Effects of Additives on Solid State Reaction. III. Effects of Halide Additives on the Formation of MgFe2O4

Abstract

Abstract The promoting effects of halide additives on the formation of MgFe2O4 have been studied on the basis of both kinetic and thermoanalytical data. A mixture of MgO and α-Fe2O3 powder containing 10 mol% additive (LiF, NaF, MgF2, BaF2, NaCl, or KCl) and that without additive were isothermally heated in a vacuum (Po2=100–101 mmHg) in the temperature range 666–1018 °C. High temperature X-ray analysis on MgO–Fe2O3 and MgO–Fe2O3–additive systems was carried out at a heating rate of 3 °C/min in vacuo, (Po2=1−1 mmHg). In the case of fluoride, it seems that the reactions between the fluoride and the reactants, α-Fe2O3 or MgO, promote MgFe2O4 formation in the initial stage and that compounds produced by the initial reaction accelerate diffusion in the later stage. The same promoting mechanism seems to be applicable to the case of chloride additives. The interaction between solids of NaCl and α-Fe2O3 occurring just before the melting of NaCl seems to initiate MgFe2O4 formation.