A study on sodium iron oxides by laser Raman spectroscopy

High-temperature sodium on exposure to the air produces a corrosive melt including Na2O, Na2O2 and NaOH. If the melt contacts with steel, corrosion reaction occurs and several sodium-iron complex oxides (Na4FeO3, Na5FeO4, Na3FeO3, etc.) produce depending on temperature, basicity and oxygen potential. In this study, as an approach to clarify the crystalline structure of the complex oxides, laser Raman measurements of the complex oxides were carried out to obtain fundamental Raman spectra of synthesized pure Na4FeO3, Na3FeO3 and Na5FeO4 in room temperature. Additionally, the results were compared with commercially available sodium-iron compounds and distinguishable patterns in the typical spectra of each complex oxide were examined. As the results, the distinguishable patterns were found for each oxide. Moreover, irreversible changes of the spectra under exposure to the higher laser power were found out so that appropriate laser power was recognized for Raman analysis of the complex oxides. In addition, the same irreversible spectra change was also found under high temperature up to 573 K in Ar gas atmosphere as under exposure to the higher laser power. (author)