The reaction of Ni-20Cr with SO2 at 600-900°c

A Ni-20Cr alloy has been reacted in SO₂ at 600–900°C. Reaction kinetics have been studied as a function of temperature, pressure and experimental procedure. Reaction products have been characterized by X-ray diffraction, scanning electron microscopy, and differential thermal analyses. Depending upon the reaction conditions, the primary reaction products are NiO and Ni₃S₂, and Cr₂O₃ and (Ni-S)_hq. Under conditions where Ni₃S₂ is formed, reactions are rapid, while the formation of (NiS)_liq (>800°C) leads to slow reactions. The molten sulfide phase facilitates transport of chromium to the scale-gas interface where a protective layer of Cr₂O₃ is formed. Reaction mechanisms are discussed in terms of thermodynamic stability of the reaction products.