Thermal analysis study of solid-phase synthesis of zinc- and titanium-substituted lithium ferrites from mechanically activated reagents

摘要

The solid-phase synthesis of Li0.4Fe2.4Zn0.2O4 and Li0.6Fe2.2Ti0.2O4 lithium-substituted ferrites from mechanically activated Li2CO3-Fe2O3-ZnO and Li2CO3-TiO2-Fe2O3 initial reagent mixtures was investigated using X-ray powder diffraction (XRD) and thermal analysis (TG/DSC) techniques. The mechanical milling of powder mixtures was carried out by a planetary ball mill with a rotation speed of 2220 rpm for 5 or 60 min. According to the XRD data, the crystallite sizes of initial reagents decrease by increasing the milling time. From thermal analysis for both unmilled mixtures, it was shown that the mass loss process due to CO2 evaporation occurs in the temperature range 500-730 A degrees C and corresponds to the interaction between reagents and lithium carbonate decomposition. As for milled samples, the mass loss process starts at room temperature, and by increasing the milling time, the end process shifts toward lower temperatures up to 500 A degrees C for 60-min milled ferrites. Thus, a preliminary mechanical activation of the initial reagents considerably enhances the reactivity of the solid-phase system and thus reduces the temperature of the thermal synthesis of lithium-substituted ferrites. It was established that lithium-zinc and lithium-titanium ferrites can be obtained at 700 A degrees C (at least 200 A degrees C lower than in the case of using unmilled reagents) for 120 min from mechanically activated 60-min milled reagents. Moreover, reactivity of the solid system remains high for a long time (at least no less than 2 years).