An investigation was made of H permeation through membranes of Ta, and Ta which was coated with a thin film of Pd, by using direct flow measurements. At temperatures ranging from 400 to 600C, and pressures of up to 175psia, the permeation rate through Pd-coated membranes was substantially greater than that through pure Ta membranes of the same thickness and under the same conditions. The permeation rate through Ta decayed with time, especially at temperatures of 500C and above. By using known solubility data, the diffusivity at a H/Ta ratio of 0.07 and temperatures of 400 to 600C, was found to be described by:

D (cm2/s) = 7.5 x 10-2 exp[-14.4(kcal/g-atom)/RT]

D.Jewett, A.C.Makrides: Federal Scientific and Technical Information, Report N67-30359