Oxidation of Fe–Si alloys in CO₂–H₂O atmospheres

Abstract

Iron and model alloys containing 1, 2, and 3wt% Si were reacted with dry and wet CO₂ gases at 800°C. All oxidised in dry CO₂ according to approximately linear kinetics. Additions of H₂O accelerated the reaction until steady-state parabolic kinetics were achieved. However, the effect of H₂O was small in the steady-state reaction stage of Fe – 3Si. Alloy reaction products were a duplex scale consisting of an outer FeO+Fe₃O₄ layer and an inner FeO+Fe₂SiO₄ layer, plus an internal oxidation zone, in all gases. In Fe – 1Si, amorphous SiO₂ precipitates in the internal oxidation zone grew with rod-like morphologies in all gases. However, internal amorphous SiO₂ precipitates grown in Fe – 2Si and Fe – 3Si formed network patterns. Internal penetration rates were initially rapid in Fe – 1Si, but slowed considerably at longer times. In Fe – 3Si, the internal oxidation zone grew wider in the first 20 h of reaction, and then remained constant in dry gas. In the wet gases this zone subsequently diminished, and disappeared after 50 h reaction.

Keywords:

• high temperature oxidation
• Fe –Si alloy
• water vapour
• internal oxidation