Solid-solid interactions between ferric oxide and lithium carbonate and the thermal stability of the lithium ferrites produced

Abstract

The interaction between α-Fe 2O 3, and Li 2CO 3 was studied using DTA, TG DTG and X-ray diffraction techniques. The results obtained revealed that ferric oxide and lithium carbonate, when mixed in a molar ratio of 1 : 2, underwent solid-solid interaction at temperatures starting from 500 °C, yielding α-LiFeO 2. The degree of crystallinity of the ferrite produced was much increased by increasing the precalcination temperature of the mixed solids. The unreacted portion of lithium carbonate decomposed readily at 735 °C forming Li 2O which dissolved in the α-LiFeO 2 lattice, giving a stable solid solution. The dissolved lithium oxide increased the thermal stability of α-LiFeO 2 and prevented its phase transformation into any other type of lithium ferrite. The heating of the mixed solids at 1080 ° C resulted in sublimation of about 50% of the Li 2O from the lattice of LiFeO 2 without effecting its transformation into another phase. However, Fe 2O 3 and Li 2CO 3, in an equimolar ratio, interacted with each other at temperatures starting from 500 ° C also giving α-LiFeO 2 which was transformed in part into β-LiFeO 2 and β-LiFe 5O 8 at temperatures between 700 and 1000 °C. At 1100°C, the β lithium ferrites and an important portion of α-LiFeO 2 underwent phase transformation forming well-crystallized α-LiFe 5O 8.