COBALT IRON HYDROXIDE CARBONATE AS A PRECURSOR FOR THE SYNTHESIS OF HIGH-DISPERSITY SPINEL MIXED OXIDES

Iron-cobalt hydroxide carbonates of pyroaurite-like structure have bee n synthesized by a coprecipitation technique. The structure is preserv ed within the limits 0.33 less-than-or-equal-to Fe/Co less-than-or-equ al-to 2 with no additional phases being found. Up to 10% of the iron c ations are stabilized as Fe(II), replacing Co(II) in the coprecipitate , but the main cation substitution in the lattice is Co(II)-Fe(III), e videnced by X-ray diffraction study, differential thermal analysis, IR and Mossbauer spectroscopy. The spinel mixed oxides, synthesized at 5 70 K, are of high dispersity, with specific surface areas 90-185 m2/g and particle sizes 6-12 nm, cationic vacancies being detected for samp les with prevailing iron content. A good correlation exists between th e bulk and surface iron/cobalt ratios of the mixed oxides, determined by X-ray fluorescence analysis and ESCA. The oxygen-to-metal ratios on the surface are for all oxide samples higher than expected on the bas is of the formulas of the spinel or sesquioxides.