METHOD FOR PRODUCING CrTiV HYDROGEN STORAGE ALLOYS.docx

1、METHOD FOR PRODUCING CrTiV HYDROGEN STORAGE ALLOYS ( 1 of 24 )United States Patent Application20040134308 Kind Code A1 Takata, Hiroaki ; et al. July 15, 2004 METHOD FOR PRODUCING Cr-Ti-V HYDROGEN STORAGE ALLOYS AbstractThe invention relates to a method for producing high-performance Cr-Ti-V hydrogen

2、 storage alloys utilizing thermit process, whereby residence of adversely affecting impurities is inhibited, addition of not less than 10 at % of Ti as an alloy component is realized, and thermal burden on the crucible used in the method is reduced. The method includes the steps of: (A) providing an

3、 alloy material (1) comprising a Cr oxide, a V oxide, and a reducing agent Al, and an alloy material (2) comprising Ti; (B) placing said alloy materials in a crucible for thermit reduction so that the alloy material (1) is placed above the alloy material (2); (C) igniting the alloy material (1) plac

4、ed in step (B) and melting all metal elements contained in the alloy materials with heat of thermit reaction of the alloy material (1); and (D) making an alloy melt obtained in step (C) into an alloy. Inventors:Takata, Hiroaki; (Himeji-shi, JP) ; Oka, Yutaka; (Kobe-shi, JP) ; Nakagawa, Junichi; (Tak

5、araduka-shi, JP) ; Neoda, Akira; (Uji-shi, JP) Correspondence Name and Address: DARBY & DARBY P.C. P. O. BOX 5257 NEW YORK NY 10150-5257 USSerial No.: 476070Series Code: 10 Filed: October 24, 2003PCT Filed: April 25, 2002PCT NO: PCT/JP02/04129U.S. Current Class:75/10.27 U.S. Class at Publication:075

6、/010.27 Internl Class: C22B 004/06Foreign Application DataDateCodeApplication NumberApr 27, 2001JP2001-132799Aug 21, 2001JP2001-250225ClaimsWhat is claimed is: 1. A method for producing a Cr-Ti-V hydrogen storage alloy utilizing thermit process comprising: material preparation step (A) of providing

7、an alloy material (1) comprising a Cr oxide, a V oxide, and a reducing agent Al, and an alloy material (2) comprising Ti; material introduction step (B) of placing said alloy materials in a crucible for thermit reduction so that the alloy material (1) is placed above the alloy material (2); metal me

8、lting step (C) of igniting the alloy material (1) placed in the crucible in step (B) for thermit reaction and melting all metal elements contained in the alloy materials with heat of the thermit reaction of the alloy material (1) to obtain an alloy melt; and step (D) of making said alloy melt obtain

9、ed in step (C) into an alloy. 2. The method of claim 1, wherein said alloy material (1) further comprises an oxidizing agent for providing additional heat by thermit reaction, and wherein a content of said Al is a sum of 70 to 90% of a theoretical Al amount required for reducing the Cr oxide and the

10、 V oxide, and an amount required for reducing said oxidizing agent. 3. The method of claim 2, wherein said oxidizing agent is selected from the group consisting of barium peroxide, potassium chlorate, sodium chlorate, and mixtures thereof. 4. The method of claim 1, wherein in said step (B), a separa

11、tion layer having a melting point higher than that of Al is provided between the alloy materials (1) and (2). 5. The method of claim 4, wherein said separation layer is selected from the group consisting of an iron plate, a steel plate, and an alloy steel plate, each of 0.05 to 3.0 mm thick. 6. The

12、method of claim 5, wherein said separation layer contains an auxiliary component selected from the group consisting of Fe, Mn, Mo, Ni, Co, and mixtures thereof. 7. The method of claim 1, wherein said crucible for thermit reduction comprises a separator plate having a sliding nozzle, said separator p

13、late being capable of separating an interior of said crucible into at least upper and lower compartments, and wherein in placing the alloy materials (1) and (2) in the crucible in said step (B), the alloy materials (1) and (2) are arranged separated by said separator plate. 8. The method of claim, w

14、herein at least one of the alloy materials (1) and (2) further comprises an auxiliary component selected from the group consisting of Fe, Mn, Mo, Ni, Co, and mixtures thereof. 9. The method of claim 1, wherein said alloy materials (1) and (2) are provided so that a resulting Cr-Ti-V hydrogen storage

15、 alloy contains 25 to 70 at % Cr, 15 to 45 at % Ti, 5 to 45 at % V, and 0.01 to 2 at % Al, and has a melting point not higher than 1600.degree. C. 10. The method of claim 1, further comprising step (E) of melting said alloy obtained in step (D) with a rare earth metal selected from the group consist

16、ing of La, Ce, and misch metal in an amount of not less than 0.2 at % of said alloy to obtain an alloy melt, deoxidizing said alloy melt to lower its oxygen content to not higher than 0.1 wt %, and cooling and solidifying said deoxidized alloy melt. DescriptionFIELD OF ART 0001 The present invention

17、 relates to a method for producing hydrogen storage alloys having excellent hydrogen storage performance, in particular, a method for producing Cr-Ti-V hydrogen storage alloys used for storage and transportation of hydrogen, negative electrodes for rechargeable batteries, or heat pumps. BACKGROUND A

18、RT 0002 Hydrogen storage alloys have been manufactured in a drastically increasing amount since the alloys were used for anodes of batteries. The hydrogen storage alloys presently used for batteries are mostly AB, type alloys, which contain La or misch metal, a mixture of light rare earth elements,

19、on the A-site, and Ni on the B-site, which is partially substituted by Co, Mn, Al, or the like element. The amount of hydrogen that such AB.sub.5 type alloys are capable of absorbing and desorbing under the hydrogen pressure of 0.01 to 4 MPa (defined as effective hydrogen storage capacity) is at mos

20、t 1.2 wt %. When the alloy having such an effective hydrogen storage capacity is used for producing a hydrogen storage tank mounted on a fuel cell electric vehicle, which is under active development, the required amount of the alloy weighs too much. In order to overcome this drawback, Cr-Ti-V alloys

21、 principally of a body-centered cubic crystal structure (BCC structure) are recently under development as a different line of hydrogen storage alloys, which have an effective hydrogen storage capacity of over 2 wt %. 0003 Cr-Ti-V alloys have excellent properties, but require higher temperatures in t

22、heir production for melting the essential elements V and Cr for alloying, which have melting points of 1910.degree. C. and 1863.degree. C., respectively. In addition, Ti, which also has a melting point of as high as 1670.degree. C., is an active element, and thus requires careful selection of a cruc

23、ible in which it is melted. That is, if a Cr-Ti-V alloy is melted in a crucible made of a metal oxide such as alumina, magnesia, or zirconia, Ti reacts with the main component of the crucible to corrode the walls of the crucible, which are cracked and become unusable for melting. Thus in practice, a

24、lloys containing active Ti with a high melting point are merely under pilot production by arc melting in a water-cooled copper crucible. However, in melting an alloy in a water-cooled copper crucible, the portion of the alloy melt that is in contact with the crucible is not melted, which leads to se

25、gregation and poor thermal efficiency. Thus this method is not suitable for mass-production. 0004 It is known that the reaction of Ti with an oxide crucible becomes severer as the temperature increases. Thus, the burden to the crucible may be alleviated if the melting point of the master alloy is lo

26、wered. In this regard, JP-9-49034-A discloses a method for producing a BCC hydrogen storage alloy containing at least V and Ni, in which a V-Ni, Ti-V, or Fe-V alloy produced by thermit reduction is used as a starting material. JP-2000-96160-A discloses a method for producing a material for a V-conta

27、ining hydrogen storage alloy having the Al content of less than 1 wt % by thermit reduction of an alloy material containing V-oxide and optionally Ni, Fe, Cu, Co, Mn, Cr, Nb, Ta, and the like element, using Al or an Al alloy as a reducing agent. JP-11-106847-A discloses a method for reducing the oxy

28、gen content of a V-containing hydrogen storage alloy produced by thermit reduction, wherein the alloy is melted under heating with a deoxidizing agent such as Ca, Mg, rare earth elements, or the like, for improving the properties of the alloy. 0005 As can be seen from these methods, production metho

29、ds are being developed which employ alloys of V and a transition metal as a master alloy of a hydrogen storage alloy, instead of metal V, which is high in both melting point and cost. Also the thermit reduction is recognized as a favorable method for mass-production, compared to the above-mentioned

30、arc melting in a water-cooled copper crucible. 0006 In producing a Cr-Ti-V hydrogen storage alloy, however, when a Ti oxide and a V oxide are reduced with metal Al by thermit reaction for obtaining a Ti-V alloy in accordance with the method disclosed in JP-9-49034-A, the Ti oxide cannot be reduced s

31、ufficiently with Al, so that a large amount of Al remains in the resulting alloy, in particular in producing an alloy having the Ti content of not lower than 10 at %. Such an alloy containing an excess amount of Al has a remarkably low hydrogen storage capacity, and cannot achieve the effective hydr

32、ogen storage capacity of not lower than 2 wt %. 0007 In order to overcome this problem, JP-2000-96160-A discloses to use, as a reducing agent, 85 to 99% of the theoretical amount of Al required for reducing all the oxides in the alloy material, in order to reduce the Al content in the resulting alloy to not higher than 1 wt %. However, when this method is applied to production of a Cr-Ti-V alloy, the Cr-V alloy produced by thermit reducti