FORPRODUCINGCrTiVHYDROGENSTORAGEALLOYS

1、 ( 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 storage alloys utilizing thermit process, whereby

2、 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 alloy material (1) comprising a cr oxide, a v oxi

3、de, 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) placed in step (b) and melting all metal elements cont

4、ained 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; (takaraduka-shi, jp) ; neoda, akira; (uji-shi, jp) cor

5、respondence 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:075/010.27 internl class: c22b 004/06foreign applicat

6、ion 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 an alloy material (1) comprising a cr oxide, a v o

7、xide, 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 melting step (c) of igniting the alloy material (1)

8、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 obtained in step (c) into an alloy. 2. the method of cla

9、im 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 v oxide, and an amount required for reducing said

10、 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 separation layer having a melting point higher than that

11、 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 method of claim 5, wherein said separation layer c

12、ontains 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 plate being capable of separating an interior of sa

13、id 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, wherein at least one of the alloy materials (1) and

14、 (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 alloy contains 25 to 70 at % cr, 15 to 45 at % ti

15、, 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 consisting of la, ce, and misch metal in an amount of not

16、 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 relates to a method for producing hydrogen storag

17、e 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 art 0002 hydrogen storage alloys have been manufact

18、ured 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, on the a-site, and ni on the b-site, which is part

19、ially 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 most 1.2 wt %. when the alloy having such an effectiv

20、e 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 principally of a body-centered cubic crystal stru

21、cture (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 their production for melting the essential elements

22、 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 crucible in which it is melted. that is, if a cr-ti-v

23、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, alloys containing active ti with a high melting poi

24、nt 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 segregation and poor thermal efficiency. thus this m

25、ethod 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 lowered. in this regard, jp-9-49034-a discloses a me

26、thod 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-containing hydrogen storage alloy having the al content

27、 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 oxygen content of a v-containing hydrogen storage all

28、oy 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 methods are being developed which employ alloys of v an

29、d 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 arc melting in a water-cooled copper crucible. 000

30、6 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 sufficiently with al, so that a large amount of al

31、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 hydrogen storage capacity of not lower than 2 wt %. 00

32、07 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 me

33、thod is applied to production of a cr-ti-v alloy, the cr-v alloy produced by thermit reduction has to be remelted before ti is added. for remelting, the cr-v alloy has to be heated to as high as not lower than 1750.degree. c., which severe temperature condition remarkably impairs the life of the cru

34、cible. further in this method, wherein the amount of the reducing agent al is lowered below its theoretical amount for lowering the residual al content to not higher than 1 wt %, enough heat is not generated in the reducing reaction when the al content is not higher than 95%, in particular not highe

35、r than 90% of the theoretical amount. this makes it difficult to maintain the alloy melt at a required high temperature for a required duration, which results in insufficient separation of the oxides from the alloy melt by floating. 0008 in the above-described prior art, no method has been establish

36、ed that realizes intensive production of a high-purity, multi-element alloy containing v, utilizing thermit reduction, without remarkably impairing the service life of an expensive crucible. in particular for production of the alloy also containing ti as an essential element, v produced by thermit r

37、eduction or an alloy of v and other alloy elements than ti has to be the master alloy, to which metal ti is added, and remelted at a high temperature. this inevitably involves additional consumption of thermal energy and wearing of the crucible. summary of the invention 0009 it is therefore an objec

38、t of the present invention to provide an effective method for producing a high-performance cr-ti-v hydrogen storage alloy by thermit process, whereby residence of adversely-affecting impurities such as al is inhibited, addition of not less than 10 at % of ti as an alloy component is realized, and th

39、ermal burden on the crucible used in the method is reduced. 0010 according to the present invention, there is provided a method for producing a cr-ti-v hydrogen storage alloy utilizing thermit process comprising: 0011 material preparation step (a) of providing an alloy material (1) comprising a cr o

40、xide, a v oxide, and a reducing agent al, and an alloy material (2) comprising ti; 0012 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); 0013 metal melting step (c) of igniting th

41、e 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 0014 step (d) of making said alloy melt obtained in step (c) into an a

42、lloy. brief description of the drawings 0015 fig. 1 is a schematic view of an apparatus that may be used in the method of the present invention, provided for explaining experiments for deciding an al content for the invention. 0016 fig. 2 is a graph showing the results of the experiments for decidin

43、g an al content for the present invention, illustrating the relationship between the ratio of the al content to the theoretical amount and the al content in the cr-ti-v alloy after reduction and cooling. preferred embodiments of the invention 0017 the present invention will now be explained in detai

44、l. 0018 the method of the present invention utilizes thermit process, and includes as the first step the material preparation step (a), wherein an alloy material (1) containing a cr oxide, a v oxide, and a reducing agent al, and an alloy material (2) containing ti, are provided. 0019 in step (a), al

45、 contained in the alloy material (1) may be metal al and/or an al alloy. al acts as a reducing agent for the cr oxide, the v oxide, and an oxidizing agent optionally contained in the alloy material (1). 0020 the al alloy may be any alloy as long as it contains an effective amount of al for thermit r

46、eaction of the present invention, and as long as the kinds and amounts of the alloy elements do not have adverse effects on the performance of the resulting hydrogen storage alloy even if included therein. examples of the al alloy may include al-si alloys, al-mg alloys, al-si-cu alloys, alloys for a

47、l castings, al alloys distributed in the market as die-cast alloys, and scraps thereof. use of al as a reducing agent reduces the production cost. 0021 the alloy material (1) may contain an oxidizing agent for providing additional heat by thermit reaction. this oxidizing agent functions to provide s

48、upplemental heat in addition to the heat generated by the thermit reaction of the essential components, so that the addition of the oxidizing agent may reduce the content of the reducing agent al. preferred oxidizing agents are those generate a large amount of heat upon oxidation-reduction reaction

49、with al, such as barium peroxide (bao.sub.2), potassium chlorate (kclo.sub.3), and sodium chlorate (naclo.sub.3). for example, the amount of heat generated by reduction of potassium chlorate with al is as large as 3.16 times the amount of heat generated by reduction of chromic oxide with al, and 2.3

50、2 times the amount of heat generated by reduction of vanadium oxide with al (denki kagaku binran, 4th edition, maruzen) with such amount of heat being provided, the overall temperature of the alloy materials (1) and (2) maybe raised sufficiently to promote floating and separation of the slag from th

51、e alloy melt, and thus a clean alloy may be obtained. 0022 the amount of the oxidizing agent to be added may suitably be decided in accordance with the amount obtained from the sum of the amount of heat in need due to the al content reduced from the theoretical amount for reducing the starting oxide

52、 materials and the amount of heat escaping from the walls of the crucible, divided by the amount of heat generated by reduction of the oxidizing agent. 0023 in step (a), the content of al as the reducing agent may be the amount required for reducing the cr oxide and the v oxide, and when the oxidizi

53、ng agent is contained in the alloy material (1), the sum of 70 to 90% of the theoretical amount required for reducing the cr oxide and the v oxide and the amount required for reducing the oxidizing agent. this al content has been decided based on the experimental data discussed below. 0024 experimen

54、ts in thermit reduction were conducted using starting materials containing six different amounts of al powders ranging from 3.87 kg (70% of the theoretical amount) to 4.84 kg (100% of the theoretical amount), with respect to 3.0 kg of vanadium oxide and 9.0 kg of chromium oxide. 0025 in the experime

55、nts, crucible 10 for thermit reaction was used, composed of refractory bricks 10a and 10b as shown in fig. 1. above the separator plate 11 having sliding nozzle 11a of the crucible 10 was placed the alloy material (1) containing the above starting materials and 1.0 kg of potassium chlorate as the ox

56、idizing agent and 440 g of al powders as the reducing agent therefor. below the plate 11 was placed 3.4 kg of sponge titanium as the alloy material (2) as shown in the figure. with an argon gas blowing in through gas supply conduit 12, the alloy material (1) was ignited on top to initiate thermit re

57、action. when the alloy in the alloy material (1) was in a molten state, the sliding nozzle 11a was slid open to pour the alloy melt onto the alloy material (2). after cooling, the obtained alloy was taken out of the lower furnace, and the aluminum content of the alloy was analyzed. 0026 the relation

58、ship between the ratio of the al amount used to the theoretical al amount and the al content in the cr-ti-v alloy after reduction and cooling is shown in fig. 2. from the figure, it is observed that the al content in the alloy cannot be lowered to below 1 wt % when the amount of al used is not less than 95% of the theoretical amount required for the reduction. when the amount of al used is less than 70% of the theoretical amount, the yield of the cr-ti-v alloy is lowered, which is not economical. consequentl