Reactive evaporation and condensation of chromium: A review

The reactive evaporation of chromium (Cr) from stainless steels in high-temperature (>500 °C) service environments (e.g., air, steam) has been extensively investigated. The subsequent condensation of Cr-containing vapors and deleterious impacts on solid oxide fuel cell components has also received significant research attention. However, the condensation of Cr-containing vapors onto silica-based insulation and other common materials in high-temperature applications is poorly understood. This review briefly covers the reactive evaporation of Cr from stainless steels but focuses on reactive condensation processes and their dependencies on materials and environmental conditions. First, known Cr sources and associated health hazards are presented. Next, the corrosion behaviors of stainless steels under different exposure conditions are discussed along with the reactive evaporation of Cr species and the pathways of Cr vapor condensation on various surfaces under differing conditions. Lastly, the effects of Cr condensation on SOFC components and other industries in which Cr(VI) formation has been identified are discussed in context of ongoing research into the mobility and evolution of condensed Cr species. Current research includes expanding on the condensation mechanisms of volatile Cr species and exploring the mobility of surface Cr species. For example, the importance of substrate surface chemistry and morphology on Cr collection/surface speciation are of interest to researchers. Long-term saturation conditions via transpiration experiments for high surface area substrate materials such as glass fibers and wools are topics of investigation.