Alloys or metallic compositions – Containing over 50 per cent metal but no base metal – Iron containing
Reexamination Certificate
2001-12-12
2004-09-07
Jenkins, Daniel (Department: 1742)
Alloys or metallic compositions
Containing over 50 per cent metal but no base metal
Iron containing
C420S900000, C148S538000
Reexamination Certificate
active
06787103
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
The present invention is based on Japanese Patent Application No. 2000-217187, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hydrogen storage alloy having a Laves phase containing vanadium.
2. Description of Related Art
Recently, hydrogen energy is focused as a new energy, and development of the hydrogen storage alloy reversibly absorbing and discharging hydrogen, is promoted elaborately in various fields, such as the hydrogen storage, heat pumps, actuators, and electrodes for secondary batteries. Among the hydrogen storage alloys, a Ti—Zr—Mn—V based hydrogen storage alloy has a large rechargeable hydrogen capacity, and the excellent alloy performance.
Conventionally, in order to obtain the alloy, a method of utilizing metals of elemental substances as the raw materials is applied, adjusting the component thereof at the time of melting, and providing the raw material melted mainly by the Ar arc melting method or the high frequency induction melting method into a dye. Moreover, after forming the alloy, a high temperature heat treatment is executed for a long time in order to improve the alloy performance.
In the above-mentioned Ti—Zr—Mn—V based hydrogen storage alloy, the oxygen content of the raw materials, in particular, of the vanadium drastically influences the hydrogen absorbing and discharging performance. In the case the content is large, the hydrogen absorbing amount of the alloy is deteriorated. However, since a vanadium has ordinarily a relatively large oxygen content of 10,000 ppm or more, a desired performance cannot be obtained in the case that the vanadium is directly used as the raw material for the hydrogen storage alloy. Therefore an oxygen reduction treatment is required. As a result, the alloy production cost is increased and a problem is caused that realization of a system containing the alloy is disturbed.
Moreover, the heat treatment to be performed after forming the alloy also increases the production cost and the production time, Furthermore, it may lead to oxidization of the alloy so as to deteriorate the performance, and thus a problem of difficulty in handling is also involved.
SUMMARY OF THE INVENTION
In view of the circumstances, an object of the invention is to provide a Ti—Zr—Mn—V—Fe hydrogen storage alloy with the excellent hydrogen absorbing and discharging performance by optimizing the components. Another object thereof is to provide a production method for a hydrogen storage alloy capable of producing the alloy efficiently at a low cost.
In order to solve the problems, a first aspect of the invention is a hydrogen storage alloy having Laves phase represented by the general formula: Ti
1−x
Zr
x
Mn
w−y−z
V
y
Fe
z
, wherein 0≦x≦0.5, 0<y≦0.6, 0<z≦0.2, and 1.8≦w≦2.2.
A second aspect of the invention is the hydrogen storage alloy having a Laves phase according to the first aspect, wherein the content of the oxygen is 5,000 ppm or less.
A third aspect of the invention is a production method for a hydrogen storage alloy having a Laves phase, wherein the hydrogen storage alloy according to the first or second aspect is formed by using a ferrovanadium (alloy of a vanadium and an iron) as one of the raw materials.
A fourth aspect of the invention is the production method for a hydrogen storage alloy having a Laves phase according to the third aspect, wherein the oxygen content of the ferrovanadium is 4,000 ppm or less.
A fifth aspect of the invention is the production method for a hydrogen storage alloy having a Laves phase according to the third or fourth aspect, wherein the melted raw materials are rapidly quenched and solidified.
Hereinafter, the atomic ratio defined in the invention, or the like, will be explained.
Atomic Ratio of the Alloy
Ti: Atomic Ratio 0.5 to 1.0
Since the titanium is an element capable of increasing the hydrogen absorbing amount, it is added as an essential component. However, in order to certainly obtain the above-mentioned effect, the atomic ratio should be 0.5 or more. In contrast, in the case it is added by more than a 1.0 amount, the hydrogen dissociation pressure is lowered. Therefore, the atomic ratio is set in the range of 0.5 to 1.0.
Zr: Atomic Ratio 0.5 or Less
Since the zirconium is an element capable of adjusting the hydrogen equilibrium dissociation pressure, it is optionally added. However, in the case it is added by a more than 0.5 atomic ratio, the hydrogen equilibrium dissociation pressure is lowered. Therefore, the upper limit of the atomic ratio is set at 0.5.
Mn: Atomic Ratio 1.0 to Less than 2.2
Since the manganese is an element capable of lowering the hydrogenation reaction temperature, it is added as an essential component. However, in order to certainly obtain the above-mentioned effect, the atomic ratio should be 1.0 or more. In contrast, in the case it is added by a 2.2 or more amount, the hysteresis is enlarged. Therefore, the atomic ratio is set in the range of 1.0 to less than 2.2.
V: Atomic Ratio 0.6 or Less
Since the vanadium is an element capable of increasing the hydrogen absorbing amount, it is added as an essential component. However, in the case it is added by a more than 0.6 atomic ratio, the reaction rate is lowered. Therefore, the upper limit of the atomic ratio is set at 0.6.
Fe: Atomic Ratio 0.2 or Less
Since the iron is an element contained at the time of using a ferrovanadium, it is added as an essential component. However, in the case it is added by a more than 0.2 atomic ratio, the hydrogen equilibrium dissociation pressure is raised. Therefore, the upper limit of the atomic ratio is set at 0.2.
Impurity Oxygen: 5,000 ppm or Less
The impurity oxygen contained in a hydrogen storage alloy influences the hydrogen absorbing and discharging ability. In the case the amount thereof is large, the absorbing and discharging ability is deteriorated. Therefore, the contained oxygen amount is preferably as little as possible. In consideration of the industrial applicability, the content thereof is preferably 5,000 ppm or less, and further preferably 1,000 ppm or less.
Laves Phase
Since a hydrogen storage alloy according to the invention has a Laves phase structure, it provides a high hydrogen absorbing effect owing to the Laves structure.
Use of Ferrovanadium
Since the alloy of the invention provides a good hydrogen absorbing and discharging performance owing to an appropriate component adjustment (including the iron), the ferrovanadium can be used as the raw material. Since the ferrovanadium is produced at a low cost compared with the case of a vanadium single metal, a desired hydrogen storage alloy can be produced efficiently at a low cost. As the ferrovanadium, for example, those containing a vanadium by 80 to 85% mass ratio, and an iron as the substantially remainder, can be presented. Furthermore, it is desirable that the ferrovanadium has the oxygen included as the impurity, limited to 4,000 ppm or less. More preferably, the ferrovanadium may contain the oxygen not more than 3,000 ppm. According to the limitation of the oxygen content, the oxygen content of a hydrogen storage alloy prepared with the ferrovanadium as the raw material can be sufficiently lowered so that the averse effect to the hydrogen absorbing and discharging performance can be eliminated.
Rapid Solidification
Furthermore, in the production of a hydrogen storage alloy according to the invention, the raw materials with the components adjusted, are melted, and rapidly quenched and solidified for preparation.
By preparing the hydrogen storage alloy by quenching and solidifying, by for example, roll quenching, the plateau properties and the hysteresis properties can be improved dramatically so that the storage and transportation efficiency of the hydrogen can be improved. In the conventional production method, the cooling operation at the time of forming an alloy is carried out by natural cooling or water cooling. In contrast, in the invention, the above-mention
Aoki Yasuhiro
Miyaki Takaaki
Japan Steel Works Ltd.
Jenkins Daniel
Sughrue & Mion, PLLC
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