Diffusion coefficients of hydrogen in a Pd81Pt19 membrane with time dependent boundary conditions

The solution of Fick's equation was found at the following initial and boundary conditions: constant initial concentration in a whole membrane c = c(0) at t = 0, constant concentration c = c(1) at x = 0 and time dependent concentration at x = L: c = b(0) + b(1)t + b(2) exp(-b(3)t) - (b(2)/4) exp(-4b(3)t), where L is thickness of membrane, b(0), b(1), b(2), b(3) are coefficients, and t is time. The mass Q of hydrogen, which permeated through the membrane was determined and theoretical lines were fitted to experimental curves p(t) (pressure of hydrogen in inside volume of the system as a function of time). The stationary flows and the diffusion coefficients (dependent and independent of stresses) were determined for the Pd81Pt19 membrane with initial contents of hydrogen up to n = H/M = 0.015 (atomic ratio of hydrogen to metal) during absorption and desorption of hydrogen at 288.4 K. (C) 2001 Elsevier Science B.V. All rights reserved.