Temperature driven hydrogen-induced disproportionation of Zr2Cu

The absorption of hydrogen by Zr2Cu was studied by the aid of the Zr2Cu–H phase diagram elaborated by Kadel and Weiss. It was found that Zr2Cu hydride was formed at ambient temperature after moderate hydrogen absorption. Hydrogen-induced disproportionation of Zr2Cu occurred at temperatures exceeding 550 K. The unknown compound of the γ phase reported by Kadel and Weiss was identified as Zr7Cu10. It was also found that the β phase consisted of ZrCu and Zr hydride instead of Zr2CuHx, x = 1.0–1.4. The disproportionation behavior was found to follow a different mechanism below and above 973 K. Below 973 K the disproportionation was found to proceed by the reaction sequence, Zr2Cu + H2 → Zr7Cu10 + ZrHx + H2(γ phase) → Zr14Cu51 + ZrHx + H2(δ phase), and above 973 K via the sequence, Zr2Cu + H2 → ZrCu + ZrHx + H2(β phase) → Zr7Cu10 + ZrHx + H2(δ phase). The difference could be explained by the thermodynamic stability of ZrCu intermetallic compounds.