DIFFERENTIAL THERMAL-ANALYSIS OF HYDROGEN-INDUCED AMORPHIZATION IN C15 LAVES PHASE GDFE2

Stuctural changes of the C15 Laves phase GdFe2 during differential thermal analysis in a hydrogen atmosphere have been investigated by X-ray diffraction and transmission electron microscopy. The DTA curves exhibit four exothermic peaks resulting from hydrogen absorption, hydrogen-induced amorphization (HIA), precipitation of GdH2 and crystallization. As the hydrogen pressure increases, the onset temperatures of hydrogen absorption, HIA and crystallization become lower. Correspondingly, the activation energies for hydrogen absorption and for HIA decrease from 125 to 110 kJ/mol and from 130 to 95 kJ/mol, respectively, but that for the precipitation of GdH2 is almost constant as 200 kJ/mol. These results indicate that as the hydrogen pressure increases, both the hydrogen absorption and amorphization occur easily.