Functionality of the nanoscopic crystalline Al/amorphous Al50Ti50 surface embedded composite observed in the NaAlH4 + xTiCl3 system after milling
The NaAlH4 + xTiCl3 (x < 0.1) system has been studied by a combination of X-ray synchrotron and neutron diffraction, and isotopic H2/D2 scrambling after the completion of the milling process, and the first thermal release of hydrogen (H). An in situ X-ray synchrotron diffraction study of the isoc...
| Main Authors: | , , , , , , , , , |
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| Format: | Journal Article |
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Elsevier B.V.
2012
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| Online Access: | http://hdl.handle.net/20.500.11937/36016 |
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| author | Pitt, M. Vullum, P. Sørby, M. Sulic, M. Emerich, H. Paskevicius, Mark Buckley, Craig Walmsley, J. Holmestad, R. Hauback, B. |
| author_facet | Pitt, M. Vullum, P. Sørby, M. Sulic, M. Emerich, H. Paskevicius, Mark Buckley, Craig Walmsley, J. Holmestad, R. Hauback, B. |
| author_sort | Pitt, M. |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | The NaAlH4 + xTiCl3 (x < 0.1) system has been studied by a combination of X-ray synchrotron and neutron diffraction, and isotopic H2/D2 scrambling after the completion of the milling process, and the first thermal release of hydrogen (H). An in situ X-ray synchrotron diffraction study of the isochronal release of hydrogen from planetary milled (PM) NaAlH4 + 0.1TiCl3 shows that crystalline (c-) Al1-xTix phases do not form until almost all H is released from the sample, demonstrating that the surface embedded nanoscopic crystalline Al/amorphous (a-) Al50Ti50 composite facilitates the release of H during the very first thermal desorption. Planetary milled (PM) NaAlH4 + xTiCl3 is observed to disproportionate at room temperature, with no NaAlH4 remaining after ca. 200 days. A complete lack of ambient hydrogen release from PM NaAlH4 + 0.1Al (80 nm) measured over 200 days suggests that the nanoscopic a-Al50Ti50 phase is entirely responsible for the hydrogen release during thermal desorption of milled NaAlH4 + xTiCl3. Isotopic H/D exchange has been observed by combined neutron and X-ray synchrotron diffraction on a PM NaAlD4 + 0.04TiCl3 sample, after exposing the milled sample to 20 bar H2 at 50 °C for ca. 6 days. Under these pressure/temperature (P/T) conditions, disproportionation of NaAlD4 is avoided, and ca. 32% of D atoms are exchanged with H atoms. Asymmetrically broadened reflections in the synchrotron data show peak splitting into two unit cell types, one expanded with H, the other remaining close to pure D based unit cell dimensions.The 2-phase model when fitted to the neutron data demonstrates that ca. 56% of D atoms in ca. 58% of all unit cells are exchanged with H, yielding a NaAl(H0.56D0.44)4 composition for the expanded unit cells. HD scrambling (1 bar mixture of H2 and D2 at 23 °C) performed on desorbed H empty PM NaAlH4 + 0.1TiCl3 shows classic H2 + D2 ↔ 2HD equilibrium mixing, demonstrating that nanoscopic Ti containing Al1-xTix surface embedded phases perform a H2 dissociation/recombination function that unadulterated NaAlH4 cannot. |
| first_indexed | 2025-11-14T08:43:49Z |
| format | Journal Article |
| id | curtin-20.500.11937-36016 |
| institution | Curtin University Malaysia |
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| last_indexed | 2025-11-14T08:43:49Z |
| publishDate | 2012 |
| publisher | Elsevier B.V. |
| recordtype | eprints |
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| spelling | curtin-20.500.11937-360162017-09-13T15:55:36Z Functionality of the nanoscopic crystalline Al/amorphous Al50Ti50 surface embedded composite observed in the NaAlH4 + xTiCl3 system after milling Pitt, M. Vullum, P. Sørby, M. Sulic, M. Emerich, H. Paskevicius, Mark Buckley, Craig Walmsley, J. Holmestad, R. Hauback, B. synchrotron radiation transition metal alloys and compounds. gas–solid reactions amorphous materials metal hydrides neutron diffraction The NaAlH4 + xTiCl3 (x < 0.1) system has been studied by a combination of X-ray synchrotron and neutron diffraction, and isotopic H2/D2 scrambling after the completion of the milling process, and the first thermal release of hydrogen (H). An in situ X-ray synchrotron diffraction study of the isochronal release of hydrogen from planetary milled (PM) NaAlH4 + 0.1TiCl3 shows that crystalline (c-) Al1-xTix phases do not form until almost all H is released from the sample, demonstrating that the surface embedded nanoscopic crystalline Al/amorphous (a-) Al50Ti50 composite facilitates the release of H during the very first thermal desorption. Planetary milled (PM) NaAlH4 + xTiCl3 is observed to disproportionate at room temperature, with no NaAlH4 remaining after ca. 200 days. A complete lack of ambient hydrogen release from PM NaAlH4 + 0.1Al (80 nm) measured over 200 days suggests that the nanoscopic a-Al50Ti50 phase is entirely responsible for the hydrogen release during thermal desorption of milled NaAlH4 + xTiCl3. Isotopic H/D exchange has been observed by combined neutron and X-ray synchrotron diffraction on a PM NaAlD4 + 0.04TiCl3 sample, after exposing the milled sample to 20 bar H2 at 50 °C for ca. 6 days. Under these pressure/temperature (P/T) conditions, disproportionation of NaAlD4 is avoided, and ca. 32% of D atoms are exchanged with H atoms. Asymmetrically broadened reflections in the synchrotron data show peak splitting into two unit cell types, one expanded with H, the other remaining close to pure D based unit cell dimensions.The 2-phase model when fitted to the neutron data demonstrates that ca. 56% of D atoms in ca. 58% of all unit cells are exchanged with H, yielding a NaAl(H0.56D0.44)4 composition for the expanded unit cells. HD scrambling (1 bar mixture of H2 and D2 at 23 °C) performed on desorbed H empty PM NaAlH4 + 0.1TiCl3 shows classic H2 + D2 ↔ 2HD equilibrium mixing, demonstrating that nanoscopic Ti containing Al1-xTix surface embedded phases perform a H2 dissociation/recombination function that unadulterated NaAlH4 cannot. 2012 Journal Article http://hdl.handle.net/20.500.11937/36016 10.1016/j.jallcom.2011.11.045 Elsevier B.V. restricted |
| spellingShingle | synchrotron radiation transition metal alloys and compounds. gas–solid reactions amorphous materials metal hydrides neutron diffraction Pitt, M. Vullum, P. Sørby, M. Sulic, M. Emerich, H. Paskevicius, Mark Buckley, Craig Walmsley, J. Holmestad, R. Hauback, B. Functionality of the nanoscopic crystalline Al/amorphous Al50Ti50 surface embedded composite observed in the NaAlH4 + xTiCl3 system after milling |
| title | Functionality of the nanoscopic crystalline Al/amorphous Al50Ti50 surface embedded composite observed in the NaAlH4 + xTiCl3 system after milling |
| title_full | Functionality of the nanoscopic crystalline Al/amorphous Al50Ti50 surface embedded composite observed in the NaAlH4 + xTiCl3 system after milling |
| title_fullStr | Functionality of the nanoscopic crystalline Al/amorphous Al50Ti50 surface embedded composite observed in the NaAlH4 + xTiCl3 system after milling |
| title_full_unstemmed | Functionality of the nanoscopic crystalline Al/amorphous Al50Ti50 surface embedded composite observed in the NaAlH4 + xTiCl3 system after milling |
| title_short | Functionality of the nanoscopic crystalline Al/amorphous Al50Ti50 surface embedded composite observed in the NaAlH4 + xTiCl3 system after milling |
| title_sort | functionality of the nanoscopic crystalline al/amorphous al50ti50 surface embedded composite observed in the naalh4 + xticl3 system after milling |
| topic | synchrotron radiation transition metal alloys and compounds. gas–solid reactions amorphous materials metal hydrides neutron diffraction |
| url | http://hdl.handle.net/20.500.11937/36016 |