Reactions between gas phase, deposits and metallic materials in chlorine containing atmospheres

Abstract

Laboratory experiments were carried out in simulated waste incineration atmospheres at 500°C on 2.25Cr-1Mo-steel covered by deposits. In He-5 vol.% O₂ enhanced corrosion takes place due to the formation of chlorine from the reaction of chlorides in the deposit with the oxide scale of the material. The Cl₂ diffuses through cracks and pores of the oxide scale and FeCl₂ is formed at the metal/scale interface. By evaporation and outward diffusion through the oxide scale, FeCl₂ oxidizes to Fe₂O₃ (‘active oxidation’). In He-5 vol.% O₂−500 vppm HCl catastrophic corrosion occurs; the sulfates in the deposits are converted to (K, Na)Cl and heavy metal chlorides (PbCl₂, ZnCl₂). Additions of SO₂ (1000 vppm SO₂) retards the corrosion process due to stabilization of the sulfates in the deposits. Experiments on 2.25Cr-lMo and Fe-32Ni-27Cr (AC 66) covered with PbCl₂ indicates a deleterious effect of heavy metal chlorides on the corrosion process.

Keywords:

• waste incineration
• chlorine containing atmosphere