Stoichiometry of iron oxide phases by laser induced breakdown spectroscopy (LIBS)

In this work, the process of iron oxidation (corrosion) is extensively investigated by LIBS. At first, several identical samples were polished and heated at certain temperatures. A Nd:YAG laser beam(150 mj/pulse) was focused through a quartz lens on the targets to generate a microplasma whose radiation was detected by CCD spectrograph. The emission lines due to the excited oxygen and Fe atoms are observed at short (nsec) and long (musec) delay times respectively after the onset of plasma formation. The corresponding plasma temperatures were obtained, using Boltzman equation based on LTE condition due to various pre-heating temperatures subsequently. The corresponding densities of oxygen(N0) and iron(NFe) within the microplasma were determined to be ~10¹⁶cm^-3-10¹⁸cm^-3 respectively. In addition, It was shown that the stoichiometry of samples, regarding the ratio S= N_O /N_Fe identifies the iron phase based on the phase diagram . We conclude that, LIBS offers a novel in-situ technique for the stoichiometry of iron phases.