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Thermodynamic and kinetic factors effecting hydrogen absorption on metal hydrides
international journal of hydrogen energy 33 (2008) 7505–7506
Available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/he
Technical Communication
Thermodynamic and kinetic factors effecting hydrogen absorption on metal hydrides M.R. Reda*, A. Moewes Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon SK S7N 5E2, Canada
article info
abstract
Article history:
The work of Guvendiren et al. on the effects of additives on mechanical milling and
Available online 17 November 2008
hydrogenation of Magnesium Powder which is published in this journal [Guvendiren M, Bayboru E, Ozturk T. International Journal of Hydrogen Energy 2004; 29: 491–496] shows excellent experimental work which agrees with previous published work. However they
Keywords:
did not explain the right phenomenon which is undergoing during hydrogen absorption on
Kinetics
magnesium hydride’s system. In this communication it is the objective to distinguish
Thermodynamics
between thermodynamic and kinetics factor effecting hydrogen absorption. It will be
Hydrogen absorption
shown that the phase rule of thermodynamics will determine the variation of Pressure–
Metal hydrides
composition isotherms at constant temperature during hydrogen absorption in Magne-
Phase rule
sium or Titanium. This is because the Pressure–composition isotherms at constant temperature is different for a single-phase (e.g. beta-Titanium) than two phases (e.g. delta and epsilon phases). Thus the data of Guvendiren et al. published in this journal (Fig. 5) can be explained by this effect. ª 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
1.
Summary and conclusion
In recent years there has been considerable interest in magnesium and titanium based systems for hydrogen applications. It is the purpose here to confirm that the published data of Guvendiren et al. on the effects of additives on mechanical milling and hydrogenation of Magnesium Powder which is published in this journal [1] is in excellent agreement with previous published work [2–6]. In compliance with the phase rule of thermodynamics, at constant temperature the hydrogen pressure varies with the hydrogen concentration in the metal undergoing absorption if the magnesium hydride solid has a single-phase structure,
but the hydrogen pressure should remain constant independent of the amount of hydrogen absorbed if two phases are present in the magnesium hydride. Isothermal plot of the variation of the pressure of hydrogen with the concentration of absorbed hydrogen should therefore, exhibit a plateau over any two-phase region. McQuillan [7] made the first detailed study of equilibrium in for example, the titanium–hydrogen system and although his experimental data showed slight deviations from ideal behavior (probably because of contamination with oxygen), the two-phase region could be clearly identified from the sections parallel to C axis (C is the hydrogen concentration in the metal). The same trend was obtained experimentally by Gibb et al. [8]. In the experimental
* Corresponding author. E-mail address: [email protected] (M.R. Reda). 0360-3199/$ – see front matter ª 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2008.10.023
7506
international journal of hydrogen energy 33 (2008) 7505–7506
work of Guvendiren published in this journal [1] in which the pressure–composition isotherms at constant temperature were measured and plotted in Fig. 5. The figure shows that the hydrogen absorbed in Magnesium is independent of pressure (plateau pressure) up to dissolved (absorbed) hydrogen concentrations of 5–6% for carbon/magnesium milled samples. This confirm the presence of a two phase system in this case. Beyond these concentrations there is no increase in absorbed hydrogen with increasing pressure. This indicates that all the sites for hydrogen absorption is occupied. Thus in this case the determining factor is thermodynamics rather than kinetics. In the un-milled Mg-Hydride samples the presence of a two-phase system at the surface is confirmed by the independence of dissolved hydrogen on hydrogen pressure up to dissolve hydrogen concentrations of 6%. Above this dissolve hydrogen concentrations, there is a gradual increase of hydrogen absorption with increasing hydrogen pressure. This indicates the presence of one phase system at this level of hydrogen concentrations. Again thermodynamics has a detrimental factor on the amount of hydrogen dissolved.
references
[1] Guvendiren M, Bayboru E, Ozturk T. Effects of additives on mechanical milling and hydrogenation of magnesium powders. International Journal of Hydrogen Energy 2004;29:491. 2222. [2] Libowitz G. Titanium–hydrogen. Solid state phenomena, vol. 49–50; 1996. p. 239 [chapter 6]. [3] Yamanaka S, Miyake M, Katsura M. Study on the hydrogen solubility in zirconium alloys. Journal of Nuclear Materials 1997;247:315. [4] Yamanaka S, Miyake M. Influence of interstitial elements on hydrogen solubility in the Group IV metals. Journal of Nuclear Materials 1993;201:134. [5] San-Martin A, Manchester FD. The H-Ti(Hydrogen-Titanium) System. Bulletin of Alloys Phase Diagrams 1987;8:30. [6] Zuzek E, Abriata JP, San-Martin A, Manchester FD. The H-Zr(Hydrogen-Zirconium) System. Bulletin of Alloys Phase Diagrams 1990;11:385. [7] McQuillan AD. An Experimental and Thermodynamic Investigation of the Hydrogen-Titanium System. Proceedings of the Royal Society 1950;A204:309. [8] Gibb Jr TRP, McSharry JJ, Bragdon RW. The Titanium-Hydrogen System and Titanium Hydride. II. Studies at High Pressure. Journal of the American Chemical Society 1951;73:1751.
Available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/he
Technical Communication
Thermodynamic and kinetic factors effecting hydrogen absorption on metal hydrides M.R. Reda*, A. Moewes Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon SK S7N 5E2, Canada
article info
abstract
Article history:
The work of Guvendiren et al. on the effects of additives on mechanical milling and
Available online 17 November 2008
hydrogenation of Magnesium Powder which is published in this journal [Guvendiren M, Bayboru E, Ozturk T. International Journal of Hydrogen Energy 2004; 29: 491–496] shows excellent experimental work which agrees with previous published work. However they
Keywords:
did not explain the right phenomenon which is undergoing during hydrogen absorption on
Kinetics
magnesium hydride’s system. In this communication it is the objective to distinguish
Thermodynamics
between thermodynamic and kinetics factor effecting hydrogen absorption. It will be
Hydrogen absorption
shown that the phase rule of thermodynamics will determine the variation of Pressure–
Metal hydrides
composition isotherms at constant temperature during hydrogen absorption in Magne-
Phase rule
sium or Titanium. This is because the Pressure–composition isotherms at constant temperature is different for a single-phase (e.g. beta-Titanium) than two phases (e.g. delta and epsilon phases). Thus the data of Guvendiren et al. published in this journal (Fig. 5) can be explained by this effect. ª 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
1.
Summary and conclusion
In recent years there has been considerable interest in magnesium and titanium based systems for hydrogen applications. It is the purpose here to confirm that the published data of Guvendiren et al. on the effects of additives on mechanical milling and hydrogenation of Magnesium Powder which is published in this journal [1] is in excellent agreement with previous published work [2–6]. In compliance with the phase rule of thermodynamics, at constant temperature the hydrogen pressure varies with the hydrogen concentration in the metal undergoing absorption if the magnesium hydride solid has a single-phase structure,
but the hydrogen pressure should remain constant independent of the amount of hydrogen absorbed if two phases are present in the magnesium hydride. Isothermal plot of the variation of the pressure of hydrogen with the concentration of absorbed hydrogen should therefore, exhibit a plateau over any two-phase region. McQuillan [7] made the first detailed study of equilibrium in for example, the titanium–hydrogen system and although his experimental data showed slight deviations from ideal behavior (probably because of contamination with oxygen), the two-phase region could be clearly identified from the sections parallel to C axis (C is the hydrogen concentration in the metal). The same trend was obtained experimentally by Gibb et al. [8]. In the experimental
* Corresponding author. E-mail address: [email protected] (M.R. Reda). 0360-3199/$ – see front matter ª 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2008.10.023
7506
international journal of hydrogen energy 33 (2008) 7505–7506
work of Guvendiren published in this journal [1] in which the pressure–composition isotherms at constant temperature were measured and plotted in Fig. 5. The figure shows that the hydrogen absorbed in Magnesium is independent of pressure (plateau pressure) up to dissolved (absorbed) hydrogen concentrations of 5–6% for carbon/magnesium milled samples. This confirm the presence of a two phase system in this case. Beyond these concentrations there is no increase in absorbed hydrogen with increasing pressure. This indicates that all the sites for hydrogen absorption is occupied. Thus in this case the determining factor is thermodynamics rather than kinetics. In the un-milled Mg-Hydride samples the presence of a two-phase system at the surface is confirmed by the independence of dissolved hydrogen on hydrogen pressure up to dissolve hydrogen concentrations of 6%. Above this dissolve hydrogen concentrations, there is a gradual increase of hydrogen absorption with increasing hydrogen pressure. This indicates the presence of one phase system at this level of hydrogen concentrations. Again thermodynamics has a detrimental factor on the amount of hydrogen dissolved.
references
[1] Guvendiren M, Bayboru E, Ozturk T. Effects of additives on mechanical milling and hydrogenation of magnesium powders. International Journal of Hydrogen Energy 2004;29:491. 2222. [2] Libowitz G. Titanium–hydrogen. Solid state phenomena, vol. 49–50; 1996. p. 239 [chapter 6]. [3] Yamanaka S, Miyake M, Katsura M. Study on the hydrogen solubility in zirconium alloys. Journal of Nuclear Materials 1997;247:315. [4] Yamanaka S, Miyake M. Influence of interstitial elements on hydrogen solubility in the Group IV metals. Journal of Nuclear Materials 1993;201:134. [5] San-Martin A, Manchester FD. The H-Ti(Hydrogen-Titanium) System. Bulletin of Alloys Phase Diagrams 1987;8:30. [6] Zuzek E, Abriata JP, San-Martin A, Manchester FD. The H-Zr(Hydrogen-Zirconium) System. Bulletin of Alloys Phase Diagrams 1990;11:385. [7] McQuillan AD. An Experimental and Thermodynamic Investigation of the Hydrogen-Titanium System. Proceedings of the Royal Society 1950;A204:309. [8] Gibb Jr TRP, McSharry JJ, Bragdon RW. The Titanium-Hydrogen System and Titanium Hydride. II. Studies at High Pressure. Journal of the American Chemical Society 1951;73:1751.