Applicability of ToF-SIMS and stable oxygen isotopes in KCl-induced corrosion studies at high temperatures

The applicability of Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) in combination with the use of stable oxygen isotopes (¹⁶O and ¹⁸O) in high-temperature corrosion research was addressed in this study. In terms of the corrosion reaction timescale, the focus was on the initiation of KCl-induced high-temperature corrosion and on the behaviour of three commercial alloys under conditions where multiple oxygen sources (air and water vapour) were present.ToF-SIMS proved to be an applicable tool in high-temperature corrosion studies, in this case, providing detailed information about the distribution of the two oxygen isotopes at the sample surfaces. Oxygen from air prefers to form a solid intermediate, potassium chromate (K₂CrO₄), when reacting with a chromia-forming alloy, whereas oxygen from both sources was found in the oxide formed at the alloy surface. Regardless of the prevailing conditions, the nickel-based austenitic alloy withstood corrosion the best, then the iron-based high alloy austenitic steel, whereas the low alloy ferritic steel had the poorest corrosion resistance ability.