MN AND CO SUBSTITUTION IN DELTA-FEOOH AND ITS DECOMPOSITION PRODUCTS

Cobalt and manganese substituted δ-FeOOH were obtained and used in the preparation of Fe, Co and Mn, Fe mixed oxides. Cobalt is present in the oxyhydroxide with 2.8-3.0, oxidation states. Lattice parameters and oxidation state decrease with cobalt content. Mn-substituted phases contain manganese in oxidation states decreasing from 4.0 to 3.3 as the degree of substitution is higher. These Mn-oxidation states imply cation vacancies which are alternatively ordered in octahedral sites along the [001] direction of the δ-oxyhydroxide structure. The thermal decomposition of the cobalt and Mn-substituted samples at 200 ° C leads to mixed oxides with distorted α-Fe2O3 structure and high manganese and cobalt oxidation states. From 200 to 400 ° C, a reduction process takes place, leading to Mn-substituted sesquioxides, while Co-containing samples decompose into mixtures of spinel and α-Fe2O3-structure phases. © 1990 Chapman and Hall Ltd.