Resisting Attack by Hot CO₂—A Comparison of Fe- and Ni-Base Alloys

Model alloys of Fe-20Cr and Ni-20Cr (all compositions in weight %) and variants containing small amounts of Si or Mn were exposed to Ar-20CO₂ and Ar-20CO₂-H₂O (volume %) at 650 or 700°C. Protective Cr₂O₃ scale was more readily formed on Fe-20Cr than Ni-20Cr, as a result of the different alloy diffusion coefficients. Silicon additions slowed chromia scale growth, promoting passivation of both alloy types. Water vapour accelerated chromia scaling, but slowed NiO growth.