Ball milling of Fe75-C25: formation of Fe3C and Fe7C3

Powder mixtures of Fe75-C25 (both graphite and activated carbon) have been ball-milled in vacuum for periods of up to 285 h. X-ray diffraction, Mِssbauer spectroscopy and thermal analysis measurements indicate that an amorphous Fe3C-type phase is produced on short-term milling (less than 70 h), with a crystalline Fe3C being obtained on further milling to 140 h. This Fe3C-type phase was found to undergo partial carbon oxidation between 500 and 1000 °C during thermogravimetric measurement, indicating the metastable state of this phase. The carbon-rich Fe7C3 phase was observed on extended milling of Fe75C25 (graphite) to 285 h, in agreement with earlier findings.