On the relative efficacy of electropermeation and isothermal desorption approaches for measuring hydrogen diffusivity

TL;DR

This study compares electrochemical permeation and isothermal desorption spectroscopy methods for measuring hydrogen diffusivity in pure iron, highlighting ITDS's improved repeatability and analyzing factors affecting EP measurement accuracy.

Contribution

The paper provides a systematic comparison of EP and ITDS methods, revealing ITDS's superior repeatability and identifying key factors influencing EP measurement errors.

Findings

ITDS shows similar diffusivity to second EP transient.

ITDS has 2-3 times lower variability than EP.

Electrochemical boundary conditions significantly impact EP results.

Abstract

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.