Phenomenological treatment of hydrogen transport in a metal/metal hydride system .1. Steady-state systems

Steady-state H-atom transport across a metal foil of uniform thickness is described using the phenomenological transport equation and the gradient of chemical potential deduced from the operative pressure-composition isotherm. The approach follows from that described by Wicke and Brodowsky(1) and leads directly to a description of the steady-state flux and the concentration profile of H-atoms across a metal/metal hydride foil of uniform thickness. As a demonstration we fabricate a simple chemical potential-composition isotherm which mimics the salient features of any of a number of experimentally observed isotherms, including (and especially) those describing two-phase systems, and which allows straightforward mathematical manipulation. We then show how the shape of the isotherm defines the steady-state flux of H-atoms across a metal/metal hydride foil of uniform thickness and defines the steady-state distribution of H-atoms across the foil, as well as the loading of H-atoms in the foil.