Initial oxidation mechanisms of stainless steel Sanicro 28 (35Fe27Cr31Ni) exposed to KCl, NaCl, and K2CO3 under dry and humid conditions at 535 °C

The initial stage of oxidation reactions at the surface of the stainless steel Sanicro 28 (Fe31Cr27Ni) exposed to KCl, NaCl, or K₂CO₃ in flowing dry and humid air at 535 °C was investigated using chronoamperometry, SEM–EDX and XPS. All studied salts accelerated the corrosion process. Na⁺ resulted in a higher amount of Na₂CrO₄ and a thicker chromium–rich scale compared to K⁺. CO₃²⁻ was involved in a reaction with iron only under humid conditions. The results show that humidity affects the corrosion mechanisms and it should thus be taken into account especially in the combustion of biomasses with high humidity.