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 carrie d out at 400 degrees C under atmospheric pressure by in situ weight gain me asurements with thermo-gravimetric apparatus (TGA) and transmission electro n microscope/energy dispersive X-ray spectrometer (TEM/EDX) analysis. It is confirmed that the hydriding kinetics follow a linear rate law after incub ation time. It is found that the hydriding reaction rate decreases with inc reasing 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-0.8 Sn- 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 t here is no strong relationship between the intermetallic precipitates and t he kinetic rate in the Zr-XSn-YNb alloy system. It is revealed in this stud y that the solubility limit of Sn in the Zr-0.4Nb-XSn ternary system become s higher than that in the Zr-Sn binary system. On the other hand, the Nb so lubility limit remains unchanged in the Zr-0.8Sn-YNb ternary system. Optimi zed 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. (C) 2000 Elsevier Science B.V. All rights reserved.