Redox Processes of Manganese Ions Dispersed in Oxide Matrices
Several oxide matrices (MgO, Ti02, Sn02, and Al2O3) containing a few per cent of manganese oxide (up to 2 atomic per cent), prepared in oxidizing (air) or reducing (hydrogen) atmosphere, have been investigated by X-ray and ESR techniques.
The results are different for each system. For manganese-doped MgO prepared in hydrogen, the Mn2+ in solid solution is oxidised in air to Mn2+ starting from 400°C. At the same time Mg6MnO8 forms. For specimens prepared in air, the manganese is present predominantly as Mg6MnO8. The treatment in hydrogen of these oxidised samples causes the disappearence of this phase and the reduction to Mn2+. In the case of matrices of rutile structure (TiO2, SnO2) the manganese ions are incorporated in solid solution as Mn4+ when these samples are prepared in air. The dissolved ions are reduced by hydrogen at lower temperature (100–200°C). The redox processes take place in solid solution and are reversible. For the system based on alumina, only a small amount of manganese is detected as Mn2+.
KeywordsSolid Solution Manganese Oxide Redox Process Rutile Structure Oxide Matrice
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