By using an electrochemical technique, the diffusivity in a foil sample of 5N-purity material was found to be equal to 2.3 x 10-9cm2/s at 23C. It was noted that the diffusivity was affected by the purity of the material, and that surface properties were important in limiting permeation.

D.W.DeWulf, A.J.Bard: Journal of the Electrochemical Society, 1985, 132[12], 2965-7