Hot Corrosion of Preoxidized Ni by a Thin Fused Na2 SO 4 Film at 900°C

The hot corrosion of preoxidized 99% and 99.99% pure Ni covered with a thin Na 2 SO 4 film in a SO 2 ‐ O 2 gas atmosphere was investigated at 900°C by an electrochemical method using a sodium sensor and an oxygen probe. The preoxidation conditions were varied in order to affect the sulfidation of Ni, which resulted in an increase in salt basicity and thereafter catastrophic corrosion. The basicity gradient generated across the thin salt film supported a self‐sustaining basic fluxing and reprecipitation of the protective NiO scale.