DIFFUSION-COEFFICIENT OF HYDROGEN IN A PD-AG MEMBRANE - EFFECT OF HYDROGEN SOLUBILITY

The permeabilities of hydrogen through a Pd-75-Ag-25 membrane have bee n measured at temperatures ranging from 423 to 573 K and under hydroge n pressure differences ranging from 69 to 256 kPa. From the available literature solubility data a neural network model has been developed i n order to simulate the variation of the hydrogen content in the alloy as a function of pressure and temperature. Then, from steady state pe rmeability measurements and calculated solubilities, the diffusion coe fficients of hydrogen have been computed. At a given temperature, the diffusion coefficient has been found to decrease with the hydrogen con tent (0.1 less than or equal to n = H/M less than or equal to 0.37). A simple relation is then suggested to predict the variation of the dif fusion coefficient on both temperature and hydrogen content. To accoun t for the variation of the diffusion coefficient with n, the integrati on of Fick's law of diffusion has been performed numerically, resultin g in non-linear profile of hydrogen content through the membrane under steady state permeation.