Investigation of solid-solid interactions between pure and Li2O-doped magnesium and ferric oxides

Ga. Ei-shobaky et al., Investigation of solid-solid interactions between pure and Li2O-doped magnesium and ferric oxides, THERMOC ACT, 380(1), 2001, pp. 27-35
Citations number
Categorie Soggetti
Spectroscopy /Instrumentation/Analytical Sciences
Journal title
ISSN journal
0040-6031 → ACNP
Year of publication
27 - 35
SICI code
The solid-solid interactions between pure and lithium-doped magnesium and f erric oxides have been investigated using DTA and X-ray diffractograms (XRD ) techniques. Equimolar proportions of basic magnesium carbonate and alpha -Fe2O3 were employed and lithium was added as lithium nitrate. The amounts of dopant were 0.75, 1.5, 3 and 6 mol% Li2O. The results obtained showed that the addition of small amounts of lithium n itrate to the reacting mixed solids much enhanced the thermal decomposition of magnesium carbonate to an extent proportional to its amount added. The addition of 12 mol% LiNO3 decreased the decomposition temperature Of MgCO3 from 525.5 to 362 degreesC. MgO underwent solid-solid interaction with Fe2O 3 at temperatures starting from 800 degreesC yielding MgFe2O4. The amount o f ferrite produced increased when the precalcination temperature of the mix ed solids was increased. However, the completion of this reaction required prolonged heating at elevated temperature > 1100 degreesC owing to the form ation of MgFe2O4 phase which covered the surfaces of the grains of each sol id, thus, hindering the diffusion of Mg2+ and Fe3+ ions. Doping with Li2O M uch enhanced the solid-solid interaction between the mixed oxides to an ext ent proportional to the amount of Li2O added leading to the formation of Mg Fe2O4 phase at temperatures starting from 700 degreesC. The addition of 6 m ol% Li2O to the mixed solids followed by precalcination at 1050 degreesC fo r 4 h resulted in complete conversion of the reacting oxides into magnesium ferrite. The promotion effect of Li2O towards the ferrite formation was at tributed to an effective increase in the mobility of the various reacting c ations. The activation energy of formation (AE) of magnesium ferrite was de termined for pure and variously doped solids and the values obtained were 2 03, 126, 95 and 61 U mol(-1) for pure mixed solids and those treated with 1 .5, 3 and 6 mol% Li2O, respectively. (C) 2001 Elsevier Science B.V. All rig hts reserved.