Moessbauer-Effect Studies of Crystalline and Amorphous Iron-Based Alloys and of Corrosion Processes at Iron Surfaces

摘要

Moessbauer effect spectroscopy was used to measure the temperature dependence of the exp 57 Fe effective magnetic hyperfine field H/sub eff/ and isomer shift delta of Fe sub 3 Al/sub x/Si/sub 1-x/ (0 less than or equal to x less than or equal to 1) from 77K to the Curie temperature. The observed dependence of H/sub eff/ and delta on Al concentration can be qualitatively understood in terms of the calculated band structure of Fe sub 3 Si. exp 57 Fe Moessbauer spectra was also obtained at liquid nitrogen and room temperatures for metallic glasses Fe exp 82 B/sub 18-x/Be/sub x/ with 0 less than or equal to x less than or equal to 6. Width of the probability distribution function of the effective magnetic hyperfine field remains constant at 80 k0e. However, the effective magnetic hyperfine field at 77 exp 0 K initially increases with Be content, but starts to decrease as x exceeds four. The isomer shift is -0.032 mm/s for samples with x less than or equal to 4 but changes to -0.050 mm/s for samples with x > 4. The crystallization products obtained upon annealing the samples were identified. Moessbauer spectroscopy and electrochemical measurements were used to study effects of chloride ions on a passivated iron surface in boric acid-sodium borate buffer solution at pH 8.4. The Moessbauer spectrum of the oxide film formed after breakdown of the passive film by aggressive chloride ions consists of a doublet with linewidth of 0.51 +- 0.03 mm/s, isomer shift of 0.35 +- 0.02 mm/s relative to the metallic iron, and quadrupole splitting of 0.79 +- 0.01 mm/s. The quadrupole splitting differs from that of the passive film which has line-widths of 0.55 +- 0.08 mm/s, an isomer shift of 0.36 +- 0.01 mm/s, and a quadrupole splitting of 0.94 +- 0.06 mm/s. (ERA citation 08:012675)