Effect of temperature on the passive state of Alloy 31 in a LiBr solution: Passivation and Mott‐Schottky analysis

Abstract

The passive behaviour of Alloy 31, a highly‐alloyed austenitic stainless steel (UNS N08031), has been investigated in a LiBr heavy brine (700 g/l) at different temperatures using potentiostatic polarisation and Mott‐Schottky analysis. Cation vacancies have been found to be the dominant defect in the passive films formed on Alloy 31. An increase in temperature enhanced the generation of cation vacancies at the film/solution interface and raised the steady‐state passive current density. The density of defects within the passive film also increased significantly with temperature, making the film more conductive and less protective against localised attacks.

Electrochemical corrosion of FV520B stainless steel in solutions bearing hydrogen bromide and acetic acid at high temperature from 130 to 200 °C

“…When the HBr was involved, the role of H + ion and Br − ion on the cathodic and anodic polarisation behaviour become particularly important. First, increasing the H + content could enhance the cathode depolarisation ability [2,5,19,20], which could then lead to the shift of the cathodic part of the polarisation curves towards the high current density region (Figure 2). Second, the water chemical equilibrium could be modified by H + and temperature, and the microstructure of the surface oxide film could thus be changed [22][23][24].…”

“…The above results demonstrated that the general corrosion resistance of the FV520B stainless steel decreased when the temperature and the HBr increased; meanwhile, the active dissolution current density and the passive current density also increased (Figures 2 and 3). Different from the passive film in the conventional solution below 100 °C [17], a non-dense oxide film usually formed on the surface of stainless steel at temperatures above 100 °C [18 20]. The dissolution of 304 stainless steel occurred through the oxide film, thus resulting in the appearance of an activation peak [21].…”