Thermal analysis study of LiFeO2 formation from Li2CO3–Fe2O3 mechanically activated reagents

Abstract

The solid-phase synthesis of LiFeO2 lithium ferrite from mechanically activated Fe2O3–Li2CO3 initial reagent mixtures was investigated by X-ray powder diffraction and thermal analysis techniques. The mechanical milling of powder mixture was carried out by AGO-2S planetary ball mill with a rotation speed of 2220 rpm for 60 min. According to the XRD data, the crystallite sizes of milled reagents decrease as a result of ball milling. From thermal analysis, it was shown that the ferrite synthesis starts with the interaction between reagents and lithium carbonate decomposition and accompanied by mass loss process due to CO2 evaporation. For non-milled mixtures, the mass loss process occurs in the temperature range 400–740 °C and comprises two steps. As for milled samples, this process shifts toward lower temperatures, where a slight mass loss process is observed from 100 °C up to 400 °C, while the main mass loss occurs in the temperature range of 400–550 °C in one stage. The results indicate that the major mechanism of solid-state reaction can be attributed to the two-step model of the reaction proceed, whose rate is diffusion controlled over the entire temperature range for non-milled mixture, but corresponds to the diffusion and n-order equation depending on conversion degree for milled mixture. Generally, a preliminary mechanical activation of Fe2O3–Li2CO3 considerably enhances the reactivity of the solid-phase system, thereby reducing the temperature of lithium ferrite thermal synthesis. Thus, LiFeO2 ferrite can be obtained from reagents mixture mechanically activated for 60 min at temperature of 600 °C for 2 h, that is, at a significantly lower synthesis time and temperature than in the case of using conventional solid-state synthesis from non-milled reagents.