JP2006028621A - Heat-treatment method for hydrogen-storage alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the durability of a hydrogen-storage alloy having BCC (body-centered cubic) single-phase structure. <P>SOLUTION: Solution-treatment is applied to the melt-produced hydrogen-storage alloy having BCC single-phase structure under non-oxidizing atmosphere and thereafter, the temperature is dropped to ≤350°C at ≤300°C/h cooling rate under non-oxidizing atmosphere. Fluctuation of a host phase and fine precipitation in the crystal grain, are restrained and the lattice defect, strain, etc., can be reduced and thus, the hydrogen storage alloy having more excellent durability can be produced. Particularly, in V or Ti-V-Mn system, Ti-V-Cr system alloy, having high V concentration, the remarkable improving effect can be obtained. For example, the excellent characteristic at 100°C and ≤50 atmospheric pressure, can be displayed and further, the efficiency deterioration with the repetition of the hydrogen absorption/exhaustion, is small and the deterioration of the hydrogen storage capacity up to 500 times of the repetition can be made to be almost 0%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heat treatment method for a hydrogen storage alloy that absorbs and releases hydrogen.

  Hydrogen storage alloy uses hydrogen absorption / release action to store hydrogen storage material, heat absorption hydrogen absorption material, fuel cell hydrogen supply material, Ni-hydrogen battery negative electrode material, hydrogen refining and recovery material, hydrogen It is used as a hydrogen absorbing material for gas actuators. In the practical application of various applications, it is necessary to further improve the characteristics of hydrogen storage materials.For example, increasing the amount of hydrogen storage, lowering raw materials, improving plateau characteristics, improving durability, etc. ing.

For example, Patent Document 1 is characterized in that a Ti-V-based solid solution alloy characterized by precipitating a second phase having a three-dimensional network structure is manufactured and then heat-treated.
Further, in Patent Document 2 and Patent Document 3, a Ti—Cr—V alloy having a certain composition range is produced by a rapid solidification method with an average particle size side of 40 μm or less, and Ni is coated and heat-treated, or the surface is coated. A hydrogen storage alloy coated with Ni by a mechanical alloying method has been proposed.
In Patent Document 4, a hydrogen storage alloy having a main composition of a body-centered cubic crystal and an average particle size of 100 μm or less in a constant composition range is subjected to a rapid solidification method or 200 ° C./sec. A method has been proposed in which a solution treatment is performed at the above cooling rate.

Patent Document 5 proposes a hydrogen storage alloy having a single-phase body-centered cubic structure in which a Ti—Cr—V alloy having a certain composition range is produced by a mechanical alloying method and an average particle size is 0.5 μm or more and 40 μm or less. ing.
Patent Document 6 proposes a hydrogen storage alloy in which a surface of an alloy powder produced by rapidly solidifying a hydrogen storage alloy having a certain composition range is coated with Ni by a mechanical alloying method and heat-treated.
In Patent Document 7, a Ti—C —— (Mo—No—Fe) hydrogen storage alloy having a body-centered cubic structure as a main phase is coated with Cu and Ni in order by electroless plating or mechanical alloying, and then heat-treated. Has been proposed.

Furthermore, Patent Document 8 proposes a method of cooling and / or aging treatment of a Ti—Cr—V hydrogen storage alloy having a body-centered cubic structure as a main phase after solution treatment.
Patent Document 9 is characterized in that the crystal structure of the main phase is a body-centered cubic structure in a constant composition range of Ti-Cr-V-Ni-X, and is characterized by having a body-centered cubic structure by heat treatment. A hydrogen storage alloy excellent in durability and the like has been proposed, and a cooling treatment and an aging treatment are proposed as the treatment after the solution treatment, and the quenching treatment is preferable for the cooling treatment.

Patent Document 10 proposes a hydrogen storage alloy in which a Ti—Cr—VA-based alloy (A is a metal such as a group IIIb) in a certain composition range is heated and rapidly cooled to be single-phased into a BBC phase.
Patent Document 11 proposes cooling a T-Cr-Mo-Fe-based hydrogen storage alloy having a constant composition range having a body-centered cubic structure as a main phase by water cooling or more.
In Patent Document 12, as a method for improving the durability and the like of an alloy having a BCC structure, a method is proposed in which the alloy is heated to a melting point or higher and then solidified while being gradually cooled.
JP-A-8-269655 Japanese Patent Laid-Open No. 10-080865 JP 10-310833 A JP 2000-303101 A JP 2001-98336 A JP 2002-105511 A Japanese Patent Laid-Open No. 2002-60804 JP-A-10-110225 JP-A-11-310844 Japanese Patent Application Laid-Open No. 11-106859 JP 2002-21663 A JP 2002-080199 A

By the way, alloys having a BCC structure such as Ti-V-Mn series and Ti-V-Cr series alloys are 1.5 times larger than AB ₅ type alloys and AB ₂ type alloys already in practical use. However, the deterioration due to repeated hydrogen absorption / release is very fast. Since the alloy having the BCC structure is mainly manufactured by the rapid cooling method as described above, there is more or less solidification segregation, precipitates or distortion, and phase separation, crystallinity breakage, defects due to repeated hydrogenation. There is a drawback of stable trapping of hydrogen into the metal, and repeated absorption and release of hydrogen causes a significant deterioration of the alloy, and the equilibrium dissociation pressure decreases greatly as the number of repeated absorption and release cycles increases. There is a problem above.

  The basic object of the present invention is to solve the above-mentioned problems, and in the hydrogen storage alloy having a BCC single phase structure, the compositional fluctuation of the parent phase and the fine precipitation in the crystal grains are suppressed, and the lattice defects and strains are reduced. It aims at obtaining the hydrogen storage alloy which reduced and improved durability.

  In general, the BCC structure of Ti-Cr-V alloys is a high-temperature equilibrium phase, which eliminates the solidification segregation of each component formed during melting and casting, particularly dendritic solidification segregation of Ti and V components, and homogenizes them. For this purpose, a solution treatment in a stable high temperature region of the BCC structural phase is required. The conditions regarding the solution treatment temperature and time are described in many patent documents including the above-mentioned patent document 8. However, in a hydrogen storage alloy having a BCC structure, even if the solution treatment temperature and time are performed under the same conditions, a difference appears in durability by changing the cooling rate after the heat treatment. Control of the cooling rate is extremely important in controlling lattice defects and distortion of the BCC structure. In the rapid cooling treatment such as quenching treatment with water or oil from the solution treatment temperature, many defects and strains are introduced into the crystal grains. In order to suppress the introduction of such defects and strains, the cooling rate in the temperature lowering process must be controlled within the allowable range of alloy production. The present invention has been made based on the above findings by the present inventors.

  That is, among the heat treatment methods of the hydrogen storage alloy of the present invention, the invention according to claim 1 is a solution treatment of a hydrogen storage alloy having a BCC single-phase structure produced in a non-oxidizing atmosphere, and then non-oxidizing. The temperature is lowered to 350 ° C. or lower at a cooling rate of 300 ° C./hour or lower in a neutral atmosphere.

  An invention of a heat treatment method for a hydrogen storage alloy according to claim 2 is characterized in that, in claim 1, the non-oxidizing atmosphere is an inert gas atmosphere or a reducing gas atmosphere.

  According to a third aspect of the present invention, there is provided a hydrogen storage alloy heat treatment method according to the first or second aspect, wherein the solution treatment is performed at a heating temperature of 1100 to 1450 ° C. and a holding time of 1 minute to 48 hours. It is characterized by.

  According to a fourth aspect of the present invention, there is provided a hydrogen storage alloy heat treatment method according to any one of the first to third aspects, wherein the hydrogen storage alloy is a powder having an average particle size of 100 μm or more.

  The invention according to claim 5 is characterized in that in the invention according to any one of claims 1 to 4, the hydrogen storage alloy is an alloy having a V-based solid solution type BCC structure. To do.

  That is, according to the present invention, the composition after the heat treatment of the hydrogen storage alloy having a BCC single phase structure is cooled at a rate slower than 300 ° C./hr, thereby suppressing the compositional fluctuation of the matrix and the fine precipitation in the crystal grains. In addition, a hydrogen storage alloy with reduced lattice defects and strains can be obtained.

  That is, according to the hydrogen storage alloy heat treatment method of the present invention, the melted BCC single-phase structure hydrogen storage alloy is subjected to a solution treatment in a non-oxidizing atmosphere, and then 300 ° C. in a non-oxidizing atmosphere. Since the temperature is lowered to 350 ° C. or less at a cooling rate of / hour or less, the compositional fluctuation of the parent phase and the fine precipitation in the crystal grains, which were difficult in the production of the hydrogen storage alloy by the conventional quenching method, are suppressed, and lattice defects and strains are suppressed. Etc. can be reduced, and there is an effect that a hydrogen storage alloy having more excellent durability can be manufactured. In particular, the effect is remarkable in a hydrogen storage alloy having a high V concentration and having a stable BCC single-phase structure. By making the cooling rate after solution treatment slower than 300 ° C./hour, it has a high hydrogen storage capacity. Excellent characteristics can be exhibited at 50 ° C. and below 50 ° C. Further, performance degradation due to repeated hydrogen absorption / release is small, and degradation of hydrogen storage capacity up to 500 times can be reduced to almost 0%.

In the present invention, the melted alloy is subjected to a solution treatment. In the present invention, the melting method of the alloy is not limited to a specific one, and can be performed by a conventional method. Moreover, although the appropriate conditions can also be selected as heating temperature and holding time in solution treatment as this invention, the conditions hold | maintained at 1100-1450 degreeC suitably for 1 minute-48 hours are illustrated. This is because the effect of mitigating defects is insufficient when the temperature is lower than 1100 ° C., and the alloy melts when the temperature exceeds 1450 ° C. Further, when the holding time is less than 1 minute, the solution treatment is insufficient, and when it exceeds 48 hours, the oxygen content in the alloy increases and the characteristics are deteriorated. The solution treatment is performed in a non-oxidizing atmosphere. The non-oxidizing atmosphere can be performed under a reduced pressure of 1 × 10 ⁻² Torr or less, an inert gas atmosphere, or a reducing gas atmosphere. As the inert gas, a gas of an element belonging to Group 18 of the periodic table such as nitrogen gas or argon is shown. Examples of the reducing gas include hydrogen and CO.

  The cooling rate after the solution treatment is unique to the present invention, and it is necessary to set the cooling rate below a specified value. If the cooling rate here exceeds 300 ° C./hour, defects such as lattice defects and distortion occur, and the durability of the alloy in absorbing and releasing hydrogen deteriorates. In addition, the said cooling rate which avoided rapid cooling needs to satisfy | fill the said conditions to 350 degrees C or less. The effect of the present invention cannot be obtained if a process of rapid cooling at a temperature higher than 350 ° C. without including the above conditions is included. In the cooling process, a non-oxidizing atmosphere is required as described above.

  Further, the hydrogen storage alloy of the present invention desirably has an equivalent circle diameter of 100 μm or more in the powder form. This is because when the particle size is less than 100 μm, the influence of grain boundary segregation increases. In the present invention, the method of forming a powder is not particularly limited, and can be performed by a conventional method.

  Furthermore, the heat treatment method of the hydrogen storage alloy of the present invention can provide a remarkable effect in a hydrogen storage alloy having a high V concentration. In particular, an alloy having a V-based solid solution type BCC structure is very rapidly deteriorated due to repeated hydrogen absorption and desorption, and the effect of improving the durability by the heat treatment method of the present invention is remarkable. In the Ti-V-Cr system, which is a typical alloy having the V-based solid solution type BCC structure, the amount ratio of V is 20% or more, the amount ratio of Ti is 8 to 35%, and the amount ratio of Cr is 12 to 12%. 50% can be exemplified.

Embodiments of the present invention will be described below with reference to the drawings.
The composition ratio of Ti and Cr is 2 to 3 so that a plateau pressure near atmospheric pressure can be obtained at room temperature, V concentration is blended at 40at% and 80at%, and after melting in arc under high purity Ar gas atmosphere, And cooled to room temperature to solidify. Next, after cooling to 1400 ° C. at a temperature increase rate of 400 ° C./hour using an argon atmosphere siliconite heat treatment furnace, the cooling after holding for 3 hours is performed at room temperature in the furnace at a cooling rate of 300 ° C./hour to 20 ° C./hour. The sample was cooled to a measurement sample (invention material) as an example of the present invention. In addition, for comparison, a raw material was blended with the same composition, subjected to dissolution and solution treatment under the same conditions, and then subjected to water quenching treatment as a measurement sample (comparative material) as a comparative example.

  When the crystal structure of the obtained alloy was investigated by XRD, it was found that all the alloys were BCC single phase. The hydrogenation characteristics were measured on the alloy before and after the durability test in a hydrogen gas atmosphere for a sample pulverized to a range of about 50 to 200 mesh. The activation treatment of the alloy was performed by applying vacuum at 20 ° C. and 4.5 MPa after vacuum degassing at 100 ° C. for 1 hour, and the hydrogenation characteristics were measured at 20 ° C. after vacuum degassing at 100 ° C. for 1 hour. In the durability test, the change in the amount of hydrogen transferred was measured by changing the pressure at a constant temperature of 20 ° C.

FIG. 1 shows the hydrogenation characteristics of samples obtained by the example and the comparative example at a measurement temperature of 20 ° C. in the Ti ₂₄ Cr ₃₆ V ₄₀ composition before the durability test, and FIG. 2 shows the measurement in the Ti ₂₄ Cr ₃₆ V ₄₀ composition. Results of durability tests of samples obtained in Examples and Comparative Examples at a temperature of 20 ° C. up to 100 times, FIG. 3 shows an example at a measurement temperature of 20 ° C. in a Ti ₂₄ Cr ₃₆ V ₄₀ composition after the durability test, The hydrogenation characteristics of the samples obtained in the comparative example were shown.

  In the examples, the solution was cooled at a cooling rate of 300 ° C./hr after the solution treatment. As is clear from these figures, the hydrogen storage amount before durability shows the same amount of hydrogen storage regardless of the cooling conditions, but the difference in the hydrogen absorption amount each time the number of repeated hydrogen storage / release is repeated. As a result of the comparison of the alloys that repeatedly absorbed and released hydrogen 100 times, it was found that the alloy of the example (invention material) clearly absorbs more hydrogen than the alloy of the comparative example (comparative material).

  Next, the existence state of defects such as dislocations in the obtained alloy was investigated by transmitting an electron beam through the sliced alloy using a transmission electron microscope. FIG. 4 shows an image of the inventive material, and FIG. 5 shows an image of the comparative material. As shown in FIG. 4, the inventive material has a relatively low contrast indicating defects such as dislocations, whereas the comparative material has a relatively large amount of contrast indicating the presence of defects such as dislocations as shown in FIG. It was done. When the dislocation density was actually measured, a difference of several tens to one hundred times was observed.

Further, the same test was performed on the alloy whose composition was changed. FIG. 6 shows the hydrogenation characteristics of the samples obtained in the example and the comparative example at a measurement temperature of 20 ° C. in the Ti ₈ Cr ₁₂ V ₈₀ composition before the durability test, and FIG. 7 shows the measurement temperature in the Ti ₈ Cr ₁₂ V ₈₀ composition. Results of durability test of samples obtained in Example and Comparative Example at 20 ° C. up to 100 times, and comparison with Example at measurement temperature of 20 ° C. in Ti ₈ Cr ₁₂ V ₈₀ composition after durability test in FIG. The hydrogenation characteristics of the sample obtained in the examples are shown. In the examples, the solution was cooled at a cooling rate of 30 ° C./hr after the solution treatment. As with the Ti ₂₄ Cr ₃ 6V ₄₀ composition, even in the Ti ₈ Cr ₁₂ V ₈₀ composition alloy with a different composition, the hydrogen storage amount before durability shows almost the same hydrogen storage amount regardless of the cooling conditions. However, every time the number of repeated hydrogen absorption / desorption is repeated, the difference in the hydrogen absorption amount is increased, and in the comparison of the alloys repeatedly absorbed and released 1000 times, the alloy of the example (invention material) is the alloy of the comparative example ( It was found that it absorbs more hydrogen than the comparative material. Further, in the alloy of the example of the Ti ₈ Cr ₁₂ V ₈₀ composition, the decrease in the hydrogen storage amount was almost 0% until 500 times.

  As described in the above examples, by carrying out the heat treatment method of the present invention in a TiCrV-based hydrogen storage alloy having a BCC single-phase structure, by reducing lattice defects, strains, etc. of the BCC structure, It has been found that it is possible to suppress a decrease in the amount of hydrogen occlusion and to obtain a hydrogen occlusion alloy having excellent practicality. In the above examples, TiCrV-based hydrogen storage alloys have been demonstrated. However, the present invention is not limited to TiCrV-based hydrogen storage alloys, and other V, TiCrMn-based, as well as other BCC single-phase structure hydrogens. It was confirmed that the same effect can be obtained in the occlusion alloy.

Shows the initial hydrogenation characteristic of Ti ₂₄ Cr ₃₆ V ₄₀ composition. It is a diagram showing a durability test results of the Ti ₂₄ Cr ₃₆ V ₄₀ composition. Is a diagram showing the hydrogenation characteristics after the 100 times repeated hydrogen absorption and desorption tests Ti ₂₄ Cr ₃₆ V ₄₀ composition. It is a view showing a TEM photograph of the inventive materials of Ti ₂₄ Cr ₃₆ V ₄₀ composition. It is a view showing a TEM photograph of the comparative material of Ti ₂₄ Cr ₃₆ V ₄₀ composition. Shows the initial hydrogenation characteristic of Ti ₈ Cr ₁₂ V ₈₀ composition. It is a diagram showing a durability test results of the Ti ₈ Cr ₁₂ V ₈₀ composition. Is a diagram showing the hydrogenation characteristics after the 1000 times repeating a hydrogen absorption and desorption tests Ti ₈ Cr ₁₂ V ₈₀ composition.

Claims (5)

  The solution of the melted BCC single-phase hydrogen storage alloy is treated in a non-oxidizing atmosphere, and then the temperature is lowered to 350 ° C. or less at a cooling rate of 300 ° C./hour or less in the non-oxidizing atmosphere. A heat treatment method of a hydrogen storage alloy characterized by   2. The method for heat-treating a hydrogen storage alloy according to claim 1, wherein the non-oxidizing atmosphere is an inert gas atmosphere or a reducing gas atmosphere.   The method for heat treatment of a hydrogen storage alloy according to claim 1 or 2, wherein the solution treatment is performed at a heating temperature of 1100 to 1450 ° C and a holding time of 1 minute to 48 hours. The said hydrogen storage alloy is a powder with an average particle diameter of 100 micrometers or more, The heat processing method of the hydrogen storage alloy in any one of Claims 1-3 characterized by the above-mentioned. The method for heat-treating a hydrogen storage alloy according to claim 1, wherein the hydrogen storage alloy is an alloy having a V-based solid solution type BCC structure.