On the robustness of the Kelvin probe based potentiometric hydrogen electrode method and its application in characterizing effective hydrogen activity in metal: 5 wt. % Ni cold-rolled ferritic steel as an example

Abstract

Quantitative detection of hydrogen in metal is important in providing a better basis for fundamental investigations of hydrogen embrittlement and hydrogen-related corrosion phenomena. Thermal desorption spectroscopy (TDS) has long been used in characterizing different hydrogen traps inside materials. However, in TDS measurements, the diffusible hydrogen (hydrogen at interstitial sites and weakly bound hydrogen) is usually not detected. The Davanathan-Starchurski permeation technique can cover this shortage. However, for such experiments, the stability of the palladium at the exit side, i.e. in aqueous solution under high potential polarization is an important issue. Alternatively, a Kelvin probe-based (KP-based) potentiometric method developed a few years ago has shown to allow quantitative determination of hydrogen in metal. This method is based on measuring the hydrogen electrode potential on the Pd-coated surface. The aim of this work is to check the reliability of this method and to demonstrate its potential applications in determining the hydrogen amount distributed in both shallow and deep traps in steel. The results reveal that different crystallographic orientation, grain shapes and grain sizes of the deposited palladium film (in the range of variation in this work) do not cause relevant effects on the KP-based hydrogen detection. It is shown in this work that the time lag and permeation rate derived from the permeation curves obtained by this method show a very good reliability and the calculated hydrogen amount shows a good agreement with TDS results. 5 wt.% Ni ferritic steel is used as a model material in this work.

In situ nanoindentation during electrochemical hydrogen charging: a comparison between front-side and a novel back-side charging approach

“…The KP chamber was purged with dry N 2 gas during the measurements. More details on the KP approach can be found in [25,26].…”

“…The recorded potential changes (Fig. 7d) were then used to calculate the time lag and the effective diffusion rate according to [26]. The calculated diffusion rate was estimated as 1.5 9 10 -6 cm 2 /s.…”

Chemical heterogeneity enhances hydrogen resistance in high-strength steels

“…The increase of the H concentration in the Pd layer then leads to a reduction in the surface potential that can be very sensitively measured by the Kelvin probe method 48 . The permeation curves obtained by this method can be used for calculating the effective diffusion coefficient of H, which is directly comparable with the traditional Devanathan-Stachurski method 48,49 . The effective diffusion coefficient, determined from the breakthrough time 50 , is 6.0 (±1.7) × 10 -14 m 2 s -1 for the non-deformed HOM specimen and 8.3 (±1.2) × 10 -14 m 2 s -1 for the non-deformed HET specimen.…”

Exploring the Effect of Microstructure and Surface Recombination on Hydrogen Effusion in Zn–Ni‐Coated Martensitic Steels by Advanced Computational Modeling

“…[41] The calculation of time lag and diffusivity using the Kelvin probe-based technique has been discussed in detail elsewhere. [42] The obtained value of diffusivity is one order lesser than that of martensite and, considering the much lower diffusion coefficient of the interface, the coating will act as a barrier to the flow of hydrogen. Depending on the coating morphology, the Zn-Ni coatings might have microcracks in them.…”