Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2001-02-14
2001-12-11
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C419S061000, C420S590000, C420S900000, C428S649000, C428S660000, C428S668000, C428S926000, C428S940000
Reexamination Certificate
active
06329076
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a hydrogen storage material, and more particularly, relates to a hydrogen storage material having excellent hydrogen storage capability and also a reduced hydrogen desorption temperature, and a manufacturing method of the same.
BACKGROUND ART
With growing interest in the hydrogen energy systems, research and development of the hydrogen storage materials have been actively conducted searching for materials for use in storage and transport of hydrogen, separation and refinement of hydrogen gas, energy conversion apparatuses, and the like. The research and development has shown that the hydrogen storage materials subjected to repeated hydrogen absorption and desorption are pulverized in a crumbling manner. Thus, materials having excellent hydrogen storage capability and also being highly resistant to pulverization resulting from the repeated absorption and desorption of hydrogen have been strongly demanded. In response to this, a proposal has been made to recommend a material having a thin-film laminated structure formed from a group 4A metal and any one of the group 6A, 7A and 8A metals (Japanese Laid-Open Publication No. 9-59001). Such a laminated, thin film body has a highly increased resistance to pulverization resulting from absorption and desorption of hydrogen. Moreover, since the group 4A metals having an hcp structure in the state of a bulk material have a bcc structure in the thin-film, laminated structure, the number of interstitial sites that may store hydrogen is increased. Since the group 4A metals originally have strong bonding power with hydrogen and thus have high hydrogen absorbing capability, the increased interstitial site density results in increased hydrogen storage capability. Accordingly, materials being less susceptible to pulverization and having extremely high hydrogen storage capability can be obtained from the above-mentioned material having a thin-film, laminated structure formed from a group 4A metal and any one of the group 6A, 7A and 8A metals.
However, the above-mentioned thin-film, laminated material includes a group 4A element, Ti, and therefore is heavy in weight. Moreover, mass production of the thin-film, laminated material is restricted in terms of resources, thereby necessarily making the material highly expensive beyond the price suitable for practical use, as an industrial material of this type. Accordingly, an element alternative to the group 4A metals had been sought. As a result, it was found that the group 2A and 3A metals have the capability similar to that of the group 4A metals in terms of the hydrogen storage capability, and a hydrogen storage laminated material was proposed which has a group 2A or 3A metal substituted for a group 4A metal (Japanese Patent Application No. 11-165890). For example, Mg of the group 2A elements is rich in resources and also light in weight. Therefore, it has become possible to obtain an inexpensive, lightweight laminated material being less susceptible to pulverization and also having excellent hydrogen storage capability.
It is an object of the present invention to provide a hydrogen storage material having high hydrogen storage capability and also having such a low hydrogen desorption temperature as not to significantly hinder the daily, easy use of the nickel-hydrogen secondary batteries, hydrogen-utilizing fuel cells, hydrogen-utilizing energy conversion systems and the like, and more specifically, as low as 150° C. or less, and capable of being mass-produced, and a manufacturing method of the same.
DISCLOSURE OF INVENTION
A hydrogen storage material of the present invention includes a layered deformation structure formed in a starting material subjected to plastic deformation, wherein one layer of the layered deformation structure is formed from an alloy or compound including an element of groups 2A, 3A and 4A or an element of at least one of the groups 2A, 3A and 4A, and another layer being in contact with the one layer is formed from an alloy or compound including an element of groups GA, 7A and 8A or an element of at least one of the groups 6A, 7A and 8A.
With this layered deformation structure, contact between one layer and another layer is assured, and one layer is likely to include a bcc crystal structure, whereby the interstitial site density for storing hydrogen can be increased. Moreover, since the layered deformation structure is realized by plastic deformation, defects such as dislocations and lamination defects are formed at a high density, so that hydrogen is trapped in the defect portions, resulting in improved hydrogen storage capability. Moreover, since the defect portions serve as a fast hydrogen diffusion path, formation of the defect portions at a high density significantly reduces the hydrogen desorption temperature. In addition, since the hydrogen storage material can be manufactured by processing means such as rolling, a practically required amount on the order of tons can be produced in a short period with high efficiency.
Note that, the layered deformation structure refers to the structure formed from laminated dissimilar materials subjected to strong deformation working involving plastic deformation as shown in
FIGS. 1 and 2
, and is different from the structure shown in
FIG. 3
that is conventionally known as a laminated structure. In the structure shown in
FIG. 1
, each layer extends uniformly in the rolling, wire-drawing direction, whereas in the structure shown in
FIG. 2
, a portion where each layer extends uniformly is randomly folded.
In the case where fast diffusion of the hydrogen atoms in the defect portions is important, or otherwise, the above-mentioned hydrogen storage material has a defect density resulting from such strong deformation working that causes a half-band width of at least one of main diffraction peaks in an X-ray diffraction pattern of the layered deformation structure to be 0.2° or more.
The density of defects such as dislocations and lamination defects can be evaluated by the half-band width of an X-ray diffraction peak. Normally, in order to increase the hydrogen diffusion velocity, the half-band width is 0.2° or more, preferably 0.5° or more, and most preferably 1° or more. Impurity segregation is likely to occur in the defect portions, and such impurity segregation results in biased charges. These biased charges are considered to have a function to attract and trap hydrogen. In order to clearly induce this hydrogen trapping function, the half-band width is preferably 0.5° or more. However, it is not necessarily desirable to increase the half-band width, and it is not preferable that the strong deformation working causes an amorphous state, i.e., the state where X-ray diffraction does not have clear diffraction peaks. In the amorphous state, the bond structure forming the crystal structure is disconnected, and the hydrogen atoms are strongly trapped in this disconnected bond structure. Therefore, the hydrogen storage capacity is increased, but the amount of hydrogen capable of being desorbed at a practical temperature is significantly reduced. Note that the main diffraction peaks refer to the highest three peaks among the diffraction peaks of a material that is to be subjected to the X-ray diffraction. Alternatively, in the case of a material having many diffraction peaks, the main diffraction peaks may refer to the highest five peaks, instead of the highest three peaks. A half-band width can be easily read on the chart. However, a diffraction peak that already has a half-band width of 0.2° or more before plastic working is excluded from the measurement. Alloys having precipitations produced therein and the like have a diffraction line with a half-band width of 0.2° or more. Accordingly, such a diffraction line is excluded from the measurement.
In the case where it is important in the above-mentioned hydrogen storage material to assure a large contact area between one layer and another layer and obtain a high defect density, or otherwise, one layer of the layered deformation structure has
Kawabe Nozomu
Sogabe Kouichi
Takeda Yoshinobu
Uemura Takashi
Yamanaka Shousaku
Fasse W. F.
Fasse W. G.
Koehler Robert R.
Sumitomo Electric Industries Ltd.
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