On the thermal stability of the zirconium/cobalt–hydrogen system

From the known getter materials proposed for the storage, supply, and recovery of hydrogen isotopes the interalloy ZrCo was selected by the international thermonuclear experimental reactors (ITER) team because it has very similar properties to uranium and is more acceptable for Regulatory Agencies. The only known drawback of ZrCo is its potential of loosing the ability to reversibly absorb or desorb tritium during prolonged thermal cycling. Under these conditions, the getter hydride ZrCoHx (x≤3), tends to disproportionate yielding the more stable hydride ZrH2, which is associated with performance degradation in the gettering properties. In this paper, previous studies on the rate of hydrogen induced disproportionation/reproportionation of ZrCo were extended to a broader temperature range. In addition, comparative measurements were performed with protium and deuterium with the aim of determining possible isotope effect. On the basis of the structural modifications that samples undergo during hydrogenation a qualitative explanation is given for the disproportionation mechanism.