Oxygen exchange in oxidation of an Fe-20Cr-10Al alloy in similar to 10 mbar O-2/H2O-gas mixtures at 920 degrees C

The oxidation of an alumina-forming Fe-20Cr-10Al alloy was studied in situ, The gas-phase components in isotopically labeled similar to 10 mbar O-2/H2O-gas mixtures were measured from a virtually closed system at 920 degrees C, Oxidation rates and oxygen-exchange rates were measured and related to each other, From the exchange rates the dissociation rates of O-2 and H2O were calculated, These dissociation rates were in the early stage of oxidation found to be the same as the oxidation rare, The rate of oxygen exchange with the oxide can exceed the oxidation rate, From this follows that in analysis of a two-stage oxidation in O-16,16(2)/O-18,18(2) the exchange rate of O between the oxide and gas phase has to be considered, The oxides for med in H2O containing gas had a H/O-ratio of similar to 0.1, Vacuum annealing of the alloy before oxidation increased the oxidation rate by a factor of similar to 2.