Alloying Effects on Hydrogen Gettering Properties for Zr-Al System

Alloying effects on absorption and desorption kinetics of deuterium for Zr-Al alloys were studied with mass analyzed thermal desorption spectroscopy using a conventional high vacuum system. It was found that the absorption rate of deuterium was proportional to the 1/2 power of deuterium gas pressure. On the other hand, the desorption process obeyed the second order kinetics with respect to the amount of absorbed deuterium. The temperature dependence of the rate constants revealed that the activation energies for both the absorption and desorption processes were lowered by the increase in the Al content in the alloys. Through potential diagrams for the absorption and desorption of deuterium, it was also found that the heat of deuterium (hydrogen) solution decreased with increasing Al composition. In addition, the x-ray diffraction spectroscopy showed the formation of a Zr₄Al₃ phase in the Zr₃>Al₂ sample owing to repeated absorption and desorption cycles. The results suggest that the electronic factors, for example, work function, electron density, d-band character and so on, play an important role for the alloying effects rather than crystallographic structures. In addition, it becomes evident that the absorption/desorption properties for such alloys are limited not only by the side reactions with impurity gases but also changes in their crystallographic nature owing to interactions with hydrogen and/or heat cycles.