JP4524384B2 - Quasicrystal-containing titanium alloy and method for producing the same - Google Patents

Description

The present invention relates to a quasicrystal-containing titanium alloy having a high hydrogen storage capacity and a method for producing the same, and more specifically, a metal element having a larger absolute value of oxide formation enthalpy than Zr is added to form a high quasicrystal. The present invention relates to a method for producing a titanium alloy having a volume ratio by melt solidification, mechanical pulverization or alloying, and a novel hydrogen storage member. The quasicrystal-containing titanium alloy of the present invention has more sites capable of trapping hydrogen than LaNi ₅ and TiFe, which are conventional hydrogen storage alloys, and does not form hydrides due to hydrogen absorption / release. Therefore, it can be expected to be practically used as a hydrogen storage alloy having a high hydrogen storage capacity and difficult to be pulverized. The present invention provides a novel hydrogen storage alloy having an excellent hydrogen storage capacity in the technical field related to hydrogen energy, which is in the limelight from the viewpoint of escape from fossil energy and improvement of global environmental problems.

  In recent years, hydrogen energy has attracted attention as a clean alternative energy due to environmental problems such as global warming caused by carbon dioxide emissions and energy problems such as exhaustion of petroleum resources. For the practical application of hydrogen energy, it is important to develop technology for safely storing and transporting hydrogen. As hydrogen storage materials capable of storing hydrogen, development of carbon materials such as activated carbon, fullerene, and nanotubes, and hydrogen storage alloys are underway. Among these, hydrogen storage alloys are expected as a new transportable storage medium because hydrogen can be stored in large quantities in the form of a safe solid called a metal hydride.

As an alloy having a hydrogen storage capacity, alloys having many compositions have been developed. For example, hydrogen storage of Ni—Zr alloy (see Patent Document 1), Ti—Cr—V alloy (see Patent Document 2), Zr—Ti— (V, Ni) alloy having MgZn ₂ type crystal structure Alloys (see Patent Document 3) and the like are manufactured by a melt casting method or the like, but the hydrogen storage ability of these alloys cannot be said to be sufficiently practical.

  An alloy composed of transition metals such as Ti, Zr, and Ni having a five-fold symmetry axis and a regular icosahedron structure is known as an Icosahedral quasicrystalline alloy (phase I). al. has published its effectiveness as a hydrogen storage alloy (see Non-Patent Document 1). The quasicrystal is generally a metastable phase, and is synthesized by rapid solidification such as a single roll method. However, in the production of this type of alloy by rapid solidification, there is a problem that the quality is not stabilized by mixing impurities due to reaction with the melting crucible in order to dissolve active titanium.

On the other hand, Takasaki et al. Showed that an alloy powder containing quasicrystals can be synthesized by synthesizing an elementary powder composed of Ti, Zr, and Ni by mechanical alloying and heat-treating at 500 ° C. . However, the synthesized alloy powder contains a large amount of Ti ₂ Ni type intermetallic compound (T phase) having a low hydrogen storage capacity, and the volume fraction of the I phase is low. I couldn't. Thus, until now, quasicrystal-containing titanium alloys have been mainly produced by melting and quenching methods, but in recent years, powder metallurgy methods using mechanical alloying methods have been used due to technical difficulties in melting active metals. It is being considered. However, an alloy powder having a high quasicrystal volume ratio has not been obtained, and it is considered necessary to increase the quasicrystal volume ratio in order to use it as a hydrogen storage alloy. The fact is that there is no simple method.

Japanese Patent Publication No. 6-39646 Japanese Patent No. 3626298 JP-A-2-220355 A. M. Viano, R. M. Stroud, P. C. Gibbsons, A. F. McDowell, M. S. Conradi and K. F. Kelton: Physical Review B, Vol. 51 (1995) 12026-12029. Akito Takasaki, V.T.Huett and K. F. Kelton: MaterialsTransactions, Vol.43 (2002) 2165-2168.

  Under such circumstances, the present inventors have made it possible to solve the problems of the above prior art in view of the above prior art and efficiently produce a quasicrystal-containing titanium alloy. As a result of intensive research aimed at developing a new technology that enables it, the present inventors have succeeded in producing a titanium alloy having a high quasi-crystal content, thereby completing the present invention.

  That is, an object of the present invention is to provide a new titanium alloy having an excellent hydrogen storage capacity as a medium for storing hydrogen, that is, a hydrogen storage alloy. Further, the present invention provides at least one selected from metals (Dy, Er, Hf, Ho, Lu, Sc, Tb, Th, Tm, Y) having a larger absolute value of oxide formation enthalpy than Zr in the titanium alloy. A homogeneous alloy powder is produced by adding seed elements to make the powder non-equilibrium, and in the subsequent heat treatment or sintering process, by generating fine oxides, the matrix oxygen is trapped and stable. An object of the present invention is to produce and provide a titanium alloy containing a quasicrystalline phase at a high volume ratio. Further, the present invention synthesizes a non-equilibrium alloy powder while introducing strain by mechanical pulverization or alloying method, and heat-treats or sinters this at 300 to 650 ° C. It aims at providing the method of manufacturing the alloy to contain. Another object of the present invention is to provide a novel hydrogen storage member that has a larger hydrogen storage capacity than conventional alloys, has a high-efficiency hydrogen storage capacity, and is less prone to pulverization associated with hydrogen absorption / release. It is.

The present invention for solving the above-described problems comprises the following technical means.
(1) General formula: (Ti _a Zr _b M _100-ab ) _100-c N _c (wherein, M represents at least one element selected from transition metals, and a is 40 ≦ a ≦ 50 at% , B is a number satisfying 30 ≦ b ≦ 45 at%, N is at least one element selected from metals having a larger absolute value of oxide formation enthalpy than Zr, and c is 0.1 ≦ c ≦ 10 at. % is a number satisfying.) has a composition represented by a Ruchi Tan alloy to contain quasicrystals into its constituent phases,
The transition metal is at least one element selected from Ni, Fe, Co, Mn, and Cr, and the metal having a larger absolute value of oxide formation enthalpy than Zr is Dy, Er, Hf, Ho, Lu, Sc Titanium alloy characterized by being at least one element selected from Tb, Th, Tm, and Y.
(2) The titanium alloy according to (1), which has a quasicrystalline phase of 50% or more by volume ratio.
( 3 ) A hydrogen storage alloy comprising the titanium alloy described in (1) or (2 ) above.
( 4 ) A hydrogen storage alloy member comprising the titanium alloy molded sintered body described in (1) or (2 ) above.
( 5 ) A method for producing a titanium alloy having a composition represented by the general formula described in (1) above, wherein mechanically pulverizing raw metal powder or alloy powder blended to have a predetermined composition Alternatively, after forming an alloy in a non-equilibrium state by alloying, forming a quasicrystalline phase by heat treatment , the transition metal is at least one element selected from Ni, Fe, Co, Mn, Cr, and more than Zr Quasicrystal-containing , characterized in that the metal having a large absolute value of oxide formation enthalpy is at least one element selected from Dy, Er, Hf, Ho, Lu, Sc, Tb, Th, Tm, Y A method for producing a titanium alloy.
( 6 ) The method for producing a quasicrystal-containing titanium alloy according to the above ( 5 ), wherein a quasicrystal is formed by heat treatment at 300 to 650 ° C.
( 7 ) A method for producing a hydrogen storage alloy member containing a quasicrystal, characterized in that the titanium alloy produced by the method described in ( 5 ) or ( 6 ) above is molded and sintered.

Next, the present invention will be described in more detail.
The present invention has the general formula: (Ti _a Zr _b M _100-ab ) _100-c N _c (wherein M represents at least one element selected from transition metals, and a is 40 ≦ a ≦ 50 at. %, B is a number satisfying 30 ≦ b ≦ 45 at%, N represents at least one element selected from metals having an absolute value of oxide formation enthalpy larger than Zr, and c is 0.1 ≦ c ≦ It is characterized by the point of a quasicrystalline phase (I phase) -containing titanium alloy having a composition represented by: In the present invention, the raw metal powder or alloy powder blended to have a predetermined composition is converted into a non-equilibrium alloy by mechanical pulverization or alloying, and then heat-treated at a temperature of 300 to 650 ° C. This is characterized by the method of producing the quasicrystal-containing titanium alloy that forms a quasicrystalline phase by the above method.

In the titanium alloy represented by the general formula: (Ti _a Zr _b M _100-ab ) _100-c N _c of the present invention, M is at least one metal selected from transition metals, For example, at least one element selected from Ni, Fe, Co, Mn, and Cr is exemplified. N is at least one element selected from metals having a larger absolute value of oxide formation enthalpy than Zr. For example, Dy, Er, Hf, Ho, Lu, Sc, Tb, Th, Tm, Y The at least 1 sort (s) of element chosen from is illustrated. These elements are thought to contribute to trapping oxygen present in the alloy matrix to form a stable I phase.

  As for the alloy composition, when a ≧ 50 or b ≧ 45, the powder cannot be recovered by adhering to the pulverization container or the ball, and when a ≦ 40 or b ≦ 30, a non-equilibrium powder cannot be obtained. Further, when c ≦ 0.1, no increase in the I phase is observed, and when c ≧ 10, an intermetallic compound other than the I phase is generated, so that the target powder cannot be obtained. In the titanium alloy of the present invention, the ranges of a, b, and c are as follows: a is 43 ≦ a ≦ 47 at%, b is 35 ≦ b ≦ 42 at%, and c is 3 ≦ c ≦ 5 at%. Is preferred. In addition, the titanium alloy of the present invention preferably contains a quasicrystalline phase of 50% by volume or more, and further 75% by volume or more.

  In order to manufacture the titanium alloy of the present invention, for example, a raw material powder blended so as to have a predetermined composition is processed by mechanical pulverization or alloying, and a non-equilibrium alloy in which a large amount of strain is introduced. This is performed by a step of synthesizing the powder and heat-treating it at 300 to 650 ° C. to obtain a quasicrystalline phase state. The starting materials used in the present invention are Ti, Zr, M (M is at least one element selected from transition metals, for example, Ni, Fe, Co, Mn, Cr, etc.), and N (N is more oxidized than Zr) At least one element selected from metals having a large absolute value of product formation enthalpy (for example, Dy, Er, Hf, Ho, Lu, Sc, Tb, Th, Tm, Y, etc.) is in powder form. Moreover, each powder does not need to be comprised from a pure metal, For example, the alloy powder of Ti and Ni etc. can also be utilized. In the present invention, this is necessary in order to efficiently perform alloying because an alloy in a non-equilibrium state is formed by mechanical pulverization or alloying.

  When pure metal is used as a starting material for mechanical alloying, it is generally known that adhesion to pulverized balls and containers increases depending on the alloying conditions. Cheap. On the other hand, by using an alloy powder, adhesion to a pulverized ball or a container is reduced, and a target composition is easily obtained. The powder of the quasicrystalline composition obtained by the mechanical pulverization or alloying treatment of the present invention is a state in which each element constituting the alloy is finely and homogeneously mixed, and in a non-equilibrium state in which a large amount of strain is introduced. Therefore, the X-ray diffraction pattern has a broad shape indicating amorphous (see FIG. 1).

  The material of the container or ball used for the mechanical pulverization or alloying treatment is not particularly limited, but generally stainless steel, cemented carbide, ceramics, or the like is used. In addition, in order to prevent the powder from adhering to the container or ball during mechanical pulverization or alloying treatment, an appropriate amount of a lubricant such as alcohol or oil may be added. Addition is not preferable because it contains oxygen. However, there is no problem even if an appropriate amount is added as long as the lubricant does not contain oxygen.

  The atmosphere for the mechanical pulverization or alloying treatment is preferably an inert gas atmosphere or a reduced pressure atmosphere in order to prevent oxidation of the metal powder. However, when mechanical pulverization or alloying treatment is performed in a state where the degree of vacuum is high, mixing of the powder does not become uniform and a long-time treatment is required, which is not preferable. In addition, if the mechanical pulverization or alloying treatment is performed for a long time, the amount of oxygen mixed in from the atmosphere increases, so it is desirable to perform the treatment as short as possible.

  For the mechanical pulverization or alloying treatment, a general pulverizer such as a planetary ball mill, a vibration ball mill, or a rolling ball mill can be used. The treatment time depends on the mechanism of the apparatus for performing the mechanical alloying treatment. For example, in a planetary ball mill, the alloy powder of the present invention can be produced in about 50 to 400 hours.

An alloy synthesized by mechanical pulverization or alloying treatment is a powder having an amorphous structure, and it is necessary to heat-treat the powder for industrial use. The atmosphere for the heat treatment is preferably a vacuum or an inert gas atmosphere from the viewpoint of preventing oxidation of the metal powder. A powder synthesized by mechanical pulverization or alloying is a powder in a non-equilibrium state in which a large amount of strain is introduced, and changes to a stable crystalline phase through a quasicrystalline phase by heating. It is estimated that the temperature range in which the powder synthesized by mechanical pulverization or alloying transitions to a quasicrystalline phase when heated and stably exists as a quasicrystal is 300 to 650 ° C, preferably 400 to 550 ° C. When heated to the temperature or higher, a stable crystalline phase (Ti ₂ Ni type compound) is obtained.

  A general sintering method can be used for forming the powder. The sintering atmosphere is preferably a vacuum or an inert gas atmosphere from the viewpoint of preventing oxidation of the metal powder. The die and jig used during sintering are not particularly limited, but materials such as graphite, ceramics and cemented carbide can be used. Furthermore, there is no particular limitation on the pressurizing mechanism for pressurizing during sintering, but generally, hydraulic pressure, pneumatic pressure, mechanical pressurization, or the like can be used.

  The present invention provides a novel titanium alloy having a high hydrogen storage capacity as compared with conventional products. In the present invention, the absolute value of oxide formation enthalpy is larger than Zr added to the titanium alloy. The metal traps oxygen present in the alloy matrix to facilitate the formation of a quasicrystalline phase, and as shown in FIG. 3, the presence of Tb, Er, and Y causes the I phase to be in the alloy. In addition, as shown in FIG. 4, these metals exist in the form of fine oxides in the alloy, and pulverization occurs due to the absorption and release of hydrogen. It has been demonstrated that it has a difficult structure. The present invention is a titanium alloy in which the raw material powder is made into an alloy in a non-equilibrium state by mechanical alloying or the like and then heat-treated at 300 to 650 ° C. so that the content of the I phase reaches 50% or more by volume In addition, since the titanium alloy has a specific structure in which pulverization associated with hydrogen absorption / release is difficult to occur, it is a conventional product as a hydrogen storage alloy having high hydrogen absorption / release performance. Thus, it is possible to achieve excellent hydrogen storage characteristics that could not be achieved.

  According to the present invention, (1) a novel titanium-based quasicrystalline alloy represented by the above general formula, and a medium for storing hydrogen using the same, that is, a hydrogen storage alloy can be provided. Until now, quasicrystal-containing titanium alloys have been mainly produced by melting and quenching methods, but due to technical difficulties in melting active metals, powder metallurgy using mechanical alloying has recently been studied. It is possible to manufacture and provide a titanium alloy having a high quasicrystal volume fraction by improving the prior art that an alloy powder having a high quasicrystal volume fraction has not been obtained. (3) Oxide formation than Zr By adding at least one element selected from metals having a large absolute value of enthalpy and making the powder non-equilibrium, a homogeneous alloy powder is produced. Oxygen in the matrix can be trapped by generating an oxide, and a stable I phase can be synthesized. (4) The amount of hydrogen storage in the I phase in the quasicrystal-containing titanium alloy is much larger than that of conventional alloys Therefore, it is expected as a highly efficient hydrogen storage alloy, and since it is difficult to generate a fine powder due to the absorption and release of hydrogen, it is possible to provide a new hydrogen storage member that is expected to be applied as a hydrogen storage alloy member. Is done.

  EXAMPLES Next, although this invention is demonstrated concretely based on an Example, this invention is not limited at all by the following Examples.

  In this example, a titanium alloy containing Tb, Er, Y, or Ce and a titanium alloy containing no metal element were synthesized. As starting materials, Ti powder (made by Rare Metallic Co., Ltd., purity 99.9% by weight), Zr powder (made by Rare Metallic Co., Ltd., purity 99% by weight), Ni powder (made by Rare Metallic Co., Ltd., purity 99) .9 wt%), Ce powder (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9 wt%), Tb powder (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9 wt%), Y powder (Manufactured by Rare Metallic, purity 99.9% by weight) and Er (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9% by weight) were used.

A predetermined amount of these raw materials are weighed, and subjected to mechanical alloying treatment for 200 hours by a planetary ball mill, thereby Ti ₄₅ Zr ₃₈ Ni ₁₇ , Ti ₄₄ Zr ₃₇ Ni ₁₆ Ce ₃ , Ti ₄₄ Zr ₃₇ Ni ₁₆ Tb ₃ , Ti _44. An alloy powder having a composition composed of Zr ₃₇ Ni ₁₆ Y ₃ and Ti ₄₄ Zr ₃₇ Ni ₁₆ Er ₃ was synthesized. As shown in FIG. 1, these were powders having a particle size of about 100 microns in a non-equilibrium state showing a broad X-ray diffraction pattern. Here, the oxide formation enthalpy (ΔH) of each metal element is ΔH (Zr) = − 366 (kJ / mol), ΔH (Ce) = − 364 (kJ / mol), ΔH (Tb) = −, respectively. 373 (kJ / mol), ΔH (Y) = − 381 (kJ / mol), ΔH (Er) = − 380 (kJ / mol).

When the obtained Ti ₄₅ Zr ₃₈ Ni ₁₇ powder was subjected to thermal analysis with a differential scanning calorimeter, it was considered to be a phase transition to a quasicrystal in the range of 300 to 650 ° C. as shown in FIG. An exothermic peak was observed.

  50 mg of the obtained alloy powder was filled in an alumina cell having a diameter of 6 mm, and heat-treated up to 520 ° C. while flowing argon at a flow rate of 20 ml / min. The judgment of the I phase and the T phase in the produced quasicrystal and the estimation of the quantity ratio are performed based on the presence of the peaks of 101000I (I phase) and 660T (T phase) indicated by arrows in FIG. It was. For the metal element-free powder and Ce-added powder, the T-phase peak was clearly observed, but only the I-phase was observed for the Tb, Er, and Y-added powder. Thus, for the sample to which Tb, Er, and Y having a larger oxide formation enthalpy than Zr were added, only the I phase was observed.

The obtained Ti ₄₄ Zr ₃₇ Ni ₁₆ Y ₃ powder is composed of an I phase having a crystal grain size of about 100 nm and a very small amount of oxide having a crystal grain size of about 10 to 20 nm, as shown in FIG. It had been.

In this example, Ti powder (Rare Metallic Co., Ltd., purity 99.9% by weight), Zr powder (Rare Metallic Co., Ltd., purity 99% by weight), Ni powder (Rare Metallic Co., Ltd., purity) 99.9% by weight), and Y powder (rare metallic, purity 99.9% by weight) as a starting material, a mechanical alloying treatment of 400 hours with a planetary ball mill gave a Ti ₄₄ Zr ₃₇ Ni ₁₆ Y ₃ composition. An alloy powder was synthesized.

  0.5 g of the obtained alloy powder was filled into a cemented carbide mold having an outer diameter of 20 mm, an inner diameter of 6 mm, and a height of 20 mm, and energized and heated while flowing a pulsed current at a pressure of 500 MPa. The sintering atmosphere was performed in a vacuum of about 10 Pa and heated to 520 ° C. for solidification molding. The shape of the obtained sintered body was a disk shape with a diameter of 6 mm and a height of 3 mm, and the X-ray diffraction pattern thereof showed a diffraction pattern peculiar to the I phase as shown in FIG.

As described above in detail, the present invention relates to a quasicrystal-containing titanium alloy and a method for producing the same, and according to the present invention, the general formula: (Ti _a Zr _b M _100-ab ) _100-c N _c Provided is a titanium alloy having a composition represented by the formula (wherein M is a transition metal and N is a metal having a larger absolute value of oxide formation enthalpy than Zr) and the quasicrystal volume ratio is 50% or more. Can do. So far, the quasicrystal-containing titanium alloy produced using the mechanical alloying method includes a small amount of I-type quasicrystalline alloy (I phase) and a large amount of Ti ₂ Ni type intermetallic compound (T phase). However, since the quasicrystal-containing titanium alloy of the present invention contains a large amount of the I phase and has a specific structure in which pulverization due to absorption and release of hydrogen hardly occurs, It can be used as a highly efficient hydrogen storage alloy member.

  In addition, the present invention makes it possible to synthesize a titanium alloy containing the I phase at a high volume ratio, and is useful as a hydrogen storage and transportation means that has been attracting attention as a clean alternative energy in recent years. Further, it is possible to provide a titanium alloy having a novel hydrogen storage capacity. The present invention has a high potential as a new hydrogen storage alloy member that can be applied to various applications including, for example, a nickel-hydrogen secondary battery, a fuel cell, a fuel tank for a hydrogen automobile, and the like. It is what you have.

Shows _Ti 45 _Zr 38 _Ni 17 _N 3 was treated mechanical alloying (N = Ce, Tb, Er , Y) and X-ray diffraction pattern of the alloy powder. The result of the differential scanning calorimetric analysis of the Ti ₄₅ Zr ₃₈ Ni ₁₇ alloy powder subjected to mechanical alloying treatment is shown. Mechanical alloying-treated _{Ti 44 Zr 37 Ni 16 N 3} (N = Ce, Tb, Er, Y) alloy powder, an X-ray diffraction pattern was heat-treated at 520 ° C.. The _Ti 44 _Zr 37 _Ni 16 _{Y 3} alloy powder treated mechanical alloying, shows a bright field image and an electron diffraction image by a transmission electron microscope samples heat treated at 520 ° C.. The _Ti 44 _Zr 37 _Ni 16 _{Y 3} alloy powder treated mechanical alloying, an X-ray diffraction pattern of the sintered samples at 520 ° C..

Claims (7)

General formula: (Ti _a Zr _b M _100-ab ) _100-c N _c (wherein M represents at least one element selected from transition metals, a is 40 ≦ a ≦ 50 at%, b is 30 ≦ b ≦ 45 at%, N represents at least one element selected from metals having a larger absolute value of oxide formation enthalpy than Zr, and c satisfies 0.1 ≦ c ≦ 10 at% is a number.) has a composition represented by a Ruchi Tan alloy to contain quasicrystals into its constituent phases,
The transition metal is at least one element selected from Ni, Fe, Co, Mn, and Cr, and the metal having a larger absolute value of oxide formation enthalpy than Zr is Dy, Er, Hf, Ho, Lu, Sc Titanium alloy characterized by being at least one element selected from Tb, Th, Tm, and Y.   The titanium alloy according to claim 1, having a quasicrystalline phase of 50% or more by volume ratio. Hydrogen storage alloy, characterized in that a titanium alloy according to claim 1 or 2. A hydrogen-absorbing alloy member comprising the titanium alloy shaped sintered body according to claim 1 or 2 . A method for producing a titanium alloy having a composition represented by the general formula according to claim 1, wherein raw material metal powder or alloy powder blended to have a predetermined composition is mechanically pulverized or alloyed. After forming an alloy in a non-equilibrium state, forming a quasicrystalline phase by heat treatment , the transition metal is at least one element selected from Ni, Fe, Co, Mn, and Cr, and the oxide formation enthalpy than Zr Production of a quasicrystal-containing titanium alloy characterized in that the metal having a large absolute value is at least one element selected from Dy, Er, Hf, Ho, Lu, Sc, Tb, Th, Tm, and Y Method. The manufacturing method of the quasicrystal containing titanium alloy of Claim 5 which forms a quasicrystal by heat-processing at 300-650 degreeC. A method for producing a hydrogen storage alloy member containing a quasicrystal, wherein the titanium alloy produced by the method according to claim 5 or 6 is molded and sintered.