Effects of magnetic field on the anodic dissolution of alloy 690 in NaCl + Na₂S₂O₃ solution

Purpose The purpose of this paper is to study the anodic dissolution processes of alloy 690 in NaCl + Na 2 S 2 O 3 solutions by using digital holography. Design/methodology/approach The digital holography technique was used to in situ observe the dynamic processes occurring at the electrode|electrolyte interface during the anodic dissolution of alloy 690 in NaCl + Na 2 S 2 O 3 solutions, both in the presence and absence of a magnetic field (MF). Findings In 3.5% NaCl + 0.01 M Na 2 S 2 O 3 solutions, MF inhibited intergranular corrosion (IGC) because it increased the defects in the oxide film and facilitated the uniform adsorption of low concentration of S on these defects due to its stirring effects, which resulted in a weakened adsorption of S at the grain boundaries. Conversely, in 3.5% NaCl + 0.1 M Na 2 S 2 O 3 solutions, MF promoted IGC by increasing the number of defects in the oxide film, with lots of S species preferentially adsorbing at the grain boundaries. The resultant salt films formed more readily, inhibiting the formation of the oxide film at the grain boundaries. Originality/value Through the use of digital holography, it was possible to in situ observe the initiation of IGC at a single grain boundary and its progression to adjacent grain boundaries, regardless of the presence or absence of MF.