HYPERFINE FIELDS IN IRON DILUTE ALLOYS AND INTERNAL OXIDATION

An Fe-V 2.5 at% foil was annealed at various temperatures in the range from 120-degrees-C to 1000-degrees-C for 10 min and analysed by Transmission Mossbauer Spectroscopy (TMS) and Conversion Electron Mossbauer Spectroscopy (CEMS) after each thermal process. A computational method to fit the spectra to obtain a parameter related to the concentration of the alloy was studied and applied to the data. No surprising effects were found on the bulk measurements (TMS), but there is a clear decrease of the alloy concentration in the 550-degrees-C to 700-degrees-C annealing temperature range, observed for the surface analysis (CEMS measurements). The phenomenon was attributed to the preferential internal oxidation of vanadium atoms in this range of temperature. Probably some vanadium oxide decomposition occurs at higher temperatures, recovering the original state of the sample.