Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Patent
1999-05-14
2000-11-28
Wyszomierski, George
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
148421, 420421, 420424, 420428, 420900, C01B 624, C22C 1400, C22C 2702, C22C 2706, C22C 118
Patent
active
061530328
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a hydrogen-absorbing alloy. More particularly, the present invention relates to a hydrogen absorbing alloy which makes it possible to control a very fine structure formed by a spinodal decomposition so as to improve the flatness of an equilibrium pressure (flatness of a plateau portion), and which is excellent in activation performance and absorption and desorption amounts, and a method of producing such a hydrogen-absorbing alloy.
BACKGROUND ART
Solar energy, atomic power, wind power, geothermal heat, re-utilization of waste heat, etc, have been proposed as new energy sources to replace fossil fuel from the aspect of the environmental problems of the earth. For all of these sources, a common problem is how to store and transport energy. A system which electrolyzes water by using solar energy or water power and uses the resulting hydrogen as an energy medium can be said to provide ultimate clean energy in the sense that the starting material is water and the product obtained by consuming this energy is also water.
As one of the means for storing and transporting this hydrogen, a hydrogen-absorbing alloy can absorb and store a hydrogen gas to a capacity about 1,000 times the volume of the alloy itself, and its volume density is substantially equal to, or greater than, that of liquid or solid hydrogen. It has long been known that metals and alloys having a body-centered cubic lattice structure (hereinafter called the "BCC structure"), such as V, Nb, Ta, Ti--V alloys, etc, absorb and store greater amounts of hydrogen than an AB.sub.5 type alloys such as LaNi.sub.5 and AB.sub.2 type alloys such as TiMn.sub.2 that have been already put into practical application. This is because the number of hydrogen absorbing sites in the crystal lattice is large in the BCC structure, and the hydrogen absorbing capacity according to calculation is as great as H/M=2.0 (about 4.0 wt % in alloys of Ti or V having an atomic weight of about 50).
A pure vanadium alloy absorbs and stores about 4.0 wt %, which is substantially similar to the value calculated from the crystal structure, and desorbs about half this amount at normal pressure and room temperature. It is known that Nb and Ta as the elements of the same Group 5A of the Periodic Table exhibit a large hydrogen storage capacity and excellent hydrogen desorption characteristics in the same way as vanadium.
Because pure V, Nb, Ta, etc, are extremely high in cost, however, the use of these elements is not realistic in industrial application which requires a considerable amount of the alloys, such as a hydrogen tank or a Ni--MH cell. Therefore, properties of alloys have been examined within the range having the BCC structure such as Ti--V, but new problems have arisen in that these BCC alloys merely absorb and store hydrogen at a practical temperature and pressure but that their hydrogen desoprtion amount is small, in addition to the problems encountered in V, Nb and Ta in that the reaction rate is low and activation is difficult. As a result, alloys having a BCC phase as the principal constituent phase have not yet been put into practical application.
The conventional attempt to control the characteristics by alloying has been carried out by component design in all of the AB.sub.5 type, the AB.sub.2 type and the BCC type. However, the set range of the components does not exceed the category of the inter-metallic compound single-phase and the BCC solid solution single-phase in all of these examples. As one of the known references in this field, Japanese Unexamined Patent Publication (Kokai) No. 7-252560 discloses an alloy which has a composition of five or more elements, has a body-centered cubic structure as a crystal structure, comprises a Ti--Cr system as the basic system and is expressed by the general formula Ti.sub.100-x-y-z Cr.sub.x A.sub.y B.sub.z, where A is at least one member selected from the group consisting of V, Nb, Mo, Ta and W, and B is at least one member selected from the group consisting of Zr, Mn, Fe, Co, N
REFERENCES:
patent: 4440737 (1984-04-01), Libowitz et al.
"Hydrogen absorption properties of Ti-Cr-A (A.ident.V, Mo or other transition metal) B.C.C. solid solution alloys", T. Kabutomori et al., The Journal of Alloys and Compounds, vol. 231, No. 1, Dec. 15, 1995, pp. 528-532.
Akiba Etsuo
Iba Hideki
Morillo Janelle
Toyota Jidosha & Kabushiki Kaisha
Wyszomierski George
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