Thermodynamic, thermogravimetric and permittivity studies of hausmannite (Mn3O4) in air

Some manganese oxides are considered hyperactive under microwave irradiation because of their extremely high heating rates in air. In order to further understand this hyperactivity, thermodynamic calculations, thermogravimetric analysis and both real and imaginary permittivity determinations were performed for hausmannite (Mn3O4) as a function of temperature in an air atmosphere. The thermodynamic results demonstrated reasonable agreement with the thermogravimetric analysis data. A comparison of the derivative thermogravimetric analysis data with the derivative of both the real and the imaginary permittivities confirmed that the extremely high values of the permittivities were due to the conversion of the hausmannite to bixbyite (Mn2O3). The microwave hyperactivity of the manganese oxides in air is explained in terms of the high permittivities of bixbyite.