Effects of Ammonium Thiocyanate and pH of Aqueous Solutions on Hydrogen Absorption into Iron under Cathodic Polarization

Abstract

To evaluate the susceptibility of steels to hydrogen embrittlement, it must be hydrogen charged and have its hydrogen content controlled before any mechanical testing. In this study, hydrogen permeation tests of an iron sheet were performed during potentiostatic hydrogen charging in various solutions containing ammonium thiocyanate to obtain a guideline for efficient hydrogen charging for a wide range of hydrogen contents. As the polarization potential shifted in the negative direction, the hydrogen permeation current increased before becoming almost constant. In all cases, besides when an aqueous sodium hydroxide solution was employed, the hydrogen permeation current increased due to the addition of ammonium thiocyanate. The effect of adding ammonium thiocyanate was enhanced as the aqueous solution pH was decreased. The hydrogen permeation current under various hydrogen charging conditions obtained in this study can be used as a reference for hydrogen charging of steels.

Effect of Hydrogen on the Tensile Behavior of Austenitic Stainless Steels 316L Produced by Laser-Powder Bed Fusion

“…The samples were immersed in a distilled water solution containing 3 wt.% NaCl and 0.3 wt.% NH 4 SCN. The efficiency of this solution in the H permeation was reported several times in the literature [19,[21][22][23][24][25][26][27][28][29]. Ammonium thiocyanate (NH 4 SCN) is widely used as a reagent (hydrogen recombination poison) for promoting hydrogen absorption by steels, and during hydrogen charging, the solution was de-aerated with N 2 [22,30].…”

Effect of Ammonium Thiocyanate on Hydrogen Absorption by Cathodic Charging in Weak Alkaline Solution

“…( 17) when η = 0, a H + is the hydrogen ion activity, θ P is the promoter surface coverage, and β P is the symmetry coefficient in Eq. (17). In a weak alkaline solution where pH is about 9, a H + is about 10 − 9 , resulting in v 1 and v 2 > > v P .…”

“…Similar current density changes have been reported in previous literature. 17) Figure 2 shows the relationship between i C and η and between i ∞ and η. η was determined using the equilibrium potential of the HER at pH 9 for all conditions. Regardless of the NH 4 SCN concentration, the slope of i C was almost zero at -0.19 V < η, probably due to the observed oxygen reduction reaction.…”

“…[12][13][14][15] In particular, NH 4 SCN is widely utilized thanks to its low toxicity and high hydrogen absorption enhancement effect. 16,17) If we can accurately understand the hydrogen absorption enhancement mechanism of these promoters, we should be able to clarify the effects of the amount of promoter added and the cathodic polarization conditions on changes in hydrogen absorption, thus resulting in more efficient evaluations.…”

Hydrogen Impact: A Review on Diffusibility, Embrittlement Mechanisms, and Characterization

“…For the charging cell, the electrolyte can be either acidic or basic. Widely used electrolytes include 0.1 M 𝐻 2 𝑆𝑂 4 or 0.1 M 𝑁𝑎𝑂𝐻, but the pH of the electrolyte can influence the experimental results [51]. Additionally, a recombination poison is introduced to the charging side to prevent hydrogen atoms in the charging cell from recombining into 𝐻 2 .…”