ABSTRACT:The hydrogen desorption reaction of magnesium hydride (MgH 2 ), MgH 2 3 MgϩH 2 , is accelerated by mixing catalytic metal oxides (e.g., Nb 2 O 5 ). This catalytic effect of metal oxides, MxOy, is theoretically estimated in a quantitative way using atomization energy concept. The atomization energies, ⌬E M for metal ion and ⌬E O for oxide ion in various metal oxides are evaluated using the energy density analysis of the total energy. It is shown that the hydrogen desorption rate increases monotonously with increasing y ϫ ⌬E O values of metal oxides. This indicates that the oxide ion in MxOy interacts mainly with hydrogen atoms in MgH 2 . The y ϫ ⌬E O value is a measure of the magnitude of the OOH interaction operating between MxOy and MgH 2 , and hence, it is indeed a good parameter to show the catalytic activities of metal oxides. This approach is useful for the analysis of other catalyst and catalytic reactions.

In order to estimate the strain energies of pure Cu and pure Al prepared by ECAP and ARB processes, dislocation densities remaining in these metals after each process were analyzed by the Warren-Abervach method based on the Williamson-Hall plot from a series of data taken by conventional X-ray diffractometry. The measured dislocation density was higher by several times in pure Cu than in pure Al regardless of ECAP and ARB, resulting in the higher strain energy stored in pure Cu than in pure Al. Also, the dislocation density was found to be lower in the f.c.c. phase in pure Cu than that in the lath martensite phase in high Cr ferritic steels. Furthermore, it was observed that the amount of stored strain energy in pure Al depended considerably on its purity.

The hydrogen desorption (or decomposition) reaction of NaAlH 4 is expressed as NaAlH 4 ! 1=3Na 3 AlH 6 þ 2=3Al þ H 2 , and its desorption rate is accelerated by mixing metal chloride catalysts (e.g., TiCl 3 ). This catalytic effect of metal chlorides, MCl n , is theoretically estimated in a quantitative way using atomization energy concept. The atomization energies, DE M for metal ion and DE Cl for chloride ion in various metal chlorides are evaluated using the energy density analysis of the total energy. It is shown that the hydrogen desorption reaction rate increases with increasing n  DE M values of metal chlorides. This indicates that the metal ion in MCl n interacts mainly with hydrogen or [AlH 4 ] À complex anion in NaAlH 4 . To confirm this calculated result, experiments are performed using NaAlH 4 mixed with Ti-based catalysts. The hydrogen desorption rate is enhanced in the order, TiCl 3 > TiO 2 > Ti metal nanopowder, indicating that the Ti ions in TiCl 3 or TiO 2 work to promote the catalytic reaction more effectively than the neutral Ti atoms in Ti metal nanopowder. V C 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: [950][951][952][953][954][955][956][957][958][959][960] 2011