  The relative efficacy of electrochemical permeation (EP) and isothermal
desorption spectroscopy (ITDS) methods for determining the hydrogen diffusivity
is investigated using cold-rolled pure iron. The diffusivities determined from
13 first transient and 8 second transient EP experiments, evaluated using the
conventional lag and breakthrough time methods, are compared to the results of
10 ITDS experiments. Results demonstrate that the average diffusivity is
similar between the second EP transient and ITDS, which are distinctly
increased relative to the first EP transient. However, the coefficient of
variation for the ITDS experiments is reduced by 2 and 3-fold relative to the
first and second EP transients, confirming the improved repeatability of ITDS
diffusivity measurements. The source of the increased error in EP measurements
is systematically evaluated, revealing an important influence of assumed
electrochemical boundary conditions on the analysis and interpretation of EP
experiments.
