The Oxidation of a 1.5 Percent Silicon-Iron Alloy in Carbon Dioxide - Carbon Monoxide Atmospheres

Abstract

<p> The oxidation kinetics of a 1.5 ʷ/ₒ silicon-iron alloy in atmospheres of carbon dioxide - carbon monoxide at 890ºC and 1000ºC have been determined with a gravimetric balance as a function of gas composition. The reaction was observed to proceed in three stages. </p> <p> In The initial stage simultaneous growth of wustite-fayalite nodules and an amorphous silica film on different regions of the specimen was observed and this mixed reaction continued until complete coverage by a uniform scale was achieved. A model involving bother lateral and vertical growth of the oxide nodules and vertical growth of the silica film has been proposed to rationalize these kinetics. </p> <p> The second stage involving fluctuations in the reaction rate was observed in atmospheres of low oxidizing potential. These fluctuations were associated with the formation of massive fayalite bands, brought about by silicon supersaturation of the wustite and alloy. At high oxidizing potentials, this stage was not observed. </p> <p> At long times, a third stage consisting of linear reaction kinetics was observed. A model based on gas-oxide interfacial reaction control, involving the dissociation of carbon dioxide and incorporation of the chemisorbed oxygen into the wustite lattice has been advanced to describe these kinetics. The observed gas pressure dependence of the linear rate constants is consistent with the model. </p>