Sulphur diffusion through a growing chromia scale and effects of water vapour

Fe-30Cr (wt%) alloy was exposed to Ar-0.5%SO2 and Ar-10%H2O-0.5%SO2 gases at 650 degrees C, forming Cr2O3 scales. In dry SO2 for 20 h, sulphur enrichment and scattered Cr-sulphides were observed at the scale-alloy interface, together with internal Cr-sulphide precipitates. After 100 h, sulphur disappeared from the interface, while more internal Cr-sulphides were produced. In wet SO2, the sulphur enrichment and Cr-sulphides were maintained in both times, but no internal sulphidation was seen. Atom probe analysis revealed sulphur enrichment on chromia grain boundaries in both gases, to a greater extent in wet SO2. These effects are discussed in terms of chromia grain boundary diffusion.

Automated summary

Fe-30Cr (wt%) alloy was exposed to Ar-0.5%SO2 and Ar-10%H2O-0.5%SO2 gases at 650 degrees C, forming Cr2O3 scales. Sulphur enrichment and scattered Cr-sulphides were observed at the scale-alloy interface in dry SO2 for 20 h, along with internal Cr-sulphide precipitates. After 100 h, sulphur disappeared from the interface, while more internal Cr-sulphides were produced. In wet SO2, sulphur enrichment and Cr-sulphides were maintained in both times, but no internal sulphidation was seen. Atom probe analysis revealed sulphur enrichment on chromia grain boundaries in both gases, more pronounced in wet SO2. These effects are discussed in terms of chromia grain boundary diffusion.