High temperature behavior of Na-Fe oxides in H2O+CO2 atmosphere

The equilibrium states of sodium ferrates in H2O+CO2 environments were calculated by using a user database of the Na-Fe-O-H-C system. Chemical potential diagrams as functions of P(O2) and P(Na) were constructed by Thermo-Calc. The simulation calculation suggested that NaFeO2 should be the most stable sodium ferrite together with Na2CO3 in the atmosphere while other sodium ferrites such as Na5FeO4, Na3FeO3, etc., would be no longer stable in equilibrium state even if the pressure of CO2 is very low. However, experiments showed that the reaction of sodium ferrates with CO2 was a rate-limiting process and the formation of NaOH at the initial period was actually the dominant process instead of that of Na2CO3. It indicates that reaction kinetics plays a great role in chemical behaviors of sodium ferrates in H2O+CO2 environments.