Kinetics of hydrogen absorption in Zr-based alloys

► Hydrogen absorption in Zr–Nbx–Tay alloys (x=2.5, 10wt.%; y=0, 3, 12 wt.%) is studied. ► Influence of repeated hydriding on rate constant and particle size is determined. ► Dominant mechanism of hydrogen absorption is found to be contracting volume. ► Surface reactions determine reaction rate as Ta and Nb content increase in alloy. 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 673–973K at 1bar 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 973K Zr–2.5Nb–3Ta at 673K and 973K; 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.