Isotope effect in the diffusion of hydrogen and deuterium in titanium, Ti88Al12 and Ti3Al

Diffusion coefficients of hydrogen and deuterium in titanium, titanium-aluminium alloy Ti88Al12 and intermetallic Ti3Al have been measured in the temperature range 873-1298 K. The activation energy for diffusion has been found to be almost the same for hydrogen and deuterium and to increase, as the aluminium content in the metals increases, from ca. 0.44 eV for titanium to ca. 0.85 eV for Ti3Al. The ratio of the measured diffusion coefficient of deuterium to that of hydrogen also increases from the classical value 1/root 2 for titanium to ca. 0.8 for Ti3Al. An application of the classical rate theory to the measured ratio shows that the hydrogen atom at the saddle point of the diffusion path is more tightly bound to the metal atoms and has a larger vibration energy in Ti3Al than in titanium.