Effects of Sn and Nb on massive hydriding kinetics of Zr–XSn–YNb alloy

Kinetic studies on the massive hydriding of Zr–0.4Nb–XSn (X=0.5, 0.8, 1.5, 2.0) and Zr–0.8Sn–YNb (Y=0.2, 0.4, 0.8, 1.0) ternary alloys are carried out at 400°C under atmospheric pressure by in situ weight gain measurements with thermo-gravimetric apparatus (TGA) and transmission electron microscope/energy dispersive X-ray spectrometer (TEM/EDX) analysis. It is confirmed that the hydriding kinetics follow a linear rate law after incubation time. It is found that the hydriding reaction rate decreases with increasing Sn content up to 1.5% and then sharply increases in the case of Zr–0.4Nb–XSn while it steadily increases with Nb content in the case of Zr–0.8Sn–YNb. The rate does not seem to be affected by the grain size in the XSn alloys, but is influenced in the YNb alloys. TEM/EDX analysis shows that there is no strong relationship between the intermetallic precipitates and the kinetic rate in the Zr–XSn–YNb alloy system. It is revealed in this study that the solubility limit of Sn in the Zr–0.4Nb–XSn ternary system becomes higher than that in the Zr–Sn binary system. On the other hand, the Nb solubility limit remains unchanged in the Zr–0.8Sn–YNb ternary system. Optimized compositions in the Zr–XSn–YNb ternary alloy are suggested to be about 1.5% Sn and as low Nb as possible in order to minimize hydrogen uptake.