MOSSBAUER-EFFECT IN ULTRAFINE PARTICLES WITH FE-C SOLID-SOLUTION, GAMMA-FE AND FE3C PHASES

Ultrafine particles prepared by evaporating pure Fe in CH4 atmosphere using arc-discharge-heating method. were found to consist of Fe-C soli d solution, gamma-Fe and Fe3C phases. Effect of annealing temperature on phase transformation and hyperfine interactions has been investigat ed by Mossbauer spectroscopy, X-ray diffraction (XRD), differential th ermal analysis and thermogravimetry (DTA-TG), transmission electron mi croscopy (TEM), oxygen determination and vibrating sample magnetometer (VSM) measurements. It was observed that phase transformation of gamm a-Fe to alpha-Fe occurs during annealing in vacuum. The mechanism caus ing the change of hyperfine interactions with annealing temperature di ffers for Fe-C solution and interstitial compounds. Difference of hype rfine interactions of Fe-C solid solution in the starting sample and i ts annealed samples is ascribed to the improvement of activation of in terstitial carbon atoms. Stress-relieving in structure of annealed Fe3 C particle can result in a weak influence on hyperfine interactions. P arameters fitted to the Mossbauer spectra show the existence of superp aramagnetism in all the samples. Absorbed and combined oxygen on parti cle surface of the starting sample were determined.