Mechanochemical treatment of α-Fe 2O 3 powder in air atmosphere

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 245; no. 1; pp. 109 - 117
• Main Authors: Zdujić, M., Jovalekić, Č., Karanović, Lj, Mitrić, M., Poleti, D., Skala, D.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1998
• Subjects: Ball milling; Hematite; Magnetite; Hematite; Magnetite; Ball milling
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/S0921-5093(97)00715-6

Powder of α-Fe 2O 3 was mechanochemically treated in a planetary ball mill in an air atmosphere. Structural changes were followed by X-ray diffraction analysis, magnetization measurements and differential scanning calorimetry after various milling times. It was found that complete transformation of α-Fe 2O 3 to Fe 3O 4 is possible during milling in an air atmosphere under appropriate milling conditions. Presumably, the decrease in the oxygen partial pressure during milling has a critical influence on promoting the dissociation of α-Fe 2O 3. Before nucleation of the Fe 3O 4 phase, the crystallites of the α-Fe 2O 3 phase are reduced to a minimal size accompanied by the introduction of atomic-level strain. Local modeling of a collision event, coupled with a classical thermodynamic assessment of the Fe 2O 3-Fe 3O 4 system, were used to rationalize the experimental results. It is proposed that the mechanochemical reactions proceed at the moment of impact by a process of energization and freezing of highly localized sites of a short lifetime. Excitation on a time scale of ∼10 −5 s corresponds to a temperature rise of the order of (1–2)×10 3 K. Decay of the excited state occurs rapidly at a mean cooling rate higher than 10 6 K s −1.