Mechanochemical effects in the synthesis of ZnFe2O4

PABLO M. BOTTA; ESTEBAN F. AGLIETTI; JOSÉ M. PORTO LÓPEZ

Bordeaux, Francia

Jornada; 5èmes Journées du Réseau Français de Mécanosynthése; 2000

The reaction of formation of franklinite (ZnFe2O4) from mechanochemically activated Zn - Fe3O4 mixtures is studied at temperatures up to 800°C. The starting mixtures, with a molar ratio Zn:Fe3O4 of 3:2, were activated in a Herzog HSM-100 mill during measured times up to 30 minutes in air atmosphere. A milling media to powder mass ratio of 60:1 was used, at a frequency of 12.5 Hz. The obtained materials were analyzed by XRD, DTA and SEM. The main effect observable by XRD after activation was the diminution in intensity of the Fe3O4 peaks, and a rapid disappearance of the Zn peaks. SEM observations also revealed the gradual deterioration of the Fe3O4 crystals, and the total loss of the original spherical morphology of the Zn particles, after 30 minutes of treatment. Subsequent thermal treatment of 30 minutes at 400°C resulted in partial oxidation of the reactants, but no reaction was observed. At 600°, the formation of franklinite in the activated samples was almost complete, while in the non-activated mixture the main effect was the oxidation of magnetite and Zn. At 800°C, the reaction was complete for the activated sample, while the original mixture consisted in ZnFe2O4 together with non-reacted hematite and ZnO. XRD measurements of cell parameters of magnetite and franklinite showed that the temperature interval of reaction for the activated samples is located between 500 and 600°C, and that the reaction does not seem to involve a gradual incorporation of the Zn2+ into the magnetite structure. Magnetic measurements performed on the activated and reacted samples agreed with this analysis. The possible mechanisms for the reaction, both in activated and non-activated systems, are discussed.