission electron microscope (TEM), this corresponds to the area A of the parent phase confirmed in the visual field and the area B of the high Ti phase confirmed in the visual field.

  The second aspect of the present invention contains at%, Ti: 5 to 10%, Cr: 5 to 15%, V: 70 to 89%, and Mo: 1 to 10%, and the balance from inevitable impurities A first step of casting the molten metal, a second step of cooling the mold into which the molten metal has been poured to 860 ° C. in a time period of 5 minutes to 15 minutes after the first step, and 5 steps after the second step. And a third step of cooling the mold to 670 ° C. for a period of time not shorter than 30 minutes and not longer than 30 minutes.

  In the second aspect of the present invention, it is preferable that a fourth step of cooling the mold to 200 ° C. in a time of 50 minutes or less is further provided after the third step.

  Here, “the fourth step is preferably provided” means that the fourth invention is provided with the fourth step, and the hydrogen storage alloy is manufactured through the first to fourth steps. Means preferred.

  According to the first aspect of the present invention, there is provided a hydrogen storage alloy in which a needle-like or plate-like high Ti phase is precipitated in crystal grains constituting a parent phase. According to the hydrogen storage alloy of this form, the inside of the parent phase can be subdivided into a plurality of regions surrounded by a plurality of high Ti phases precipitated in the crystal grains instead of a single region. Thus, when the region in the crystal grain is subdivided, the strain generated during the hydrogen storage / release can be dispersed, so that a hydrogen storage alloy in a form in which the strain can be easily reduced can be provided. Therefore, according to the first aspect of the present invention, it is possible to provide a hydrogen storage alloy capable of improving durability by adopting a form in which distortion is easily reduced.

  Further, the hydrogen storage alloy according to the first aspect of the present invention is manufactured through the first to third steps, so that a plurality of needle-like or plate-like high Ti phases are precipitated in the matrix (inside the crystal grains). It is possible to provide a hydrogen storage alloy of the above form.

  In addition, the hydrogen storage alloy according to the first aspect of the present invention is manufactured through the first to fourth steps, thereby reducing the precipitation of the high Ti phase at the grain boundary, and in the parent phase (inside the crystal grains). Many high Ti phases can be precipitated. Therefore, by adopting such a configuration, a hydrogen storage alloy having good hydrogen storage / release characteristics can be provided.

  In the first aspect of the present invention, the relationship of 0.05 ≦ B / (A + B) ≦ 0.2 is established between the cross-sectional area A of the parent phase and the cross-sectional area B of the high Ti phase. A hydrogen storage alloy capable of improving the effect can be provided.

  According to the second aspect of the present invention, the hydrogen storage alloy is manufactured through the first to third steps. By setting the second step to 5 minutes or more and 15 minutes or less, a hydrogen storage alloy having a uniform solidification structure while suppressing gravity segregation can be produced, and the third step is set to 5 minutes or more and 30 minutes or less. Thus, a hydrogen storage alloy in which a needle-like or plate-like high Ti phase is precipitated in the matrix phase can be produced. Therefore, according to the second aspect of the present invention, it is possible to provide a method for producing a hydrogen-absorbing alloy capable of producing a hydrogen-absorbing alloy capable of improving durability by adopting a form in which strain is easily reduced. .

  In addition, the hydrogen storage alloy according to the second aspect of the present invention is manufactured through the first to fourth steps, thereby reducing the precipitation of the high Ti phase at the grain boundary, and in the parent phase (inside the crystal grains). Many high Ti phases can be precipitated. Therefore, by adopting such a configuration, it is possible to provide a method for producing a hydrogen storage alloy capable of producing a hydrogen storage alloy having good hydrogen storage / release characteristics.

  Hydrogen loading in fuel cell vehicles is one of the major issues for practical application. Currently, high-pressure tanks are the mainstay because of their convenience. However, since the cruising distance is insufficient, further downsizing is desired, and a high-pressure hydrogen storage alloy tank is expected as a countermeasure. However, the high-pressure hydrogen storage alloy tank is advantageous for downsizing, but is currently heavy and urgently required to reduce its weight. Among hydrogen storage alloys, BCC-based hydrogen storage alloys are known as hydrogen storage alloys having a large amount of hydrogen storage. However, since the hydrogen storage alloy has a large degree of expansion / contraction during hydrogen storage / release, defects (dislocations and vacancies) are likely to occur, and the structure change during hydrogen storage / release is complicated (body-centered cubic lattice). Structure (BCC structure) → Body-centered tetragonal lattice structure (BCT structure) → Face-centered cubic lattice structure (FCC structure)). Therefore, once a defect occurs at the time of hydrogen storage / release, it is difficult to cause the planned tissue change. As a result, the amount of effective hydrogen that accompanies repeated hydrogen storage / release (the amount of hydrogen that can actually be used under specified operating conditions) For example, the amount of hydrogen that can be occluded / released between 35 MPa and 0.1 MPa at room temperature), and the initial high effective hydrogen amount cannot be used. . In order to solve such a problem, conventionally, the use temperature-pressure range is expanded (for example, hydrogen storage is performed at -5 ° C. and 35 MPa, and hydrogen release is performed at 80 ° C. and 0.01 MPa), and the composition is changed (high V), uniform organization, and measures such as tissue homogenization using the floating body melting method (FZ method) have been studied. However, these measures are not practical for vehicles and are not appropriate for reasons such as lack of mass productivity, and the effects are not so great.

  In order to solve the above problem, the present inventors investigated the reason for the occurrence of the problem through experiments. As a result, it has been found that the amount of decrease in the effective hydrogen amount is determined by the change in crystal lattice volume during occlusion. The present invention has been made based on such knowledge.

  The present invention will be described below with reference to the drawings. In the following description, “%” means “at%” unless otherwise specified.

1. Hydrogen Storage Alloy FIG. 1 is a conceptual diagram schematically showing a form example when a cross section of a hydrogen storage alloy according to the present invention is observed with an electron microscope. FIG. 1A is a diagram showing an example of a cross-sectional form of a hydrogen storage alloy before repeated hydrogen storage / release, and FIG. 1B shows an example of a cross-sectional form of the hydrogen storage alloy after repeated hydrogen storage / release. FIG. FIG. 2 is a conceptual diagram schematically showing a form example when a cross section of a conventional hydrogen storage alloy is observed with an electron microscope. FIG. 2A is a diagram showing a cross-sectional configuration example of the hydrogen storage alloy before repeated hydrogen storage / release, and FIG. 2B shows a cross-sectional configuration example of the hydrogen storage alloy after repeated hydrogen storage / release. FIG.

  As shown to Fig.1 (a), the hydrogen storage alloy 10 of this invention contains Ti: 5-10%, Cr: 5-15%, V: 70-89%, and Mo: 1-10%. In addition, needle-like or plate-like high Ti phases 2, 2,... Are deposited on the parent phase 1 of the BCC-based hydrogen storage alloy consisting of inevitable impurities. When hydrogen is stored in the hydrogen storage alloy 10 having such a form, the crystal grains 3, 3,... Constituting the parent phase 1 are expanded by hydrogen that has entered, and hydrogen is released from the hydrogen storage alloy 10. , The hydrogen that has entered is released to the outside, and the crystal grains 3, 3,. Therefore, when the hydrogen storage / release is repeated, the matrix 1 is likely to be distorted. However, in the hydrogen storage alloy 10 of the present invention, a plurality of high Ti phases 2, 2,... Are precipitated on the crystal grains 3, 3,. Therefore, the region of each crystal grain 3, 3,... Surrounded by the crystal grain boundary can be subdivided by a plurality of high Ti phases 2, 2,. In this way, when a plurality of high Ti phases are precipitated in each crystal grain 3, 3,..., The crystal grains 3, 3,... Constituting the parent phase 1 and the high Ti phases 2, 2,. The interface can be increased, and the strain can be dispersed through the interface. Therefore, according to the hydrogen storage alloy 10 of the present invention, the occurrence of cracks due to strain can be suppressed, and as a result, substantially the same structure can be maintained before and after repeated hydrogen storage / release. (See FIG. 1 (a) and FIG. 1 (b)). Therefore, according to this invention, the hydrogen storage alloy 10 which can improve durability can be provided.

  On the other hand, as shown in FIG. 2A, the conventional hydrogen storage alloy 20 has no high Ti phase precipitated on the crystal grains 3, 3,. Therefore, the strain in the crystal grains 3, 3,... Cannot be dispersed, and cracks and large deformations caused by the strain occur when hydrogen storage / release is repeated (see FIG. 2B). When cracks are generated in this way, it is difficult to continuously perform the structural change of BCC → BCT → FCC → BCT → BCC →... As a result, the hydrogen storage / release characteristics deteriorate. Therefore, in order to avoid such a situation, in the present invention, a high Ti phase in the form of needles or plates is precipitated on the crystal grains 3, 3,. The storage alloy 10 is used.

  The essential elements contained in the hydrogen storage alloy 10 of the present invention will be described below.

1.1. Ti: 5 to 10%
Ti is an element necessary for constituting a precipitated phase. If the Ti content is less than 5%, the desired precipitation amount cannot be obtained, so the lower limit of the Ti content is 5%. On the other hand, if the Ti content exceeds 10%, the effective hydrogen amount decreases, so the upper limit of the Ti content is 10%.

1.2. Cr: 5 to 15%
Cr is an element necessary for facilitating hydrogen storage. When the Cr content is less than 5%, hydrogen storage is delayed, so the lower limit of the Cr content is 5%. On the other hand, if the Cr content exceeds 15%, the effective hydrogen content and Ti precipitation phase decrease, so the upper limit of the Cr content is set to 15%. A more preferable Cr content is 5% to 10%.

1.3. V: 70-89%
V is an element necessary for hydrogen storage and high Ti phase precipitation. When the V content is less than 70%, the high Ti phase decreases, so the lower limit of the V content is 70%. On the other hand, if the V content exceeds 89%, the high Ti phase is reduced and the occlusion becomes extremely difficult, so the upper limit of the V content is 89%. A more preferable V content is 70% to 85%.

1.4. Mo: 1-10%
Mo is an element necessary for adjusting the equilibrium pressure. If the Mo content is less than 1%, the equilibrium pressure becomes not more than atmospheric pressure, so the lower limit of the Mo content is 1%. On the other hand, if the Mo content exceeds 10%, the equilibrium pressure is excessive and the effective hydrogen amount is greatly reduced, so the upper limit of the Mo content is 10%. More preferable Mo content is 5% to 10%.

  In the hydrogen storage alloy 10 of the present invention, the proportion of the high Ti phases 2, 2,... Occupying the matrix 1 is within a range in which strain can be dispersed and the hydrogen storage / release characteristics are not adversely affected. If there is, it will not be specifically limited. When the cross-sectional area of the parent phase 1 at an arbitrary cut surface of the hydrogen storage alloy 10 is A and the cross-sectional area of the high Ti phase 2, 2,... At the cut surface is B, the strain is such that durability can be improved. Is preferably 0.05 ≦ B / (A + B) from the viewpoint of precipitating high Ti phases 2, 2,. On the other hand, B / (A + B) ≦ 0.2 from the viewpoint of preventing the coarsened high Ti phases 2, 2,... From occluding a sufficient amount of hydrogen. It is preferable. More preferably, 0.05 ≦ B / (A + B) ≦ 0.14.

  In addition, it is manufactured through a predetermined manufacturing process from the viewpoint of making it possible to manufacture the hydrogen storage alloy 10 in a form in which needle-like or plate-like high Ti phases 2, 2,... Are precipitated on the crystal grains 3, 3,. It is preferable. In order to avoid duplication, the details of the production process will be specifically described in the column of the method for producing a hydrogen storage alloy according to the present invention.

2. 3. Method for Producing Hydrogen Storage Alloy FIG. 3 is a flowchart showing an example of a method for producing a hydrogen storage alloy according to the present invention (hereinafter sometimes referred to as “production method of the present invention”). FIG. 4 is a conceptual diagram showing the relationship between post-casting time and temperature. Hereinafter, the manufacturing method of the present invention will be described with reference to FIGS. 1, 3, and 4.

  As shown in FIG. 3, the manufacturing method of the present invention includes a first step (step S1), a second step (step S2), a third step (step S3), and a fourth step (step S4). The hydrogen storage alloy 10 is manufactured through steps S1 to S4.

2.1. 1st process (process S1)
Step S1 contains Ti: 5 to 10%, Cr: 5 to 15%, V: 70 to 89%, and Mo: 1 to 10%, and the remainder is made of inevitable impurities into a mold. This is a casting process by pouring. In the present invention, the molten metal poured into the mold is not particularly limited as long as it satisfies the above composition, and step S1 can be cast by a known method.

2.2. Second step (Step S2)
Step S2 is performed so that the temperature of the mold becomes 860 ° C. in a time period from 5 minutes to 15 minutes from the time when the molten metal is poured into the mold in Step S1 (the temperature range indicated by A in FIG. 4 is 5 minutes or more). Step S2 is an essential step for controlling the structure of the parent phase 1 of the hydrogen storage alloy 10. If the time of step S2 is less than 5 minutes, the solidified structure remains strongly and the mother phase 1 is not uniformized. If the structure of the matrix 1 is not uniform, the predetermined storage alloy characteristics are lost, which is not preferable. On the other hand, if the time of step S2 exceeds 15 minutes, gravity segregation is likely to occur, and the predetermined storage alloy characteristics are lost.

2.3. Third step (step S3)
Step S3 is a step of cooling the mold so that the temperature of the mold becomes 670 ° C. in a time period from 5 minutes to 30 minutes from the time when the mold is cooled to 860 ° C. in Step S2. Is an essential step for controlling the amount and form of precipitation of the high Ti phases 2, 2,... Deposited on the parent phase 1 of the hydrogen storage alloy 10. In the hydrogen storage alloy 10, the high Ti phases 2, 2,... Are precipitated in a temperature range of 860 ° C. to 670 ° C. (temperature range indicated by B in FIG. 4). It is necessary to allow sufficient time for the ... to precipitate. On the other hand, in the production stage of the hydrogen storage alloy, rapid cooling is often performed in order to prevent gravity segregation during casting. In the conventional method for producing a hydrogen storage alloy, the cooling time from 860 ° C. to 670 ° C. is short (for example, 3 minutes). In this respect, the manufacturing method of the present invention is greatly different from the prior art.

  In the production method of the present invention, when the time of step S3 is less than 5 minutes, precipitation of the high Ti phases 2, 2,... Is suppressed, and a sufficient amount of the high Ti phases 2, 2,. This is not preferable because it becomes difficult to precipitate the. In contrast, when the time of step S3 exceeds 30 minutes, the high Ti phase is granulated due to strain relaxation by thermal diffusion or the like. Here, even if only the granulated high Ti phase is provided in the parent phase of the hydrogen storage alloy, it is difficult to obtain the durability improvement effect, which is not preferable. Therefore, in the manufacturing method of this invention, the time of process S3 shall be 5 minutes or more and 15 minutes or less, and the acicular or plate-shaped high Ti phase is deposited.

2.4. Fourth step (step S4)
Step S4 is performed so that the temperature of the mold becomes 200 ° C. in a time of 50 minutes or less from the time when the mold is cooled to 670 ° C. in Step S3 (the temperature range indicated by C in FIG. 4 is 50 minutes or less). This is the step of cooling the mold. By setting the time of step S4 to 50 minutes or less, it is possible to suppress the amount of high Ti phases 2, 2,... Precipitated to the crystal grain boundaries and to convert many high Ti phases 2, 2,. , ... can be deposited. When the time of step S4 exceeds 50 minutes, the high Ti phase precipitated inside the crystal grain boundaries and crystal grains 3, 3,... Is coarsened, and the hydrogen storage alloy is in a form that cannot substantially contribute to hydrogen storage. Therefore, it is not preferable.

  In the said description regarding the manufacturing method of this invention, although the form with which a 4th process is provided was illustrated, the manufacturing method of this invention is not limited to the said form. However, the provision of the fourth step makes it possible to suppress the amount of high Ti phase precipitated at the grain boundaries and to suppress the coarsening of the high Ti phase, and to increase the effective hydrogen amount to a high level. Since it becomes possible to manufacture a hydrogen storage alloy capable of improving durability while maintaining it, it is preferable.

1. Manufacture of hydrogen storage alloy A plurality of types of hydrogen storage alloys were prepared by changing the composition and cooling conditions. And the ratio (value of said "B / (A + B)"), effective hydrogen amount, and deterioration rate of the high Ti phase which precipitated in the mother phase of the produced hydrogen storage alloy were measured. Table 1 shows the composition of the produced hydrogen storage alloy, the cooling conditions, the area ratio of the high Ti phase, the effective hydrogen amount, and the deterioration rate.

“Heat treatment condition X1” in Table 1 is that after casting the molten metal, it is cooled to 860 ° C. in 5 minutes, then cooled to 670 ° C. in 10 minutes, and then cooled to 200 ° C. in 30 minutes or less. “Heat treatment condition X2” means cooling to 860 ° C. in 1 minute, then cooling to 670 ° C. in 3 minutes, and then cooling to 200 ° C. over 60 minutes. It means that it was manufactured under the conditions. Furthermore, “heat treatment condition Y” in Table 1 means that the molten metal was cast under the condition of being allowed to stand for 2 hours, and “heat treatment condition Z” was 2 after casting the molten metal. It means that it was manufactured after being left for a period of time and then subjected to a heat treatment performed at 1250 ° C. for 10 hours.
“Effective hydrogen amount” in Table 1 means the amount of hydrogen released when the pressure is changed between 33 MPa and 0.1 MPa at 25 ° C. The “deterioration rate” in Table 1 is an index representing the degree to which the durability of the hydrogen storage alloy has decreased due to repeated hydrogen storage and release. More specifically, one cycle includes the step of occluding hydrogen in the process of increasing the pressure from 0.1 MPa to 33 MPa at 25 ° C. and releasing the hydrogen in the process of decreasing the pressure from 33 MPa to 0.1 MPa, When the effective hydrogen amount at the first cycle is α and the effective hydrogen amount at the 40th cycle is β, the deterioration rate is represented by “100 × (α−β) / α”.

2. Results 2.1. High Ti Phase By observing the structure of the hydrogen storage alloy according to Example 2 and the structure of the hydrogen storage alloy according to Comparative Example 1 and Comparative Example 6 with a transmission electron microscope (hereinafter referred to as “TEM”), a high Ti phase was obtained. The phase morphology was investigated. The observation result of the hydrogen storage alloy according to Example 2 is shown in FIG. 5, the observation result of the hydrogen storage alloy according to Comparative Example 1 is shown in FIG. 6, and the observation result of the hydrogen storage alloy according to Comparative Example 6 is shown in FIG. . Furthermore, elemental analysis of the high Ti phase of the hydrogen storage alloy according to Example 2 was performed by using an energy dispersive X-ray analyzer (EDX) under a transmission electron microscope. The results are shown in Table 2.

In Table 2, “average” means the average composition of all high Ti phases subjected to elemental analysis. “Ti maximum” means a composition obtained by performing elemental analysis on high Ti phases mainly scattered at grain boundaries. Further, “Ti minimum” means a composition obtained by performing elemental analysis on a high Ti phase mainly precipitated in crystal grains.
From Table 2, the Ti content contained in the high Ti phase of the hydrogen storage alloy according to Example 2 included in the technical scope of the present invention was in the range of 21.6% to 93.6%.

From FIG. 5, in the hydrogen storage alloy according to Example 2 included in the technical scope of the present invention, it was observed that a needle-like or plate-like high Ti phase was precipitated in the parent phase. On the other hand, from FIG. 6, in the hydrogen storage alloy according to Comparative Example 1 not included in the technical scope of the present invention, the high Ti phase was spheroidized. Moreover, from FIG. 7, in the hydrogen storage alloy concerning the comparative example 6 which is not contained in the technical scope of this invention, the high Ti phase segregated to the grain boundary, and the shape was different from needle shape or plate shape. That is, from FIG. 5 to FIG. 7, even if the composition is the same, if the cooling conditions are different, a hydrogen storage alloy with acicular or plate-like high Ti phase precipitated may not be obtained, and the cooling conditions are controlled. It can be seen that the hydrogen storage alloy of the present invention is manufactured.
Further, from Table 1, in the hydrogen storage alloys according to Comparative Examples 2, 4, and 5, no high Ti phase was precipitated. Further, in the hydrogen storage alloys according to Comparative Examples 1 and 3, a high Ti phase was precipitated, but the hydrogen storage alloy according to Comparative Example 1 was not included in the technical scope of the present invention because the high Ti phase was spheroidized. The hydrogen storage alloy according to Example 3 is not included in the technical scope of the present invention as described later. In addition, although the high Ti phase precipitates in the hydrogen storage alloy according to Comparative Example 7, the ratio is as low as 1%, and precipitates at grain boundaries, and the durability is inferior to that of the hydrogen storage alloy of the present invention.

2.2. Deterioration rate FIG. 8 shows the relationship between the number of hydrogen storage / release cycles and the amount of effective hydrogen investigated for the hydrogen storage alloy according to Example 2 and the hydrogen storage alloy according to Comparative Example 7. The vertical axis in FIG. 8 is the effective hydrogen amount [wt%], and the horizontal axis is the number of cycles [times]. FIG. 9 shows a PCT curve of the hydrogen storage alloy according to Example 2. In FIG. 9, the vertical axis represents the hydrogen pressure [MPa], and the horizontal axis represents the hydrogen storage amount [wt%].

From FIG. 8, the hydrogen storage alloy according to Example 2 included in the technical scope of the present invention hardly decreases the effective hydrogen amount even when the number of cycles is increased, and the shape of the PCT curve at the second cycle is 40. The shape of the PCT curve at the cycle was almost the same (see FIG. 9). On the other hand, in the hydrogen storage alloy according to Comparative Example 7 not included in the technical scope of the present invention, the amount of effective hydrogen decreased with an increase in the number of cycles, and the durability was remarkably lowered.
Further, from Table 1, the hydrogen storage alloys of Examples 1 to 3 included in the technical scope of the present invention have a deterioration rate of 5% (Example 1), 6% (Example 2), and 11% (Example 3), whereas the deterioration rate of the hydrogen storage alloy not included in the technical scope of the present invention (Comparative Example 2: 21%, Comparative Example 4: 26%, Comparative Example 5 and Comparative Example) Example 6: 25%). In addition, although the deterioration rate of the hydrogen storage alloy concerning the comparative example 3 was 9%, since the amount of effective hydrogen falls, it is not included in the technical scope of this invention.
As mentioned above, according to this invention, the hydrogen storage alloy which can improve durability was obtained.

2.3. Effective hydrogen amount From Table 1, the hydrogen storage alloys of Examples 1 to 3 included in the technical scope of the present invention have effective hydrogen amounts of 1.9% (Example 1) and 2.1%. (Example 2 and Example 3), which is the same amount of effective hydrogen as a hydrogen storage alloy not included in the technical scope of the present invention (Comparative Example 1: 1.7%, Comparative Example 2 and Comparative Example 4: 2.0%, Comparative Example 3: 1.6%, Comparative Example 5 and Comparative Example 6: 1.8%). That is, according to the present invention, a hydrogen storage alloy having improved durability without reducing the effective hydrogen amount was obtained.
In addition, the hydrogen storage alloy concerning Example 4 which the time of the said 4th process exceeded 50 minutes is more than the hydrogen storage alloy concerning Example 1-Example 3 whose time of the said 4th process was 50 minutes or less. However, the value of the effective hydrogen amount was small. Therefore, from the viewpoint of obtaining a hydrogen storage alloy having good hydrogen storage characteristics, it is preferable that the fourth step with a time of 50 minutes or less be provided.

2.4. Relationship between Deterioration Rate and Lattice Volume Change Rate FIG. 10 shows the relationship between the deterioration rate and the lattice volume change rate investigated for the hydrogen storage alloy according to Example 2 and the hydrogen storage alloy according to Comparative Example 7. The vertical axis in FIG. 10 is the deterioration rate [%], and the horizontal axis is the lattice volume change rate [%]. Here, the “lattice volume change rate” refers to a lattice constant (L1) derived by observing the structure of the hydrogen storage alloy before storing hydrogen with a transmission electron microscope or the like, and a predetermined amount of hydrogen stored. And the lattice constant derived by observing the structure of the hydrogen storage alloy with a transmission electron microscope or the like, and the lattice constant of the hydrogen storage alloy when the maximum amount of hydrogen is stored (L2) Is a value (L) obtained by substituting L1 and L2 into the following equation.
L = 100 × (L2−L1) / L1

  From FIG. 10, the hydrogen storage alloy according to Example 2 and the hydrogen storage alloy according to Comparative Example 7 had the same value of the lattice volume change rate, but the hydrogen storage alloy according to Comparative Example 7 was performed more than the hydrogen storage alloy. The deterioration rate of the hydrogen storage alloy according to Example 2 was smaller. That is, in these hydrogen storage alloys, the same degree of strain is generated during hydrogen storage, but in the hydrogen storage alloy according to Example 2 in which a needle-like or plate-like high Ti phase is precipitated in the matrix. As a result of the strain being dispersed at the interface between the parent phase and the high Ti phase, it is considered that the hydrogen storage alloy according to Example 2 has a low deterioration rate and can improve durability. Therefore, according to this invention, it was confirmed that the hydrogen storage alloy which can reduce distortion and can improve durability can be provided.

It is a conceptual diagram which shows roughly the example of the form of the cross section of the hydrogen storage alloy concerning this invention. FIG. 1A shows a form before repeated hydrogen storage / release. FIG. 1 (b) shows the form after repeated hydrogen storage / release. It is a conceptual diagram which shows roughly the example of the cross section of the conventional hydrogen storage alloy. FIG. 2A shows a form before repeated hydrogen storage / release. FIG. 2B shows a form after repeated hydrogen storage / release. It is a flowchart which shows the example of a form of the manufacturing method of this invention. It is a conceptual diagram which shows the relationship between time after casting and temperature. It is a TEM observation photograph of a hydrogen storage alloy. It is a TEM observation photograph of a hydrogen storage alloy. It is a TEM observation photograph of a hydrogen storage alloy. It is a figure which shows the relationship between the number of hydrogen storage / release cycles and the amount of effective hydrogen. It is a PCT curve of a hydrogen storage alloy. It is a figure which shows the relationship between a deterioration rate and a lattice volume change rate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Mother phase 2 ... High Ti phase 3 ... Crystal grain 10, 20 ... Hydrogen storage alloy

Claims (6)

It is a hydrogen storage alloy containing at least 5% to 10% of Ti, 5% to 15% of Cr, 70% to 89% of V, and 10% to 10% of Mo, with the balance being inevitable impurities. ,
A hydrogen storage alloy, characterized in that a needle-like or plate-like high Ti phase is precipitated in a matrix phase. at%, casting a molten metal containing Ti: 5 to 10%, Cr: 5 to 15%, V: 70 to 89%, and Mo: 1 to 10%, and the balance of inevitable impurities. 1 process,
A second step of cooling the mold into which the molten metal has been poured to 860 ° C. in a period of 5 minutes to 15 minutes after the first step;
A third step of cooling the mold to 670 ° C. in a time period of 5 minutes to 30 minutes after the second step;
The hydrogen storage alloy according to claim 1, wherein the hydrogen storage alloy is manufactured through the following process. The hydrogen storage alloy according to claim 2, further comprising a fourth step of cooling the mold to 200 ° C. in a time of 50 minutes or less after the third step. 0.05 ≦ B / (A + B) ≦ 0.2, where A is the cross-sectional area of the parent phase at an arbitrary cut surface and B is the cross-sectional area of the high Ti phase at the cut surface. The hydrogen storage alloy according to any one of claims 1 to 3. at%, casting a molten metal containing Ti: 5 to 10%, Cr: 5 to 15%, V: 70 to 89%, and Mo: 1 to 10%, and the balance of inevitable impurities. 1 process,
A second step of cooling the mold into which the molten metal has been poured to 860 ° C. in a period of 5 minutes to 15 minutes after the first step;
A third step of cooling the mold to 670 ° C. in a time period of 5 minutes to 30 minutes after the second step;
A method for producing a hydrogen storage alloy, comprising: The method for producing a hydrogen storage alloy according to claim 5, further comprising a fourth step of cooling the mold to 200 ° C. in a time of 50 minutes or less after the third step.