Liquid-Phase Ion Gun for Local Acidification of Na₂S Aqueous Solution and Local Sulfidation of Fe-Cr Alloy Surface

Abstract

Local sulfidation of Fe-Cr alloy surfaces was attempted by using a liquid-phase ion gun (LPIG), in which a platinum microelectrode was anodically polarized in the vicinity of the alloy surface in 0.1 M Na 2 S aqueous solution. An increase in H + -concentration, namely local acidification, of the solution in the narrow space between the microelectrode and alloy surface successfully induced the formation of an H 2 S-concentrated environment and resulted in local sulfidation of the Fe-Cr alloy surface. The degree of sulfidation was dependent on acidification conditions such as the microelectrode current, specimen electrode potential and Cr concentration of the alloy. The use of an LPIG enables a sulfidation test not only to restrict the amount of H 2 S generated but also to evaluate sulfidation of a material surface quantitatively.

Initiation of Sulfide Stress Cracking Using Potentiostatic Liquid-Phase Ion Gun

“…Two types of LPIG experimental set-ups were used in this study. One was identical to the previous one 3 and used for resin-embedded specimens with an electrode area of 0.25 cm 2 . Another was shown in Fig.…”

“…However, there are many constraints to conducting tests that ensure the safety of H 2 S handling because H 2 S is highly toxic. In the previous reports, [1][2][3] the use of a liquid phase ion gun (LPIG) was proposed as an alternative test method to solve this problem. LPIG is an application of a scanning electrochemical microscopy (SECM), called generation-collection mode, in which electrochemically generated chemical species from an SECM tip electrode placed near the substrate (specimen) surface interact chemically or electrochemically with the specimen electrode.…”

“…Furthermore, the LPIG technique was modified to generate an H 2 S-rich local environment by galvanostatic, anodic polarization of the Pt tip electrode in a 0.1 M Na 2 S solution to acidify the local solution, allowing local sulfidation of even corrosion-resistant materials such as Fe-Cr alloy. 3 The resistance to sulfidation of Fe-Cr alloys was dependent on the Crconcentration. However, it was noted that the local acidic environment formed by galvanostatic polarization of the LPIG tip electrode at potentials above 2.00 V vs SHE contains a highly active species S 2 O 8 2in addition to H 2 S, and that sulfidation may be induced by S 2 O 8 2-.…”

A Liquid-phase Ion Gun Technique for Generating Sulfide Ions on Metal Surfaces

“…as a condition containing H 2 S, because the amount of generated HS is determined by the electric charge to form Ag 2 S on the Ag microelectrode. In order to overcome this drawback of the LPSIG, the polarization of a Pt microelectrode in Na 2 S aqueous solution has been used for local sulfidation of the Fe-Cr alloy surface 22 . During anodic polarization of the Pt microelectrode in a narrow space between the microelectrode and the alloy surface, H 2 S was concentrated to a concentration as high as the Na 2 S concentration of the solution used and induced local sulfidation of the alloy surface.…”