Pressure dependence of hydrogen-induced amorphization in C15 Laves phase TbFe2 : Special issue on hydrogen absorbing materials

Abstract

The pressure dependence of structural changes of C 15 Laves phase TbFe 2 heated in a hydrogen atmosphere was investigated using a pressure differential scanning calorimeter (PDSC), a powder X-ray diffractometer (XRD), a differential scanning calorimeter (DSC) and a hydrogen analyzer. Hydrogen absorption in the crystalline state, hydrogen-induced amorphization (HIA), precipitation of TbH 2 and decomposition of the remaining amorphous alloy into α-Fe and TbH 2 occurred exothermally with increasing temperature above 0.5 MPa H 2 , independent of the heating rate. HIA and precipitation of TbH 2 occurred simultaneously in 0.2 MPa H 2 (0.33 K/s) and in 0.1 MPa H 2 (0.17 K/s). On the contrary, hydrogen absorbed crystalline c-TbFe 2 H 3.5 decomposed directly into α-Fe and TbH 2 in 0.1 MPa H 2 (0.33 K/s). That is, no amorphous phase was formed at the lower hydrogen pressure and at a high heating rate. The reason why HIA occurs above, the critical hydrogen pressure and below the critical heating rate was discussed on the basis of the hydrogen content absorbed in the crystalline state or TbFe 2 .