Defect and Diffusion Forum Vol. 349

Abstract: The role of the thermodynamic factor in determining the magnitude of Ficks diffusion constant, DH, for H in metals and alloys is discussed using mainly Pd and its fcc alloys as examples because data are available for some of these systems over a wide range of H contents. Procedures are given for obtaining DH*, the concentration-independent diffusion constant, from DH under permeation conditions where the H concentration varies through the membrane; which is the common situation for H₂ purification membranes where p_upstream >> p_downstream. The role of the thermodynamic factor in H diffusion through multi-layer membranes will also be discussed.