Cathodic charging in a solution containing ammonium thiocyanate (NH4SCN) is commonly used to absorb hydrogen into a specimen in accelerated hydrogen embrittlement tests. However, the temperature dependence of hydrogen content in a specimen absorbed by cathodic charging in a solution containing NH4SCN has not been clarified. In this study, we evaluated the temperature dependence of saturated hydrogen content Cs by thermal desorption analysis, and it was found that Cs decreased as the temperature increased at a cathodic current density ic of 5 and 10 A/m2 and increased as the temperature increased at a ic of 100 A/m2. We also analyzed the hydrogen evolution reaction by fitting cathodic polarization curves, and it was found that the equilibrium constant of the hydrogen absorption-adsorption reaction K was almost constant regardless of temperature, while the changes in surface hydrogen coverage θ were in good agreement with the changes in Cs. Therefore, the changes in Cs can be explained as mainly due to the changes in θ.
Steel bars used in pre-stressed concrete structures are constantly subjected to tensile stress, and some steel bars have been reported to fracture due to hydrogen embrittlement.1 It is important to know the hydrogen embrittlement behavior in steel bars to prevent fracture.
To study hydrogen embrittlement behavior in steel bars, several accelerated hydrogen embrittlement tests have been conducted.2 In these tests, hydrogen embrittlement is accelerated by absorbing a large amount of hydrogen into a specimen.
Cathodic charging in an aqueous solution is commonly used to absorb hydrogen into a specimen in accelerated hydrogen embrittlement tests. To accelerate hydrogen absorption during cathodic charging, accelerators are often added to aqueous solutions, such as hydrogen cyanide (HCN), sodium arsenate (NaAsO2), hydrogen sulfide (H2S), and ammonium thiocyanate (NH4SCN). In particular, NH4SCN is widely used because it is less toxic than other accelerators.3
