Competing redox reactions in Fe-containing AlO(OH) and Al_2O_3 matrices: A combined investigation by Mossbauer, ESR spectroscopy and thermal analysis

摘要

The investigation of iron-doped AlO(OH)/Al_2O_3 systems revealed that the combined employment of M8ssbauer and ESR spectroscopies together with thermal analysis yields meaningful data with complementary information. This mutual complementarity is based on the coexistence of Fe point defects with the corresponding aggregated FeO_x species which has been observed even for very low Fe concentrations. Competing redox processes between the dopant, the A1O_X matrix, and the gas atmosphere during the thermal treatment enable the generation of solid phases exhibiting specific chemical properties. The entire reaction process is influenced by a specific mechanical and thermal pre-treatment that affects predominantly oxydative processes in the matrix. A protecting influence of the matrix preventing further reductive attack of the Fe~(3+) and Fe~(2+) ions by hydrogen has been established.