Application of palladium coating on group 5 metals for vacuum permeator. Possible problems and solutions

Permeation of hydrogen through Pd-Ta-Pd composite membrane was measured at 500 and 600degC to examine the feasibility of the concept to use this type of membrane as permeation window to recover tritium from liquid Pb-Li alloy. At 500degC, the permeation rate gradually decreased with increasing operation time due to surface contamination by carbon. These observations indicated that partial pressures of residual hydrocarbons in vacuum permeator have to be strictly controlled to avoid carbon deposition. Nevertheless, permeability could be restored by removal of carbon through reaction with O2 gas. At 600degC, however, permanent degradation took place due to development of open porosity in Pd layer and interdiffusion between Pd and Ta. Preparation of HfN intermediate layer between Pd and Ta hindered the porosity development and interdiffusion. (author)