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Hydrogen storage properties of Mg76Ti12Fe12-xNix (x=0,4,8,12) alloys by mechanical alloying
International Journal of Hydrogen Energy 32 (2007) 2412 – 2416 www.elsevier.com/locate/ijhydene
Hydrogen storage properties of Mg76Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys by mechanical alloying Jin Guo a,b,∗ , Kun Yang a , Liqin Xu a , Yixin Liu a , Kaiwen Zhou a a College of Physics Science and Technology, Guangxi University, Nanning 530004, China b International Centre for Materials Physics, Chinese Academy of Sciences, Shenyang 110016, China
Received 11 August 2006; received in revised form 23 November 2006; accepted 23 November 2006 Available online 10 January 2007
Abstract Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys were prepared by mechanical alloying and the hydrogen storage properties were investigated systematically. In Mg76 Ti12 Fe12 and Mg76 Ti12 Ni12 Ti12 alloys, the main binary alloy phase is Fe2 Ti and Mg2 Ni, respectively. There are same binary alloy phase structures included Fe2 Ti, Mg2 Ni and NiTi in Mg76 Ti12 Fe8 Ni4 and Mg76 Ti12 Fe4 Ni8 alloys. For Mg76 Ti12 Fe12−x Nix (x =0, 4, 8, 12) alloys, the hydrogen storage capacity is 2.88, 3.31, 3.12 and 2.24 wt%, respectively. The hysteresis between hydrogen absorption and desorption decreases gradually with increasing the amount of substitution Ni for Fe. Mg76 Ti12 Fe8 Ni4 shows the highest hydrogen absorption and desorption rate among Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys. Fe and Ni coexistence is favorable to improve hydrogen storage properties. For Mg76 Ti12 Fe8 Ni4 alloy, the amorphous degree increase with the milling time, and the amorphous degree increase is unfavorable to improve hydrogen storage capacity. 䉷 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. Keywords: Hydrogen storage alloy; Thermodynamic performances; Hydrogen storage properties
1. Introduction Mg and Mg rich alloys have attracted attention in recent years for high hydrogen capacity, abundance and low cost. However, high temperature for the hydrogen absorption and desorption reaction and poor kinetic characteristic hinder the applications of Mg-based alloys. In order to improve thermodynamic and electrochemical performances of Mg-based alloys many efforts have been made [1–7]. On the other hand, Ti-based alloys are also among the most promising materials for electrode materials, because of their relatively good kinetics. Based on the high hydrogen capacity for both Mg and Ti-based alloy, new compounds, Mg–Ti–Ni alloys, are developed [8–11]. In view of the excellent hydrogen storage properties of Mg–Ti–Ni alloys, in this paper we prepared Mg76 Ti12 Fe12−x Nix
∗ Corresponding author. College of Physics Science and Technology, Guangxi University, Nanning 530004, China. E-mail address: [email protected] (J. Guo).
(x = 0, 4, 8, 12) alloys by mechanical alloying and investigated the hydrogen storage properties systematically. 2. Experimental The starting materials for ball milling were Mg (200 mesh), Ni (250 mesh), Fe (300 mesh) and Ti (300 mesh), and the purities were all above 99.9%. Metal powders were mixed in the desired composition and mechanically milled in a planetary miller (QM-BP ball miller) at 300 rpm under argon atmosphere. These metal powders were placed in a stainless steel vials with stainless steel balls of 2, 4 and 8 mm diameter. The ball-topowder ratio was 20:1. The crystal structures of Mg76 Ti12 Fe12−x Nix (x=0, 4, 8, 12) alloys were determined by Rigaku D/max 2500 V diffractometer with Cu K radiation and graphite monochromator operated at 40 kV and 200 mA. The Materials Data Inc. software Jade 5.0 [12] and a Powder Diffraction File (PDF release 2002) were used to determine the phase relationships. The pressure-composition isotherms (PCI) of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) hydrogen storage alloys were measured by
0360-3199/$ - see front matter 䉷 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2006.11.024
J. Guo et al. / International Journal of Hydrogen Energy 32 (2007) 2412 – 2416
JY-1 automatic gas reactivity controller. The thermal properties of as-milled alloys were studied by differential scanning calorimeter (DSC) using NETZSCH STA 409 PC/PG instrument with a heating rate of 10 ◦ C/ min in a pure Ar flow.
Fig. 1 shows the XRD pattern of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys milled after 40 h. For Mg76 Ti12 Fe12 and Mg76 Ni12 Ti12 alloy, the main binary alloy phase is Fe2 Ti and Mg2 Ni, respectively. These binary alloy phase structures along with NiTi are also seen in Mg76 Ti12 Fe8 Ni4 and Mg76 Ti12 Fe4 Ni8 alloys. It can be seen from Fig. 1 that the intensities of Mg peaks weakened with alloying of additive Ni. In order to investigate the effect of milling time on hydrogen storage properties of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys, based on the hydrogen storage property testing (seen below), Mg76 Ti12 Fe8 Ni4 was chosen. The XRD patterns of Mg76 Ti12 Fe8 Ni4 alloy milled after 20, 40, 60 and 80 h are presented in Fig. 2. With the milling time the intensities of Mg peaks are weakened gradually and the diffraction profiles are broadened which means the amorphous degree increase. 3.2. Hydrogen storage properties 3.2.1. Hydrogen storage properties of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys At first the alloys were activated five cycles at 450 ◦ C, and then the pressure-composition isotherms for absorption/desorption of hydrogen on Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys were tested at 300 ◦ C. The PCI curves of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys milled after 40 h Mg Ti Fe Mg2Ni Fe2Ti
Ni NiTi
intensity
Mg76Fe4Ni8Ti12
Mg76Ni12Ti12
30
40
50 2θ, degree
60
70
40h
60h
80h
20
30
40
50 2θ degree
60
70
80
Fig. 2. XRD patterns of Mg76 Ti12 Fe8 Ni4 alloys milled after different times.
10
1 Mg76Ti12Fe12 Mg76Ti12Fe8Ni4 Mg76Ti12Fe4Ni8
0.1
Mg76Ti12Ni12
0
1
2 H , wt%
3
Fig. 3. The PCI curves of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys milled after 40 h at 300 ◦ C.
Mg76Fe8Ni4Ti12
20
Ni NiTi
20h
P, atm.
3.1. Crystal structures
Mg76Fe12Ti12
Mg Ti Fe Mg2Ni Fe2Ti
intensity
3. Results and discussion
2413
80
Fig. 1. XRD patterns of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys milled after 40 h.
are presented in Fig. 3. The PCI curve of Mg76 Ti12 Fe12 alloy contains one plateau and the second plateau appears with Ni added. From Fig. 3 the plateau pressures and hydrogen storage capacities of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys can be obtained and are listed in Table 1. The plateau pressures listed in Table 1 are defined as the mean of two points of inflexions in PCI curve. The Mg76 Ti12 Fe8 Ni4 and Mg76 Ti12 Fe4 Ni8 alloys exhibit much more hydrogen storage capacity than that of the other two alloys, and Mg76 Ti12 Fe8 Ni4 alloy has the maximum hydrogen storage capacity (H/M), the weight ratio of hydrogen to metal, of 3.31 wt%. In addition, the hydrogen absorption plateau pressure for Mg76 Ti12 Fe8 Ni4 and Mg76 Ti12 Fe4 Ni8 alloys are also decreased evidently. The resulting, large hydrogen storage capacity for Mg76 Ti12 Fe8 Ni4 and Mg76 Ti12 Fe4 Ni8 alloys, may be due to both Mg2 Ni and TiNi phases contribute
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J. Guo et al. / International Journal of Hydrogen Energy 32 (2007) 2412 – 2416
Table 1 The plateau pressures and hydrogen content of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys
↓ exo
6
Mg76Ti12Fe12
H-absorption plateau (atm.)
H-desorption plateau (atm.)
Hydrogen content (wt%)
Mg76 Ti12 Fe12 Mg76 Ti12 Fe8 Ni4 Mg76 Ti12 Fe4 Ni8 Mg76 Ti12 Ni12
2.95 1.87 1.92 2.29
1.60 1.27 1.41 1.77
2.88 3.31 3.12 2.24
Mg76Ti12Fe8Ni4
4 DSC, mW/mg
Alloy composition
Mg76Ti12Fe4Ni8 Mg76Ti12Ni12
2
0
a H-absorption
300
400
500
T, °C Fig. 5. DSC heating curves for Mg76 Ti12 Fe12−x Nix (x=0, 4, 8, 12) hydrides.
2 Mg76Ti12Fe12 Mg76Ti12Fe8Ni4 Mg76Ti12Fe4Ni8
1
20h 40h 60h 80h
10
Mg76Ti12Ni12
0 0
500
1000 1500 2000 2500 3000 3500 4000 Time, s
P,atm.
Hydrogen Content, wt%
200 3
1
b Mg76Ti12Ni12
H-desorption
0.1
Hydrogen Content,wt%
Mg76Ti12Fe8Ni4 Mg76Ti12Fe4Ni8
3
0
Mg76Ti12Fe12
1
2 H, wt%
3
Fig. 6. The PCI curves of Mg76 Ti12 Fe8 Ni4 alloys milled after 20, 40, 60, 80 h at 300 ◦ C.
2
1
0 0
500
1000
1500
2000 Time, s
2500
3000
3500
Fig. 4. Absorption–desorption kinetic curves of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys milled after 40 h at 300 ◦ C and 2 atm.
to the hydrogen storage capacity [11]. It is also observed from Table 1 that the hysteresis between hydrogen absorption and desorption decreases gradually with increasing the amount of substitution Ni for Fe. The hydrogen absorption and desorption kinetic curves of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys milled after 40 h at 300 ◦ C are plotted in Fig. 4. Mg76 Ti12 Fe8 Ni4 alloy
shows the highest hydrogen absorption and desorption rate, and Mg76 Ti12 Fe4 Ni8 alloy also has much higher hydrogen absorption and desorption rate than that of the other two alloys studied. The result reveals that TiNi phase contributes not only to hydrogen storage capacity but also to catalytic effect for hydrogen absorption and desorption kinetics. Fig. 5 shows DSC heating curves for Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) hydrides. It can be seen that the hydrogen desorption temperatures of Mg76 Ti12 Fe8 Ni4 and Mg76 Ti12 Fe4 Ni8 alloys are 270 and 330 ◦ C, respectively, which lower than that for Mg76 Fe12 Ti12 and Mg76 Ti12 Ni12 alloys. The enthalpies of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) hydride decomposition are obtained from Fig. 5, and the values are 2145, 1712, 1887 and 2444 kJ/mol H2 , respectively. It is indicated that Mg76 Ti12 Fe8 Ni4 alloy has best kinetic property of hydrogen desorption among Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys. For Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys, Fe and Ni coexistence may reduce the temperature and enthalpies of
J. Guo et al. / International Journal of Hydrogen Energy 32 (2007) 2412 – 2416
hysteresis appears after 80 h milling. For Mg76 Ti12 Fe8 Ni4 alloy too short (20 h) or too long (80 h) milling time would lead to hysteresis increasing. The hydrogen absorption and desorption kinetic curves of Mg76 Ti12 Fe8 Ni4 alloy milled after 20, 40, 60, 80 h at 300 ◦ C are shown in Fig. 7. The alloy milled for 40 h displays the highest hydrogen absorption rate shown in Fig. 7(a), while the hydrogen absorption rates of the alloy milled at 20 and 80 h are very slow by comparison. In spite of the different hydrogen absorption rates, the desorption rates for Mg76 Ti12 Fe8 Ni4 alloy milled different times are almost the same as shown in Fig. 7(b). Based on the arguments above, it can be concluded that the Mg76 Ti12 Fe8 Ni4 alloy milled after 40 h possessed good hydrogen storage properties.
4
H, wt%
3
2
20h 40h 60h 80h
1
2415
4. Conclusions
0 0
1000
2000
3000
4000
5000
t, s
4
H, wt%
3
2
20h 40h 60h 80h
1
0 0
500
1000
1500 t, s
2000
2500
1. In Mg76 Ti12 Fe12 and Mg76 Ni12 Ti12 alloy, the main binary alloy phase is Fe2 Ti and Mg2 Ni, respectively. The binary alloy phase structures, namely Fe2 Ti, Mg2 Ni and NiTi are found in Mg76 Ti12 Fe8 Ni4 and Mg76 Ti12 Fe4 Ni8 alloy. 2. For Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys, the hydrogen storage capacity is 2.88, 3.31, 3.12 and 2.24 wt%, respectively. The hysteresis between hydrogen absorption and desorption decreases gradually with increasing the amount of substitution Ni for Fe. Mg76 Ti12 Fe8 Ni4 alloy shows the highest hydrogen absorption and desorption rate among Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys. Fe and Ni coexistence is favorable to improve hydrogen storage properties. 3. For Mg76 Ti12 Fe8 Ni4 alloy, the amorphous degree increase with the milling time, and the amorphous degree increase is unfavorable to improve hydrogen storage capacity. Acknowledgments
Fig. 7. Absorption–desorption kinetic curves of Mg76 Ti12 Fe8 Ni4 alloys milled after 20, 40, 60, 80 h at 300 ◦ C and 2 atm.
Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) hydride decomposition, which is favorable to improve hydrogen storage properties. 3.2.2. Hydrogen storage properties of Mg76 Ti12 Fe8 Ni4 alloy In view of good hydrogen storage properties of Mg76 Fe8 Ni4 Ti12 alloy, the effect of milling time on hydrogen storage property is presented in this section. Fig. 6 shows the PCI curves of Mg76 Ti12 Fe8 Ni4 alloy milled after 20, 40, 60, 80 h at 300 ◦ C. It can be observed that the hydrogen storage capacity of Mg76 Ti12 Fe8 Ni4 alloy decreases with the milling duration. Fig. 2 reveals that the amorphous degree of Mg76 Fe8 Ni4 Ti12 alloy increases with the times of milling. The results indicate that an increase in the degree of amorphicity is unfavorable to improve hydrogen storage capacity for Mg76 Ti12 Fe8 Ni4 alloy. Although the alloy milled after 20 h has the maximum hydrogen storage capacity, the hysteresis between hydrogen absorption and desorption is also the maximum. The second large
This work was supported by the National Nature Science Foundation of China (Grant no. 50561002), the Key Project of China Ministry of Education (Grant no. 03104) and Guangxi University Key Program for Science and Technology Research (Grant no. 2004ZD04). References [1] Orimo S, Fujii H. Materials science of Mg–Ni-based new hydrides. Appl Phys A 2001;72:167–86. [2] Orimo S, Züttel A, Ikeda K, Saruki S, Fukunaga T, Fujii H. et al. Hydriding properties of the MgNi-based systems. J Alloys Compds 1999;293–295:437–42. [3] Gasiorowski A, Iwasieczko W, Skoryna D, Drulis H, Jurczyk M. Hydriding properties of nanocrystalline Mg2−x Mx Ni alloys synthesized by mechanical alloying (M = Mn, Al). J Alloys Compds 2004;364: 283–8. [4] Spassov T, Rangelova V, Solsona P, Baro MD, Zander D, Koster U. Hydriding/dehydriding properties of nanocrystalline Mg87 Ni3 Al3 M7 (M = Ti, Mn, Ce, La) alloys prepared by ball milling. J Alloys Compds 2005;398:139–44.
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[5] Doppiu S, Solsona P, Spassov T, Barkhordarian G, Dornheim M, Klassen T. et al. Thermodynamic properties and absorption–desorption kinetics of Mg87 Ni10 Al3 alloy synthesised by reactive ball milling under H2 atmosphere. J Alloys Compds 2005;404–406:27–30. [6] Delchev P, Solsona P, Drenchev B, Drenchev N, Spassov T, Baro MD. J Alloys Compds 2005;388:98. [7] Spassov T, Lyubenova L, Koster U, Baro MD. Mater Sci Eng A 2004;375–377:794. [8] Ruggeri S, Roue L, Huo J, Schulz R, Aymard L, Tarascon J-M. Properties of mechanically alloyed Mg–Ni–Ti ternary hydrogen storage alloys for Ni–MH batteries. J Power Sources 2002;112:547–56.
[9] Lomness JK, Hampton MD, Giannuzzi LA. Hydrogen uptake characteristics of mechanically alloyed mixtures of Ti–Mg–Ni. Int J Hydrogen Energy 2002;27:915–20. [10] Hong T-W, Kim Y-J. Synthesis and hydrogenation behavior of Mg–Ti–Ni–H systems by hydrogen-induced mechanical alloying. J Alloys Compds 2002;330–332:584–9. [11] Han SS, Goo NH, Lee KS. Effects of sintering on composite metal hydride alloy of Mg2 Ni and TiNi synthesized by mechanical alloying. J Alloys Compds 2003;360:243–9. [12] Materials Data JADE Release 5, XRD Pattern Processing, Materials Data Inc., 1999.
Hydrogen storage properties of Mg76Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys by mechanical alloying Jin Guo a,b,∗ , Kun Yang a , Liqin Xu a , Yixin Liu a , Kaiwen Zhou a a College of Physics Science and Technology, Guangxi University, Nanning 530004, China b International Centre for Materials Physics, Chinese Academy of Sciences, Shenyang 110016, China
Received 11 August 2006; received in revised form 23 November 2006; accepted 23 November 2006 Available online 10 January 2007
Abstract Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys were prepared by mechanical alloying and the hydrogen storage properties were investigated systematically. In Mg76 Ti12 Fe12 and Mg76 Ti12 Ni12 Ti12 alloys, the main binary alloy phase is Fe2 Ti and Mg2 Ni, respectively. There are same binary alloy phase structures included Fe2 Ti, Mg2 Ni and NiTi in Mg76 Ti12 Fe8 Ni4 and Mg76 Ti12 Fe4 Ni8 alloys. For Mg76 Ti12 Fe12−x Nix (x =0, 4, 8, 12) alloys, the hydrogen storage capacity is 2.88, 3.31, 3.12 and 2.24 wt%, respectively. The hysteresis between hydrogen absorption and desorption decreases gradually with increasing the amount of substitution Ni for Fe. Mg76 Ti12 Fe8 Ni4 shows the highest hydrogen absorption and desorption rate among Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys. Fe and Ni coexistence is favorable to improve hydrogen storage properties. For Mg76 Ti12 Fe8 Ni4 alloy, the amorphous degree increase with the milling time, and the amorphous degree increase is unfavorable to improve hydrogen storage capacity. 䉷 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. Keywords: Hydrogen storage alloy; Thermodynamic performances; Hydrogen storage properties
1. Introduction Mg and Mg rich alloys have attracted attention in recent years for high hydrogen capacity, abundance and low cost. However, high temperature for the hydrogen absorption and desorption reaction and poor kinetic characteristic hinder the applications of Mg-based alloys. In order to improve thermodynamic and electrochemical performances of Mg-based alloys many efforts have been made [1–7]. On the other hand, Ti-based alloys are also among the most promising materials for electrode materials, because of their relatively good kinetics. Based on the high hydrogen capacity for both Mg and Ti-based alloy, new compounds, Mg–Ti–Ni alloys, are developed [8–11]. In view of the excellent hydrogen storage properties of Mg–Ti–Ni alloys, in this paper we prepared Mg76 Ti12 Fe12−x Nix
∗ Corresponding author. College of Physics Science and Technology, Guangxi University, Nanning 530004, China. E-mail address: [email protected] (J. Guo).
(x = 0, 4, 8, 12) alloys by mechanical alloying and investigated the hydrogen storage properties systematically. 2. Experimental The starting materials for ball milling were Mg (200 mesh), Ni (250 mesh), Fe (300 mesh) and Ti (300 mesh), and the purities were all above 99.9%. Metal powders were mixed in the desired composition and mechanically milled in a planetary miller (QM-BP ball miller) at 300 rpm under argon atmosphere. These metal powders were placed in a stainless steel vials with stainless steel balls of 2, 4 and 8 mm diameter. The ball-topowder ratio was 20:1. The crystal structures of Mg76 Ti12 Fe12−x Nix (x=0, 4, 8, 12) alloys were determined by Rigaku D/max 2500 V diffractometer with Cu K radiation and graphite monochromator operated at 40 kV and 200 mA. The Materials Data Inc. software Jade 5.0 [12] and a Powder Diffraction File (PDF release 2002) were used to determine the phase relationships. The pressure-composition isotherms (PCI) of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) hydrogen storage alloys were measured by
0360-3199/$ - see front matter 䉷 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2006.11.024
J. Guo et al. / International Journal of Hydrogen Energy 32 (2007) 2412 – 2416
JY-1 automatic gas reactivity controller. The thermal properties of as-milled alloys were studied by differential scanning calorimeter (DSC) using NETZSCH STA 409 PC/PG instrument with a heating rate of 10 ◦ C/ min in a pure Ar flow.
Fig. 1 shows the XRD pattern of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys milled after 40 h. For Mg76 Ti12 Fe12 and Mg76 Ni12 Ti12 alloy, the main binary alloy phase is Fe2 Ti and Mg2 Ni, respectively. These binary alloy phase structures along with NiTi are also seen in Mg76 Ti12 Fe8 Ni4 and Mg76 Ti12 Fe4 Ni8 alloys. It can be seen from Fig. 1 that the intensities of Mg peaks weakened with alloying of additive Ni. In order to investigate the effect of milling time on hydrogen storage properties of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys, based on the hydrogen storage property testing (seen below), Mg76 Ti12 Fe8 Ni4 was chosen. The XRD patterns of Mg76 Ti12 Fe8 Ni4 alloy milled after 20, 40, 60 and 80 h are presented in Fig. 2. With the milling time the intensities of Mg peaks are weakened gradually and the diffraction profiles are broadened which means the amorphous degree increase. 3.2. Hydrogen storage properties 3.2.1. Hydrogen storage properties of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys At first the alloys were activated five cycles at 450 ◦ C, and then the pressure-composition isotherms for absorption/desorption of hydrogen on Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys were tested at 300 ◦ C. The PCI curves of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys milled after 40 h Mg Ti Fe Mg2Ni Fe2Ti
Ni NiTi
intensity
Mg76Fe4Ni8Ti12
Mg76Ni12Ti12
30
40
50 2θ, degree
60
70
40h
60h
80h
20
30
40
50 2θ degree
60
70
80
Fig. 2. XRD patterns of Mg76 Ti12 Fe8 Ni4 alloys milled after different times.
10
1 Mg76Ti12Fe12 Mg76Ti12Fe8Ni4 Mg76Ti12Fe4Ni8
0.1
Mg76Ti12Ni12
0
1
2 H , wt%
3
Fig. 3. The PCI curves of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys milled after 40 h at 300 ◦ C.
Mg76Fe8Ni4Ti12
20
Ni NiTi
20h
P, atm.
3.1. Crystal structures
Mg76Fe12Ti12
Mg Ti Fe Mg2Ni Fe2Ti
intensity
3. Results and discussion
2413
80
Fig. 1. XRD patterns of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys milled after 40 h.
are presented in Fig. 3. The PCI curve of Mg76 Ti12 Fe12 alloy contains one plateau and the second plateau appears with Ni added. From Fig. 3 the plateau pressures and hydrogen storage capacities of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys can be obtained and are listed in Table 1. The plateau pressures listed in Table 1 are defined as the mean of two points of inflexions in PCI curve. The Mg76 Ti12 Fe8 Ni4 and Mg76 Ti12 Fe4 Ni8 alloys exhibit much more hydrogen storage capacity than that of the other two alloys, and Mg76 Ti12 Fe8 Ni4 alloy has the maximum hydrogen storage capacity (H/M), the weight ratio of hydrogen to metal, of 3.31 wt%. In addition, the hydrogen absorption plateau pressure for Mg76 Ti12 Fe8 Ni4 and Mg76 Ti12 Fe4 Ni8 alloys are also decreased evidently. The resulting, large hydrogen storage capacity for Mg76 Ti12 Fe8 Ni4 and Mg76 Ti12 Fe4 Ni8 alloys, may be due to both Mg2 Ni and TiNi phases contribute
2414
J. Guo et al. / International Journal of Hydrogen Energy 32 (2007) 2412 – 2416
Table 1 The plateau pressures and hydrogen content of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys
↓ exo
6
Mg76Ti12Fe12
H-absorption plateau (atm.)
H-desorption plateau (atm.)
Hydrogen content (wt%)
Mg76 Ti12 Fe12 Mg76 Ti12 Fe8 Ni4 Mg76 Ti12 Fe4 Ni8 Mg76 Ti12 Ni12
2.95 1.87 1.92 2.29
1.60 1.27 1.41 1.77
2.88 3.31 3.12 2.24
Mg76Ti12Fe8Ni4
4 DSC, mW/mg
Alloy composition
Mg76Ti12Fe4Ni8 Mg76Ti12Ni12
2
0
a H-absorption
300
400
500
T, °C Fig. 5. DSC heating curves for Mg76 Ti12 Fe12−x Nix (x=0, 4, 8, 12) hydrides.
2 Mg76Ti12Fe12 Mg76Ti12Fe8Ni4 Mg76Ti12Fe4Ni8
1
20h 40h 60h 80h
10
Mg76Ti12Ni12
0 0
500
1000 1500 2000 2500 3000 3500 4000 Time, s
P,atm.
Hydrogen Content, wt%
200 3
1
b Mg76Ti12Ni12
H-desorption
0.1
Hydrogen Content,wt%
Mg76Ti12Fe8Ni4 Mg76Ti12Fe4Ni8
3
0
Mg76Ti12Fe12
1
2 H, wt%
3
Fig. 6. The PCI curves of Mg76 Ti12 Fe8 Ni4 alloys milled after 20, 40, 60, 80 h at 300 ◦ C.
2
1
0 0
500
1000
1500
2000 Time, s
2500
3000
3500
Fig. 4. Absorption–desorption kinetic curves of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys milled after 40 h at 300 ◦ C and 2 atm.
to the hydrogen storage capacity [11]. It is also observed from Table 1 that the hysteresis between hydrogen absorption and desorption decreases gradually with increasing the amount of substitution Ni for Fe. The hydrogen absorption and desorption kinetic curves of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys milled after 40 h at 300 ◦ C are plotted in Fig. 4. Mg76 Ti12 Fe8 Ni4 alloy
shows the highest hydrogen absorption and desorption rate, and Mg76 Ti12 Fe4 Ni8 alloy also has much higher hydrogen absorption and desorption rate than that of the other two alloys studied. The result reveals that TiNi phase contributes not only to hydrogen storage capacity but also to catalytic effect for hydrogen absorption and desorption kinetics. Fig. 5 shows DSC heating curves for Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) hydrides. It can be seen that the hydrogen desorption temperatures of Mg76 Ti12 Fe8 Ni4 and Mg76 Ti12 Fe4 Ni8 alloys are 270 and 330 ◦ C, respectively, which lower than that for Mg76 Fe12 Ti12 and Mg76 Ti12 Ni12 alloys. The enthalpies of Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) hydride decomposition are obtained from Fig. 5, and the values are 2145, 1712, 1887 and 2444 kJ/mol H2 , respectively. It is indicated that Mg76 Ti12 Fe8 Ni4 alloy has best kinetic property of hydrogen desorption among Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys. For Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys, Fe and Ni coexistence may reduce the temperature and enthalpies of
J. Guo et al. / International Journal of Hydrogen Energy 32 (2007) 2412 – 2416
hysteresis appears after 80 h milling. For Mg76 Ti12 Fe8 Ni4 alloy too short (20 h) or too long (80 h) milling time would lead to hysteresis increasing. The hydrogen absorption and desorption kinetic curves of Mg76 Ti12 Fe8 Ni4 alloy milled after 20, 40, 60, 80 h at 300 ◦ C are shown in Fig. 7. The alloy milled for 40 h displays the highest hydrogen absorption rate shown in Fig. 7(a), while the hydrogen absorption rates of the alloy milled at 20 and 80 h are very slow by comparison. In spite of the different hydrogen absorption rates, the desorption rates for Mg76 Ti12 Fe8 Ni4 alloy milled different times are almost the same as shown in Fig. 7(b). Based on the arguments above, it can be concluded that the Mg76 Ti12 Fe8 Ni4 alloy milled after 40 h possessed good hydrogen storage properties.
4
H, wt%
3
2
20h 40h 60h 80h
1
2415
4. Conclusions
0 0
1000
2000
3000
4000
5000
t, s
4
H, wt%
3
2
20h 40h 60h 80h
1
0 0
500
1000
1500 t, s
2000
2500
1. In Mg76 Ti12 Fe12 and Mg76 Ni12 Ti12 alloy, the main binary alloy phase is Fe2 Ti and Mg2 Ni, respectively. The binary alloy phase structures, namely Fe2 Ti, Mg2 Ni and NiTi are found in Mg76 Ti12 Fe8 Ni4 and Mg76 Ti12 Fe4 Ni8 alloy. 2. For Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys, the hydrogen storage capacity is 2.88, 3.31, 3.12 and 2.24 wt%, respectively. The hysteresis between hydrogen absorption and desorption decreases gradually with increasing the amount of substitution Ni for Fe. Mg76 Ti12 Fe8 Ni4 alloy shows the highest hydrogen absorption and desorption rate among Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) alloys. Fe and Ni coexistence is favorable to improve hydrogen storage properties. 3. For Mg76 Ti12 Fe8 Ni4 alloy, the amorphous degree increase with the milling time, and the amorphous degree increase is unfavorable to improve hydrogen storage capacity. Acknowledgments
Fig. 7. Absorption–desorption kinetic curves of Mg76 Ti12 Fe8 Ni4 alloys milled after 20, 40, 60, 80 h at 300 ◦ C and 2 atm.
Mg76 Ti12 Fe12−x Nix (x = 0, 4, 8, 12) hydride decomposition, which is favorable to improve hydrogen storage properties. 3.2.2. Hydrogen storage properties of Mg76 Ti12 Fe8 Ni4 alloy In view of good hydrogen storage properties of Mg76 Fe8 Ni4 Ti12 alloy, the effect of milling time on hydrogen storage property is presented in this section. Fig. 6 shows the PCI curves of Mg76 Ti12 Fe8 Ni4 alloy milled after 20, 40, 60, 80 h at 300 ◦ C. It can be observed that the hydrogen storage capacity of Mg76 Ti12 Fe8 Ni4 alloy decreases with the milling duration. Fig. 2 reveals that the amorphous degree of Mg76 Fe8 Ni4 Ti12 alloy increases with the times of milling. The results indicate that an increase in the degree of amorphicity is unfavorable to improve hydrogen storage capacity for Mg76 Ti12 Fe8 Ni4 alloy. Although the alloy milled after 20 h has the maximum hydrogen storage capacity, the hysteresis between hydrogen absorption and desorption is also the maximum. The second large
This work was supported by the National Nature Science Foundation of China (Grant no. 50561002), the Key Project of China Ministry of Education (Grant no. 03104) and Guangxi University Key Program for Science and Technology Research (Grant no. 2004ZD04). References [1] Orimo S, Fujii H. Materials science of Mg–Ni-based new hydrides. Appl Phys A 2001;72:167–86. [2] Orimo S, Züttel A, Ikeda K, Saruki S, Fukunaga T, Fujii H. et al. Hydriding properties of the MgNi-based systems. J Alloys Compds 1999;293–295:437–42. [3] Gasiorowski A, Iwasieczko W, Skoryna D, Drulis H, Jurczyk M. Hydriding properties of nanocrystalline Mg2−x Mx Ni alloys synthesized by mechanical alloying (M = Mn, Al). J Alloys Compds 2004;364: 283–8. [4] Spassov T, Rangelova V, Solsona P, Baro MD, Zander D, Koster U. Hydriding/dehydriding properties of nanocrystalline Mg87 Ni3 Al3 M7 (M = Ti, Mn, Ce, La) alloys prepared by ball milling. J Alloys Compds 2005;398:139–44.
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