Hydrogen-Induced Superabundant Vacancies and Diffusion Enhancement in Some FCC Metals

The Phase Diagram of Mo-H Alloys under High Hydrogen Pressures

“…5) divided by the relaxation volume of a vacancy calculated for a hypothetical fcc Mo v R = ¼ À0:40 18) leads to the concentration of vacancy-hydrogen clusters x cl ¼ 0:02. This value is smaller than the equilibrium concentrations observed in other fcc hydrides; x cl ¼ 0:09 for Cr-H, 4) 0.1 for Mn-H, 13) 0.19 for Fe-H, 6) 0.10 for Co-H, 13) 0.30 for Ni-H 24) and 0.10 for Pd-H. 25) Considering the extreme sluggishness of atomic processes experienced in phase determinations, it appears very probable that the equilibrium cluster concentration was not yet achieved in the experiment shown in Fig. 5.…”

“…13) A high-purity (99.99%) powder sample was sealed in a capsule of NaCl together with an internal hydrogen source (NaBH 4 + Ca(OH) 2 ) and a pressure marker (NaCl diluted with BN to suppress grain growth at high temperatures), and was placed at the center of an 8 mm cube of amorphous Bepoxy resin composite. Pressures up to 6 GPa could be applied to the sample by compression from six perpendicular directions, and temperatures could be raised to 1200 C by sending an electric current to a graphite tube heater around the capsule.…”

Repulsive Nature for Hydrogen Incorporation to Fe3C up to 14 GPa

“…The decomposition temperature of LiAlH4 has been estimated to 423-493 K at ambient pressure, 573 K at 4.7 GPa, 873 K at 12 GPa, and 973 K at 18.5 GPa based on the hydrogenation temperature of iron-alloys in previous studies. 9,7,17) According to these results, most of the temperature conditions in this study are well above the decomposition temperature, suggesting that hydrogen was supplied to Fe3C sample at the present conditions (only except for the conditions below 873 K at 14 GPa).…”

“…The Fe3C sample and LiAlH4 layers were separated by a thin MgO disc. After a thermal decomposition of LiAlH4 at high temperature (423-493 K at ambient pressure), 9) H2 was released and then supplied to the Fe3C sample. Schematic picture of the cell assembly used are illustrated in Fig.…”

“…The sample was enclosed in a cylindrical NaCl capsule, which was reported to seal hydrogen at high pressure. 9) LiAlH4 was used as a hydrogen source and it was enclosed at the bottom of NaCl capsule. The Fe3C sample and LiAlH4 layers were separated by a thin MgO disc.…”