An electrodeposited gamma-manganese dioxide has been studied by thermal analysis in vacuum, oxygen and water vapour environments between room temperature and 450°C. Water was the predominant desorption product and five types have been identified. Textural changes occuring as a result of dehydration were monitored by nitrogen adsorption at liquid nitrogen temperature and the isotherms obtained analysed by the as method. A micropore network was generated on outgassing above 160°C due to elimination of hydroxyl groups from the oxide lattice. The products obtained by partial chemical reduction of gamma-manganese dioxide have been characterised by X-ray diffraction and magnetic measurements and their thermal behaviour investigated. The microporosity revealed on outgassing was evaluated by nonane adsorption and the results compared with those obtained from nitrogen adsorption data. The thermal decomposition of gamma- and alpha-MnOOH has been studied in vacuum and at low oxygen pressures (10 Torr). In vacuum, gamma-MnOOH decomposed below 400°C to a mixture of Mn5O8, alpha-Mn3O4 and water. Above this temperature Mn5O8 was converted to alpha-Mn3O4 as a result of oxygen removal. The vacuum dehydration of alpha-MnOOH led to a new modification of manganese sesquioxide (Mn2O3) isostructural with corundum (alpha-A12O3). In oxygen both oxyhydroxides decomposed to beta-MnO2. gamma-MnOOH transformed directly to beta-MnO2 whilst alpha-MnOOH appeared to proceed via Mn2O3. The existence of two new oxides of manganese, namely Mn7O12 and Mn7O10 has been established by thermal measurements and chemical analysis.
|Date of Award||1975|