SYNTHESIS OF NANO-DIMENSIONAL IRON-COBALT SPINEL MIXED OXIDES FROM LAYERED-TYPE CARBONATE HYDROXIDE PRECURSORS

Pyroaurite-like carbonate hydroxide precursors Co1-xFex(CO3)(x/2)(OH)( 2) . nH(2)O, where x varies in the range 0.25 less than or equal to x less than or equal to 0.75, yield cation deficient mixed oxides with p article dimensions in the nano-scale range. The thermal decomposition and spinel structure formation processes have been studied by thermal analysis and IR spectroscopy, revealing an intermediate of hydroxide o xide type. Mesoporous mixed oxides with cubic spinel structure were sy nthesised at 300-400 degrees C with significant contribution of small pores of radii < 200 Angstrom. Oxygen desorption from cobalt ferrite, synthesised at 350 degrees C, suggests the existence of a high content of extraframework oxygen. The temperature-programmed reduction (TPR) with hydrogen occurs in one stage for all cobalt/iron compositions. Th e peak maxima shift to higher temperatures and a broadening is observe d with increasing the iron content. Partly inverse cation distribution s of the spinel ferrites are deduced from the Moessbauer spectra.