Kinetics of hydrogen absorption in Zr-based alloys

The kinetics of hydrogen absorption in Zr-based alloys Zr-2.5Nb, Zr-10Nb, Zr-2.5Nb-3Ta and Zr-10Nb-12Ta have been investigated in the temperature range 673-973 K at 1 bar hydrogen pressure. The improvement in hydrogen kinetics and a slight decrease of maximal amount of hydrogen absorbed were observed upon cycling. The rate determining steps are as follows: geometrical contraction for all samples except Zr-10Nb-12Ta; diffusion in the beginning for Zr-10Nb at 973 K Zr-2.5Nb-3Ta at 673 K and 973 K; first order reaction Zr-10Nb-12Ta at all temperatures. The amount of additives, Nb and Ta, is found to have major influence on the mechanism of the absorption process