| Mn3O4 is a good material to prepare ferrites and lithium manganate. An effective method to prepare Mn3O4 is the decomposition of MnO2 in air. The data of the decomposition kinetics is the basis to optimize the preparation of Mn3O4 from MnO2.The results from TG/DTA, XRD and SEM show that the decomposition of MnO2 includes two steps. The first decomposition reaction from 500℃to 900℃is 4MnO2=2Mn2O3+O2↑, and it is controlled by the nucleation and growth, where the number of crystal nucleus reduces constantly with the proceeding of reaction, and the crystal nucleus growth at phase interface along two-dimensional direction. The Kinetics equation is G(α) = [-ln(1-α)]1/2 (T＜650℃) and G(α)=[-ln(1-α)]1/3 (T=650℃, and its activation energy and pre-exponential factor is calculated to be 90.239kJ·mol-1 and 3.12×104s-1 respectively.The second decomposition reaction is 6Mn2O3=4Mn3O4+O2↑(900℃～1170℃), and its key step is also the nucleation and growth. In this reaction, the number of crystal nucleus reduces constantly with the proceeding of reaction, but the crystal nucleus growth is controlled by phase interface along three-dimensional direction. The kinetics of the second reaction is G(α)=[-ln(1-α)]1/3, and its activation energy and pre-exponential factor is 204.67kJ·mol-1 and 4.78×107s-1.Based on the investigation of the decomposition kinetics, the effects of temperature, time and cooling method on the manganese content of Mn3O4 prepared from MnO2 were studied by orthogonal experiment and single factor experiment. The optimization conditions were obtained: the sintering temperature was 1050℃, the sintering time was 2.0h, and the product is cooled naturally in the air. The manganese content of the prepared Mn3O4 was 71.70％, which is coincidental with the standard of electronic grade Mn3O4.The results provided here can be considered as the base for optimizing the preparation processes to control the qaulity of Mn3O4.
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