Structural changes and surface properties of Cox Fe3—x O4 spinels

Abstract

AbstractThe cobalt ferrite spinel oxide series, CoxFe3–xO4 (0 ≤ x ≤ 3), has been prepared by coprecipitation. The adsorption–desorption isotherms of all the compositions calcined between 200 and 600°C have been measured using nitrogen gas at −196°C. The structural and the phase changes were characterized by TGA and XRD techniques. The results obtained revealed that the transformation of γ‐ to α‐Fe2O3 was accompanied by a sharp decrease in the SBET values. The addition of Co2+ ions into Fe2O3 up to × = 0.6 led to an observable increase in the SBET value. This behaviour was attributed to the incorporation of Co2+ ions into the Fe2O3 lattice and the retardation of the phase transition of γ‐ to α‐Fe2O3. The minimum SBET values obtained at a lattice composition of × = 1·0 corresponded to the formation of a cobalt ferrite normal spinel which is associated with the existence of narrow pores. The increase in SBET values in the cobalt‐rich region, with a maximum at x = 2·6 is explained on the basis of the cationic replacement of Fe3+ ions in the Co3O4 lattice. Finally, calculation of pore volume distribution was carried out, in addition to Va–t plots, in order to study the nature of the surface porosity, which was found to be mesoporous.