Solid-solid interactions between ZnO and Fe2O3 as influenced by Al2O3-doping

The solid-solid interactions between pure and alumina-doped zinc and ferric oxides have been investigated by using XRD technique. The investigated sol ids were calcined at 600-900 degrees C. The amounts of alumina were 3, 6 an d 9 mol%. The results obtained showed that Fe2O3 interacted readily with ZnO at tempe ratures starting from 700 degrees C producing zinc ferrite. The degree of r eaction propagation increased with temperature. The completion of this reac tion required a prolonged heating at temperatures >900 degrees C. Al2O3-dop ing promoted the ferrite formation to an extent proportional to its amount added. Furthermore, the doping process resulted in the formation of ZnFe2O4 at 600 degrees C. The stimulation effect of Al2O3 was evidenced by followi ng up the change of peak heights of certain diffraction lines characteristi c for ZnFe2O4, alpha-Fe2O3 and ZnO phases located at "d" spacings of 2.54, 2.69 and 2.47 Angstrom, respectively. The activation energies Delta E of th e ferrite formation for pure and variously doped mixed oxide solids were co mputed. The Delta E values were 73.5, 66.8, 57.3 and 68.8 kJ mol(-1) for pu re mixed oxide solid samples and those doped with 3, 6 and 9 mol% Al2O3, re spectively. The mechanism of Al2O3 doping is discussed. (C) 2000 Elsevier S cience B.V. All rights reserved.