Manganosite

Abstract: Detailed methods are described for the laboratory preparation of the manganese minerals manganosite, hausmannite, manganite, partridgeite, birnessite, cryptomelane, pyrolusite, and todorokite New data are presented on the conversion of birnessite to cryptomelane, and on the exchange properties of potassium in these two minerals It was found that the upper limit of potassium in cryptomelane is about 7 % K, while the lower limit lies between 0·25 % and 2·2 % K

Abstract: Transposed temperature drop calorimetry and hightemperature drop solution calorimetry in molten 2PbO·B2O3 at 977 K were used to study the energetics of some manganese oxides, namely pyrolusite (MnO2), bixbyite (Mn2O3), hausmannite (Mn3O4), and manganosite (MnO). The enthalpies of oxidation at 298 K in the manganeseoxygen system, which were determined by appropriate thermodynamic cycles, were (in kJ/mol of oxygen): –441.4 ± 5.8 for the reaction 6MnO + O2→ 2Mn3O4, –201.8 ± 8.7 for the reaction 4Mn3O4+ O2→ 6Mn2O3, and –162.1 + 7.2 for the reaction 2Mn2O3+ O2→ 4MnO2. These values agreed very well with previous data that were obtained using equilibrium measurements that were reported in the literature. Thus, direct calorimetric measurements were well suited to obtain reliable enthalpy of formation data for oxides that contain manganese in the 2+, 3+, and 4+ states. Using these new values of enthalpies and reliable standard entropies, the phase-stability diagram of the manganeseoxygen system was constructed.

Abstract: Thermal expansion of manganosite MnO at temperatures between 20°C and 850°C has been carefully determined by a dilatometric technique. The theory of thermal expansion by Gruneisen is improved and the acquired data are analyzed to derive the harmonic and anharmonic parameters of MnO. Gruneisen's parameter γ is 1.56, Debye temperature is 441 K, and pressure derivative of bulk modulus is 7. The volume expansion coefficient is 34.3×10-6/K at 20°C and 47.1×10-6/K at 850°C; almost the same in magnitude to those of MgO and FeO.

Abstract: Experimental data on the thermodynamics and the phase diagram of the Mn-O system were reviewed, and by application of the CALPHAD method, a consistent set of thermodynamic model parameters was optimized. The phases pyrolusite (MnO2), bixbyite (Mn2O3), and hausmannite (Mn3O4) were described as stoichiometric compounds. Manganosite (Mn1−xO) was described using the compound-energy model and the liquid described using the two-sublattice model for ionic liquids.