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Effect of Al on hydrogen storage properties of V30Ti35Cr25Fe10 alloy
Journal of Alloys and Compounds 426 (2006) 253–255
Effect of Al on hydrogen storage properties of V30Ti35Cr25Fe10 alloy Yigang Yan, Yungui Chen ∗ , Hao Liang, Chaoling Wu, Mingda Tao, Tu Mingjing School of Materials Science and Engineering, Sichuan University, Chengdu 610064, PR China Received 8 November 2005; accepted 12 December 2005 Available online 17 April 2006
Abstract The effect of 0.6–5 at.% Al on the structure and hydrogen storage properties of V30 Ti35 Cr25 Fe10 hydrogen storage alloy was investigated by XRD and PCT measurement. It was found by XRD analysis and Reitveld method that all Al-containing alloys are single phases with BCC structures, and with the addition of Al content from 0.6 to 5 at.%, the lattice parameters of the alloys become larger, the hydrogen absorption and desorption capacities decrease, the desorption plateau pressures increase, but no evident effect is found when the content of Al is no more than l at.%. The formation of ␥ phase is inhibited by the addition of Al, and nearly no ␥ phase is formed when Al content reaches 5 at.%. © 2006 Elsevier B.V. All rights reserved. Keywords: Hydrogen storage alloy; BCC alloy; Al
1. Introduction V-based alloys with BCC structures have been regarded as promising candidates used in hydrogen storage tanks for fuel cells, since they have high capacities and can desorb most of the absorbed hydrogen at room temperature [1,2]. V–Ti–Cr alloys were reported to desorb about 2.4–2.6 wt.% hydrogen [3,4]. However, high price of pure vanadium limits the application of V-based alloys. Using ferrovanadium alloys as a cheap vanadium source is a good choice to prepare low-cost V-based alloys, but it will bring impurities such as Al, Si and C into the BCC alloys. The effects of Al on V0.9 Ti0.1 alloy have ever been researched, and they decrease the hydrogen storage capacity and increase the plateau pressure dramatically even at a low Al content [5]. In our previous work, a V30 Ti35 Cr25 Fe10 alloy shows a high capacity of 3.6 wt.% and an efficient hydrogen capacity of 2.0 wt.% at 298 K [6]. In this paper, the effect of Al on the hydrogen storage properties and microstructure of the V30 Ti35 Cr25 Fe10 alloy was investigated. 2. Experimental The purities of the raw materials vanadium, titanium, chromium, iron and aluminum in this experiment were 99.9, 99.6, 99.9, 99.8 and 99.5 wt.%, respectively. The addition of Al changes from 0.6 to 5 at.% in
∗
Corresponding author. Tel.: +86 28 8540 7335; fax: +86 28 8540 7335. E-mail address: [email protected] (Y. Chen).
0925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2005.12.122
(V30 Ti35 Cr25 Fe10 )100 − x Alx alloys. The samples were arc-melted into buttonshaped ingots under argon atmosphere. To ensure the compositional homogeneity, the samples were re-melted four times. Then they were crushed into 100-mesh powders under air atmosphere for the pressure–composition– temperature (PCT) tests. PCT curves were measured using a Sieverts-type apparatus. The initial activation treatments were as follows: each sample was put into a stainless steel reactor and vacuumized at 313 K for 30 min, and then at 673 K for 30 min. Later, hydrogen with a pressure of 4 MPa was introduced into the reactor and kept for 30 min, and then the reactor was cooled down to room-temperature slowly. Finally, the samples were vacuumized for 2 h at 673 K to ensure that hydrogen in the alloys was dehydrogenized completely for the PCT measurement. The crystal structures of the alloy powders were determined by X-ray diffraction (XRD) analysis using Cu K␣ radiation and the lattice parameters were calculated by Reitveld method [7].
3. Results and discussion 3.1. Phase and structure XRD curves (Fig. 1) indicate that all the alloys are single phases with BCC structures, which implies that the addition of Al does not change the lattice structure type of V30 Ti35 Cr25 Fe10 alloy. To obtain the lattice parameters of the alloys accurately, the structures of the alloys were refined and the lattice parameters were calculated by Reitveld method. Fig. 2 shows the relationship between Al content and the lattice parameters. When x ≤ 1.0 in (V30 Ti35 Cr25 Fe10 )100 − x Alx alloys, the lattice parameters increase little. However, when x ≥ 2.5, the lattice parameters increase largely.
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Fig. 3. Desorption PCT curves at 298 K of (V30 Ti35 Cr25 Fe10 )100 − x Alx (x = 0–5) alloys.
Fig. 1. XRD patterns of (V30 Ti35 Cr25 Fe10 )100 − x Alx (x = 0–5) alloys.
Fig. 2. Lattice parameters by Reitveld method of (V30 Ti35 Cr25 Fe10 )100 − x Alx .
3.2. Hydrogen storage properties The desorption PCT curves of (V30 Ti35 Cr25 Fe10 )100 − x Alx (x = 0–5 at.%) alloys at 298 K and in hydrogen pressure from 4 to 0.01 MPa were shown in Fig. 3, and the relationship between Al content and hydrogen storage properties is summarized in Table 1.Both the absorption and desorption capacities of the alloys decline and the plateau pressures rise with the increase
of Al content. However, when x ≤ 1.0, the Al-containing alloys show their absorption and desorption capacities and plateau properties nearly as the same as the Al-free alloy. When x ≥ 1.0, the absorption and desorption capacities of the Al-containing alloys decrease sharply and the plateau pressures increase obviously. The alloy with 5 at.% Al shows no plateau region and can only absorb 1.71 wt.% H and desorb 0.23 wt.% H. A single phase of a BCC structure is found in the alloy with 5 at.% Al after absorption (Fig. 4), which implies that di-hydride cannot be formed in this alloy. Thus its absorption and desorption capacities are very low. The Al-free alloy shows both a FCC main phase and a BCC second phase after absorption. Another phenomenon in Table 1 is that the hydrogen capacities remained in the alloys after desorption decrease little with the increase of Al content, while the absorption and efficient desorption capacities decrease rapidly. It is well known that V-based alloys form two kinds of hydrides in the absorption process, which are called  phase (mono-hydride) and ␥ phase (di-hydride), respectively. The mono-hydride, which is too stable to be decomposed, has a plateau pressure as low as 0.1–1 Pa at room temperature. While the di-hydride has a comparatively high plateau pressure and can desorb hydrogen under moderate conditions. In our experiments, the hydrides desorb hydrogen at 298 K above 0.01 MPa. Under such conditions, di-hydride can desorb hydrogen almost completely, while mono-hydride nearly cannot be decomposed. Hence, it could be deduced that the remained hydrogen capacities in Table 1
Table 1 Relationship between Al content and hydrogen storage properties Al content (at.%)
Absorption capacity (wt.%)
Desorption capacity (wt.%)
Capacity remained (wt.%)
Plateau pressure (MPa)
0 0.6 1 2.5 5
3.6 3.58 3.55 2.98 1.71
2.0 1.99 1.96 1.43 0.23
1.6 1.59 1.59 1.55 1.48
0.071 0.073 0.085 0.21 –
Y. Yan et al. / Journal of Alloys and Compounds 426 (2006) 253–255
255
means that the formation of ␥ phase (di-hydride) is inhibited by the addition of Al, and no ␥ phase can be formed in the alloy containing 5 at.% Al. It might be explained by different effect of Al on the hole sizes of octahedral sites and tetrahedral sites. In V-based alloys, hydrogen in ␥ phase occupies the center of the octahedral sites and ␥ phase occupies the center of the tetrahedral sites. And the sizes of the former are much bigger than that of the latter. Hence, the effect of Al on the sizes of the octahedral sites is less than that of the tetrahedral sites. The sizes of the efficient hole in the tetrahedral sites decrease, which causes the decrease of the absorption and desorption capacities and the increase of plateau pressures of ␥ phase then. 4. Conclusion The effects of 0.6–5 at.% Al on the structure and hydrogen storage properties of V30 Ti35 Cr25 Fe10 alloy were investigated and the main conclusions were as follows: Fig. 4. XRD patterns of (V30 Ti35 Cr25 Fe10 )100 − x Alx (x = 0, 5) alloys after absorption.
represent the hydrogen capacities of mono-hydrides. It can be seen that the effect of Al on di-hydride of V30 Ti35 Cr25 Fe10 alloy is larger than that on mono-hydride. Al mostly deteriorates the absorption and desorption properties of di-hydride, which is the main reason of deterioration of hydrogen absorption and desorption properties of Al-containing alloys. 3.3. Discussion Generally, for BCC alloys, when the lattice parameters increase, the hydrogen absorption capacities increase, and the plateau pressures decrease. For example, in V–Ti–Cr system, when Ti content increases or Cr content decreases, the lattice parameters of V–Ti–Cr alloys increase, then the hydrogen storage capacities are improved. However, in this paper, an opposite rule was found. For BCC structure alloys (V30 Ti35 Cr25 Fe10 )100 − x Alx (x = 0–5), the hydrogen absorption capacities decrease and the plateau pressures increase when the lattice parameters rise with the increase of Al content. This phenomenon might be caused by the large differences between the atomic characters of Al and the transitional elements, V, Ti, Cr, and Fe. Thus, the effect of Al on the lattice structures and hydrogen storage properties of V-based BCC alloys is different from that of transitional elements. Similar phenomenon is found in Ti–Fe system, where the effects of Al partly substituting Fe are very different from those of Ni and Co on the hydrogen storage properties of TiFe [8]. In this paper, we find that H capacity in ␥ phase decreases rapidly with the increase of Al content, which
(1) The Al-containing alloys are single phases with BCC structures. The lattice parameters of the alloys become larger with the increase of Al content. (2) The hydrogen absorption and desorption capacities decrease and the plateau pressures increase with the addition of Al, but no evident effect is found when the content of Al is no more than 1 at.%. (3) The capacity of  phase (mono-hydride) decrease little but that of ␥ phase (di-hydride) decrease rapidly with the increase of Al content. The formation of ␥ phase is inhibited by the addition of Al, and nearly no ␥ phase is formed when Al content reaches 5 at.%. Acknowledgement This work is supported by the Science and Technology Bureau of Panzhihua City, Sichuan Province, China. References [1] E. Akiba, H. Iba, Intermetallics 6 (1998) 461. [2] T. Kuriiwa, T. Tamura, T. Amemiya, T. Fuda, A. Kamegawa, H. Takamura, M. Okada, J. Alloys Compd. 293–295 (1999) 433–436. [3] M. Okada, T. Kuriiwa, A. Kamegawa, et al., Mater. Sci. Eng. A329–A331 (2002) 305–312. [4] T. Tamura, T. Kazumi, A. Kamegawa, J. Alloys Compd. 356–357 (2003) 505–509. [5] A. Kagawa, E. Ono, T. Kusakabe, Y. Sakamoto, J. Less-Common Met. 172–174 (1991) 64–70. [6] Y. Yigang, C. Yungui, L. Hao, L. Jie, W. Chaoling, Proceedings of the Eighth Asian Hydrogen Energy Conference, May 20–27, Beijing, 2005, pp. 179–186. [7] F. Izumi, in: R.A. Young (Ed.), The Rietveld Method, International Union of Crystallography, Oxford University Press, 1993, Chapter 13. [8] S.-M. Lee, T.-P. Perng, J. Alloys Compd. 291 (1999) 254–261.
Effect of Al on hydrogen storage properties of V30Ti35Cr25Fe10 alloy Yigang Yan, Yungui Chen ∗ , Hao Liang, Chaoling Wu, Mingda Tao, Tu Mingjing School of Materials Science and Engineering, Sichuan University, Chengdu 610064, PR China Received 8 November 2005; accepted 12 December 2005 Available online 17 April 2006
Abstract The effect of 0.6–5 at.% Al on the structure and hydrogen storage properties of V30 Ti35 Cr25 Fe10 hydrogen storage alloy was investigated by XRD and PCT measurement. It was found by XRD analysis and Reitveld method that all Al-containing alloys are single phases with BCC structures, and with the addition of Al content from 0.6 to 5 at.%, the lattice parameters of the alloys become larger, the hydrogen absorption and desorption capacities decrease, the desorption plateau pressures increase, but no evident effect is found when the content of Al is no more than l at.%. The formation of ␥ phase is inhibited by the addition of Al, and nearly no ␥ phase is formed when Al content reaches 5 at.%. © 2006 Elsevier B.V. All rights reserved. Keywords: Hydrogen storage alloy; BCC alloy; Al
1. Introduction V-based alloys with BCC structures have been regarded as promising candidates used in hydrogen storage tanks for fuel cells, since they have high capacities and can desorb most of the absorbed hydrogen at room temperature [1,2]. V–Ti–Cr alloys were reported to desorb about 2.4–2.6 wt.% hydrogen [3,4]. However, high price of pure vanadium limits the application of V-based alloys. Using ferrovanadium alloys as a cheap vanadium source is a good choice to prepare low-cost V-based alloys, but it will bring impurities such as Al, Si and C into the BCC alloys. The effects of Al on V0.9 Ti0.1 alloy have ever been researched, and they decrease the hydrogen storage capacity and increase the plateau pressure dramatically even at a low Al content [5]. In our previous work, a V30 Ti35 Cr25 Fe10 alloy shows a high capacity of 3.6 wt.% and an efficient hydrogen capacity of 2.0 wt.% at 298 K [6]. In this paper, the effect of Al on the hydrogen storage properties and microstructure of the V30 Ti35 Cr25 Fe10 alloy was investigated. 2. Experimental The purities of the raw materials vanadium, titanium, chromium, iron and aluminum in this experiment were 99.9, 99.6, 99.9, 99.8 and 99.5 wt.%, respectively. The addition of Al changes from 0.6 to 5 at.% in
∗
Corresponding author. Tel.: +86 28 8540 7335; fax: +86 28 8540 7335. E-mail address: [email protected] (Y. Chen).
0925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2005.12.122
(V30 Ti35 Cr25 Fe10 )100 − x Alx alloys. The samples were arc-melted into buttonshaped ingots under argon atmosphere. To ensure the compositional homogeneity, the samples were re-melted four times. Then they were crushed into 100-mesh powders under air atmosphere for the pressure–composition– temperature (PCT) tests. PCT curves were measured using a Sieverts-type apparatus. The initial activation treatments were as follows: each sample was put into a stainless steel reactor and vacuumized at 313 K for 30 min, and then at 673 K for 30 min. Later, hydrogen with a pressure of 4 MPa was introduced into the reactor and kept for 30 min, and then the reactor was cooled down to room-temperature slowly. Finally, the samples were vacuumized for 2 h at 673 K to ensure that hydrogen in the alloys was dehydrogenized completely for the PCT measurement. The crystal structures of the alloy powders were determined by X-ray diffraction (XRD) analysis using Cu K␣ radiation and the lattice parameters were calculated by Reitveld method [7].
3. Results and discussion 3.1. Phase and structure XRD curves (Fig. 1) indicate that all the alloys are single phases with BCC structures, which implies that the addition of Al does not change the lattice structure type of V30 Ti35 Cr25 Fe10 alloy. To obtain the lattice parameters of the alloys accurately, the structures of the alloys were refined and the lattice parameters were calculated by Reitveld method. Fig. 2 shows the relationship between Al content and the lattice parameters. When x ≤ 1.0 in (V30 Ti35 Cr25 Fe10 )100 − x Alx alloys, the lattice parameters increase little. However, when x ≥ 2.5, the lattice parameters increase largely.
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Fig. 3. Desorption PCT curves at 298 K of (V30 Ti35 Cr25 Fe10 )100 − x Alx (x = 0–5) alloys.
Fig. 1. XRD patterns of (V30 Ti35 Cr25 Fe10 )100 − x Alx (x = 0–5) alloys.
Fig. 2. Lattice parameters by Reitveld method of (V30 Ti35 Cr25 Fe10 )100 − x Alx .
3.2. Hydrogen storage properties The desorption PCT curves of (V30 Ti35 Cr25 Fe10 )100 − x Alx (x = 0–5 at.%) alloys at 298 K and in hydrogen pressure from 4 to 0.01 MPa were shown in Fig. 3, and the relationship between Al content and hydrogen storage properties is summarized in Table 1.Both the absorption and desorption capacities of the alloys decline and the plateau pressures rise with the increase
of Al content. However, when x ≤ 1.0, the Al-containing alloys show their absorption and desorption capacities and plateau properties nearly as the same as the Al-free alloy. When x ≥ 1.0, the absorption and desorption capacities of the Al-containing alloys decrease sharply and the plateau pressures increase obviously. The alloy with 5 at.% Al shows no plateau region and can only absorb 1.71 wt.% H and desorb 0.23 wt.% H. A single phase of a BCC structure is found in the alloy with 5 at.% Al after absorption (Fig. 4), which implies that di-hydride cannot be formed in this alloy. Thus its absorption and desorption capacities are very low. The Al-free alloy shows both a FCC main phase and a BCC second phase after absorption. Another phenomenon in Table 1 is that the hydrogen capacities remained in the alloys after desorption decrease little with the increase of Al content, while the absorption and efficient desorption capacities decrease rapidly. It is well known that V-based alloys form two kinds of hydrides in the absorption process, which are called  phase (mono-hydride) and ␥ phase (di-hydride), respectively. The mono-hydride, which is too stable to be decomposed, has a plateau pressure as low as 0.1–1 Pa at room temperature. While the di-hydride has a comparatively high plateau pressure and can desorb hydrogen under moderate conditions. In our experiments, the hydrides desorb hydrogen at 298 K above 0.01 MPa. Under such conditions, di-hydride can desorb hydrogen almost completely, while mono-hydride nearly cannot be decomposed. Hence, it could be deduced that the remained hydrogen capacities in Table 1
Table 1 Relationship between Al content and hydrogen storage properties Al content (at.%)
Absorption capacity (wt.%)
Desorption capacity (wt.%)
Capacity remained (wt.%)
Plateau pressure (MPa)
0 0.6 1 2.5 5
3.6 3.58 3.55 2.98 1.71
2.0 1.99 1.96 1.43 0.23
1.6 1.59 1.59 1.55 1.48
0.071 0.073 0.085 0.21 –
Y. Yan et al. / Journal of Alloys and Compounds 426 (2006) 253–255
255
means that the formation of ␥ phase (di-hydride) is inhibited by the addition of Al, and no ␥ phase can be formed in the alloy containing 5 at.% Al. It might be explained by different effect of Al on the hole sizes of octahedral sites and tetrahedral sites. In V-based alloys, hydrogen in ␥ phase occupies the center of the octahedral sites and ␥ phase occupies the center of the tetrahedral sites. And the sizes of the former are much bigger than that of the latter. Hence, the effect of Al on the sizes of the octahedral sites is less than that of the tetrahedral sites. The sizes of the efficient hole in the tetrahedral sites decrease, which causes the decrease of the absorption and desorption capacities and the increase of plateau pressures of ␥ phase then. 4. Conclusion The effects of 0.6–5 at.% Al on the structure and hydrogen storage properties of V30 Ti35 Cr25 Fe10 alloy were investigated and the main conclusions were as follows: Fig. 4. XRD patterns of (V30 Ti35 Cr25 Fe10 )100 − x Alx (x = 0, 5) alloys after absorption.
represent the hydrogen capacities of mono-hydrides. It can be seen that the effect of Al on di-hydride of V30 Ti35 Cr25 Fe10 alloy is larger than that on mono-hydride. Al mostly deteriorates the absorption and desorption properties of di-hydride, which is the main reason of deterioration of hydrogen absorption and desorption properties of Al-containing alloys. 3.3. Discussion Generally, for BCC alloys, when the lattice parameters increase, the hydrogen absorption capacities increase, and the plateau pressures decrease. For example, in V–Ti–Cr system, when Ti content increases or Cr content decreases, the lattice parameters of V–Ti–Cr alloys increase, then the hydrogen storage capacities are improved. However, in this paper, an opposite rule was found. For BCC structure alloys (V30 Ti35 Cr25 Fe10 )100 − x Alx (x = 0–5), the hydrogen absorption capacities decrease and the plateau pressures increase when the lattice parameters rise with the increase of Al content. This phenomenon might be caused by the large differences between the atomic characters of Al and the transitional elements, V, Ti, Cr, and Fe. Thus, the effect of Al on the lattice structures and hydrogen storage properties of V-based BCC alloys is different from that of transitional elements. Similar phenomenon is found in Ti–Fe system, where the effects of Al partly substituting Fe are very different from those of Ni and Co on the hydrogen storage properties of TiFe [8]. In this paper, we find that H capacity in ␥ phase decreases rapidly with the increase of Al content, which
(1) The Al-containing alloys are single phases with BCC structures. The lattice parameters of the alloys become larger with the increase of Al content. (2) The hydrogen absorption and desorption capacities decrease and the plateau pressures increase with the addition of Al, but no evident effect is found when the content of Al is no more than 1 at.%. (3) The capacity of  phase (mono-hydride) decrease little but that of ␥ phase (di-hydride) decrease rapidly with the increase of Al content. The formation of ␥ phase is inhibited by the addition of Al, and nearly no ␥ phase is formed when Al content reaches 5 at.%. Acknowledgement This work is supported by the Science and Technology Bureau of Panzhihua City, Sichuan Province, China. References [1] E. Akiba, H. Iba, Intermetallics 6 (1998) 461. [2] T. Kuriiwa, T. Tamura, T. Amemiya, T. Fuda, A. Kamegawa, H. Takamura, M. Okada, J. Alloys Compd. 293–295 (1999) 433–436. [3] M. Okada, T. Kuriiwa, A. Kamegawa, et al., Mater. Sci. Eng. A329–A331 (2002) 305–312. [4] T. Tamura, T. Kazumi, A. Kamegawa, J. Alloys Compd. 356–357 (2003) 505–509. [5] A. Kagawa, E. Ono, T. Kusakabe, Y. Sakamoto, J. Less-Common Met. 172–174 (1991) 64–70. [6] Y. Yigang, C. Yungui, L. Hao, L. Jie, W. Chaoling, Proceedings of the Eighth Asian Hydrogen Energy Conference, May 20–27, Beijing, 2005, pp. 179–186. [7] F. Izumi, in: R.A. Young (Ed.), The Rietveld Method, International Union of Crystallography, Oxford University Press, 1993, Chapter 13. [8] S.-M. Lee, T.-P. Perng, J. Alloys Compd. 291 (1999) 254–261.