The high-temperature corrosion of Fe–28Al and Fe–18Al–10Nb in a H 2/H 2S/H 2O gas mixture

Abstract

The corrosion behavior of Fe–28Al and Fe–18Al–10Nb (at.%) was investigated over the temperature range of 700–900°C in a H 2/H 2S/H 2O gas mixture with varying sulfur partial pressures of 10 −2–10 3 Pa and oxygen partial pressures of 10 −19–10 −15 Pa. In general, the corrosion kinetics followed the parabolic rate law although two-stage kinetics were noted in some cases. The steady-state parabolic rate constants increased with increasing temperature. Based on the equivalent addition (28 at.%)of alloying elements, it was found that Fe–18Al–10Nb exhibited a better corrosion resistance, being 2.1–3.9 orders of magnitude lower than Fe–28Al(depending on temperature). The scales formed on Fe–28Al consisted of mostly FeS, -Al 2O 3, and minor FeAl 2S 4, while the scales formed on Fe–18Al–10Nb consisted of mostly α-Al 2O 3, Nb 3S 4, Nb 2O 5, and minor Fe xNbS 2 (FeNb 2S 4/FeNb 3S 6) at T ≤ 800°C and of α-Al 2O 3, Nb 3S 4, and Fe xNbS 2 at 900°C. The formation of Al 2O 3 and Nb 3S 4 resulted in the significant reduction of corrosion rates.