Oxidation of Fe atoms by O 2 based on Fe- and O-concentration measurements

Abstract

The reaction of Fe atoms with O 2 was studied over the temperature range of 950–2500 K at pressures between 0.3 and 1 bar behind incident shock waves. Atomic resonance absorption spectroscopy was applied for time-resolved measurement of Fe and O atoms in gas mixtures containing Fe(CO) 5 and O 2 , highly diluted in argon. The experiments showed that two reaction channels have to be considered during the Fe atom oxidation: F e + O 2 + M ⇌ k 1 a F e O 2 + M ( R 1 a ) F e + O 2 ⇌ k 1 b F e O + O ( R 1 b ) At temperatures below 1650 K, reaction R la is the dominant oxidation channel, and a rate coefficient of k 1a =8.9×10 17±0.2 exp(−1100±240 K/ T ) cm 6 mol −2 s −1 was obtained from pseudo-first-order analysis of the observed Fe-atom consumption. At high temperatures, the formation of FeO and O via reaction R1b gets more important, and a rate coefficient of k 1b =3.1×10 15±0.2 exp(−13,200±600 K/ T ) cm 3 mol −1 s −1 was determined. For the further interpretation of the experimental results, a simplified reaction mechanism was suggested, enabling simulations of the complete Fe- and O-atom concentration profiles, which were also influenced by secondary reactions of FeO and FeO 2 with CO and of FeO with O 2 .