JP2000219926A - Hydrogen or hydrogen isotope occluding material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the reversibly repeated absorbing and discharging of hydrogen or hydrogen isotopes at high density under sufficiently low equilibrium pressure by specifying the compsn. composed of Zr, Ni and Co, moreover executing cooling at a low cooling rate in the heat treating stage and forming its crystal structure into the prescribed one. SOLUTION: A ZrNi alloy is used as a base, in which a part of Ni is substituted by a suitable amt. of Co to form a compsn. shown by Zr1(Ni1-xCox)y (where 0.2<=x<=0.8, preferably, 0.4<=x<0.8, and 0.8<=y<=1.2), and also, the structure is formed of the mixed phases of a cubic system B2 structure and a rhombic system Bf structure to obtain a hydrogen occluding material capable of absorbing and discharging hydrogen or hydrogen isotopes such as heavy hydrogen and tritium at high density under sufficiently low equilibrium pressure and moreover excellent in durability in repeated absorbing and discharging. The mixed phases of this crystal structure can be formed, in a heat treating stage at the time of material production, e.g. in homogenizing treatment at about 950 to 1,100 deg.C, after heating, by executing cooling at a sufficiently slow rate to a degree equal to or below that in furnace cooling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to hydrogen capable of storing and releasing hydrogen (H ₂ ) or hydrogen isotopes, ie, deuterium (D ₂ ) and tritium (T ₂ ) at high density and reversibly. Or, it relates to a hydrogen isotope storage alloy.

[0002]

2. Description of the Related Art Until now, hydrogen storage materials have been used for the separation and separation of hydrogen isotopes generated in hydrogen and nuclear power.
It has been used for recovery and storage, heat utilization such as heat pump and heat transport utilizing reaction heat accompanying occlusion and release, and application to secondary battery materials and the like. In these applications, the most basic properties required of the hydrogen storage material are that the hydrogen storage density is high, the reaction between the material and hydrogen or hydrogen isotope is fast and reversible, the material cost is low, It is also safe to use.

Conventionally, from the above viewpoints, TiFe-based and MmNi _5- based materials have been used as hydrogen storage materials, TiMn _1.5- based, TiCr _2- based materials have been used as heat utilizing materials, and MmNi has been used as a secondary battery hydrogen storage material. Uranium (U), a ZrNi alloy, a ZrCo alloy, or other hydrogen storage material is used as the storage material for handling system ₅ or hydrogen isotopes.
To further improve the properties, multi-component alloys derived from these basic alloys have also been proposed.

[0004]

However, uranium, Zr
Except for the Ni and ZrCo alloys, all of the alloys have a hydrogen storage density of about 1 in terms of a hydrogen / metal atomic ratio (H / M), and cannot be said to have a sufficient hydrogen storage capacity. On the other hand, uranium has a high storage density of H / M = 3, but its use is extremely difficult because of its high material costs and strictly regulated nuclear fuel supplies. In addition, uranium has the property of reacting with hydrogen isotopes to cause significant pulverization and then burning violently when exposed to the atmosphere, which poses a problem in terms of safety. The ZrNi alloy has a hydrogen storage density of H /
Although M is as high as about 1.4, the material for handling hydrogen isotopes has disadvantages such as high equilibrium dissociation pressure.

[0005] The present inventors have proposed a new alloy obtained by improving the ZrNi alloy in order to solve the above-mentioned disadvantages of the ZrNi alloy (Japanese Patent Application Laid-Open No. Hei 9-227974). This new alloy has a high hydrogen storage capacity, and is deteriorated (disproportionated) by repeated absorption and release of hydrogen compared to ZrNi alloy.
The improved ease of use makes it suitable for use with absorption and release cycles, such as absorbing hydrogen and tritium and reusing the released gas. However, the plateau pressure remained higher than that of uranium. Further, although the ZrCo alloy had a lower plateau pressure than the ZrNi alloy, the ZrCo alloy had poor durability and could not withstand repeated use. The present invention has been made in view of the above circumstances, and provides a hydrogen storage material capable of absorbing and releasing hydrogen or hydrogen isotopes at a sufficiently low equilibrium pressure at a high density and having excellent durability in repeated absorption and release. The purpose is to do.

[0006]

Means for Solving the Problems In order to solve the above problems, the first invention of the hydrogen or hydrogen isotope storage material of the present invention has a composition represented by the following general formula, and has a cubic B2 structure and an orthorhombic structure. It is characterized by being composed of a mixed phase having a crystalline Bf structure. General formula Zr ₁ (Ni _1-x Co _x ) _y However, 0.2 <x ≦ 0.8, 0.8 ≦ y ≦ 1.2 The hydrogen or hydrogen isotope storage material of the second invention is the first compound. Is characterized in that the quantity ratio x satisfies 0.4 ≦ x <0.8.

[0007] As described above, the material of the present invention is made of ZrNi.
Based on the alloy, it has a ternary composition in which a part of Ni is replaced by Co at an appropriate quantitative ratio, and has a mixed phase of a cubic B2 structure and an orthorhombic Bf structure. According to the material of the present invention, the hydrogen equilibrium dissociation pressure is lowered by the substitution of Co in an appropriate amount, and hydrogen or a hydrogen isotope can be favorably absorbed. In addition, since it is a mixed phase of the cubic B2 structure and the orthorhombic Bf structure, the durability in repeated hydrogen absorption and desorption is improved.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The alloy of the present invention has a ternary composition in which a part of Ni is replaced with an appropriate amount of Co based on a ZrNi alloy, and can be prepared by an ordinary method as an alloy with adjusted components. it can. Here, the addition of Co makes it possible to lower the equilibrium dissociation pressure in the hydrogenation characteristics without reducing the hydrogen storage capacity. In addition, the plateau property which appears on the pressure-composition-isothermal diagram (PCT diagram) is improved. Here, the improvement of the plateau property means that the inclination of the plateau portion is reduced and the flatness is increased, and that the step in the multi-stage plateau portion is reduced.
In addition, within the appropriate range of Co addition, the resulting material can be a mixed phase having a cubic B2 structure and an orthorhombic Bf structure. However, it is difficult to obtain the above-mentioned mixed phase only by adjusting the amount of Co added. In the heat treatment process (for example, homogenization treatment) during material production, the desired mixed phase is obtained by cooling at a sufficiently low cooling rate after heating. Phase can be obtained. For example, by cooling a material adjusted to an appropriate Co addition amount in a furnace, a mixed phase material having a cubic B2 structure and an orthorhombic Bf structure can be obtained.

The change in the average dissociation pressure is not directly related to the Ni substitution amount.
Without a linear change, the local minimum value is reached when x exceeds 0.7.
However, if Ni is replaced by Co even a little,
Zr ₁Co₁Lower plateau pressure than alloy
Wear. However, make sure that the hydrogen equilibrium dissociation pressure is
Placement exceeding 0.2 from the viewpoint of improving the rattling property
A replacement amount is required. If x is 0.2 or less, hydrogen
Equilibrium dissociation pressure cannot be lowered sufficiently and plateau
Is also not satisfactory. On the other hand, the replacement amount exceeds 0.8
The durability in repeated absorption and release is impaired
And the substitution amount of Co is set in the range of 0.2 <x ≦ 0.8.
You. In addition, x is 0.4 or more for each of the above reasons.
It is more desirable to further make it 0.5 or more.
desirable. On the other hand, for the same reason as above,
It is more desirable that the value be 0.7 or less.
New The amount ratio y of (Ni + Co) to Zr is:
It is set in the range of 0.8 to 1.2. This is where y is in this range
Out of phase, a phase other than the B2 and Bf structures precipitates and becomes stable.
This is because the characteristics cannot be obtained.

The material adjusted to the above-mentioned quantitative ratio is usually subjected to a homogenization treatment. In this homogenization treatment, the material is heated to a high temperature (for example, 950 to 1100 ° C.) in a desired atmosphere such as an inert gas atmosphere or a vacuum atmosphere, and is kept for a predetermined time (for example, 24 to 60 hours), and then cooled. The cooling rate at this time is desirably sufficiently low in order to obtain a mixed phase of the cubic B2 structure and the orthorhombic Bf structure.
For example, cooling is performed at a cooling rate equal to or lower than furnace cooling.

The obtained material can be used for desired applications without being limited to forms such as solid, granular, and molded products. Such uses include separation, recovery and storage of hydrogen or hydrogen isotopes, heat utilization such as heat pump and heat transport utilizing reaction heat, and secondary battery materials. In particular, the material of the present invention has a low hydrogen equilibrium pressure, and thus is suitable for recovering hydrogen isotopes having only a low partial pressure, which are generated in nuclear power.

[0012]

EXAMPLES Examples (inventive materials) of the present invention will be described below in comparison with comparative materials outside the scope of the present invention. The component raw materials are weighed, and Zr ₁ Ni _1-x Co _x (x =
0, 0.2, 0.4, 0.6, 0.7, 0.8, 1.
0) were blended so as to be seven kinds of compositions. These compounds are stored in a copper crucible of an arc vacuum melting apparatus,
Arc melting was performed in a high-purity Ar gas atmosphere, and the solidified material was cooled to room temperature in a melting device. After further melting, in order to homogenize the alloy composition, about 10
Heat treatment was performed at a temperature of 00 ° C. for about 50 hours, and then the furnace was cooled. After the obtained alloy was pulverized to 50 to 200 mesh, the crystal structure was defined by X-ray diffraction measurement, and the PCT characteristics and durability were evaluated by hydrogen absorption and desorption (20 ° C.).

FIG. 1 is a PCT diagram for each sample, and FIG. 2 is a partially enlarged view of FIG. The plateau portion of each sample was composed of two stages, and the hydrogen equilibrium pressure was evaluated using the plateau pressure of the first stage. In evaluating the plateau property, the pressure ratio with the plateau pressure of the second stage was calculated in consideration of not only the gradient at the plateau portion but also the pressure difference at the step portion. Furthermore, in order to evaluate the durability, the number of repetitions of hydrogen absorption and desorption repeatedly until the hydrogen transfer amount is reduced by 80% from the initial stage is defined as durability (the larger the number of repetitions, the better the durability). The results are shown in Table 1.

[0014]

[Table 1]

As is clear from Table 1 and the figures, the materials within the scope of the present invention have a hydrogen equilibrium pressure, a plateau property,
Good results were obtained in all durability. On the other hand, in Comparative Example No. No. 1 ZrNi has a high hydrogen equilibrium pressure and N
o. ZrCo of No. 7 was inferior in durability.

[0016]

As described above, according to the hydrogen or hydrogen isotope storage material of the present invention, the composition is represented by the general formula:
Zr ₁ (Ni _1-x Co _x ) _y (where 0.2 <x
≦ 0.8, 0.8 ≦ y ≦ 1.2) and a mixed phase of a cubic B2 structure and an orthorhombic Bf structure.
A low hydrogen equilibrium dissociation pressure can be obtained, and there is an effect of exhibiting excellent durability in repeated absorption and release.

[Brief description of the drawings]

FIG. 1 is a PCT diagram of each test material in an example of the present invention.

FIG. 2 is a partially enlarged view of FIG. 1;

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiki Kabumori 4th Chazu-cho, Muroran-shi, Hokkaido Inside Japan Steel Works, Ltd. Masamitsu Murai 4th Chazu-cho, Muroran-shi, Hokkaido Japan Steel Works, Ltd. (72) Kunihiko Tsuchiya Inventor 3607 Niibori, Narita-cho, Oarai-cho, Higashiibaraki-gun, Japan 3607 Niibori, Narita-cho, Oarai-machi, Ibaraki

Claims (2)

[Claims] 1. A hydrogen or hydrogen isotope storage material having a composition represented by the following general formula and a mixed phase of a cubic B2 structure and an orthorhombic Bf structure, wherein Zr ₁ (Ni _{1 −x} Co _x ) _y where 0.2 <x ≦ 0.8, 0.8 ≦ y ≦ 1.2 2. The hydrogen or hydrogen isotope storage material according to claim 1, wherein the quantity ratio x satisfies 0.4 ≦ x <0.8.