Hydrogen Concentration Dependence of Tritium Tracer Diffusion Coefficient in Alpha Phase of Niobium

Abstract

In order to examine influences of coexistent hydrogen isotopes on diffusion behavior of tritium in niobium, tracer diffusion coefficients Dt of tritium in alpha phase of hydrogenated and deuterized niobium (α-NbHxTy and α-NbDxTy (x<0,8,y<<x)) have been measured at 473 K, 493 K and 553 K. The data on Dt show typical hydrogen concentration dependence: Dt of tritium for both α-NbHxTy, and α-NbDxTy, decreases with hydrogen concentration under all experimental conditions. The obtained concentration dependence of Dt of tritium differs from that of Dt of protium in α-NbHx or of deuterium in α-NbHxTy. On the other hand, no appreciable differences in the concentration dependence of Dt of tritium between α-NbHxTy, and α-NbDxTy, are observed: there are no definite isotope effects due to the coexisting hydrogen isotopes. This result suggests that Dt of tritium for a tritiated niobium (α-NbTx) is not very different from that for α-NbHxTy and α-NbDxTy. The chemical diffusion coefficient D* of tritium is also evaluated on the basis of the obtained Dt of tritium and of a literature value of a thermodynamic factor F for Nb-H and Nb-D systems.