Is KCl(g) Corrosive at Temperatures Above its Dew Point? Influence of KCl(g) on Initial Stages of the High Temperature Corrosion of 11 Cr Steel at 600℃

摘要

The influence of gaseous KCl on the high temperature oxidation of CrMoV111 (X20) steel at 600℃ is reported. The sample temperature was above the dew point of KCl, the partial pressure of KCl being about 5ppm. The samples were investigated by a number of surface analytical techniques including grazing angle XRD, SEM/EDX, and SAM. CrMoV11 1 steel shows protective behaviour in clean dry O_2 and O_2/H_2O environment because of the formation of a chromium-rich oxide (α-(Fe,Cr)_2O_3). It is often considered that alkali salts accelerate the corrosion of steel only when present on the surface in solid or liquid form. In contrast, the present result shows that gaseous KCl is very corrosive, also in the absence of condensation. KCl(g) reacts with chromium in the scale, forming K_2CrO_4(s). This depletes the protective oxide in chromium and leads to the formation of non-protective hematite, Fe_2O_3.