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Structural changes and surface properties of Co x Fe 3— x O 4 spinels
Author(s) -
Said Abd ElAziz A.,
Hassan Ehsan A.,
ElAwad Ahmed M.,
Abd ElSalaam KhalfAlla M.,
Abd ElWahab Mohamed M. M.
Publication year - 1994
Publication title -
journal of chemical technology and biotechnology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.64
H-Index - 117
eISSN - 1097-4660
pISSN - 0268-2575
DOI - 10.1002/jctb.280600208
Subject(s) - spinel , cobalt , bet theory , coprecipitation , materials science , ion , lattice constant , analytical chemistry (journal) , ferrite (magnet) , mesoporous material , calcination , desorption , oxide , adsorption , crystallography , chemistry , inorganic chemistry , diffraction , metallurgy , biochemistry , physics , organic chemistry , chromatography , optics , composite material , catalysis
The cobalt ferrite spinel oxide series, Co x Fe 3– x O 4 (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‐Fe 2 O 3 was accompanied by a sharp decrease in the S BET values. The addition of Co 2+ ions into Fe 2 O 3 up to × = 0.6 led to an observable increase in the S BET value. This behaviour was attributed to the incorporation of Co 2+ ions into the Fe 2 O 3 lattice and the retardation of the phase transition of γ‐ to α‐Fe 2 O 3 . The minimum S BET 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 S BET values in the cobalt‐rich region, with a maximum at x = 2·6 is explained on the basis of the cationic replacement of Fe 3+ ions in the Co 3 O 4 lattice. Finally, calculation of pore volume distribution was carried out, in addition to V a – t plots, in order to study the nature of the surface porosity, which was found to be mesoporous.