水素の吸蔵・放出サイクルに対するZrCo及びZrNiの耐久性

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Zirconium-alloys such as ZrNi and ZrCo have been developed so far as promising materials for storage, supply and recovery of tritium. They, however, easily lose their ability of reversible absorption-desorption of tritium in the presence of impurity gases such as O2, H2O, CO2, CO and others. Although we have developed a method to lower this contamination effect, there is another possibility for the degradation of their properties by repeated heat cycles in a hydrogen atmosphere. To examine this possibility, we studied the changes in the characteristics of those alloys for hydrogen absorption and desorption owing to the heat cycles in the presence of hydrogen in a system. The samples were used as grains. They were first exposed to a hydrogen gas to prepare respective hydrides of a form of ZrMH3, where M is Ni or Co. Subsequently, the changes in the absorption-desorption characteristics were measured in a closed system during heat cycles between room temperature and 600℃. No significant change in the equilibrium pressure of hydrogen was observed up to 50 heat cycles for ZrNi. X-ray diffraction analysis revealed that the sample kept ZrNi structure before and after the heat cycles. The hydride formed was always ZrNiH3. Contrarily, ZrCo showed drastic changes in the absorption-desorption characteristics in 50 heat cycles. X-ray diffraction analysis showed that the ZrCoH3 initially formed was decomposed to ZrHx + ZrCo2. Namely, the disproportionation of ZrCo took place. It is noteworthy that the disproportionation reaction did not occur in the absence of hydrogen isotopes in the system. On account of these observations, it was concluded that the degradation of absorption-desorption characteristics of ZrCo is due to the ease in disproportionation, and hence its ability is kept for a large number of heat cycles, namely storage, supply and recovery operations.
富山大学の論文

水素の吸蔵・放出サイクルに対するZrCo及びZrNiの耐久性

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