The Effect of Mechanical Activation on the Synthesis of MgFe₂O₄ from Mixtures of MgCO₃· Mg(OH)₂ · xH₂O and FeC₂O₄ ·2H₂O

Abstract

The synthesis of MgFe 2 O 4 has been attempted starting from mixtures of 4MgCO 3 · Mg(OH) 2 · xH 2 O and FeC 2 O 4 · 2H 2 O by combining mechanical activtion of the mixtures (by high-energy milling) with annealing at temperatures between 673 and 1073 K. TG measurements of mixtures of the precursors have been performed to assess the reaction mechanism, and to determine the minimum temperature where the two binary oxides (MgO and Fe 2 O 3 ) are formed. X-Ray powder patterns of the milled / annealed mixtures have shown that MgFe 2 O 4 is formed in an amorphous state already upon thermal treatment at 673 K, while annealing of the mixtures (not mechanically activated) at temperatures as high as 1473 K of the mixtures does not lead to the complete formation of MgFe 2 O 4 . The molar specific heat and the Curie temperature of the milled / annealed mixtures have been determined by DSC: MgFe 2 O 4 is obtained provided that the annealing of the milled mixture is performed at temperatures as low as 873 K. The effect of the annealing temperature on the surface area of MgFe 2 O 4 has been determined by BET measurements.

Investigations of M3Al8O15:Eu3+,Dy3+ (M = Ba, Ca, Mg) phosphors

“…the decomposition of MgCO 3 changing into MgO [2,8]. The TG curve exhibits a total mass loss of about ∼25.5 %, which is very similar to the calculated mass loss (∼27.0 %) after the decompositions of the sample were completed.…”

Eu3+- and Ho3+-doped Ba3Al2O6- and MgAl2O4-type phosphors and their photoluminescent properties

“…The first endothermic peak (at 260°C) is associated with the departure of the hydroxyl group from Mg(OH) 2 (2 and 3). The second endothermic peak (at 442°C) shows the decomposition of MgCO 3 which changes into MgO [7,8]. At the end of the decompositions, the TG curve exhibits a total mass loss equal to *42.1%, which is very similar to the calculated mass loss (*44.0%).…”