Pressure dependence of Hydrogen-Induced Transformations in C15 Laves phase DyCo2

Haiwen Li, Kazuhiro Ishikawa, kiyoshi aoki

Research output: Contribution to journalArticle

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Abstract

Structural changes in C15 Laves phase DyCo2 heated in a hydrogen atmosphere between 0.1 and 5.0 MPa were investigated using a pressure differential scanning calorimeter (PDSC) and were compared with those of DyFe2. Four exothermic reactions resulting from 1) hydrogen absorption forming crystalline and amorphous hydrides, 2) hydrogen-induced amorphization (HIA), 3) the precipitation of BiF3-type DyH3 in the amorphous hydride and 4) the decomposition of the remaining amorphous hydride into DyH3 + β-Co were observed with increasing temperature. HIA in DyCo2 occurred for every hydrogen pressure in contrast to DyFe2, because the pressure dependence of it is small. The mechanism of the phase transformations for DyCo2 in a hydrogen atmosphere was discussed on the basis of the experimental results such as the pressure dependence of Tp and Tp/Tm (the peak temperature/the melting point of DyCo2), the enthalpy change ΔH, the activation energy EA and so on.
Original languageEnglish
Pages (from-to)3050-3055
JournalMaterials Transactions
Publication statusPublished - 2004

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Laves phases
pressure dependence
Hydrogen
hydrogen
Hydrides
hydrides
Amorphization
atmospheres
differential pressure
Exothermic reactions
exothermic reactions
Calorimeters
melting points
calorimeters
phase transformations
Melting point
Enthalpy
Activation energy
Phase transitions
enthalpy

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Pressure dependence of Hydrogen-Induced Transformations in C15 Laves phase DyCo2. / Li, Haiwen; Ishikawa, Kazuhiro; aoki, kiyoshi.

In: Materials Transactions, 2004, p. 3050-3055.

Research output: Contribution to journalArticle

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AB - Structural changes in C15 Laves phase DyCo2 heated in a hydrogen atmosphere between 0.1 and 5.0 MPa were investigated using a pressure differential scanning calorimeter (PDSC) and were compared with those of DyFe2. Four exothermic reactions resulting from 1) hydrogen absorption forming crystalline and amorphous hydrides, 2) hydrogen-induced amorphization (HIA), 3) the precipitation of BiF3-type DyH3 in the amorphous hydride and 4) the decomposition of the remaining amorphous hydride into DyH3 + β-Co were observed with increasing temperature. HIA in DyCo2 occurred for every hydrogen pressure in contrast to DyFe2, because the pressure dependence of it is small. The mechanism of the phase transformations for DyCo2 in a hydrogen atmosphere was discussed on the basis of the experimental results such as the pressure dependence of Tp and Tp/Tm (the peak temperature/the melting point of DyCo2), the enthalpy change ΔH, the activation energy EA and so on.

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