Diffusion of Hydrogen and Deuterium in High Purity Zirconium

Kinetics of the reaction of zirconium with pure hydrogen and deuterium was studied for60°–250°C, H 2 pressures of 1.1–5.0 cm Hg, and composition range , using a vacuum microbalance method. The reaction was shown to be diffusion‐controlled with diffusion occurring from a surface of constant concentration into a heterogeneous system. The diffusion equation was solved for these conditions using the method originally developed by Neuman and recently applied by Wagner to this type of problem. Average concentration according to this view is given by where is diffusion coefficient in cm 2 /sec, is time in seconds, and is specimen thickness in centimeters. Plots of show this relationship to hold over wide variations in time, temperature, pressure, and specimen thickness. Diffusion coefficients were calculated and when plotted against on a logarithmic plot gave a heat of activation of 11,400 cal/mole. The corresponding entropy of activation was2.7cal/mole/°C The following equation expresses data for diffusion of hydrogen in zirconium: For the composition range of Zr to , experimental data fit the proposed explanation for the reaction. At higher compositions, deviations were observed. Diffusion of deuterium in zirconium was also studied and data found to fit the equation: The relationship between the diffusion coefficient of hydrogen and deuterium was found to be 1.5. The theoretical value should be . The diffusion mechanism proposed was verified by experimental results.