JPH10158755A - Production of bcc type hydrogen storage alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a BCC type hydrogen storage alloy excellent in hydrogen occluding and releasing property while obviating the necessity of heat treatment and crushing stages by rapidly solidifying a molten Ti-Cr alloy of specific composition in an inert gas atmosphere by using a twin-roll method, a single-roll method, an atomizing method, etc. SOLUTION: A molten alloy, having a composition enclosed with line segments obtained by connecting points A(Ti30 Cr70 ), B(Ti10 Cr70 X20 ), C(Ti40 Cr40 X20 ), and D(Ti60 Cr40 ) in the ternary diagram and represented by the formula Ti100-a-b Cra Xb [where X is at least either of Mo and W and the symbols (a) and (b) satisfy, by atomic %, 40<=a<=70 and 0<b<=20, respectively], is prepared. This molten alloy is rapidly solidified in an inert gas atmosphere by using a rotary body rotating at high speed or by means of an atomizing method and formed into a state of BCC phase at room temp. At this time, it is preferable to regulate cooling rate at the time of cooling to >=10<2> K/sec. Owing to this composition, the BCC phase as nonequilibrium phase can be obtained at room temp. without requiring heat treatment stage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a hydrogen storage alloy, and more particularly to a method of rapidly cooling directly from a molten metal to maintain the state of a BCC phase at room temperature without heat treatment, thereby improving the amount of hydrogen absorbed and released. The present invention relates to a method for producing a hydrogen storage alloy of the BCC type.

[0002]

2. Description of the Related Art As a means for storing and transporting hydrogen, a hydrogen storage alloy can store and store hydrogen gas of about 1000 times or more the volume of the alloy itself. , Ta and TiVMn system, metal having a body-centered cubic structure, such as TiVCr alloy (hereinafter referred to as BCC) is, AB _5, such as LaNi ₅ has been already put to practical use
It has been known for a long time to absorb a large amount of hydrogen as compared with an AB ₂ type alloy such as a type alloy or TiMn ₂ . Such a BCC type hydrogen storage alloy containing Ti has a high capacity but contains expensive V. Therefore, a hydrogen storage alloy which does not contain V and has the same level of capacity,
In applications that require a high-capacity hydrogen storage alloy, such as an EV hydrogen tank, a breakthrough cost advantage can be expected.

The present inventors have filed a Japanese Patent Application No. Hei 8-27 filed earlier.
No. 3438, a compound represented by the general formula Ti _{100 -ab} C _a X _b ,
Here, X is at least one of Mo and W, wherein a and b are represented by atomic%, and a hydrogen storage alloy represented by 40 ≦ a ≦ 70 and 0 <b ≦ 20 has been proposed. For the production of this BBC type hydrogen storage alloy, BCC (body-centered cubic structure) which is a high-temperature stable phase
In order to freeze the phase at room temperature, it is usually necessary to melt and cast the master alloy, hold it at 1200 to 1400 ° C. for 1 to 5 hours, and cool it in oil or ice water.

Further, in order to make the state capable of absorbing and releasing hydrogen, it is necessary to pulverize the alloy to about several tens of microns and activate it in a hydrogen atmosphere. In this regard, as a method of controlling the average particle size and omitting the pulverization and classification steps, for example, Japanese Patent Application Laid-Open No. 6-192712 discloses a direct production method of a raw material powder. A method of manufacturing by gas atomization is disclosed. However, in the production of hydrogen storage alloys as general alloys,
It requires four steps: melting and casting of the master alloy, heat treatment, pulverization and activation. However, in these four steps, it is necessary to simplify as much as possible from the viewpoint of production efficiency and cost. Therefore, it has been desired to develop a production method that can omit the two steps of the heat treatment and the pulverization step.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is to provide a BC
It is an object of the present invention to provide a method of manufacturing a BCC type hydrogen storage alloy which allows a quenching step for bringing a BCC phase at room temperature as a C type hydrogen storage alloy and at the same time, omit the heat treatment and pulverization steps.

Another object of the present invention is to consider roll quenching as the quenching step, to make the alloy into a ribbon shape, to increase the contact area with hydrogen gas, and to facilitate the activation of BCC.
To provide a method for producing a hydrogen storage alloy. Further, another object of the present invention is to provide an alloy capable of producing a hydrogen storage alloy having a high capacity of hydrogen absorption / desorption characteristics as an alloy characteristic at a low cost, thereby making it applicable to an industrial scale. It is an object of the present invention to provide a method for producing a BCC type hydrogen storage alloy which is excellent in quality.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is to provide a composition comprising:
General formula Ti _100-ab C _a X _b , wherein X is at least one of Mo and W, wherein a and b are represented by atomic% and 40 ≦
a ≦ 70, 0 <b ≦ 20.
This is achieved by a method for producing a BCC-type hydrogen storage alloy, characterized by rapidly cooling in an inert gas atmosphere and forming a BCC phase at room temperature. Further, the object of the present invention is to produce a BCC type hydrogen storage alloy, wherein the rapid cooling is a twin roll method, a single roll method or an atomizing method, and the cooling rate during cooling is 10 ² K / sec or more. It is also achieved by the method.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION As an alloy composition of the present invention, Ti-
FIG. 2 shows the range for the Cr-X alloy. In the ternary phase diagram, there is a single phase region of the C14 Laves phase, which is Ti—Cr-based TiCr ₂ , and the present invention avoids this range. On the other hand, an alloy melted by an induction heating method, an arc melting method, or the like transforms to a more stable C14 Laves phase at 1200 ° C. or less during normal cooling. Therefore, in the present invention, in order to form a BCC phase with the above composition, the BCC phase which is stable at a high temperature is frozen to normal temperature to make the range of the BCC phase in which the alloy is uniform. That is, point A in FIG.
_{(Ti 30 Cr 70), B} (Ti 10 Cr 7 0 X 20), C (Ti 40 Cr 40 X 20), and within the range surrounded by line segments consisting of D (Ti ₆₀ Cr _40), however, The composition includes a line segment other than AD.

According to the findings of the present inventors, BCC
Among the alloys, by spinodal decomposition inside,
In the state where it is regularly decomposed into two fine phases of nano order,
Hydrogen release characteristics are significantly affected. This is a binary phase diagram that is the basis of the ternary alloy, especially Ti-Cr-based, Cr-Mo
It can be seen that the system and the Cr-W system have a region of two-phase separation. As an example, FIG. 3 shows a binary phase diagram of a Ti—Cr system. In this figure, there is a solid phase line of two-phase separation connecting the eutectic point to 1370 ° C. of TiCr ₂ , and at a temperature higher than this, it is a homogeneous BCC phase. In the present invention, by bringing this state to a room temperature and rapidly cooling it, it is possible to produce a ribbon-like alloy which is a BCC phase and has significantly improved hydrogen release characteristics.

Further, the ribbon-like alloy has a thickness of 50 to 1
By setting the thickness to about 00 μm and the width of about 3 to 4 mm,
Large area, direct contact surface with hydrogen gas during hydrogenation
One that can increase the volume and can be activated sufficiently without grinding
And This quenching method uses liquid quenching suitable for industrial production.
A type of cooling method, such as the twin-roll method or the single-roll method.
Or the atomizing method, in which case the cooling rate is 10
^TwoK / sec or more. In this liquid quenching method, an electric furnace
Alternatively, a given alloy is melted by a high-frequency melting furnace,
The molten alloy is ejected from the nozzle at the crucible tip by gas pressure.
And contact solidify on the surface of the high-speed rotating rotor for cooling.
You. FIG. 1 shows an outline of the manufacturing apparatus of the present invention.

In order to prevent oxidation from the molten metal to the product from the atmosphere, the entire apparatus is made into an inert gas atmosphere 1, in which an injection nozzle 2, a high frequency coil 3, and a Cu roll 4 as a quenching device are provided. The master alloy adjusted to the alloy composition of the present invention is melted by the induction current generated by the high-frequency coil 3. This melting is performed, for example, in a refractory injection nozzle 2 as shown in FIG. 1 so that the molten alloy is continuously supplied and injected under a constant pressure condition. In the melting by the induced current by the high-frequency coil 3,
This is advantageous in that the stirring is sufficiently performed and the components of the molten metal 8 are made uniform. In the present invention, the melting apparatus is not particularly limited as long as melting and cooling are continuously performed in an inert atmosphere.

The quenching device rotates at a high speed as indicated by an arrow 5, for example.
Of molten metal 8 on a Cu roll 4 as a cooling rotator
Are thinly stretched and rapidly solidified. Cooling speed in this case
The degree is the characteristic value (heat transfer
Rate, heat capacity, etc.) and the thickness of the molten metal stream 8.
The amount of molten metal spouted depends on the physical properties of the molten metal depending on the alloy composition
Related characteristics (nozzle diameter, pressure, etc.) and the peripheral speed of the rotating body
I can decide. For example, Cu made of high-speed rotation at speed V
When the molten metal Q is ejected onto the roll 4, Q∝πa ^Twop
(A: nozzle diameter, p: ejection pressure)
As a result, a quenched ribbon 6 having a thickness t and a width w is obtained.
Then, it is expressed as a relational expression of Q∝wtV. The present invention
In other words, the calculation from the above relational expression
Understand the relationship between values and actual production and optimize the conditions.
Manufacturing conditions are obtained.

Next, the reasons for limiting the components of the present invention will be described. This alloy has the general formula Ti _100-ab C _a X _b , where
X is Mo and / or W, wherein a and b are represented by atomic% and represented by 40 ≦ a ≦ 70 and 0 <b ≦ 20. In the above composition range, there is a homogeneous phase of the BCC phase, after quenching to bring it to room temperature, the distortion of the crystal structure in the two-phase separated state in the alloy is optimized, and the movement of hydrogen as a hydrogen storage alloy It is adjusted to a microstructure that can promote the degree.

That is, when Cr is less than 40 at%, the hydrogen storage / release characteristics of the hydrogen storage alloy (pressure composition isotherm: PCT
(Diagram), the equilibrium pressure is low, and it becomes difficult to remove the stored hydrogen at room temperature again. In addition, Cr is 70 at
%, The equilibrium pressure is high and the amount of hydrogen absorbed at room temperature is small. Further, when Mo and / or W is 0 at%, the alloy is not converted to BCC even if heat treatment is performed. Also, 2
If it exceeds 0 at%, the amount of hydrogen storage decreases, which is not practical. For this reason, it was limited to the above composition range.

According to the present invention, the BCC phase of the alloy is made uniform.
Manufacture so that the amount of hydrogen absorbed and released when it appears
The quenching conditions as a method were specified. In other words,
The cooling rate after melting may be twin roll method, single roll method or
In the atomization method, 10 ^TwoIf less than K / sec
Is difficult to freeze the BCC phase uniformly,
Because hydrogen absorption and desorption characteristics of^TwoK / sec
The cooling rate was limited to the above. Also, in the present invention, cooling
The upper limit of the speed is not particularly limited.
Even with this alloy system, the effect of uniform freezing of the BCC phase
Except for saturation, no problem in material especially
by. However, as the cooling rate increases,
This is not advantageous.

As described above, in the composition of the present invention, although the BCC phase is used as the high-temperature phase, the C14 Laves phase easily forms at room temperature. However, by rapid cooling, a high-temperature phase BCC appears from the molten metal as a solidified structure, and then C14 is further added.
Room temperature is reached before transformation to the Laves phase takes place. Therefore, a BCC phase as a non-equilibrium phase can be obtained at room temperature without going through a heat treatment step. Hereinafter, the present invention will be described in more detail based on examples.

[0017]

EXAMPLES In the examples of the present invention, the composition of the hydrogen storage alloy was adjusted to Ti ₃₉ Cr ₅₄ Mo ₇ and Ti ₄₁ Cr ₅₆ W ₃ within the range of the present invention. In the example of the present invention, the dissolution amount was set to 6 g / time and 1800
The temperature of the cooling roll was 200 mm, the number of rotations was 4000 rpm, and the initial temperature of the roll was set to room temperature. It was confirmed that the cooling rate at this time was 10 ² K / sec or more. The quenched ribbon obtained after cooling had a thickness of 50 to 100 μm, a width of 3 to 4 mm, and a length of 30 to 40 mm. The comparative example is arc melting,
A button ingot having a diameter of 2 cm and a weight of 20 g was prepared, and then a button ingot crushed into about 10 mm square was used.

The composition of each phase in the alloy was determined using a transmission electron microscope and an attached EDX (energy dispersive X-ray diffraction). For the measurement of the ratio of the phase fraction, a crystal structure model was created based on information obtained by a transmission electron microscope, and Rietveld analysis of powder X-ray diffraction data was performed. In the Rietveld analysis, unlike the ordinary X-ray diffraction method, the crystal structure parameters can be refined by using the diffraction intensity, and the weight fraction of each phase can be obtained by calculation. For the Rietveld analysis, the analysis software Rietan94 developed by Dr. Izumi, Inorganic Materials Laboratory was used. Table 1 shows the BCC phase / Laves phase fraction of the quenched ribbon alloy of the example of the present invention prepared according to the present invention and the arc-melted alloy of the comparative example having the same composition.

[0019]

[Table 1]

From Table 1, the Laves phase fraction of the arc-melted alloy of the comparative example is 80% for Ti ₃₉ Cr ₅₄ Mo ₇ and a Laves single phase for Ti ₄₁ Cr ₅₆ W ₃ , whereas the roll of the present invention example The BCC phase fraction of the quenched alloy is 92% for Ti ₃₉ Cr ₅₄ Mo ₇ and Ti ₄₁ Cr ₅₆
W significantly it can be seen that turned into BCC ₃ in 89%.
Table 2 shows that Ti ₃₉ Cr ₅₄ Mo ₇ and Ti _{41 having} the above-mentioned composition of the present example.
The measurement results of the amount of hydrogen absorbed and released at 40 ° C. for the samples of the present invention example and the comparative example of Cr ₅₆ W ₃ are shown.

[0021]

[Table 2]

The hydrogen absorption / desorption characteristics of this component at 40 ° C. are as follows. The hydrogen storage capacity of the roll quenched alloy of the present invention is Ti ₃₉ Cr ₅₄
248 cc / g for Mo _{7 and} 222 cc / g for Ti ₄₁ Cr ₅₆ W ₃
g, hydrogen release amount is 209 cc / g for Ti ₃₉ Cr ₅₄ Mo ₇ , Ti
Against ₄₁ in the range of Cr ₅₆ W ₃ in 181cc / g, the hydrogen storage capacity of arc melting the alloy of the comparative example in Ti ₃₉ Cr ₅₄ Mo ₇ 96
_{cc / g, Ti 41 Cr 56} W 3 in 75 cc / g, the amount of desorbed hydrogen
10 cc / g in Ti ₃₉ Cr ₅₄ Mo _7, 40cc the Ti ₄₁ Cr ₅₆ W ₃
/ G, which shows that the hydrogen absorption / desorption characteristics are improved in the examples of the present invention.

[0023]

As described above, according to the present invention,
An alloy having characteristics equivalent to those of a conventional heat-treated alloy can be produced only by roll cooling. Furthermore, since the ribbon-shaped alloy has a very large specific surface area, it has a large direct contact area with hydrogen gas during hydrogenation, and can be activated without being pulverized. For this reason, the mother alloy melting casting required in the conventional manufacturing process,
The four steps of heat treatment, grinding and activation can be reduced to two steps of alloy melting / roll quenching and activation.
Therefore, according to the present invention, a high-capacity BCC-type hydrogen storage alloy can be manufactured at extremely low cost, and can be put to practical use in various applications.

[Brief description of the drawings]

FIG. 1 is a view showing an outline of a roll quenching apparatus according to the present invention.

FIG. 2 is a diagram showing the composition of a TiCrX (Mo and / or W) -based ternary phase diagram according to the present invention.

FIG. 3 is a Ti-Cr based binary phase diagram related to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Inert gas atmosphere 2 ... Injection nozzle 3 ... High frequency coil 4 ... Cu roll 5 ... High speed rotation 6 ... Quench ribbon 7 ... Molten metal 8 ... Molten metal flow

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI C22C 27/06 C22C 27/06

Claims (2)

[Claims] 1. The composition according to claim 1, wherein said composition is of the general formula Ti _100-ab Cr
_{a Xb} , wherein X is at least one of Mo and W, wherein a and b are represented by atomic%, and 40 ≦ a ≦ 70, 0 <b ≦ 20.
A method for producing a BCC-type hydrogen storage alloy, comprising rapidly cooling a molten alloy having a composition represented by the following formula in an inert gas atmosphere to form a BCC phase at room temperature. 2. The BCC type hydrogen storage alloy according to claim 1, wherein the rapid cooling is a twin roll method, a single roll method or an atomizing method, and the cooling rate at the time of cooling is 10 ² K / sec or more. Manufacturing method.