1994 Fiscal Year Final Research Report Summary
A novel mode of metal-hydride formation undr high pressures
| Project/Area Number |
05452276
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Physical properties of metals
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| Research Institution | CHUO UNIVERSITY |
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Principal Investigator |
FUKAI Yu Chuo Univ.Physics, Professor, 理工学部, 教授 (80055136)
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| Co-Investigator(Kenkyū-buntansha) |
KINO T Hiroshima Denki Inst. of Tech. Professor, 教授 (10033797)
SAITO Y Chuo Univ.Physics, Lecturer, 理工学部, 講師 (00055196)
WATANABE K Chuo Univ.Physics, Lecturer, 理工学部, 講師 (80055160)
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| Project Period (FY) |
1993 – 1994
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| Keywords | Mental-hydrogen system / metal hydride / vacancy / vacancy formation / defect structure / diffusion / hydrogen-induced diffusion / high pressure |
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| Research Abstract |
Most experiments to investigate hydrogenation processes at high temperatures and high hydrogen pressures were performed by x-ray diffraction at Synchrotron Radiation Facility of National Laboratory of High Energy Physics (Tsukuba).
First results of lattice contraction that took place in Pd and Ni under these conditions were interpreted as being due to the formation of extraordinarily high concentration of metal-atom vacancies. Subsequent experiments on Pd hydride revealed that metal-atom vacancies. amount to 18 at.% and they form an ordered structure of L2_2 type, i.e.Pd_3Vac_<alpha> (alpha*1). In Ni, numerous voids formed by vacuum-annealing of samples after heat-treatments for vacancy formation were ascribed to agglomeration of the hydrogen-induced, superabundant vacancies.
The superabundant vacancies thus formed were found to accelerate the diffusion of metal atoms by many orders of magnitudes, and lead to novel high-pressure phases, particularly hydrides of superstoichiometric compositions.
An important conclusion was drawn from these observations : In metal-hydrogen systems, structures containing superabundant metal-atom vacancies (defect phases) are thermodynamically more stable than ordinary defect-free interstitial solutions. All the phase diagrams reported heretofore are therefore metastable ones. These general statements certainly deserve further investigations.
On the whole, the project is deemed successful. Some of the first results on superabundant vacancy formation were published, and have been attracting world-wide attention of metal-hydriders. More extensive studies are being performed with a view to clarifying the generality of the phenomenon, its possible dependence on crystal structure and its possible applications in metals engineering.
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