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Materials Science and Engineering A 459 (2007) 204–208

Influence of Ni or Mn on hydrogen absorption–desorptionperformance of V–Ti–Cr–Fe alloys

Liang Hao a,b,∗, Chen Yungui a, Yan Yigang a, Wu Chaoling a, Tao Mingda a

a School of Materials Science and Engineering, Sichuan University, Chengdu 610064, Chinab Institute of System Engineering, CAEP, Mianyang 621900, Sichuan Province, China

Received 4 April 2006; received in revised form 20 December 2006; accepted 11 January 2007

bstract

The hydrogen desorption performance of the BCC alloys V Ti Cr Fe Ni (x = 0.1, 0.3, 0.5 and 1) and V Ti Cr Fe Mn (y = 0.3,

55−x 20.5 18.1 6.4 x 55−y 20.5 18.1 6.4 y

.7 and 1) were evaluated by pressure-composition-temperature tests. Their hydrogen absorption kinetic properties were studied through hydrogenbsorption curves. The crystallographic structures of these alloys before hydrogen absorption and after hydrogen desorption PCT test were identifiedy X-ray diffraction (XRD). The mechanism affecting their hydrogen absorption–desorption characteristics by Ni or Mn were discussed. 2007 Elsevier B.V. All rights reserved.

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eywords: Hydrogen storage materials; V–Ti–Cr–Fe alloys; Pressure-composi

. Introduction

The hydrogen storage alloys are classified as AB5-type, AB-ype, AB2-type, A2B-type and so on. AB5-type alloys such asaNi5 contain only 1.4 wt% of hydrogen [1]. The hydrogenapacities of AB (e.g. TiFe) and AB2 (e.g. TiCr2) alloys are alsomall [2,3]. A2B (e.g. Mg2Ni) alloys can absorb large capacitiesf hydrogen, but the desorbing temperature is relatively high [4].

Vanadium-based solid solution alloys with b.c.c. structurere widely concerned especially for V–Ti–Cr alloys. V–Ti–Crlloys which show b.c.c. structure [5,6] are known to absorbbout 3.8 wt% of hydrogen [7]. They are easily activatednd hardly pulverized [8] besides that H2 can be released atild conditions. However, these alloys are usually prepared

y very expensive vanadium metal, so their application isestricted. The cost will be brought down if FeV raw mate-ial could be used instead of pure V. As a result, the hydrogenbsorbing–desorbing characteristics of V–Ti–Cr alloys will benfluenced because of the addition of Fe from FeV raw material.

55Ti20.5Cr18.1Fe6.4 which exhibits a favorable hydrogen stor-

ge characteristics has been found in our previous experiments.he purpose of the present work is to develop new alloys withetter hydrogen absorbtion and desorption performance based

∗ Corresponding author. Tel.: +86 816 2485460; fax: +86 816 2495884.E-mail address: lh-lhm@163.com (L. Hao).

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921-5093/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.msea.2007.01.030

emperature test; X-ray diffraction; Hydride

n V55Ti20.5Cr18.1Fe6.4. The elements forming AB type hydro-en storage alloys are usually classified as elements of A sidend B side. A side elements react with H atom absorbing heatnd forming strong bond, while B side elements react with Htom releasing heat and forming weak bond only. As a result, Aide elements could increase hydrogen absorption content and Bide elements might play an key role in promoting hydrogen des-rption. V55Ti20.5Cr18.1Fe6.4 alloy like V–Ti–Cr ternary alloysas a limitation that there is much amount of residual hydro-en after desorption process which could not be used as theource of hydrogen. The method adding B side elements shoulde attempted to improve the based alloy’s performance. Ni orn as important additive elements for AB type hydrogen stor-

ge alloy is used to substitute partial V of V55Ti20.5Cr18.1Fe6.4lloy in which V55Ti20.5 could be regarded as A side part andr18.1Fe6.4 could be regarded as B side part. So the purpose of theresent work is to improve the hydrogen absorption and desorp-ion performance of V55Ti20.5Cr18.1Fe6.4 by adding Ni or Mn.

. Experimental procedures

The compositions were designed as V55−xTi20.5Cr18.1Fe6.4

ix (x = 0, 0.1, 0.3, 0.5 and 1) and V55−yTi20.5Cr18.1Fe6.4Mny

y = 0, 0.3, 0.7 and 1). The alloys were prepared from pure–Ti–Cr–Fe–Ni and Mn by arc melting on a water-cooled

opper hearth under argon atmosphere. The alloy ingots were

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L. Hao et al. / Materials Science a

e-melted four times to ensure their composition homogeneitynd then crushed into 100 �m powders under air atmosphere forests.

Pressure-composition-temperature (PCT) curves were mea-ured using a Sieverts-type apparatus. Activation process wasarried out before tests. The activation treatments were as fol-ows. Each sample was put into a stainless steel reactor andvacuated at 313 K for 15 min, then at 673 K for 30 min. Later,ydrogen with a pressure of 4 MPa was introduced into theeactor and kept for 30 min, and then the reactor was cooledown to room temperature slowly and kept for 30 min. After thathe reactor was evacuated at 673 K for 50 min again to ensureesorbing hydrogen completely. At last the activation was com-leted. During the activation process the vacuum level was below0−2 Pa after the stainless steel reactor was evacuated. The des-rbing PCT curves were obtained under constant temperatureith a pressure change from 4 to 0.01 MPa. In measuring theydrogen absorption kinetic curves the reactor was evacuatedo 1 × 10−1 Pa for 1 h to remove any gas in experiment systemefore hydrogen was introduced into it. Hydrogen purity wasigher than 99.99%.

In this paper, the hydrogen absorption capacity is defined ashe hydrogen content under a pressure of 4 MPa. The hydro-en desorption capacity obtained during PCT tests means theeversible hydrogen storage quantity, which is defined as themount of hydrogen desorbed from 4 to 0.01 MPa at 298 K.

The samples were shivered and sieved through 200 meshesor phase analysis and structure determination by X-ray diffrac-ometer (XRD) using Cu K� radiation (Rigaku, D/MAX-Bystem).The scanning speed was 10◦ min−1 in a step of 0.02◦rom 30◦ to 90◦.The tube voltage was 50 kV and tube electricurrent was 160 mA. The counting was 2KCPS.

. Results and discussion

.1. The properties of hydrogen absorption and desorption

A perfect hydrogen storage alloy should have not only a large

apacity for hydrogen absorption but also a large enough capac-ty to desorb the absorbed hydrogen, because only the desorbedydrogen could be used as the source of hydrogen [9]. In otherords, the alloy should have a good character for reversible

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Fig. 1. Hydrogen desorption PCT curves at 298 K. (a) V55−xT

gineering A 459 (2007) 204–208 205

ydrogen storage and hydrogen desorption property. So the des-rption PCT curve is more convictive than the absorption PCTn reflecting a kind of alloy’s hydrogen storage characteristics.

The hydrogen desorption PCT curves of the hydrided55−x(y)Ti20.5Cr18.1Fe6.4Nix(Mny) alloys at 298 K are shown inig. 1(a and b). From Fig. 1(a) it could be observed that, with an

ncrease of Ni content, the plateau pressures of hydrogen des-rption increase except for the alloy with 0.5 at.% of Ni. Thelopes of plateau for these alloys are almost the same with eachther except that 0.1 at.% of Ni makes the plateau flat. Fromig. 1(b) it could be seen that, the plateau pressures increaseith an increase of Mn content in the alloys, but the slope of thelateau for the Mn-containing alloys is more inclined than thator the based alloy.

The hydrogen content of absorption and desorption of55−x(y)Ti20.5Cr18.1Fe6.4Nix(Mny) alloys at 298 K are plotted

imultaneously in Fig. 2(a and b).The hydrogen absorptionontent remains constant when Ni content changes from 0 to.3 at.%, however, the hydrogen absorption content decreasesbviously with increasing Ni content when it is over 0.3 at.%.he hydrogen desorption content increases first then decreasesith increasing Ni content and the value is the largest at the.1 at.% Ni content. The hydrogen absorption contents of thelloys with 0 at.% Mn and 0.3 at.% Mn are almost the same,hile the content decreases with increasing Mn content. Similar

o the influence of Ni, the hydrogen desorption content increasesrst then decreases with increasing Mn content and the value is

he largest at the 0.3 at.% Mn content.In practical use, the hydrogen absorption kinetic prop-

rty is one of the most important properties, and how longn alloy could reach its maximum hydrogen storage con-ent is what many researchers concern very much. Fig. 3(a)nd (b) shows the hydrogen absorption kinetic curves of55−xTi20.5Cr18.1Fe6.4Nix and V55−yTi20.5Cr18.1Fe6.4Mny in

he first 10 min, respectively, and the time that each alloy reachests maximum hydrogen storage content is listed as a function ofi or Mn content in Fig. 3(c). It can be found that 0.1 at.% Ni

nd 0.3 at.% Ni addition can improve the hydrogen absorption

inetic performance of the based alloy, however, the perfor-ance is deteriorated when Ni content exceeds 0.3 at.%. It is

nteresting that for the 1 at.% Ni alloy, hydrogen is absorbedery slowly in the initial 8.5 min, and then, the absorption is

i20.5Cr18.1Fe6.4Nix and (b) V55−yTi20.5Cr18.1Fe6.4Mny.

206 L. Hao et al. / Materials Science and Engineering A 459 (2007) 204–208

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Fig. 2. Hydrogen absorption and desorption content at 298 K.

uicken up in the following 1 min and slowed down again. Aimilar phenomenon occurs in the Mn-adding alloys. A 0.3 at.%n addition can improve the hydrogen absorption kinetic per-

ormance, but performance is deteriorated when Mn contentxceeds 0.3 at.%. Besides, the alloy with 0.7 at.% Mn or 1 at.%n needs a pregnant time (0.5 and 1 min, respectively) before

ydrogen absorption.

.2. Mechanism affecting hydrogen storage content

The XRD patterns of V55−x(y)Ti20.5Cr18.1Fe6.4Nix(Mny)lloys before hydrogen absorption and after hydrogen desorptionCT tests are presented in Fig. 4(a–c). The relationship between

he lattice parameter and cell volume of BCC main phase and Ni

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Fig. 3. Hydrogen absorption kinetic property at 298 K. (a) V55−

55−xTi20.5Cr18.1Fe6.4Nix and (b) V55−yTi20.5Cr18.1Fe6.4Mny.

r Mn content before hydrogen absorption is shown in Fig. 5(a)nd (b). It can be seen from Figs. 4 and 5 that, with the increasef Ni or Mn content, the 2θ diffraction angle shifts to higherngle, the lattice parameter and unit cell volume decrease, wherehere is a good linear relationship between the lattice parame-er and Ni or Mn content. This is attributed to the fact that theadius of Ni or Mn atom is smaller than that of V atom, andhe fact that adding Ni and Mn atoms causes the unit cell tohrink. Fig. 6 reflects the relationship between the cell volumend the hydrogen desorption pressure that the decrease of the

ell volume leads to the increase of the desorption pressure. Ass displayed in Fig. 4(a), V-based BCC phase is dominant inll Ni-containing alloys except minor FeCr phase existing inhe alloys with 0.5 and 1 at.% Ni content, and FCC phase in

xTi20.5Cr18.1Fe6.4Nix and (b) V55−yTi20.5Cr18.1Fe6.4Mny.

L. Hao et al. / Materials Science and En

Fig. 4. XRD patterns before hydrogen absorption and after hydrogen desorp-tion PCT test. (a) V55−xTi20.5Cr18.1Fe6.4Nix, (b) V55Ti20.5Cr18.1Fe6.4, and (c)V55−yTi20.5Cr18.1Fe6.4Mny.

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gineering A 459 (2007) 204–208 207

he 1.0 at.% Ni alloy coexists with BCC phase in the alloy withat.% Ni after PCT test. The reason that he hydrogen desorptionontent increased first and then deceased in Fig. 2(a) could bexplained as follows. An increase of hydrogen desorption pres-ure with increasing Ni content implies the decrease of hydridetability and the more hydrogen desorption content .On the otherand, the decrease of the cell volume with increasing Ni contentmplies the less lattice interstitial space and the less hydrogenbsorption content. When Ni content is no more than 0.1 at.%,he former factor is predominated, so the alloy with 0.1 at.%i shows the largest hydrogen desorption content. In the fol-

owing steps, the latter factor is predominated, so the hydrogenesorption content is brought down. Furthermore, FeCr phasexisting in the alloys with 0.5 and 1 at.% Ni is not a good hydro-en storage phase, which deteriorates the hydrogen absorptionharacteristics in another manner. For the alloys with Mn, Mnhase appears in the alloy with 0.7 at.% Mn. TiMn-based phasend Mn phase appear in the alloy with 1 at.% Mn. The influenceechanism of Mn operates as the same as that of the Ni on these

lloys.

.3. Mechanism affecting hydrogen absorption kineticroperty

Fig. 3(a) shows that the hydrogen absorption kinetic per-ormance of the Ni-containing alloys was deteriorated for the.5 at.% Ni alloy and specially for the 1.0 at.% Ni alloy. Thisay be due to the impurity phases of FeCr phase which has bad

ydrogen absorption kinetics property. Fig. 3(b) shows that thewo alloys with 0.7 and 1 at.% Mn exhibited hydrogen absorp-ion pregnant time of 0.5 and 1 min, respectively, as may beue to the impurity phases of Mn phase and TiMn-based phasehich has bad hydrogen absorption kinetics property, too. But it

s interesting to find that the kinetics property was improvedhen a little amounts of Ni or Mn was added in to substi-

ute for V, as may be attributed to the fact that the reducedell volume caused by Ni or Mn makes the hydrogen diffusionhannels become short, where the FeCr, Mn or TiMn impurityhases have hardly formed. When Ni or Mn content increasesore, the impurity phases have an adverse effect on the hydro-

en absorption kinetics despite the reduction of the unit cellolume.

.4. Influence of Ni or Mn on structure transformation andolume expansion

The reversibility of structure transformation might reflecthe hydrogen absorption and desorption cyclic ability. As isnown to all that the hydrogen absorption and desorptionrocess in V-based alloys includes BCC(�) → FCC(�) andCC(�) → BCC(�) transformation [10]. From the XRD patternsf the alloys after hydrogen desorption PCT test in Fig. 4(a), itan be seen that the alloys with Ni do not contain FCC phase

xcept the 1.0 at.% Ni alloy. The reversibility of structure trans-ormation for the alloys with Mn is worse than that of the alloysith Ni. For example, there exists large amounts of FCC phase

or the alloys with 0.7 and 1 at.% Mn after hydrogen desorption

208 L. Hao et al. / Materials Science and Engineering A 459 (2007) 204–208

Fig. 5. Relationship between lattice parameters and Ni or Mn content. (

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ig. 6. Relationship between cell volume and hydrogen desorption pressure at98 K.

CT test in Fig. 4(c). So it can be deduced that when Ni or Mnddition is large, the alloy’s hydrogen absorption and desorptionyclic property will be deteriorated.

The alloy’s volume expansion may reflect the hydrogenbsorption and desorption cyclic ability, too. The relationshipetween the �V/V ratio of BCC phase and the Ni or Mn contenturing hydrogen absorption and desorption process is plotted inig. 7. The �V/V ratio has an increasing tendency with increas-

ng Ni content, while the �V/V ratio increases monotonously

ith increasing Mn content. The two curves reveal that the alloysith Ni have weaker volume expansion than the alloys withn, so it can be stated that the former have better pulverization

esistance than the latter.

Fig. 7. Volume expansion at 298 K.

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a) V55−xTi20.5Cr18.1Fe6.4Nix and (b) V55−yTi20.5Cr18.1Fe6.4Mny.

. Conclusions

The hydrogen absorption–desorption performance and struc-ure of V55−x(y)Ti20.5Cr18.1Fe6.4Nix(Mny) (x = 0.1, 0.3, 0.5 and; y = 0.3, 0.7 and 1) were studied in this paper.

1) With the increase of Ni or Mn content, the effective hydro-gen absorption content increases first and then decreases,and the hydrogen desorption pressure increases. The hydro-gen absorption kinetic property is improved first and thendeteriorated. Adding 0.1 at.% Ni or 0.3 at.% Mn has ben-eficial effect on the hydrogen absorption and desorptionperformance of the based alloy, i.e. V55Ti20.5Cr18.1Fe6.4.The change of unit cell volume, the increase of hydrogendesorption pressure and the occurring of impurity phasescaused by Ni or Mn substituting for V are the main influ-ence factors on the alloys’ effective hydrogen absorptioncontent and their kinetic property.

2) The Ni-containing alloys have a better reversibility ofstructure transformation during hydrogen absorption anddesorption process than that of the Mn-containing alloys,and the effect of volume expansion of the former alloys isweaker than that of the latter alloys.

cknowledgement

This work is supported by the Science and Technologyureau of Panzhihua City, Sichuan Province, China.

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