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

The results obtained showed that the addition of small amounts of LiNO3 to the reacting mixed solids, consisting of equimolar proportion of Fe2O3 and basic MgCO3 much enhanced the thermal decomposition of magnesium carbonate. The addition of 12 mol% LiNO3 (6 mol% Li2O) decreased the decomposition temperature of MgCO3 from 525.5 to 362degreesC. MgO underwent solid-solid interaction with Fe2O3 at temperatures starting from 800degreesC yielding MgFe2O4, The amount of ferrite produced increased by increasing the precalcination temperature of the mixed solids. However, the completion of this reaction required prolonged heating at elevated temperature above 1100degreesC, Doping with Li2O much enhanced the solid-solid interaction between the mixed oxides leading to the formation of MgFe2O4 phase at temperatures starting from 700degreesC, The addition of 6 mol% Li2O to the mixed solids followed by precalcination at 1050degreesC for 4 h resulted in complete conversion of the reacting oxides into magnesium ferrite. The heat treatment of pure and doped solids at 900-1050degreesC effected the disappearance of most of IR transmission bands of the free oxides with subsequent appearance of new bands characteristic for MgFe2O4 structure. The promotion effect of Li2O towards the ferrite formation was attributed to an effective increase in the mobility of the various reacting cations, The activation energy of formation (DeltaE) of magnesium ferrite was determined for pure and variously doped solids and the values obtained were 203, 126, 95 and 61 kJ mol(-1) for pure mixed solids and those treated with L5, 3.0 and 6.0 mol% Li2O, respectively.