Analysis of the various processes downstream cathodic hydrogen charging, I: Diffusion, laboratory permeation and measurement of hydrogen content and diffusion coefficient

Consultant, 36 Chemin Mirassou, 64140 Lons, France
jean-louis.crolet@wanadoo.fr

Received: 2 November 2015
Accepted: 16 February 2016

Abstract

The new views of 2000 on cathodic hydrogen charging are introduced in the numerical modelling of the downstream hydrogen diffusion, and this Part I deals with artificial laboratory permeation with electrochemical measurements on a Pd coated exit face. The “true” transients and steady state are thus calculated for the concentration profiles c(x,t) and the permeation flux J_perm, as well as the permeation efficiency E_p. The former nomenclature in term of thin vs thick membranes is indeed altered by high vs low charging fluxes, or high, medium and low, or still better, very high and moderately high, and very low and moderately low. Results are then compared to the historical calculation tools based on the boundary condition of a constant surface concentration c₀ at the entry face. These mathematical tools had been developed a long time ago for permeation under gaseous charging, and they are still valid in this case, but since the abandonment of the Bockris mechanism of discharge-recombination, they are basically invalid for the new cathodic charging by direct proton transfer. More generally, it is emphasised how the two charging modes are different for any subsequent transport process, and more will be addressed in Part II. Then, the totally unexpected consequences on the mechanism of sulfide stress cracking (SSC) will be addressed in Parts III and IV.